Non-access point multi-link devices and the method of performing uplink transmissions by these devices.

Abstract

The invention relates to a method for transmitting and receiving data in a non-access point (AP) multi-link device (MLD) of a wireless communication system. A non-AP MLD can perform a transmission wait-to-transmit procedure to perform simultaneous transmissions through the MLD's multi-links, and simultaneously perform uplink transmissions to an AP MLD through each of the first and second links included in the multi-link. Here, when both the first and second transmission wait-to-transmit counters are equal to “0”, if the transmission time of the uplink transmission in the first link is the edge of the first slot which is the slot adjacent to the slot in which the first transmission wait-to-transmit counter is equal to “0”, the uplink transmission in the second link can be performed within a predetermined time from the transmission time of the first link.

Description

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

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

[0002]

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

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

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

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

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

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

[0009]

[0010] An embodiment of the present invention aims to provide a wireless communication method using multiple links and a wireless communication terminal using the same.

[0011] In addition, the present invention aims to provide a wireless communication terminal for a multi-link device to simultaneously perform uplink transmission using multiple links.

[0012] In addition, the present invention aims to provide a wireless communication terminal for performing uplink transmission simultaneously in multiple links when the value of a back off counter in each link reaches '0' at different times when performing uplink transmission using multiple links.

[0013] In addition, the present invention aims to provide a wireless communication terminal for simultaneously performing uplink transmission in multiple links by delaying the uplink transmission time when the slot boundary of each link is different when performing uplink transmission simultaneously using multiple links.

[0014] The technical problems to be achieved in this specification are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0015]

[0016] In a wireless communication system, a terminal for transmitting a response frame, a TB PPDU (Trigger Based Physical layer Protocol Data Unit), based on a trigger frame is a communication module; A processor controlling the communication module is included, and the processor performs a back off procedure for performing uplink transmission through multiple links of the non-AP MLD, wherein the back off procedure is individually performed 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 back off procedure in the first link is performed using a first back off counter, and the back off procedure in the second link is performed using a second back off counter, and the uplink transmission is simultaneously performed to the AP MLD through each of the first link and the second link, wherein when both the first back off counter and the second back off counter have a 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 a slot next to a slot in which the first back off counter is '0', the uplink transmission in the second link is performed within a predetermined time from the transmission time of the first link.

[0017] Additionally, in the present invention, when both the first back-off counter and the second back-off counter are '0', the transmission time of the uplink transmission in the second link is adjusted to be included within the predetermined time from the slot boundary of the first slot.

[0018] In addition, in the present invention, when the first back off counter is '0' and the second back off counter is '0', the slot boundary of the second slot, which is the next slot of the slot in which the second back off counter of the first slot and the second link is '0', does not match, and the slot boundary of the second slot is not included within the predetermined time.

[0019] In addition, in the present invention, if one back-off counter among the first back-off counter and the second back-off counter reaches '0' before the remaining back-off counters, the link using the one back-off counter among the first link and the second link does not perform the uplink transmission and maintains the one back-off counter as '0' until the remaining back-off counter reaches '0'.

[0020] In addition, in the present invention, if one of the first back off counter and the second back off counter reaches '0' before the remaining back off counter, and if the slot boundary of the second slot, which is the next slot of the first slot of the first link and the slot of the second back off counter of the second link in which the second back off counter is '0', does not match when the remaining back off counter reaches '0', the transmission time point of the uplink transmission in the second link is adjusted to be before or after the slot boundary of the second slot so as to be included within the predetermined time from the slot boundary of the first slot.

[0021] Additionally, in the present invention, when the slot boundary of the second slot is located earlier or later on the time axis than the slot boundary of the first slot, the transmission time point of the second link is delayed or shortened for a specific time from the slot boundary of the first slot.

[0022] Additionally, in the present invention, the maximum value of the above-mentioned period of time is 4 us.

[0023] Additionally, in the present invention, the 4us is a change time for performing the uplink transmission in the channel access procedure.

[0024] Additionally, in the present invention, the processor performs channel sensing before the transmission time of the second link, but the transmission time of the second link does not coincide with the slot boundary of the second slot of the second link.

[0025] Additionally, in the present invention, the uplink transmission is performed in the slot following the slot in which the first back-of counter and the second back-off counter reach '0'.

[0026] Additionally, in the present invention, the first link and the second link are an NSTR link pair that does not support simultaneous transmit and receive (STR).

[0027] Additionally, in the present invention, the processor senses whether a channel is idle in the first link and the second link, and the first back-off counter and the second back-off counter are decremented when the first link and the second link are idle, respectively.

[0028] In addition, the present invention provides a method for performing a back off procedure for performing uplink transmission through multiple links of the non-AP MLD, wherein the back off procedure is individually performed 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 back off procedure in the first link is performed using a first back off counter, and the back off procedure in the second link is performed using a second back off counter, and the uplink transmission is simultaneously performed to an AP MLD through each of the first link and the second link, wherein when both the first back off counter and the second back off counter have a 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 a slot next to a slot in which the first back off counter is '0', the uplink transmission in the second link is performed within a certain time from the transmission time of the first link.

[0029]

[0030] One embodiment of the present invention provides a wireless communication method efficiently using a multi-link and a wireless communication terminal using the same.

[0031] In addition, according to an embodiment of the present invention, a wireless communication terminal is provided in which a multi-link device simultaneously performs uplink transmission using multiple links.

[0032] In addition, according to an embodiment of the present invention, when performing uplink transmission using multiple links, a wireless communication terminal is provided that simultaneously performs uplink transmission on multiple links when the value of a back off counter on each link reaches '0' at different times.

[0033] In addition, according to an embodiment of the present invention, when performing uplink transmission simultaneously using multiple links and the slot boundary of each link is different, a wireless communication terminal is provided that delays the uplink transmission time and performs uplink transmission simultaneously on multiple links.

[0034] The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present invention belongs from the description below.

[0035] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0036] Figure 2 illustrates a wireless LAN system according to another embodiment of the present invention.

[0037] Figure 3 shows the configuration of a station according to one embodiment of the present invention.

