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 use of mobile devices has become more widespread, wireless LAN technology that can provide them with high-speed wireless Internet services has been attracting attention. Wireless LAN technology is a technology that enables mobile devices such as smartphones, smart pads, laptop PCs, portable multimedia players, embedded devices, etc. to wirelessly connect to the Internet at home, in business, or in specific service areas based on short-distance wireless communication technology.

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

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

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

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

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

[0008] An object of one embodiment of the present invention is to provide a wireless communication method using 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 allowing 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 transmitting uplinks when the slot boundaries of each link are different when simultaneously transmitting uplinks via multiple links.

[0012] The technical problem to be achieved in the specification is not limited to the technical problem mentioned above, and other technical problems not mentioned will be clearly understood by a person having ordinary skill 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, the backoff procedure being performed individually 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 is 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, which is the slot next to a 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.

[0016] Furthermore, in the present invention, 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".

[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] Also, 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 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 period of time is 4 us.

[0020] Also, in the present invention, the 4 us is a change time for performing the uplink transmission in a 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 a 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 performing 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 the first backoff counter and the second backoff counter both 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. Effect of the Invention

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

[0027] Also, 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, there is provided a wireless communication terminal that simultaneously performs 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.

[0029] In addition, according to an embodiment of the present invention, when performing uplink transmission simultaneously using multiple links, if the slot boundaries for 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 description of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Diagram 2] FIG. 11 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing a configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram showing the configuration of an access point according to an embodiment of the present invention. [Diagram 5] 1 is a diagram illustrating a process in which a STA sets up a link with an AP. [Figure 6]FIG. 1 is a diagram illustrating a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7] FIG. 1 is a diagram showing an example of various standard generation PPDU (PLCP Protocol Data Unit) formats. [Figure 8] 1A to 1C are diagrams illustrating examples 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. [Figure 9] FIG. 1 illustrates an example of a multi-link device according to an embodiment of the present invention. [Figure 10] FIG. 13 is a diagram illustrating 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. [Figure 11] 13 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] 11 is a diagram illustrating a multi-link device postponing transmission on one of the links when the multi-link device has first succeeded in channel access in accordance with an embodiment of the present invention; [Figure 13] FIG. 11 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. 11 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]FIG. 11 is a diagram illustrating operations in multiple multi-link devices when the multiple multi-link devices postpone 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. [Figure 16] FIG. 13 is a diagram illustrating the operation of a multilink device according to an embodiment of the present invention when the multilink device postpones transmission on the first link after first successfully accessing the channel on the first link and the channel on the first link is detected as being occupied (busy). [Figure 17] FIG. 13 is a diagram illustrating the operation of a multilink device according to an embodiment of the present invention when the multilink device postpones transmission on the first link after first successfully accessing the channel on the first link and the channel on the first link is detected as being occupied (busy). [Figure 18] 13 is a diagram showing that 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] 4 is a diagram illustrating an operation method when a station in a multilink device according to an embodiment of the present invention detects that a channel is busy during transmission. [Figure 20] 4 is a diagram illustrating an operation method when a station in a multilink device according to an embodiment of the present invention detects that a channel is busy during transmission. [Figure 21] 11 is a diagram illustrating 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 a channel is busy during a transmission delay. [Figure 22] FIG. 11 is a diagram showing 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; [Diagram 23] 1 illustrates an operation of the multilink when a station in the multilink apparatus according to an embodiment of the present invention is delaying transmission and the channel for which transmission is being delayed is sensed as being occupied (busy). [Figure 24]1 illustrates an operation of the multilink when a station in the multilink apparatus according to an embodiment of the present invention is delaying transmission and the channel for which transmission is being delayed is sensed as being occupied (busy). [Diagram 25] FIG. 2 illustrates an EDCA queue used when applying EDCA according to an embodiment of the present invention. [Figure 26] 2 illustrates a method for performing channel access based on slot boundaries according to an embodiment of the present invention. [Figure 27] FIG. 13 is a diagram showing an operation of a multilink device performing synchronized transmission by EDCAF operation according to an embodiment of the present invention. [Figure 28] FIG. 13 is a diagram showing an operation of a multilink device performing synchronized transmission by EDCAF operation according to an embodiment of the present invention. [Figure 29] FIG. 13 is a diagram showing an operation of a multilink device performing synchronized transmission by EDCAF operation according to yet another embodiment of the present invention. [Diagram 30] 1 is a diagram illustrating an embodiment in which an MLD performs PPDU transmission simultaneously on two links by delaying a channel access procedure for a specific channel according to an embodiment of the present invention. [Diagram 31] 1 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. [Diagram 32] 11 is a diagram showing an example of a failure in simultaneous transmission of MLD that may occur when there is no clear provision for the start time of simultaneous transmission according to an embodiment of the present invention. FIG. [Diagram 33] This figure shows an embodiment of the present invention in which, when STAs of an MLD start transmission in accordance with different slot boundaries, the transmission that starts earlier does not affect the CCA results of other STAs (the same MLD operated on other links). [Diagram 34] 13 is a diagram illustrating an embodiment of a method for determining a time to start transmission on each link based on a slot boundary time difference between links for which an MLD is to perform simultaneous transmission according to an embodiment of the present invention. [Diagram 35]FIG. 13 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. [Diagram 36] This figure shows an embodiment of a simultaneous transmission method 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] A figure showing one embodiment of signaling that can be used when an AP MLD indicates a Slot Sync Budget available in a BSS using an operation element according to an embodiment of the present invention. [Figure 38] FIG. 11 is a diagram showing an example of a simultaneous transmission procedure taking into account 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. [Diagram 40] 2 illustrates an example of a method for a multi-link device to perform simultaneous transmission over multiple links according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The terms used in this specification are selected as general terms that are currently widely used as much as possible in consideration of the functions of the present invention, but this may vary depending on the intentions, customs, or the emergence of new technologies of the engineers in the relevant technical field. In addition, in certain cases, the applicant may arbitrarily select terms, and in such cases, the meanings of the terms will be described in the description of the relevant invention. Therefore, it is clear that the terms used in this specification should be interpreted not simply as terms, but based on the substantial meanings of the terms and the contents of this specification as a whole.

[0033] Throughout the specification, when a certain component is "connected" to another component, this includes not only when it is "directly connected" to another component, but also when it is "electrically connected" with another component therebetween. Furthermore, when a certain component "includes" a certain component, this means that it may further include the other component, not excluding the other component, unless otherwise specified. In addition, limitations such as "greater than" or "less than" based on a specific critical value may be appropriately replaced with "more than" or "less than", 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 (BSS), which are a set of devices that can successfully synchronize and communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

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

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

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

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

[0040] 2 is a diagram showing an independent BSS, which is a wireless LAN system according to another embodiment of the present invention, in which the same or corresponding parts in the embodiment of FIG. 2 are the same as or correspond to the embodiment of FIG.

[0041] BSS3 shown in Figure 2 is an independent BSS and does not include an AP, so all stations (STA6, STA7) are not connected to an AP. An independent BSS is not allowed to connect to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) is directly connected to each other.

[0042] 3 is a block diagram showing a configuration of a station 100 according to an embodiment of the present invention. As shown in the figure, the station 100 according to the embodiment of the present invention includes a processor 110, a communication unit 120, a user interface unit 140, a display unit 150, and a memory 160.

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

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

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

[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 transmission and reception of data between the units. According to an embodiment of the present invention, the processor 110 executes a program for connection to an AP stored in the memory 160 and receives a communication setup message transmitted by the AP. The processor 110 also reads information on the priority conditions of the station 100 included in the communication setup message and requests a connection to the AP based on the information on the priority conditions of the station 100. The processor 110 of the present invention may refer to a main control unit of the station 100, or may refer to a control unit for individually controlling some components of the station 100, for example, the communication unit 120, depending on the embodiment. That is, the processor 110 may be a modem that modulates and demodulates a wireless signal transmitted and received from the communication unit 120, or a modulator and / or demodulator. The processor 110 controls various operations of transmitting and receiving wireless signals of the station 100 according to an embodiment of the present invention. A detailed embodiment of the present invention will be described later.

