Method for transmitting and receiving data through multi-link in wireless communication system, and wireless communication terminal

Abstract

To provide a method for transmitting and receiving data in a non-AP (Access Point) multi-link device (MLD) of a wireless communication system.SOLUTION: A non-AP MLD performs a back-off procedure for performing simultaneous transmission through a multi-link of the non-AP MLD, and can simultaneously perform uplink transmission in an AP MLD through each of a first link and a second link included in the multi-link. In this case, when a first back-off counter and a second back-off counter both have a value of '0', if a transmission point of time of the uplink transmission in the first link is a slot boundary of a first slot which is a slot next to a slot in which the first back-off counter is '0', the uplink transmission in the second link may be performed within a certain time from the transmission point of time of the first link.SELECTED DRAWING: Figure 40

Description

[Technical Field]

[0001] The present invention relates to a wireless communication system, and more particularly to a method for transmitting and receiving data by a multi-link device (MLD) in a wireless communication system, and a wireless communication terminal. [Background technology]

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

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

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

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

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

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

[0008] An object of one embodiment of the present invention is to provide a wireless communication method using multiple links and a wireless communication terminal using the same.

[0009] Another object of the present invention is to provide a wireless communication terminal for a multi-link device to simultaneously perform uplink transmission using multiple links.

[0010] Another object of the present invention is to provide a wireless communication terminal for simultaneously performing uplink transmission using multiple links when the values ​​of backoff counters for each link reach "0" at different times when performing uplink transmission using multiple links.

[0011] Another object of the present invention is to provide a wireless communication terminal for simultaneously transmitting uplinks via multiple links by delaying the time of uplink transmission when the slot boundaries of each link are different when simultaneously transmitting uplinks via multiple links.

[0012] The technical problems to be solved by the present specification are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention pertains from the following description. [Means for solving the problem]

[0013] A terminal for transmitting a TB PPDU (Trigger Based Physical layer Protocol Data Unit), which is a response frame based on a trigger frame, in a wireless communication system includes a communication module and a processor for controlling the communication module, and the processor performs a backoff procedure for performing uplink transmission through multiple links of the non-AP MLD, and the backoff procedure is performed separately through each of a first link of a first STA and a second link of a second STA included in the non-AP MLD, the backoff procedure in the first link is performed using a first backoff counter, and the backoff procedure in the second link is performed using a second backoff counter, and the uplink transmission is performed simultaneously using AP MLD through each of the first and second links, and when both the first and second backoff counters have a value of '0', if a transmission time point of the uplink transmission in the first link is a slot boundary of a first slot, which is the slot next to the slot in which the first backoff counter is '0', the uplink transmission in the second link is performed within a certain time from the transmission time point of the first link.

[0014] In addition, in the present invention, when the first backoff counter and the second backoff counter are both '0', the transmission time of the uplink transmission in the second link is adjusted to be included within the certain time from the slot boundary of the first slot.

[0015] Furthermore, in the present invention, when the first backoff counter is "0" and the second backoff counter is "0", the slot boundaries of the first slot and the second slot, which is the next slot after the slot in which the second backoff counter of the second link is "0", do not coincide, and the slot boundary of the second slot is not included within the certain time period.

[0016] Furthermore, in the present invention, when one of the first backoff counter and the second backoff counter reaches "0" before the remaining backoff counters, the link using the one backoff counter of the first link and the second link does not perform the uplink transmission, and maintains the one backoff counter at "0" until the remaining backoff counters reach "0".

[0017] In addition, in the present invention, when one of the first backoff counter and the second backoff counter reaches '0' before the remaining backoff counter, if the slot boundaries of the first slot of the first link and the second slot, which is the next slot after the slot in which the second backoff counter of the second link is '0', do not coincide when the remaining backoff counter reaches '0', the transmission time of the uplink transmission in the second link is adjusted to be before or after the slot boundary of the second slot so as to be included within the certain time from the slot boundary of the first slot.

[0018] In addition, in the present invention, when the slot boundary of the second slot is located earlier or later on the time axis than the slot boundary of the first slot, the transmission time point of the second link is delayed or shortened by a specific time from the slot boundary of the first slot.

[0019] In the present invention, the maximum value of the certain time period is 4 us.

[0020] In addition, in the present invention, the 4 us is a change time for performing the uplink transmission in the channel access procedure.

[0021] Also, in the present invention, the processor performs channel sensing up to the transmission time point of the second link, and the transmission time point of the second link does not coincide with the slot boundary of the second slot of the second link.

[0022] Also, in the present invention, the uplink transmission is performed in the slot next to the slot in which the first back-off counter and the second back-off counter reach "0".

[0023] In addition, in the present invention, the first link and the second link are an NSTR link pair that does not support simultaneous transmission and reception (STR).

[0024] In addition, in the present invention, the processor performs sensing to determine whether the channels are idle in the first link and the second link, and the first backoff counter and the second backoff counter are decreased, respectively, when the first link and the second link are idle.

[0025] The present invention also provides a method for performing a backoff procedure for uplink transmission through multiple links of the non-AP MLD, the backoff procedure being performed separately through each of a first link of a first STA and a second link of a second STA included in the non-AP MLD, the backoff procedure in the first link being performed using a first backoff counter, and the backoff procedure in the second link being performed using a second backoff counter, the uplink transmission being performed simultaneously in AP MLD through each of the first link and the second link, and when both the first backoff counter and the second backoff counter have a value of '0', if a transmission time point of the uplink transmission in the first link is a slot boundary of a first slot that is the slot next to the slot in which the first backoff counter is '0', the uplink transmission in the second link is performed within a certain time from the transmission time point of the first link. [Effects of the Invention]

[0026] An embodiment of the present invention provides a wireless communication method that efficiently uses multilinks and a wireless communication terminal that uses the same.

[0027] Furthermore, according to an embodiment of the present invention, there is provided a wireless communication terminal in which a multi-link device simultaneously performs uplink transmission using multiple links.

[0028] In addition, according to an embodiment of the present invention, when performing uplink transmission using multiple links, if the values ​​of the back-off counters for each link reach "0" at different times, a wireless communication terminal is provided that simultaneously performs uplink transmission using multiple links.

[0029] In addition, according to an embodiment of the present invention, when performing uplink transmission simultaneously using multiple links, if the slot boundaries of each link are different, a wireless communication terminal is provided that delays the uplink transmission time and performs uplink transmission simultaneously using multiple links.

[0030] The effects obtained from the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those having ordinary skill in the art to which the present invention pertains from the following description. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing the configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating a configuration of an access point according to an embodiment of the present invention. [Figure 5] 1 is a diagram illustrating a process in which a STA establishes a link with an AP. [Figure 6]FIG. 1 is a diagram illustrating a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7] 1A and 1B are diagrams illustrating examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. [Figure 8] 1A and 1B are diagrams illustrating examples of various EHT (Extremely High Throughput) PPDU (Physical Protocol Data Unit) formats and methods for indicating the same according to an embodiment of the present invention. [Figure 9] 1 is a diagram illustrating an example of a multi-link device according to an embodiment of the present invention. [Figure 10] 10 is a diagram illustrating an example of whether or not devices (STRs of MLD#1 and MLD#2) support a relatively narrow frequency separation distance according to an embodiment of the present invention. [Figure 11] 10 is a diagram illustrating an embodiment in which a PPDU transmission performed by a specific STA in a non-STR MLD interferes with channel access operations performed by other STAs in the non-STR MLD. [Figure 12] 10 is a diagram illustrating a multi-link device postponing transmission on one link when the multi-link device has first succeeded in channel access on the link according to an embodiment of the present invention; [Figure 13] 10 is a diagram illustrating the operation of a multilink device according to an embodiment of the present invention when the channel of a second link is sensed as being occupied when the multilink device postpones transmission on the first link after first successfully accessing the channel on the first link. [Figure 14] FIG. 10 is a diagram illustrating the operation of a multilink device according to another embodiment of the present invention when the channel of the second link is sensed as being occupied when the multilink device postpones transmission on the first link after first successfully accessing the channel on the first link. [Figure 15]10 is a diagram illustrating the operation of multiple multi-link devices when a multi-link device postpones transmission on the first link after the multiple multi-link devices have first successfully accessed the channel on the first link according to an embodiment of the present invention; FIG. [Figure 16] FIG. 10 is a diagram illustrating the operation of a multilink device according to an embodiment of the present invention when the multilink device first successfully accesses a channel on the first link, the multilink device postpones transmission on the first link, and the channel on the first link is detected as being occupied (busy). [Figure 17] FIG. 10 is a diagram illustrating the operation of a multilink device according to an embodiment of the present invention when the multilink device first successfully accesses a channel on the first link, the multilink device postpones transmission on the first link, and the channel on the first link is detected as being occupied (busy). [Figure 18] 10 is a diagram illustrating a case in which a multi-link device according to an embodiment of the present invention performs channel access for synchronized transmission and the transmission is delayed. [Figure 19] 10 is a diagram illustrating an operation method when a station in a multi-link device according to an embodiment of the present invention senses that a channel is busy during transmission. [Figure 20] 10 is a diagram illustrating an operation method when a station in a multi-link device according to an embodiment of the present invention senses that a channel is busy during transmission. [Figure 21] 10 is a diagram illustrating a method for acquiring a new backoff counter value when a station in a multi-link device according to an embodiment of the present invention senses that a channel is busy during a transmission delay. [Figure 22] 10 is a diagram illustrating an operation of determining whether to perform synchronized transmission while a station of a multilink device according to an embodiment of the present invention is delaying transmission. FIG. [Figure 23] 1 illustrates the operation of the multilink when a station in the multilink apparatus according to the embodiment of the present invention is delaying transmission and the channel for which transmission is being delayed is detected as being occupied (busy). [Figure 24]1 illustrates the operation of the multilink when a station in the multilink apparatus according to the embodiment of the present invention is delaying transmission and the channel for which transmission is being delayed is detected as being occupied (busy). [Figure 25] FIG. 2 illustrates an EDCA queue used when applying EDCA according to an embodiment of the present invention. [Figure 26] 1 illustrates a method for performing channel access based on slot boundaries according to an embodiment of the present invention. [Figure 27] FIG. 10 is a diagram illustrating an operation in which a multilink device performs synchronized transmission by EDCAF operation according to an embodiment of the present invention. [Figure 28] FIG. 10 is a diagram illustrating an operation in which a multilink device performs synchronized transmission by EDCAF operation according to an embodiment of the present invention. [Figure 29] FIG. 10 is a diagram illustrating an operation in which a multilink device performs synchronized transmission by EDCAF operation according to yet another embodiment of the present invention. [Figure 30] 10 is a diagram illustrating an embodiment in which an MLD performs simultaneous PPDU transmission on two links by delaying a channel access procedure for a specific channel according to an embodiment of the present invention. [Figure 31] 10 is a diagram illustrating an embodiment in which STAs in an MLD operate based on different slot boundaries according to an embodiment of the present invention. [Figure 32] 10 is a diagram illustrating an example of a simultaneous transmission failure of MLD that may occur when there is no clear definition of the start time of simultaneous transmission according to an embodiment of the present invention. [Figure 33] This figure shows an example of a case where, when STAs of an MLD start transmission at different slot boundaries according to an embodiment of the present invention, the transmission that starts earlier does not affect the CCA results of other STAs (the same MLD operated on other links). [Figure 34] 10 is a diagram illustrating an embodiment of a method for determining the time to start transmission on each link based on the slot boundary time difference between links on which an MLD intends to perform simultaneous transmission according to an embodiment of the present invention. [Figure 35]10 is a diagram illustrating an example of a case where simultaneous transmission fails when two link pairs in an MLD have a slot boundary difference within a specific range according to an embodiment of the present invention. [Figure 36] This figure shows an example of a simultaneous transmission technique in which an MLD STA that has completed a channel access procedure according to an embodiment of the present invention and has reserved the start of transmission starts transmission at a time different from its own slot boundary. [Figure 37] 10 is a diagram illustrating an example of signaling that can be used when an AP MLD indicates the Slot Sync Budget available in a BSS using an operation element according to an embodiment of the present invention. FIG. [Figure 38] FIG. 10 is a diagram illustrating an example of a simultaneous transmission procedure taking into consideration inter-link information exchange delay according to an embodiment of the present invention. [Figure 39] This figure shows an example of a simultaneous transmission technique in which an MLD STA that has completed a channel access procedure and has reserved the start of transmission begins transmission at a time different from its own slot boundary after recognizing that other STAs have completed their channel access procedures, according to one embodiment of the present invention. [Figure 40] 1 illustrates an example of a method for a multi-link device to simultaneously transmit over multiple links according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The terms used in this specification are generally used as widely as possible, taking into consideration the functions of the present invention. However, these may vary depending on the intentions of engineers in the relevant technical field, customs, or the emergence of new technologies. In addition, in certain cases, the applicant may have arbitrarily selected terms, and in such cases, the meanings thereof will be described in the relevant description of the invention. Therefore, it is made clear that the terms used in this specification should be interpreted not simply as names of terms, but based on the substantive meanings of the terms and the overall content of this specification.

[0033] Throughout this specification, when a component is referred to as being "connected" to another component, this includes not only when the component is "directly connected" to the other component, but also when the component is "electrically connected" to the other component via another component therebetween. Furthermore, when a component is referred to as "comprising" a specific component, this does not mean that the component excludes the other component, but that the component may further include the other component, unless otherwise specified. Additionally, limitations such as "greater than" or "less than" based on a specific critical value may be appropriately substituted with "exceeds" or "less than," respectively, depending on the embodiment. Hereinafter, in the present invention, the terms "field" and "subfield" may be used interchangeably.

[0034] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention.

[0035] A wireless LAN system includes one or more Basic Service Sets (BSSs), which are a set of devices that can synchronize and communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

[0036] As shown in FIG. 1, the infrastructure BSSs BSS1 and BSS2 include one or more stations STA1, STA2, STA3, STA4, and STA5, access points AP-1 and AP-2 that are stations providing distribution services, and a distribution system DS that connects multiple access points AP-1 and AP-2.

[0037] A station (STA) is any device that includes a medium access control (MAC) and a physical layer interface for a wireless medium according to the IEEE 802.11 standard. In a broad sense, the term "station" encompasses not only non-AP stations but also APs. In this specification, the term "terminal" refers to either a non-AP or an AP, or both. A station for wireless communication includes a processor and a communication unit, and may further include a user interface and a display unit, depending on the embodiment. The processor generates frames to be transmitted over a wireless network, processes frames received over the wireless network, and performs various other processes for controlling the station. The communication unit is functionally connected to the processor and transmits and receives frames over the wireless network for the station. In this specification, the term "terminal" encompasses user equipment (UE).

[0038] An access point (AP) is an entity that provides a connection to a distribution system (DS) via a wireless medium for associated stations. In an infrastructure BSS, communication between non-AP stations is generally performed via the AP. However, if a direct link is established, direct communication is also possible between non-AP stations. Meanwhile, in the present invention, the term AP is used as a concept including a personal BSS coordination point (PCP), but in a broader sense, it also includes concepts such as a central controller, a base station (BS), a node B, a base transceiver system (BTS), or a site controller. In the present invention, an AP is also referred to as a base wireless communication terminal, but in a broader sense, the term base wireless communication terminal is used as a term including an AP, a base station, an eNodeB (eNB), and a transmission point (TP). In addition, the base wireless communication terminal includes various types of wireless communication terminals that allocate communication medium resources and perform scheduling for communication with multiple wireless communication terminals.

[0039] A plurality of infrastructure BSSs are connected to each other via a distribution system DS, and the plurality of BSSs connected via the distribution system are called an Extended Service Set (ESS).

[0040] 2 is a diagram showing an independent BSS, which is a wireless LAN system according to another embodiment of the present invention. In the embodiment of FIG. 2, the same or corresponding parts as those in the embodiment of FIG. 1 will not be described again.

[0041] BSS3 shown in Figure 2 is an independent BSS and does not include an AP, so none of the stations (STA6, STA7) are connected to an AP. An independent BSS is not allowed to connect to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) is directly connected to each other.

[0042] 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.

[0043] First, the communication unit 120 transmits and receives wireless signals such as WLAN packets and may be incorporated into or external to the station 100. According to an embodiment, the communication unit 120 may include at least one communication module using different frequency bands. For example, the communication unit 120 may include communication modules using different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to an embodiment, the station 100 may include a communication module using a frequency band above 7.125 GHz and a communication module using a frequency band below 7.125 GHz. Each communication module may perform wireless communication with an AP or an external station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 120 may operate only one communication module at a time or multiple communication modules simultaneously, depending on the performance and requirements of the station 100. When the station 100 includes multiple communication modules, each communication module may be provided independently, or multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit 120 may represent a radio frequency (RF) communication module that processes RF signals.

