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

Abstract

A method for transmitting frames in a wireless communication system is disclosed. A non-AP STA receives a beacon frame including a request type field from an AP, and can receive a downlink frame or transmit an uplink frame according to a value of a specific field included in the beacon frame. In this case, the request type field includes a specific field for indicating a target wake time (TWT) for low latency operation, and when the value of the specific field is set to a first specific value, the broadcast TWT service period (SP) is the TWT SP for the low latency operation.

Description

Technical Field

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

Background Art

[0002] Recently, as the popularity of mobile devices has expanded, Wireless LAN technology that can provide fast wireless Internet services to them has been in the spotlight. Wireless LAN technology is a technology that enables mobile devices such as smartphones, smart pads, laptop PCs, portable multimedia players, and embedded devices to be wirelessly connected to the Internet in homes, enterprises, or specific service-providing areas based on wireless communication technology at short distances.

[0003] Since IEEE (Istitute of Electronics Engineers) 802.11 supported the initial wireless LAN technology using a 2.4GH z frequency, various technology standards have been put into practical use or are under development. First, IEEE 802.11b uses a frequency in the 2.4GHz band and supports a communication speed of up to 11Mbps. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses a frequency in the 5GHz band instead of the 2.4GHz band, thereby reducing the impact on interference compared to the rather congested 2.4GHz band frequency, and using OFDM technology to improve the communication speed up to 54Mbps. However, IEEE 802.11a has the disadvantage of a shorter communication distance compared to IEEE 802.11b. And IEEE 802.11g uses the same 2.4GHz band frequency as IEEE 802.11b to implement a maximum communication speed of 54Mpbs and satisfies backward compatibility, attracting considerable attention, but it is also superior to IEEE 802.11a in terms of communication distance.

[0004] And, as a technical standard established to overcome the limitations regarding communication speed pointed out as vulnerabilities in Wi-Fi, there is IEEE 802.11n. The purpose of IEEE 802.11n is to increase the speed and reliability of the network and extend the operating distance of the wireless network. Specifically, IEEE 802.11n supports a high throughput (HT) with a maximum data processing speed of 540 Mbps or more, and is based on the MIMO (Multiple Inputs and Multiple Outputs) technology that uses multiple antennas at both the transmitting and receiving ends to minimize transmission errors and optimize the data speed. Also, this standard uses a coding method that transmits multiple copies of redundant transcripts to increase the reliability of the data.

[0005] As the popularity of Wi-Fi has been activated and the applications using it have diversified, there has been a growing need for a new Wi-Fi system that supports a processing rate (Very High Throughput, VHT) higher than the data processing speed supported by IEEE 802.11n. Among them, IEEE 802.11ac supports a wide bandwidth (80 MHz to 160 MHz) at 5 GHz frequency. Although the IEEE 802.11ac standard is defined only in the 5 GHz band, it is considered that the initial 11ac chipset supports operation in the 2.4 GHz band for backward compatibility with conventional 2.4 GHz band products. Theoretically, according to this standard, the speed of the Wi-Fi with multiple stations can be up to 1 Gbps at minimum and the maximum single link speed can be up to 500 Mbps at minimum. This is achieved by expanding the concepts of the wireless interface accepted in 802.11n, such as a wider wireless frequency bandwidth (up to 160 MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high-density modulation (up to 256QAM). Also, as a method of transmitting data using the 60 GHz band instead of the conventional 2.4 GHz / 5 GHz, there is IEEE 802.11ad. IEEE 802.11ad is a transmission standard that uses beamforming technology to provide a speed of up to 7 Gbps and is suitable for streaming high-bitrate videos such as large-capacity data and uncompressed HD videos. However, the 60 GHz frequency band has the disadvantage that it is difficult for obstacles to pass through and it can be used only between devices in a short-distance space.

[0006] On the other hand, as a Wi-Fi standard after 802.11ac and 802.11ad, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard has been developed and is in the completion stage to provide high-efficiency and high-performance Wi-Fi communication technology in a high-density environment where APs and terminals are dense. In an 802.11ax-based Wi-Fi environment, it is necessary to provide high-frequency efficiency communication indoors / outdoors in the presence of a high density of stations and APs (Access Points), and various technologies have been developed to implement this.

[0007] In addition, in order to support new multimedia applications such as high-quality videos and real-time games, a new Wi-Fi standard has been developed to increase the maximum transmission speed. The 7th generation Wi-Fi standard, IEEE 802.11be (Extremely High Throughput, EHT), aims to support a maximum transmission rate of up to 30 Gbps by using a wider bandwidth, increased spatial streams, and multi-AP cooperation in the 2.4 / 5 / 6 GHz bands. In IEEE 802.11be, technologies such as a 320 MHz bandwidth, multi-link operation, multi-AP (Multi-Access Point) operation, and hybrid automatic repeat request (HARQ) have been proposed.

[0008] The multi-link operation can be operated in various forms depending on its operation method and implementation method. At this time, problems that did not occur in the conventional IEEE 802.11-based Wi-Fi communication operation may occur, so it is necessary to define the detailed operation method in the multi-link operation.

[0009] On the other hand, the background art of the invention is created to enhance the understanding of the background of the invention, and includes content that is not prior art already known to those with ordinary knowledge in the field to which this technology belongs.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] The present invention aims to provide a method, apparatus, and system for multi-link transmission operation using Wi-Fi, in which a wireless access point efficiently performs transmission and reception operations of frames that require a low delay time.

[0011] In addition, the present invention aims to provide a method, apparatus, and system for setting a section for transmission and reception restrictions for the transmission and reception of frames that require a low delay time.

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

[0013] The technical problems to be solved in the specification are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those having ordinary knowledge in the technical field to which the present invention pertains from the following description.

Means for Solving the Problems

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

[0015] In addition, in the present invention, when the TWT SP for the low latency operation is set, only frames that require low latency can be transmitted in the TWT SP for the low latency operation.

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

[0017] Also, in the present invention, the interval set by the quiet information element is the same as the start time of the TWT SP for the low-latency operation.

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

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

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

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

[0022] Also, 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 in which the frame transmission is restricted by the TWT for the low-latency operation.

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

[0024] Also, in the present invention, the frame transmission operation ends before the start time of the TWT SP for the low-latency operation.

Advantages of the Invention

[0025] According to an embodiment of the present invention, a frame requiring low latency can be efficiently transmitted.

[0026] Also, according to an embodiment of the present invention, by setting a section for restricting frame transmission, a frame requiring low latency can be efficiently transmitted.

[0027] According to the present invention, when a wireless access point (Access Point, AP) and an AP MLD including a plurality of wireless access points assist in the transmission and reception operations of frames requiring a low delay time, a specific section that enables only the transmission of frames requiring a low delay time is defined and announced in a broadcast frame. When a wireless LAN station (station, STA) attempts to transmit and receive a frame that meets the requirements, a process of negotiating with the AP or the AP MLD for the operation is performed. Here, the section information for the low delay time is made known in a beacon frame or a probe response frame, etc. Here, the section announcement and negotiation method for the low delay time are performed in the same or a similar method as the negotiation method of the TWT (Target Wake Time) operation. In order to perform the operation efficiently, the AP or the AP MLD allows only the connection of terminals that support the operation for the link in operation. By using the low-latency transmission operation, when a terminal or an AP attempts to transmit a frame requiring a low delay time, the transmission and reception operations of the frame can be stably performed, and the communication efficiency can be improved.

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

Brief Description of the Drawings

[0029]

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Mode for Carrying Out the Invention

[0030] The terms used in this specification are selected as generally widely used common terms as much as possible in consideration of the functions in the present invention, but this may vary depending on the intention, convention, or emergence of new technologies of those skilled in the relevant technical field. Also, there are terms arbitrarily selected by the applicant in specific cases, and in such cases, the meaning thereof is described in the explanatory part of the corresponding invention. Therefore, it is clarified that the terms used in this specification should not be merely the names of the terms, but should be interpreted based on the substantial meaning of the terms and the content throughout this specification.

[0031] Throughout the specification, when a component is "connected" to another component, this includes not only cases where they are "directly connected", but also cases where they are "electrically connected" with other components interposed therebetween. Also, when a component "includes" a specific component, this means that, unless otherwise stated to the contrary, it may further include other components rather than excluding them. In addition, limitations such as "above" or "below" based on a specific threshold value may be appropriately replaced by "exceeding" or "less than" respectively according to the embodiments. Hereinafter, in the present invention, a field and a subfield may be used in the same meaning.

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

[0033] The wireless LAN system includes one or more Basic Service Sets (BSSs), where a BSS represents a set of devices that have successfully synchronized and can communicate with each other. Generally, BSSs are classified into infrastructure BSSs and Independent BSSs (IBSSs), and FIG. 1 shows an infrastructure BSS among them.

[0034] As shown in FIG. 1, the infrastructure BSSs BSS1 and BSS2 include one or more stations STA1, STA2, STA3, STA4, STA5, access points AP-1 and AP-2 which are stations providing a Distribution Service, and a Distribution System (DS) that connects the plurality of access points AP-1 and AP-2.

[0035] A station (STA) is any device that includes a Medium Access Control (MAC) and a Physical Layer interface for a wireless medium in accordance with the IEEE 802.11 standard. In a broad sense, it includes not only non-access point non-AP stations but also all access points AP. Also, in this specification, the term "terminal" is used to refer to either a non-AP or an AP, or both. A station for wireless communication includes a processor and a communication unit, and in some embodiments, further includes a user interface unit, a display unit, etc. The processor generates frames to be transmitted via a wireless network, or processes frames received via the wireless network, and performs various other processes for controlling the station. And the communication unit is functionally connected to the processor and transmits and receives frames via the wireless network for the station. In the present invention, the term "terminal" is used to include a user equipment (UE).

[0036] An access point (AP) is an entity that provides a connection to a distribution system DS via a wireless medium for stations associated with itself. In an infrastructure BSS, in principle, communication between non-AP stations is carried out via the AP, but direct communication is also possible between non-AP stations if a direct link is set up. On the other hand, in the present invention, the AP is used as a concept including a PCP (Personal BSS Coordination Point), but in a broad sense, it includes concepts such as a centralized controller, a base station (BS), a Node B, a BTS (Base Transceiver System), or a site controller. In the present invention, the AP is also referred to as a base wireless communication terminal, but the base wireless communication terminal is used as a term that includes, in a broad sense, the AP, a base station, an eNB (eNodeB), and a transmission point TP. Moreover, the base wireless communication terminal includes various forms of wireless communication terminals that allocate communication medium resources and perform scheduling in communication with a plurality of wireless communication terminals.

[0037] A plurality of infrastructure BSSs are connected to each other via a distribution system DS. At this time, a plurality of BSSs connected via the distribution system are called an extended service set (ESS).

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

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

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

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

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

[0043] Next, the display unit 150 outputs an image on the display screen. The display unit 150 outputs various display objects such as content performed by the processor 110 or a user interface based on the control instructions of the processor 110. Also, the memory 160 stores control programs used in the station 100 and various data thereby. Such control programs include connection programs necessary for the station 100 to connect to an AP or an external station.

[0044] The processor 110 of the present invention executes various instructions or programs and processes the data inside the station 100. Further, the processor 110 controls each unit of the station 100 described above and controls the transmission and reception of data between the units. According to an embodiment of the present invention, the processor 110 executes a program for connection with the AP stored in the memory 160 and receives a communication setting message transmitted by the AP. Further, the processor 110 reads information regarding the priority conditions of the station 100 included in the communication setting message and requests a connection regarding the AP based on the information regarding the priority conditions of the station 100. The processor 110 of the present invention may refer to the main control unit of the station 100, or may refer to a control unit for individually controlling a part of the configuration of the station 100, for example, the communication unit 120, etc. according to an embodiment. That is, the processor 110 may be a modem, or a modulator and / or demodulator, which demodulates and modulates the radio signal transmitted and received from the communication unit 120. The processor 110 controls various operations of wireless signal transmission and reception of the station 100 according to an embodiment of the present invention. Detailed embodiments thereof will be described later.

[0045] The station 100 shown in FIG. 3 is a block diagram according to an embodiment of the present invention, and the separately shown blocks logically distinguish the elements of the device. Therefore, the above-described elements of the device may be attached to one chip or a plurality of chips according to the design of the device. For example, the processor 110 and the communication unit 120 may be integrated and implemented on one chip, or may be implemented on separate chips. Further, in an embodiment of the present invention, some configurations of the station 100, for example, the user interface unit 140 and the display unit 150, etc. may be selectively provided in the station 100.

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

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

[0048] Next, the memory 260 stores the control program used in the AP200 and various data thereby. Such control programs include a connection program for managing the connection of stations. Further, the processor 210 controls each unit of the AP200 and controls the transmission and reception of data between units. According to an embodiment of the present invention, the processor 210 executes a program for connection to the station stored in the memory 260 and transmits a communication setting message for one or more stations. At this time, the communication setting message includes information regarding the connection priority conditions of each station. Further, the processor 210 performs connection setting in response to a connection request from the station. According to one embodiment, the processor 210 is a modem or a modulation / demodulation unit that modulates and demodulates a radio signal transmitted and received by the communication unit 220. The processor 210 controls various operations of radio signal transmission and reception of the AP200 according to an embodiment of the present invention. Detailed embodiments thereof will be described later.

[0049] FIG. 5 is a diagram schematically showing a process in which a STA sets a link with an AP.

[0050] Referring to FIG. 5, the link between the STA100 and the AP200 is set through three major steps: scanning, authentication, and association. First, the scanning step is a step in which the STA100 acquires connection information of the BSS operated by the AP200. As a method for performing scanning, there are a passive scanning method of acquiring information by utilizing only the beacon message S101 periodically transmitted by the AP200, and an active scanning method in which the STA100 transmits a probe request to the AP S103, receives a probe response from the AP S105, and acquires connection information.

[0051] In the scanning step, the STA100 that has successfully received the wireless connection information transmits an authentication request to S107a, receives an authentication response from the AP200 to S107b, and performs the authentication step. After the authentication step is performed, the STA100 transmits an association request to S109a, receives an association response from the AP200 to S109b, and performs the association step. In this specification, "association" basically means a wireless connection, but the present invention is not limited thereto, and the association in a broad sense includes all wireless connections and wired connections.

[0052] On the other hand, additionally, an 802.1X-based authentication step S111 and an IP address acquisition step S113 via DHCP are performed. In FIG. 5, the server 300 is a server that processes 802.1X-based authentication with the STA100, and may be physically connected to the AP200 or exist as a separate server.

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

[0054] A terminal that performs wireless LAN communication checks whether the channel is in an occupied state (busy) by performing carrier sensing before transmitting data. If a wireless signal with a certain intensity or higher is detected, the corresponding channel is determined to be in an occupied state, and the terminal delays access to the corresponding channel. Such a process is called Clear Channel Assessment (CCA), and the level for determining the presence or absence of detection of the corresponding signal is called the CCA threshold. If a wireless signal equal to or higher than the CCA threshold received by the terminal has the corresponding terminal as the receiver, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected from the corresponding channel or a wireless signal with an intensity lower than the CCA threshold is detected, the channel is determined to be in an idle state.

[0055] If the channel is determined to be in an idle state, each terminal with data to transmit performs a backoff procedure after a time of IFS (Inter Frame Space) according to the situation of each terminal, for example, AIFS (Arbitration IFS), PIFS (PCF IFS), etc. According to an embodiment, the AIFS is used as a configuration to replace the conventional DIFS (DCF IFS). Each terminal waits while reducing the slot time by the random number determined for the corresponding terminal during the interval of the idle state of the channel, and the terminal that has exhausted all the slot times attempts access to the corresponding channel. In this way, the section where each terminal performs the backoff procedure is called the contention window section.

[0056] If a specific terminal successfully accesses the channel, the corresponding terminal transmits data via the channel. However, if the terminals attempting access collide with other terminals, the colliding terminals are each assigned a new random number and perform a further backoff procedure. According to one embodiment, the new random number newly assigned to each terminal is determined within a range (2*CW) that is twice the range (contention window, CW) of the random number previously assigned to the corresponding terminal. On the other hand, each terminal performs a further backoff procedure in the next contention window period to attempt access. At this time, each terminal performs the backoff procedure from the slot time remaining in the previous contention window period. In this way, each terminal performing wireless LAN communication can avoid mutual collisions with respect to a specific channel.

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

[0058] <Examples of Various PPDU Formats>

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

[0060] Referring to FIG. 7(a), the preamble of the legacy PPDU includes an L-STF (Legacy Short Training field), an L-LTF (Legacy Long Training field), and an L-SIG (Legacy Signal field). In an embodiment of the present invention, the L-STF, L-LTF, and L-SIG can be referred to as a legacy preamble.

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

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

[0063] The L-SIG field included in the preamble of the PPDU applies 64 FFT OFDM and is composed of a total of 64 subcarriers. Among these, 48 subcarriers excluding the guard subcarriers, DC subcarriers, and pilot subcarriers are used for data transmission of L-SIG. Since BPSK and MCS (Modulation and Coding Scheme) with a rate of 1 / 2 are applied to L-SIG, it can contain a total of 24 bits of information. FIG. 7(d) shows the 24-bit information configuration of L-SIG.

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

[0065] The unit of the L_LENGTH field is bytes. A total of 12 bits are allocated and can signal up to 4095, and in combination with the L_RATE field, it can indicate the length of the corresponding PPDU. At this time, the legacy terminal and the non-legacy terminal can interpret the L_LENGTH field in different ways.

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

[0067]

Equation

[0068] At this time,

Number

[0069]

Number

[0070] Here, TXTIME is the total transmission time that constitutes the PPDU and is as shown in Equation 3 below. At this time, TX represents the transmission time of X.

[0071]

Number

[0072] Referring to the above equations, the length of the PPDU is calculated based on the ceiling value of L_LENGTH / 3. Therefore, for any k value, three different values of L_LENGTH = {3k + 1, 3k + 2, 3(k + 1)} indicate the same PPDU length.

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

[0074] The VI bits continue to maintain the current bit configuration later. Even if subsequent generations of PPDUs are defined, current 11be terminals can obtain information about the PPDU from the VI field of the PPDU. For this purpose, the VI field is composed of a PHY version, UL / DL, BSS color, TXOP, and Reserved field. The PHY version field is 3 bits and is responsible for sequentially differentiating 11be and subsequent generations of wireless LAN standards by version. 11be has a value of 000b. The UL / DL field differentiates whether the PPDU is an uplink / downlink PPDU. The BSS color means the BSS identifier defined in 11ax and has a value of 6 bits or more. The TXOP means the transmit opportunity duration transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP included in the PPDU can be inferred without decoding the MPDU and has a value of 7 bits or more.

[0075] The VD field may be composed of signaling information that is only useful for PPDUs in the 11be version, 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 discriminator that distinguishes between EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), EHT ER (Extended Range) PPDUs, etc. The BW field mainly signals five basic PPDU BW options of 20, 40, 80, 160 (80 + 80), 320 (160 + 160) MHz (the BW that can be expressed in the form of 20 * 2 to the power of n can be called the basic BW), and various remaining PPDU BWs formed by preamble puncturing. Also, after being signaled at 320 MHz, some 80 MHz may be signaled in a punctured form. Also, the channel form that has been punctured and deformed may be directly signaled in the BW field, or may be signaled using both the BW field and fields that appear after the BW field (for example, fields within the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signalings are possible, so the puncturing mode can signal a maximum of 3. If the BW field is 4 bits, a total of 16 BW signalings are possible, so the puncturing mode can signal a maximum of 11.

[0076] The fields located after the BW field vary depending on the form and format of the PPDU. The MU PPDU and the SU PPDU may be signaled in the same PPDU format. Before the EHT-SIG field, a field for distinguishing between the MU PPDU and the SU PPDU may be located, and additional signaling may be performed for that purpose. Both the SU PPDU and the MU PPDU contain the EHT-SIG field, but some fields that are unnecessary in the SU PPDU may be compressed. At this time, the information of the fields to which compression is applied may be omitted, or may have a size smaller than the size of the original fields included in the MU PPDU. For example, in the case of the SU PPDU, the common fields of the EHT-SIG may be omitted or replaced, the user-specific fields may be replaced, or it may have different configurations such as being reduced to one.

[0077] Alternatively, the SU PPDU can further include a compression field indicating whether it is compressed, and some fields (such as the RA field, etc.) may be omitted depending on the value of the compression field.

[0078] When a part of the EHT-SIG field of the SU PPDU is compressed, the information contained in the compressed field may be signaled together with the uncompressed fields (such as the common fields). 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 obligatorily after the U-SIG field, and the amount of information to be signaled may be variable. That is, since a plurality of MU PPDUs are transmitted to a plurality of STAs, each STA must recognize the position of the RU to which the MU PPDU is transmitted, the STA to which each RU is assigned, and whether the transmitted MU PPDU is transmitted to itself. Therefore, the AP must transmit the above information in the EHT-SIG field. For this purpose, the U-SIG field signals information for efficiently transmitting the EHT-SIG field, which may be the number of symbols of the EHT-SIG field and / or the MCS which is the modulation method. The EHT-SIG field can include the size and position information of the RUs assigned to each user.

[0079] In the case of the SU PPDU, a plurality of RUs may be assigned to the STA, and the plurality of RUs may be consecutive or non-consecutive. When the RUs assigned to the STA are not consecutive, the STA can efficiently receive the SU PPDU only by recognizing the RUs punctured in the middle. Therefore, the AP can transmit the SU PPDU including the information of the punctured RUs among the RUs assigned to the STA (such as the RU puncturing pattern). That is, in the case of the SU PPDU, a puncturing mode field including information indicating whether the puncturing mode is applied and the puncturing pattern in a bitmap format or the like may be included in the EHT-SIG field, and the puncturing mode field can signal the form of the discontinuous channels appearing within the bandwidth.

[0080] The form of the discontinuous channel signaled is restricted and indicates the BW of the SU PPDU and the discontinuous channel information in combination with the value of the BW field. For example, in the case of an SU PPDU, which is a PPDU transmitted only to a single terminal, the STA can recognize the bandwidth assigned to itself from the BW field included in the PPDU, and can recognize the punctured resources among the assigned bandwidths from the puncturing mode field of the U-SIG field or the EHT-SIG field included in the PPDU. In this case, the terminal can receive the PPDU with the resource units other than the specific channels of the punctured resource units. At this time, the plurality of RUs assigned to the STA may be composed of different frequency bands or tones from each other.

[0081] The reason why only the restricted form of the discontinuous channel form is signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing may be performed for each 20 MHz subchannel, when puncturing is performed for a BW having a plurality of 20 MHz subchannels such as 80, 160, and 320 MHz, in the case of 320 MHz, it is necessary to signal the form of the discontinuous channel (including the case where only the end 20 MHz is punctured as discontinuous) by expressing the availability of each of the remaining 15 20 MHz subchannels excluding the primary channel. Using 15 bits to signal the discontinuous channel form of single-user transmission can result in excessive signaling overhead when considering the low transmission rate of the signaling part.

[0082] The present invention proposes a method for signaling the discontinuous channel form of the SU PPDU and shows the discontinuous channel form determined by the proposed method. In addition, a method for signaling the puncturing forms of the main (Primary) 160 MHz and the secondary (Secondary) 160 MHz in the 320 MHz BW configuration of the SU PPDU is proposed.