[0047] The station 100 shown in FIG. 3 is a block diagram according to an embodiment of the present invention, and the separate blocks are used to logically distinguish between elements of the device. Thus, the above-mentioned device elements may be mounted on one chip or multiple chips depending on the design of the device. For example, the processor 110 and the communication unit 120 may be integrated and embodied on one chip, or may be embodied on separate chips. In addition, in an embodiment of the present invention, some components of the station 100, such as the user interface unit 140 and the display unit 150, may be selectively provided in the station 100.

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

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

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

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

[0052] 5, the link between the STA 100 and the AP 200 is set up through three steps: scanning, authentication, and association. First, the scanning step is a step in which the STA 100 acquires connection information of the BSS operated by the AP 200. There are two methods for performing scanning: a passive scanning method in which the AP 200 acquires information only by using a beacon message S101 periodically transmitted by the AP, 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 has successfully received wireless connection information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200 (S107b), and performs an authentication step. After the authentication step is performed, the STA 100 transmits an association request (S109a), receives an association response from the AP 200, and performs an association step (S109b). In this specification, association basically means wireless association, but the present invention is not limited thereto, and association in a broad sense includes both wireless association and wired association.

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

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

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

[0058] If a specific terminal succeeds in accessing the channel, the terminal transmits data through the channel. However, if the terminal attempting access collides with another terminal, the colliding terminals are assigned new random numbers and perform a backoff procedure again. According to one embodiment, the random numbers newly assigned to each terminal are determined within a range (2*CW) twice the range of the random numbers previously assigned to the terminal (contention window, CW). Meanwhile, each terminal attempts access by performing a backoff procedure again in the next contention window period, and at this time, each terminal performs the backoff procedure from the slot time remaining in the previous contention window period. In this manner, each terminal performing wireless LAN communication can avoid collision with each other on a specific channel.

[0059] Hereinafter, in the present invention, a terminal can be called a non-AP STA, an AP STA, an AP, an STA, a receiving device, or a transmitting device, and the present invention is not limited thereto. Also, in the present invention, an AP STA can be called an AP.

[0060] <Examples of various PPDU formats>

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

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

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

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

[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 speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which is a combination of a modulation method such as BPSK / QPSK / 16-QAM / 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The total length of the PPDU can be indicated by combining the information in the L_RATE field and the L_LENGTH field. In the non-legacy PPDU format, the L_RATE field is set to the minimum speed of 6 Mbps.

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

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

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

[0076] The VI bit will maintain the current bit configuration, and even if a subsequent generation PPDU is defined, a current 11be terminal can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field is composed of PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits, and serves to sequentially distinguish 11be and subsequent generation WLAN standards by version. 11be has a value of 000b. The UL / DL field distinguishes whether the corresponding PPDU is an uplink / downlink PPDU. The BSS color means a BSS-specific identifier defined in 11ax, and has a value of 6 bits or more. The TXOP means a transmit opportunity duration that was transmitted in the MAC header, but by adding it to the PHY header, the length of the TXOP containing the corresponding PPDU can be inferred without decoding the MPDU, and has a value of 7 bits or more.

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

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

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

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

[0081] In the case of a SU PPDU, a plurality of RUs may be allocated to a STA, and the plurality of 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 if it recognizes the punctured RUs in between. Therefore, the AP can transmit the SU PPDU including information on the punctured RUs among the RUs allocated to the STA (e.g., the puncturing pattern of the RUs, etc.). That is, in the case of a SU PPDU, a puncturing mode field including information indicating whether a puncturing mode is applied and the puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field may signal the type of discontinuous channels that appear within the bandwidth.

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

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

[0084] The present 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 puncturing types of the primary 160 MHz and secondary 160 MHz in the 320 MHz BW configuration of the SU PPDU.

[0085] In addition, in one embodiment of the present invention, a method is proposed in which the configuration of the PPDU indicated by the preamble puncturing BW value is changed according to the PPDU format signaled in the PPDU format field. Assuming that the length of the BW field is 4 bits, in the case of an EHT SU PPDU or TB PPDU, one symbol of EHT-SIG-A may be further signaled after the U-SIG, or EHT-SIG-A may not be signaled at all. Taking this into consideration, it is necessary to signal up to 11 puncturing modes using only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, since an EHT-SIG-B is further signaled after the U-SIG, up to 11 puncturing modes may be signaled in a different manner from the SU PPDU. In the case of an EHT ER PPDU, the BW field is set to 1 bit, and it is possible to signal whether the PPDU uses a bandwidth of 20 MHz or 10 MHz.

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

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

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

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

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

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

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

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

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

[0098] FIG. 9 is a diagram showing 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 yet another embodiment, according to an embodiment of the present invention, a device to which more than one STA is affiliated can be defined. In this case, the device can be a logical concept. Therefore, such a concept of a device to which one or more STAs are affiliated can be called 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), and the MLD may have one MAC medium access control service access point (SAP) to a logical link control (LLC), and the 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 of different frequency bands such as 2.4 GHz, 5 GHz, and 6 GHz. As a result, MLD can obtain gains in channel access and improve the performance of the entire network. While the existing wireless LAN operates on a single link, MLD operation can obtain more channel access opportunities using multiple links, or STA can operate efficiently on multiple links taking into account channel conditions.

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

[0103] Referring to Fig. 9, there may be an MLD including multiple STAs, and the multiple STAs included in the MLD can operate on multiple links. In Fig. 9, the MLD including AP1, AP2, and AP3 that are APs can be called an AP MLD, and the MLD including non-AP STA1, non-AP STA2, and non-AP STA3 that are non-AP STAs can be called a non-AP MLD. The STAs included in the MLD can operate on Link 1, Link 2, Link 3, or some of the 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 an association performed in a single-link operation. In order to exchange frames in the multi-link, the multi-link setup should be preceded. 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 multi-link, and the capability information may include information related to whether a STA included in the MLD can receive a frame in one link and another STA included in the MLD can transmit a frame in another link at the same time. 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 a link included in the MLD. In addition, the capability information may further include information regarding an available link or an operating channel. The multi-link configuration may be established through negotiation between peer STAs, and multi-link operation may be established through a single link.

[0105] According to an embodiment of the present invention, a mapping relationship may exist between TIDs and MLD links. For example, when a TID and a link are mapped, the TID may be transmitted through the mapped link. The mapping between TIDs and links may be directional-based. For example, mapping may be performed for each of both directions between MLD1 and MLD2. Also, the mapping between TIDs and links may have a default setting. For example, the mapping between TIDs and links 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 FIG. 10, Link1 and Link2 are 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 lattices. 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. Also, MLD#2 is an MLD having STA2-1 and STA2-2, and the STA2-1 and STA2-2 operate on Link1 and Link2, respectively. At this time, the links used by STAx-1 and STAx-2 belonging to each MLD#1 and MLD#2 are Link1 and Link2, respectively, which 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 the MLD#1 transmits via Link 1, STA1-2 can successfully decode a packet received via Link 2, but when STA2-1 of the MLD#2 transmits via Link 1, relatively strong interference occurs on Link 2, which may hinder the decoding of STA2-2. Therefore, whether STR is possible between STAs in a single MLD may differ depending on the MLD.

[0108] In order 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 the AP in the AP MLD and whether STR is supported between the STA 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 embodiment, the STR support element may indicate whether STR is supported between STAs and APs in the MLD with one bit each. 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. Meanwhile, one bit may be set to 0 to indicate that STR is not supported between STA2 and STA3, and another bit may be set to 1 to indicate that STR is supported between STA1 and STA3. As a result, the STR support element may signal whether STR is supported between STA1 and STA2, between STA2 and STA3, and between STA1 and STA3 with 101 using a total of three bits. In this case, if the Link1 used by STA1 is 2.4 GHz, the STA1 may assume that STR is always supported in relation to other STAs in the STA MLD, and therefore only whether STR is supported by STA2 and STA3 may be signaled with one bit (or may always be indicated with one bit when there are two STAs in the STA MLD).