[0044] Next, the user interface 140 includes various types of input / output means provided in the station 100. That is, the user interface unit 140 receives user input using various input means, and the processor 110 controls the station 100 based on the received user input. Also, the user interface unit 140 performs output based on instructions from the processor 110 using various output means.

[0045] Next, the display unit 150 outputs an image on a display screen. The display unit 150 outputs various display objects, such as a user interface, based on the contents processed by the processor 110 or the control commands of the processor 110. The memory 160 also stores control programs and various data used by the station 100. The control programs include a connection program required for the station 100 to connect to an AP or an external station.

[0046] The processor 110 of the present invention executes various commands or programs to process data within the station 100. The processor 110 also controls each unit of the station 100 and controls the transmission and reception of data between the units. According to an embodiment of the present invention, the processor 110 executes a program for connection with an AP stored in the memory 160 and receives a communication setup message transmitted by the AP. The processor 110 also reads information about the station 100's preferences contained in the communication setup message and requests connection to the AP based on the information about the station 100's preferences. The processor 110 of the present invention may refer to a main control unit of the station 100, or, depending on the embodiment, may refer to a control unit for individually controlling some components of the station 100, such as the communication unit 120. That is, the processor 110 may be a modem that modulates and demodulates wireless signals transmitted and received by the communication unit 120, or a modulator and / or demodulator. The processor 110 controls various operations for transmitting and receiving wireless signals in the station 100 according to an embodiment of the present invention. A detailed embodiment of this will be described later.

[0047] The station 100 shown in FIG. 3 is a block diagram according to an embodiment of the present invention, and the separate blocks indicate the logically separated elements of the device. Therefore, the above-described device elements may be implemented on a single chip or multiple chips depending on the device design. For example, the processor 110 and the communication unit 120 may be integrated into a single chip or may be implemented on separate chips. Furthermore, in embodiments of the present invention, some components of the station 100, such as the user interface unit 140 and the display unit 150, may be selectively included in the station 100.

[0048] 4 is a block diagram showing the configuration of an AP 200 according to an embodiment of the present invention. As shown, the AP 200 according to the embodiment of the present invention includes a processor 210, a communication unit 220, and a memory 260. In FIG. 4, duplicated descriptions of parts of the configuration of the AP 200 that are the same as or correspond to the configuration of the station 100 in FIG. 3 will be omitted.

[0049] Referring to FIG. 4, the AP 200 according to the present invention includes a communication unit 220 for operating a BSS in at least one frequency band. As described above in the embodiment of FIG. 3, the communication unit 220 of the AP 200 may also include multiple communication modules using different frequency bands. That is, the AP 200 according to the embodiment of the present invention may include two or more communication modules using different frequency bands, for example, 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP 200 may include a communication module using a frequency band above 7.125 GHz and a communication module using a frequency band below 7.125 GHz. Each communication module may perform wireless communication with a station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 220 may operate only one communication module at a time or multiple communication modules simultaneously, depending on the performance and requirements of the AP 200. In the embodiment of the present invention, the communication unit 220 may represent an RF (Radio Frequency) communication module that processes RF signals.

[0050] The memory 260 stores control programs used by the AP 200 and various data associated therewith. These control programs include a connection program that manages station connections. The processor 210 also controls each unit of the AP 200 and controls data transmission and reception between the units. According to an embodiment of the present invention, the processor 210 executes a program for connecting with a station stored in the memory 260 and transmits a communication setup message to one or more stations. The communication setup message includes information about connection preferences for each station. The processor 210 also performs connection setup in response to a station connection request. According to an embodiment, the processor 210 is a modem or a modulation / demodulation unit that modulates and demodulates wireless signals transmitted and received by the communication unit 220. The processor 210 controls various operations for transmitting and receiving wireless signals by the AP 200 according to an embodiment of the present invention. A detailed embodiment of this will be described later.

[0051] FIG. 5 is a diagram illustrating a process in which a STA establishes a link with an AP.

[0052] 5, a link between the STA 100 and the AP 200 is established through three steps: scanning, authentication, and association. First, the scanning step is a step in which the STA 100 acquires connection information for the BSS operated by the AP 200. There are two scanning methods: a passive scanning method in which the STA 100 acquires information using only a beacon message S101 periodically transmitted by the AP 200, and an active scanning method in which the STA 100 transmits a probe request to the AP S103, receives a probe response from the AP S105, and acquires connection information.

[0053] The STA 100 that successfully receives wireless connection information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200, and performs the authentication step (S107b). After the authentication step is performed, the STA 100 transmits an association request (S109a), receives an association response from the AP 200, and performs the association step (S109b). In this specification, association basically means wireless association, but the present invention is not limited to this, and association in a broad sense includes both wireless association and wired association.

[0054] Meanwhile, an 802.1X-based authentication step S111 and an IP address acquisition step S113 via DHCP are additionally performed. In Fig. 5, server 300 is a server that processes 802.1X-based authentication with STA 100, and may be physically connected to AP 200 or may exist as a separate server.

[0055] FIG. 6 is a diagram showing a Carrier Sense Multiple Access (CSMA) / Collision Avoidance (CA) method used in wireless LAN communication.

[0056] A terminal performing WLAN communication performs carrier sensing to check whether a channel is occupied before transmitting data. If a wireless signal above a certain strength is detected, the channel is determined to be occupied, and the terminal delays access to the channel. This process is called Clear Channel Assessment (CCA), and the level that determines whether or not a signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold is received by the terminal and the terminal is the receiver, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected from the channel or a wireless signal with a strength below the CCA threshold is detected, the channel is determined to be idle.

[0057] If the channel is determined to be idle, each terminal with data to transmit performs a backoff procedure after an Inter Frame Space (IFS), such as an Arbitration IFS (AIFS) or a PCF IFS (PIFS), depending on the status of each terminal. In some embodiments, the AIFS is used as a configuration replacing the conventional DCF IFS (DIFS). Each terminal waits while decreasing a slot time by a random number determined for the corresponding terminal during the idle interval of the channel, and a terminal that has exhausted all slot times attempts to access the corresponding channel. The period during which each terminal performs the backoff procedure is called a contention window period.

[0058] If a specific terminal successfully accesses the channel, the corresponding terminal transmits data via the channel. However, if the terminal that attempts access collides with other terminals, the collided terminals are each assigned a new random number and further perform a backoff procedure. According to one embodiment, the newly assigned random number for 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 attempts access by performing a further backoff procedure in the next contention window period. At this time, each terminal performs the backoff procedure from the slot time remaining in the previous contention window period. By such a method, each terminal performing wireless LAN communication can avoid mutual collisions with respect to a specific channel.

[0059] 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.

[0060] <Examples of various PPDU formats>

[0061] FIG. 7 shows an example of various standard-generation-based PPDU (PLCP Protocol Data Unit) formats. More specifically, FIG. 7(a) shows an example of a legacy PPDU format based on 802.11a / g, FIG. 7(b) shows an example of a HE PPDU format based on 802.11ax, and FIG. 7(c) shows an example of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. Also, FIG. 7(d) shows the detailed field configurations of L-SIG and RL-SIG commonly used in the PPDU formats.

[0062] 7(a), the preamble of the legacy PPDU includes a Legacy Short Training field (L-STF), a Legacy Long Training field (L-LTF), and a Legacy Signal field (L-SIG). In an embodiment of the present invention, the L-STF, L-LTF, and L-SIG may be referred to as a legacy preamble.

[0063] Referring to FIG. 7(b), the preamble of the HE PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a High Efficiency Signal A field (HE-SIG-A), a High Efficiency Signal B field (HE-SIG-B), a High Efficiency Short Training field (HE-STF), and a High Efficiency Long Training field (HE-LTF) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF can be referred to as an HE preamble. The specific configuration of the HE preamble may vary depending on the HE PPDU format. For example, HE-SIG-B may be used only in the HE MU PPDU format.

[0064] Referring to FIG. 7(c), the preamble of the EHT PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a Universal Signal field (U-SIG), an Extremely High Throughput Signal A field (EHT-SIG-A), an Extremely High Throughput Signal B field (EHT-SIG-A), an Extremely High Throughput Short Training field (EHT-STF), and an Extremely High Throughput Long Training field (EHT-LTF) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF may be referred to as an EHT preamble. The specific configuration of the non-legacy preamble may vary depending on the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some EHT PPDU formats.

[0065] The L-SIG field included in the PPDU preamble is configured with a total of 64 subcarriers using 64 FFT OFDM. Of these, 48 subcarriers, excluding guard subcarriers, DC subcarriers, and pilot subcarriers, are used for L-SIG data transmission. BPSK and Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, so it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of the L-SIG.

[0066] Referring to FIG. 7(d), the L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field is composed of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission rates of 6, 9, 12, 18, 24, 36, 48, or 54 Mbps, which is a combination of a modulation scheme such as BPSK, QPSK, 16-QAM, or 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The combined information in the L_RATE and L_LENGTH fields indicates the total length of the PPDU. In a non-legacy PPDU format, the L_RATE field is set to the minimum rate of 6 Mbps.

[0067] The unit of the L_LENGTH field is bytes, and a total of 12 bits are allocated, allowing a maximum of 4095 to be signaled. In combination with the L_RATE field, it can indicate the length of the corresponding PPDU. In this case, legacy and non-legacy terminals can interpret the L_LENGTH field in different ways.

[0068] First, a legacy or non-legacy terminal interprets the length of the corresponding PPDU using the L_LENGTH field as follows. When the value of the L_RATE field is set to indicate 6 Mbps, 3 bytes (i.e., 24 bits) may be transmitted during 4 us, which is one symbol duration of the 64FFT. Therefore, by adding the 3 bytes corresponding to the SVC field and Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the transmission amount of one symbol, the number of 64FFT reference symbols after the L-SIG is obtained. The obtained number of symbols is multiplied by 4 us, which is one symbol duration, and then 20 us, which is required to transmit the L-STF, L-LTF, and L-SIG, to obtain the length of the corresponding PPDU, i.e., the reception time (RXTIME). This can be expressed mathematically as shown in Equation 1 below.

[0069]

number

[0070] At this time,

number

[0071]

number

[0072] Here, TXTIME is the total transmission time constituting the PPDU, and is expressed as the following equation 3. In this case, TX represents the transmission time of X.

[0073]

number

[0074] Referring to the above formula, the length of the PPDU is calculated based on the rounded up value of L_LENGTH / 3. Therefore, for any value of k, three different values ​​of L_LENGTH={3k+1, 3k+2, 3(k+1)} indicate the same PPDU length.

[0075] Referring to Figure 7(e), the U-SIG (Universal SIG) field remains in the EHT PPDU and subsequent generation WLAN PPDUs, and serves to distinguish which generation of PPDU it is, including 11be. The U-SIG is two 64FFT-based OFDM symbols and can transmit a total of 52 bits of information. Of these, 43 bits excluding 9 bits of CRC / tail are roughly divided into a VI (Version Independent) field and a VD (Version Dependent) field.

[0076] The VI bit will maintain its current bit configuration, so even if a subsequent generation PPDU is defined, current 11be UEs can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field consists of the PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits long and serves to sequentially distinguish between 11be and subsequent generations of WLAN standards. 11be has a value of 000b. The UL / DL field identifies whether the PPDU is an uplink or downlink PPDU. The BSS color represents a BSS identifier defined in 11ax and has a value of 6 or more bits. The TXOP represents the transmit opportunity duration (Transmit Opportunity Duration) transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP containing the PPDU can be inferred without decoding the MPDU, and has a value of 7 or more bits.

[0077] The VD field, which is signaling information useful only for 11be version PPDUs, may consist of fields commonly used in any PPDU format, such as the PPDU format and BW, as well as fields defined differently for each PPDU format. The PPDU format is a separator that distinguishes between EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs. The BW field broadly signals five basic PPDU BW options: 20, 40, 80, 160 (80 + 80), and 320 (160 + 160) MHz (BWs that can be expressed in the form of a power of 20 * 2 can be called basic BWs), as well as various remaining PPDU BWs formed by preamble puncturing. After signaling at 320 MHz, a portion of 80 MHz may be punctured. In addition, the punctured and modified channel shape may be signaled directly in the BW field, or may be signaled using both the BW field and a field that appears after the BW field (for example, a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signalings are possible, so a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signalings are possible, so a maximum of 11 puncturing modes can be signaled.

[0078] The fields located after the BW field vary depending on the type and format of the PPDU. MU PPDUs and SU PPDUs may be signaled in the same PPDU format, and a field for distinguishing between MU PPDUs and SU PPDUs may be located before the EHT-SIG field, and additional signaling may be performed for this purpose. Both SU PPDUs and MU PPDUs include an EHT-SIG field, but some fields not required for the SU PPDU may be compressed. In this case, the information of the compressed fields may be omitted or may have a reduced size compared to the size of the original fields included in the MU PPDU. For example, the SU PPDU may have a different configuration, such as the common fields of the EHT-SIG being omitted or replaced, or the user-specific fields being replaced or reduced to one.

[0079] Alternatively, the SU PPDU may further include a compression field indicating whether or not it is compressed, and some fields (such as the RA field) may be omitted depending on the value of the compression field.

[0080] When a portion of the EHT-SIG field of the SU PPDU is compressed, the information included in the compressed field may be signaled together in an uncompressed field (e.g., a common field). In the case of an MU PPDU, since it is a PPDU format for simultaneous reception by multiple users, the EHT-SIG field must be transmitted after the U-SIG field, and the amount of information signaled may be variable. That is, since multiple MU PPDUs are transmitted to multiple STAs, each STA must recognize the location of the RU to which the MU PPDU is transmitted, the STA to which each RU is assigned, and whether the transmitted MU PPDU was sent to it. Therefore, the AP must transmit the above information in the EHT-SIG field. To this end, the U-SIG field signals information for efficiently transmitting the EHT-SIG field, which may be the number of symbols in the EHT-SIG field and / or the MCS, which is the modulation method. The EHT-SIG field may include information on the size and location of the RU assigned to each user.

[0081] In the case of an SU PPDU, multiple RUs may be allocated to a STA, and the multiple RUs may be contiguous or discontinuous. If the RUs allocated to a STA are not contiguous, the STA can efficiently receive the SU PPDU only by recognizing punctured RUs in between. Therefore, the AP can transmit the SU PPDU including information on punctured RUs among the RUs allocated to the STA (e.g., puncturing pattern of the RUs). That is, in the case of an SU PPDU, a puncturing mode field including information indicating whether a puncturing mode is applied and the puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field can signal the type of discontinuous channels appearing within the bandwidth.

[0082] The type of signaled discontinuous channel is limited, and indicates the BW and discontinuous channel information of the SU PPDU in combination with the value of the BW field. For example, since the SU PPDU is a PPDU transmitted only to a single UE, the STA can recognize its allocated bandwidth from the BW field included in the PPDU and can recognize punctured resources within the allocated bandwidth from the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the UE can receive the PPDU in the remaining resource units excluding specific channels of the punctured resource units. In this case, multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0083] The reason why only limited discontinuous channel types are signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing can be performed for each 20 MHz subchannel, if puncturing is performed on a BW having multiple 20 MHz subchannels, such as 80, 160, or 320 MHz, in the case of 320 MHz, the discontinuous channel type (when only the end 20 MHz is punctured and considered discontinuous) must be signaled by expressing whether or not each of the remaining 15 20 MHz subchannels excluding the primary channel is in use. Using 15 bits to signal the discontinuous channel type for single-user transmission can result in excessive signaling overhead when considering the low transmission rate of the signaling part.

[0084] This invention proposes a method for signaling the discontinuous channel type of the SU PPDU, shows the discontinuous channel type determined by the proposed method, and proposes a method for signaling the primary 160 MHz and secondary 160 MHz puncturing types in the 320 MHz BW configuration of the SU PPDU.

[0085] In addition, one embodiment of the present invention proposes a method of varying the PPDU configuration indicated by the preamble puncturing BW value according to the PPDU format signaled in the PPDU format field. Assuming the length of the BW field is 4 bits, in the case of an EHT SU PPDU or TB PPDU, an EHT-SIG-A symbol of one symbol may be further signaled after the U-SIG, or no EHT-SIG-A may be signaled at all. Taking this into consideration, up to 11 puncturing modes must be signaled using only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, an EHT-SIG-B symbol is further signaled after the U-SIG, so up to 11 puncturing modes may be signaled in a different manner than in the SU PPDU. In the case of an EHT ER PPDU, the BW field can be set to 1 bit to signal whether the PPDU uses a 20 MHz or 10 MHz bandwidth.