[0038] Figure 4 shows the configuration of an access point according to one embodiment of the present invention.

[0039] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0040] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0041] Figure 7 illustrates one embodiment of various standard generation-specific PPDU (PLCP Protocol Data Unit) formats.

[0042] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) PPDU formats and a method for indicating the same according to an embodiment of the present invention.

[0043] FIG. 9 illustrates an example of a multi-link device according to an embodiment of the present invention.

[0044] FIG. 10 shows an example of whether devices (STRs of MLD#1 and MLD#2) support a relatively narrow frequency separation distance according to an embodiment of the present invention.

[0045] FIG. 11 illustrates an embodiment in which a channel access operation performed by another STA of a non-STR MLD is interrupted due to a PPDU transmission performed by a specific STA of the non-STR MLD.

[0046] FIG. 12 shows that a multi-link device according to an embodiment of the present invention postpones transmission on a link when the multi-link device succeeds in channel access on one link first.

[0047] FIG. 13 illustrates the operation of a multi-link device when the channel of the second link is detected as occupied when the multi-link device postpones transmission on the first link after first successfully accessing the channel on the first link according to an embodiment of the present invention.

[0048] FIG. 14 illustrates the operation of a multi-link device when the channel of the second link is detected as occupied when the multi-link device postpones transmission on the first link after first successfully accessing the channel on the first link according to another embodiment of the present invention.

[0049] FIG. 15 illustrates an operation in a plurality of multi-link devices when the multi-link devices postpone transmission in a first link after the multi-link devices first succeed in channel access in the first link according to an embodiment of the present invention.

[0050] FIGS. 16 and 17 illustrate the operation of a multi-link device according to an embodiment of the present invention when the multi-link device first succeeds in channel access on the first link, and then postpones transmission on the first link and the channel of the first link is detected to be busy.

[0051] FIG. 18 shows that a transmission is delayed when a multi-link device according to an embodiment of the present invention performs channel access for synchronized transmission.

[0052] FIGS. 19 and 20 illustrate an operating method when a station of a multi-link device according to an embodiment of the present invention detects that a channel is busy during transmission.

[0053] FIG. 21 illustrates a method for obtaining a new backoff counter value when a station of a multi-link device according to an embodiment of the present invention detects that a channel is busy during a transmission delay.

[0054] FIG. 22 shows an operation for determining whether a station of a multi-link device according to an embodiment of the present invention will perform synchronized transmission while delaying transmission.

[0055] FIG. 23 and FIG. 24 illustrate the operation of a multi-link device according to an embodiment of the present invention when a station of the multi-link device detects that a channel on which transmission is being delayed is busy.

[0056] Figure 25 shows an EDCA queue used when applying EDCA according to an embodiment of the present invention.

[0057] FIG. 26 illustrates a method for performing channel access based on slot boundaries according to an embodiment of the present invention.

[0058] Figures 27 and 28 show an operation in which a multi-link device performs synchronized transmission according to an EDCAF operation according to an embodiment of the present invention.

[0059] FIG. 29 shows an operation in which a multi-link device performs synchronized transmission according to an EDCAF operation according to another embodiment of the present invention.

[0060] FIG. 30 illustrates an embodiment in which MLD performs PPDU transmission simultaneously on two links by delaying a channel access procedure of a specific channel according to an embodiment of the present invention.

[0061] FIG. 31 illustrates an embodiment in which STAs of an MLD operate based on different slot boundaries according to an embodiment of the present invention.

[0062] FIG. 32 illustrates an example of a simultaneous transmission failure of MLD that may occur when there is no clear specification for the start time of simultaneous transmission according to an embodiment of the present invention.

[0063] FIG. 33 illustrates an example of a case where, when STAs of an MLD start transmissions at different slot boundaries according to an embodiment of the present invention, the transmission that starts first does not affect the CCA results of other STAs (same MLDs operating on different links).

[0064] FIG. 34 illustrates an embodiment of a method for determining a time point at which transmission begins on each link based on a difference in slot boundary time points of links on which MLD wishes to perform simultaneous transmission, according to an embodiment of the present invention.

[0065] FIG. 35 illustrates an embodiment of a case where simultaneous transmission fails when two link pairs of MLD have a difference in slot boundaries within a specific range according to an embodiment of the present invention.

[0066] FIG. 36 illustrates an embodiment of a simultaneous transmission technique performed by an STA of an MLD that has completed a channel access procedure and reserved the start of transmission, thereby initiating transmission at a time different from its own slot boundary, according to an embodiment of the present invention.

[0067] FIG. 37 illustrates an embodiment of signaling that may be utilized when an AP MLD indicates a Slot Sync Budget that may be utilized in a BSS using an Operation element according to an embodiment of the present invention.

[0068] Figure 38 illustrates an example of a simultaneous transmission procedure that takes into account information exchange delay between links according to one embodiment of the present invention.

[0069] FIG. 39 illustrates an example of a simultaneous transmission technique in which an STA of an MLD, which has completed a channel access procedure and reserved the start of transmission, initiates transmission at a time different from its own slot boundary after recognizing that another STA's channel access procedure has been completed, according to one embodiment of the present invention.

[0070] FIG. 40 illustrates an example of a method for a multi-link device to perform simultaneous transmissions over multiple links, according to one embodiment of the present invention.

[0071] The terms used in this specification have been selected from widely used and current terms, taking into account the functions of the present invention. However, these terms may vary depending on the intentions of those skilled in the art, customs, or the emergence of new technologies. Furthermore, in certain cases, the applicant may arbitrarily select terms, in which case their meanings will be described in the description of the relevant invention. Therefore, it should be noted that the terms used in this specification should be interpreted based on their substantive meaning and the overall content of this specification, rather than simply their names.

[0072] Throughout the specification, when a component is said to be "connected" to another component, this includes not only cases where it is "directly connected," but also cases where it is "electrically connected" with another component in between. Furthermore, when a component is said to "include" a specific component, this does not exclude other components, but rather allows the inclusion of other components, unless specifically stated otherwise. Furthermore, the terms "more than" or "less than" based on a specific threshold may be appropriately replaced with "exceeds" or "less than", respectively, depending on the embodiment. In the following, fields and subfields may be used interchangeably in the present invention.