[0110] As described above, whether STR is supported depends on the frequency separation distance of each link, so when the AP MLD changes the center frequency of each link or the operation BW of each link, the STA MLD associated with the AP MLD may change whether STA supports STR. Therefore, when the AP MLD changes the operation BW or center frequency of a part or the entire link, 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 by a request and a 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, when STR support is not possible between the internal 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. At this time, the link change request may be transmitted to the AP MLD through the link that the STA MLD requests to change, or may be transmitted from the AP MLD through another STA (another link) in the same STA MLD. At this time, the link change request transmitted through the other link may include information on the link to be changed (such as a link number). At this time, the meaning of link change used in this embodiment may be interpreted as a change of operating channel within 2.4, 5, and 6 GHz, rather than a frequency movement between 2.4, 5, and 6 GHz bands.

[0112] The link change request may also include information about how to change the link. As an example, the link change request may indicate that the center frequency of the link should be moved to a higher frequency or a lower frequency. Or, the link change request may implicitly indicate that the center frequency of the link should be changed in a direction away from the adjacent link. 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 frequency or a higher frequency.

[0113] An AP that receives the link change request from a STA MLD can either accept the STA's request and change the link for which the change request was received (center frequency or 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 described above, the STAs operated by a specific MLD may support STR depending on the relationship (e.g., distance) between the links operated by the STAs. If STA1 and STA2 operated by a specific MLD are operated on Link1 and Link2, which are link pairs that do not support STR, respectively, the operations of the STA1 and STA2 are restricted by the operation state of each other. To explain in more detail, while the STA1 is transmitting PPDU through Link1, the STA2 may not be able to properly decode a packet received through Link2 due to the in-device interference caused by the transmission of the STA1 through Link1. In this way, when the STAs operated on a specific link pair are hindered in receiving operation due to the 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 as 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 embodiment in which a PPDU transmission performed by a specific STA in a non-STR MLD interferes with a channel access operation 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, the 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 Fig. 11, the CCA operation of STA1 performing the backoff procedure on Link1 may be disturbed by the interference occurring when STA2 transmits a PPDU on Link2. In other words, the 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, and as a result, STA1 performing the backoff procedure on Link1 may determine that Link1 is BUSY. As a result, STA1 may not be able to complete the backoff procedure because it mistakenly determines that Link1 is BUSY at the time when STA2 transmits a PPDU, even though there is no other device occupying Link1.

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

[0121] In this way, when a STA of a non-STR MLD goes into the BLIND state, the MLD cannot receive packets through the BLIND STA, nor can it perform independent channel access (for transmission), and therefore cannot obtain any gain 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 going into 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] Then, 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, and as a result, transmission may be performed simultaneously on the specific link and another link other than the specific link. For this purpose, a mechanism for delaying the channel access procedure rather than starting transmission immediately after the channel access procedure is completed may be allowed in the MLD. In this case, the mechanism for delaying the channel access procedure may allow transmission to be reserved while maintaining a backoff counter (BO) at 0.

[0124] That is, 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 reached "0", the MLD STA can maintain the back-off counter value at "0" without performing uplink transmission in that link. In other words, if the back-off counter value reaches "0" in a specific link, the MLD STA can select to maintain the back-off counter value at "0" without performing uplink transmission if the back-off counter values ​​of the other links of the MLD have not reached "0".

[0125] For example, a multiple link of the MLD may be composed of a first link and a second link, a back-off procedure for a channel connection in the first link may be performed by a first back-off counter, and a back-off procedure for a channel connection in the second link may be performed by a second back-off counter, in which case the back-off procedure may be performed separately through each of the first link and the second link included in the multiple link.

[0126] In this case, when one of the first backoff counter and the second backoff counter reaches "0" before the remaining 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 remaining backoff counters reach the value of "0". Alternatively, the one backoff counter may continue to maintain the value of "0" even after the remaining backoff counters reach the value of "0".

[0127] In this case, the time when the specific link and the other link other than the specific link are simultaneously transmitted may be a slot boundary (slot boundary) at which the channel access procedure is completed at the other link other than the specific link, or the slot next to the slot at which the channel access procedure is completed at the other link. Alternatively, the time when the specific link and the other link other than the specific link are simultaneously transmitted may be a specific slot boundary after the channel access procedure is completed at 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 the channel access procedure is completed at the other link.

[0128] That is, the slot setting in each link may be different, and the boundaries of the slots between the links may not coincide. Therefore, the boundaries of the slots between the links may not coincide in each slot in which the back-off counter is decreased, and when the back-off counters in the back-off procedure reach "0" in each of the multiple links of the MLD by the above-mentioned reservation operation, the slot boundaries in each link may not coincide. Since the slots in each link may be set individually, the slot boundaries in each link may not coincide. Therefore, even if the back-off counters in each link all have the value "0", the slot boundaries may be different from each other. In this case, the simultaneous transmission may be performed according to the slot boundary of a specific link when the back-off counter value of a specific link among the multiple links is "0". That is, each link does not perform uplink transmission according to the slot boundary of the link, but can 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, 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 remaining backoff counter, the slot boundaries of the first link and the second link may not coincide when the remaining backoff counter reaches '0.' In this case, the transmission time point of the uplink transmission in the second link may be adjusted by shortening or delaying depending on the slot boundary of the slot where the first backoff counter of the first link is '0' or the slot boundary of the first slot which is the next slot of 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 transmissions can be performed simultaneously on the first and second links by performing uplink transmissions at other times 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 a case where transmission is performed on each link within a certain period of time.

[0133] An operation of a multilink device accessing a channel with 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 the multi-link device according to the embodiment of the present invention has successfully accessed a channel in any one of the links first, the multi-link device postpones transmission in that link.

[0135] For ease of explanation, it is assumed that a first station of a multi-link device operates on a first link and a second station operates on a second link. In this case, if the second station succeeds in channel access and the first station does not succeed in channel access, the second station can wait until the first station succeeds in channel access while maintaining a back-off counter value of 0. When the first station succeeds in channel access, the first station and the second station can start synchronized transmission. The synchronized transmission may be a transmission whose transmission start time is within a pre-specified time. The second station can perform channel sensing while maintaining the back-off counter value. In this case, the channel sensing may include at least one of energy detection (ED), preamble detection (PD), and NAV (network allocation vector) confirmation. The second station can start synchronized transmission when the first station succeeds in channel access 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) through a first link (Link1). A second station (STA2) is connected to a second AP (AP) through a second link (Link2). The second station (STA2) succeeds in channel access first, and the second station (STA2) does not transmit while maintaining the back-off counter value at 0 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 in an occupied (busy) state. At this time, 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 sensed as being 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 sensed as being occupied (busy) while the first station delays transmission, the first station may acquire a new back-off counter and perform a channel access procedure. At this time, if the first station succeeds in channel access, the first station may perform unsynchronized transmission. In a specific embodiment, the first station may perform channel sensing with the newly acquired back-off counter x slot duration. That is, an operation of sensing whether the channel is idle during AIFS in general channel access may be omitted. In yet another specific embodiment, if the channel is idle during AIFS as in general channel access, the first station may perform channel sensing with the newly acquired back-off counter x slot duration. As described above, when the second station acquires a new back-off counter, the first station may maintain the size of the CW previously used by the first station. At this time, the second station continues to perform the channel access procedure.

[0140] In the embodiment of FIG. 13, a first station (STA1) of a multi-link device is connected to a first AP (AP1) through a first link (Link1). A second station (STA2) is connected to a second AP (AP) through a second link (Link2). The first station (STA1) first succeeds in channel access, and the first station (STA1) does not transmit while maintaining the back-off counter value at 0 until the second station (STA2) succeeds in channel access. At this time, the channel of the second link is sensed as being occupied (busy). The first station (STA1) acquires a new back-off counter and performs channel sensing in the slots of the back-off counter only. When the first station (STA1) succeeds in channel access, the first station (STA2) starts 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 sensed as being 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 busy 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) through a first link (Link1). A second station (STA2) is connected to a second AP (AP) through a second link (Link2). The first station (STA1) first succeeds in channel access, and the first station (STA1) does not transmit while maintaining the back-off counter value at 0 until the second station (STA2) succeeds in channel access. At this time, the channel of the second link is sensed as being occupied (busy). The first station (STA1) performs channel sensing and delays transmission until the second station (STA2) succeeds in channel access. When the second station (STA2) succeeds in channel access, the first station (STA2) starts unsynchronized transmission.