[0083] In addition, in one embodiment of the present invention, a method is proposed to vary the configuration of the PPDU according to the preamble puncturing BW value indicated by the PPDU format signaled in the PPDU format field. Assuming that the length of the BW field is 4 bits, in the case of an EHT SU PPDU or a TB PPDU, since it is possible to further signal 1 symbol of EHT-SIG-A after U-SIG or not signal EHT-SIG-A at all, considering this, it is necessary to signal all up to 11 puncturing modes using only the BW field of U-SIG. However, in the case of an EHT MU PPDU, since EHT-SIG-B is further signaled after U-SIG, up to 11 puncturing modes may 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 bandwidth.

[0084] FIG. 7(f) shows the configuration of the format-specific field of the VD field when indicated as an EHT MU PPDU in the PPDU format field of U-SIG. In the case of a MU PPDU, SIG-B, which is a signaling field for simultaneous reception by multiple users, is essential, and SIG-B may be transmitted without a separate SIG-A after U-SIG. Therefore, U-SIG must signal information for decoding SIG-B. Such fields include the SIG-B MCS, SIG-B DCM, number of SIG-B symbols, SIG-B compression, number of EHT-LTF symbols fields, etc.

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

[0086] Referring to FIG. 8, the PPDU may be composed of a preamble and a data part, and the format of one type of EHT PPDU may be distinguished by the U-SIG field included in the preamble. Specifically, based on the PPDU format field included in the U-SIG field, whether the format of the PPDU is an EHT PPDU may be indicated.

[0087] FIG. 8(a) shows an example of the EHT SU PPDU format for a single STA. The EHT SU PPDU is a PPDU used for single-user (SU) transmission between an AP and a single STA, and an EHT-SIG-A field for additional signaling may be located after the U-SIG field.

[0088] FIG. 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. Different from the EHT SU PPDU, the EHT-SIG-A field is not located after the U-SIG field in the EHT PPDU.

[0089] FIG. 8(c) shows an example of the EHT MU PPDU format, which is an EHT PPDU for multiple users. The EHT MU PPDU is a PPDU used for transmitting the PPDU to one or more STAs. The EHT MU PPDU format may have an HE-SIG-B field located after the U-SIG field.

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

[0091] The EHT MU PPDU described in (c) of FIG. 8 can be used by the AP for downlink transmission to multiple STAs. At this time, the EHT MU PPDU can include scheduling information so that multiple STAs can receive the PPDU transmitted from the AP simultaneously. The EHT MU PPDU can transmit the AID information of the receiver and / or transmitter of the PPDU transmitted through the user specific field of the EHT-SIG-B to the STA. Therefore, multiple terminals that have received 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.

[0092] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU can include information regarding the configuration of resource units (e.g., the division form of resource units) in a specific bandwidth (e.g., 20 MHz, etc.) on the frequency axis. That is, the RA field can indicate the configuration of resource units divided by the bandwidth for the transmission of the HE MU PPDU for the STA to receive the PPDU. The information of the STA assigned (or specified) to each divided 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 can include one or more user fields corresponding to each divided resource unit.

[0093] For example, among a plurality of divided resource units, the user field corresponding to at least one resource unit used for data transmission can include the AID of the recipient or the sender, and the user field corresponding to the remaining resource units not used for data transmission can include the already set Null STA ID.

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

[0095] Also, some of the fields shown in FIG. 8 or some of the information in the fields may be omitted, and the case where some of the fields or some of the information in the fields are omitted can be defined as the compression mode or the compressed mode.

[0096] On the other hand, in the AP and the STA, a low-latency operation can be requested for specific traffic that requires a low latency time. At this time, the traffic that requires a low latency time may be transmitted to the MAC layer as follows.

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

[0098] Referring to FIG. 9, the communication device included in the STA is composed of an Application layer that performs various operations in the uppermost layer, a Transport Layer that guarantees the transmission reliability between terminals, a Network Layer that searches for a path to the destination communication node and transmits signals in that direction, a Data Link Layer that performs transmission operations on the communication link between terminals, and a Physical Layer that actually performs transmission operations using physical signals. At this time, the Data Link Layer may include LLC (Logical Link Control) and MAC (Medium Access Control).

[0099] On the other hand, in each layer, data and additional parameters for data transmission can be sent to the upper or lower layer of that layer through the SAP (Service Access Point). For example, information regarding data, source address, destination address, etc. from the upper layer may be transmitted to the LLC layer through the LSAP (Link Service Access Point). Also, the MAC layer can transmit the received data to the upper layer through the MAC SAP, and data to be transmitted from the upper layer and additional parameters for data transmission may be transmitted.

[0100] When the data to be transmitted in the above hierarchical structure is data that requires a low delay time, the MAC layer can receive the data and related parameters from the upper layer in the form of MA-UNITDATA.request. At this time, when the data to be transmitted is data that requires a low delay time, an appropriate indicator can be included when transmitting the data from the upper layer to the MAC layer through the MAC SAP. For example, it can be transmitted including that the data is data that requires a low delay time in the MA-UNITDATA.request. When the indicator for the low delay time is included, the MA-UNITDATA.request can include parameters as shown in Table 1 below.

[0101]

Table 1

[0102] Each parameter included in DA-UNITDATA.request may be as shown in Table 2 below.

[0103]

Table 2

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

[0105] On the other hand, when an AP or a STA supports a low-latency transmission operation for a frame that requires a low latency time, internal variables can be specified for the terminal. For example, one of the MIB (Management Information Base) values indicating whether or not the low-latency operation is activated can be generated and managed within the terminal. At this time, the MIB value may be dot11rTWTActivated. At this time, the low-latency operation is an operation for transmitting latency-sensitive traffic (e.g., latency sensitive traffic) or a frame, and the latency-sensitive traffic or frame may be a traffic or frame that has already been set. For example, the latency-sensitive traffic or frame may be indicated by a TID (or, Access Category: AC) that the traffic or frame is a latency-sensitive traffic or frame.

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

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

[0108] Referring to FIG. 10, an AP MLD (Multi-link Device) may be a device including one or more wireless access points (APs), and may be a device connected to an upper layer through one interface. That is, the AP MLD may be connected to the LLC (Logical Link Control) layer through one interface. A plurality of APs included in the AP MLD can share some functions at the MAC layer. Each AP within the AP MLD can operate on different links. A STA MLD may be a device including one or more non-AP STAs, and may be a device connected to an upper layer through one interface. That is, the STA MLD may be connected to the LLC layer through one interface. A plurality of STAs included in the STA MLD can share some functions at the MAC layer. Also, the STA MLD can be called a non-AP MLD. At this time, the AP MLD and STA MLD can perform a multi-link operation of communicating using a plurality of individual links. That is, when the AP MLD includes a plurality of APs, each AP constitutes a separate link and can perform frame transmission and reception operations using a plurality of 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 bandwidth expansion operations can be performed on each link. For example, when the AP MLD sets 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 by the bandwidth expansion method in the 2.4 GHz band, and frame transmission can be performed with a maximum bandwidth of 320 MHz by utilizing discontinuous bandwidths on each link using the 5 GHz band.

[0109] On the one hand, due to interference problems within the device, while one terminal in the MLD is performing a transmission operation, other terminals may not be able to perform a reception operation. In this way, when one AP or terminal in the MLD is performing a transmission operation, the operation of other APs or terminals in the MLD receiving is called STR (Simultaneous Transmit and Receive). The AP MLD may be capable of performing the STR operation for all links. Alternatively, the STR operation may not be possible for some links of the AP MLD. Terminal MLDs capable of performing the STR operation may be connected to the AP MLD, and MLDs that are not capable of performing the STR operation for some or all links may be connected. Also, terminals that do not belong to the MLD (for example, IEEE 802.11a / b / g / n / ac / ax terminals or IEEE 802.11be terminals not in the MLD form) may be further connected to the APs included in the AP MLD.

[0110] The AP MLD and the 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 processes described in FIG. 5. The AP MLD and the STA MLD can perform a negotiation process for multi-link usage operation during the scanning and connection processes described in FIG. 5. When the negotiation process for multi-link operation is performed during the connection process, the AP MLD and the STA MLD can operate as follows.

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

[0112] Referring to FIG. 11, the AP MLD and the STA MLD can perform a negotiation process for multi-link operation during the scanning and connection processes. For example, in the scanning process described in FIG. 5, the AP included in the AP MLD can transmit, including an indicator indicating that multi-link operation is available, the number of available links, and information on a plurality of available links, etc., in the beacon frame. Or, when the AP MLD transmits a probe response frame in the form of a broadcast frame, it can transmit, including an indicator indicating that multi-link operation is available, the number of available links, and information on a plurality of available links, etc., in the probe response frame. The terminal belonging to the STA MLD can transmit, including an indicator indicating that multi-link operation is available, in the probe request frame. When the STA MLD attempts to perform a negotiation process for multi-link operation, it can further request operation information for all APs belonging to the AP MLD. When the STA belonging to the STA MLD requests information on all APs belonging to the AP MLD, it can transmit, including the request indicator, in the probe request frame. The AP belonging to the AP MLD can confirm the request indicator in the probe request frame and transmit, including all parameters used for multi-link operation (for example, information on the AP and beacon frame information transmitted from other APs belonging to the AP MLD, etc.), in the probe response frame. At this time, the all parameters may include the number of available links, link information, etc., that can be used during multi-link operation.

[0113] The STA MLD that has confirmed whether the AP MLD operates in a multi-link mode and the link information to be used during the scanning process can perform a connection process with the AP MLD. At this time, the AP MLD and the STA MLD can simultaneously perform a negotiation process for multi-link operation. That is, any terminal (for example, STA1) belonging to the STA MLD can send an indication indicating that the multi-link operation of the terminal is available and a request indicator requesting to perform the multi-link operation while sending a connection request frame to any AP (for example, AP1) belonging to the AP MLD. The AP that has received the connection request frame from the terminal can confirm the indicator requesting the multi-link operation, and when the multi-link operation is possible, the AP can send a connection response frame allowing the multi-link operation to the terminal, including the link information used for the multi-link operation and the parameters used for each link. The parameters for the multi-link operation can include one or more of the bandwidth of each link used, the bandwidth expansion direction, the Target Beacon Transmission Time (TBTT), and the availability of the STR operation. The AP MLD and the STA MLD for which the use of the multi-link operation has been confirmed by exchanging the connection request frame and the response frame can perform a frame transmission operation using a plurality of links through the plurality of APs included in the AP MLD and the plurality of terminals included in the STA MLD after the connection process.

[0114] On the other hand, when assisting the low-latency transmission operation for frames that require a low delay time by the AP or the AP MLD, it may be restricted so that only the terminals capable of such an operation are connected to one or more links. That is, in order to efficiently perform the channel reservation process and the transmission process for the low-latency operation, only the connection of the terminals that can decode and understand such an operation on a specific link can be allowed. At this time, the low-latency transmission operation may be a low-latency transmission operation that utilizes the TWT operation. For example, when transmitting by including the reserved time TWT SP (Target Wake Time Service Period) for the low-latency terminal in the beacon frame, in the STA that supports the low-latency operation that utilizes the TWT function, if it is not the STA reserved at the TWT SP time, the channel contention process for frame transmission may not be performed. On the other hand, the STA that does not support the function can perform the channel access process for frame transmission even at the TWT SP. At this time, due to the channel access operation by the STA that does not support the low-latency function that utilizes the TWT operation, a situation may occur where the transmission of the frame reserved to be transmitted at the TWT SP is postponed or collided. Therefore, the required delay time of the frame that requires a low delay time may not be satisfied. To prevent such a situation, the AP and the AP MLD can specify that a specific link is used only by the terminals that perform the channel reservation process by the low-latency operation.

[0115] On the other hand, when the AP or the AP MLD designates a link only for the terminals that support the low-latency operation, the connection request may be rejected for the STA that does not support the function as follows.

[0116] At this time, the low-latency operation is an operation for transmitting latency-sensitive traffic (e.g., latency sensitive traffic) or frames, and the latency-sensitive traffic or frames may be pre-set traffic or frames. For example, the latency-sensitive traffic or frames may be indicated by a TID (or, Access Category: AC) that the traffic or frames are latency-sensitive traffic or frames. Or, the latency-sensitive traffic or frames can mean traffic or frames to be transmitted within a certain latency time, and may be indicated by a TID (or, Access Category: AC).

[0117] TWT schedules STAs to operate at different times so that STAs can manage activities in the BSS in order to minimize contention and reduce the time required for STAs using the power management mode to wake up. The TWT operation may be individual TWT (individual TWT) or broadcast TWT (broadcast TWT) set individually by the AP. That is, the AP can set whether to perform the TWT operation individually for each STA or set whether to perform the TWT operation for multiple STAs using the broadcast TWT, and can transmit to non-AP STAs. The non-AP STA can perform the TWT operation in the interval of the TWT service period (service period: SP) when the execution of the TWT operation is scheduled from the AP.

[0118] At this time, when the broadcast TWT operation is used for low-latency operation, it can be called a Restricted TWT operation. That is, the broadcast TWT operation is such that a non-AP STA supports a restricted TWT operation according to specific parameters of a capability element (for example, when a specific element is set to "1"), and when a beacon frame is set as a frame for a restricted TWT operation by a specific field of the beacon frame, a restricted TWT operation may be performed. At this time, the SP set for broadcast TWT may be an SP for a restricted TWT operation.

[0119] At this time, the restricted TWT, which is a TWT operation for transmitting a frame that requires low latency, may be used to support improved medium access protection and resource reservation for latency-sensitive traffic.

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

[0121] Hereinafter, the restricted TWT operation for low-latency operation can be called a TWT operation.

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

[0123] Referring to FIG. 12, the AP MLD may include a plurality of APs, and each AP can operate a link. At this time, the AP MLD can specify one or more of the links it operates as links only for terminals that support low-latency operations. For example, the link operated by AP1 among the APs belonging to the AP MLD can be specified as a link only for terminals that support low-latency operations. Or, an AP that does not belong to the AP MLD may be operated only for terminals that support low-latency operations.

[0124] The AP or AP MLD can include an indicator indicating whether it supports low-latency operations in a probe response frame transmitted in the form of a beacon frame or a broadcast frame. The low-latency operation may be a low-latency operation using the TWT function described later in FIGS. 18 to 19 and FIGS. 21 to 23.

[0125] For example, when the AP or AP MLD supports the low-latency operation, a field indicating whether to support the low-latency operation can be set to 1 and transmitted in the capability elements included in the beacon frame and the broadcast probe response frame. Also, an indicator indicating that the link is a link only for low-latency terminals can be included in the beacon frame and the broadcast probe response frame and transmitted. For example, an EHT Operation information element can be included in the beacon frame or the broadcast probe response frame, and an indicator (e.g., rTWT Required field, etc.) indicating that support for the low-latency operation is required can be included in the EHT Operation information element and transmitted. Or, by setting both the IBSS STA sub-field and the ESS sub-field values in the Capability information field within the beacon frame or the broadcast probe response frame to 1, existing STAs that do not support the low-latency operation may not be able to recognize the BSS form of the AP. As yet another example, the beacon frame or the broadcast probe response frame may further include an Interworking information element as an addition, and within the Interworking information element, in the Access Network Type sub-field within the Access Network Options field, it can be indicated that the link is a link for the low-latency operation. Among the STA MLD or STAs not belonging to the STA MLD, when it is an STA that does not support the low-latency operation, an indicator indicating that it is a link only for low-latency terminals within the beacon frame or the broadcast probe response frame can be confirmed, and the STA or STA MLD that has confirmed the indicator does not need to perform the active scanning process and the connection process with the AP or AP MLD.

[0126] A STA MLD or a STA not belonging to the STA MLD can attempt the scanning and connection process with the AP or the AP MLD as described in FIG. 5. For example, the STA MLD or the STA can send a probe request frame to the AP or the AP MLD. At this time, the STA or the STA MLD can include function information supported by the STA or the STA MLD in the probe request frame. For example, when the STA or the STA MLD supports low-latency operation, an indicator field for supporting the function can be set to 1 in the capabilities element within the probe request frame and then sent. On the other hand, when the STA or the STA MLD does not support the function, a field indicating whether low-latency operation is supported among the capabilities elements within the probe request frame can be set to 0 and then sent.

[0127] The AP or the AP MLD can receive the probe request frame from the STA or the STA MLD and can confirm whether the STA or the STA MLD supports low-latency operation. When it is confirmed that the STA or the STA MLD does not support low-latency operation, the AP or the AP MLD does not have to send a probe response frame, which is a response to the probe request frame. Or, the AP or the AP MLD can indicate that the AP is an AP that supports only low-latency terminals while sending a probe response frame, which is a response to the probe request frame. The indicator indicating that the AP is an AP that supports only low-latency terminals can be an indicator indicating that it is a link only for the aforementioned low-latency terminals. When the STA or the STA MLD does not support low-latency operation, an indicator indicating that it is a link only for low-latency terminals within the probe response frame can be confirmed, and the connection process with the AP or the AP MLD does not have to be performed.

[0128] On the one hand, when the STA supports the low-latency operation or when the indicators in the beacon frame and the probe response frame cannot be decoded, the STA can send 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 can send a connection response frame as a response to the connection request frame. When the STA that sent the connection request frame supports the low-latency operation, the connection response frame can include an indicator accepting the connection request. On the other hand, when the STA that sent the connection request frame does not support the low-latency operation, the connection response frame can include an indicator rejecting the connection request. At this time, the AP can indicate in the status code field of the connection response frame rejecting the connection request that the connection request was rejected because the STA does not support the low-latency operation. For example, a field value (e.g., 133, etc.) meaning LOW_LATENCY_SUPPORT_NEEDED can be set in the status code field to send a probe response frame. When the AP included in the AP MLD rejects the connection request by responding to the connection request frame, other link information can be further included as an addition to propose a connection to another link. Information about a general link that is not a link only for the low-latency terminal may be sent in the form of a Neighbor Report information element. The Neighbor Report information element may include at least one of BSSID, channel and operation class, and timing information.

[0129] In the STA that has received a connection response frame including a rejection indicator from the AP, the content of the received connection response frame can be confirmed, and it can be confirmed that the connection request has been rejected. At this time, the STA can confirm the state code field value in the connection response frame, confirm that the link requires support for low-latency operation, and confirm the presence or absence of the Neighbor Report information element in the connection response frame. When the response frame includes a Neighbor Report information element, the STA can confirm the content and confirm the proposed BSS information. The STA can confirm other link information included in the Neighbor Report information element and move to the channel indicated by the information to perform the connection process with the AP of the link as described in FIG. 5 or FIG. 11.

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

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

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

[0133] The AP or AP MLD can transmit a probe response frame sent 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 to support low-latency operation using the TWT function can be set to 1 and transmitted in the capability element within the beacon frame or the broadcast probe response frame. Also, the beacon frame or the broadcast probe response frame can be transmitted including an indicator indicating that the link is a link only for terminals that support the TWT operation. For example, the beacon frame or the broadcast probe response frame can include an EHT Operation information element, and the EHT Operation information element can include an indicator (such as a TWT Operation Required field) notifying that support for the TWT operation is required. Or, as described in FIG. 12, among the Capability information field or the interworking information element, the Access Network Type sub-field within the Access Network Options field can be used to request support for the TWT function. When the STA MLD or a STA that does not belong to the STA MLD does not support the TWT operation, an indicator indicating that the link is a link only for terminals that support the TWT function within the beacon frame or the broadcast probe response frame can be confirmed, and the STA or STA MLD that has confirmed the indicator does not need to perform the active scanning process and the connection process with the AP or AP MLD. On the other hand, the AP or AP MLD can indicate that although the TWT function itself is supported, a negotiation process for the TWT operation is required for a STA or STA MLD that does not support low-latency operation using the TWT function by setting the TWT Required field in the HE Operation information element within the beacon frame or the broadcast probe response frame to 1.

[0134] A STA MLD or a STA not belonging to the STA MLD can attempt the scanning and connection process with the AP or the AP MLD as described in FIG. 5. For example, the STA MLD or the STA can send a probe request frame to the AP or the AP MLD. At this time, the STA or the STA MLD can include function information supported by the STA or the STA MLD in the probe request frame. For example, when the STA or the STA MLD supports TWT, an indicator field (e.g., TWT Requester Support field) for supporting the function can be set to 1 in the HE capability element in the probe request frame and then sent. Also, when the STA or the STA MLD supports low-latency operation utilizing the TWT function, an indicator for supporting the function can be further included as an addition in the probe request frame and then sent. For example, an indicator field for supporting the function can be set to 1 in the EHT capability element in the probe request frame and then sent. On the other hand, when the STA or the STA MLD does not support the function, in the HE capability element and the EHT capability element in the probe request frame, a field indicating whether to support the TWT function and a field indicating whether to support low-latency operation utilizing the TWT function can be set to 0 and then sent.

[0135] The AP or AP MLD can receive the probe request frame from the STA or STA MLD, and can confirm whether the STA or STA MLD supports the TWT function and the low-latency operation utilizing the TWT function. When it is confirmed that the STA or STA MLD does not support the TWT function, the AP or AP MLD does not have to send a probe response frame, which is a response to the probe request frame. Or, the AP or AP MLD can send a probe response frame, which is a response to the probe request frame, and can indicate that the AP requires support for the TWT function. The indicator indicating the need for support for the TWT function may be the indicator notifying the need for support for the aforementioned TWT operation. When the STA or STA MLD does not support the TWT function, the indicator requesting the TWT function in the probe response frame can be confirmed, and the connection process with the AP or AP MLD does not have to be performed. On the other hand, the AP or AP MLD can indicate that although the TWT function itself is supported, a negotiation process for the TWT operation is required for the STA or STA MLD that does not support the low-latency operation utilizing the TWT function, by setting the TWT Required field to 1 in the HE Operation information element within the probe response frame.

[0136] On the one hand, when a STA or a STA MLD supports the TWT function or when the indicators in the beacon frame and the probe response frame cannot be decoded, the STA can send 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 can send a connection response frame as a response to the connection request frame. When the STA that sends the connection request frame supports the TWT operation, the connection response frame can include an indicator accepting the connection request. At this time, by setting the TWT Required field to 1 in the HE Operation information element in the connection response frame, it can be indicated that although the TWT function itself is supported, a negotiation process for the TWT operation is required for a STA or a STA MLD that does not support low-latency operation using the TWT function. On the other hand, when the STA that sends the connection request frame does not support the TWT operation, the connection response frame can include an indicator rejecting the connection request. At this time, the AP can indicate in the status code field of the connection response frame rejecting the connection request that the connection request has been rejected because the STA does not support the TWT function. For example, a field value (e.g., 134, etc.) meaning TWT_REQUESTER_SUPPORT_NEEDED can be set in the status code field to send a probe response frame. When the AP included in the AP MLD rejects the connection request by responding to the connection request frame, as shown in FIG. 12, other link information can be further included as an addition to propose a connection to another link. Information about a general link that is not a link only for the low-latency terminal may be sent in the form of a Neighbor Report information element. The Neighbor Report information element may include at least one of BSSID, channel and operation class, and timing information.

[0137] In the STA that has received a connection response frame including a rejection indicator from the AP, the content of the received connection response frame can be confirmed, and it can be confirmed that the connection request has been rejected. At this time, the STA can confirm the value of the status code field in the connection response frame, confirm that the link requires the support of the TWT operation, and confirm whether the Neighbor Report information element is included in the connection response frame. When the Neighbor Report information element is included in the response frame, the STA can confirm the content as shown in FIG. 12 and perform the connection process with the AP indicated by the information element.