[0073] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0074] A wireless LAN system includes one or more Basic Service Sets (BSSs), which represent a collection of devices that have successfully synchronized and can communicate with each other. BSSs can generally be categorized as infrastructure BSSs and independent BSSs (IBSSs). Figure 1 illustrates an infrastructure BSS.

[0075] As illustrated in FIG. 1, the infrastructure BSS (BSS1, BSS2) includes one or more stations (STA1, STA2, STA3, STA4, STA5), an access point (AP-1, AP-2) that provides a distribution service, and a distribution system (DS) that connects multiple access points (AP-1, AP-2).

[0076] A station (STA) is any device that includes a medium access control (MAC) and a physical layer interface for a wireless medium that complies with the IEEE 802.11 standard, and broadly includes both non-access point (AP) stations and access points (APs). In addition, the term "terminal" in this specification may refer to a non-AP STA or an AP, or both. A station for wireless communication includes a processor and a communication unit, and may further include a user interface unit and a display unit, depending on the embodiment. The processor may generate a frame to be transmitted through a wireless network or process a frame received through the wireless network, and may perform various other processes for controlling the station. In addition, the communication unit is functionally connected to the processor and transmits and receives frames through the wireless network for the station. In the present invention, a terminal may be used as a term that includes a user equipment (UE).

[0077] An Access Point (AP) is an entity that provides access to a distribution system (DS) via a wireless medium for stations associated with it. In an infrastructure BSS, communication between non-AP stations is in principle performed via the AP, but direct communication is also possible between non-AP stations when a direct link is established. Meanwhile, in the present invention, the AP is used as a concept including a Personal BSS Coordination Point (PCP), and in a broad sense, it can include concepts such as a centralized controller, a base station (BS), a node-B, a base transceiver system (BTS), or a site controller. In the present invention, the AP may also be referred to as a base wireless communication terminal, and the base wireless communication terminal may be used as a term including, in a broad sense, an AP, a base station, an eNodeB (eNB), and a transmission point (TP). In addition, the base wireless communication terminal may include various types of wireless communication terminals that allocate communication medium resources and perform scheduling in communication with multiple wireless communication terminals.

[0078] Multiple infrastructure BSSs can be interconnected via a distribution system (DS). Multiple BSSs connected via the distribution system are referred to as an Extended Service Set (ESS).

[0079] FIG. 2 illustrates an independent BSS, a wireless LAN system, according to another embodiment of the present invention. Parts of the embodiment of FIG. 2 that are identical or corresponding to those of the embodiment of FIG. 1 will not be redundantly described.

[0080] BSS3, illustrated in Figure 2, is an independent BSS and does not include an AP. Therefore, all stations (STA6, STA7) are not connected to an AP. An independent BSS does not allow access to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) can be directly connected to another.

[0081] FIG. 3 is a block diagram showing the configuration of a station (100) according to one embodiment of the present invention. As illustrated, the station (100) according to the embodiment of the present invention may include a processor (110), a communication unit (120), a user interface unit (140), a display unit (150), and a memory (160).

[0082] First, the communication unit (120) transmits and receives wireless signals such as wireless LAN packets, and may be built into or externally installed in the station (100). According to an embodiment, the communication unit (120) may include at least one communication module using different frequency bands. For example, the communication unit (120) may include communication modules of different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to one embodiment, the station (100) may include a communication module using a frequency band of 7.125 GHz or higher and a communication module using a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with an AP or an external station according to the wireless LAN standard of the frequency band supported by the corresponding communication module. The communication unit (120) may operate only one communication module at a time or may operate multiple communication modules simultaneously, depending on the performance and requirements of the station (100). When the station (100) includes multiple communication modules, each communication module may be provided in an independent form, or multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit (120) may represent an RF (Radio Frequency) communication module that processes RF (Radio Frequency) signals.

[0083] Next, the user interface unit (140) includes various types of input / output means provided in the station (100). That is, the user interface unit (140) can receive user input using various input means, and the processor (110) can control the station (100) based on the received user input. In addition, the user interface unit (140) can perform output based on a command of the processor (110) using various output means.

[0084] Next, the display unit (150) outputs an image on the display screen. The display unit (150) can output various display objects, such as content executed by the processor (110) or a user interface based on the control commands of the processor (110). In addition, the memory (160) stores a control program used in the station (100) and various data corresponding thereto. Such a control program may include a connection program required for the station (100) to connect to an AP or an external station.

[0085] The processor (110) of the present invention can execute various commands or programs and process data within the station (100). In addition, the processor (110) can control each unit of the above-described station (100) and control data transmission and reception between the units. According to an embodiment of the present invention, the processor (110) can execute a program for connection to an AP stored in the memory (160) and receive a communication setup message transmitted by the AP. In addition, the processor (110) can read information on the priority conditions of the station (100) included in the communication setup message and request connection to the AP based on the information on the priority conditions of the station (100). The processor (110) of the present invention may refer to the main control unit of the station (100), and according to an embodiment, may refer to a control unit for individually controlling some components of the station (100), such as the communication unit (120). That is, the processor (110) may be a modem or modulator and / or demodulator that modulates and / or demodulates wireless signals transmitted and received from the communication unit (120). The processor (110) controls various operations of transmitting and receiving wireless signals of the station (100) according to an embodiment of the present invention. A specific embodiment thereof will be described later.

[0086] The station (100) illustrated in FIG. 3 is a block diagram according to one embodiment of the present invention, and the blocks shown separately are logically distinguished elements of the device. Accordingly, the elements of the above-described device may be mounted as one chip or as multiple chips depending on the design of the device. For example, the processor (110) and the communication unit (120) may be implemented by being integrated into one chip or may be implemented as separate chips. In addition, in the embodiment of the present invention, some components of the station (100), such as the user interface unit (140) and the display unit (150), may be selectively provided in the station (100).

[0087] Fig. 4 is a block diagram illustrating the configuration of an AP (200) according to one embodiment of the present invention. As illustrated, the AP (200) according to the embodiment of the present invention may include a processor (210), a communication unit (220), and a memory (260). In Fig. 4, redundant descriptions of portions of the configuration of the AP (200) that are identical or corresponding to the configuration of the station (100) of Fig. 3 will be omitted.