[0144] In the embodiment described in FIG. 13 and FIG. 14, the first station can determine whether to perform synchronized transmission based on the duration of time that the channel of the second link maintains an occupied state. For example, if the duration of time that the channel of the second link maintains an occupied state is greater than a pre-specified value, the first station can perform unsynchronized transmission. At this time, the first station can obtain a new back-off counter and perform channel access based on the obtained back-off 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 pre-specified value, the first station can perform synchronized transmission. The first station can delay transmission until the second station succeeds in channel access. At this time, the first station can perform channel sensing until the second station succeeds in channel access.

[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 described 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 the multiple multilink devices have first successfully accessed the channel on the first link.

[0148] When a plurality of multilink devices all operate on a first link and a 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 embodiment of Fig. 15, a first multilink device (STA MLD1) and a second multilink device (STA MLD2) both operate on a first link (Link1) and a 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 successfully access the channel on the first link (Link1), and transmission collision occurs on both the first link (Link1) and the second link (Link2).

[0150] The operation of a multilink unit when one of its links is sensed as occupied while the multilink unit 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 sensed as being busy while the first station is delaying transmission, the first station may obtain a new backoff counter and perform a channel access procedure, at which time the first station may maintain the value of the CW as the previously used CW value.

[0153] While the first station delays transmission, the second station may successfully access the channel when the channel accessed by the first station is sensed as being busy. 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 FIG. 16 and FIG. 17, a first station (STA1) of a multi-link device is connected to a first AP (AP1) through a first link (Link1). A second station (STA2) is connected to a second AP (AP) through a second link (Link2). The first station (STA1) succeeds in channel access first, and the first station (STA1) delays transmission. At this time, the first station (STA1) determines that the channel of the first link (Link1) is occupied. The first station (STA1) obtains a new back-off counter and performs channel access. In the embodiment of FIG. 17, the second station (STA2) succeeds in channel access first, and delays transmission until the first station (STA1) succeeds in channel access. When the first station (STA1) succeeds in channel access, the first station (STA1) and the second station (STA2) start synchronized transmission. In the embodiment of FIG. 17, a second station (STA2) successfully accesses the channel first and performs unsynchronized transmission without delaying transmission.

[0155] As in the above embodiment, in order to perform synchronized transmission, the channels of different links must be successfully accessed and idle at the same time. Therefore, the time at which the multilink device can perform synchronized transmission is limited, and the transmission of the multilink device may be excessively delayed. This will be described with reference to FIG. 19.

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

[0157] A first station (STA1) of a multi-link device is connected to a first AP (AP1) through a first link (Link1). A second station (STA2) is connected to a second AP (AP) through a second link (Link2). The first station (STA1) succeeds in channel access first, and so the first station (STA1) delays transmission. Before the second station (STA2) succeeds in channel access, the first station (STA1) senses that the channel of the first link (Link1) is occupied (busy). Therefore, the first station (STA1) acquires a new back-off counter and starts the channel access procedure again. The second station (STA2) succeeds in channel access, but delays transmission while the first station (STA1) is accessing the channel. Before the first station (STA1) succeeds in channel access, 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) have successfully accessed the channel but have not transmitted.

[0158] In this way, if the transmission delay and the channel access procedure are repeated unconditionally, 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 a method of operation when a station in a multilink system according to an embodiment of the present invention detects that a channel is busy during transmission.

[0160] During the transmission delay, a station of the multilink device may sense that the channel is occupied. At this time, when the station determines that the channel is idle again, it can determine whether to start the channel access procedure again according to the channel access state of the other stations of the multilink device. Specifically, when the station determines that the channel is idle again, it can determine whether to obtain a new back-off counter and perform channel access according to the channel access state of the other stations of the multilink device. When the first station determines that the channel is idle again, if the back-off 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 obtain a new back-off counter and perform the channel access procedure.

[0161] In this case, the station may determine that the channel is idle if it is detected as being idle continuously for a pre-specified time period. The pre-specified time period may be an AIFS. In another specific embodiment, the pre-specified time period may be a time period excluding a receive / transmit conversion time required in the AIFS.

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

[0163] In the embodiment 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 the process of delaying transmission. Therefore, the first station (STA1) obtains a new backoff counter and performs channel access. 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 illustrates a method for acquiring a new back-off counter value when a station in a multi-link apparatus according to an embodiment of the present invention senses that the channel is busy during a transmission delay.

[0165] In the above embodiment, when a station of a multilink device senses that the channel is busy during transmission and then acquires a back-off 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 the previously used CW value. In yet another specific embodiment, the station can set the CW value to a floor value of 1 / 2 the previously used CW value. Immediately after a successful channel access procedure using the newly acquired back-off 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 value of CW to the value of CW before adjustment x 2 - 1. That is, the station can set the value of CW to the value of CW before the transmission delay x 2 - 1.

[0167] In the embodiment of FIG. 21, a first station (STA1) is connected to a first AP (AP1) through a first link (Link1). A second station (STA2) is connected to a second AP (AP) through a second link (Link2). The first station (STA1) succeeds in channel access first, and the first station (STA1) delays transmission. Before the second station (STA2) succeeds in channel access, the first station (STA1) senses that the channel of the first link (Link1) is occupied (busy). The first station (STA1) sets the CW to 1 / 2 the value of the CW previously used to obtain a new backoff counter value. After the second station (STA2) succeeds in channel access, when the first station (STA1) succeeds in channel access again, the first station (STA1) and the second station (STA2) perform synchronized transmission.

[0168] FIG. 22 shows an operation of determining whether or not to perform synchronized transmission while a station in a multilink apparatus according to an embodiment of the present invention is delaying transmission.

[0169] For convenience of explanation, it is assumed that a first station of the multilink device operates in a first link, and a second station of the multilink device operates in a second link. When the second station succeeds in channel access 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 is continuously idle for a pre-specified interval until the second station succeeds in channel access. Specifically, when the channel of the first link is continuously idle for a pre-specified interval until the second station succeeds in channel access, the first station can perform synchronized transmission with the second station. In this case, the pre-specified interval may be a DIFS. Also, the pre-specified interval may be a PIFS. Also, the pre-specified interval 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 embodiment of FIG. 22, a first station (STA1) is connected to a first AP (AP1) through a first link (Link1). A second station (STA2) is connected to a second AP (AP) through a second link (Link2). The second station (STA2) first succeeds in channel access, and the second station (STA2) delays transmission. Before the first station (STA1) succeeds in channel access, 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 to be occupied (busy), the second station (STA2) continues to maintain the transmission delay. When the first station (STA1) succeeds in channel access, 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 transmission.

[0171] 23 and 24 show 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 sensed 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 back-off 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 to obtain the back-off counter. In yet another specific embodiment, the first station can obtain a new back-off 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 to obtain the back-off 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) succeeds in channel access first, 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 continuously in AIFS.

[0174] In the embodiment of Figure 23, the first station (STA1) obtains a new backoff counter and performs channel access. The second station (STA2) delays transmission. Then, when the first station (STA1) succeeds in channel access, it senses that the channel of the second link (Link2) is continuously idle in AIFS. Therefore, the first station (STA1) and the second station (STA2) perform synchronized transmission.

[0175] In the embodiment of Figure 24, the second station (STA2) obtains a new backoff counter and performs channel access. The first station (STA1) delays transmission. Then, when the second station (STA2) succeeds in channel access, the channel of the first link (Link1) is sensed as being idle continuously in AIFS. Therefore, the first station (STA1) and the second station (STA2) perform synchronized transmission.

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

[0177] FIG. 25 illustrates 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 according to the priority of traffic to be transmitted. The priority of traffic may be determined according to the type of traffic or a Traffic ID (TID). The priority of 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 priority order may be AC_VO, AC_VI, AC_BE, and AC_BK. 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 one slot time, which is a unit used when a station performs a backoff operation for frame transmission. When 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 a 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. FIG. 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 occupancy state occurs due to a frame transmitted by another terminal and no frame reception error state occurs, if the channel state is in the channel idle state for AIFSN[AC]*SlotTime-aRxTxTurnaroundTime after the SIFS time following the completion of the occupancy 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, or when a frame reception error occurs, the time (EIFS-DIFS+AIFSN[AC]*aSlotTime+aSIFSTime-aRxTxTurnaroundTime) from the time when the channel occupancy state due to physical detection is completed and the channel state is a channel idle state has elapsed.