[0138] On the other hand, the AP or AP MLD can set the TWT Required field in the HE Operation element to be transmitted to 1. At this time, among the STA MLD or STAs that do not belong to the STA MLD and support the TWT function but do not support the low-latency operation using the TWT function, it can be recognized that a negotiation process for the TWT operation is required after the connection process with the AP or AP MLD. Thereby, the STA or STA MLD can perform a negotiation process for the TWT operation with the AP or AP MLD during or after the connection process with the AP or AP MLD. After negotiating the TWT operation, it is not necessary to perform a frame transmission operation at times other than the negotiated TWT SP. On the other hand, when the STA or STA MLD supports all of the TWT operation and the low-latency operation using the TWT function, it is not necessary to perform a separate negotiation process for the TWT operation after the connection operation. At this time, the STA or STA MLD can confirm the TWT SP for the low-latency operation transmitted by the AP in the beacon frame or the broadcast probe response frame, and can complete the frame transmission process before the start time of the TWT SP. That is, a STA or STA MLD that supports the low-latency operation does not have to perform frame transmission during the TWT SP time for the low-latency operation when not negotiated with the AP in advance. In other words, the frame transmission operation may be completed before the start time of the TWT SP for the low-latency operation.

[0139] On one hand, an AP MLD or an AP not belonging to an AP MLD can measure information regarding the frame transmission delay time for the link it operates. The specification of the transmission delay time may be continuously updated and stored in the AP at a fixed time interval (e.g., 100 ms). An AP MLD that supports low-delay transmission operations can provide statistical information related to the transmission delay time of frames transmitted on each link it operates. 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 itself and other APs belonging to the same AP MLD. The statistical information may be included and transmitted in beacon frames, probe response frames, connection response frames, etc. transmitted by the AP MLD. When the STA that has confirmed the statistical information has a frame that requires a low delay time, it can perform the connection process with the AP belonging to the AP MLD according to the operations shown in FIGS. 5 and 12 to 13 based on this information. On the other hand, when the STA MLD that has confirmed the statistical information has a frame that requires a low delay time, it can perform the connection process and the negotiation process for multi-link operations with the AP MLD according to the operations shown in FIGS. 5 and 11 to 13 based on this information. Also, the STA MLD can determine through which link to transmit a frame that requires a low delay time based on this information.

[0140] The statistical information may be transmitted in the form of a Measurement Report information element. The information element related to the transmission delay time may be STA statistics with the Measurement type field of the Measurement Report information element set to 7, among which the average channel access time (Access Delay) by access category (AC) within the BSS can be included. Or, it can include the retransmission count information for each UP (User Priority) value. Alternatively, as follows, the Measurement Report information element can include the average transmission time and transmission success probability by AC.

[0141] FIG. 14 is a block diagram showing a link state information element including transmission state information at the link according to an embodiment of the present invention.

[0142] Referring to FIG. 14, the Measurement Report information element including transmission state information at the link may include an element ID field, a length field, a field indicating the form of the measured information, a field indicating the measurement period, a field indicating the measurement information group, and a field indicating the measured data information. At this time, the element ID field, the length field, the field indicating the form of the 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 regarding the transmission delay time transmitted by the AP. The measurement information may include at least one of the average transmission time for all frames transmitted on the link, the average transmission time for each AC of the frames transmitted on the link, the variance of the average transmission time for each AC of the frames transmitted on the link, the upper 95% value of the transmission time for each AC of the frames transmitted on the link, the transmission failure probability for all frames transmitted on the link, and the transmission failure probability for each AC of the frames transmitted on the link. At this time, the transmission time may be calculated from the time when the frame transmitted by the AP is generated to the time when the ACK frame is received due to the completion of the transmission of the frame. Alternatively, the transmission time may be calculated from the time when the frame transmitted by the AP is generated to the end time of transmission or retransmission before receiving the ACK when receiving the ACK due to the completion of the transmission of the frame. The transmission failure probability may be calculated as “(the number of times of transmission failure exceeding the frame retransmission limit count) / (the number of times of receiving ACK for frame transmission + the number of times of transmission failure exceeding the frame retransmission limit count)” during the measurement period.

[0143] On one hand, a STA or STA MLD attempting to transmit a frame that requires a low latency can indicate information such as the required latency time for the frame to an AP or AP MLD. At this time, the frame having the low latency may be identified with a specific traffic stream (TS). When the frame requiring the low latency is data assigned to a specific TS, the STA or STA MLD can perform a negotiation process with the AP or AP MLD to add a TS for the data. For example, a process can be performed in which the STA transmits a TS addition request frame to the AP to add a TS for traffic requiring a low latency, and the AP transmits a TS addition response frame as a response to the TS addition request frame. Through this TS addition negotiation operation, the STA can transmit to the AP, including one or more of the latency time information, data size, and required transmission rate of the data of the TS to be added.

[0144] A STA or STA MLD attempting to transmit a frame that requires a low latency can perform a negotiation process with the AP or AP MLD for a low latency operation. The negotiation process for the low latency operation may be performed in the same or a similar manner as the negotiation process for the TWT operation. That is, when transmitting a request frame to the AP for a low latency operation from the STA, the request frame may be a TWT request frame. The response frame for the low latency operation transmitted from the AP to the STA may be a TWT response frame.

[0145] On the other hand, information such as the required latency time for the frame to be transmitted in the request frame for the low latency operation can be included and transmitted. When the low latency operation request frame includes the required latency time and frame generation information, etc., the low latency operation request frame will be described in FIG. 15 below.

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

[0147] Referring to FIG. 15, the frame requiring the low-latency operation may be configured in the form of a TWT request frame. Accordingly, the request frame may include a TWT information element. The TWT information element included in the low-latency operation request frame may include an element ID field, a length field, a control field, and a parameter field for the low-latency operation utilizing the TWT operation. It may include an NDP Paging indicator field which is a field related to the channel measurement operation, a field indicating whether the PS mode conversion of the TWT responder is possible, a field indicating the TWT negotiation form, a field indicating whether the TWT schedule adjustment is possible, a field indicating the unit of the required delay time, and the like. Among the control fields, fields other than the field indicating the unit of the required delay time may be set in the same manner as the setting method during negotiation for the broadcast TWT operation. For example, in the TWT request frame for the low-latency operation, by setting the NDP Paging indicator field to 0 and the field indicating whether the PS mode conversion of the TWT responder is possible to 0, the function can be set not to be used. By setting the field indicating the TWT negotiation form to 3, it can be indicated that the TWT operation is a request frame for negotiation of the broadcast TWT form in which the TWT SP for the low-latency terminal is periodically transmitted in the beacon frame. The unit field of the required delay time indicates the unit of the maximum delay time that the frame requiring the low-latency operation generally requires. When the field is 0, it can display a unit of 256 μs, and when it is 1, it can display a unit of 32 μs.

[0148] The parameter field for the low-latency operation utilizing the TWT operation may include one or more of a request type field, a field indicating the point in time when low-latency traffic is predicted to occur, a required delay time field, a significant figure field for the period of the low-latency time based on the requested TWT operation, and a broadcast TWT information field.

[0149] The request form field may include a field indicating whether it is a TWT request frame, a TWT setting instruction field, a trigger field, an operation mode field, an operation mode field in the broadcast TWT time (or, broadcast TWT SP), an exponent field for the period of the required low-latency time, a field indicating that the TWT operation is a TWT for low-latency operation, and the like. For example, the request form field may include a specific field indicating that the TWT operation by the frame is a restricted TWT operation. At this time, depending on the value of the specific field, the frame that can be transmitted in the TWT SP by the TWT operation may be restricted to a specific frame for the downlink frame, or the broadcast SP may be set to a restricted TWT SP. That is, if the value of the specific field (for example, the broadcast TWT recommendation field) is "1", the frame that can be transmitted in the TWT SP is restricted to a specific frame for the downlink frame, and if the value of the specific field is "4", the broadcast TWT SP may be set to a restricted TWT SP.

[0150] At this time, for fields other than the operation mode field in the broadcast TWT time, the exponent field for the period of the required low-latency time, the TWT field, and the field indicating that the TWT operation is a TWT for low-latency operation among the request form fields, they may be set in the same form as the TWT information element included in the existing broadcast TWT request frame.

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

[0152] Also, when requesting to limit the AC transmitted within the TWT SP period for the low-latency terminal, this field can be set to 4. When requesting an additional protection operation (such as a Quiet Time Setup frame, or an RTS frame, or a MU-RTS frame, etc.) to protect the SP at the start point of the TWT SP for the low-latency terminal, this field can be set to 5. Or, when requesting that communication between STAs be possible in the TWT SP, this field can be set to 6. The exponent field for the requested low-latency time period can indicate the SP period for the TWT-based low-latency operation together with the significant digit field for the aforementioned low-latency time period. 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 time period) × 2 ^ (exponent field value for the low-latency time period)". Also, the field indicating that the TWT operation is a TWT for a low-latency operation can indicate that the TWT information element is for a low-latency operation when set to 1.

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

[0154] On the other hand, the field indicating the time point when low-latency traffic is predicted to occur can indicate the time point when a frame requiring the low latency time is expected to occur. The required delay time field is the maximum delay time required by the frame, and can display the delay time required in the uplink and downlink for the frame of this form together with the unit field for the required delay time described above. The broadcast TWT information field may be set in the same way as the field setting method in the existing broadcast TWT operation. Or, 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 this (for example, when the operation mode field in the TWT time is set to 4), the broadcast TWT information field may include the AC or TID to be restricted instead of the broadcast TWT ID field.

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

[0156] Specifically, the broadcast TWT information field may include a field including information related to the TID. The field including information related to the TID may include a control field, a DL bitmap (or, restricted TWT DL TID bitmap) field, and a UL bitmap (or, restricted TWT UL TID bitmap) field.

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

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

[0159] The UL bitmap valid field is a field indicating the validity of the UL bitmap field. When set to "0", it indicates that the uplink frames for all TIDs are delay-sensitive traffic. When set to "1", it indicates that the uplink traffic of the TID corresponding to the value "1" in the UL bitmap is delay-sensitive traffic, and the uplink traffic of the TID corresponding to the value "0" is non-delay-sensitive traffic. On the other hand, information regarding the low-delay time period based on the TWT operation may have the generation period of frames that require a low delay time to be transmitted in the low-delay operation set.

[0160] On the other hand, before the negotiation process for the low-delay operation utilizing the TWT function, when the TS negotiation for traffic requiring a low delay time has been completed, the negotiation process for the low-delay operation may not include a required delay time or the like. In this case, the low-delay operation request frame may be configured as shown in FIG. 16 described below.

[0161] FIG. 16 is a second embodiment showing the structure of a low-delay operation request frame for requesting a low-delay operation utilizing the TWT function according to an embodiment of the present invention. The same description as in FIG. 15 in FIG. 16 is omitted.

[0162] Referring to FIG. 16, a delay operation request frame that requests low-latency operation by utilizing the TWT function may be configured similarly to a TWT operation request frame for negotiating a broadcast TWT operation. Therefore, the frame may include a TWT information element, and the TWT information element may 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 may be set the same as those set in the request frame for negotiating a broadcast TWT.

[0163] The TWT parameter information field may include a request form field, a TWT field, the minimum time for the STA to maintain an awake state among the TWT times, the significant digits of the interval between TWT SPs, and broadcast TWT information. Among the request fields, fields other than the operation mode field at the TWT time and the field indicating that the TWT operation is a TWT for low-latency operation may be set the same as the existing broadcast TWT setting method. The operation mode field at the TWT time and the field indicating that the TWT operation is a TWT for low-latency operation may be set as shown in FIG. 15. Alternatively, when the exchange of the TWT operation request frame is transmitted after a negotiation process for adding a TS, it may be possible to request the allocation of a TWT SP limited to a specific traffic stream ID (TSID). At this time, the operation mode field at the TWT time may be set to 7. An indication field may be added to the request field to indicate that the TWT request frame is a TWT request frame for low-latency operation, as described in FIG. 15. The broadcast TWT information field may be set the same as the low-latency operation request frame using the TWT described in FIG. 15. Alternatively, when the TWT operation request frame requests the provision of a TWT SP limited to a specific TSID (for example, when the operation mode field at the TWT time is set to 7), the broadcast TWT information field may include the lower 3 bits of the TSID for limitation instead of the broadcast TWT ID field.

[0164] On the one hand, as shown in FIG. 15 or FIG. 16, the AP or the AP MLD can confirm from the content of the request frame the low-latency operation utilizing the TWT function. Based on information such as the required delay time and traffic generation period confirmed from the request frame, the AP can allocate one of the broadcast TWTs for the low-latency operation it has allocated. Or, a new broadcast TWT only for the traffic can be generated to allocate the TWT SP for the low-latency operation. When allocating the broadcast TWT in the above manner for the low-latency operation request using the TWT operation, a low-latency operation response frame can be transmitted as a response to the low-latency operation request frame using the TWT operation. Or, 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 may be configured as follows.

[0165] FIG. 17 is a block diagram showing a low-latency operation response frame which is a response to a request frame requesting a low-latency operation utilizing the TWT function. At this time, the description of the parts having the same configuration as the request frame requesting the low-latency operation utilizing the TWT function in FIGS. 15 to 16 may be omitted.

[0166] Referring to FIG. 17, the low-latency operation response frame utilizing the TWT may be configured similarly to the response frame for the broadcast TWT operation. That is, it may include the TWT information element included in the response frame for the 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 the same as those set in the response frame for the negotiation of the broadcast TWT.

[0167] The TWT parameter information field may include a request form field, a TWT field, the minimum time for the STA to maintain the awake state among the TWT times, the significant digits of the interval between TWT SPs, and broadcast TWT information. Among the request form fields, fields other than the operation mode field at the TWT time and the field indicating that the TWT operation is a TWT for low-latency operation may be set the same as the existing broadcast TWT setting method. The field indicating that the TWT operation is a TWT for low-latency operation may be set the same as in FIGS. 15 and 16. The operation mode field at the broadcast TWT time is used when attempting to restrict frame transmission at the TWT SP time, as shown in FIGS. 15 and 16. For example, when attempting to restrict transmission only in the form of a response frame to a downlink frame (e.g., an ACK or BlockAck frame for a downlink data frame, or an uplink frame transmitted as a response to a trigger frame) in the negotiated TWT SP presented in the response frame, the field can be set to 1. Also, when setting to restrict the AC transmitted within the TWT SP period for the low-latency terminal, the field can be set to 4. When attempting to perform an additional protection operation (e.g., Quiet Time Setup frame or RTS frame or 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 STA-to-STA communication to be possible in 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, an allocation of a TWT SP limited to a specific traffic stream ID (TSID) can be requested. At this time, the operation mode field at the TWT time may be set to 7. An indication field indicating that the TWT request frame is a TWT request frame for low-latency operation may be added to the request field, as described in FIGS. 15 and 16. The broadcast TWT information field may be set the same as the response frame for the existing broadcast TWT negotiation.Or, when attempting to restrict so that only frames with a priority equal to or higher than a specific AC are transmitted during the TWT SP period for the low-latency operation (for example, when the operation mode field in the TWT time is set to 4), the broadcast TWT information field of the response frame may further include the AC to be restricted as an addition. Or, when attempting to restrict the specific TSID of the frames that can be transmitted to the TWT SP (for example, when the operation mode field in the TWT time is set to 7), the broadcast TWT information field of the response frame may further include the TSID as an addition for the restriction.

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

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

[0170] Referring to FIG. 18, the process of performing the low-latency operation for the TWT operation may include a stage of confirming the low-latency operation function at the STA and the AP, a stage of transmitting a low-latency operation request frame at the STA, and transmitting the low-latency operation response frame at the AP to negotiate the low-latency operation utilizing the TWT operation, and a stage of allocating a TWT SP for the low-latency operation to a broadcast probe response frame, a beacon frame, etc. at the AP and performing the low-latency operation. At this time, before the stage of negotiating the low-latency operation utilizing the TWT operation, a stage of negotiating to add a TS to the STA and the AP may further be included. Also, after the stage of negotiating the low-latency operation utilizing the TWT operation, a stage of negotiating to exchange the timing of the beacon frame to which the negotiated TWT SP is allocated at the STA may further be included.

[0171] The step of verifying the function of the low-latency operation may 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 may be performed according to the processes shown in FIGS. 5 and 11 to 13. At this time, the AP and STA can send an indicator indicating whether to support the low-latency operation using the TWT function in the capability element. Also, the AP or AP MLD can include statistical information related to the transmission time of frames transmitted on each link in operation in the beacon frame and probe response frame, etc., and send them. The statistical information may be a Measurement Report information element. Or, the statistical information may be the Measurement Report information element shown in FIG. 14. The STA or STA MLD can check the statistical information sent by the AP or AP MLD and perform the connection process with the AP or AP MLD based on the information.

[0172] The process of negotiating to perform the low-latency operation using the TWT operation after the scanning and connection process may start with the process of the STA sending a low-latency operation request frame using the TWT operation to the AP. At this time, the low-latency operation request frame using the TWT operation may be configured as shown in FIG. 15 or FIG. 16. The request frame may be an action frame. An AP that supports the low-latency operation can receive the low-latency operation request frame using the TWT operation from the STA and confirm, based on the received content, that it requests the TWT SP allocation for the frame in which the STA requests a low delay time. When the AP can allocate the TWT SP corresponding to the request frame, the AP can send a low-latency operation response frame using the TWT as a response to the request frame. At this time, the low-latency operation response frame using the TWT operation may be configured as shown in FIG. 17.

[0173] Alternatively, when the STA and the AP perform a negotiation process for adding a TS, the AP can transmit a low-latency operation response frame using a TWT operation that it has not requested to support the TS. In this case, after the STA performs the negotiation for adding the TS, it can transmit a frame requesting a low delay time to the TWT SP without separately transmitting a request frame. At this time, if the low-latency operation is not performed according to the parameters included in the low-latency operation response frame not requested by the STA, the low-latency operation can be cancelled with a TWT cancellation frame, a low-latency operation request frame using a new TWT operation can be transmitted, and a low-latency operation based on the TWT operation can be requested from the AP.

[0174] When the low-latency operation negotiation process using the TWT operation ends, the AP can assign a broadcast TWT ID to the TWT SP assigned to the STA. The broadcast TWT ID can be received with the low-latency operation response frame described in FIG. 17. At this time, the same TWT ID may be assigned to a plurality of STAs. The low-latency operation method using the TWT operation may proceed similarly to the operation method of the broadcast TWT. That is, a TWT element including a broadcast TWT SP can be transmitted for all the broadcast TWT IDs set in the AP in the beacon frame and the broadcast probe response frame. At this time, some of the broadcast TWT IDs may be TWT SPs for low-latency operations. The STA that has completed the low-latency operation negotiation by the TWT operation can confirm the broadcast TWT ID assigned by the low-latency operation response frame, and can confirm the TWT parameter including the assigned broadcast TWT ID among the TWT elements included in the beacon frame. Frames requesting a low delay time can be transmitted and received at the time indicated by the TWT parameter. On the other hand, for the STA to which the broadcast TWT ID has not been assigned, when the TWT SP displayed in the TWT element is confirmed as a TWT SP for low-latency operations, it does not have to perform a frame transmission operation in the TWT SP.

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

[0176] At this time, in order to further protect the transmission of frames for the low-latency operation, the AP can further transmit an information element for protecting the time in the beacon frame. For example, when transmitting the TWT SP for the low-latency operation in the beacon frame, one or more Quiet information elements set as the same time for some or all of the plurality of TWT SPs for the low-latency operation can be further transmitted. Among the STAs that have received the Quiet information element, the STAs to which the TWT SP is not assigned at the same time as the time can set the NAV at the time included in the Quiet information element and do not have to perform frame transmission. At this time, when the TWT SP time indicated by the TWT parameter including the assigned broadcast TWT ID matches the time of the received Quiet information element, the STA can ignore the Quiet information element and perform a frame transmission operation at the time. Through this process, the STA to which the TWT SP is assigned for the low-latency operation can transmit a frame that requires a low delay time without interference from other terminals at the time.

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

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

[0179] When the TWT SP and the quiet information element are both set for a non-AP STA and a part or all of the TWT SP for the interval and delay operation set by the quiet information element overlap, the non-AP STA can ignore a part or all of the overlapping portions of the intervals set by the quiet information element. That is, the non-AP STA can operate as if there is no quiet interval, which is an interval set by the quiet information element that overlaps with the limited TWT SP for low latency.

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

[0181] On the other hand, a process of negotiating the transmission time of a beacon frame including a broadcast TWT ID agreed between the STA and the AP after the negotiation process for low-latency operation using the TWT function may be further performed. The process may be performed by exchanging a broadcast TWT request frame and a broadcast TWT response frame. At this time, the TWT field may be set to the time when the beacon frame is transmitted. At this time, the field indicating the period between TWT SPs may be set as the period of the beacon frame including the corresponding broadcast TWT ID.

[0182] On the other hand, the negotiation process for low-latency operation using the TWT function may be performed during the connection process between the STA and the AP. Therefore, the STA attempting to perform low-latency operation does not need to perform a separate negotiation process after connecting to the AP. At this time, the negotiation and operation process using the TWT operation may be performed as follows.

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

[0184] Referring to FIG. 19, the process of performing low-latency operation for the TWT operation may include a stage of confirming the low-latency operation function in the STA and the AP, a stage of transmitting a low-latency operation request frame in the STA and transmitting the low-latency operation response frame in the AP to negotiate the low-latency operation using the TWT operation, and a stage in which the AP allocates a TWT SP for low-latency operation to a broadcast probe response frame, a beacon frame, etc. and performs low-latency operation. At this time, before the stage of negotiating the low-latency operation using the TWT operation, a stage of negotiating to add a TS to the STA and the AP may be further included. Also, after the stage of negotiating the low-latency operation using the TWT operation, a negotiation stage for exchanging the timing of the beacon frame to which the negotiated TWT SP is allocated in the STA may be further included.

[0185] The step of checking the function of the low-latency operation may 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 may be performed according to the processes of FIG. 5 and FIGS. 11 to 13. At this time, the AP can include an indicator indicating whether to support the low-latency operation using the TWT function in the beacon frame, the broadcast probe response frame, and the capability element in the probe response frame and then transmit them. The STA can receive the beacon frame, the broadcast probe response frame, and the probe response frame, and confirm that the AP supports the low-latency operation using the TWT operation. In addition, the AP or AP MLD can include statistical information related to the transmission time of the frames transmitted on the link for all the links to be operated in the beacon frame and the probe response frame and then transmit them. The statistical information may be the Measurement Report information element. Alternatively, the statistical information may be the Measurement Report information element shown in FIG. 14. On the other hand, the STA can include an indicator indicating whether to support the low-latency operation using the TWT function in the capability elements of the probe request frame and the connection request frame and then transmit them. The AP can confirm that the STA performs the low-latency operation function using the TWT operation based on the probe request frame and the connection request frame received from the STA.

[0186] When the STA has confirmed that the AP supports the function through the beacon frame, broadcast probe response frame, and probe response frame received from the AP, if a frame that requires a low delay time is generated, the connection request frame can include a low-latency operation request indicator that utilizes the TWT function to request the use of the function. At this time, the low-latency operation request indicator that utilizes the TWT function may be the TWT information element described in FIG. 16 or FIG. 17. The AP can receive the connection request frame from the STA and can confirm the low-latency operation request indicator that utilizes the TWT function included in the frame. The AP can confirm that, based on the content of the confirmed request indicator, the STA requests a TWT SP allocation for a frame that requires a low delay time. When the AP can allocate the corresponding TWT SP to the request frame, the AP can include a low-latency operation response indicator that utilizes TWT as a response to the request frame in the connection response frame and transmit it. At this time, the low-latency response indicator that utilizes the TWT operation may be the TWT information element described in FIG. 17.