[0088] Referring to FIG. 4, the AP (200) according to the present invention has a communication unit (220) for operating a BSS in at least one frequency band. As described above in the embodiment of FIG. 3, the communication unit (220) of the AP (200) may also include a plurality of communication modules that utilize different frequency bands. That is, the AP (200) according to the embodiment of the present invention may include two or more communication modules for different frequency bands, such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP (200) may include a communication module that utilizes a frequency band of 7.125 GHz or higher and a communication module that utilizes a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with a station according to the wireless LAN standard of the frequency band supported by the corresponding communication module. The communication unit (220) may operate only one communication module at a time or may operate multiple communication modules simultaneously, depending on the performance and requirements of the AP (200). In an embodiment of the present invention, the communication unit (220) may represent an RF communication module that processes an RF (Radio Frequency) signal.

[0089] Next, the memory (260) stores the control program used in the AP (200) and various data according to the control program. This control program may include a connection program that manages the connection of the station. In addition, the processor (210) controls each unit of the AP (200) and may control data transmission and reception between the units. According to an embodiment of the present invention, the processor (210) may execute a program for connection with a station stored in the memory (260) and transmit a communication setup message to one or more stations. At this time, the communication setup message may include information on the connection priority conditions of each station. In addition, the processor (210) performs connection setup according to a connection request from a station. According to one embodiment, the processor (210) may be a modem or a modulator and / or demodulator that modulates and demodulates a wireless signal transmitted and received from the communication unit (220). The processor (210) controls various operations of wireless signal transmission and reception of the AP (200) according to an embodiment of the present invention. Specific examples of this will be described later.

[0090] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0091] Referring to FIG. 5, the link between STA (100) and AP (200) is largely established through three stages: scanning, authentication, and association. First, the scanning stage is a stage in which STA (100) acquires access information of the BSS operated by AP (200). Methods for performing scanning include a passive scanning method in which information is acquired only by utilizing a beacon message (S101) periodically transmitted by AP (200), and an active scanning method in which STA (100) acquires access information by transmitting a probe request to AP (S103) and receiving a probe response from AP (S105).

[0092] The STA (100) that successfully receives wireless access information in the scanning step transmits an authentication request (S107a) and receives an authentication response from the AP (200) (S107b) to perform the authentication step. After the authentication step is performed, the STA (100) transmits an association request (S109a) and receives an association response from the AP (200) (S109b) to perform the association step. In this specification, association basically means wireless association, but the present invention is not limited thereto, and association in a broad sense may include both wireless association and wired association.

[0093] Meanwhile, an additional 802.1X-based authentication step (S111) and an IP address acquisition step (S113) via DHCP may be performed. In Fig. 5, the authentication server (300) is a server that processes STA (100) and 802.1X-based authentication, and may be physically connected to the AP (200) or may exist as a separate server.

[0094] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0095] A terminal performing wireless LAN communication performs carrier sensing before transmitting data to check whether the channel is busy. If a wireless signal above a certain strength is detected, the channel is determined to be busy, and the terminal delays access to the channel. This process is called clear channel assessment (CCA), and the level that determines whether the signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold received by the terminal is intended for the terminal, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected on the channel or a wireless signal with a strength lower than the CCA threshold is detected, the channel is determined to be idle.

[0096] When the channel is determined to be idle, each terminal with data to transmit performs a backoff procedure after an Inter Frame Space (IFS) time, such as an Arbitration IFS (AIFS) or a PCF IFS (PIFS), depending on the status of each terminal. In some embodiments, the AIFS may be used as a configuration to replace the existing DIFS (DCF IFS). Each terminal waits while decreasing the slot time by a random number determined for the terminal during the interval of the channel's idle state, and a terminal that has exhausted all of its slot time attempts to access the channel. The period during which each terminal performs the backoff procedure is called a contention window period.

[0097] If a specific terminal successfully accesses the channel, the terminal can transmit data through the channel. However, if the terminal attempting access collides with another terminal, the collided terminals are each assigned a new random number and perform a backoff procedure again. According to one embodiment, the random number newly assigned to each terminal may be determined within a range twice (2*CW) of the random number range (contention window, CW) previously assigned to the terminal. Meanwhile, each terminal performs the backoff procedure again in the next contention window period to attempt access, and at this time, each terminal performs the backoff procedure starting from the slot time remaining in the previous contention window period. In this way, each terminal performing wireless LAN communication can avoid collisions with each other for a specific channel.

[0098] Hereinafter, in the present invention, a terminal may be referred to as a non-AP STA, an AP STA, an AP, an STA, a receiving device, or a transmitting device, and the present invention is not limited thereto. In addition, in the present invention, an AP STA may be referred to as an AP.

[0099] <Various PPDU format examples>

[0100] Fig. 7 illustrates examples of various standard generation-specific PPDU (PLCP Protocol Data Unit) formats. More specifically, Fig. 7(a) illustrates an embodiment of a legacy PPDU format based on 802.11a / g, Fig. 7(b) illustrates an embodiment of a HE PPDU format based on 802.11ax, and Fig. 7(c) illustrates an embodiment of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. In addition, Fig. 7(d) illustrates detailed field configurations of L-SIG and RL-SIG commonly used in the above PPDU formats.

[0101] Referring to FIG. 7(a), the preamble of a legacy PPDU includes a legacy short training field (L-STF), a legacy long training field (L-LTF), and a legacy signal field (L-SIG). In an embodiment of the present invention, the L-STF, L-LTF, and L-SIG may be referred to as a legacy preamble.

[0102] Referring to FIG. 7(b), the preamble of the HE PPDU additionally includes RL-SIG (Repeated Legacy Short Training field), HE-SIG-A (High Efficiency Signal A field), HE-SIG-B (High Efficiency Signal B field), HE-STF (High Efficiency Short Training field), and HE-LTF (High Efficiency Long Training field) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF may be referred to as a HE preamble. The specific configuration of the HE preamble may be modified according to the HE PPDU format. For example, HE-SIG-B may be used only in the HE MU PPDU format.