[0086] Figure 7(f) shows the format-specific field configuration of the VD field when the PPDU format field of the U-SIG indicates an EHT MU PPDU. For an MU PPDU, SIG-B, a signaling field for simultaneous reception by multiple users, is required. SIG-B may be transmitted after the U-SIG without a separate SIG-A. For this purpose, the U-SIG must signal information for decoding SIG-B. These fields include the SIG-B MCS, SIG-B DCM, number of SIG-B symbols, SIG-B compression, and number of EHT-LTF symbols.

[0087] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and methods for indicating the same according to an embodiment of the present invention.

[0088] 8, a PPDU may be configured with a preamble and a data portion, and the format of one type, EHT PPDU, may be distinguished by a U-SIG field included in the preamble. Specifically, whether the format of the PPDU is EHT PPDU may be indicated based on a PPDU format field included in the U-SIG field.

[0089] 8(a) shows an example of an EHT SU PPDU format for a single STA. The EHT SU PPDU is a PPDU used for single user (SU) transmission between an AP and a single STA, and an EHT-SIG-A field for additional signaling may be located after the U-SIG field.

[0090] 8(b) shows an example of an EHT trigger-based PPDU format, which is an EHT PPDU transmitted based on a trigger frame. The EHT trigger-based PPDU is an EHT PPDU transmitted based on a trigger frame and is an uplink PPDU used for responding to the trigger frame. Unlike the EHT SU PPDU, the EHT PPDU does not have an EHT-SIG-A field after the U-SIG field.

[0091] 8(c) shows an example of an EHT MU PPDU format, which is an EHT PPDU for multiple users. The EHT MU PPDU is a PPDU used to transmit a PPDU to one or more STAs. In the EHT MU PPDU format, an HE-SIG-B field may be located after the U-SIG field.

[0092] 8(d) shows an example of an EHT ER SU PPDU format used for single-user transmission with STAs in an extended range. The EHT ER SU PPDU may be used for single-user transmission with STAs in a wider range than the EHT SU PPDU described in FIG. 8(a), and the U-SIG field may be repeated on the time axis.

[0093] The EHT MU PPDU described in (c) of Figure 8 can be used by the AP for downlink transmission to multiple STAs. In this case, the EHT MU PPDU can include scheduling information so that multiple STAs can simultaneously receive the PPDU transmitted from the AP. The EHT MU PPDU can convey AID information of the receiver and / or sender of the transmitted PPDU to the STA through the user specific field of the EHT-SIG-B. Therefore, multiple terminals receiving the EHT MU PPDU can perform spatial reuse based on the AID information of the user specific field included in the preamble of the received PPDU.

[0094] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information regarding the configuration of resource units (e.g., the division type of resource units) in a specific bandwidth (e.g., 20 MHz) on the frequency axis. That is, the RA field may indicate the configuration of resource units divided by the bandwidth for transmitting the HE MU PPDU so that the STA can receive the PPDU. Information about the STA allocated (or designated) to each divided resource unit may be included in a user specific field of the EHT-SIG-B and transmitted to the STA. That is, the user specific field may include one or more user fields corresponding to each divided resource unit.

[0095] For example, among the multiple divided resource units, the user field corresponding to at least one resource unit used for data transmission may include the AID of the receiver or sender, and the user field corresponding to the remaining resource units not used for data transmission may include a previously set null STA ID.

[0096] Two or more PPDUs shown in FIG. 8 can be indicated by a value indicating the same PPDU format. That is, two or more PPDUs can be indicated as the same PPDU format by the same value. For example, an EHT SU PPDU and an EHT MU PPDU can be indicated by the same value using the U-SIG PPDU format subfield. In this case, the EHT SU PPDU and the EHT MU PPDU can be distinguished depending on the number of STAs receiving the PPDU. For example, a PPDU received by only one STA may be identified as an EHT SU PPDU, and when the number of STAs is set so that two or more STAs can receive the PPDU, it may be identified as an EHT MU PPDU. In other words, two or more PPDU formats shown in FIG. 8 can be indicated using the same subfield value.

[0097] In addition, some of the fields or some information of the fields shown in Figure 8 may be omitted, and such a case where some of the fields or some information of the fields is omitted can be defined as a compression mode or a compressed mode.

[0098] FIG. 9 is a diagram illustrating a multi-link device according to an embodiment of the present invention.

[0099] Referring to FIG. 9, the concept of a device to which one or more STAs are affiliated can be defined. As another example, according to an embodiment of the present invention, a device to which more than one STA is affiliated (i.e., two or more) can be defined. In this case, the device can be a logical concept. Therefore, such a device to which one or more STAs are affiliated can be referred to as a multi-link device (MLD), a multi-band device, or a multi-link logical entity (MLLE).

[0100] Alternatively, the above conceptual device can be called a multi-link entity (MLE). Also, an MLD may have one MAC medium access control service access point (SAP) to a logical link control (LLC), and an MLD may have one MAC data service.

[0101] A STA included in an MLD can operate on one or more links or channels. That is, a STA included in an MLD can operate on multiple different channels. For example, a STA included in an MLD can operate using channels in different frequency bands such as 2.4 GHz, 5 GHz, and 6 GHz. This allows MLD to gain benefits from channel access and improve overall network performance. While existing WLANs operate on a single link, MLD operation allows STAs to use multiple links to obtain more channel access opportunities or to operate efficiently on multiple links taking into account channel conditions.

[0102] Also, if the STA affiliated with the MLD is an AP, the MLD to which the AP is affiliated may be an AP MLD, but if the STA affiliated with the MLD is a non-AP STA, the MLD to which the non-AP is affiliated may be a non-AP MLD.

[0103] 9, an MLD including multiple STAs may exist, and the multiple STAs included in the MLD may operate on multiple links. In FIG. 9, an MLD including APs AP1, AP2, and AP3 may be referred to as an AP MLD, and an MLD including non-AP STAs non-AP STA1, non-AP STA2, and non-AP STA3 may be referred to as a non-AP MLD. STAs included in the MLD may operate on Link 1, Link 2, Link 3, or some of Links 1 to 3.

[0104] According to an embodiment of the present invention, the multi-link operation may include a multi-link setup operation. The multi-link setup operation may be an operation corresponding to the association performed in the single-link operation. In order to exchange frames over the multiple links, the multi-link setup must be performed first. The multi-link setup operation may be performed using a multi-link setup element. Here, the multi-link setup element may include capability information related to the multiple links. The capability information may include information related to whether a STA included in the MLD can receive a frame over one link while another STA included in the MLD can transmit a frame over another link. That is, the capability information may include information related to whether a STA (non-AP STA) and / or an AP (or AP STA) can simultaneously transmit / receive frames in different transmission directions through the links included in the MLD. The capability information may also include information related to available links or operating channels. The multi-link configuration may be established through negotiation between peer STAs, and multi-link operation may be established through one link.

[0105] According to one embodiment of the present invention, a mapping relationship may exist between a TID and a link of an MLD. For example, when a TID and a link are mapped, the TID may be transmitted through the mapped link. The mapping between a TID and a link may be directional-based. For example, a mapping may be performed for each of the two directions between MLD1 and MLD2. Furthermore, a default setting may exist for the mapping between a TID and a link. For example, the mapping between a TID and a link may be such that all TIDs are basically mapped to a certain link.

[0106] FIG. 10 illustrates an example of whether or not devices (STRs of MLD#1 and MLD#2) support a relatively narrow frequency separation according to an embodiment of the present invention.

[0107] According to the embodiment of Figure 10, Link1 and Link2 are shown as links using BWs that are located close to each other in frequency. The frequency domain used by Link1 is displayed as a rectangle filled with diagonal lines, and the frequency domain used by Link2 is displayed as a rectangle filled with a grid. In this embodiment, MLD#1 is an MLD having STA1-1 and STA1-2, and the STA1-1 and STA1-2 operate on Link1 and Link2, respectively. Furthermore, MLD#2 is an MLD having STA2-1 and STA2-2, and the STA2-1 and STA2-2 operate on Link1 and Link2, respectively. In this case, the links used by STAx-1 and STAx-2 belonging to each MLD#1 and MLD#2 are Link1 and Link2, respectively, and are the same, but the interference between STAs in MLD#1 may be smaller than the interference between STAs in MLD#2. Therefore, when STA1-1 of MLD#1 transmits via Link 1, STA1-2 can successfully decode a packet received via Link 2. However, when STA2-1 of MLD#2 transmits via Link 1, relatively strong interference occurs on Link 2, which may hinder the decoding of STA2-2. Therefore, whether STR between STAs existing within a single MLD can occur may differ depending on the MLD.

[0108] To determine the operation of the AP and STA using each link, the AP MLD and the STA MLD can exchange whether STR is supported between APs in the AP MLD and whether STR is supported between STAs in the STA MLD. In this case, an STR support element may be used to indicate whether STR is supported for each link. In this case, the STR support element may be an element with a different name that exchanges whether STR is supported between devices in each MLD between both MLDs.

[0109] As an example, the STR support element may use one bit each to indicate whether STR is supported between the STAs and APs in the MLD. For example, when the STA MLD operates STA1, STA2, and STA3, one bit may be set to 1 to indicate that STR is supported between STA1 and STA2. On the other hand, one bit may be set to 0 to indicate that STR is not supported between STA2 and STA3, and the other bit may be set to 1 to indicate that STR is supported between STA1 and STA3. As a result, the STR support element may use a total of three bits to signal whether STR is supported between STA1 and STA2, between STA2 and STA3, and between STA1 and STA3, as 101. In this case, if Link1 used by STA1 is 2.4 GHz, STA1 is assumed to always support STR in relation to other STAs in the STA MLD, and therefore, only the STR support status of STA2 and STA3 may be signaled with one bit (or, if there are two STAs in the STA MLD, it may always be indicated with one bit).

[0110] As described above, whether STR is supported depends on the frequency separation distance of each link. Therefore, when the AP MLD changes the center frequency of each link or the operation BW of each link, the STA MLD's support for STR between STAs may be changed. Therefore, when the AP MLD changes the operation BW or center frequency of some or all of the links, the STR support element may be exchanged as necessary. In this case, the exchange of the STR support element may be performed by the AP and the STA through a request and response, respectively, or the STA may need to automatically send it to the AP after changing the center frequency and / or operation BW.

[0111] In addition, if STR support is not possible between the STAs, the STA MLD can request the AP to change the center frequency of some or all of the links used by the STAs that do not support STR, change the operation bandwidth (BW), or change the primary 20 MHz channel. In this case, the link change request may be transmitted to the AP MLD through the link for which the STA MLD requests change, or may be transmitted from the AP MLD through another STA (another link) within the same STA MLD. In this case, the link change request transmitted through the other link may include information about the link to be changed (e.g., link number). In this case, the meaning of link change used in this embodiment may be interpreted as meaning a change of operating channel within 2.4, 5, or 6 GHz, rather than a frequency movement between 2.4, 5, and 6 GHz bands.

[0112] The link change request may also include information regarding how to change the link. As one example, the link change request may indicate that the center frequency of the link should be moved to a higher or lower frequency. Alternatively, the link change request may implicitly indicate that the center frequency of the link should be changed in a direction away from adjacent links. As another example, the link change request may indicate that the BW of the link should be reduced. As yet another example, the link change request may indicate that the main channel position of the link should be changed to a lower or higher frequency.

[0113] When an AP receives the link change request from a STA MLD, it can either accept the STA's request and change the link for which the change request was received (center frequency, BW, or main channel position), or ignore the STA's link change request and maintain the link-related settings.

[0114] <Simultaneous transmission using multiple links>

[0115] As mentioned above, STAs operated by a specific MLD may support STR depending on the relationship (e.g., distance) between the links on which they operate. For example, if STA1 and STA2 operated by a specific MLD are operated on Link1 and Link2, respectively, which are link pairs that do not support STR, STA1 and STA2's operations will be restricted by the other's operating status. More specifically, while STA1 is transmitting a PPDU through Link1, STA2 may be unable to properly decode a packet received through Link2 due to in-device interference caused by STA1's transmission through Link1. In this way, when STAs operating on a specific link pair are hindered in their receiving operations due to in-device interference (of the same MLD), the STAs are said to be in a non-STR relationship. In this case, an MLD including STAs that are in a non-STR relationship with each other may be considered a non-STR MLD.

[0116] On the other hand, non-STR related STAs may be disturbed not only in their receiving operations but also in their channel access operations due to interference within the device, as will be explained below with reference to an example in FIG.

[0117] FIG. 11 shows an example in which a PPDU transmission performed by a specific STA in a non-STR MLD interferes with channel access operations performed by other STAs in the non-STR MLD.

[0118] 11, non-STR MLD can operate STA1 and STA2 on Link1 and Link2, respectively. In this case, if Link1 and Link2 are a link pair having a non-STR relationship, transmissions performed by STA1 and STA2 may induce interference large enough to prevent successful reception of packets received on Link2 and Link1, respectively.

[0119] As shown in Figure 11, interference occurring when STA2 transmits a PPDU on Link2 may disrupt the CCA operation of STA1, which is performing the backoff procedure on Link1. In other words, interference occurring when STA2 transmits a PPDU on Link2 may induce interference on Link1 that is higher than a CCA energy (e.g., Energy Detection) threshold. As a result, STA1, which is performing the backoff procedure on Link1, may determine that Link1 is busy. As a result, STA1 may mistakenly determine that Link1 is busy at the time STA2 transmits a PPDU, even though no other device is occupying Link1, and may not be able to complete the backoff procedure.

[0120] As described above, when other STAs in the non-STR MLD are unable to receive packets or perform channel access procedures due to interference within the device when a specific STA in the non-STR MLD transmits, the other STAs are said to be in a BLIND state.

[0121] Thus, when a STA of a non-STR MLD enters the BLIND state, the MLD cannot receive packets through the BLIND STA or perform independent channel access (for transmission), and therefore cannot obtain any benefit through the link on which the BLIND STA operates. Therefore, non-STR MLD can use a special channel access mechanism to prevent STAs operating on a non-STR related link pair from entering the BLIND state due to mutual transmission operations.

[0122] In order to prevent STAs operating on non-STR related link pairs from entering a BLIND state due to mutual transmission operations, MLD may reserve (delay) the start of transmission on a specific link even after the channel access procedure for the specific link has ended.

[0123] Thereafter, the start of transmission of the specific link may be synchronized with the completion of the channel access procedure of another link other than the specific link, resulting in simultaneous transmission of the specific link and another link other than the specific link. To this end, the MLD may be allowed to have a mechanism for delaying the channel access procedure rather than starting transmission immediately after the channel access procedure is completed. In this case, the mechanism for delaying the channel access procedure may be such that transmission can be suspended while a backoff counter (BO) is maintained at 0.

[0124] That is, even if the channel access procedure is completed in one of the multiple links of the MLD and the backoff counter value reaches "0," if the backoff counter values ​​of the other links have not yet reached "0," the MLD STA can maintain the backoff counter value at "0" without performing uplink transmission in that link. In other words, if the backoff counter value reaches "0" in a specific link and the backoff counter values ​​of the other links of the MLD have not yet reached "0," the MLD STA can choose to maintain the backoff counter value at "0" without performing uplink transmission.

[0125] For example, an MLD multiple link may be configured with a first link and a second link, and a backoff procedure for a channel access in the first link may be performed by a first backoff counter, and a backoff procedure for a channel access in the second link may be performed by a second backoff counter, where the backoff procedure may be performed separately through each of the first and second links included in the multiple link.

[0126] In this case, if one of the first backoff counter and the second backoff counter reaches "0" before the other backoff counters, the specific link of the first link and the second link that uses the one backoff counter may not perform the uplink transmission, and the one backoff counter may maintain the value of "0" until the other backoff counters reach the value of "0". Alternatively, the one backoff counter may continue to maintain the value of "0" even after the other backoff counters reach the value of "0".

[0127] In this case, the time when simultaneous transmission is performed on the specific link and the other link other than the specific link may be a slot boundary at which a channel access procedure is completed on the other link other than the specific link, or the slot next to the slot at which a channel access procedure is completed on the other link. Alternatively, the time when simultaneous transmission is performed on the specific link and the other link other than the specific link may be a specific slot boundary after a channel access procedure is completed on the other link other than the specific link. In this case, the specific slot boundary may be the slot boundary of the specific link immediately after a channel access procedure is completed on the other link.