[0187] Alternatively, when the STA has confirmed that the STA supports low-latency operations that utilize the TWT function through the probe request frame and connection request frame transmitted by the STA, the AP can transmit a low-latency operation response indicator that uses a TWT operation not requested in the connection response frame. In this case, the STA can transmit a frame that requires a low delay time to the TWT SP without transmitting a separate request frame. At this time, if the low-latency operation is not performed according to the parameters included in the low-latency operation response frame not requested by the STA, the low-latency operation can be cancelled with a TWT cancellation frame, a low-latency operation request frame that utilizes a new TWT operation can be transmitted, and the low-latency operation can be requested from the AP.

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

[0189] On the other hand, during the low-latency operation utilizing the TWT operation, the following problem may occur when a terminal incapable of performing the STR operation is connected to the link.

[0190] FIG. 20 shows an operation in which, when the STR operation is impossible for the AP MLD and the STA MLD performing the low-latency operation, the beacon frame cannot be received, so that the TWT information element is missed and the TWT time for the low-latency operation is not protected.

[0191] Referring to FIG. 20, the AP MLD may include two or more APs. At this time, each AP can operate a separate link. For example, the AP MLD may include AP1 and AP2. AP1 can operate on Link 1, and AP2 can operate on Link 2. On the other hand, the STA MLD may include STA1 and STA2. 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 STA1 of the STA MLD is performing a frame transmission operation on Link 1, due to the interference effect of the transmission, STA2 may not be able to perform a channel sensing operation and a frame reception operation on Link 2. Or, while STA2 of the STA MLD is performing a frame transmission operation on Link 2, due to the interference effect of the transmission, STA1 may not be able to perform a channel sensing operation and a frame reception operation on Link 1.

[0192] The characteristic that the STR operation in the STA MLD is impossible can interfere with the low-latency transmission operation using the TWT operation. For example, when performing a low-latency transmission operation using a TWT terminal on Link 1, the TWT SP can be indicated by a beacon frame. At this time, if the STA MLD is performing a frame transmission operation using Link 2, it may not be able to receive the beacon frame transmitted on Link 1 and may not be able to recognize the TWT SP for the low-latency operation included in the beacon frame. STA1 of the STA MLD that cannot recognize the TWT SP for the low-latency terminal may perform a channel access operation for frame transmission using the TWT SP, and the transmission of a frame that requests a low latency time using the TWT SP may not be protected.

[0193] To solve the above problems, the AP MLD can perform the update operation of the TWT-related parameters for the low-latency operation at the same time as follows.

[0194] FIG. 21 is a diagram showing an operation of performing parameter change at the same time when the AP MLD utilizes the TWT operation to perform a low-latency operation.

[0195] Referring to FIG. 21, it is possible to set the parameter change time point to be the same for all TWT SPs for all low-latency terminals assigned by AP MLD. For example, the TWT SP-related parameters for low-latency terminals may be allowed to be changeable only in the beacon frame including DTIM (Delivery Traffic Indication Map). That is, the broadcast TWT maintenance field of all TWT parameter information fields for low-latency terminals included in the TWT information element for assigning the TWT SP for low-latency terminals transmitted in the beacon frame can be set to the same value. Except for the beacon frame transmitted at the specific time point (for example, the DTIM beacon frame), the TWT SP for low-latency terminals may occur periodically at the same time after the TBTT time point. On the other hand, for a STA MLD that cannot perform the STR operation, at the time when the beacon frame transmitted at the specific time point (for example, the DTIM beacon frame) is transmitted, it does not have to perform a frame transmission operation on other links. Through this process, even if a STA MLD that cannot perform the STR operation cannot receive a specific beacon frame, it is possible to confirm the TWT SP for low-latency terminals based on the content of the TWT information element included in the previously transmitted beacon frame.

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

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

[0198] FIG. 22 is an example showing an operation of further transmitting a protection frame for protecting the TWT time at the start point of the TWT time in order for the AP MLD to protect the TWT time for low-latency operation.

[0199] Referring to FIG. 22, in order to prevent a terminal not assigned to the TWT SP for the low-latency terminal from transmitting a frame at that time, a reservation frame can be transmitted from the AP at the start point of the TWT SP. The reservation frame may be an unagreed Quiet Time setting frame. The Duration field value of the Quiet Time setting frame is specified as the TWT SP time, and in the TWT SP for the low-latency terminal, a non-negotiated STA can be prevented from performing a channel contention process. On the other hand, an STA negotiated with the AP to transmit a frame in the TWT SP can transmit a frame requiring a low delay time during that period.

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

[0201] On the other hand, when a STA MLD that cannot perform the STR operation performs a low-latency operation using the TWT function, when frame transmission is performed on another link during the TWT SP time for the low-latency operation, it may not be possible to transmit a frame that requires a low delay time during the TWT SP time. That is, when frame transmission operations are being performed on other links that cannot perform the STR operation during the TWT SP time, the transmission operation of a frame that requires a low delay time may not be possible due to the interference effect of the transmission. To solve this problem, when the STR operation is not possible for a STA MLD that performs a low-latency operation using TWT as follows, frame transmission on other links may be restricted as follows.

[0202] FIG. 23 is an example showing a process in which a STA that cannot perform AP MLD and STR operations performs low-latency operations using the TWT function. At this time, the content overlapping with the descriptions of FIGS. 18 or 19 and FIG. 22 may be omitted.

[0203] Referring to FIG. 23, a STA MLD that cannot perform STR operations can also perform low-latency operations using the AP MLD and the TWT function using some links. For example, the STA MLD can perform multi-link operations with the AP MLD using Link 1 and Link 2. At this time, the STA MLD may not be able to perform STR operations on Link 1 and Link 2. That is, while STA1 of the STA MLD is performing a frame transmission operation on Link 1, STA2 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. Or, while STA2 of the STA MLD is performing a frame transmission operation on Link 2, STA1 may not be able to perform a channel sensing operation and a frame reception operation on Link 1 due to the influence of interference caused by the transmission. At this time, the TWT operation for low-latency operations can be negotiated with the STA MLD on Link 1 of the AP MLD. The connection process and the negotiation process for the MLD operation may be performed in the manner of FIGS. 11 to 13. At this time, when the STA MLD attempts to perform low-latency operations using the TWT function for some links, the negotiation process for performing low-latency operations using the AP MLD and the TWT function can be advanced by the method of FIGS. 18 to 19. For example, it may be negotiated with AP1 of the AP MLD so that STA1 belonging to the STA MLD performs low-latency operations using the TWT function on Link 1.

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

[0205] STA1 of STA MLD that has recognized the TWT SP for the low-latency operation can perform a frame transmission operation that requires a low delay time after the start time of the TWT SP. At this time, in order not to delay the transmission of the frame that requires the low delay time, STA1 operating on Link 1 and STA2 that cannot perform STR operation can end the transmission operation of the frame transmitted before the start time of the TWT SP. STA2 does not have to perform frame transmission at the TWT SP time for the low-latency operation recognized by the STA MLD.

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

[0207] Referring to FIG. 24, an AP MLD (Multi-link Device) may be a device including one or more wireless access points (APs), and may be a device connected to an upper layer through one interface. That is, the AP MLD may be connected to the LLC (Logical Link Control) layer through one interface. Multiple APs included in the AP MLD can share some functions at the MAC layer. Each AP within the AP MLD can operate on different links. A STA MLD may be a device including one or more non-AP STAs, and may be a device connected to an upper layer through one interface. That is, the STA MLD may be connected to the LLC layer through one interface. Multiple STAs included in the STA MLD can share some functions at the MAC layer. Also, the STA MLD can be called a non-AP MLD. At this time, the AP MLD and STA MLD can perform a multi-link operation of communicating using multiple individual links. That is, when the AP MLD includes multiple APs, each AP constitutes a separate link and can 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 bandwidth expansion operations can be performed on each link. For example, when the AP MLD sets 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 by the bandwidth expansion method in the 2.4 GHz band, and for each link using the 5 GHz band, frame transmission can be performed with a maximum bandwidth of 320 MHz by utilizing discontinuous bandwidths.

[0208] On the one hand, due to interference problems inside the device for some or all of the APs or terminals belonging to the AP MLD or the STA MLD, when one AP or terminal performs a transmission operation, other APs or terminals in the same device may not be able to perform a reception operation. Thus, while one AP or terminal in the MLD is performing a transmission operation, the operation of other APs or terminals in the MLD receiving is called STR (Simultaneous Transmit and Receive). The AP MLD may be capable of performing the STR operation for all links. Or, the STR operation may be impossible for some links of the AP MLD. When the STR operation is impossible for some links, among the APs operating on these multiple links, when one AP is performing a transmission operation, other APs may not be able to perform a reception operation. An STA MLD capable of performing the STR operation may be connected to the AP MLD, and an STA MLD for which the STR operation is impossible for some or all links may be connected. When an STA MLD for which the STR operation is impossible for some or all links is connected, for the links for which the STR operation is impossible in the STA MLD, when one terminal using the link is transmitting, the reception operation on other links may be impossible. Further, terminals not belonging to the MLD (for example, IEEE 802.11a / b / g / n / ac / ax terminals) may be further connected to the APs included in the AP MLD.

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

[0210] Referring to FIG. 25, the AP MLD and the STA MLD can perform a negotiation process for multi-link usage operations during the scanning and connection processes described in FIG. 5. For example, during the scanning process described in FIG. 5, the AP included in the AP MLD can transmit, in the beacon frame, an indicator indicating that multi-link operations are available, the number of available links, a plurality of available links, and information about the AP that operates the link. At this time, only a part of the information about the AP belonging to the AP MLD that does not transmit the beacon frame may be transmitted. At this time, the information about the AP that does not transmit the beacon frame may be transmitted in the form of an RNR (Reduced Neighbor Report) 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 AP among the information about the AP included in the information element, and a counter that informs the update status of the parameters used by the AP.

[0211] On the other hand, the terminal belonging to the STA MLD can receive the beacon frame and confirm that the AP that transmits the beacon frame is an AP belonging to the AP MLD. Also, a part of the information about other APs belonging to the AP MLD (for example, link ID, used channel information, parameter update counter in the AP, etc.) can be confirmed. Alternatively, the terminal belonging to the STA MLD can transmit, in the probe request frame during the scanning process shown in FIG. 5, an indicator indicating that multi-link operations are available, and the AP belonging to the AP MLD can include an indicator indicating that multi-link operations are available in the probe response frame. At this time, the AP can further include, in the probe response frame, the number of available links, link information, and information about the AP that operates the link during multi-link operations.

[0212] The AP is an AP belonging to the AP MLD. The STA MLD that has confirmed some information about other APs belonging to the AP MLD can send a multi-link probe request frame to the AP requesting all information about other APs in the AP MLD in order to perform multi-link operation. The multi-link probe request frame can indicate the necessary information for the AP that the STA MLD intends 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, the time when a beacon is transmitted (Target Beacon Transmission Time, TBTT), EDCA parameter setting information, the channel information on which the AP operates, and the bandwidth information supported by the AP. The STA MLD can request information about one or more specific APs in the multi-link probe request frame. Alternatively, the STA MLD can request information about all APs operated by the AP MLD.

[0213] The AP MLD can receive a multi-link probe request frame from the STA MLD, and can confirm that the STA MLD requests some or all of the information elements related to the operation of the AP for some or all of the APs to which the STA MLD belongs. The AP MLD that has confirmed the requested information can send it 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, the information overlapping with the information used by the AP that sends the multi-link probe response frame may be omitted. On the other hand, since the multi-link probe response frame contains more information than the probe response frame in FIG. 5, it may occupy the channel for a longer time when the multi-link probe response frame is sent. Therefore, in order to prevent the channel occupancy phenomenon caused by the excessive transmission of multi-link probe response frames from becoming excessive, when a multi-link probe response frame has already been sent to a specific STA MLD, it is not necessary to send a response to the multi-link probe request frame received from the same STA MLD. On the other hand, the AP MLD can send a multi-link probe response frame containing the information of all APs belonging to the AP MLD in the form of a broadcast frame. The multi-link probe response frame sent in the form of the broadcast frame may be sent at a specific period or more. At this time, if a multi-link probe response frame has been sent in the form of a broadcast frame within a specific time before receiving a multi-link probe request frame from the STA MLD, it is not necessary to send the multi-link probe response frame. At this time, the specific time may be after the time when the STA belonging to the STA MLD sends the probe request frame in FIG. 5.

[0214] The STA MLD that has received the multi-link probe response frame from the AP MLD can check the operating parameters of each AP belonging to the AP MLD, etc., and can 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 may be performed in the connection process between the AP belonging to the AP MLD and the terminal belonging to the STA MLD. That is, while any terminal (for example, STA1) belonging to the STA MLD sends a connection request frame to any AP (for example, AP1) belonging to the AP MLD, an indicator indicating that the multi-link operation of the terminal is available and a request indicator requesting to perform the multi-link operation can be sent. At this time, the STA MLD can send a connection request frame to the AP MLD including the link information to be used and the capability information of the terminal related to the link (for example, information indicating whether STR with other links is possible, the maximum bandwidth that can be transmitted, or the maximum number of spatial streams that can be used, etc.). The AP that has received the connection request frame from the terminal can check the indicator requesting the multi-link operation, and when the AP is capable of the multi-link operation, can send a connection response frame allowing the multi-link operation including the link information used for the multi-link operation and the parameters used for each link to the terminal. 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 the availability of STR operation of each link used. The AP MLD and STA MLD for which the use of the multi-link operation has been confirmed by exchanging the connection request frame and the response frame can perform a frame transmission operation using a plurality of links through the plurality of APs included in the AP MLD and the plurality of terminals included in the STA MLD after the connection process.

[0215] FIG. 26 is a timing diagram showing a transmission method using multi-links according to an embodiment of the present invention.

[0216] Referring to FIG. 26, the AP MLD and STA MLD that have completed the negotiation for the multi-link operation can perform frame transmission and reception operations using the multi-link by using the link-by-link independent transmission method. When the multi-link operation is performed using the link-by-link independent transmission method, each AP or terminal belonging to the AP MLD or STA MLD independently performs the channel contention process for frame transmission on each link and performs frame transmission on each link. At this time, the transmission start time and the transmission end time of the frames transmitted on each link do not have to be the same. When performing the independent transmission method, the TXOP (Transmission Opportunity) obtained by the channel contention process on each link may be independently obtained on each link.

[0217] When performing the independent transmission method, there is an advantage that each link can perform more efficiently only by independently performing channel access on each link according to the channel occupancy state. At this time, since the interval between the operating bands of each AP operated by the AP MLD is not sufficiently wide, when the STR operation is impossible with the AP MLD or STA MLD, the multi-link operation may not be performed by the independent transmission method.

[0218] On the other hand, when the STR operation is impossible for some or all of the links for the receiving MLD, the frame transmission and reception process using the link for which the STR operation is impossible may be performed as follows.

[0219] FIG. 27 is an embodiment showing the frame transmission and reception operations between a receiving MLD for which the STR operation is impossible for some or all of the links and a transmitting MLD for which the STR operation is possible according to an embodiment of the present invention.

[0220] Referring to FIG. 27(a), when the STR operation is not possible in the MLD, it may be impossible to perform the frame reception operation on another link while transmitting a frame on one link. For example, in the AP MLD, AP1 and AP2 belong. AP1 can operate on Link 1, and AP2 can operate on Link 2. In the STA MLD, STA1 and STA2 belong. STA1 may be connected to AP1 and STA2 may be connected to AP2 through a negotiation process for the multi-link operation. At this time, the STA MLD may not be able to perform the STR operation on Link 1 and Link 2. That is, while STA1 is performing the frame transmission operation on Link 1, STA2 may not be able to perform the frame reception operation on Link 2. Conversely, while STA2 is performing the frame transmission operation on Link 2, STA1 may not be able to perform the frame reception operation on Link 1. The situation where the STR operation is not possible may be caused by interference inside the device that occurs during the frame transmission operation on one link. As a result, when the STA MLD cannot perform the STR operation on some links, the channel sensing operation may not be performed on another link while transmitting a frame on one of the links. For example, while transmitting a frame to STA1 on Link 1, the channel sensing operation for frame transmission by STA2 on Link 2 may not be performed. Therefore, while STA1 is transmitting a frame on Link 1, STA2 may not be able to start the frame transmission operation after the channel contention process on Link 2. That is, when the STR operation is not possible on one of the MLDs of the transmitting MLD and the receiving MLD on the link, the multi-link communication operation by the independent transmission method in FIG. 11 above may be impossible.

[0221] When the STR operation is impossible for the AP MLD or the STA MLD with the plurality of links (for example, when the bandwidth interval between the links is not sufficient for performing the multi-link operation), the AP MLD and the STA MLD can perform the multi-link operation in the form of the simultaneous transmission operation as shown in FIG. 12(b). The simultaneous transmission operation may be performed by a process of making the transmission start time or the transmission end time of the frame transmitted on each link the same. At this time, the transmission start time or the transmission end time of the frame can be referred to as the transmission start time or the transmission end time of the PPDU including the frame. That is, when the lengths of the frames transmitted by the AP or the terminal on each link are different, padding or padding bits can be added and transmitted in order to match the transmission end points. Also, the TXOP time for frame transmission on each link can be made the same. At this time, the multi-link operation in the simultaneous transmission form may include a negotiation stage for simultaneous transmission on a plurality of links and a stage of performing simultaneous transmission using the plurality of links. The negotiation stage for the simultaneous transmission includes a stage of sending a request frame for obtaining a TXOP for simultaneous transmission on one or more links at the same time by an MLD (for example, the AP MLD or the STA MLD) having data to be transmitted, and a stage of transmitting a response frame after SIFS (Short Interframe Space) from the 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 have received the request frame. The request frame may be a control frame. For example, the request frame may be an RTS or a MU (Multi-user)-RTS frame, and the response frame may be a CTS frame. On the other hand, when the channel of one link is in an occupied state during the execution of the channel contention for performing the simultaneous transmission operation, a channel access process for performing the simultaneous transmission operation can be performed, or a frame transmission operation using only the link whose channel is free can be performed.

[0222] The channel access process for the simultaneous transmission operation may be performed in various ways. For example, a backoff process is performed on multiple links that perform simultaneous transmission. Carrier sensing is performed on all links until the backoff value becomes 0 on all links. When the channels on all links are idle as a result of the carrier sensing, a simultaneous transmission method can be performed using multiple links. Alternatively, after performing a backoff operation on one link, when the channel of another link is idle at a specific time (e.g., AIFS, DIFS, or PIFS) before the end of the backoff, a simultaneous transmission method using multiple links can be performed by utilizing the link with the idle channel.

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

[0224] 1) After the end of the occupied period, carrier sensing is performed on the channels of both links at a specific time (e.g., PIFS, AIFS, or AIFS + backoff time). After confirming that the channels of both links are idle, simultaneous transmission is performed by the method of FIG. 27(b) above.

[0225] 2) Transmission operation is performed only on the link with the idle channel.

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

[0227] On the other hand, when the transmitting MLD can perform the STR operation on the link and the receiving MLD cannot perform the STR operation on the link, in (b) of FIG. 12, when the channel state of one or some of the links is in the occupied (busy) state during the channel access process for frame transmission, one of the following methods can be used:

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

[0229] 2) Perform the transmission operation only on the link with an idle channel.

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

[0231] On the one hand, when the transmitting MLD is capable of performing the STR operation and the receiving MLD is not capable of performing the STR operation on the link, the transmission start time and the transmission end time of the frames transmitted on multiple links from the transmitting MLD do not have to be the same. That is, as shown in Fig. 12(c), 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 another link. For example, the AP MLD can perform the STR operation on Link 1 and Link 2, and the STA MLD may not be capable of performing the STR operation on Link 1 and Link 2. At this time, in Fig. 12(b), when the channel state of Link 2 is in the occupied (busy) state during the process of approaching the channel for frame transmission, AP1 of the AP MLD can first perform the frame transmission operation on Link 1. Since the AP MLD is capable of performing the STR operation, during the transmission of the frame by AP1 on Link 1, AP2 on Link 2 can perform the channel contention process for frame transmission. After completing the channel contention process and the channel approaching operation, AP2 can perform the frame transmission operation using Link 2. Since the STA MLD is not in the middle of frame transmission on Link 1, STA2 on Link 2 can receive the frame transmitted by AP2. On the other hand, when one or more of the frames transmitted by the transmitting MLD require an immediate response (e.g., BlockAck frame, etc.) from the receiving MLD, the transmission of the response frame may be performed while the receiving operation is being performed on another link. In this case, the frame reception operation on another link may not be smoothly performed due to the transmission of the response frame. To prevent such a situation, when one or more of the frames transmitted from the transmitting MLD require the transmission of a response frame, the transmission end time of the PPDU including the frames transmitted on the multiple links may be the same.

[0232] On the one hand, when performing a frame transmission and reception operation between an AP and an STA, a channel reservation process can be performed to protect the frame transmission and reception operation. The channel reservation process may be performed by a process of transmitting an RTS (Request to Send) frame from a transmitting STA that intends to transmit a frame to a receiving STA and transmitting a CTS (Clear to Send) from the receiving STA. At this time, after receiving the RTS frame, the receiving STA performs a channel sensing operation at the SIFS time and can transmit a CTS only when the channel is in an idle state.

[0233] On the other hand, when an AP intends to reserve a channel for multi-user transmission with a plurality of STAs, an exchange process of MU (Multi-user)-RTS frames and CTS frames can be performed. The exchange procedure of MU-RTS frames and CTS frames between the AP and the plurality of STAs may be performed as follows.

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

[0235] Referring to FIG. 28, when AP attempts to transmit a frame to a plurality of STAs, in order to protect the frame transmission operation, the procedure of exchanging MU-RTS frames and CTS frames can be performed before the frame transmission. The MU-RTS frame may be transmitted using one of the following channels: the primary 20 MHz channel, the primary 40 MHz channel, the primary 80 MHz channel, the primary 160 MHz or 80+80 MHz channel, the primary 240 MHz or primary 160+80 MHz channel, the primary 320 MHz or 160+160 MHz channel. At this time, the MU-RTS can indicate the ID of the STA that will transmit CTS (for example, Association ID), the channel on which each STA will transmit the CTS frame (for example, the primary 20 MHz channel, the primary 40 MHz channel, the primary 80 MHz channel, the primary 160 MHz or 80+80 MHz channel, the primary 240 MHz or primary 160+80 MHz channel, the 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 described later. The MU-RTS frame may be a frame that requests a plurality of STAs to transmit CTS frames simultaneously. At this time, the plurality of STAs may include HE STAs defined in IEEE 802.11ax and may include EHT STAs defined in IEEE 802.11be.

[0236] Multiple STAs that receive a MU-RTS frame from an AP can check the information contained in the MU-RTS frame. The multiple STAs can check the information of the received MU-RTS frame and can check the AID value contained in one or more user information fields included in the MU-RTS frame. At this time, when the AID value matches the AID value assigned to the STA, the STA can check that the MU-RTS frame requests the transmission of a CTS frame to the STA. The STA included with the AID in the MU-RTS frame can perform a channel sensing operation at the SIFS time on the channel indicated by the MU-RTS frame after receiving the MU-RTS frame. At this time, the channel may be one of a primary 20 MHz channel, a primary 40 MHz channel, a primary 80 MHz channel, a primary 160 MHz / 80+80 MHz channel, a primary 240 MHz / 160+80 MHz channel, and a primary 320 MHz / 160+160 MHz. At this time, when the STA that has received the MU-RTS frame is a HE STA, the bandwidth of the channel for transmitting the CTS frame may be at most 160 MHz or 80+80 MHz. When the STA that has received the MU-RTS frame is an EHT STA, the maximum bandwidth of the channel for transmitting the CTS frame may be 320 MHz or 160+160 MHz. The channel sensing operation may include a physical sensing, a virtual sensing, and a NAV (Network Allocation Vector) confirmation process.