[0103] Referring to FIG. 7(c), the preamble of the EHT PPDU additionally includes, in addition to the legacy preamble, an RL-SIG (Repeated Legacy Short Training field), a U-SIG (Universal Signal field), an EHT-SIG-A (Extremely High Throughput Signal A field), an EHT-SIG-A (Extremely High Throughput Signal B field), an EHT-STF (Extremely High Throughput Short Training field), and an EHT-LTF (Extremely High Throughput Long Training field). In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF may be referred to as an EHT preamble. The specific configuration of the non-legacy preamble may be modified according to the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some of the EHT PPDU formats.

[0104] The L-SIG field included in the PPDU preamble applies 64FFT OFDM and consists of a total of 64 subcarriers. Of these, 48 subcarriers, excluding the guard subcarrier, DC subcarrier, and pilot subcarrier, are used for L-SIG data transmission. Since L-SIG applies BPSK, Rate=1 / 2 Modulation and Coding Scheme (MCS), it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of L-SIG.

[0105] Referring to Fig. 7(d), L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field consists of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which combine modulation methods such as BPSK / QPSK / 16-QAM / 64-QAM and inefficiencies such as 1 / 2, 2 / 3, and 3 / 4. Combining the information in the L_RATE field and the L_LENGTH field can indicate the total length of the corresponding PPDU. In non-legacy PPDU formats, the L_RATE field is set to the minimum speed of 6 Mbps.

[0106] The L_LENGTH field is allocated in bytes, with a total of 12 bits, allowing for signaling up to 4095. In combination with the L_RATE field, it can indicate the length of the corresponding PPDU. At this time, legacy and non-legacy terminals may interpret the L_LENGTH field in different ways.

[0107] First, the method by which a legacy terminal or non-legacy terminal interprets the length of the PPDU using the L_LENGTH field is as follows. If the value of the L_RATE field is set to indicate 6 Mbps, 3 bytes (i.e., 24 bits) can be transmitted during 4 us, which is the duration of one symbol of 64 FFT. Therefore, by adding 3 bytes corresponding to the SVC field and Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the transmission amount of one symbol, the number of symbols based on 64 FFT after L-SIG is obtained. Multiplying the obtained number of symbols by 4 us, which is the duration of one symbol, and then adding 20 us required for transmission of L-STF, L-LTF, and L-SIG, the length of the PPDU, i.e., the reception time (RXTIME) is obtained. This can be expressed as a formula as shown in Mathematical Expression 1 below.

[0108]

[0109] At this time, represents the smallest natural number greater than or equal to x. Since the maximum value of the L_LENGTH field is 4095, the length of the PPDU can be set to a maximum of 5.484 ms. A non-legacy terminal transmitting the PPDU must set the L_LENGTH field as in Mathematical Expression 2 below.

[0110]

[0111] Here, TXTIME is the total transmission time that constitutes the corresponding PPDU, as shown in mathematical expression 3 below. In this case, TX represents the transmission time of X.

[0112]

[0113] Referring to the above formulas, the length of the PPDU is calculated based on the rounded value of L_LENGTH / 3. Therefore, for any value of k, three different values ​​of L_LENGTH={3k+1, 3k+2, 3(k+1)} indicate the same PPDU length.

[0114] Referring to Fig. 7(e), the U-SIG (Universal SIG) field continues to exist in EHT PPDUs and subsequent generation wireless LAN PPDUs, and serves to distinguish which generation of PPDU it is, including 11be. U-SIG is an OFDM 2 symbol based on 64FFT and can convey a total of 52 bits of information. Of these, 43 bits, excluding the 9 bits of CRC / Tail, are largely divided into the VI (Version Independent) field and the VD (Version Dependent) field.

[0115] The VI bit maintains its current bit configuration in the future so that even if a subsequent generation PPDU is defined, current 11be terminals can obtain information about the PPDU through the VI fields of the PPDU. To this end, the VI field consists of PHY version, UL / DL, BSS Color, TXOP, and Reserved fields. The PHY version field is 3 bits and sequentially distinguishes 11be and subsequent generation wireless LAN standards by version. For 11be, it has the value 000b. The UL / DL field distinguishes whether the PPDU is an uplink / downlink PPDU. BSS Color means an identifier for each BSS defined in 11ax and has a value of 6 bits or more. TXOP means the Transmit Opportunity Duration transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP including the PPDU can be inferred without having to decode the MPDU, and has a value of 7 bits or more.

[0116] The VD field is signaling information that is only useful for PPDUs of version 11be. It can be composed of fields that are commonly used in any PPDU format, such as PPDU format and BW, and fields that are defined differently for each PPDU format. The PPDU format is a delimiter that distinguishes EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs. The BW field signals five basic PPDU BW options (a BW that can be expressed in the form of an exponential power of 20*2 can be called a basic BW) of 20, 40, 80, 160 (80+80), and 320 (160+160) MHz, as well as various remaining PPDU BWs configured through Preamble Puncturing. In addition, after being signaled at 320 MHz, some 80 MHz can be signaled in a punctured form. Additionally, the punctured and modified channel shape can be signaled directly in the BW field, or can be signaled using the BW field together with a field appearing after the BW field (e.g., a field within the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signaling is possible, so only 3 puncturing modes can be signaled at most. If the BW field is 4 bits, a total of 16 BW signaling is possible, so a maximum of 11 puncturing modes can be signaled.

[0117] The fields located after the BW field vary depending on the type and format of the PPDU. MU PPDUs and SU PPDUs can be signaled in the same PPDU format, and a field to distinguish between MU PPDUs and SU PPDUs can be located before the EHT-SIG field, and additional signaling can be performed for this. Both SU PPDUs and MU PPDUs include the EHT-SIG field, but some fields that are not necessary in the SU PPDU may be compressed. In this case, the information in the compressed fields may be omitted or may have a reduced size compared to the original fields included in the MU PPDU. For example, in the case of the SU PPDU, the common field of the EHT-SIG may be omitted or replaced, or the user-specific field may be replaced or reduced to one, etc., and may have a different configuration.