[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 times:

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

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

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

[0195] When the channel state is in the channel idle state for AIFSN[AC]*aSlotTime+aSIFSTime-aRxTxTurnaroundTime after any channel occupancy time that does not satisfy 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 4us.

[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 the 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, a station has a frame to transmit in its EDCA queue, the backoff value is 0, and no frames belonging to an AC with a higher priority than the EDCA queue are in a condition to be transmitted (i.e., there is no internal collision condition), 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 a backoff operation 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 an EDCA queue and the AC of the colliding frame has a higher priority than the frame to be transmitted.

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

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

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

[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 subchannel 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, 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 generating the frame, the station may generate a backoff value and perform a backoff operation. In this case, the backoff value may be set to a number randomly selected from 0 to (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 may be obtained by the backoff operation. After the channel occupancy time, according to the definition of slot boundary 1), the next slot boundary may be the time when AIFS-aRxTxTurnaroundTime has passed after the channel occupancy time has ended. If the channel continues to be in an idle state after the channel occupancy time, the subsequent slot boundaries may come every time aSlotTime has passed. 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 a transmit mode to transmit a frame, and then the station can transmit the frame.

[0215] The EDCAF operation for synchronized transmission is illustrated 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 time when a station can transmit a frame may be the time when the station completes a channel access procedure by EDCA operation on the link on which the station operates. When the backoff value is 0 at a slot boundary, the station can start 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 the station maintains the backoff value at 0 and delays frame transmission, the operation of the station transmitting a frame at an arbitrary slot boundary may not be allowed. 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. When 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, when a transmission is delayed on one link, the other links can perform synchronized transmission at the boundary of the slot immediately after the backoff value becomes 0. As a result, the station 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 is operating

[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 a slot boundary point 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 became 0 to the next slot boundary.

[0222] In the embodiments of FIG. 27 and FIG. 28, the first station (STA1) is connected to the first AP (AP1) through the first link (Link1). The second station (STA2) is connected to the second AP (AP) through the second link (Link2). In the embodiment of FIG. 28, 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 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 from when the backoff counter value of the first station (STA1) becomes 0. Therefore, actual transmission begins after the transmitter / receiver is switched to a transmission mode from the next slot boundary from when the backoff counter value of the first station (STA1) becomes 0.

[0223] In the embodiment of FIG. 28, the first station (STA1) first succeeds in channel access, 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) becomes 0. Therefore, actual transmission begins after the transceiver is switched to transmission mode at the next slot boundary after the backoff counter value of the second station (STA2) becomes 0.

[0224] A station can transmit a frame at the slot boundary where the backoff value is 0, thus simplifying synchronized transmission.

[0225] FIG. 29 illustrates an 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 occupancy state occurs due to a frame transmitted by another station and no frame reception error occurs, if the channel state is in the channel idle state for (AIFSN[AC]+1)*aSlotTime-aRxTxTurnaroundTime after the SIFS time following the completion of the occupancy time, the time when the channel state has passed

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

[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 including the frame, if the channel state is in the channel idle state for (AIFSN[AC]+1)*aSlotTime+aSIFSTime-aRxTxTurnaroundTime after the reception expiration time for receiving the response frame, the time when (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 including 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 in the channel idle state 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 in the channel idle state for (AIFSN[AC]+1)*aSlotTime+aSIFSTime-aRxTxTurnaroundTime) after any channel occupancy time that does not satisfy conditions 1-4, the time when (AIFSN[AC]+1)*aSlotTime+aSIFSTime-aRxTxTurnaroundTime has elapsed.

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

[0235] The time at which a station on each link can switch its transceiver to a 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) At the boundary of multiple link slots when the backoff value of the corresponding link is already 0 and the frame transmission operation is in a deferred state, and the backoff value of another link becomes 0

[0238] In the embodiment of FIG. 30, a first station (STA1) is connected to a first AP (AP1) through a first link (Link1). A second station (STA2) is connected to a second AP (AP) through 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 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 back-off counter value of the first station (STA1) becomes 0. Therefore, actual transmission begins after the transceiver is switched to a transmission mode from the slot boundary when the back-off counter value of the first station (STA1) becomes 0.

[0239] FIG. 30 illustrates an embodiment in which an MLD performs simultaneous PPDU transmission on two links by delaying a channel access procedure for a particular channel according to an embodiment of the present invention.

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

[0241] Specifically, as shown in FIG. 30, the MLD may include STA1 and STA2. The links on which the STA1 and STA2 operate may be a link pair having a non-STR relationship, and the MLD may attempt to perform simultaneous transmission using the non-STR-related link pair. In this case, the MLD may select to postpone the transmission of PPDU2 without starting the transmission of PPDU2 using STA2 even after the channel access procedure of STA2 is completed (i.e., BO becomes 0 by the backoff procedure). In this case, the time when the channel access procedure is completed may mean the slot boundary at which BO becomes 0 when DCF is used, and may mean the next slot boundary after the slot boundary at which BO becomes 0 when EDCA is used. In the transmission postponement period of the PPDU2, STA1, which is another STA of the MLD, completes the channel access procedure, and the MLD may start transmitting PPDU1 and PPDU2 simultaneously using STA1 that has just completed the channel access procedure and STA2 that has been waiting (transmission postponement) after completing the channel access procedure. In the present invention, the PPDU may include a frame. Additionally, the operation of transmitting or not transmitting a PPDU may include the operation of transmitting or not transmitting a frame.

[0242] That is, the EDCA rule in each link can allow channel connection in all links, so that 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 reached "0", the STA of the MLD can maintain the back-off counter value at "0" without performing uplink transmission in that link. In other words, when the back-off counter value reaches "0" in a specific link, the STA of the MLD can select to maintain the back-off counter value at "0" without performing uplink transmission if the back-off counter values ​​of the other links of the MLD have not reached "0".

[0243] 30, if STA2 immediately starts transmitting a PPDU after the channel access procedure of STA2 ends because the back-off counter value of STA2 reaches "0", the PPDU transmission of STA2 may cause interference (or blockage) in the channel access procedure of STA1. However, as described above, by adjusting the PPDU transmission start time on the link of the STA that has completed the channel access procedure between STA1 and STA2, the MLD can simultaneously transmit PPDUs using a link pair in a non-STR relationship.

[0244] Therefore, when the MLD has an intention to perform simultaneous transmission, the STA of the MLD may not immediately start transmitting a PPDU or perform a new channel access procedure even if the channel access procedure is completed. In other words, the STA of the MLD may perform an operation of maintaining BO in a state of 0 after the channel access procedure is completed. However, as described above, the operation of maintaining BO in a state of 0 after a specific STA completes a channel access procedure may be limited to the case where the specific STA is an STA of the MLD. In this case, the operation may be limited to the case where 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 in a state of 0 after the specific STA completes a channel access procedure may be permitted only when the MLD including the specific STA has an intention 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 of other links by 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 pair of non-STR links, the value of the first backoff counter in the backoff procedure of the channel access procedure of 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 of the second link of STA2. In this case, STA1 can select not to transmit PPDU on the first link and to continue to maintain the value of the backoff counter at "0". <Slot boundary mismatch when performing simultaneous transmissions> As described above, the MLD can perform simultaneous transmission using two or more links, and the meaning of "simultaneous" used in the simultaneous transmission does not mean exactly the same time physically. More specifically, the simultaneous transmission performed by the MLD can mean that the start points of transmission performed by two or more links have a difference within a specific time interval. For example, if the specific time interval is aSlotTime, and the MLD starts PPDU transmission at time "t" on Link1 and starts transmission on another link, Link2, "after t-aSlotTime and before t+aSlotTime," the MLD may be considered to have performed simultaneous transmission using Link1 and Link2. At this time, aSlotTime used as an example of the specific time interval is for illustrative purposes, and the time interval that the MLD should consider / observe to perform simultaneous transmission may be other time values ​​(1us, 2us, 3us...xus, etc.) other than aSlotTime. At this time, the time interval that should be considered to perform the simultaneous transmission may be a value specified by the AP of the BSS. As an example, an AP MLD can indicate, in an OM (Operating Mode) element, the time value that the STA MLD associated with itself should take into consideration when performing simultaneous transmission.