[0237] After the STA receives the MU-RTS frame, when the channel indicated at the SIFS time is in the channel idle state, the plurality of STAs indicated in the MU-RTS frame can simultaneously transmit CTS frames after the SIFS from the end time of transmission of the PPDU including the MU-RTS frame. At this time, the CTS frame may be transmitted in the non-HT PPDU form or the non-HT duplicated PPDU form that repeats for each 20 MHz band in the indicated channel. At this time, the CTS frames transmitted by the plurality of STAs may be configured identically. Therefore, for the AP, as shown in Fig. 28(a), CTS frames can be received on each 20 MHz channel for the MU-RTS frame transmitted as such. At this time, the received power of the CTS frames received for each 20 MHz channel may be different. When the AP receives a CTS frame as a response to the MU-RTS, the AP can perform MU-OFDMA or MU-MIMO operations with the plurality of STAs based on the bandwidth of the received CTS frame.

[0238] On the other hand, as described above, the transmission bandwidths of the CTS frames transmitted by the STAs that receive the MU-RTS frame may be different from each other. For example, referring to Fig. 13(b), when the channel indicated for STA1 to send a CTS frame in the MU-RTS frame is the primary 20 MHz channel, STA1 can transmit a CTS frame after performing a channel sensing operation only on the primary 20 MHz channel. At this time, the CTS frame may be transmitted in the non-HT PPDU form. After transmitting the CTS frame, STA1 can receive a downlink frame within the 20 MHz channel.

[0239] Referring to FIG. 28(c), when the channel instructed to send a CTS frame in the MU-RTS frame is the primary 40 MHz channel, the STA (e.g., STA2) indicated in the user information field of the MU-RTS frame can send a CTS frame after performing a channel sensing operation only on the primary 40 MHz channel. At this time, the CTS frame may be sent in the non-HT duplicated PPDU format. STA2 can receive a downlink frame within the 40 MHz channel after sending the CTS frame.

[0240] Referring to FIG. 28(d), when the channel instructed to send a CTS frame in the MU-RTS frame is the primary 80 MHz channel, the STA (e.g., STA3) indicated in the user information field of the MU-RTS frame can send a CTS frame after performing a channel sensing operation only on the 80 MHz channel. At this time, the CTS frame may be sent in the non-HT duplicated PPDU format. STA3 can receive a downlink frame within the 80 MHz channel after sending the CTS frame.

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

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

[0243] Referring to FIG. 29, the MU-RTS frame may be configured in the form of a trigger frame and may be composed of a common field and one or more user information fields. The common field may be composed of a trigger type field, an indication field indicating whether a trigger frame is further transmitted after the frame, a field indicating whether a carrier sensing operation is required at the receiving terminal, an uplink frame bandwidth field, an uplink frame bandwidth extension field, and a reserved field. The common field may further include an MURTS type field as an addition. Alternatively, the MURTS type field may be included in the user information field. The trigger type field may be set to 3 to indicate that the trigger frame is an MU-RTS frame. Also, when 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 when the MU-RTS frame is transmitted with a bandwidth of 160 MHz or less and no separate form of user information field is set for the EHT STA. When the MU-RTS frame is transmitted with a bandwidth exceeding 160 MHz, it may be set to 10. The field indicating whether the carrier sensing operation is required may be set to 1 to indicate that the STA receiving the MU-RTS frame performs a carrier sensing operation. The uplink frame bandwidth field and the bandwidth extension field can indicate the bandwidth of the CTS frame that the AP transmitting the MU-RTS frame attempts to receive. That is, in FIG. 13(a), when multiple STAs transmit CTS frames, the bandwidth of the CTS frame that the AP must finally receive can be indicated. The bandwidth field can be indicated as shown in Table 3 below.

[0244]

Table 3

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

[0246]

Table 4

[0247] On the other hand, when the STA that receives the MU-RTS frame is a HE STA, among the common fields of the MU-RTS frame, the MURTS type field and the bandwidth extension field value may be undecodable. Therefore, when the AP transmits the MU-RTS frame, the bandwidth for transmitting the CTS frame from the HE STA may be indicated as up to 160 MHz or 80 + 80 MHz regardless of the bandwidth extension field value. When the STA that receives the MU-RTS frame is an EHT STA, the bandwidth for transmitting the CTS frame can be confirmed only after checking all the bandwidth field and the bandwidth extension field values of the MU-RTS frame.

[0248] The user information field may be configured to be different 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 composed of a 12-bit AID field and an 8-bit RU (Resource Unit) allocation field. When the MURTS type field is 10 and the user information field indicates a HE STA, it may be composed of a 12-bit AID field and an 8-bit RU (Resource Unit) allocation field. When the MURTS type field value is 10 and the user information field indicates an EHT STA, it may be composed of a 12-bit AID field and a 9-bit RU (Resource Unit) allocation field. Alternatively, the user information field may be different depending on whether the receiving terminal is a HE STA or an EHT STA regardless of the MURTS type field value. For example, when 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. Also, when 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.

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

[0250] The transmission bandwidth and the detailed position of the transmission band of the CTS frame may be indicated by B7 - B1 of the RU allocation field, that is, the 7 upper bits of the RU allocation field. At this time, the B7 - B1 value of the RU allocation field may be set as shown in Table 5 below.

[0251]

Table 5

[0252] When the RU allocation field is composed of 9 bits, B1 - B0 of the RU allocation field, that is, the 2 lowest bits, can indicate the segment position of the 80 MHz band where the main channel to which the CTS frame is transmitted is located when dividing a 320 MHz bandwidth channel into 4 80 MHz channel segments.

[0253] The transmission bandwidth of the CTS frame and its position in the 80 MHz segment may be indicated by B8 - B2 of the RU allocation field. At this time, the B8 - B2 value of the RU allocation field may be set as shown in Table 6 below.

[0254]

Table 6

[0255] On the other hand, when 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.

[0256] On the other hand, when attempting to maintain the length of the RU allocation field in the user information field transmitted to the EHT STA at 8 bits as well, the MU - RTS frame may be configured as follows.

[0257] FIG. 30 is a second embodiment showing the structure of the MU-RTS frame according to an embodiment of the present invention. At this time, the description of the same or similar parts as the structure of the MU-RTS frame in FIG. 28 may be omitted.

[0258] Referring to FIG. 30, the MU-RTS frame may be configured in the form of a trigger frame and may be composed of a common field and one or more user information fields. The common field may be composed of a trigger type field, an instruction field indicating whether a trigger frame is further transmitted after the frame, a field indicating whether a carrier sensing operation at the receiving terminal is required, an uplink frame bandwidth field, an uplink frame bandwidth extension field, and a reserved field. The common field may further include an MURTS type field as an addition. The configuration of the fields other than the MURTS type field may be the same as that of the MU-RTS frame in FIG. 28. The MURTS type field may be set to 00 when the MU-RTS frame is transmitted with a bandwidth of 160 MHz or less and no separate form of user information field is set for the EHT STA. When the MU-RTS frame is transmitted with a bandwidth exceeding 160 MHz, it may be set to 10.

[0259] The user information field may be composed of a 12-bit AID field, an 8-bit RU allocation field, and a reserved field. When the AID field of the user information field indicates an 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 the same as the 8-bit RU allocation field in FIG. 13. That is, B0 of the RU allocation field indicates whether it is transmitted with a bandwidth of 160 MHz or 80 + 80 MHz, and B7 - B1 of the RU allocation field may be configured as shown in Table 3.

[0260] When the 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 RU allocation field, that is, the two least significant bits, can indicate the segment position of the 80 MHz band where the CTS frame is transmitted when dividing a 320 MHz bandwidth channel into four 80 MHz channel segments.

[0261] The transmission bandwidth of the CTS frame and its position in the 80 MHz segment may be indicated by B7-B2 of the RU allocation field. At this time, the B7-B2 value of the RU allocation field may be set as shown in Table 7 below.

[0262]

Table 7

[0263] On the other hand, when 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.

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

[0265] FIG. 31 shows a second embodiment of an operation for protecting frame transmission and reception using a MU-RTS frame and a CTS frame exchange procedure between an AP and a plurality of STAs according to an embodiment of the present invention. At this time, the description same as or similar to the operation of FIG. 28 may be omitted.

[0266] Referring to FIG. 31, the AP can simultaneously perform frame transmission and reception procedures with a plurality of STAs. The process of simultaneously transmitting and receiving frames with the plurality of STAs may be performed by 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 a MU-RTS frame and a CTS frame before transmitting the frame. The MU-RTS frame may 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, when one or more of the 20 MHz channels other than the primary 20 MHz channel are in an occupied state or the 20 MHz channel is not to be used, the corresponding one or more 20 MHz channels can be left empty and the MU-RTS frame can be transmitted using only the remaining channels. That is, when transmitting the MU-RTS frame using a primary 80 MHz channel, a primary 160 MHz or 80+80 MHz channel, a primary 240 MHz or primary 160+80 MHz channel, or a primary 320 MHz or 160+160 MHz channel, the MU-RTS frame may not be transmitted on a specific 20 MHz channel. For example, when trying to transmit the MU-RTS frame using the primary 80 MHz channel, if one of the 20 MHz channels in the secondary 40 MHz channel is in an occupied state, the channel can be left empty and the MU-RTS frame can be transmitted using only the remaining channels.

[0267] The MU-RTS can indicate the ID of the STA that transmits CTS (e.g., Association ID), the channels on which each STA transmits CTS frames (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. At this time, a punctured 20 MHz channel left without transmitting the MU-RTS can be further indicated. The MU-RTS frame may be configured as shown in FIG. 17 described later. The MU-RTS frame may be a frame that requests a plurality of STAs to transmit CTS frames simultaneously. At this time, the plurality of STAs may include HE STAs defined in IEEE 802.11ax and may include EHT STAs defined in IEEE 802.11be.

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

[0269] On the other hand, as described above, the transmission bandwidths of the CTS frames transmitted from the STAs that have received the MU-RTS frame may be different. For example, referring to FIG. 16(b), when the channel instructed to send the CTS frame in the MU-RTS frame is the primary 20 MHz channel, STA1 can perform the channel sensing operation only on the primary 20 MHz channel. The channel sensing operation may be performed within the SIFS time. The CTS frame can be transmitted when the primary 20 MHz channel is idle. At this time, the CTS frame may be transmitted in the non-HT PPDU format. STA1 can receive the downlink frame within the 20 MHz channel after transmitting the CTS frame. At this time, the STA that transmits the CTS frame may be an HE STA or an EHT STA.

[0270] Referring to FIG. 31(c), when the channel instructed to send the CTS frame in the MU-RTS frame is the primary 40 MHz channel, the STA (for example, STA2) indicated in the user information field of the MU-RTS frame can perform the channel sensing operation only on the primary 40 MHz channel. The channel sensing operation may be performed within the SIFS time. The CTS frame can be transmitted when the primary 40 MHz channel is idle. At this time, the CTS frame may be transmitted in the non-HT duplicated PPDU format. STA2 can receive the downlink frame within the 40 MHz channel after transmitting the CTS frame. At this time, the STA that transmits the CTS frame may be an HE STA or an EHT STA.

[0271] Referring to FIG. 31(d), when the channel instructed to send the CTS frame in the MU-RTS frame is the primary 80 MHz channel and the specific 20 MHz channel is available, the STA (e.g., STA3) indicated in the user information field of the MU-RTS frame can perform the channel sensing operation only on the channels other than the 20 MHz channel instructed to be vacated among the corresponding primary 80 MHz channels. As a result of the channel sensing, if the channel is idle, the CTS frame can be transmitted. At this time, the CTS frame may be transmitted in the non-HT duplicated PPDU format. STA3 can receive the downlink frame within the channel where the MU-RTS frame and the CTS frame are exchanged after transmitting the CTS frame. The STA that transmits the CTS frame may be an EHT STA.

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

[0273] FIG. 32 is a third embodiment showing the structure of the MU-RTS frame according to an embodiment of the present invention. At this time, the description of the part having the same configuration as the MU-RTS frame in FIG. 29 may be omitted.

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

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

[0276] When the EHT STA that has received the MU-RTS frame from the AP, when the MURTS type field is 11, can check the bandwidth field and the bandwidth extension field to confirm the bandwidth in which the MU-RTS frame is transmitted. From the punctured channel field, the channel to be vacated at the time of CTS transmission can be confirmed. Also, from the RU allocation field, the bandwidth that the STA should transmit can be confirmed. The method of interpreting the RU allocation field may vary depending on the bandwidth in which the MU-RTS frame is transmitted and the MURTS type field. The EHT STA that has checked the RU allocation field and the punctured channel interpreted by the bandwidth in 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 to the remaining channels according to the value indicated in the RU allocation field.

[0277] On the one hand, when receiving the MU-RTS frame, the HE STA may be unable to decode the punctured channel field. Therefore, the HE STA may send a CTS frame on the channel indicated in the RU allocation field without leaving a specific 20 MHz channel empty.

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

[0279] FIG. 33 is a third embodiment of an operation for protecting frame transmission and reception by an MU-RTS frame and a CTS frame exchange procedure between an AP and a plurality of STAs according to an embodiment of the present invention. At this time, descriptions the same as or similar to the operations in FIGS. 28 and 31 may be omitted.

[0280] Referring to FIG. 33, the AP can simultaneously perform frame transmission and reception procedures with a plurality of STAs. The process of simultaneously transmitting and receiving frames with the plurality of STAs may be performed by MU-OFDMA or MU-MIMO operations. 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 may 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, among the 20 MHz channels other than the primary 20 MHz channel, if the channel state is occupied or the 20 MHz channel is not to be used, only the 20 MHz channel may be left empty and the remaining channels can be used for transmission. For example, when trying to transmit an MU-RTS frame using the primary 80 MHz channel, if one 20 MHz channel in the secondary 40 MHz channel is occupied, the channel can be left empty and the MU-RTS frame can be transmitted using only the remaining channels.

[0281] The MU-RTS can indicate the ID of the STA that transmits the CTS (e.g., Association ID), the channel on which each STA transmits the CTS frame, etc. The channel for transmitting the CTS frame may be a specific 20 MHz channel or a plurality of 20 MHz channels. At this time, the form of the plurality of 20 MHz channels may be restricted. Also, a 20 MHz channel (punctured channel) left unused without transmitting the MU-RTS can be further indicated. The MU-RTS frame may be configured as shown in FIG. 34 described later. The MU-RTS frame may be a frame that requests a plurality of STAs to simultaneously transmit CTS frames. At this time, the plurality of STAs may include HE STAs defined in IEEE 802.11ax and may include EHT STAs defined in IEEE 802.11be. At this time, it is not possible to instruct the HE STA to transmit the CTS frame on a channel that is not the primary 20 MHz channel, primary 40 MHz channel, primary 80 MHz channel, primary 160 MHz channel, or primary 80+80 MHz channel.

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

[0283] On the one hand, as described above, the transmission bandwidths of the CTS frames transmitted from the STAs that have received the MU-RTS frame may be different from each other. For example, referring to FIG. 18(b), when the channel instructed to send the CTS frame in the MU-RTS frame is the primary 20 MHz channel, STA1 can perform the channel sensing operation only on the primary 20 MHz channel. The channel sensing operation may be performed within the SIFS time. The CTS frame can be transmitted when the primary 20 MHz channel is idle. At this time, the CTS frame may be transmitted in the non-HT PPDU format. After transmitting the CTS frame, STA1 can receive the downlink frame within the 20 MHz channel. At this time, the STA that transmits the CTS frame may be a HE STA or an EHT STA.

[0284] Referring to FIG. 33(c), when the channel instructed to send the CTS frame in the MU-RTS frame is the second lowest 20 MHz channel, the STA (for example, STA2) indicated in the user information field of the MU-RTS frame can perform the channel sensing operation only on the 20 MHz channel. The channel sensing operation may be performed within the SIFS time. The CTS frame can be transmitted when the 20 MHz channel is idle. At this time, the CTS frame may be transmitted in the non-HT PPDU format. After transmitting the CTS frame, STA2 can receive the downlink frame within the 20 MHz channel. At this time, the STA that transmits the CTS frame may be an EHT STA.

[0285] Referring to FIG. 33(d), when the channel instructed to send a CTS frame in the MU-RTS frame is the primary 80 MHz channel and the specific 20 MHz channel is available, the STA (e.g., STA3) indicated in the user information field of the MU-RTS frame can perform channel sensing operations only on channels other than the 20 MHz channel indicated by the primary 80 MHz channel. As a result of channel sensing, if the channel is idle, a CTS frame can be transmitted. At this time, the CTS frame may be transmitted in the form of a non-HT duplicated PPDU. STA3 can receive a downlink frame within the channel where the MU-RTS frame and the CTS frame were exchanged after transmitting the CTS frame. The STA that transmits the CTS frame may be an EHT STA.

[0286] The MU-RTS frame used in the MU-RTS frame and CTS frame exchange procedure may be in a form modified so that the RU allocation field can indicate a plurality of 20 MHz bands in the existing MU-RTS frame. At this time, a field for indicating a punctured channel may be added to the MU-RTS frame to configure it. Alternatively, the MU-RTS frame may be configured as follows.

[0287] FIG. 34 is a fourth embodiment showing the structure of the MU-RTS frame according to an embodiment of the present invention. At this time, the description of the parts configured identically to the MU-RTS frame in FIG. 29 or FIG. 32 may be omitted.

[0288] Referring to FIG. 34, the MU-RTS frame may be configured in the form of a trigger frame and may be composed of a common field and one or more user information fields. The common field may be composed of a trigger type field, an instruction field indicating whether a trigger frame is further transmitted after the frame, a field indicating whether a carrier sensing operation at the receiving terminal is required, an uplink frame bandwidth field, an uplink frame bandwidth extension field, and a reserved field. The common field may further include a MURTS type field. At this time, among the common fields, fields other than the field indicating the MURTS type field may be set the same as those in FIG. 14. The field indicating the MURTS type field can indicate that the MU-RTS frame is transmitted with some 20 MHz channels left empty. For example, the MURTS type field may be set to 11. On the other hand, the common field may further include a punctured channel field. The punctured field may be included when the MURTS type field is set to 11. When the punctured channel field is included, the field may be set the same as the MU-RTS frame in FIG. 17.

[0289] The user information field may be configured to be different depending on whether the terminal indicated by the field is a HE STA or an EHT STA. When the user information field indicates a HE STA, the user information field may be composed of a 12-bit AID field and an 8-bit RU allocation field. At this time, B0 of the RU allocation field may indicate whether it is a 160 MHz or 80 + 80 MHz bandwidth, and B7 - B1 may be indicated as shown in Table 3. When the user information field indicates an EHT STA, the user information field may be composed of a 12-bit AID field and an RU allocation field composed of 8 bits or 9 bits. When the RU allocation field is 9 bits, B1 - B0 of the RU allocation field can indicate the segment position of the 80 MHz band where the main channel to which the CTS frame is transmitted is located when dividing a 320 MHz bandwidth channel into 4 80 MHz channel segments. At this time, B0 can specify the position of the segment of the 80 MHz band. For example, when B0 is set to 0, it can be indicated that the 80 MHz segment is included in the 160 MHz channel of the lower band among the lower 320 MHz or 160 + 160 MHz main channels. When B0 is set to 1, it can be indicated that the 80 MHz segment is included in the 160 MHz channel of the higher band among the lower 320 MHz or 160 + 160 MHz main channels.

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

[0291]

Table 8-1

Table 8-2

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

[0293] On the other hand, when the B8 - B2 value indicates a 320 MHz or 160 + 160 MHz main channel, or when indicating a plurality of RUs within 320 MHz or 160 + 160 MHz, the B1 - B0 value of the RU allocation field may be indicated as 11.

[0294] On the other hand, when the RU allocation field is composed of 8 bits, B1 - B0 of the RU allocation field can indicate the segment position of the 80 MHz band where the main channel where the CTS frame is transmitted is located when dividing the 320 MHz bandwidth channel into 4 80 MHz channel segments.

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

[0296]

Table 9 - 1

Table 9 - 2

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

[0298] On the other hand, when the B8 - B2 value indicates a 320 MHz or 160 + 160 MHz main channel, or when indicating a plurality of RUs within 320 MHz or 160 + 160 MHz, the B1 - B0 value of the RU allocation field may be indicated as 11.

[0299] When an EHT STA receives the MU-RTS frame from an AP, if the MURTS type field is 11, it can check the bandwidth field and the bandwidth extension field to confirm the bandwidth on which the MU-RTS frame is transmitted. Also, from the RU allocation field, the STA can check one or more 20 MHz channels on which the STA should transmit the CTS frame. The method of interpreting the RU allocation field may vary depending on the type of the terminal receiving the MU-RTS frame (e.g., HE STA or EHT STA) and the MURTS type field. The EHT STA that has checked the RU allocation field interpreted by the MURTS type field can transmit the 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, referring to this, the CTS frame can be transmitted on one or more 20 MHz channels indicated in the RU allocation field.

[0300] On the other hand, an HE STA that has received the MU-RTS frame may not be able to decode the added punctured channel field. Therefore, the HE STA can transmit the CTS frame on the channels indicated in the RU allocation field without leaving a specific 20 MHz channel empty.

[0301] On the other hand, an indicator may be added to the MU-RTS frame in FIG. 19 above to request transmitting the CTS frame on the primary 20 MHz channel. When the indicator for transmitting the CTS frame on the primary 20 MHz channel is set, in the STA that has received the MU-RTS frame, even if the primary 20 MHz channel is not indicated in the RU allocation field, the CTS frame can be transmitted on a plurality of 20 MHz channels including the primary 20 MHz channel.

[0302] On the other hand, the exchange operation of the MU-RTS frame and the CTS frame shown in FIG. 13, FIG. 16, or FIG. 18 above may also be performed between the AP belonging to the AP MLD and the terminal belonging to the STA MLD. At this time, the STR operation may be impossible for some links in the STA MLD. Therefore, by transmitting the MU-RTS frame to the terminal belonging to the STA MLD on one link in the AP MLD and transmitting the MU-RTS frame to a plurality of terminals including other terminals of the STA MLD on other links, the exchange operation of the MU-RTS frame and the CTS frame can be started. At this time, the operation between the AP MLD and the STA MLD may be performed as follows.

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

[0304] Referring to FIG. 35, even if some STAs cannot transmit CTS frames due to characteristics that make the STR operation impossible for the MU-RTS frames transmitted from the APs belonging to the AP MLD, when other STAs transmit CTS frames on the channel, the AP can perform a channel reservation process using the exchange procedure of the MU-RTS frame and the CTS frame. For example, a plurality of APs may belong to the AP MLD. At this time, each AP can operate its respective link. For example, the AP MLD may include AP1 and AP2. AP1 can operate Link 1, and AP2 can operate Link 2. The STA MLD, or a STA not belonging to the STA MLD, may be connected to the APs 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, the STR operation may be impossible for STA1-1 and 1-2 belonging to STA MLD1. That is, when STA1-1 is performing a transmission operation on Link 1, STA1-2 may not be able to perform a reception operation. The STR operation may be possible for STA2-1 and STA2-2 belonging to STA MLD2. Also, STA3 not belonging to the STA MLD may be connected to AP1.