[0118] Alternatively, the SU PPDU may further include a compression field indicating whether compression is performed, and some fields (e.g., RA field, etc.) may be omitted depending on the value of the compression field.

[0119] If part of the EHT-SIG field of the SU PPDU is compressed, information to be included in the compressed field may be signaled together in an uncompressed field (e.g., a common field, etc.). In the case of the MU PPDU, since it is a PPDU format for simultaneous reception by multiple users, the EHT-SIG field must be transmitted after the U-SIG field, and the amount of signaled information may be variable. That is, since multiple MU PPDUs are transmitted to multiple STAs, each STA must recognize the location of the RU to which the MU PPDU is transmitted, the STA to which each RU is allocated, and whether the transmitted MU PPDU was transmitted to itself. Therefore, the AP must include and transmit the above information in the EHT-SIG field. To this end, the U-SIG field signals information for efficiently transmitting the EHT-SIG field, which may be the number of symbols in the EHT-SIG field and / or the MCS modulation method. The EHT-SIG field may include information on the size and location of the RU allocated to each user.

[0120] In the case of an SU PPDU, multiple RUs may be allocated to an STA, and the multiple RUs may or may not be consecutive. If the RUs allocated to the STA are not consecutive, the STA must recognize RUs that are punctured in the middle to efficiently receive the SU PPDU. Therefore, the AP may transmit information on punctured RUs among the RUs allocated to the STA in the SU PPDU (e.g., puncturing patterns of the RUs). That is, in the case of an SU PPDU, a puncturing mode field including information indicating whether a puncturing mode is applied and a puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field may signal the type of a discontinuous channel that appears within the bandwidth.

[0121] The form of the signaled discontinuous channel is limited, and the BW and discontinuous channel information of the SU PPDU are indicated in combination with the value of the BW field. For example, in the case of the SU PPDU, since it is a PPDU transmitted to only a single terminal, the STA can recognize the bandwidth allocated to it through the BW field included in the PPDU, and can recognize the punctured resource among the allocated bandwidth through the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the terminal can receive the PPDU in the remaining resource units except for a specific channel of the punctured resource unit. At this time, multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0122] The reason why only a limited number of discontinuous channel types are signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing can be performed on a per-20 MHz subchannel basis, if puncturing is performed on a BW with multiple 20 MHz subchannels, such as 80, 160, and 320 MHz, the discontinuous channel type (if only the edge 20 MHz is punctured, it is also considered discontinuous) must be signaled by individually indicating whether the remaining 15 20 MHz subchannels, excluding the primary channel, are used. Dedicating 15 bits to signaling the discontinuous channel type of single-user transmission can result in excessive signaling overhead considering the low data rate of the signaling portion.

[0123] The present invention proposes a technique for signaling the discontinuous channel type of an SU PPDU, and illustrates the discontinuous channel type determined according to the proposed technique. In addition, the present invention proposes a technique for signaling the puncturing types of the Primary 160MHz and Secondary 160MHz in a 320MHz BW configuration of an SU PPDU, respectively.

[0124] In addition, one embodiment of the present invention proposes a technique for differentiating the configuration of a PPDU indicated by preamble puncturing BW values ​​according to the PPDU format signaled in the PPDU format field. Assuming that the BW field is 4 bits long, in the case of an EHT SU PPDU or a TB PPDU, an EHT-SIG-A of 1 symbol may be additionally signaled after the U-SIG, or EHT-SIG-A may not be signaled at all. Therefore, considering this, it is necessary to fully signal up to 11 puncturing modes through only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, an EHT-SIG-B is additionally signaled after the U-SIG, so up to 11 puncturing modes can be signaled in a different way from the SU PPDU. In the case of an EHT ER PPDU, the BW field can be set to 1 bit to signal whether the PPDU uses a 20 MHz or 10 MHz band.

[0125] Figure 7(f) illustrates the configuration of the Format-specific field of the VD field when the PPDU format field of the U-SIG indicates an EHT MU PPDU. In the case of the MU PPDU, the SIG-B signaling field for simultaneous reception by multiple users is essential, and SIG-B can be transmitted after the U-SIG without a separate SIG-A. To this end, the U-SIG must signal information for decoding SIG-B. These fields include the SIG-B MCS, SIG-B DCM, Number of SIG-B Symbols, SIG-B Compression, and Number of EHT-LTF Symbols fields.

[0126] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) PPDU formats and a method for indicating the same according to an embodiment of the present invention.

[0127] Referring to FIG. 8, a PPDU can be composed of a preamble and a data portion, and the format of one type of EHT PPDU can be distinguished according to the U-SIG field included in the preamble. Specifically, whether the format of the PPDU is an EHT PPDU can be indicated based on the PPDU format field included in the U-SIG field.

[0128] Figure 8 (a) shows an example of an EHT SU PPDU format for a single STA. The EHT SU PPDU is a PPDU used for single user (SU) transmission between an AP and a single STA, and an EHT-SIG-A field for additional signaling may be located after the U-SIG field.

[0129] Figure 8 (b) shows an example of the EHT Trigger-based PPDU format, which is an EHT PPDU transmitted based on a trigger frame. The EHT Trigger-based PPDU is an EHT PPDU transmitted based on a trigger frame and is an uplink PPDU used for responding to the trigger frame. Unlike the EHT SU PPDU, the EHT PPDU does not have an EHT-SIG-A field located after the U-SIG field.

[0130] Figure 8 (c) illustrates an example of the EHT MU PPDU format, which is an EHT PPDU for multiple users. The EHT MU PPDU is a PPDU used to transmit a PPDU to one or more STAs. The EHT MU PPDU format may include a HE-SIG-B field after the U-SIG field.

[0131] Fig. 8(d) illustrates an example of an EHT ER SU PPDU format used for single-user transmission with STAs in an extended range. The EHT ER SU PPDU can be used for single-user transmission with STAs in a wider range than the EHT SU PPDU described in Fig. 8(a), and the U-SIG field can be repeatedly positioned on the time axis.