[0128] That is, the slot settings for each link may be different, and slot boundaries between links may not coincide. Therefore, the slot boundaries between links may not coincide in each slot in which the backoff counter is decremented. When the backoff counters of each of the multiple links of the MLD reach "0" through the backoff procedure due to the reservation operation described above, the slot boundaries between the links may not coincide. Since the slots for each link may be set independently, the slot boundaries between the links may not coincide. Therefore, even if the backoff counters of each link all have a value of "0," the slot boundaries may differ from each other. In this case, simultaneous transmission may be performed according to the slot boundary of a specific link when the backoff counter of the specific link among the multiple links has a value of "0." That is, each link may not perform uplink transmission according to the slot boundary of the corresponding link, but may perform uplink transmission simultaneously by delaying or shortening the transmission time of the uplink transmission according to the slot boundary of the specific link.

[0129] For example, if an MLD multiplexed link is composed of a first link and a second link, and one of the first backoff counter of the first link and the second backoff counter of the second link reaches '0' before the other backoff counter, the slot boundaries of the first link and the second link may not coincide when the other backoff counter reaches '0'. In this case, the transmission time point of the uplink transmission of the second link can be adjusted by shortening or delaying it depending on the slot boundary of the slot in which the first backoff counter of the first link is '0' or the slot boundary of the first slot, which is the slot next to the slot.

[0130] In this case, the time of uplink transmission in the first link and the time of uplink transmission in the second link may be within a certain time period. For example, the time of uplink transmission in the second link may be within 4 us of the time of uplink transmission in the first link.

[0131] In this manner, uplink transmission can be performed simultaneously on the first and second links by performing uplink transmission at a time other than the slot boundary of the slot in which the second backoff counter of the second link is "0" or the slot boundary of the second slot, which is the next slot of the slot.

[0132] In this case, simultaneous transmission can mean that transmission is performed on each link within a certain period of time.

[0133] The operation of the multilink device accessing a channel via multiple links will be described with reference to Figures 12 to 24. At this time, the multiple links may be NSTR link pairs.

[0134] FIG. 12 shows that when a multi-link device according to an embodiment of the present invention first succeeds in channel access on one of the links, the multi-link device postpones transmission on that link.

[0135] For ease of explanation, it is assumed that a first station in a multi-link device operates on the first link and a second station operates on the second link. In this case, if the second station successfully accesses the channel but the first station does not, the second station can maintain a backoff counter value of 0 and wait until the first station successfully accesses the channel. When the first station successfully accesses the channel, the first and second stations can begin synchronized transmission. Synchronized transmission may be transmission whose transmission start time is within a predetermined time period. The second station can perform channel sensing while maintaining the backoff counter value. In this case, channel sensing may include at least one of energy detection (ED), preamble detection (PD), and NAV (network allocation vector) confirmation. The second station can begin synchronized transmission when the first station successfully accesses the channel and the sensing result is idle.

[0136] In the embodiment of FIG. 12, a first station (STA1) of a multi-link device is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). The second station (STA2) first succeeds in channel access, and the second station (STA2) maintains the backoff counter value at 0 and does not transmit until the first station (STA2) succeeds in channel access. At this time, the second station (STA2) performs channel sensing. When the first station (STA1) succeeds in channel access, the first station (STA1) and the second station (STA2) begin synchronized transmission.

[0137] While the second station delays transmission, the channel accessed by the first station may be sensed as being occupied (busy). In this case, the second station (STA2) may begin unsynchronized transmission. Another specific embodiment will be described with reference to FIGS. 13 and 14.

[0138] FIG. 13 shows the operation of a multilink device according to an embodiment of the present invention when the channel of the second link is detected as occupied when the multilink device postpones transmission on the first link after first successfully accessing the channel on the first link.

[0139] If the channel accessed by the second station is detected as being occupied while the first station delays transmission, the first station can acquire a new backoff counter and perform a channel access procedure. If the first station successfully accesses the channel, the first station can perform unsynchronized transmission. In a specific embodiment, the first station can perform channel sensing using the newly acquired backoff counter x slot duration. That is, the operation of detecting whether the channel is idle during an AIFS in general channel access can be omitted. In yet another specific embodiment, if the channel is idle during an AIFS, as in general channel access, the first station can perform channel sensing using the newly acquired backoff counter x slot duration. When the second station acquires a new backoff counter, the first station can maintain the size of the CW previously used by the first station. In this case, the second station continues the channel access procedure.

[0140] In the embodiment of FIG. 13, a first station (STA1) in a multi-link device is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). The first station (STA1) successfully accesses the channel first, and the first station (STA1) maintains the backoff counter value at 0 and does not transmit until the second station (STA2) successfully accesses the channel. At this time, the channel of the second link is detected as occupied (busy). The first station (STA1) acquires a new backoff counter and performs channel sensing in the slots containing only the backoff counter. When the first station (STA1) successfully accesses the channel, the first station (STA2) begins unsynchronized transmission.

[0141] FIG. 14 shows the operation of a multilink device according to another embodiment of the present invention when the channel of the second link is detected as occupied when the multilink device postpones transmission on the first link after first successfully accessing the channel on the first link.

[0142] If the channel accessed by the second station is sensed as being occupied while the first station delays transmission, the first station can also delay transmission until the second station successfully accesses the channel. In this case, the first station can perform channel sensing until the second station successfully accesses the channel.

[0143] In the embodiment of FIG. 14, a first station (STA1) of a multi-link device is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). The first station (STA1) successfully accesses the channel, and the first station (STA1) maintains the backoff counter value at 0 and does not transmit until the second station (STA2) successfully accesses the channel. At this time, the channel of the second link is detected as occupied (busy). The first station (STA1) performs channel sensing and delays transmission until the second station (STA2) successfully accesses the channel. When the second station (STA2) successfully accesses the channel, the first station (STA2) begins unsynchronized transmission.

[0144] In the embodiments described in Figures 13 and 14, the first station can determine whether to perform synchronized transmission based on the duration of time the channel of the second link maintains an occupied state. For example, if the duration of time the channel of the second link maintains an occupied state is greater than a predetermined value, the first station can perform unsynchronized transmission. At this time, the first station can acquire a new backoff counter and perform channel access based on the acquired backoff counter. If the first station has successfully accessed the channel, the first station can perform unsynchronized transmission.

[0145] If the duration of time that the channel of the second link is maintained in an occupied state is equal to or less than a predetermined value, the first station can perform synchronized transmission. The first station can delay transmission until the second station has successfully accessed the channel. In this case, the first station can perform channel sensing until the second station has successfully accessed the channel.

[0146] In the above-described embodiment, if a multi-link device excessively delays transmission on any one of the links, the probability of transmission collision may increase. This will be explained with reference to FIG.

[0147] FIG. 15 illustrates the operation of multiple multilink devices in an embodiment of the present invention when the multiple multilink devices postpone transmission on the first link after first successfully accessing the channel on the first link.

[0148] When a plurality of multilink devices all operate on the first link and the second link, and the plurality of multilink devices perform synchronized transmission on the first link and the second link, and a transmission collision occurs on the first link, a transmission collision also occurs on the second link.

[0149] In the example of Figure 15, a first multilink device (STA MLD1) and a second multilink device (STA MLD2) both operate on the first link (Link1) and the second link (Link2). Both the first multilink device (STA MLD1) and the second multilink device (STA MLD2) successfully access the channel on the second link (Link2), and delay transmission on the second link (Link2) until channel access on the first link (Link1) is successful. The first multilink device (STA MLD1) and the second multilink device (STA MLD2) simultaneously succeed in channel access on the first link (Link1), and transmission collision occurs on both the first link (Link1) and the second link (Link2).

[0150] The operation of the multilink device when one of the links is sensed as being occupied while the multilink device delays transmission on that link is described in FIG.

[0151] 16 and 17 show the operation of a multilink device according to an embodiment of the present invention when the multilink device first successfully accesses a channel on the first link, the multilink device postpones transmission on the first link, and the channel on the first link is detected as being occupied (busy).

[0152] If the channel accessed by the first station is detected as being busy while the first station is delaying transmission, the first station can obtain a new backoff counter and perform a channel access procedure, where the first station can maintain the CW value at the previously used CW value.

[0153] While the first station delays transmission, if the channel accessed by the first station is sensed as being busy, the second station may successfully access the channel. In this case, the second station may delay transmission until the first station successfully accesses the channel. In yet another specific embodiment, the second station may not delay transmission and may perform unsynchronized transmission.

[0154] In the embodiments of FIGS. 16 and 17, a first station (STA1) in a multi-link device is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). The first station (STA1) successfully accesses the channel first, and delays transmission. At this time, the first station (STA1) determines that the channel of the first link (Link1) is occupied. The first station (STA1) acquires a new backoff counter and accesses the channel. In the embodiment of FIG. 17, the second station (STA2) successfully accesses the channel first, and delays transmission until the first station (STA1) successfully accesses the channel. When the first station (STA1) successfully accesses the channel, the first station (STA1) and the second station (STA2) begin synchronized transmission. In the example of FIG. 17, the second station (STA2) successfully accesses the channel first and performs unsynchronized transmission without delaying transmission.

[0155] As in the above-described embodiment, for synchronized transmission, the channels of different links must be successfully accessed and idle at the same time. This limits the time at which a multilink device can perform synchronized transmission, and the transmission of the multilink device may be excessively delayed. This is explained in FIG. 19.

[0156] FIG. 18 shows that the transmission in which the multi-link device according to the embodiment of the present invention performs channel access for synchronized transmission is delayed.

[0157] A first station (STA1) in a multi-link device is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). The first station (STA1) successfully accesses the channel, so the first station (STA1) delays transmission. Before the second station (STA2) successfully accesses the channel, the first station (STA1) senses that the channel of the first link (Link1) is occupied (busy). Therefore, the first station (STA1) acquires a new backoff counter and starts the channel access procedure again. The second station (STA2) successfully accesses the channel, but delays transmission because the first station (STA1) is still accessing the channel. Before the first station (STA1) successfully accesses the channel, the second station (STA2) senses that the channel of the second link (Link2) is occupied (busy). Therefore, the second station (STA2) acquires a new backoff counter and starts the channel access procedure again. In the end, both the first station (STA1) and the second station (STA2) successfully access the channel but do not transmit.

[0158] If the transmission delay and channel access procedure are repeated unconditionally in this manner, the transmission may be delayed too long. A method for a station in a multilink device to determine whether to perform a new backoff procedure during a transmission delay is described with reference to FIG.

[0159] 19 and 20 show an operation method when a station in a multi-link device according to an embodiment of the present invention senses that the channel is busy during transmission.

[0160] A station in the multilink device may sense that the channel is occupied during a transmission delay. In this case, when the station determines that the channel is idle again, it can determine whether to restart the channel access procedure based on the channel access status of other stations in the multilink device. Specifically, when the station determines that the channel is idle again, it can determine whether to acquire a new backoff counter and perform channel access based on the channel access status of other stations in the multilink device. When the first station determines that the channel is idle again, if the backoff procedure of the second station is ongoing, the first station can delay transmission. Also, when the first station determines that the channel is idle again, if the second station has successfully accessed the channel, the first station can acquire a new backoff counter and perform the channel access procedure.

[0161] In this case, a station can determine that a channel is idle if it detects that the channel is idle for a predetermined time period. The predetermined time period may be an AIFS. In another specific embodiment, the predetermined time period may be a time period excluding a time required for receive / transmit conversion in an AIFS.

[0162] In the embodiments of FIGS. 19 and 20, a first station (STA1) in a multi-link device is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). The first station (STA1) successfully accesses the channel first, and therefore delays transmission. Before the second station (STA2) successfully accesses the channel, the first station (STA1) senses that the channel of the first link (Link1) is busy. In the embodiment of FIG. 20, when the first station (STA1) again senses that the channel is idle, the second station (STA2) is performing a channel access procedure. Therefore, the first station (STA1) only performs channel sensing without acquiring a new backoff counter. When the second station (STA2) successfully accesses the channel, the first station (STA1) and the second station (STA2) perform synchronized transmission.

[0163] In the example of Figure 20, when the first station (STA1) senses that the channel is idle again, the second station (STA2) has successfully accessed the channel and is in a transmission delay. Therefore, the first station (STA1) obtains a new backoff counter and accesses the channel. When the first station (STA1) has successfully accessed the channel, the first station (STA1) and the second station (STA2) perform synchronized transmission.

[0164] FIG. 21 shows a method for acquiring a new back-off counter value when a station in a multi-link device according to an embodiment of the present invention senses that the channel is busy during a transmission delay.

[0165] In the above-described embodiment, when a station in a multilink device senses that the channel is busy during transmission and then acquires a backoff counter again, the station can set the CW value to a value smaller than the previously used CW value. For example, the station can set the CW value to 1 / 2 of the previously used CW value. In yet another specific embodiment, the station can set the CW value to a floor value of 1 / 2 of the previously used CW value. Immediately after successfully completing the channel access procedure using the newly acquired backoff counter, the station can transmit only pre-specified types of frames. In this case, the pre-specified frame may be an RTS frame or an MU-RTS frame. In yet another specific embodiment, the pre-specified frame may be a BQRP frame.

[0166] If a transmission fails immediately after a successful channel access procedure using a newly acquired backoff counter, the station can set the CW value to the value of the CW before adjustment × 2 - 1. That is, the station can set the CW value to the value of the CW before the transmission delay × 2 - 1.

[0167] In the example of FIG. 21, a first station (STA1) is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). The first station (STA1) successfully accesses the channel first, and so the first station (STA1) delays transmission. Before the second station (STA2) successfully accesses the channel, the first station (STA1) senses that the channel of the first link (Link1) is occupied (busy). The first station (STA1) sets the CW to half the previously used CW value to obtain a new backoff counter value. After the second station (STA2) successfully accesses the channel, when the first station (STA1) again successfully accesses the channel, the first station (STA1) and the second station (STA2) perform synchronized transmissions.

[0168] FIG. 22 shows the operation of determining whether to perform synchronized transmission while a station in a multilink apparatus according to an embodiment of the present invention is delaying transmission.

[0169] For ease of explanation, it is assumed that a first station of a multilink device operates on the first link and a second station of the multilink device operates on the second link. If the second station successfully accesses the channel while the first station delays transmission, the first station can determine whether to perform synchronized transmission with the second station based on whether the channel of the first link remains idle for a predetermined period until the second station successfully accesses the channel. Specifically, if the channel of the first link remains idle for a predetermined period until the second station successfully accesses the channel, the first station can perform synchronized transmission with the second station. In this case, the predetermined period may be a DIFS. Alternatively, the pre-designated period may be a PIFS. Alternatively, the pre-designated period may be an AIFS. In this case, the value of the AIFS may be determined by the AC of a frame to be transmitted by the first station. Specifically, the value of the AIFS may be an AIFS corresponding to an AC with a higher priority among the ACs of the frame to be transmitted by the first station.

[0170] In the example of FIG. 22, a first station (STA1) is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). The second station (STA2) successfully accesses the channel first, and therefore delays transmission. Before the first station (STA1) successfully accesses the channel, the second station (STA2) senses that the channel of the second link (Link2) is occupied (busy). Even though the channel of the second link (Link2) is sensed as being occupied (busy), the second station (STA2) continues to delay transmission. When the first station (STA1) successfully accesses the channel, the second station (STA2) determines whether the channel of the second link (Link2) is continuously idle in AIFS. When the first station (STA1) succeeded in channel access, the channel of the second link (Link2) was continuously idle in AIFS, so the first station (STA1) and the second station (STA2) perform synchronized transmissions.

[0171] 23 and 24 show the operation of the multilink when a station in the multilink device according to the embodiment of the present invention is delaying transmission and the channel for which transmission is being delayed is detected as being occupied (busy).

[0172] In the embodiment described in FIG. 22, when the first station is waiting to transmit and the second station has successfully accessed the channel, the first station can determine that the channel of the first link is occupied (busy). At this time, the second station can obtain a new backoff counter to access the channel. At this time, the second station can set the CW to the same value as the previously used CW value and obtain the backoff counter. In yet another specific embodiment, the first station can obtain a new backoff counter to access the channel. At this time, the first station can set the CW to the same value as the previously used CW value and obtain the backoff counter.

[0173] In the embodiments of Figures 23 and 24, a first station (STA1) is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). The second station (STA2) first succeeds in channel access, and the second station (STA2) delays transmission. When the first station (STA1) succeeds in channel access, the second station (STA2) senses that the channel of the second link (Link2) has not been idle for a consecutive AIFS.