[0305] Referring to FIG. 35(a), AP1 belonging to the AP MLD can perform frame transmission and reception operations with a plurality of terminals connected to the AP. For example, AP1 can simultaneously transmit downlink frames to STA1-1, STA2-1, and STA3 by utilizing the OFDMA operation. At this time, in order to protect the frame transmission and reception operations, the exchange procedure of the MU-RTS frame and the CTS frame can be performed with the corresponding plurality of terminals.

[0306] On the other hand, when the STR operation is possible between APs belonging to AP MLD, during the frame transmission / reception operation at AP1, AP2 can independently perform a channel access operation for frame transmission. After performing the channel access operation, a frame transmission / reception operation with a plurality of terminals can be performed. For example, when there is downlink data to be transmitted to a plurality of terminals, AP2 can utilize the downlink MIMO operation with STA1-2 and STA2-2 or the downlink OFDMA operation to simultaneously transmit frames. At this time, in order to protect the frame transmission / reception operation, it is possible to attempt to transmit a MU-RTS frame to the corresponding plurality of terminals and perform the exchange procedure of the MU-RTS frame and the CTS frame.

[0307] At this time, referring to FIG. 35(b), since STA MLD1 for which the STR operation is impossible on Link 1 and Link 2 is receiving a frame on Link 1, even if the MU-RTS frame is received on Link 2, it may not be able to transmit a CTS frame as a response thereto. At this time, referring to FIG. 35(c), a STA that can transmit a CTS frame as a response to the MU-RTS frame can transmit the CTS frame using the channel indicated by the MU-RTS. At this time, the STA that transmits the CTS frame may be a STA MLD that is not transmitting a frame on Link 1 at the time of receiving on Link 2, a STA MLD for which the STR operation is possible on Link 1 and Link 2, or a STA that does not belong to the STA MLD. The operation of transmitting a CTS frame as a response to the MU-RTS may be performed as in FIGS. 13, 16, or 18.

[0308] Referring to Fig. 35(a), from the perspective of the AP MLD, even if the STA MLD that is unable to perform the STR operation on the transmitted MU-RTS frame cannot receive the CTS frame from the STA, when another terminal instructed to transmit the CTS frame using the same band transmits the CTS frame, it can be determined that the exchange of the MU-RTS frame and the CTS frame has succeeded. Therefore, the AP2 of the AP MLD can transmit the downlink frame to the terminal that could not transmit the CTS frame because it was unable to perform the STA operation. At this time, since the frame to be transmitted to the terminal that is unable to perform the STR operation is included, when the frame transmitted on Link 1 or Link 2 requests the transmission of a response frame (for example, an ACK frame or a BlockAck frame), the end points of the transmission of the downlink frames transmitted on Link 1 and Link 2 may coincide.

[0309] On the other hand, referring again to Fig. 35(b), STA1-2, which could not transmit a CTS response to the MU-RTS frame received on Link 2 because it was unable to perform the STR operation, can receive the downlink frame transmitted by AP2 on that link when another terminal (for example, STA2-2) transmits a CTS frame on the channel.

[0310] On the other hand, when the MLD that is unable to perform the STR operation participates in the process of exchanging MU-RTS frames, there may be a situation where it cannot transmit a CTS response to the received MU-RTS and there is no CTS frame transmitted on a specific channel.

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

[0312] Referring to Fig. 36(a), when performing a channel extension operation as shown in Fig. 13 to transmit a MU-RTS frame, if the extended channel only includes STAs that are receiving downlink frames on a link where the STR operation is not possible and that are indicated by a CTS frame using the extended channel, a CTS frame does not have to be transmitted on the extended channel. That is, the AP MLD can perform the exchange operation of the MU-RTS frame and the CTS frame by extending the channel after completing the channel access operation on another link while transmitting a frame on one 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, a STA for which the STR operation is possible or that is not receiving a frame on another link can transmit a CTS frame for the received MU-RTS frame as shown in Fig. 20(c). On the other hand, a STA that has already received a frame on another link where the STR operation is not possible may not be able to transmit a CTS frame as a response to the received MU-RTS as shown in Fig. 35(b). At this time, if the STA instructed to transmit a CTS frame on the extended channel only includes STAs that cannot transmit a CTS frame for the received MU-RTS frame as shown in Fig. 35(b), a CTS frame for the transmitted MU-RTS frame may not be transmitted on the extended channel. For example, AP1 and AP2 may belong to the AP MLD. AP1 can operate link 1 and AP2 can operate link 2. STA1-1 and STA1-2 may belong to STA MLD1. STA2-1 and STA2-2 may belong to STA MLD2. STA1-1, STA2-1, and STA3 may be connected to AP1, and STA1-2 and STA2-2 may be connected to AP2. At this time, STA1-1 and STA1-2 of STA MLD1 may not be able to perform the STR operation on link 1 and link 2.At this time, AP1 can transmit a downlink frame to STA1-1, STA2-1, and STA3 by multi-user OFDMA operation. Alternatively, AP1 can transmit a downlink frame to STA1-1. To protect the downlink frame, AP1 can further perform the exchange procedure of an RTS frame or a MU-RTS frame and a CTS frame. On the other hand, while AP1 is performing frame transmission and reception operations with STA1-1 or a plurality of terminals including STA1-1, AP2 may complete the channel contention process for frame transmission on Link 2.

[0313] At this time, the AP2 may attempt to transmit a downlink frame to a plurality of terminals including STA1-2. For example, it may attempt 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, the MU-RTS frame and CTS frame exchange operation can be performed before transmitting the frame. The MU-RTS frame can be transmitted using the same bandwidth as the downlink frame. For example, when attempting to transmit a downlink frame on the main 80 MHz channel, the MU-RTS frame can also be transmitted using an 80 MHz bandwidth. The transmission bandwidth of the CTS frame transmitted by STA2-2 in the MU-RTS frame can be specified as the main 40 MHz channel, and the transmission bandwidth of the CTS frame transmitted by STA1-2 can be specified 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, which is a response to the MU-RTS frame received on Link 2. On the other hand, the STA2-2 can transmit a CTS frame as a response to the MU-RTS frame. On the other hand, since AP2 only receives the CTS frame for the MU-RTS frame transmitted in the 80 MHz band in the 40 MHz band, it can transmit the downlink frame only using the 40 MHz band. That is, even if the actual channel is idle on a secondary 40 MHz channel that is not the main 40 MHz channel, frame transmission and reception operations may not be possible.

[0314] Also, even when performing the exchange operation of the MU-RTS frame and the CTS frame while leaving a specific 20 MHz channel empty as shown in FIG. 31 or FIG. 33, a situation may occur where the CTS frame cannot be received for the MU-RTS frame transmitted to the specific 20 MHz channel. Referring to FIG. 36(b), as in FIG. 36(a), the AP MLD may include AP1 and AP2, the STA MLD1 may include STA1-1 and STA1-2, and the STA MLD2 may include STA2-1 and STA2-2. At this time, AP1 and AP2 can each operate link 1 and link 2, and STA1-1 and STA1-2 may not be able to perform the STR operation on link 1 and link 2. At this time, AP1 can perform an operation of transmitting a downlink frame to STA1-1 or a plurality of terminals including STA1-1. During the transmission of the frame, AP2 on link 2 may complete the channel access operation for frame transmission. At this time, AP2 can further perform the exchange operation of the MU-RTS frame and the CTS frame to protect the downlink frame to be transmitted. The receiving STA of the MU-RTS frame may be the STA that receives the downlink frame. For example, when AP2 attempts to transmit a downlink frame to STA1-2 and STA2-2, the MU-RTS frame can be transmitted to the terminal. At this time, the AP2 can transmit the MU-RTS frame while leaving the specific 20 MHz band empty as shown in FIG. 16 or FIG. 18. STA1-2 and STA2-2 that have received the MU-RTS frame can transmit a CTS frame as a response to the received MU-RTS frame. At this time, the CTS frame can be transmitted only on the channel instructed to transmit the CTS frame with the MU-RTS frame as shown in FIG. 18. At this time, since STA1-1 is receiving a frame on link 1, STA1-2 may not be able to transmit a CTS frame for the MU-RTS frame. STA2-2 can transmit a CTS frame as a response to the MU-RTS frame.At this time, when only STA1-2 is instructed to transmit the CTS frame for a specific 20 MHz channel, the 20 MHz channel may be in a state where CTS transmission is not being performed. An AP2 that has not been able to receive a CTS frame as a response to the MU-RTS frame in the 20 MHz band can transmit a downlink frame by vacating the 20 MHz channel even if the 20 MHz channel is actually idle. At this time, when the channel that has not been able to receive a CTS response to the MU-RTS frame is the primary 20 MHz channel, the AP2 may not be able to perform uplink and downlink frame transmission and reception operations with STA1-2 and STA2-2 even if it receives a CTS frame on another channel for the MU-RTS frame. Also, when a CTS response to the MU-RTS frame is received at least on the primary 20 MHz channel, it is possible to perform downlink frame transmission following the reception of the CTS response.

[0315] Alternatively, even when some of the STAs communicating with the AP temporarily change the primary channel, a phenomenon may occur where no CTS frame is transmitted for the MU-RTS frame. Referring to Fig. 36(c), in the situation where the AP MLD transmits frames to the STA MLD1 and STA MLD2 as shown in Fig. 36(a) above, when the primary channel of STA2-2 temporarily moves to another channel other than the primary channel of the AP before frame transmission by AP2 on Link 2, the STA2-2 can transmit a CTS response to the received MU-RTS frame based on the primary channel of STA2-2. For example, when instructed to transmit a CTS frame with a bandwidth of 40 MHz for the MU-RTS frame in Fig. 14 or Fig. 15, the STA2-2 can transmit a CTS frame using the primary 40 MHz channel of the STA2-2 as a response to the MU-RTS frame received from the AP2. On the other hand, the STA1-2 can use the same primary channel as the primary channel of AP2. At this time, the STR operation is not possible for the STA1-1 and STA1-2, and since the STA1-1 is receiving a frame on Link 1, the STA1-2 may not be able to transmit a CTS frame as a response to the received MU-RTS frame. At this time, when only the STA1-2 is instructed to transmit the CTS frame for a specific 20 MHz channel, the 20 MHz channel may be in a state where no CTS transmission is performed. At this time, when the channel that could not receive the CTS response for the MU-RTS frame is the primary 20 MHz channel, even if the AP2 receives a CTS frame on another channel for the MU-RTS frame, the downlink frame transmission and reception operations with the STA1-2 and STA2-2 may not be possible.

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

[0317] FIG. 37 is a first embodiment of an operation of adding a condition to an AP MLD according to an embodiment of the present invention to omit transmission of a MU-RTS frame.

[0318] Referring to FIG. 37, when the AP MLD performs the frame transmission process on one link and the channel access operation for frame transmission is completed on another link during the process, when transmitting a downlink frame including a terminal that cannot perform a CTS response for transmitting an 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 (for example, dot11RTSThreshold) and the transmission of an RTS frame or an 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 can operate on Link 1, and AP2 can operate on Link 2. STA1-1 and STA1-2 may belong to STA MLD1. STA2-1 and STA2-2 may belong to STA MLD2. STA1-1, STA2-1, and STA3 may be connected to AP1, and STA1-2 and STA2-2 may be connected to AP2. At this time, the STR operation of STA1-1 and STA1-2 of STA MLD1 may be impossible on Link 1 and Link 2. At this time, AP1 can transmit a downlink frame to STA1-1, STA2-1, and STA3 by multi-user OFDMA operation. Or, AP1 can transmit a downlink frame to STA1-1. In order to protect the downlink frame, AP1 can further perform the exchange procedure of an RTS frame or an MU-RTS frame and a CTS frame. On the other hand, while AP1 is performing frame transmission and reception operations with STA1-1 or a plurality of terminals including STA1-1, AP2 may complete the channel contention process for frame transmission on Link 2. AP2 may attempt to transmit a downlink frame to a plurality of terminals including STA1-2. At this time, when one or more of the receiving STAs of the frame to be transmitted belong to a STA MLD that cannot perform the STR operation with Link 1 and the STA belonging to the MLD is receiving a frame on Link 1, the downlink frame can be transmitted without performing the exchange operation of the MU-RTS frame and the CTS frame.At this time, when the completion time of the channel contention process is before the end time of the transmission of the CTS frame on Link 1, even if the channel access operation on Link 2 is completed, after performing the channel sensing operation until the start time of the PPDU including the downlink frame on Link 1, the frame transmission operation can be performed according to that time point.

[0319] On the other hand, when the completion time of the channel contention process on Link 2 occurs during the transmission time of the downlink frame on Link 1, the following operations can be performed according to the remaining transmission time of the PPDU including the downlink frame on Link 1 as follows.

[0320] FIG. 38 is a second embodiment of an operation for adding conditions to the AP MLD according to an embodiment of the present invention to omit the transmission of the MU-RTS frame.

[0321] Referring to FIG. 38, when the AP MLD performs an operation for frame transmission on one link and the channel access operation for frame transmission is completed on another link, if there is a terminal that cannot perform a CTS response to the transmission of the MU-RTS frame on that link, the transmission of the MU-RTS frame may be omitted. At this time, when the time point when the channel access operation is completed is during the transmission time of the PPDU including the downlink frame on another link, the transmission operations of the MU-RTS frame and the CTS frame can be omitted at the time point when the channel access is completed on that link, and the downlink frame can be transmitted. That is, even when the length of the PSDU (PHY Service Data Unit) to be transmitted on that link exceeds a specific value (for example, dot11RTSThreshold) and the transmission of the RTS frame or the MU-RTS frame is required, the process of exchanging the MU-RTS frame and the CTS frame may be omitted. For example, as shown in FIG. 22 above, while AP1 belonging to the AP MLD performs frame transmission and reception operations with STA1-1 or a plurality of terminals including STA1-1, AP2 may complete the channel contention process for frame transmission on link 2. Also, AP2 may have data to be transmitted to a plurality of STAs including STA1-2. At this time, while AP1 transmits a PPDU including a downlink frame on link 1, AP2 completes the channel contention on link 2, and the remaining transmission time of the PPDU transmitted on link 1 at the completion time can be confirmed. At this time, when the remaining transmission time of the PPDU transmitted on link 1 is equal to or greater than a specific time, AP2 can omit the process of exchanging the 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. Or, the specific time may be exchanged during the negotiation process for the multi-link operation between the AP MLD and the STA MLD.

[0322] On the one hand, when the channel contention completion time at the link 2 occurs during the transmission time of the downlink frame at the link 1 and the remaining transmission time of the PPDU being transmitted at the link 1 is within the specific time, a downlink frame can be transmitted as shown in FIG. 23, and the transmission end time of the PPDU including the frame can be made to coincide with the PPDU transmission end time at the link 1. Alternatively, the process of exchanging the MU-RTS frame and the CTS frame can be performed as follows.

[0323] FIG. 39 is an example of an operation of transmitting an MU-RTS frame according to additional conditions given in the AP MLD according to an embodiment of the present invention. At this time, descriptions overlapping with FIGS. 37 and 38 may be omitted.

[0324] Referring to FIG. 39, when the AP MLD is transmitting a frame on one link and the channel access operation for frame transmission on another link is completed during the transmission, and the time from the completion point to the end point of PPDU transmission on the link that is already transmitting the frame is within a specific time, the AP MLD can perform the transmission operation of the MU-RTS frame. For example, one of the APs belonging to the AP MLD (e.g., AP1) can transmit a downlink frame. At this time, the downlink frame may be transmitted to a plurality of terminals. For example, AP1 operates on Link 1 and can 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 the STR operation. Another AP (e.g., AP2) belonging to the same AP MLD as the AP1 that is transmitting the downlink frame on Link 1 may complete the channel access operation for frame transmission. At this time, the number of STAs of the frame transmitted by the AP2 may be plural, and one or more of them may be the STAs that receive the frame on Link 1. For example, the downlink frame transmitted by AP2 on Link 2 may be transmitted to STA1-2 and STA2-2. At this time, when the remaining transmission time of the PPDU including the frame transmitted on Link 1 at the time when the AP2 completes the channel access operation on Link 2 is within a specific time, AP2 can transmit the MU-RTS frame when the transmission operation of the MU-RTS frame is required according to the length of the PSDU to be transmitted. Or, the process of exchanging the MU-RTS frame and the CTS frame can be performed to protect the downlink frame transmitted by AP2. At this time, padding bits may be added to the MU-RTS frame to align the transmission end point with the downlink frame transmitted on Link 1. Or, the channel sensing operation can be further performed so that the transmission end point of the MU-RTS frame coincides with the end point of PPDU transmission on Link 1.

[0325] On the other hand, a plurality of STAs that have received the MU-RTS frame can confirm the MU-RTS frame and can transmit a CTS frame after performing channel sensing on the channel indicated by the MU-RTS frame. The AP that has received the CTS frame can transmit a downlink frame to a plurality of STAs. At this time, when some STAs that are unable to perform STR operation on Link 1 are transmitting an uplink response frame (for example, a BlockAck frame), the downlink transmission can be postponed until the end of transmission of the PPDU including the response frame on that link (for example, Link 1). At this time, a channel sensing operation is performed during the postponement time, and it can be confirmed whether the channel is occupied by other terminals during that time.

[0326] On the other hand, when one or more terminals transmit a CTS frame as a response to the MU-RTS frame on a specific channel, the AP can determine that the transmission operation of the MU-RTS frame has been successful. Therefore, it is possible to induce one or more STAs to transmit a CTS frame on all 20 MHz band channels on which the MU-RTS frame has been transmitted by the following operation.

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

[0328] Referring to FIG. 40, when an AP belonging to an AP MLD attempts to transmit a downlink frame to a plurality of terminals including a STA that cannot transmit a CTS frame due to a situation where the STR operation is impossible, the STA that cannot transmit a CTS can be instructed to transmit a CTS frame on the primary 20 MHz channel or a part of the channels including the primary 20 MHz channel. At this time, other STAs can transmit frames on the extended channel. The other STAs can be instructed to transmit a CTS frame including the primary channel and the extended channel. That is, other STAs may be made to transmit a CTS frame including the band used by the STA that cannot transmit the CTS frame. For example, an AP1 and an AP2 may belong to the AP MLD. AP1 can operate Link 1, and AP2 can operate Link 2. A STA MLD, or a STA not belonging to the STA MLD, may be connected to the APs 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 be unable to perform the STR operation. STA2-1 and STA2-2 belonging to STA MLD2 may be able to perform the STR operation. Further, a STA3 may be connected to AP1.

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

[0330] While the AP1 is transmitting a downlink frame, the AP2 may complete a channel access operation for transmitting a downlink frame. At this time, the AP2 may have data to be transmitted to a plurality of STAs including STA1-2. At this time, the AP2 can transmit a downlink frame to a plurality of terminals including the STA1-2. At this time, when the length of the PSDU including the downlink frame becomes equal to or greater than a specific length, an exchange operation of an RTS frame or a MU-RTS frame and a CTS frame may be required. At this time, the AP can transmit the MU-RTS frame to a plurality of STAs. At this time, a STA (for example, STA1-2) that cannot transmit a CTS frame depending on the availability of the STR operation can be instructed to transmit a CTS frame on a main 20 MHz channel or a part of channels including the main channel. At this time, a STA capable of the STR operation or a STA that does not receive a frame on the link 1 can be instructed to transmit a CTS frame on an extended channel among the channels on which the MU-RTS frame is transmitted. The STA capable of the STR operation may be a STA belonging to a STA MLD capable of the STR operation. Or, it may be a STA belonging to a STA MLD that does not perform a frame reception operation on the link 1. Or, it may be a STA that does not belong to a STA MLD. At this time, each STA can transmit the CTS frame by the operation of FIG. 13 or FIG. 16. Therefore, even if the STA1-2 cannot transmit a CTS frame because the STR operation is impossible, the AP2 can receive a CTS frame for the transmitted MU-RTS frame by other STAs transmitting CTS frames on a plurality of channels including the main channel. The AP2 that has received the CTS frame for the MU-RTS frame can determine that the transmission operation of the MU-RTS frame has been successful. Thereby, the AP2 can transmit a downlink frame to a plurality of terminals.

[0331] On the other hand, when some STAs cannot transmit a CTS response to the received MU-RTS frame because the STR operation is impossible due to interference inside the device, the following request can be made to other STAs to transmit a CTS frame over the entire band.

[0332] Figure 41 shows a second embodiment of an operation for avoiding a situation where a CTS frame at a specific 20 MHz is not transmitted by the operation of the STA MLD according to an embodiment of the present invention. At this time, descriptions overlapping with those in FIG. 40 may be omitted.

[0333] Referring to FIG. 41, when an AP belonging to the AP MLD attempts to transmit a downlink frame to a plurality of terminals including a STA that cannot transmit a CTS frame due to a situation where the STR operation is impossible, it can instruct a STA capable of CTS transmission to transmit a CTS frame in the entire band. For example, as shown in FIG. 25, the AP MLD may be connected to the STA MLD1, the STA MLD2, and the STA3. At this time, the AP1 has completed a channel access operation on Link 1 and can transmit a downlink frame to a plurality of terminals including the STA1-1. At this time, in order to protect the frame transmission operation on the Link 1, an exchange operation of an RTS or MU-RTS frame and a CTS frame can be further performed.

[0334] While the AP1 is transmitting a downlink frame, the AP2 may complete a channel access operation for transmitting a downlink frame. At this time, the AP2 may have data to be transmitted to a plurality of STAs including STA1-2. At this time, the AP2 can transmit a downlink frame to a plurality of terminals including the STA1-2. At this time, when the length of the PSDU including the downlink frame becomes equal to or greater than a specific length, an exchange operation of an RTS frame or a MU-RTS frame and a CTS frame may be required. At this time, the AP can transmit the MU-RTS frame to a plurality of STAs. At this time, a terminal that cannot perform the STR operation may not be able to transmit a CTS frame that is a response to the MU-RTS frame. When it is determined that some of the terminals cannot transmit a CTS frame and no CTS frame is transmitted on a specific 20 MHz channel, the AP2 can request another STA capable of transmitting a CTS frame to transmit a CTS frame including the channel. The other STA may be a STA belonging to a STA MLD capable of performing the STR operation. Or, it may be a STA belonging to a STA MLD that does not perform a frame reception operation on the link 1. Or, it may be a STA that does not belong to a STA MLD. For example, the AP2 can transmit a downlink frame to the STA2-2 only on the primary 40 MHz channel. At this time, a downlink frame can be transmitted to the STA1-2 on the secondary 40 MHz channel. At this time, since the STA1-1 is receiving a frame, the STA1-2 may not be able to transmit a CTS frame as a response to the MU-RTS. At this time, the AP2 can request the STA2-2 that has received the MU-RTS frame to transmit a CTS response using the entire bandwidth. The STA2-2 that has received the MU-RTS frame can transmit a CTS frame in all the bands in which the MU-RTS frame has been received. Thereby, the AP2 can receive a CTS frame for the transmitted MU-RTS frame. The AP2 that has received the CTS frame for the MU-RTS frame can determine that the transmission operation of the MU-RTS frame has been successful. Thereby, the AP2 can transmit a downlink frame to a plurality of terminals.