[0132] The EHT MU PPDU described in (c) of FIG. 8 can be used by an AP for downlink transmission to multiple STAs. At this time, the EHT MU PPDU can include scheduling information so that multiple STAs can simultaneously receive the PPDU transmitted from the AP. The EHT MU PPDU can transmit AID information of the receiver and / or transmitter of the PPDU transmitted through the user specific field of EHT-SIG-B to the STA. Accordingly, multiple terminals receiving the EHT MU PPDU can perform a spatial reuse operation based on the AID information of the user specific field included in the preamble of the received PPDU.

[0133] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information about the configuration of resource units (e.g., the partitioning form of resource units) in a specific bandwidth (e.g., 20 MHz, etc.) of the frequency axis. That is, the RA field may indicate the configuration of resource units partitioned in the bandwidth for transmission of the HE MU PPDU for the STA to receive the PPDU. Information about the STA allocated (or designated) to each partitioned resource unit may be included in the user-specific field of the EHT-SIG-B and transmitted to the STA. That is, the user-specific field may include one or more user fields corresponding to each partitioned resource unit.

[0134] For example, among the multiple resource units that are divided, a user field corresponding to at least one resource unit used for data transmission may include an AID of a receiver or a sender, and a user field corresponding to the remaining resource unit(s) that are not used for data transmission may include a preset null STA ID.

[0135] Two or more PPDUs illustrated in FIG. 8 can be indicated with a value indicating the same PPDU format. That is, two or more PPDUs can be indicated with the same PPDU format through the same value. For example, EHT SU PPDU and EHT MU PPDU can be indicated with the same value through the U-SIG PPDU format subfield. At this time, EHT SU PPDU and EHT MU PPDU can be distinguished by the number of STAs receiving the PPDU. For example, a PPDU received by only one STA can be identified as an EHT SU PPDU, and if the number of STAs is set so that two or more STAs receive it, it can be identified as an EHT MU PPDU. In other words, two or more PPDU formats illustrated in FIG. 8 can be indicated through the same subfield value.

[0136] In addition, among the fields illustrated in FIG. 8, some fields or some information of the fields may be omitted, and a case in which some fields or some information of the fields are omitted may be defined as compression mode or compressed mode.

[0137] FIG. 9 is a diagram illustrating a multi-link device according to one embodiment of the present invention.

[0138] Referring to FIG. 9, the concept of a device that is affiliated with one or more STAs may be defined. In another embodiment, according to one embodiment of the present invention, devices that are affiliated with more than one STA (i.e., two or more) may be defined. In this case, the device may be a logical concept. Accordingly, devices that are affiliated with one or more or more than one STA of this concept may be referred to as a multi-link device (MLD), a multi-band device, or a multi-link logical entity (MLLE).

[0139] Alternatively, the devices of the above concept may be referred to as multi-link entities (MLEs). Furthermore, an MLD may have one medium access control service access point (MAC SAP) up to a logical link control (LLC), and an MLD may have one MAC data service.

[0140] STAs included in MLD can operate on more than one link or channel. That is, STAs included in MLD can operate on multiple different channels. For example, STAs included in MLD can operate using channels in different frequency bands of 2.4 GHz, 5 GHz, and 6 GHz. Through this, MLD can gain benefits in channel access and improve the performance of the overall network. While conventional wireless LANs operate on a single link, MLD operation can obtain more channel access opportunities by utilizing multiple links, or STAs can operate efficiently on multiple links by considering channel conditions.

[0141] Additionally, if the STAs affiliated with an MLD are APs, the MLD to which the APs are affiliated may be an AP MLD. However, if the STAs affiliated with an MLD are non-AP STAs, the MLD to which the non-APs are affiliated may be a non-AP MLD.

[0142] Referring to FIG. 9, there may be an MLD including multiple STAs, and multiple STAs included in the MLD may operate on multiple links. In FIG. 9, an MLD including APs AP1, AP2, and AP3 may be referred to as an AP MLD, and an MLD including non-AP STAs non-AP STA1, non-AP STA2, and non-AP STA3 may be referred to as a non-AP MLD. The STAs included in the MLD may operate on Link 1, Link 2, Link 3, or some of Links 1 to 3.

[0143] According to an embodiment of the present invention, a 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 multiple links, multi-link setup may have to be performed first. The multi-link setup operation may be performed using a multi-link setup element. Here, the multi-link setup element may include capability information related to the multi-link, and the capability information may include information related to a link through which an STA included in the MLD can receive a frame while another STA included in the MLD can transmit a frame through another link. That is, the capability information may include information related to whether STAs (non-AP STAs and / or APs (or AP STAs) can simultaneously transmit / receive frames in different transmission directions through the links included in the MLD. In addition, the capability information may further include information related to available links or operating channels. Multi-link setup may be established through negotiation between peer STAs, and multi-link operation may be established through one link.

[0144] According to one embodiment of the present invention, a mapping relationship may exist between a TID and a link of an MLD. For example, when a TID and a link are mapped, the TID may be transmitted through the mapped link. The mapping between the TID and the link may be directional-based. For example, mapping may be performed for each of the two directions between MLD1 and MLD2. Furthermore, the mapping between the TID and the link may have a default setting. For example, the mapping between the TID and the link may be such that all TIDs are mapped to a certain link by default.

[0145] FIG. 10 shows an example of whether devices (STRs of MLD#1 and MLD#2) support a relatively narrow frequency separation distance according to an embodiment of the present invention.

[0146] According to the embodiment of FIG. 10, Link1 and Link2 represent links that utilize BWs that are close to each other in frequency. The frequency range used by Link1 is indicated by a hatched square, and the frequency range used by Link2 is indicated by a grid-filled square. In this embodiment, MLD#1 is an MLD having STA1-1 and STA1-2, and STA1-1 and STA1-2 operate in Link1 and Link2, respectively. In addition, MLD#2 is an MLD having STA2-1 and STA2-2, and STA2-1 and STA2-2 operate in Link1 and Link2, respectively. At this time, the links used by STAx-1 and STAx-2 belonging to MLD#1 and MLD#2 are the same as Link1 and Link2, respectively, but the interference between STAs of MLD#1 may be less than the interference between STAs of MLD#2. Accordingly, while STA1-1 of the above MLD#1 can transmit over Link1 and STA1-2 can successfully decode packets received over Link2, when STA2-1 of the above MLD#2 transmits over Link1, relatively strong interference may occur in Link2, which may hinder decoding of STA2-2. Accordingly, whether or not there is STR between STAs within a single MLD may vary depending on the MLD.