[0246] In this case, the aSlotTime means a time value defined in the standard for each PHY version, and when the corresponding slot is IDLE for each aSlotTime, a channel access procedure is performed to decrement the BO (Backoff counter) by one. In this case, 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 9us.

[0247] In this way, the reason why 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, may be because the slot boundaries of each link used in the simultaneous transmission are not aligned. A more detailed explanation of the slot boundaries will be described in one embodiment of FIG. 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 constituting 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. In this case, the slot boundary is used as a criterion for dividing each slot during a channel access procedure, and transmissions performed by the Wi-Fi device after completing the channel access procedure should be performed at a time aligned with the slot boundary.

[0251] Therefore, as shown in Fig. 31, when medium occupancy ends at different times on Link1 and Link2, MLD STAs STA1 and STA2 must perform channel access procedures based on different slot boundaries. In this way, STAs operating on different links are likely to have different slot boundaries depending on the occupancy status of the links on which they operate, and 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] In addition, the MLD may attempt to start transmission simultaneously using two or more links at a specific time, but since the two or more links are processed by separate MACs and PHYs and are to be transmitted with different PPDU BWs on different links, processing for PPDU transmission may not be completed at exactly the same time (strictly speaking, "simultaneous" transmission) Therefore, even if the MLD attempts simultaneous transmission (strictly speaking, "simultaneous" transmission) while ignoring different slot boundaries of different links, the times at which transmission starts on the different links may still be different from each other.

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

[0254] That is, the slot setting in each link may be different, and therefore the boundaries of the slots between the links may not coincide. Therefore, the boundaries of the slots between the links may not coincide in each slot where the back-off counter is decreased, and when the back-off counters in the back-off procedure reach "0" in each of the multiple links of the MLD by the above-mentioned reservation operation, the slot boundaries in each link may not coincide. Since the slots in each link may be set individually, the slot boundaries in each link may not coincide. Therefore, even when the back-off counter values ​​in each link are all "0", the slot boundaries may be different from each other. In this case, simultaneous transmission may be performed according to the slot boundary for the slot or the next slot of the slot in which the back-off counter value of a specific link among the multiple links is "0". That is, when the link serving as the reference for multiplex transmission among multiple links of the non-AP MLD is a specific link, when the back-off counter value in slot 1 of the specific link is decreased to "0", other links may perform uplink transmission based on the slot boundary of slot 1 for the specific link or slot 2 which is the next slot on the time axis of slot 1.

[0255] That is, each link may not transmit uplink transmissions at the slot boundary of the link, but may transmit uplink transmissions at the same time by delaying or shortening the uplink transmissions at the slot boundary of the particular link.

[0256] For example, when the multiple links of the MLD are composed of a first link and a second link, and the channel access procedure is completed in one of the first and second links (e.g., when the first back-off counter of the first link and one of the second back-off counters of the second link reach "0" before the remaining back-off counters), 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 counters reach "0"). In this case, the uplink transmission 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, so that the uplink transmission may be performed simultaneously in the multiple links.

[0257] That is, when the MLD multiple links are composed of the first link and the 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 remaining backoff counter, the slot boundaries of the first link and the second link may not coincide in uplink transmission when the remaining backoff counter reaches '0.' In this case, the transmission time point of the uplink transmission in the second link can be adjusted by shortening or delaying according to the slot boundary of the slot where the first backoff counter of the first link is '0' or the slot boundary of the first slot which is the next slot of 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 other times 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, the STA whose transmission is delayed due to the slot boundary can continue channel sensing of the slot during the delay time on the link, and if the backoff counter value on another link becomes "0" during channel sensing, the STA can end channel sensing and immediately transmit the PPDU. The delay or shortening time for simultaneous transmission may be 4us. In this case, 4us may mean the change time required to change to a mode for uplink transmission in the channel access procedure. If the delay or shortening time exceeds 4us, the time required to switch from downlink to uplink may be exceeded, and the channel state in the slot may be changed to an occupied state (busy).

[0261] The STA operations in aSlotTime shown in Fig. 33 are for illustrative purposes only, and each STA may perform different operations in 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 illustrates an example of a failure in simultaneous MLD transmission that may occur when there is no clear definition for the start time of simultaneous transmission according to an embodiment of the present invention.

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

[0264] However, as described above, since the slot boundaries of each link may be different from each other, when a transmission is started on a specific link for the purpose of using it for simultaneous transmission, it may affect the CCA operation of the other links to be used for simultaneous transmission, and as a result, it may be impossible to start transmission on the other links. More specifically, since the transmission started on the specific link induces in-device interference, the CCA result of the other links may be determined as BUSY due to the in-device interference. Therefore, the STAs of the other links operate as if the WM is already occupied and channel access is restricted. As a result, the transmission of the specific link started for the purpose of simultaneous transmission may induce in-device interference on the other links that were planned to transmit for the purpose of simultaneous transmission, thereby restricting channel access of the other links. As shown in (a) and (b) of Figures 14, even if STA1, which has delayed the start of transmission after completing the channel access procedure, selects and transmits from one of 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 following the slot boundary at which STA2 has completed the channel access procedure and the STA1 slot boundary immediately preceding the slot boundary at which STA2 is predicted to complete the channel access procedure), the transmission that began earlier may affect the CCA results of other links, and simultaneous transmission may fail.

[0265] Therefore, the start of transmission of a link that has delayed / deferred the start of transmission to perform simultaneous transmission after completing the channel access procedure 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 slot boundary difference between the specific link and the other link.

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

[0267] Figure 33 shows an embodiment of the present invention in which, 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 (same MLD operated on other links).

[0268] 33, the MLD operates STA1 and STA2 on Link1 and Link2, respectively, and may delay the transmission start time of STA1 in order to perform simultaneous transmission with STA2 after the channel access procedure of STA1 is completed. In this case, the MLD can determine that even if the STA2 starts transmission at the slot boundary where the channel access procedure is completed, the CCA result of STA1 is not affected because the slot of STA1 including the transmission start time of STA2 (slot displayed in a grid, the slot immediately before STA1 starts transmission) corresponds to the period where STA1 is switched from Rx mode to Tx mode. Therefore, the MLD can determine that the transmission start time of STA1, which has been delayed after completing the channel access procedure, is started at the STA1 slot boundary after the STA2 slot boundary where STA2 starts 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 to FIG. 15 again, STA1 performs an operation of switching from Rx mode to Tx mode during the last 4 us of aSlotTime corresponding to the slot displayed in the grid, and does not need to determine the slot displayed in the grid as BUSY even if intra-device interference occurs during the switching period. Therefore, since the start point of the transmission performed by STA2 is within aRxTxTurnaroundTime of STA1, STA1 can access the channel without problems caused by intra-device interference even after STA2 starts transmitting first.

[0270] Here, 4us is used as an example of a value corresponding to aRxTxTurnaroundTime, and the aRxTxTurnaroundTime may have different values ​​for each terminal depending on the hardware characteristics of each terminal. Therefore, the difference in transmission start time of each link to be considered when the MLD performs simultaneous transmission may be different 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 to start in the section after CCADel, not within the aRxTxTurnaroundTime section of the other link. However, in this embodiment, if the above description is substituted for the section after CCADel instead of the aRxTxTurnaroundTime section, it may be understood as a similar method, and detailed description thereof will be omitted. For reference, in one embodiment of FIG. 15, the section including the M2 section shown in the Rx / Tx (e.g., 4 us) section may be understood as the section 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 the MLD is to perform simultaneous transmission according to an embodiment of the present invention.

[0273] Figure 34(a) shows a situation where the slot boundary of STA1 precedes (is earlier in time) the slot boundary of STA2 by an interval smaller than aRxTxTurnaroundTime, and Figure 34(b) shows a situation where the slot boundary of STA2 precedes the slot boundary of STA1 by an interval smaller than aRxTxTurnaoundTime. In this case, the method of 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 having a difference of 1 / 2 aSlotTime or less.