[0335] On the other hand, when the STA MLD for which the STR operation is impossible is impossible to perform the STR operation only for some channels, the AP MLD can perform an operation of checking whether the channels at each STA are idle instead of the RTS or MU-RTS frame and CTS exchange operations. This operation may be performed by the process of the AP transmitting BQRP (Bandwidth Query Report Poll) frames to a plurality of STAs and the plurality of STAs transmitting BQR (Bandwidth Query Report) frames. At this time, the channel for each STA to transmit the BQR frame may be different from the channel on which the downlink data is transmitted. The process of checking whether the channel is idle by the operation of transmitting the BQR frame may be performed as follows.

[0336] FIG. 42 is a third embodiment of an operation for avoiding a situation where a CTS frame is not transmitted at a specific 20 MHz by the operation of the STA MLD according to an embodiment of the present invention. At this time, descriptions overlapping those of FIGS. 40 and 41 may be omitted.

[0337] Referring to FIG. 42, when an AP belonging to the AP MLD attempts to transmit a downlink frame to a plurality of terminals including a STA that cannot transmit a CTS frame due to a situation where the STR operation is impossible, instead of the channel reservation process using the MU-RTS frame and the CTS frame, each STA can be requested to check the presence or absence of channel occupancy for each 20 MHz channel. At this time, the channel state confirmed by the plurality of STAs may be transmitted in 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 completes the channel access operation on link 1 and can transmit a downlink frame to a plurality of terminals including STA1-1. At this time, in order to protect the frame transmission operation on the link 1, the exchange operation of the RTS or MU-RTS frame and the CTS frame can be further performed.

[0338] While the AP1 is transmitting a downlink frame, the AP2 may complete a channel access operation for transmitting a downlink frame. At this time, the AP2 may have data to be transmitted to a plurality of STAs including STA1-2. At this time, the AP2 can transmit a downlink frame to a plurality of terminals including the STA1-2. At this time, when the length of the PSDU including the downlink frame becomes equal to or greater than a specific length, an exchange operation of an RTS frame or a MU-RTS frame and a CTS frame may be required. At this time, when the STA1-2 is capable of performing STR operation with the STA1-1 on a specific channel, instead of performing a channel protection operation using the transmission of a MU-RTS frame, the AP2 can check whether the channel is occupied by a plurality of STAs that receive the downlink frame. The operation of checking the channel status of the plurality of STAs can be performed by the AP2 transmitting a request frame to the plurality of STAs to request whether each 20 MHz channel is occupied. The request frame may be a frame that requests 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 that requests a plurality of STAs to transmit a BQR. At this time, each STA can indicate the channel on which the BQR should be transmitted. At this time, when the STA1-2 can transmit a frame on some channels, the AP2 can designate the channel on which the STA1-2 transmits the BQR frame as the channel.

[0339] Multiple STAs that have received a BQRP frame from the AP2 can confirm from the BQRP to request the transmission of a BQR frame. Thereby, the multiple STAs can perform channel sensing for all the bands in which the STA is operable. Thereby, it is possible to confirm whether or not each 20 MHz channel is occupied. Each STA that has confirmed whether or not each 20 MHz channel is occupied can transmit a BQR frame on the channel indicated in the BQRP frame. At this time, the PPDU in which the BQR frame is transmitted may be transmitted in the form of an HE TB PPDU or an EHT TB PPDU.

[0340] The AP2 that has received a BQR frame from the multiple STAs can confirm the presence or absence of channel occupancy for all the bands from each STA. The AP2 can transmit a downlink frame via the channel indicated as being available in the BQR frame. At this time, the channel on which the AP2 has received BQR from each STA and the channel on which the downlink frame is transmitted to the STA may be different channels.

[0341] On the other hand, since the STR operation is impossible due to interference inside the device, when the AP cannot receive a CTS frame for the MU-RTS frame transmitted on some channels that are not the primary channel as shown in FIG. 21, the AP can extend the channel and transmit a frame after receiving a CTS frame on some channels as follows.

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

[0343] Referring to FIG. 43, when an AP belonging to the AP MLD attempts to transmit a downlink frame to a plurality of terminals including a STA that cannot transmit a CTS frame due to a situation where the STR operation is impossible, the STA capable of CTS transmission can be instructed to transmit a CTS frame over 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 can complete the channel access operation on Link 1 and transmit a downlink frame to a plurality of terminals including STA1-1. At this time, in order to protect the frame transmission operation on Link 1, the exchange operation of the RTS or MU-RTS frame and the CTS frame can be further performed.

[0344] While the AP1 is transmitting a downlink frame, the AP2 may complete a channel access operation for transmitting a downlink frame. At this time, the AP2 may have data to be transmitted to a plurality of STAs including STA1-2. At this time, the AP2 can transmit a downlink frame to a plurality of terminals including the STA1-2. At this time, when the length of the PSDU including the downlink frame is equal to or greater than a specific length, an exchange operation of an RTS frame or a MU-RTS frame and a CTS frame may be required. At this time, the AP2 can transmit a MU-RTS frame to a plurality of STAs including the STA1-2. Among the STAs that have received the MU-RTS frame, the STAs capable of transmitting a CTS frame can perform carrier sensing on the channel indicated in the MU-RTS frame and then transmit a CTS frame. At this time, a STA (for example, STA1-2) that cannot transmit a CTS frame in response to the MU-RTS frame because the STR operation is impossible may not be able to transmit a CTS frame. Due to the situation where the STA1-2 cannot perform the STR operation, the STA1-2 may not be able to transmit a CTS frame, and a specific 20 MHz channel may not be able to transmit a CTS frame in response to the transmitted MU-RTS. On the other hand, after transmitting the MU-RTS frame including the STA1-2, the AP2 can recognize that it is impossible to transmit a CTS frame in a specific 20 MHz channel due to the characteristics of the STA1-2 in which the STR operation is impossible. 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, when the STA2-2 is instructed to transmit a CTS frame in the primary 40 MHz channel and the STA1-2 is instructed to transmit a CTS frame in the primary 80 MHz channel with respect to the MU-RTS frame, the AP2 can transmit a downlink frame to the STA1-2 and the STA2-2 using the 80 MHz channel even if a CTS frame cannot be received for the secondary 40 MHz channel.At this time, the AP2 can further perform a channel sensing operation at a specific time for the channel that could not receive the CTS frame. The channel sensing operation may include only the ED (Energy Detection) operation of checking the received energy level. At this time, the reference energy level for determining that the channel is occupied during the ED operation may be set lower than the energy level for determining whether the channel is occupied in the 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 after the transmission end time of the MU-RTS frame to the time before transmitting the downlink frame. Or, the specific time may be a specific IFS time (for example, SIFS, PIFS, or AIFS).

[0345] On the other hand, the AP2 can recognize that even if it transmits the MU-RTS frame, it cannot receive the CTS frame due to a specific situation where some of the receiving STAs of the downlink frame are unable to perform STR. At this time, the AP2 can omit the transmission process of the MU-RTS frame for the band to which the frame is to be transmitted to the STA as follows, and can perform only the MU-RTS frame and CTS frame exchange procedure for other bands.

[0346] FIG. 44 is a second embodiment of the operation of continuing frame transmission even if the CTS frame cannot be received for the MU-RTS frame in a specific 20 MHz channel according to an embodiment of the present invention. At this time, the description overlapping with FIGS. 40 and 43 may be omitted.

[0347] Referring to FIG. 44, when an AP belonging to the AP MLD attempts to transmit a downlink frame to a plurality of terminals including a STA that cannot transmit a CTS frame due to a situation where the STR operation is impossible, a STA capable of CTS transmission can be instructed to transmit a CTS frame in the entire bandwidth. For example, as shown in FIG. 25, the AP MLD may be connected to the STA MLD1, the STA MLD2, and the STA3. At this time, the AP1 has completed the channel access operation on Link 1 and can transmit a downlink frame to a plurality of terminals including the STA1-1. At this time, in order to protect the frame transmission operation on the Link 1, an exchange operation of an RTS or MU-RTS frame and a CTS frame can be further performed.

[0348] While the AP1 is transmitting a downlink frame, the AP2 may complete a channel access operation for transmitting a downlink frame. At this time, the AP2 may have data to be transmitted to a plurality of STAs including STA1-2. At this time, the AP2 can transmit a downlink frame to a plurality of terminals including the STA1-2. At this time, when the length of the PSDU including the downlink frame becomes equal to or greater than a specific length, an exchange operation of an RTS frame or a MU-RTS frame and a CTS frame may be required. At this time, even if the AP2 transmits the MU-RTS frame including the STA1-2, the AP2 can recognize that the STA1-2 cannot transmit a CTS frame on a specific 20 MHz channel because the STR operation is impossible. In this case, the AP2 can vacate the channel recognized as impossible to transmit a CTS frame and perform a channel reservation process using only the exchange of the MU-RTS frame and the CTS frame for other channels. For example, when the AP2 attempts to transmit a downlink frame to STA2-2 on the primary 40 MHz channel and transmit a downlink frame to STA1-2 using the secondary 80 MHz channel, the AP2 can transmit an MU-RTS frame to the primary 40 MHz channel and receive a CTS frame. At this time, after the AP2 receives a CTS frame on the primary 40 MHz channel, the AP2 can expand the used channel to the primary 80 MHz channel and transmit frames to STA1-2 and STA2-2. At this time, the AP2 can perform a channel sensing operation at a specific time for the secondary 40 MHz channel. The channel sensing operation may include only an ED (Energy Detection) operation for checking a received energy level. At this time, a reference energy level for determining that the channel is occupied during the ED operation may be set lower than an energy level for determining whether the 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 after the end of transmission of the MU-RTS frame to before the time of transmitting a downlink frame.Alternatively, the specific time may be a specific IFS time (e.g., SIFS, PIFS, or AIFS).

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

[0350] The software AP may be an AP station. Also, the software AP may be an AP included in a multi-link device. At this time, the software AP may be included in a non-STR multi-link device. When the software AP is included in a non-STR multi-link device, such a multi-link device can be called a non-STR software AP multi-link device.

[0351] When a non-STR software AP multi-link device operates on a plurality of links, the plurality of links can be distinguished into a mandatory link and an optional link. Specifically, the plurality of links may include at least one mandatory link. The operation between the non-STR software AP multi-link device and a legacy station or a single-link station may be restricted to be performed only on the mandatory link. Specifically, the association and authentication between the non-STR software AP multi-link device and a legacy station or a single-link station may be restricted to be performed on the mandatory link. At this time, the single-link station may be a station that cannot operate on a plurality of links.

[0352] The mandatory link and the optional link of the non-STR software AP multi-link device may be specified by the non-STR software AP multi-link device. Specifically, when multi-link is set up between the non-STR software AP multi-link device and a non-AP multi-link device, the mandatory link and the optional link may be set. For example, when a mandatory link among a plurality of links is specified, the links other than the mandatory link may be optional links.

[0353] Multiple links may be specified as essential links by specific embodiments. At this time, the multiple links specified as essential links may be links capable of STR with each other. For example, when a non-STR soft AP multi-link device operates on multiple links including a first link and a second link, the non-STR soft AP multi-link device can receive on the second link when transmitting on the first link. At this time, the first link and the second link may be essential links. The essential 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 allowed for different essential links to be set for multiple devices communicating with the non-STR soft AP multi-link device.

[0354] Also, the selective links of the non-STR soft AP multi-link device may be used only for the communication between the non-STR soft AP multi-link device and the multi-link device. The selective links may not be used for the communication between the non-STR soft AP multi-link device and the legacy station or the single-link station. Also, the association and authentication between the non-STR soft AP multi-link device and the multi-link device may be performed using the essential links.

[0355] In the embodiment of FIG. 45, the non-STR soft AP multi-link device (Soft AP, non-STR AP MLD) operates on a first link (Link1) and a second link (Link2). The first link (Link1) is an essential link, and the second link (Link2) 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) through the second link (Link2). 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) through the second link (Link2). The non-STR soft AP multi-link device (Soft AP, non-STR AP MLD) communicates with the legacy station (Legacy STA) and the single link station (Single link STA) through the first link (Link1). The non-STR soft AP multi-link device (Soft AP, non-STR AP MLD) performs connection and authentication with the legacy station (Legacy STA) and the single link station (Single link STA) on the first link (Link1).

[0356] The channel access method on the essential link and the channel access method on the optional link may be different. This will be further described with reference to FIGS. 45 to 47.

[0357] FIG. 46 shows that the non-STR soft AP multi-link device according to an embodiment of the present invention transmits PPDUs on the essential link and the optional link.

[0358] When channel access is performed independently for the aforementioned essential link and selective link, when the non-STR soft AP multi-link device performs transmission on the selective link, it may not be able to receive on the essential link. To prevent such a problem, whether to perform transmission on the selective link may be determined based on whether transmission is performed on the essential link. The non-STR soft AP multi-link device can determine whether to perform transmission on the selective link based on whether to perform transmission on the essential link. Specifically, when the non-STR soft AP multi-link device performs transmission, the non-STR soft AP multi-link device can compulsorily perform transmission on the essential link. Also, the non-AP multi-link device connected to the non-STR soft AP multi-link device can determine whether to perform transmission on the selective link based on whether to perform transmission on the essential link. Specifically, when the non-AP multi-link device connected to the non-STR soft AP multi-link device performs transmission, the non-AP multi-link device can compulsorily perform transmission on the essential link.

[0359] Therefore, the non-STR soft AP multi-link device can perform transmission on the selective link only when performing transmission on the essential link. When the non-STR soft AP multi-link device does not perform transmission on the essential link, it may not be allowed for the non-STR soft AP multi-link device to perform transmission on the selective link.

[0360] When random backoff-based channel access is performed, the following embodiments may be applicable. Even if the backoff counter reaches 0 on the selective link, if the backoff counter has not reached 0 on the essential link, the non-STR soft AP multi-link device may not perform transmission on the selective link. Specifically, the non-STR soft AP multi-link device can wait until the backoff counter reaches 0 on the essential link. When the backoff counter reaches 0 on the selective link, if the backoff counter on the essential link reaches 0 or transmission is in progress on the essential link, the non-STR soft AP multi-link device can start transmission on the selective link.

[0361] When channel access is performed according to the result of channel sensing in a fixed-length time interval, the following embodiments may be applicable. Even if the non-STR soft AP multi-link device senses that the channel of the selective link is idle in a pre-specified time interval, if transmission is not being performed on the essential link, it may not be permitted to start transmission on the selective link. At this time, the pre-specified time interval may be PIFS. In still other specific embodiments, only when the non-STR soft AP multi-link device performs transmission on the essential link, the non-STR soft AP multi-link device can perform channel sensing in a pre-specified time interval on the selective link and perform channel access.

[0362] The non-STR soft AP multi-link device can align the end of the PPDU transmitted on the essential link and the end of the PPDU transmitted on the selective link. Completing the transmission of multiple PPDUs simultaneously can be said to align the ends of the PPDUs. Also, when the difference between the transmission end times of multiple PPDUs is smaller than or equal to a threshold value, it can be said that the ends of the multiple PPDUs are aligned. At this time, the threshold value may be a pre-specified value. Specifically, the threshold value may be a value set based on SIFS. Also, the threshold value may be a value set based on the length of SIFS and signal extension. For example, the threshold value may be the value obtained by dividing the sum of the length of SIFS and the signal extension by 2. At this time, the threshold value may be 8 us. The non-STR soft AP multi-link device is allowed not to align the ends of the PPDUs only when the PPDU transmitted on either the essential link or the selective link does not contain a frame that induces an immediate response. Specifically, the non-STR soft AP multi-link device can align the end of the PPDU containing a frame that induces an immediate response and the end of the PPDU not containing a frame that induces an immediate response, or can be set such that the end of the PPDU containing a frame that induces an immediate response comes before the end of the PPDU containing a frame that induces an immediate response. For example, those that do not align the ends of the PPDUs may be such that the end of the PPDU not containing a frame that induces a response is the same as or temporally earlier than the end of the PPDU containing a frame that induces an immediate response.

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

[0364] When the first AP (AP1) and the second AP (AP2) transmit PPDUs simultaneously as in the above-described embodiment, the ends of the first AP (AP1) and the second AP (AP2) PPDUs are aligned. When the first AP (AP1) transmits a PPDU including data (Data3) and the second AP (AP2) transmits a PPDU including data (Data4), the first AP (AP1) and the second AP (AP2) align the ends of the PPDUs. Also, when the PPDU transmitted on either one of the links does not include a frame that induces an immediate response, it may be allowed that the first AP (AP1) and the second AP (AP2) do not align the ends of the PPDUs. Since the data (Data5) transmitted by the first AP (AP1) does not induce an immediate response, the first AP (AP1) can abort PPDU transmission earlier than the PPDU transmitted by the second AP (AP2).

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

[0366] Among the above-described embodiments, when an exception where the ends of PPDUs are not aligned is allowed, the non-STR soft AP multi-link device may need to receive data on another link while transmitting a PPDU on any one link. For example, as shown in FIG. 45, while the second AP (AP2) is transmitting a PPDU including data (Data6), the first AP (AP1) can receive a PPDU including data (Data7) from the first station. At this time, due to the transmission of the PPDU including data (Data6), the first AP (AP1) may not be able to receive the PPDU including data (Data7). Therefore, a method may be needed such that PPDU reception is not disturbed on any one link in this way.

[0367] FIG. 47 shows that the non-STR soft AP multi-link device according to an embodiment of the present invention transmits PPDUs on an essential link and a selective link.

[0368] The non-STR soft AP multi-link device can determine whether to align the ends of the PPDU based on on which link among the essential link and the selective link a PPDU including a frame that induces an immediate response is transmitted. Specifically, when the non-STR soft AP multi-link device transmits a PPDU including a frame that induces an immediate response on the selective link, the non-STR soft AP multi-link device may need to align the ends of the PPDU transmitted on the essential link and the PPDU transmitted on the selective link. That is, when the non-STR soft AP multi-link device transmits a PPDU that does not include a frame that induces an immediate response on the selective link, it may be allowed that the non-STR soft AP multi-link device does not align the ends of the PPDU transmitted on the essential link and the PPDU transmitted on the selective link.

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

[0370] In the above-described embodiment, the operation of the non-STR soft AP multi-link device may be the same as the operation of the non-AP multi-link device that communicates.

[0371] Even if a multi-link device sets up a plurality of links, it may not be able to assist in simultaneous transmission or reception on the plurality of links. Such a multi-link device can perform transmission or reception on a plurality of links on the condition that it transmits or receives a restricted type of frame or PPDU. At this time, the restricted type of frame or PPDU may have restrictions on the type of frame, the MCS used for transmission, the number of special streams used for transmission, and the frequency bandwidth used for transmission. The operation of such a multi-link device can be called improved multi-link operation. In the improved 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 does not have to perform the improved multi-link device operation. Specifically, the operation of the improved multi-link device may not be allowed on the plurality of links set by the non-STR soft AP multi-link device. For example, the non-STR soft AP multi-link device does not have to set the operation of the improved multi-link device of the multi-link device operating on the plurality of links set by the non-STR soft AP multi-link device. Specifically, the non-STR soft AP multi-link device may be signaled to reject or not support the improved multi-link operation. This is because transmission on the essential link is impossible when transmission is performed on the selective link in the improved multi-link operation.

[0372] FIG. 48 shows that the non-STR soft AP multi-link device according to an embodiment of the present invention performs channel access on the essential link and the selective link.

[0373] While the non-STR soft AP multi-link device performs reception on the selective link, the non-STR soft AP multi-link device can delay channel access on the essential link. This is because when the non-STR soft AP multi-link device performs transmission on the essential link while performing reception on the selective link, reception on the selective link may be interfered with. Channel access deferral may mean not performing channel access during the deferral period. Also, channel access deferral may mean not starting transmission even when the backoff counter reaches 0. Further, the non-STR soft AP multi-link device can defer channel access even before the identifier or address of the transmitter of the PPDU received on the selective link is identified. At this time, the channel access deferral may continue until reception on the selective link ends.

[0374] In the embodiment of FIG. 48, the non-STR soft AP multi-link device includes a first AP (AP1) and a second AP (AP2). Each of the first AP (AP1) and the second AP (AP2) operates on a first link (Link1) which is an essential link and a second link (Link2) which is a selective link. Each of the first AP (AP1) and the second AP (AP2) is coupled to a first station (SAT1) and a second station (STA2) included in the non-STR multi-link device. The first AP (AP1) transmits data (Data1) that does not induce an immediate response to the first station (STA1), and the second AP (AP2) transmits data (Data2) that induces an immediate response to the second station (STA2). While the second AP (AP2) receives a response to the data (Data2) from the two stations (STA2), the first AP (AP1) defers channel access. Also, the first AP (AP1) transmits data (Data3) that induces an immediate response to the first station (STA1), and the second AP (AP2) transmits data (Data4) that induces an immediate response to the second station (STA2). The first AP (AP1) receives a response to the data (Data3) from the first station (STA1), and the second AP (AP2) receives a response to the data (Data4) from the second station (STA2). While the second AP (AP2) receives a response to the data (Data4) from the second station (STA2), the first AP (AP1) defers channel access.

[0375] In still other specific embodiments, the non-STR soft AP multi-link device does not have to transmit a PPDU including a frame that induces an immediate response on a selective link while transmitting a PPDU that does not include a frame that induces an immediate response on an essential link.

[0376] FIG. 49 shows that the non-STR soft AP multi-link device according to an embodiment of the present invention transmits a PPDU on an essential link and a selective link.

[0377] When the non-STR soft AP multi-link device transmits a PPDU that does not include a frame that induces an immediate response on both the essential link and the selective link, the non-STR soft AP multi-link device can finish the PPDU transmission on the selective link without delaying it more than the PPDU transmission on the essential link. That is, in this case, the end of the PPDU transmission on the selective link may be earlier than or the same as the end of the PPDU transmission on the essential link. If the PPDU transmission on the essential link finishes before the PPDU transmission on the selective link, it may interfere with the transmission of the station that transmits to the non-STR soft AP multi-link device on the essential link.

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

[0379] When a multi-link device that communicates with the non-STR soft AP multi-link device transmits a PPDU that does not include a frame that induces an immediate response on both the essential link and the selective link, the multi-link device can finish the transmission on the selective link before the PPDU transmission on the essential link. At this time, even when another station transmits to the non-STR soft AP multi-link device on the selective link, the non-STR soft AP multi-link device can receive it.

[0380] The AP multi-link device and the non-AP multi-link device can negotiate for multi-link usage during the scanning and association process described in FIG. 5 above. During the scanning process, the AP of the AP multi-link device can signal information about multiple links. Specifically, the AP of the AP multi-link device can include in the beacon frame an indicator indicating that it is operable on multiple links, the number of available links, and at least one of the information about the multiple links. Also, during the scanning process, the station of the non-AP multi-link device can signal information about multiple links. Specifically, the station of the non-AP multi-link device can include in the probe frame an indicator indicating that it is operable on multiple links. Also, the station of the non-AP multi-link device can include in the probe frame the number of available links and at least one of the information about the multiple links.

[0381] During the scanning process, a non-AP multi-link device that has confirmed the availability of the multi-link operation of the AP multi-link device and the link information to be used can be connected to the AP multi-link device. At this time, the AP multi-link device and the non-AP multi-link device can start the negotiation process for the multi-link operation. The negotiation for the multi-link operation may 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 send an indicator indicating that the multi-link operation is available and a request indicator requesting to perform the multi-link operation. The AP that has received the connection request frame from the station can confirm the indicator requesting the multi-link operation. At this time, if the multi-link operation is possible for the AP, the AP can send a connection response frame allowing the multi-link operation to the station, including the link information to be used for the multi-link operation and the parameters to be used for each link. The parameters for the multi-link operation may include at least one of the frequency bands of the respective multiple links used in the multi-link operation, the bandwidth expansion direction of the frequency bands of the respective multiple links, the TBTT (Target Beacon Transmission Time), and the availability of the STR operation. The AP multi-link device and the non-AP multi-link device for which the use of the multi-link operation has been confirmed by exchanging the connection request frame and the connection request response frame can perform a frame transmission operation using multiple links after the connection process.