[0174] In the example of Figure 23, the first station (STA1) acquires a new backoff counter and performs channel access. The second station (STA2) delays transmission. After that, when the first station (STA1) successfully accesses the channel, the channel of the second link (Link2) is sensed as being idle for consecutive AIFSs. Therefore, the first station (STA1) and the second station (STA2) perform synchronized transmissions.

[0175] In the example of Figure 24, the second station (STA2) acquires a new backoff counter and performs channel access. The first station (STA1) delays transmission. After that, when the second station (STA2) successfully accesses the channel, the channel of the first link (Link1) is sensed as being idle for a continuous period of AIFS. Therefore, the first station (STA1) and the second station (STA2) perform synchronized transmission.

[0176] A method for applying EDCA to the above-mentioned synchronized transmission will be described with reference to FIGS.

[0177] FIG. 25 shows an EDCA queue used when applying EDCA according to an embodiment of the present invention.

[0178] When EDCA is applied, the order of transmission processing is determined by the priority of the traffic to be transmitted. The priority of the traffic may be determined by the traffic type or TID (Traffic ID). The priority of the traffic may be classified into one of AC_VO, AC_VI, AC_BE, and AC_BK. In this case, each AC may be represented as follows:

[0179] 1) AC_VO: Voice

[0180] 2) AC_VI: Video

[0181] 3) AC_BE: Best Effort

[0182] 4) AC_BK: Background

[0183] Among the four ACs, the highest priority may be AC_VO, AC_VI, AC_BE, and AC_BK in that order. Specifically, the ACs may affect the channel access procedure as follows.

[0184] In the above embodiment, AIFS may be defined as SIFS+AIFSN[AC]*aSlotTime. Here, aSlotTime is the time of one slot, which is a unit used when a station performs a backoff operation for frame transmission. If the bandwidth of the basic signal used in the BSS is 20 MHz, aSlotTime may be defined as 9μ. In addition, the minimum value of CW (CWmin) and the maximum value of the contention window (CWmax) may be different for each AC. The AIFSN and CWmax values ​​set as the basis for each AC may be set as shown in Table 1 below.

[0185] [Table 1]

[0186] An independent EDCA queue may be set for each AC. When a station receives traffic to be transmitted from an upper layer, the station may store the received traffic in an EDCA queue corresponding to the AC of the received traffic. In this case, an independent EDCAF operation may be performed in each EDCA queue. Figure 25 shows that the station receives traffic to be transmitted from an upper layer and stores the received traffic in an EDCA queue corresponding to the AC of the received traffic.

[0187] FIG. 26 illustrates a method for providing channel access based on slot boundaries in accordance with an embodiment of the present invention.

[0188] In the backoff procedure, the slot boundaries may be defined as at least one of the following:

[0189] 1) When the channel occupation state occurs due to a frame transmitted by another terminal and a frame reception error state does not occur, if the channel state is in the channel idle state for the time AIFSN[AC]*SlotTime-aRxTxTurnaroundTime after the SIFS time following the end of the occupation time, the time when the channel state has passed

[0190] 2) When a channel occupancy state occurs due to a frame transmitted by another station, and a frame reception error occurs, the channel state is in an idle state for (EIFS-DIFS+AIFSN[AC]*aSlotTime+aSIFSTime-aRxTxTurnaroundTime) from the time when the channel occupancy state is completed by physical detection, and the channel state is in an idle state.

[0191] 3) After sending a frame requesting the transmission of a response frame (e.g., an ACK frame or a BlockAck frame), at the earlier of the following two points in time:

[0192] A) When the channel state is in the channel idle state, AIFSN[AC]*aSlotTime+aSIFSTime-aRxTxTurnaroundTime has elapsed since the reception expiration time for receiving a response frame after the completion of transmission of the PPDU containing the frame.

[0193] B) When a response frame is received, if the channel state is idle for the time AIFSN[AC]*aSlotTime-aRxTxTurnaroundTime after SIFS time from the completion of reception of the PPDU containing the response frame, the time when AIFSN[AC]*SlotTime-aRxTxTurnaroundTime has elapsed after SIFS time from the completion of reception of the PPDU.

[0194] 4) When the channel state is idle for AIFSN[AC]*SlotTime-aRxTxTurnaroundTime after the SIFS time at which the transmission of a PPDU including a frame that does not request the transmission of a response frame is completed, the time when AIFSN[AC]*aSlotTime-aRxTxTurnaroundTime has elapsed after the SIFS time at which the transmission of the PPDU is completed.

[0195] When the channel state is idle for AIFSN[AC]*aSlotTime+aSIFSTime-aRxTxTurnaroundTime after any channel occupation time that does not meet the conditions 1-4, the time when the AIFSN[AC]*aSlotTime+aSIFSTime-aRxTxTurnaroundTime has elapsed.

[0196] If the channel state is idle for aSlotTime after the previous slot boundary, the end of aSlotTime

[0197] aRxTxTurnaroundTime refers to the time it takes for the station's transceiver to switch from receive mode to transmit mode. The required switching time may be 4 us.

[0198] Meanwhile, at each slot boundary, the station's EDCAF can take one of the following actions:

[0199] 1) Decrease the backoff value by 1

[0200] 2) Execute frame transmission operation

[0201] 3) Generate a new backoff value due to an internal collision and perform the backoff operation

[0202] 4) Do nothing

[0203] If, at a slot boundary, there is a frame to transmit in the station's EDCA queue, the backoff value is 0, and there is no situation in which a frame belonging to an AC with a higher priority than the EDCA queue is to be transmitted (i.e., there is no internal collision situation), the station will transmit the frame stored in the EDCA queue at that slot boundary.

[0204] On the other hand, the EDCAF operating in a station may need to perform backoff operations when one or more of the following conditions occur:

[0205] 1) When a frame to be transmitted from a station is generated, the frame is the first frame stored in the EDCA queue, and the channel is occupied at the time of frame generation.

[0206] 2) When the station completes its frame transmission operation, or when the TXOP acquired by the station for frame transmission expires.

[0207] 3) When a TXOP is acquired by EDCAF operation and a frame is transmitted, but the first frame transmitted using the acquired TXOP fails to be transmitted.

[0208] 4) When a frame collision occurs in the EDCA queue and the AC of the colliding frame has a higher priority than the frame to be transmitted.

[0209] In the above situation 1), the operation of determining the channel state of the channel may be performed by checking the physical Carrier Sensing (CS) in which the station measures the received energy level, the virtual CS in which the signal length of the corresponding signal is recognized through the preamble including the received frame, and the Network Allocation Vector (NAV) value set through the Duration field of the received frame. Meanwhile, if the station is a mesh station, the channel state can be further confirmed by checking the NAV value.

[0210] On the other hand, the EDCAF operating in the station can perform backoff operation when one of the following conditions occurs:

[0211] 1) When the frame transmission operation of a frame that is not the first frame in the acquired TXOP fails

[0212] 2) When a channel expansion operation is performed to transmit a frame using the 40MHz / 80MHz / 160MHz / 320MHz bandwidth, but the channel status of the sub-channel is determined to be a channel occupied state, and a channel access operation is attempted again.

[0213] As described above, if a station has a frame to transmit in an EDCA queue at a slot boundary, and the backoff value is 0, and a frame corresponding to an AC with a higher priority than the EDCA queue is being transmitted, the station may recognize that an internal collision has occurred. In this case, the station obtains a new backoff value for the EDCA queue and performs the backoff operation again.

[0214] Meanwhile, when a frame to be transmitted to a station is generated, if the frame is the first frame stored in the EDCA queue and the channel is in a busy state at the time of frame generation, the station can generate a backoff value and perform a backoff operation. In this case, the backoff value can be set to a random number between 0 and (contention window value - 1). For example, when a frame to be transmitted by a station is generated, the channel may be in a busy state at that time, and a backoff value of 3 can be obtained through the backoff operation. After the channel is occupied, according to the definition of slot boundary 1), the next slot boundary may occur when AIFS-aRxTxTurnaroundTime has elapsed after the channel occupation time has ended. If the channel continues to be in an idle state after the channel occupation time, subsequent slot boundaries may occur every time aSlotTime has elapsed. If the backoff value is not 0 at each slot boundary, the backoff value for transmitting the frame may be decremented by 1. On the other hand, if the backoff value is 0 at a slot boundary, other than the internal collision situation described above, the station can switch the transceiver to transmit mode to transmit the frame, and then the station can transmit the frame.

[0215] The EDCAF operation for synchronized transmission is described in FIG.

[0216] 27 and 28 show the operation of a multilink device performing synchronized transmission by EDCAF operation according to an embodiment of the present invention.

[0217] The point at which a station can transmit a frame may be the point at which the station completes a channel access procedure based on EDCA operation on the link on which the station operates. When the backoff value is 0 at a slot boundary, the station can begin synchronized transmission. In this case, the slot boundary at which the frame can be transmitted may be the slot boundary immediately after the backoff value becomes 0. If a station maintains the backoff value at 0 and delays frame transmission, the station may not be allowed to transmit a frame at any slot boundary. When a frame to be transmitted is generated with a backoff value of 0, the slot boundary immediately after the backoff value becomes 0 may be the first slot boundary after the frame is generated. If a backoff value randomly selected by the backoff procedure is already 0, the slot boundary immediately after the backoff value becomes 0 may be the slot boundary immediately after the backoff value is selected.

[0218] Also, if transmission is delayed on one link, synchronized transmission can be performed on the other link at the slot boundary immediately after the backoff value becomes 0. As a result, stations can perform synchronized transmission at the following points:

[0219] 1) At the slot boundary immediately after the backoff value becomes 0 on the link on which the station operates

[0220] 2) When the backoff value of the link on which the station is operating is already maintained at 0 and transmission is delayed, the time is reached at the slot boundary immediately after the backoff value of the other link on which another station in the multilink is operating becomes 0.

[0221] In this case, referring to the definition of the slot boundary point, the slot boundary immediately after the backoff value for transmitting a frame becomes 0 may imply that the CCA (Channel Condition Check) result is idle (or not busy) from the slot boundary where the backoff value becomes 0 to the next slot boundary.

[0222] In the embodiments of Figures 27 and 28, a first station (STA1) is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). In the embodiment of Figure 28, the second station (STA2) first succeeds in channel access, and the second station (STA2) delays transmission. When the first station (STA1) successfully accesses the channel, the first station (STA1) and the second station (STA2) perform synchronized transmission. Specifically, after the backoff counter value of the first station (STA1) reaches 0, the first station (STA1) and the second station (STA2) perform synchronized transmission at the next slot boundary. Therefore, actual transmission begins after the transceiver is switched to transmit mode at the next slot boundary after the backoff counter value of the first station (STA1) reaches 0.

[0223] In the embodiment of Figure 28, the first station (STA1) succeeds in channel access first, and the first station (STA1) delays transmission. When the second station (STA2) succeeds in channel access, the first station (STA1) and the second station (STA2) perform synchronized transmission. Specifically, the first station (STA1) and the second station (STA2) perform synchronized transmission at the next slot boundary after the backoff counter value of the second station (STA2) reaches 0. Therefore, actual transmission begins after the transceiver is switched to transmit mode at the next slot boundary after the backoff counter value of the second station (STA2) reaches 0.

[0224] A station can transmit a frame at a slot boundary when the backoff value is 0. This simplifies synchronized transmission.

[0225] FIG. 29 shows the operation of a multilink device performing synchronized transmission by EDCAF operation according to yet another embodiment of the present invention.

[0226] The slot boundary times may be as follows:

[0227] 1) When the channel occupation state is caused by a frame transmitted by another station and no frame reception error state occurs, if the channel state is in the channel idle state for (AIFSN[AC]+1)*aSlotTime-aRxTxTurnaroundTime after the SIFS time from the end of the occupation time, the time when the channel state is in the channel idle state is reached.

[0228] 2) When a channel occupancy state occurs due to a frame transmitted by another terminal and a frame reception error state occurs, if the channel state is in a channel idle state within {EIFS-DIFS+(AIFSN[AC]+1)*aSlotTime+aSIFSTime-aRxTxTurnaroundTime} time from the time when the channel occupancy state is completed by physical detection, the time when that time has elapsed.

[0229] 3) After sending a frame requesting the transmission of a response frame (e.g., an ACK frame or a BlockAck frame), the earlier of the following two points in time:

[0230] A) After the completion of transmission of the PPDU containing the frame, if the channel state is idle for (AIFSN[AC]+1)*aSlotTime+aSIFSTime-aRxTxTurnaroundTime after the reception expiration time for receiving a response frame, the time (AIFSN[AC]+1)*aSlotTime+aSIFSTime-aRxTxTurnaroundTime) has elapsed.

[0231] B) When a response frame is received, if the channel state is idle for (AIFSN[AC]+1)*SlotTime-aRxTxTurnaroundTime after the SIFS time from the completion of reception of the PPDU containing the response frame, the time when (AIFSN[AC]+1)*aSlotTime-aRxTxTurnaroundTime) has elapsed.

[0232] 4) When the transmission of a PPDU including a frame that does not request the transmission of a response frame is completed, if the channel state is idle for AIFSN[AC]*aSlotTime-aRxTxTurnaroundTime after the SIFS time, the time when AIFSN[AC]*SlotTime-aRxTxTurnaroundTime has elapsed.

[0233] 5) When the channel state is idle for (AIFSN[AC]+1)*aSlotTime+aSIFSTime-aRxTxTurnaroundTime) after any channel occupation time that does not meet conditions 1-4, the time when (AIFSN[AC]+1)*aSlotTime+aSIFSTime-aRxTxTurnaroundTime has elapsed.

[0234] 6) When the channel state is in the idle state for aSlotTime after the previous slot boundary, aSlotTime has elapsed.

[0235] The time at which a station on each link can switch its transceiver into transmit mode to transmit a frame may be adjusted as follows:

[0236] 1) The time when the backoff value of the corresponding link becomes 0 at the multi-link slot boundary

[0237] 2) When the backoff value of the link is already set to 0 and the frame transmission operation is postponed, the backoff value of another link becomes 0 at the boundary of multiple link slots.

[0238] In the embodiment of Figure 30, a first station (STA1) is connected to a first AP (AP1) via a first link (Link1). A second station (STA2) is connected to a second AP (AP) via a second link (Link2). The second station (STA2) first succeeds in channel access, and the second station (STA2) delays transmission. When the first station (STA1) successfully accesses the channel, the first station (STA1) and the second station (STA2) perform synchronized transmission. Specifically, the first station (STA1) and the second station (STA2) perform synchronized transmission at the slot boundary when the backoff counter value of the first station (STA1) reaches 0. Therefore, actual transmission begins after the transceiver is switched to transmit mode from the slot boundary when the backoff counter value of the first station (STA1) reaches 0.

[0239] FIG. 30 illustrates an embodiment in which an MLD delays a channel access procedure for a specific channel to simultaneously transmit PPDUs on two links according to an embodiment of the present invention.

[0240] Referring to FIG. 30, when an MLD including multiple links performs multiplexing on each link, the value of the backoff counter of each link can be adjusted to perform multiplexing simultaneously.

[0241] Specifically, as shown in FIG. 30, the MLD may include STA1 and STA2. The links operated by STA1 and STA2 may be a link pair having a non-STR relationship, and the MLD may attempt to perform simultaneous transmission using the non-STR link pair. In this case, the MLD may choose to postpone PPDU2 transmission rather than start PPDU2 transmission using STA2 even after the channel access procedure of STA2 is completed (i.e., BO becomes 0 due to the backoff procedure). In this case, the point at which the channel access procedure is completed may refer to the slot boundary at which BO becomes 0 when DCF is used, or the slot boundary next to the slot boundary at which BO becomes 0 when EDCA is used. During the PPDU2 transmission postponement period, STA1, another STA in the MLD, completes the channel access procedure, and the MLD may start transmitting PPDU1 and PPDU2 simultaneously using STA1, which has just completed the channel access procedure, and STA2, which has been waiting (transmission postponed) after completing the channel access procedure. In the present invention, a PPDU may include a frame. Furthermore, the operation of transmitting or not transmitting a PPDU may also mean the operation of transmitting or not transmitting a frame.

[0242] That is, the EDCA rule for each link can allow channel connection for all links, and therefore, even if the channel access procedure for one of the multiple links of the MLD is completed and the backoff counter value reaches "0," if the backoff counter values ​​for the other links have not yet reached "0," the STA of the MLD can maintain the backoff counter value at "0" without performing uplink transmission for that link. In other words, when the backoff counter value for a specific link reaches "0," the STA of the MLD can choose to maintain the backoff counter value at "0" without performing uplink transmission if the backoff counter values ​​for the other links of the MLD have not yet reached "0."