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

[0275] In FIG. 34(b), the slot boundary of STA2 precedes the slot boundary of STA1. Even if STA2 starts transmitting at its own slot boundary, the slot boundary of STA2 corresponds to aRxTxTurnaroundTime in the lattice slot interval (aSlotTime) of STA1. Therefore, the 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, MLD can perform simultaneous transmission by starting transmission first through the STA operating in the link with the most advanced slot boundary when the slot boundaries of the links (STAs operating in each link) that perform simultaneous transmission have a time difference of less than aRxTxTurnaroundTime. 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 start transmission first by considering the slot boundary difference between the links performing simultaneous transmission, so that the in-device interference induced by the link that started transmission first does not affect the CCA of the other links. However, if the slot boundary difference between the links performing simultaneous transmission is within a specific value, the MLD cannot prevent channel access of the other link from being disturbed, regardless of the order in which the MLD starts transmission on each link. In this case, the difference within the specific value may mean a difference of more than (or more than) 4 us to less than (or less than) 4.5 us when 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 is more than (or more than) 4 us to less than (or less than) 4.5 us, regardless of which of the two links the MLD starts transmission first, the channel access (simultaneous transmission) of the remaining link may be restricted due to the in-device interference induced by the link that started 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 certain range according to an embodiment of the present invention.

[0279] 35, the MLD can operate STA1 and STA2 as Link1 and Link2, respectively, and the STA1 and STA2 can access the channel based on slot boundaries that are different 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 of STA1 in order to perform simultaneous transmission using the STA1 and STA2. In this case, the MLD can try to start transmission of Link1 at the slot boundary of STA1 adjacent to the slot boundary where the channel access of STA2 ends, but the simultaneous transmission may not be successful due to the difference in slot boundaries between the STA1 and STA2.

[0280] MLD may select one of two slot boundaries (T2 in FIG. 35) where STA2 is predicted to complete / have completed the channel access procedure and the adjacent slot boundary of STA1, and attempt to start transmission on Link1. If MLD starts transmission to Link1 at the slot boundary of STA1 that appears earlier (T1 in FIG. 35) at the time of predicted completion of the channel access procedure of STA2, the last backoff slot (shown as 0) of STA2 is determined to be BUSY due to the transmission started from Link1, and the channel access procedure of STA2 cannot be completed at the predicted time of T2. That is, when MLD starts transmission using STA1 at time T1, the channel access procedure of STA2 cannot be completed due to the intra-device interference induced by the transmission of Link1, and simultaneous transmission fails. Meanwhile, when MLD attempts to transmit to Link1 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 Link1 that ends at T3 may be determined as BUSY due to the transmission of Link2 that has already started at T2, and channel access to Link1 may be impossible. This may be because the time difference between T1 and T2, and between T2 and T3, are greater than aRxTxTurnaroundTime, respectively, so whichever of the two links, Link1 or Link2, starts transmission first may result in the channel access procedure of the other link being disrupted.

[0281] As mentioned above, when a particular link has a slot boundary difference within a particular range, the link may not be able to participate in simultaneous transmission by starting transmission according to its own slot boundary. Assuming a situation where aSlotTime is 9us and aRxTxTurnaroundTime is 4us as in the example of FIG. 35 above, the probability that a particular link pair has a slot boundary difference that makes simultaneous transmission impossible can be understood as 1 / 9 by simple calculation. This may be a somewhat high probability when considering that non-STR MLD actively attempts simultaneous transmission even for the purpose of preventing a particular link from switching 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 restriction due to the slot boundary difference of a specific link pair may become higher. As an example, if a STA of a specific MLD requires an aRxTxTurnaroundTime of only 1.5us and has the characteristic of being able to perform CCA during the remaining time, the specific MLD may fail to access one of the two channels with a probability of (4.5-1.5) / 9=1 / 3 when performing simultaneous transmission using two links.

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

[0284] As described above, in order to prevent the problem of simultaneous transmission (simultaneous channel access) being restricted by the slot boundary difference, when the MLD reserves the start of transmission of a specific STA for the purpose of simultaneous transmission (the specific STA has completed the backoff procedure (channel access procedure) (BO==0)), the transmission starting from the specific STA may be allowed to have an error of less than a certain level with the slot boundary of the specific STA. In other words, when the 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 the link whose backoff counter value reaches "0" first due to 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, when the backoff counters of the STAs of the non-STR link pair of the MLD reach '0', the slot boundaries of the STAs may not match, so the MLD STAs may start transmission at other times than their own slot boundaries. In this case, the error below a certain level may be a value determined in consideration of aSlotTime. As an example, the error below a certain level may not exceed 10% of aSlotTime. In this case, if aSlotTime is 9us, the transmission performed by the MLD STAs may start within +-0.9us of their own slot boundaries. In this case, the reason for considering aSlotTime when determining the allowable range (error) for starting transmission at a time different from the slot boundaries may be to prevent errors that damage slot boundary synchronization between STAs operating on a specific link. In this case, the slot boundary synchronization may mean a level of synchronization that allows channel access to be performed according to the EDCA rule when performing a channel access procedure using each STA's own slot boundaries, even if each STA uses a slightly different slot boundary due to a propagation delay.

[0285] That is, it 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 most distant STAs (slots synchronized), or may be a value indicated by a parameter in the Coverage Class field of the BSS. As an example, when the aAirPropagationTime of the BSS considered by the EHT AP is 1us or less, the start time of the transmission performed by the STA of the BSS may be allowed to have a maximum error of 0.8us (+-10%*(9us-1us)) from the slot boundary. In other words, the EHT STA may allow its own transmission start time to have a difference of 0.8us or less from the slot boundary.

[0286] That is, there is a tolerable "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, the error below the certain level can be determined (ensured). 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, the STAs of the MLD can start transmitting 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 has reserved transmission is allowed to start transmission regardless of its slot boundary, the allowed error level from the slot boundary may be understood to be aSlotTime / 2.

[0288] FIG. 36 shows an embodiment of a simultaneous transmission method 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 the STA1 and STA2 can access the channel based on slot boundaries that are different 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 of STA1 in order to perform simultaneous transmission using the STA1 and STA2. This is the same situation as that considered in Figure 17, and when transmission to Link1 starts according to the slot boundary of STA1, which is the STA of the MLD, simultaneous transmission (simultaneous channel access) using STA1 and STA2 is not possible. However, in the case of STA1, since the start of transmission is reserved for the purpose of simultaneous transmission after completing the channel access procedure, it can freely adjust the start of transmission within a certain (allowed) 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 in Link2 evaluates the slot (grid) adjacent to T2, which is the slot boundary where the channel access procedure is completed, it can determine the slot as IDLE regardless of the intra-device interference induced by the transmission from STA1 and start simultaneous transmission at T2. In short, if the transmission of STA1 starts at T1 in line with its slot boundary, the channel access procedure of STA2 may not be completed at T2 and simultaneous transmission may fail, but STA1 starts transmission of Link1 in the aRxTxTurnaroundTime period of STA2 by delaying the start of transmission by the Slot Sync budget.

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

[0292] FIG. 37 illustrates an embodiment of signaling that can be used when an AP MLD indicates a 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 when the STA MLD in the BSS performs simultaneous transmission by evaluating the slot boundary synchronization integrity between the STAs in the BSS. In this case, the slot sync budget may be indicated by an action element. In this case, the name of the field and the element indicated are not restricted to be changed. The value indicated by the slot sync budget may be applied to the maximum error that may be present between the slot boundary of each link and the start time of transmission of each link when the STA MLD performs simultaneous transmission. In this case, the slot sync budget is not restricted for the purpose of simultaneous transmission, and may be applied to the timing error that the transmission performed by the EHT STA may have between the slot boundary.

[0294] For example, when the slot boundary synchronization between STAs in a BSS is strong (when synchronization is well done), the AP MLD can indicate a relatively large value according to 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, when the slot boundary difference between STAs is predicted / estimated to be large). In this case, the value indicated in the Slot Sync Budget field may 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 link starts transmission has a time difference that does not exceed the tolerance range confirmed based on the value indicated in the Slot Sync Budget field from the slot boundary used when performing the channel access procedure.

[0295] <Simultaneous transmission method considering information exchange delay between links>

[0296] The above-mentioned 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, a specific STA transmits at the time when another STA in the MLD completes the channel access procedure, which 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 the MLD basically performs a channel access procedure independently on the link it operates, and the method of each STA sharing information may not be defined. Therefore, whether the STAs in the 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 the data needs to be exchanged between each STA in the MLD every moment.