[0382] FIG. 50 shows that independent transmissions are performed on each of the multiple links according to an embodiment of the present invention.

[0383] The AP multi-link device and the non-AP multi-link device that have completed the negotiation for multi-link operation can perform transmission and reception independently for each link or simultaneously on multiple links. When transmission and reception are performed independently on each of the multiple links, the AP of the AP multi-link device and the non-AP station of the non-AP multi-link device perform channel contention for transmission independently. Therefore, the transmission start time and the transmission end time on each link do not have to be the same. Also, the TXOP (transmission opportunity) obtained in the channel access procedure for each link may be obtained independently.

[0384] In the embodiment of FIG. 50, the AP multi-link device (AP MLD) includes a first AP (AP1) and a second AP (AP2), and each of the first AP (AP1) and the second AP (AP2) operates on a first link (Link1) and a second link (Link2). The non-AP multi-link device (STA MLD) includes a first station (STA1) and a second station (STA2), and each of the first station (STA1) and the second station (STA2) operates on the first link (Link1) and the second link (Link2). Each of the first AP (AP1) and the second AP (AP2) performs channel access independently on the first link (Link1) and the second link (Link2). Each of the first station (STA1) and the second station (STA2) also performs channel access independently on the first link (Link1) and the second link (Link2). Therefore, the AP multi-link device (AP MLd) and the non-AP multi-link device (STA MLD) can perform reception on one link while performing transmission on the other link.

[0385] Such an embodiment can improve the transmission efficiency of individual links. However, when the non-AP multi-link device or the AP multi-link device does not support STR, such channel access independently performed on each of the plurality of links may not be allowed. When the non-AP multi-link device or the AP multi-link device does not support STR, other embodiments may be applied. This will be described with reference to FIG. 50.

[0386] FIG. 51 shows the operation of the multi-link device performing transmission on a non-STR link pair.

[0387] A non-STR multi-link device that does not support STR cannot receive on another link when transmitting on any one link. Therefore, when the non-STR multi-link device performs channel access independently on each of the plurality of links, transmission failures 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 each of the first AP (AP1) and the second AP (AP2) operates on a first link (Link1) and a second link (Link2). The non-AP multi-link device (STA MLD) includes a first station (STA1) and a second station (STA2), and each of the first station (STA1) and the second station (STA2) operates on a first link (Link1) and a second link (Link2). While the first station (STA1) is performing an uplink transmission (UL frame) to the first AP (AP1), the second station (STA2) may have difficulty communicating with the second AP (AP2).

[0388] When there is a non-STR link pair, a multi-link device that performs transmission using the non-STR link pair can align the transmission start time and the transmission end time of the frame transmitted by 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 the PPDU including the frame. For this purpose, the multi-link device can use padding or padding bits. Negotiation for such simultaneous transmission may be performed. The negotiation for simultaneous transmission may include a frame exchange for obtaining a TXOP for simultaneous transmission. Specifically, the multi-link device can transmit a request frame on a plurality of links that obtain a TXOP. The multi-link device that receives the request frame can transmit a response frame at an interval of SIFS (short interframe space) from the request frame. The request frame may be a control frame. Also, the request frame may be an RTS (request to send) frame or a MU (multi-user)-RTS frame. Also, the response frame may be a CTS (clear to send) frame. When any one of the links is not idle during the transmission of the above-described request frame or response frame, the multi-link device can transmit the request frame or the transmission frame on the idle link among the plurality of links. In the embodiment of FIG. 50(b), as described in FIG. 50(a), each of the first AP (AP1) and the second AP (AP2) operates on the first link (Link1) and the second link (Link2). Also, each of the first station (STA1) and the second station (STA2) operates on the first link (Link1) and the second link (Link2). 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) transmit request frames simultaneously to secure a TXOP. The first station (STA1) and the second station (STA2) transmit response frames simultaneously as a response to the request frame.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).

[0389] However, since the channel states of multiple links are different, simultaneous transmission may not be started for non-STR link pairs. Considering this, multiple stations that perform transmission to a non-STR multi-link device can align the ends of the PPDU. Specifically, multiple stations that perform transmission to a non-STR multi-link device can align the ends of the PPDU even if they cannot align the start of the PPDU. Also, as described above, when any one of the PPDUs transmitted in a non-STR link pair does not contain a frame that induces an immediate response, the ends of the other PPDUs do not have to be aligned with the ends of the PPDU that does not contain a frame that induces an immediate response. In the embodiment of FIG. 50(b), as described in FIG. 50(a), each of the first AP (AP1) and the second AP (AP2) operates on the first link (Link1) and the second link (Link2). Also, each of the first station (STA1) and the second station (STA2) operates on the first link (Link1) and the second link (Link2). Since the non-AP multi-link device is a non-STR multi-link device, the ends of the PPDUs are aligned when the first AP (AP1) and the second AP (AP2) transmit PPDUs simultaneously. When the first AP (AP1) transmits a PPDU that does not contain a frame that induces an immediate response, the first AP (AP1) and the second AP (AP2) do not align the ends of the PPDU. When the first AP (AP1) and the second AP (AP2) transmit PPDUs simultaneously, the first AP (AP1) and the second AP (AP2) align the ends of the PPDU.

[0390] The above-mentioned non-STR link pairs represent link pairs for which STR is impossible. A non-STR link group represents a group that includes a plurality of links included in the non-STR link group and contains non-STR link pairs. An example applicable when some of the plurality of links on which the AP multi-link device operates are non-SRT link pairs will be described with reference to FIG. 51.

[0391] FIG. 52 shows an embodiment of the present invention applicable when some of the plurality of links on which the AP multi-link device operates are non-STR link pairs.

[0392] A multi-link device may be coupled to a station not included in the multi-link device. At this time, it is difficult to determine whether transmission is performed on another link for a station not included in the multi-link device. Also, when stations included in different multi-link devices communicate with each other in a non-STR link pair, it is difficult to determine whether transmission is performed on a link other than the link on which the stations operate for the stations included in different multi-link devices. FIG. 51 shows a non-STR AP multi-link device communicating with a first station (STA1) and a second station (STA2) not included in the multi-link device. In the embodiment of FIG. 51(a), each of the first AP (AP1) and the second AP (AP2) attempts channel access on a first link (Link1) and a second link (Link2). The first AP (AP1) succeeds in channel access and starts a frame exchange sequence by starting to transmit an RTS frame. The second AP (AP2) fails in channel access and cannot start a 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 (Link1), the second station (STA2) can perform an uplink transmission. In the embodiment of FIG. 51(b), the first station (STA1) succeeds in channel access and starts a frame exchange sequence by starting to transmit an RTS frame. The second station (STA2) succeeds in channel access and attempts an uplink transmission. While the first AP (AP1) is receiving data transmitted by the first station (STA1) on the first link (Link1), transmission of the second station (STA2) may be completed on the second link (Link2). At this time, since the first AP (AP1) is receiving data transmitted by the first station (STA1) on the first link (Link1), the second AP (AP2) cannot transmit a response to the transmission of the second station (STA2). Also, the second STA (STA2) cannot confirm the success or failure of the transmission transmitted by the second station (STA2). An embodiment for preventing such a frame exchange failure will be described with reference to FIG. 53.

[0393] FIG. 53 shows that the multi-link device operates with a plurality of links including non-STR link pairs according to an embodiment of the present invention.

[0394] When the multi-link device operates with a plurality of links including non-STR link pairs, the multi-link device can designate at least one of the plurality of links as a basic link. At this time, the basic link may be the essential link described above. The multi-link device can designate one of the plurality of links as a basic link. A link other than the basic link among the plurality of links can be called an extended link.

[0395] 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 the links included in the non-STR link pair. Also, when a station not included in the non-AP multi-link device attempts to connect to a link included in an STR link pair, the AP multi-link device can induce the station not included in the non-AP multi-link device to connect to the link included in the STR link pair.

[0396] In yet another specific embodiment, the AP multi-link device can allow the connection of stations not included in the non-AP multi-link device only on the basic link. A station not included in the non-AP multi-link device may be connected to the AP multi-link device only on the basic link of the AP multi-link device.

[0397] In the embodiment of FIG. 53, the non-STR AP multi-link device (non-STR AP MLD) operates on the first link (Link1), the second link (Link2), and the third link (Link3), which are link pairs capable of STR. 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 link pairs capable of STR, and the second link (Link2) and the third link (Link3) are STR link pairs capable of STR. The non-STR AP multi-link device (non-SRT AP MLD) designates the first link (Link1) and the third link (Link3) as the basic links. At this time, the third station (STA3) not included in the multi-link device may be connected to the non-STR multi-link device (non-STR AP MLD) via the first link (Link1) or the third link (Link3). The third station (STA3) not included in the multi-link device does not have to be connected to the non-STR multi-link device (non-STR AP MLD) via 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) via the third link (Link3).

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

[0399] In the above-described embodiment, in the negotiation for multi-link operation, the AP multi-link device can induce connection to the basic link. This will be described with reference to FIG. 53.

[0400] FIG. 54 shows the operation of the AP multi-link device according to an embodiment of the present invention in combination with a station not included in the multi-link device.

[0401] When a station not included in the multi-link device requests connection to the AP multi-link device via an extended link, the AP multi-link device can reject the station's connection request. As a specific method, when a station not included in the multi-link device sends a probe request frame to the AP multi-link device, the AP multi-link device does not have to send a probe response frame to the station. Also, when a station not included in the multi-link device sends a connection request frame to the AP multi-link device via an extended link, the AP multi-link device can send a connection response frame containing an indicator to reject the connection request to the station. At this time, the connection response frame may include a field indicating a status code for proposing a connection to another link. For example, the status code for proposing a connection to another link may be 82. Also, the connection response frame may include information about the link for which the connection is proposed. At this time, the information about the link for which the connection is proposed may be in the form of a Neighbor Report information element. The Neighbor Report information element may include at least one of SSID, channel, operation class, and timing information. The link for which the connection is proposed may be the basic link included in the STR link pair. The station not included in the multi-link can attempt to connect to the link for which the AP multi-link device proposes a connection based on the information about the link for which the AP multi-link device proposes a connection.

[0402] In addition, the AP multi-link device can transmit beacon frames simultaneously on the extended link and the basic link. Also, the AP multi-link device can transmit beacon frames in a form that stations not included in the multi-link device cannot decode on the extended link. Specifically, for example, among the Capability information fields in the beacon frame, both the IBSS STA sub-field and the ESS sub-field values can be set to 1. At this time, stations not included in the multi-link device cannot decode the beacon, and cannot transmit a connection request based on the beacon frame. In such an embodiment, the AP multi-link device can also transmit beacon frames in a form that stations not included in the multi-link device cannot decode on the basic link included in the non-STR link pair. Also, the AP multi-link device can set some fields among the BSS load information elements of the beacon frame transmitted on the extended link to a specified value in advance. At this time, the AP multi-link device can set the BSS load information element of the beacon frame transmitted on the extended link so that the channel utilization rate shows the maximum value. Also, the AP multi-link device can set the BSS load information element transmitted on the extended link so that the number of associated stations represents the maximum value. A station that receives a beacon frame set in this way can determine that it cannot perform an association on the extended link or that performing an association will reduce efficiency, and does not need to attempt an association. In yet another specific embodiment, the AP multi-link device does not need to transmit a beacon frame on the extended link.

[0403] The above-described embodiments may also be applied to the basic link included in the non-STR link pair in addition to the extended link. For example, the AP multi-link device can transmit a frame that rejects 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.

[0404] 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). The station (STA) not included in the multi-link device transmits a connection request frame to the second AP (AP2) operating on the 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 the link on which the third AP (AP3) or the 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.

[0405] FIG. 55 shows the operation in which an AP multi-link device according to an embodiment of the present invention couples with a station included in the multi-link device.

[0406] The non-AP multi-link device can request the AP multi-link device for information about the link for multi-link operation using a probe request frame. Specifically, the probe request frame may include an indicator for requesting link information for multi-link operation. The AP multi-link device that has received the probe request frame including the information about the link for multi-link operation can transmit a probe response frame including the information about the link for multi-link operation to the non-AP multi-link device. The information about the link for multi-link operation may include at least any one of information about the STR link pair, information about the non-STR link pair, and information about the basic link. The non-AP multi-link device can acquire the information about the link for multi-link operation from the probe response frame.

[0407] The non-AP multi-link device can send a multi-link operation request to the AP multi-link device using a connection request frame. The connection request frame may include an indicator indicating a request for multi-link operation. The AP multi-link device that has received the multi-link operation request can determine whether to accept the multi-link operation. Specifically, when the connection request frame includes an indicator indicating a request for multi-link operation, the AP multi-link device can determine whether it can accept the multi-link operation. In a specific embodiment, the AP multi-link device can determine whether the non-AP multi-link device requests connection with a non-STR link pair or requests connection with the basic link of the non-STR link pair. Also, the AP multi-link device can determine whether the non-AP multi-link device requests connection with multiple links. When the non-AP multi-link device requests connection with an unusable link, the AP multi-link device can reject the connection request of the non-AP multi-link device. Specifically, when the non-AP multi-link device requests connection with the extended link of the non-STR link pair, the AP multi-link device can reject the connection request of the non-AP multi-link device. Also, when the non-AP multi-link device requests connection only with some of the links of the non-STR link pair, the AP multi-link device can reject the connection request of the non-AP multi-link device. The multi-link device can send a connection response frame indicating rejection of the connection to reject the connection request of the non-AP multi-link device. Also, the multi-link device can send a connection response frame indicating a link different from the link requested by the non-AP multi-link device for connection.

[0408] 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) for 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) acquires the 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 whether it accepts multi-link operation to the non-AP multi-link device (STA MLD) using a connection response frame.

[0409] 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 basic link. This will be described with reference to FIG. 55.

[0410] FIG. 56 shows that a multi-link device according to an embodiment of the present invention performs transmission on a non-STR link pair based on a basic link.

[0411] As described above, when an AP multi-link device communicates with a station not included in the multi-link device on a non-STR link pair or when an AP multi-link device communicates with a station of the multi-link device only on a part of the links of the non-STR link pair, the basic link may be specified. The multi-link device can perform independent channel access only on the basic link. Specifically, the multi-link device can perform transmission on the extended link on the condition that transmission is performed on the basic link. Therefore, when the basic 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.

[0412] In the embodiment of FIG. 56, the AP multi-link device includes a first AP (AP1) and a second AP (AP2). Each of the first AP (AP1) and the second AP (AP2) operates on a first link (Link1) and a second link (Link2). Further, the non-AP multi-link device includes a first station (STA1) and a second station (STA2). Each of the first station (STA1) and the second station (STA2) operates on a first link (Link1) and a second link (Link2). Also, a third station (STA3) not included in the multi-link is connected to the first AP (AP1) via the first link. When the first station (STA1) does not perform transmission on the first link (Link1), the second station (STA2) cannot perform transmission on the second link (Link2). When the first station (STA1) performs transmission on the first link (Link1), the second station (STA2) performs transmission on the second link (Link2).

[0413] The operation of performing channel access before transmission in such an embodiment will be described with reference to FIG. 57.

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

[0415] When the multi-link device successfully accesses the channel based on random backoff on the basic link and, when it has successfully accessed the channel on the basic link, the extended link is idle continuously for a specified time interval, the multi-link device can transmit simultaneously on the basic link and the extended link. The specified time interval may be a PIFS. Also, the specified time interval may be an AIFS. Further, in other specific embodiments, when the multi-link device successfully accesses the channel based on random backoff on the basic link and the extended link is idle only when the basic link is idle, the multi-link device can transmit simultaneously on the basic link and the extended link. The multi-link device may be an AP multi-link device or a non-AP multi-link device.

[0416] When the extended link is not idle even though the channel access on the basic link is successful, the AP multi-link device may not transmit. Further, in other specific embodiments, when the extended link is not idle even though the channel access on the basic link is successful, the AP multi-link device can initialize the value of the backoff counter on the basic link and start channel access again. Such an operation may be equally applicable to a non-AP multi-link device.

[0417] The embodiment of FIG. 57 illustrates the channel access operation in the embodiment of FIG. 55. When the first station (STA1) successfully accesses the channel on the first link (Link1) which is the basic link and the second station (STA2) also successfully accesses the channel on the first link (Link1), it is determined whether the second link (Link2) is continuously idle for a specified time interval. Since the second link (Link2) is continuously idle for a specified time interval when the first link (Link1) successfully accesses the channel, the first station (STA1) and the second station (STA2) transmit simultaneously.

[0418] For other channel access methods applicable to non-STR link pairs, they will be described with reference to FIG. 57.

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

[0420] In a non-STR link pair, the multi-link device can independently perform random backoff-based channel access. At this time, when the backoff counter reaches 0 on the first link but does not reach 0 on the second link, the multi-link device can wait without starting transmission. Specifically, the multi-link device does not have to start transmission until the backoff counter reaches 0 on the second link even if the backoff counter reaches 0 on the first link. At this time, when the backoff counter reaches 0 on the second link, the multi-link device can transmit simultaneously on the first link and the second link. When the first link is the basic link and the second link is sensed to be not idle, the multi-link device can transmit only on the first link. Also, even if the multi-link device succeeds in channel access only on the extended link, it is not necessarily allowed to transmit only on the extended link. The multi-link device may be an AP multi-link device or a non-AP multi-link device.

[0421] In the embodiment of FIG. 58, even when the backoff counter reaches 0 on the second link (Link2) of the second station (STA2), since the first station (STA1) fails to succeed in channel access on the first link (Link1) which is the basic link, the second station (STA2) waits without starting transmission. When the first station (STA1) succeeds in channel access on the first link (Link1) which is the basic link, the first station (STA1) and the second station (STA2) transmit simultaneously.

[0422] When one non-AP multi-link device is connected to all non-STR link pairs, the method for executing channel access will be described with reference to FIGS. 59 and 60.

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

[0424] In a non-STR link pair, the multi-link device can perform random backoff-based channel access independently. At this time, even if the backoff counter reaches 0 on the first link, the multi-link device can maintain the backoff counter at 0 without starting transmission when the backoff counter has not reached 0 on the second link. Specifically, the multi-link device does not need to start transmission until the backoff counter reaches 0 on the second link even if the backoff counter reaches 0 on the first link. At this time, when the backoff counter reaches 0 on the second link, the multi-link device can transmit simultaneously on the first link and the second link. 【04...

Claims

1. A non-AP (Access Point) STA (station) of a wireless communication system, comprising: a communication module; a processor configured to control the communication module, wherein the processor is configured to: receive a frame including a target wake time (TWT) element related to scheduling of a restricted TWT service period (R-TWT SP) and a quiet element related to a quiet interval from an AP, wherein the R-TWT SP indicates a TWT SP in which transmission of delay-sensitive traffic is prioritized, wherein the quiet interval indicates a period during which no transmission occurs, wherein the TWT element includes a TWT request type field including a specific field indicating the type of a frame transmitted during the period of the TWT SP, when one or more R-TWT SPs in the R-TWT SP are set for the non-AP STA, receive or transmit the delay-sensitive traffic according to a first specific value of the specific field, wherein one or more quiet intervals in the quiet interval set for the non-AP STA are ignored based on a comparison result between the quiet interval and the one or more R-TWT SPs. STA

2. When one or more quiet intervals in the quiet interval overlap with the one or more R-TWT SPs, the one or more quiet intervals are ignored, and the delay-sensitive traffic is transmitted and received according to the first specific value during the period of the one or more R-TWT SPs. The STA according to claim 1.

3. One or more quiet intervals are ignored based on a comparison result between a first time point of the one or more R-TWT SPs based on the TWT element and a second time point of the one or more quiet intervals based on the quiet element. The STA according to claim 1.

4. The first time point is the start time of the one or more R-TWT SPs, and the second time point is the start time of the one or more quiet intervals. The STA according to claim 3.

5. The one or more quiet intervals are ignored when the first time point and the second time point are the same time. The STA according to claim 3.

6. The non-AP STA scheduled by the AP for the quiet interval sets a NAV (Network Allocation Vector) during the quiet interval, the STA according to claim 3.

7. The first specific value indicates that transmission of traffic sensitive to the delay is prioritized during the R-TWT SP, the STA according to claim 6.

8. The second specific value of the specific field indicates that transmission of frames transmitted in response during the TWTS P is prioritized, the STA according to claim 1.

9. The TWT element further includes a TWT information field including information related to the TID for traffic sensitive to the delay, the STA according to claim 1.

10. When the non-AP STA constitutes a multi-link device (MLD), during reception of a beacon frame, frame transmission on other links is impossible for the MLD, the STA according to claim 1.

11. When transmission processing is executed before the one or more R-TWT SPs, the transmission processing ends before the start time of the one or more R-TWT SPs, the STA according to claim 1.

12. A method for a non-AP STA to transmit a frame in a wireless communication system, comprising the step of receiving a frame including a target wake time (TWT) element related to scheduling of a restricted TWT service period (R-TWT SP) and a quiet element related to a quiet interval from an AP, the R-TWT SP indicates a TWT SP in which transmission of traffic sensitive to the delay is prioritized, the quiet interval indicates a period during which no transmission occurs, the TWT element includes a TWT request type field including a specific field indicating the type of frame transmitted during the TWT SP, when one or more R-TWT SPs in the R-TWT SP are set for the non-AP STA, receiving or transmitting traffic sensitive to the delay according to the first specific value of the specific field One or more quiet intervals in the quiet interval set for the non-AP STA are ignored based on a comparison result between the quiet interval and the one or more R-TWT SPs. Method. **Claim 13** When one or more quiet intervals in the quiet interval overlap with the one or more R-TWT SPs, the one or more quiet intervals are ignored, and the traffic sensitive to the delay is transmitted and received according to the first specific value during the period of the one or more R-TWT SPs. The method according to claim 12. **Claim 14** The one or more quiet intervals are ignored based on a comparison result between a first time point of the one or more R-TWT SPs based on the TWT element and a second time point of the one or more quiet intervals based on the quiet element. The method according to claim 12. **Claim 15** The first time point is the start time of the one or more R-TWT SPs, and the second time point is the start time of the one or more quiet intervals. The method according to claim 14. **Claim 16** The one or more quiet intervals are ignored when the first time point and the second time point are the same time. The method according to claim 14. **Claim 17** The non-AP STA scheduled for the quiet interval by the AP sets a NAV (Network Allocation Vector) during the period of the quiet interval. The method according to claim 14. **Claim 18** The first specific value indicates that transmission of traffic sensitive to the delay is prioritized during the period of the R-TWT SP. The method according to claim 17. **Claim 19** The second specific value of the specific field indicates that transmission of a frame transmitted in response during the period of the TWTS P is prioritized. The method according to claim 12. **Claim 20** The TWT element further includes a TWT information field including information related to a TID for traffic sensitive to the delay. The method according to claim 12. **Claim 21** The method according to claim 12, wherein when the non-AP STA constitutes a multi-link device (MLD), the MLD is unable to transmit frames on other links while receiving beacon frames.

22. When the transmission process is executed before the one or more R-TWT SPs, the transmission process ends before the start time of the one or more R-TWT SPs, the method according to claim 12.

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