[0243] 30, if STA2 immediately starts transmitting a PPDU after the channel access procedure of STA2 has finished because the backoff counter value of STA2 has reached "0," the PPDU transmission of STA2 may interfere (or obstruct) the channel access procedure of STA1. However, as described above, by adjusting the start time of PPDU transmission on the link of the STA that has finished the channel access procedure, either STA1 or STA2, the MLD can simultaneously transmit PPDUs using a link pair in a non-STR relationship.

[0244] Therefore, when the MLD intends to perform simultaneous transmission, the STAs of the MLD may not immediately start transmitting PPDUs or perform a new channel access procedure even after the completion of the channel access procedure. In other words, the STAs of the MLD may maintain BO at 0 after the completion of the channel access procedure. However, as described above, the operation of maintaining BO at 0 after a specific STA completes the channel access procedure may be limited to when the specific STA is an STA of the MLD. In this case, the operation may be limited to when the link operated by the specific STA is a link pair having a non-STR relationship with another STA of the MLD. In this case, the operation of maintaining BO at 0 after the specific STA completes the channel access procedure may be permitted only when the MLD including the specific STA intends to perform simultaneous transmission (start time synchronous).

[0245] That is, when the links of the MLD to the STAs are a pair of links in a non-STR relationship, if the channel access procedures of the STAs are completed at different times, the MLD can reserve PPDU transmission for the other links depending on the link that completes the channel access procedure latest. For example, when the first link of STA1 and the second link of STA2 included in the MLD are a non-STR link pair, the value of the first backoff counter in the backoff procedure of the channel access procedure for the first link of STA1 may reach "0" before the value of the second backoff counter in the backoff procedure of the channel access procedure for the second link of STA2. In this case, STA1 can choose not to transmit a PPDU on the first link and to maintain the value of the backoff counter at "0." <Slot boundary mismatch when transmitting simultaneously> As described above, the MLD can perform simultaneous transmission using two or more links. The term "simultaneous" used in the simultaneous transmission does not mean that the transmissions are performed at the exact same physical time. More specifically, the simultaneous transmission performed by the MLD can mean that the start times of transmissions performed on two or more links are different by within a specific time interval. For example, if the specific time interval is aSlotTime, and the MLD starts PPDU transmission on Link1 at time "t" and starts transmission on another link, Link2, "after t-aSlotTime and before t+aSlotTime," the MLD can be considered to have performed simultaneous transmission using Link1 and Link2. Here, the aSlotTime used as an example of the specific time interval is merely an example, and the time interval that the MLD should consider / adhere to for simultaneous transmission may be other time values ​​(e.g., 1 us, 2 us, 3 us, ... x us) other than aSlotTime. Here, the time interval that should be considered for simultaneous transmission may be a value specified by the AP of the BSS. As an example, an AP MLD can use an OM (Operating Mode) element to indicate the time value that the STA MLD associated with itself should consider when performing simultaneous transmission.

[0246] Here, the aSlotTime refers to a time value defined in the standard for each PHY version, and if the corresponding slot is idle for each aSlotTime, a channel access procedure is performed to decrement a backoff counter (BO) by one. The channel access procedure may be DCF or EDCA, and is a well-known channel access procedure for conventional Wi-Fi, so a detailed description will be omitted. For example, in 11ax, aSlotTime is 9 us.

[0247] In this way, the simultaneous transmission performed by MLD does not mean only transmissions that start "at the same time" in the strict sense, but also includes transmissions that start with a difference within a specific time interval, because the slot boundaries of each link used in simultaneous transmission are not aligned. A more detailed explanation of slot boundaries is given in one embodiment of Figure 31.

[0248] FIG. 31 illustrates an embodiment in which STAs in an MLD operate based on different slot boundaries according to an embodiment of the present invention.

[0249] Referring to FIG. 31, different links of STAs that make up an MLD can operate on different slot boundaries.

[0250] When a Wi-Fi device's primary channel is occupied by another device, the Wi-Fi device determines (calculates) a slot boundary based on the time when the primary channel occupation ends. The slot boundary is used as a criterion for dividing each slot during the channel access procedure, and transmissions made by the Wi-Fi device after completing the channel access procedure should be made at times aligned with the slot boundary.

[0251] Therefore, as shown in Figure 31, when medium occupation ends at different times on Link1 and Link2, MLD STAs STA1 and STA2 must perform channel access procedures based on different slot boundaries. As such, STAs operating on different links are likely to have different slot boundaries depending on the occupation status of the links on which they operate. Therefore, it may be impossible to start transmission "simultaneously" in the strict sense on two or more links to be used for simultaneous transmission.

[0252] Furthermore, although the MLD may attempt to start transmission simultaneously using two or more links at a specific time, the two or more links are processed by separate MACs and PHYs, and the PPDUs are to be transmitted in different PPDU BWs on different links, so the processing for PPDU transmission may not be completed at exactly the same time (strictly speaking, "simultaneously"). Therefore, even if the MLD attempts simultaneous transmission (strictly speaking, "simultaneous" transmission) while ignoring the different slot boundaries of different links, the times at which transmission begins on the different links may still be different.

[0253] Therefore, in order for multiple STAs constituting an MLD to perform simultaneous transmissions through their respective links, a rule regarding the start time of transmissions performed on each link is required. The rule to be observed by the MLD for simultaneous transmission may be that the start time of transmissions on a specific link performed for simultaneous transmissions should begin within the aRxTxTurnaroundTime interval (a time interval within aSlotTime) of another link performing simultaneous transmissions. Alternatively, the rule to be observed by the MLD for simultaneous transmissions may be that the start time of transmissions on a specific link performed for simultaneous transmissions should be after the CCADel (or CCATime) interval within aSlotTime of another link performing simultaneous transmissions. The aRxTxTurnaroundTime is the time required by the PHY performing the channel access procedure to perform PPDU transmission (the time required to actually perform carrier sensing and PD for CCA within aSlotTime), and the actual time required by each device may vary depending on the implementation. In the present invention, aRxTxTurnaroundTime is mainly considered to be 4 us, but the specific value of aRxTxTurnaroundTime may be changed. CCATime may be understood as an interval within aSlotTime during which each STA should perform CCA (CS), and the time interval may be determined depending on the implementation. CCADel is an interval value obtained by adjusting CCATime to take delay into consideration, and may vary depending on the implementation.

[0254] That is, the slot settings for each link may be different, and therefore, slot boundaries between links may not coincide. Therefore, slot boundaries between links may not coincide in each slot in which the backoff counter is decremented. In addition, when the backoff counters of multiple links in MLD reach "0" through the backoff procedure as described above due to the reservation operation, the slot boundaries between links may not coincide. Since slots for each link may be set independently, the slot boundaries between links may not coincide. Therefore, even when the backoff counter values ​​for each link are "0," the slot boundaries may differ. In this case, simultaneous transmission may be performed based on the slot boundary for the slot in which the backoff counter value of a specific link among the multiple links is "0" or the slot boundary for the slot next to the slot. That is, when a specific link is the reference link for multiplexing among multiple links in non-AP MLD, if the backoff counter value in slot 1 of the specific link is decremented to "0," other links may perform uplink transmission based on the slot boundary for slot 1 for the specific link or slot 2, which is the slot next to slot 1 on the time axis.

[0255] That is, each link may not perform uplink transmission according to the slot boundary of the link, or may perform uplink transmission simultaneously by delaying or shortening the uplink transmission according to the slot boundary of the specific link.

[0256] For example, when an MLD multiple link is composed of a first link and a second link, and a channel access procedure is completed in one of the first and second links (e.g., when one of the first back-off counter of the first link and the second back-off counter of the second link reaches '0' before the remaining back-off counter), the slot boundaries of the first and second links may not coincide with each other when the channel access procedure of the remaining links is completed (e.g., when the remaining back-off counter reaches '0'). In this case, uplink transmissions in each link may be performed according to the slot boundary of a specific link for simultaneous uplink transmission among the first and second links, thereby allowing simultaneous uplink transmissions in the multiple links.

[0257] That is, when an MLD multiple link is composed of a first link and a second link, and one of the first backoff counter of the first link and the second backoff counter of the second link reaches '0' before the other backoff counter, the slot boundaries of the first link and the second link may not coincide when the other backoff counter reaches '0'. In this case, the transmission time point of the uplink transmission of the second link can be adjusted by shortening or delaying it depending on the slot boundary of the slot in which the first backoff counter of the first link is '0' or the slot boundary of the first slot, which is the slot next to the slot.

[0258] In this case, the time of uplink transmission in the first link and the time of uplink transmission in the second link may be within a certain time period. For example, the time of uplink transmission in the second link may be within 4 us of the time of uplink transmission in the first link.

[0259] In this manner, uplink transmissions can be performed simultaneously on the first and second links by performing uplink transmissions at a time other than the slot boundary of the slot in which the second backoff counter of the second link is "0" or the slot boundary of the second slot, which is the next slot of the slot.

[0260] Among the STAs included in the MLD, a STA whose transmission is delayed due to a slot boundary can continue channel sensing of the corresponding slot during the link delay time. If the backoff counter value of another link becomes '0' during channel sensing, the STA can terminate channel sensing and immediately transmit a PPDU. The delay or reduction time for simultaneous transmission may be 4 us. Here, 4 us may refer to the change time required to change to a mode for uplink transmission in the channel access procedure. If the delay or reduction time exceeds 4 us, the time required to switch from downlink to uplink may be exceeded, and the channel status in the corresponding slot may change to an occupied state (busy).

[0261] The STA operations within aSlotTime shown in Figure 33 are for illustrative purposes only, and each STA may perform different operations within aSlotTime corresponding to each slot. However, all Wi-Fi devices must meet the carrier sense (CS) accuracy defined in the Wi-Fi standard when implemented.

[0262] FIG. 32 shows an example of a simultaneous transmission failure of MLD that may occur when there is no clear definition of the start time of simultaneous transmission according to an embodiment of the present invention.

[0263] 32(a) and 32(b), the MLD delays the start of transmission by STA1 in order to perform simultaneous transmission using STA1 and STA2, even though the channel access procedure of STA1 has been completed. In this case, because the slot boundaries of STA1 and STA2 are different, the MLD may attempt to synchronize the start of transmission by STA1, which has delayed the channel access procedure, with a time similar to the time at which STA2 completes the channel access procedure. In this case, the MLD may synchronize the start of transmission by STA1 with the slot boundary of STA1 that is adjacent to the slot boundary at which STA2 completes the channel access procedure (the slot boundary used by STA2). In this case, the start of transmission initiated by STA1 may be the STA1 slot boundary that is immediately after the time at which STA2 completes channel access (the specific slot boundary of STA2), as in Case 1 of FIG. 14(a). Alternatively, the start point of transmission initiated by STA1 may be the slot boundary of STA1 that exists immediately before the point at which STA2 is predicted to complete channel access (a specific slot boundary of STA2), as in Case 2 of (b) of Figure 14. In short, when attempting to perform simultaneous transmission using two or more links, the MLD may attempt to start transmission at the slot boundaries of each link adjacent to the slot boundary of the link that last completes the channel access procedure (the slot boundary of the STA operating on that link).

[0264] However, as described above, since the slot boundaries of each link may differ from one another, starting transmission on a specific link intended for simultaneous transmission may affect the CCA operations of other links intended for simultaneous transmission, resulting in the inability to start transmission on the other links. More specifically, if transmission started on the specific link induces in-device interference, the CCA results of the other links may be determined to be BUSY due to the in-device interference. As a result, the STAs of the other links operate as if the WM is already occupied and their channel access is restricted. As a result, transmission on a specific link initiated for simultaneous transmission may induce in-device interference on other links that were planned to transmit for simultaneous transmission, thereby restricting channel access on the other links. As shown in (a) and (b) of Figure 14, even if STA1, which has delayed the start of transmission after completing the channel access procedure, selects one of the two slot boundaries adjacent to the slot boundary of STA2, which has just completed or is predicted to complete channel access (the STA1 slot boundary immediately after the slot boundary at which STA2 has completed the channel access procedure and the STA1 slot boundary immediately before the slot boundary at which STA2 is predicted to complete the channel access procedure), the transmission that started earlier may affect the CCA results of other links, and simultaneous transmission may fail.

[0265] Therefore, after completing the channel access procedure, the start of transmission of a link that has delayed / deferred the start of transmission in order to perform simultaneous transmission cannot be specified as one of the two slot boundaries (slot boundary of a specific STA) adjacent to the point at which the STA of another link performing simultaneous transmission completes or is predicted to complete the channel access procedure (slot boundary of the other STA), and must be determined by MLD each time simultaneous transmission is attempted, taking into account the difference in slot boundaries between the specific link and the other link.

[0266] As described above, the start time of a link whose transmission has been delayed for the purpose of simultaneous transmission after completing the channel access procedure should not be specified as the slot boundary (of the link whose transmission has been delayed) immediately before or after the slot boundary of the link whose channel access procedure was last completed among the channel access procedures of the links performing simultaneous transmission. Even if two or more links performing simultaneous transmission start transmission, they should be managed so as not to affect the CCA results of the other links. Therefore, to prevent the transmission started on each link from affecting the CCA results of the other links performing simultaneous transmission, the start time of transmission on each link should be determined taking into account the CCA operations performed by the other links in each slot period (aSlotTime). In this case, the start time of transmission on a specific link determined taking into account the CCA operations of the other links may be determined within aRxTxTurnaroundTime, at which the other links switch from Rx mode to Tx mode after performing CCA. In other words, a STA of a specific link performing simultaneous transmission can start transmission on the specific link in accordance with the aRxTxTurnaroundTime period of a STA of the other links performing simultaneous transmission that has not yet started transmission. Alternatively, the STA of the specific link can start transmitting on the specific link after the CCADel period of each slot of the STA that has not yet started transmitting.

[0267] Figure 33 shows an example of a case where, according to an embodiment of the present invention, when STAs of an MLD start transmission at different slot boundaries, the transmission that starts earlier does not affect the CCA results of other STAs (the same MLD operated on other links).

[0268] 33, the MLD operates STA1 and STA2 on Link1 and Link2, respectively. STA1 has completed its channel access procedure, but may delay the start of STA1's transmission in order to transmit simultaneously with STA2. In this case, the MLD determines that even if STA2 starts transmission at the slot boundary where the channel access procedure is completed, the CCA result of STA1 will not be affected because the STA1 slot (the slot shown in the grid, the slot immediately before STA1 starts transmission) including the start of STA2's transmission corresponds to the period in which STA1 switches from Rx mode to Tx mode. Therefore, the MLD may determine that the start of STA1's transmission, which was delayed after completing the channel access procedure, should start at the STA1 slot boundary after the STA2 slot boundary where STA2 started transmission after completing the channel access procedure.

[0269] In this case, the STA1 slot boundary after the STA2 slot boundary may be the STA1 slot boundary immediately after the STA2 slot boundary. For more specific explanation, referring again to FIG. 15, STA1 performs an operation of switching from Rx mode to Tx mode during the last 4 us of aSlotTime corresponding to the slot indicated by the grid, and even if intra-device interference occurs during this switching period, it does not need to determine the slot indicated by the grid as BUSY. Therefore, since the start point of transmission performed by STA2 is within aRxTxTurnaroundTime of STA1, STA1 can access the channel without problems due to intra-device interference even after STA2 starts transmitting first.

[0270] Here, 4 us is used as an example of a value corresponding to aRxTxTurnaroundTime, and the aRxTxTurnaroundTime may have a different value for each terminal depending on the hardware characteristics of each terminal. Therefore, the difference in the transmission start time of each link that should be considered when the MLD performs simultaneous transmission may be a different time value depending on the characteristics of the MLD or each STA of the MLD.

[0271] Meanwhile, as described above, the start time of transmission of the link that started transmission first may be applied so that it begins in the interval after CCADel rather than within the aRxTxTurnaroundTime interval of the other link. However, in this embodiment, if the above description is substituted for the interval after CCADel rather than the aRxTxTurnaroundTime interval, it may be understood as a similar method, and detailed description thereof will be omitted. For reference, in one embodiment of Figure 15, the interval including the M2 interval shown in the Rx / Tx (e.g., 4 us) interval may be understood as the interval after CCADel.

[0272] FIG. 34 shows an embodiment of a method for determining the time to start transmission on each link based on the slot boundary time difference between links for which an MLD is to perform simultaneous transmission according to an embodiment of the present invention.

[0273] 34(a) shows a situation in which the slot boundary of STA1 precedes (is earlier in time than) the slot boundary of STA2 by an interval smaller than aRxTxTurnaroundTime, and FIG. 34(b) shows a situation in which the slot boundary of STA2 precedes the slot boundary of STA1 by an interval smaller than aRxTxTurnaroundTime. In this case, the method for comparing the slot boundary precedence relationship of the two links (STAs) may be to compare the precedence relationship between slot boundaries of the two links that have a difference of 1 / 2 aSlotTime or less.