[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 regarding 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 a backoff procedure 1) begins transmission at the time when other STAs in the MLD are predicted to 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) above 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 an embodiment of the present invention, an MLD that is going to perform simultaneous transmission may delay a 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 of the MLD have completed the channel access procedure. In this case, the other STA may postpone the start of transmission for a specific time after the channel access procedure is completed, taking into consideration the in-device information processing delay (inter-link information exchange delay) that is 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 in consideration of 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 Fig. 38, the MLD is about to perform simultaneous transmission using STA1 and STA2. At this time, since STA1 and STA2 perform independent channel access procedures, the channel access procedures of STA1 and STA2 may be completed at different times. Referring to Fig. 20, STA1 completes the channel access procedure (BO==0) at time T1, but may postpone the transmission of PPDU1 in order to perform simultaneous transmission with STA2.

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

[0305] At this time, T3 may be a time point of a slot boundary that appears after the link information exchange delay time based on the time point (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. At this time, the time difference between T3 and T2 may be less than or equal to (link information exchange delay time + aSlotTime).

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

[0307] As a result, neither STA1 nor STA2, which transmits simultaneously, needs to transmit immediately after completing their own channel access procedures. First, a STA that has completed its channel access procedure can postpone its transmission until it confirms (by inter-link information exchange) that the other STAs have completed their channel access procedures, and a STA that completes its channel access procedure later can postpone its transmission by taking into consideration the delay time until the other STAs that have postponed transmission until it completes its channel access procedure obtain information that its channel access procedure has been completed.

[0308] On the other hand, even when performing simultaneous transmission considering the link information exchange delay, it is necessary to perform an operation considering the slot boundary time difference between the links performing simultaneous transmission, as considered in the above embodiment of the present invention. That is, when performing simultaneous transmission considering the link information exchange delay, there is still a possibility that the channel access procedure of other links is disturbed by the transmission started from a specific link. Therefore, even when the MLD performing simultaneous transmission performs simultaneous transmission considering the link information exchange delay, it still has to follow the method provided in the above embodiment of the present invention to select the slot boundary.

[0309] However, when the MLD performs simultaneous transmission while considering the delay in exchanging information between links, the STA that completes the channel access procedure first must start transmission according to its own slot boundary, and the STA that completes the channel access procedure later must determine the slot boundary at which it starts transmission. At this time, the method of determining the slot boundary is the same as that described in the embodiment of Fig. 34, and the detailed description thereof will be omitted.

[0310] In addition, the same problem as described with reference to Fig. 35 (problem of not being able to determine an appropriate slot boundary) may occur in simultaneous transmission considering interference between devices, in which case a STA that completes a 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 the transmission starting at a time different from the slot boundary may be the same as those described in the embodiment of Fig. 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 procedures of other STAs have been completed.

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

[0313] Thereafter, STA2 completes the channel access procedure at time T2, and STA1 may not be able to recognize that STA2 has completed the channel access procedure at time T2 due to a delay in information exchange between links. Therefore, STA2 does not wait for the channel access procedure of STA1, but can postpone its transmission until time T3 and then start transmitting PPDU2, taking into consideration the delay time (T_delay) for information that STA2 has completed the channel access procedure being transmitted to STA1.

[0314] At this time, T3 may be a time point of a slot boundary that appears after the link information exchange delay time based on the time point (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. At this time, the time difference between T3 and T2 may be less than or equal to (link information exchange delay time + aSlotTime).

[0315] After that, STA1, after receiving information that STA2 has completed the channel access procedure, can start transmission at its own (link's) slot boundary (T4) that exists after T3. At this time, STA2 can recognize that STA1 will start transmission at the slot boundary corresponding to T4, taking into account the link information exchange delay time, and can recognize that if STA2 starts transmission at the slot boundary (T3+aSlotTime) that exists after T3, its start of transmission will be interrupted by the transmission started by STA1. In addition, STA2 can recognize that if it starts transmission at the same slot boundary at time T3, STA1 cannot perform simultaneous transmission due to the transmission started by STA2, and as a result, it can recognize that neither the same slot boundary at time T3 nor a slot boundary that exists after T3 can be used as the start point of simultaneous transmission.

[0316] In this case, STA2 may 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 are described in the 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 multiple 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 through multiple links (S40010). The backoff procedure may be performed individually through each of 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 of '0', if the transmission time of the uplink transmission in the first link is a 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 in each link may be different, the boundaries of the slots between the links may not coincide. Therefore, the boundaries of the slots between the links may not coincide in each slot where the back-off counter is decreased, and when the back-off counters in the back-off procedure in each of the multiple links of the MLD reach "0" due to the above-mentioned reservation operation, the slot boundaries in each link may not coincide. Since the slots in each link may be set individually, the slot boundaries in each link may not coincide. Therefore, even if the back-off counters in each link all have the value "0", the slot boundaries may be different from each other. In this case, the simultaneous transmission may be performed according to the slot boundary of a specific link when the back-off counter value of a specific link among the multiple links is "0". That is, each link does not perform uplink transmission according to the slot boundary of the link, but can 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, when the multiple links of the MLD are 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 remaining backoff counter, the slot boundaries of the first link and the second link may not coincide in uplink transmission when the remaining backoff counter reaches '0.' In this case, the transmission time point of the uplink transmission in the second link may be adjusted by shortening or delaying according to 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 next slot of 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, 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 may not be included within the certain time.

[0329] In addition, 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 can maintain the one backoff counter at "0" until the remaining backoff counter reaches "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 reached "0", the MLD STA can select not to perform uplink transmission in that link and to maintain the back-off counter value at "0" if the back-off counter value in a specific link reaches "0" and the back-off counter values ​​in the other links of the MLD have not reached "0", not to perform uplink transmission and to maintain the back-off counter value at "0".

[0331] For example, a multiple link of the MLD may be composed of a first link and a second link, a back-off procedure for a channel connection in the first link may be performed by a first back-off counter, and a back-off procedure for a channel connection in the second link may be performed by a second back-off counter, in which case the back-off procedure may be performed separately through each of the first link and the second link 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 remaining 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 remaining backoff counters reach the value of "0". Alternatively, the one backoff counter may continue to maintain the value of "0" even after the remaining 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 in 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, 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 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 next to 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 idea or essential features of the present invention. Therefore, the above-described embodiments should be understood to be illustrative and not restrictive in all respects. For example, each component described as a single type may be implemented in a distributed form, and similarly, each component described as a distributed type 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 all modifications and variations that fall within the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention. [Explanation of symbols]

[0341] 100 Stations 110 Processor 120 Communications Department 140 User Interface Section 150 Display unit 150 160 Memory 200 AP 210 Processor 220 Communications Department 260 Memory

Claims

1. A non-AP (Access Point) multi-link device (MLD) of a wireless communication system, A communication module; a processor for controlling the communication module; The processor, A backoff procedure is performed to perform uplink transmission through the non-AP MLD multiple links; The backoff procedure is performed individually 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 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; The uplink transmission is simultaneously performed in AP MLD through each of the first link and the second link; 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 certain time from the slot boundary of the first slot.

3. When the first backoff counter is “0” and the second backoff counter is “0”, the slot boundaries of the first slot and a second slot, which is a slot following a 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 period of time.

4. 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 and second backoff counters reaches '0' before the remaining 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 next slot of the slot in which the second backoff counter of the second link is '0' 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.

6. The non-AP MLD of claim 5, 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 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 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 transmission time point 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 a channel is 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, respectively, are idle.

13. A method for performing uplink transmission by a non-AP (Access Point) multi-link device (MLD) in a wireless communication system, comprising: A backoff procedure is performed to perform uplink transmission through the non-AP MLD multiple links; The backoff procedure is performed individually 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 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; The uplink transmission is simultaneously performed in AP MLD through each of the first link and the second link; A method in which, 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 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 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 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. When the first backoff counter is “0” and the second backoff counter is “0”, the slot boundaries of the first slot and a second slot, which is a slot following a 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 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.

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. 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 back-off counter and the second back-off 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 a channel is 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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