[0274] In Figure 34(a), the slot boundary of STA1 precedes the slot boundary of STA2, and even if STA1 starts transmission at its own slot boundary, the slot boundary of STA1 corresponds to aRxTxTurnaroundTime in the grid slot interval (aSlotTime) of STA2, so MLD can start transmitting Link1 at the slot boundary of STA1 and then transmit Link2 at the slot boundary of STA2.

[0275] In Figure 34(b), the slot boundary of STA2 precedes the slot boundary of STA1, and even if STA2 starts transmission at its own slot boundary, the slot boundary of STA2 corresponds to aRxTxTurnaroundTime in the lattice slot interval (aSlotTime) of STA1, so MLD can start transmitting Link2 at the slot boundary of STA2 and then transmit Link1 at the slot boundary of STA1.

[0276] As a result, when the slot boundaries of the links (STAs operating on each link) that perform simultaneous transmission have a time difference of less than aRxTxTurnaroundTime, the MLD can perform simultaneous transmission by first starting transmission through the STA operating on the link with the earliest slot boundary. In this case, even if the reference time difference (aRxTxTurnaroundTime) is applied to the end point of CCADel, it can be understood as the same method except that the aRxTxTurnaroundTime is changed to M2 (see FIG. 33) + aRxTxTurnaroundTime, and detailed description thereof will be omitted.

[0277] As described above, the MLD determines which link will begin transmission first by considering the slot boundary difference between the links performing simultaneous transmission, thereby preventing the in-device interference caused by the link that begins transmission first from affecting the CCA of the other links. However, if the slot boundary difference between the links performing simultaneous transmission falls within a certain value, the MLD cannot prevent channel access of the other links from being disrupted, regardless of the order in which the MLD begins transmission on each link. In this case, the difference within the certain value may mean a difference of more than (or equal to) 4 us and less than (or equal to) 4.5 us, assuming that aSlotTime is 9 us and aRxTxTurnaroundTime is 4 us. In other words, if the slot boundary difference between two links that the MLD intends to use for simultaneous transmission exceeds (or equal to) 4 us and less than (or equal to) 4.5 us, regardless of which of the two links the MLD begins transmission on first, the channel access (simultaneous transmission) of the remaining link may be restricted due to the in-device interference caused by the link that began transmission first.

[0278] FIG. 35 illustrates an example of a case where simultaneous transmission fails when two link pairs in an MLD have a slot boundary difference within a specific range according to an embodiment of the present invention.

[0279] 35, the MLD can operate STA1 and STA2 as Link1 and Link2, respectively, and STA1 and STA2 can perform channel access based on slot boundaries that differ from each other by 1 / 2 aSlotTime. In this case, STA1 completes the channel access procedure first, and the MLD can reserve the start of transmission for STA1 in order to perform simultaneous transmission using STA1 and STA2. In this case, the MLD may attempt to start transmission for Link1 at the slot boundary of STA1 that is adjacent to the slot boundary where channel access for STA2 ends, but the simultaneous transmission may not be successful due to the difference in slot boundaries between STA1 and STA2.

[0280] The MLD may select one of two slot boundaries (T2 in FIG. 35) where STA2 is predicted to complete / have completed its channel access procedure and the adjacent slot boundary of STA1 to attempt to start transmission on Link 1. If the MLD starts transmission on Link 1 at the slot boundary of STA1 (T1 in FIG. 35) that appears earlier at the time of STA2's predicted completion of the channel access procedure, the transmission started on Link 1 will cause STA2's last backoff slot (shown as 0) to be determined as BUSY, and STA2's channel access procedure will not be completed at the predicted time T2. In other words, if the MLD starts transmission using STA1 at time T1, the channel access procedure of STA2 will not be completed due to the in-device interference caused by the transmission on Link 1, and simultaneous transmission will fail. Meanwhile, if the MLD attempts to transmit to Link 1 at the slot boundary of STA1 (T3 in FIG. 35) that appears after the completion of the channel access procedure of STA2, the last slot of Link 1, which ends at T3, may be determined to be BUSY due to the transmission of Link 2 that has already started at T2, and channel access to Link 1 may be impossible. This may be because the time difference between T1 and T2, and between T2 and T3, is greater than aRxTxTurnaroundTime, respectively, so whichever of the two links, Link 1 or Link 2, starts transmission first may result in the channel access procedure of the other link being interrupted.

[0281] As mentioned above, when specific links have a slot boundary difference within a specific range, the links may not be able to participate in simultaneous transmission by starting transmission at their own slot boundary. Assuming a situation where aSlotTime is 9 us and aRxTxTurnaroundTime is 4 us, as in the example of Figure 35 above, the probability that a specific link pair has a slot boundary difference that makes simultaneous transmission impossible can be understood by simple calculation as 1 / 9. This may be a somewhat higher probability when considering that non-STR MLD actively attempts simultaneous transmission even to prevent a specific link from transitioning to a BLIND state.

[0282] In addition, some devices may have a relatively short aRxTxTurnaroundTime, and when simultaneous transmission is performed using devices with such a relatively short aRxTxTurnaroundTime, the probability of simultaneous transmission being limited due to the slot boundary difference between a specific link pair may become even higher. For example, if a STA of a specific MLD requires an aRxTxTurnaroundTime of only 1.5 us and is capable of performing CCA during the remaining time, when the specific MLD performs simultaneous transmission using two links, it may fail to access one of the two channels with a probability of (4.5 - 1.5) / 9 = 1 / 3.

[0283] <Channel access not aligned with slot boundaries>

[0284] As described above, to prevent the problem of simultaneous transmission (simultaneous channel access) being limited due to slot boundary differences, when an MLD reserves the start of transmission from a specific STA for the purpose of simultaneous transmission (the specific STA has completed the backoff procedure (channel access procedure) (BO==0)), the transmission initiated by the specific STA may be allowed to have an error of less than a certain level with respect to the slot boundary of the specific STA. In other words, when an MLD performs simultaneous transmission through multiple links, the channel access procedures of the non-STR link pairs of the MLD may end at different times. In this case, the STA of a link whose backoff counter value reaches "0" first through the backoff procedure of each link of the non-STR link pair may maintain the backoff counter value at "0" and not transmit a PPDU until the backoff counter value of the link of the other STA reaches "0". In this case, if the backoff counter values ​​of the STAs in the MLD non-STR link pair reach '0', the slot boundaries of the STAs may not match, and the MLD STAs may begin transmission at a time other than their own slot boundary. In this case, the error below a certain level may be determined taking into account aSlotTime. For example, the error below a certain level may not exceed 10% of aSlotTime. In this case, if aSlotTime is 9 us, the transmission by the MLD STAs may begin within ±0.9 us of their own slot boundary. The reason for considering aSlotTime when determining the allowable range (error) for beginning transmission at a time other than the slot boundary may be to prevent an error that would damage slot boundary synchronization between STAs operating on a specific link. In this case, slot boundary synchronization may refer to a level of synchronization that allows channel access according to EDCA rules when performing a channel access procedure using each STA's own slot boundary, even if each STA uses slightly different slot boundaries due to propagation delay.

[0285] That is, this may mean that the error below the certain level does not exceed 10% of (aSlotTime-aAirPropagationTime). In this case, the aAirPropagationTime may be a value (in us) calculated as twice the signal propagation time between the farthest STAs (synchronized slots), or may be a value indicated by a parameter in the Coverage Class field of the BSS. As an example, if the aAirPropagationTime of the BSS considered by the EHT AP is 1 us or less, the start time of transmission performed by the STA of the BSS may be allowed to have an error of up to 0.8 us (+-10% * (9 us - 1 us)) from the slot boundary. In other words, the EHT STA may allow its transmission start time to have a difference of 0.8 us or less from the slot boundary.

[0286] That is, there is an allowable "transmission start time - slot boundary" error when considering the length of aSlotTime used by the BSS and the stability (integrity) of slot boundary synchronization between STAs, and by taking this into consideration, it is possible to determine (ensure) an error below the certain level. In simple terms, using the error between the slot boundary and the transmission start time allowed based on the slot boundary synchronization stability between STAs of a specific link, STAs in an MLD can start transmission at a time different from the slot boundary (within the error range).

[0287] Alternatively, the error below a certain level may be a value that has already been determined (promised) regardless of aSlotTime, or a value instructed by the AP MLD. If a specific STA of the MLD that has completed the channel access procedure and reserved transmission is allowed to start transmission regardless of its own slot boundary, the allowed error level from the slot boundary may be understood to be aSlotTime / 2.

[0288] Figure 36 shows an example of a simultaneous transmission technique in which an MLD STA that has completed a channel access procedure according to an embodiment of the present invention and has reserved the start of transmission starts transmission at a time different from its own slot boundary.

[0289] Referring to Figure 36, the MLD can operate STA1 and STA2 on Link1 and Link2, respectively, and STA1 and STA2 can perform channel access based on slot boundaries that differ from each other by 1 / 2 aSlotTime. In this case, STA1 completes the channel access procedure first, and the MLD can reserve the start of STA1's transmission in order to perform simultaneous transmission using STA1 and STA2. This is the same situation as considered in Figure 17, and if the MLD's STA, STA1, starts transmission to Link1 at the slot boundary, simultaneous transmission (simultaneous channel access) using STA1 and STA2 is not possible. However, in the case of STA1, since it reserved the start of transmission for the purpose of simultaneous transmission after completing the channel access procedure, it can freely adjust the start of transmission within a certain (allowable) error from its own slot boundary.

[0290] Therefore, STA1 does not start transmission at T1, which is one of its slot boundaries, but can start PPDU transmission at a time delayed by the allowed error time (compared to T1). As a result, when STA2, operating on Link2, evaluates the slot (grid) adjacent to T2, the slot boundary where the channel access procedure is completed, it can determine the slot as IDLE and start simultaneous transmission at T2 regardless of the intra-device interference caused by the transmission from STA1. In short, if STA1's transmission starts at T1, aligned with its slot boundary, the channel access procedure of STA2 may not be completed by T2, resulting in simultaneous transmission failure. However, STA1 delays its transmission start time by the Slot Sync budget, thereby starting transmission on Link1 during STA2's aRxTxTurnaroundTime period.

[0291] As described above, when a specific STA of an MLD is operated for the purpose of simultaneous transmission, the specific STA may be allowed to start transmission at a time (within a permissible error range) that is different from the slot boundary synchronization used by the specific STA in the channel access procedure. As a result, the MLD can perform simultaneous transmission by managing the transmission start time on each link, regardless of any difference in the slot boundaries of each link used for simultaneous transmission.

[0292] FIG. 37 shows an example of signaling that can be used when an AP MLD indicates the Slot Sync Budget available in a BSS using an operation element according to an embodiment of the present invention.

[0293] The AP MLD can determine and indicate a Slot Sync Budget available for simultaneous transmission by the STA MLDs in the BSS by evaluating the integrity of slot boundary synchronization between the STAs in the BSS. In this case, the Slot Sync Budget may be indicated by an action element. In this case, changes to the name of the field and the indicated element are not limited. The value indicated by the Slot Sync Budget may apply the maximum possible error between the slot boundary of each link and the start of transmission for each link when the STA MLDs perform simultaneous transmission. In this case, the Slot Sync Budget is not limited for the purpose of simultaneous transmission, and may apply the possible timing error between the slot boundary and the transmissions made by the EHT STAs.

[0294] For example, when the slot boundary synchronization between STAs in a BSS is strong (when synchronization is well performed), the AP MLD can indicate a relatively large value through the Slot Sync Budget field of the action element when the slot boundary synchronization between STAs in a BSS is weak (when synchronization is poor and the slot boundary difference between STAs is predicted / estimated to be large). In this case, the value indicated in the Slot Sync Budget field can be used to check whether the time at which each STA starts transmission has a certain tolerance with respect to the slot boundary. When performing simultaneous transmission, the STA MLD of the BSS must perform simultaneous transmission so that the time at which each STA starts transmission on each link has a time difference with the slot boundary used when performing the channel access procedure that does not exceed the tolerance range confirmed based on the value indicated in the Slot Sync Budget field.

[0295] <Simultaneous transmission method considering inter-link information exchange delay>

[0296] The above-described simultaneous transmission operation is based on the assumption that information related to the progress of the channel access procedure can be closely shared among multiple STAs included in the MLD. For example, the fact that a specific STA transmits at the time when another STA in the MLD completes its channel access procedure is based on the assumption that the specific STA knows parameters (e.g., the number of remaining backoff counters and slot boundaries) related to the channel access procedure of the other STA.

[0297] However, each STA in an MLD basically performs a channel access procedure independently on the link it operates, and the method for each STA to share information may not be defined. Therefore, whether STAs in an MLD can share parameters related to each other's channel access procedure in real time may vary depending on the implementation. In addition, the CCA performed by each STA every slot for channel access is information whose results should be updated every aSlotTime, and developers may have different views on whether this data needs to be exchanged every moment between each STA in an MLD.

[0298] That is, when considering the channel access procedure for simultaneous transmission, it must be kept in mind that there may be a certain level of delay before each STA in the MLD acquires information about each other's channel access procedure.

[0299] In this case, the method by which each STA in the MLD transmits simultaneously may be such that, as considered in one embodiment of the present invention described above, a STA that has reserved transmission after completing the backoff procedure 1) begins transmission at the time when it is predicted that other STAs in the MLD will complete the channel access procedure, or 2) begins transmission after confirming that other STAs in the MLD have completed the channel access procedure.

[0300] The simultaneous transmission operation corresponding to 1) has been described in the above-mentioned embodiment of the present invention, so a detailed description thereof will be omitted, and the simultaneous transmission operation corresponding to 2) will be described in more detail.

[0301] According to one embodiment of the present invention, an MLD attempting to perform simultaneous transmission may delay the channel access procedure of a specific STA even though the channel access procedure of the specific STA has been completed. In this case, the specific STA can start transmission after confirming that other STAs in the MLD have completed the channel access procedure. In this case, the other STAs may postpone the start of transmission for a specific time after the channel access procedure is completed, taking into account the in-device information processing delay (inter-link information exchange delay) required for the specific STA to obtain information that it has completed the channel access procedure. In this case, the specific time may be a value set taking into account the in-device information processing delay. In this case, the unit of the specific time may be us or a multiple of aSlotTime (1 aSlotTime or 2 aSlotTime).

[0302] FIG. 38 shows an example of a simultaneous transmission procedure taking into consideration inter-link information exchange delay according to an embodiment of the present invention.

[0303] Referring to Figure 38, the MLD is attempting to perform simultaneous transmission using STA1 and STA2. At this time, STA1 and STA2 perform independent channel access procedures, so the channel access procedures of STA1 and STA2 may be completed at different times. Referring to Figure 20, STA1 completes the channel access procedure (BO == 0) at time T1, but may postpone transmission of PPDU1 in order to perform simultaneous transmission with STA2.

[0304] Thereafter, STA2 completes the channel access procedure at time T2, and at time T2, STA1 may not be able to recognize that STA2 has completed the channel access procedure due to a delay in inter-link information exchange. Therefore, STA2 does not wait for STA1's channel access procedure, but rather may postpone its transmission until time T3 and then start transmitting PPDU2, taking into account the delay time (T_delay) required for information that STA2 has completed the channel access procedure being transmitted to STA1.

[0305] In this case, T3 may be a slot boundary time that appears after the link information exchange delay time based on the time (T2) when the STA2 completes the channel access procedure. In other words, the time difference between T3 and T2 may be greater than or equal to the link information exchange delay time. In this case, the time difference between T3 and T2 may be less than or equal to (link information exchange delay time + aSlotTime).

[0306] Thereafter, STA1 may start transmitting PPDU1 at its own slot boundary adjacent to T3 after receiving information that STA2 has completed the channel access procedure. In this case, the own slot boundary adjacent to T3 may be the first slot boundary after T3. Alternatively, STA1 may start transmitting PPDU1 at T3 after receiving information that STA2 has completed the channel access procedure.

[0307] As a result, both STA1 and STA2, which are transmitting simultaneously, do not need to transmit immediately even after their own channel access procedures are completed. First, a STA that has completed the channel access procedure can postpone its transmission until it confirms (through link-to-link information exchange) that the other STAs have completed the channel access procedure, and a STA that completes the channel access procedure later can postpone its transmission by taking into account the delay time until the other STAs that postponed transmission until it completed its channel access procedure obtain information that its own channel access procedure has been completed.

[0308] On the other hand, even when simultaneous transmission is performed taking into account the link information exchange delay, it is necessary to perform an operation taking into account the slot boundary time difference between the links performing simultaneous transmission, as considered in the above embodiment of the present invention. That is, when simultaneous transmission is performed taking into account the link information exchange delay, there is still a possibility that a transmission initiated from a specific link may interfere with the channel access procedure of another link. Therefore, even when an MLD performing simultaneous transmission performs simultaneous transmission taking into account the link information exchange delay, it must still follow the method provided in the above embodiment of the present invention to select a slot boundary.

[0309] However, when an MLD that performs simultaneous transmission considers the link information exchange delay, the STA that completes the channel access procedure first must start transmission according to its slot boundary, and the STA that completes the channel access procedure later must determine the slot boundary at which it will start transmission. In this case, the method for determining the slot boundary is the same as that described in the embodiment of Figure 34, and detailed description thereof will be omitted.

[0310] In addition, the same problem as described using Figure 35 (the problem of not being able to determine an appropriate slot boundary) may occur in simultaneous transmission taking into account interference between devices, and in this case, a STA that completes the channel access procedure later may be allowed to start transmission at a time different from its own slot boundary. In this case, the restrictions applied to transmission starting at a time different from the slot boundary may be the same as those described in the embodiment of Figure 36.

[0311] Figure 39 shows a simultaneous transmission method according to one embodiment of the present invention, in which an MLD STA that has completed a channel access procedure and has reserved the start of transmission begins transmission at a time different from its own slot boundary after recognizing that the channel access procedure of other STAs has been completed.

[0312] Referring to Figure 39, the MLD is attempting to perform simultaneous transmission using STA1 and STA2. At this time, STA1 and STA2 perform independent channel access procedures, so the channel access procedures of STA1 and STA2 may be completed at different times. Referring to Figure 20, STA1 completes the channel access procedure (BO == 0) at time T1, but may postpone transmission of PPDU1 in order to perform simultaneous transmission with STA2.

[0313] Thereafter, STA2 completes the channel access procedure at time T2, and at time T2, STA1 may not be able to recognize that STA2 has completed the channel access procedure due to a delay in inter-link information exchange. Therefore, STA2 does not wait for STA1's channel access procedure, but rather, it can postpone its transmission until time T3 and then start transmitting PPDU2, taking into account the delay time (T_delay) required for STA2 to transmit information that it has completed the channel access procedure to STA1.

[0314] In this case, T3 may be a slot boundary time that appears after the link information exchange delay time based on the time (T2) when STA2 completes the channel access procedure. In other words, the time difference between T3 and T2 may be greater than or equal to the link information exchange delay time. In this case, the time difference between T3 and T2 may be less than or equal to (link information exchange delay time + aSlotTime).

[0315] After receiving information that STA2 has completed the channel access procedure, STA1 can begin transmission at its own slot boundary (T4) (of the link) that occurs after T3. At this time, STA2 recognizes that STA1 will begin transmission at the slot boundary corresponding to T4, taking into account the link information exchange delay. If STA2 were to begin transmission at the slot boundary (T3+aSlotTime) that occurs after T3, it would recognize that its own transmission initiation would be interrupted by the transmission initiated by STA1. Furthermore, if STA2 were to begin transmission at the same slot boundary at time T3, it would recognize that its own transmission would prevent STA1 from performing simultaneous transmissions. Consequently, it recognizes that neither the slot boundary at time T3 nor a slot boundary that occurs after T3 can be used as the start point for simultaneous transmissions.

[0316] In this case, STA2 can start its transmission at a time different from its slot boundary within the limits allowed by the Slot Sync budget. The meaning and usage of the Slot Sync budget have been described in other embodiments of the present invention above, and detailed description thereof will be omitted.

[0317] As a result, STA2 can start its transmission at the time when STA1 performs Rx / TxTurnaround by adjusting the time when it starts transmission to the value of T3+slot Sync budget or T4.

[0318] FIG. 40 illustrates an example of how a multi-link device may transmit simultaneously over multiple links in accordance with one embodiment of the present invention.

[0319] 40, the non-AP MLD may perform a backoff procedure to perform simultaneous transmission over multiple links (S40010). The backoff procedure may be performed separately over the first link of the first STA and the second link of the second STA included in the non-AP MLD.

[0320] The backoff procedure on the first link is performed using a first backoff counter, and the backoff procedure on the second link is performed using a second backoff counter.

[0321] Thereafter, the non-AP MLD can simultaneously perform uplink transmission to the AP MLD via each of the first link and the second link (S40020).

[0322] In this case, when the first backoff counter and the second backoff counter both have the value '0', if the transmission time of the uplink transmission in the first link is the slot boundary of the first slot, which is the slot next to the slot in which the first backoff counter is '0', the uplink transmission in the second link may be performed within a certain time from the transmission time of the first link.

[0323] Specifically, since the slot settings for each link may be different, slot boundaries between links may not coincide. Therefore, slot boundaries between links may not coincide in each slot in which the backoff counter is decremented. Furthermore, when the backoff counters of each of the multiple links of the MLD reach "0" due to the backoff procedure through the above-described reservation operation, slot boundaries between each link may not coincide. Since slots for each link may be set independently, slot boundaries between each link may not coincide. Therefore, even if the backoff counters of each link all have a value of "0," the slot boundaries may differ from each other. In this case, simultaneous transmission may be performed according to the slot boundary of a specific link when the backoff counter of a specific link among the multiple links has a value of "0." That is, each link may not perform uplink transmission according to the slot boundary of the corresponding link, but may perform uplink transmission simultaneously by delaying or shortening the transmission time of the uplink transmission according to the slot boundary of the specific link.

[0324] For example, if an MLD multiple link is composed of a first link and a second link, and one of the first backoff counter of the first link and the second backoff counter of the second link reaches '0' before the other backoff counter, the slot boundaries of the first link and the second link may not coincide when the other backoff counter reaches '0'. In this case, the transmission time point of the uplink transmission of the second link can be adjusted by shortening or delaying it depending on the slot boundary of the slot in which the first backoff counter of the first link is '0' or the slot boundary of the first slot, which is the slot next to the slot.

[0325] In this case, the time of uplink transmission in the first link and the time of uplink transmission in the second link may be within a certain time period. For example, the time of uplink transmission in the second link may be within 4 us of the time of uplink transmission in the first link.

[0326] In this manner, uplink transmission can be performed simultaneously on the first and second links by performing uplink transmission at a time other than the slot boundary of the slot in which the second backoff counter of the second link is "0" or the slot boundary of the second slot, which is the next slot of the slot.

[0327] In this case, when the first backoff counter and the second backoff counter are both '0', the transmission time of the uplink transmission in the second link may be adjusted to be included within the certain time from the slot boundary of the first slot.

[0328] In this case, if the first backoff counter is '0' and the second backoff counter is '0', the slot boundaries of the first slot and the second slot, which is the next slot after the slot in which the second backoff counter of the second link is '0', do not coincide, and the slot boundary of the second slot may not be included within the certain time period.

[0329] Furthermore, if one of the first backoff counter and the second backoff counter reaches "0" before the remaining backoff counters, the link using the one backoff counter of the first link and the second link does not perform the uplink transmission and can maintain the one backoff counter at "0" until the remaining backoff counters reach "0".

[0330] That is, as described above, even if the channel access procedure is completed in one of the multiple links of the MLD and the back-off counter value reaches "0," if the back-off counter values ​​of the other links have not yet reached "0," the MLD STA can choose not to perform uplink transmission in that link and maintain the back-off counter value at "0." In other words, if the back-off counter value reaches "0" in a specific link, the MLD STA can choose not to perform uplink transmission and maintain the back-off counter value at "0" if the back-off counter values ​​of the other links of the MLD have not yet reached "0."

[0331] For example, an MLD multiple link may be configured with a first link and a second link, and a backoff procedure for a channel access in the first link may be performed by a first backoff counter, and a backoff procedure for a channel access in the second link may be performed by a second backoff counter, where the backoff procedure may be performed separately through each of the first and second links included in the multiple link.

[0332] In this case, when one of the first backoff counter and the second backoff counter reaches "0" before the other backoff counters, the specific link of the first link and the second link using the one backoff counter may not perform the uplink transmission, and the one backoff counter may maintain the value of "0" until the other backoff counters reach the value of "0". Alternatively, the one backoff counter may continue to maintain the value of "0" even after the other backoff counters reach the value of "0".

[0333] When one of the first backoff counter and the second backoff counter reaches '0' before the remaining backoff counter, if the slot boundaries of the first slot of the first link and the second slot, which is the next slot after the slot in which the second backoff counter of the second link is '0', do not coincide when the remaining backoff counter reaches '0', the transmission time of the uplink transmission on the second link may be adjusted to be before or after the slot boundary of the second slot so as to be included within the certain time from the slot boundary of the first slot.

[0334] In this case, if the slot boundary of the second slot is located earlier or later on the time axis than the slot boundary of the first slot, the transmission time of the second link may be delayed or shortened by a specific time from the slot boundary of the first slot.

[0335] In this case, the maximum value of the certain time is 4 us, and 4 us can represent the change time for performing the uplink transmission in the channel access procedure.

[0336] In addition, non-AP MLD can perform channel sensing up to the transmission time of the second link, and in this case, the transmission time of the second link may not coincide with the slot boundary of the second slot of the second link.

[0337] In this case, the uplink transmission may be performed in the slot following the slot in which the first backoff counter and the second backoff counter reach '0', and the first link and the second link may be an NSTR link pair that does not support simultaneous transmit and receive (STR).

[0338] In addition, non-AP MLD can perform sensing to determine whether the channels are idle on the first link and the second link, and the first backoff counter and the second backoff counter are decremented when the first link and the second link are idle, respectively.

[0339] The above description of the present invention is for illustrative purposes only, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. Therefore, the above-described embodiments should be understood to be illustrative in all respects and not restrictive. For example, each component described as a single component may be implemented in a distributed form, and similarly, each component described as a distributed component may be implemented in a combined form.

[0340] The scope of the present invention is indicated by the claims set forth below rather than by the above detailed description, and any modifications or variations derived from the meaning and scope of the claims and their equivalents should be interpreted as being included within the scope of the present invention. [Explanation of symbols]

[0341] 100 Stations 110 processors 120 Communications Department 140 User Interface Section 150 Display Unit 150 160 memory 200 AP 210 processors 220 Communications Department 260 memory

Claims

1. A non-AP (Access Point) multi-link device (MLD) for a wireless communication system, comprising: a communication module; a processor for controlling the communication module; The processor: performing a backoff procedure for uplink transmission through the non-AP MLD multiple links; The backoff procedure is performed individually through a first link of a first STA and a second link of a second STA included in the non-AP MLD, the backoff procedure on the first link is performed using a first backoff counter; the backoff procedure on the second link is performed using a second backoff counter; simultaneously performing the uplink transmission via each of the first link and the second link using AP MLD; When the first backoff counter and the second backoff counter both have the value of '0', if the transmission time of the uplink transmission in the first link is the slot boundary of the first slot, which is the slot next to the slot in which the first backoff counter is '0', the uplink transmission in the second link is performed within a certain time from the transmission time of the first link (non-AP MLD).

2. When the first backoff counter and the second backoff counter are both "0", The non-AP MLD of claim 1, wherein a transmission time point of the uplink transmission in the second link is adjusted to be included within the predetermined time from the slot boundary of the first slot.

3. If the first backoff counter is "0" and the second backoff counter is "0", the slot boundaries of the first slot and the second slot, which is the slot following the slot in which the second backoff counter of the second link is "0", do not coincide with each other; The non-AP MLD of claim 2 , wherein the slot boundary of the second slot is not included within the certain time period.

4. 2. The non-AP MLD of claim 1, wherein, when one of the first backoff counter and the second backoff counter reaches "0" before the remaining backoff counter, the link using the one backoff counter of the first link and the second link does not perform the uplink transmission, and maintains the one backoff counter at "0" until the remaining backoff counter reaches "0".

5. 2. The non-AP MLD of claim 1, wherein, when one of the first backoff counter and the second backoff counter reaches '0' before the other backoff counter, if a slot boundary of the first slot of the first link does not coincide with a slot boundary of a second slot that is a slot next to a slot in which the second backoff counter of the second link is '0' when the other backoff counter reaches '0', the transmission time point of the uplink transmission in the second link is adjusted to be before or after the slot boundary of the second slot so as to be included within the certain time from the slot boundary of the first slot.

6. 6. The non-AP MLD of claim 5, wherein when the slot boundary of the second slot is located earlier or later on a time axis than the slot boundary of the first slot, the transmission time of the second link is delayed or shortened by a specific time from the slot boundary of the first slot.

7. The non-AP MLD according to claim 6, wherein the maximum value of the certain time period is 4 us.

8. The non-AP MLD according to claim 7, wherein the 4 us is a change time for performing the uplink transmission in a channel access procedure.

9. The processor: performing channel sensing up to the time before the transmission of the second link; The non-AP MLD of claim 8 , wherein the transmission instant of a second link does not coincide with the slot boundary of the second slot of the second link.

10. The non-AP MLD according to claim 1, wherein the uplink transmission is performed in a slot following a slot in which the first backoff counter and the second backoff counter reach "0".

11. The non-AP MLD of claim 1, wherein the first link and the second link are a non-simultaneous transmit and receive (STR) link pair that does not support STR.

12. The processor: performing sensing to determine whether channels are idle on the first link and the second link; 2. The non-AP MLD of claim 1, wherein the first backoff counter and the second backoff counter are decremented when the first link and the second link are idle, respectively.

13. A method for performing uplink transmission in a non-AP (Access Point) multi-link device (MLD) in a wireless communication system, comprising: performing a backoff procedure for uplink transmission through the non-AP MLD multiple links; The backoff procedure is performed individually through a first link of a first STA and a second link of a second STA included in the non-AP MLD, the backoff procedure on the first link is performed using a first backoff counter; the backoff procedure on the second link is performed using a second backoff counter; simultaneously performing the uplink transmission via each of the first link and the second link using AP MLD; A method in which, when the first backoff counter and the second backoff counter both have the value '0', if the transmission time of the uplink transmission on the first link is the slot boundary of the first slot, which is the slot next to the slot in which the first backoff counter is '0', the uplink transmission on the second link is performed within a certain time from the transmission time of the first link.

14. When the first backoff counter and the second backoff counter are both "0", The method of claim 13 , wherein a transmission time point of the uplink transmission in the second link is adjusted to fall within the certain time from the slot boundary of the first slot.

15. If the first backoff counter is "0" and the second backoff counter is "0", the slot boundaries of the first slot and the second slot, which is the slot following the slot in which the second backoff counter of the second link is "0", do not coincide with each other; The method of claim 14 , wherein the slot boundary of the second slot is not included within the fixed period of time.

16. 14. The method of claim 13, wherein, when one of the first backoff counter and the second backoff counter reaches "0" before the remaining backoff counter, the link using the one backoff counter of the first link and the second link does not perform the uplink transmission and maintains the one backoff counter at "0" until the remaining backoff counter reaches "0".

17. 14. The method of claim 13, wherein, when one of the first backoff counter and the second backoff counter reaches '0' before the other backoff counter, if the slot boundaries of the first slot of the first link and the second slot, which is the next slot after the slot in which the second backoff counter of the second link is '0', do not coincide when the other backoff counter reaches '0', the transmission time point of the uplink transmission in the second link is adjusted to be before or after the slot boundary of the second slot so as to be included within the certain time from the slot boundary of the first slot.

18. 18. The method of claim 17, wherein when the slot boundary of the second slot is located earlier or later on the time axis than the slot boundary of the first slot, the transmission time point of the second link is delayed or shortened by a specific time from the slot boundary of the first slot.

19. The method of claim 18, wherein the maximum value of the fixed time period is 4 us.

20. 20. The method of claim 19, wherein the 4 us is a change time for performing the uplink transmission in a channel access procedure.

21. further comprising performing channel sensing before the transmission time of the second link; 21. The method of claim 20, wherein the transmission instant of a second link does not coincide with the slot boundary of the second slot of the second link.

22. The method of claim 13 , wherein the uplink transmission occurs in a slot following a slot in which the first backoff counter and the second backoff counter reach “0”.

23. 14. The method of claim 13, wherein the first link and the second link are a non-simultaneous transmit and receive (STR) link pair that does not support STR.

24. performing sensing to determine whether channels are idle in the first link and the second link; 14. The method of claim 13, wherein the first backoff counter and the second backoff counter are decremented when the first link and the second link, respectively, are idle.

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