[0147] The AP MLD and the STA MLD can exchange information on whether STR is supported between APs in the AP MLD and whether STR is supported between STAs in the STA MLD to determine the operation of APs and STAs utilizing each link. At this time, the STR support element can be utilized to indicate whether STR is supported by each link. At this time, the STR support element can be an element with a different name that exchanges information on whether STR is supported between devices in each MLD between the two MLDs.

[0148] In one embodiment, the STR support element may indicate with 1 bit each whether STR is supported between STAs and APs in the MLD. For example, when the STA MLD operates STA1, STA2, and STA3, one bit may be set to 1 to indicate that STR is supported between STA1 and STA2. On the other hand, one bit may be set to 0 to indicate that STR is not supported between STA2 and STA3, and another bit may be set to 1 to indicate that STR is supported between STA1 and STA3. Consequently, the STR support element may signal 101 whether STR is supported between STA1 and STA2, STA2 and STA3, and STA1 and STA3 using a total of 3 bits. At this time, if Link1 used by STA1 is 2.4 GHz, it is assumed that STA1 always supports STR in relation to other STAs in the STA MLD, so only the STR of STA2 and STA3 can be signaled with 1 bit (or, if there are 2 STAs in the STA MLD, it can always be indicated with 1 bit).

[0149] As described above, since STR support may vary depending on the frequency separation of each Link, if the AP MLD changes the center frequency of each Link or the Operation BW of each Link, STR support between STAs of the associated STA MLDs may change. Accordingly, if the AP MLD changes the Operation BW or center frequency of part or all of the Link, the STR support element may be exchanged as necessary. At this time, the STR support element may be exchanged through a request and response between the AP and the STA, or the STA may automatically transmit it to the AP after changing the center frequency and / or the Operation BW.

[0150] In addition, if STR support is not possible between STAs within the STA MLD, the STA MLD may request the AP to change the center frequency of some or all of the Links used by STAs that do not support STR, change the Operation Bandwidth (BW), or change the Primary Channel (Primary 20 Channel) of 20 MHz. At this time, the Link change request may be transmitted to the AP MLD through the Link for which the STA MLD requests a change, or may be transmitted from the AP MLD through another STA (of another Link) within the same STA MLD. At this time, the Link change request transmitted through another Link may include information on the Link to be changed (such as a Link number). At this time, the meaning of the Link change used in the present embodiment may be interpreted as meaning a change of the Operating Channel within 2.4, 5, and 6 GHz, rather than a frequency shift between the 2.4, 5, and 6 GHz Bands.

[0151] Additionally, the Link change request may include information regarding the method for changing the Link. In one embodiment, the Link change request may indicate that the center frequency of the Link is to be moved to a higher or lower frequency. Alternatively, the Link change request may implicitly indicate that the center frequency of the Link is to be changed in a direction away from the adjacent Link. In another embodiment, the Link change request may indicate that the BW of the Link is to be reduced. In yet another embodiment, the Link change request may indicate that the Primary Channel location of the Link is to be changed to a lower or higher frequency.

[0152] An AP that receives the Link change request from the STA MLD may accept the STA's request and change the Link for which the change request was received (center frequency or BW or primary channel location), or may ignore the STA's Link change request and maintain the Link-related settings.

[0153] <Simultaneous transmission using multiple links>

[0154] As described above, STAs operated by a specific MLD may have different STR support depending on the relationship (such as separation distance) between the links on which each STA operates. If STA1 and STA2 operated by a specific MLD are operated on Link1 and Link2, which are link pairs that do not support STR, STA1 and STA2 will be restricted in their operations depending on the operational statuses they are performing. More specifically, if STA1 is performing PPDU transmission over Link1, STA2 may not be able to normally decode packets received on Link2 due to in-device interference caused by the transmission performed by STA1 on Link1. In this way, when STAs operated on a specific link pair (of the same MLD) are hindered in their reception operations due to in-device interference, we can say that the STAs are in a non-STR relationship. In this case, an MLD including STAs that are in a non-STR relationship with each other can be considered a non-STR MLD.

[0155] Meanwhile, STAs in a non-STR relationship may be disturbed not only in receiving operations but also in channel access operations due to interference within the device, as explained with an example in Figure 11 below.

[0156] FIG. 11 illustrates an embodiment in which a channel access operation performed by another STA of a non-STR MLD is interrupted due to a PPDU transmission performed by a specific STA of the non-STR MLD.

[0157] Referring to Fig. 11, a non-STR MLD can operate STA1 and STA2 on Link1 and Link2, respectively. In this case, if Link1 and Link2 are a non-STR link pair, the transmissions performed by STA1 and STA2 may cause interference so great that they hinder the successful reception of packets received on Link2 and Link1, respectively.

[0158] As illustrated in FIG. 11, the CCA operation of STA1, which is performing a backoff procedure on Link 1, may be interrupted due to interference that occurs when STA2 transmits a PPDU on Link 2. In other words, the interference that occurs when STA2 transmits a PPDU on Link 2 may cause interference higher than a CCA energy (e.g., Energy Detection) threshold on Link 1, and as a result, STA1, which is performing a backoff procedure on Link 1, may determine that Link 1 is BUSY. As a result, STA1 may not be able to complete the backoff procedure because it may misunderstand that Link 1 is BUSY during the time that STA2 transmits a PPDU, even though there are no other devices occupying Link 1.

[0159] As described above, when another STA of the non-STR MLD cannot perform packet reception or channel access procedures due to interference within the device that occurs when a specific STA of the non-STR MLD performs transmission, we can say that the other STA is in a BLIND state.

[0160] In this way, when an STA of a non-STR MLD becomes BLIND, the MLD cannot receive packets through the STA in the BLIND state, nor can it perform independent channel access (for transmission), and thus cannot obtain any benefit through the link on which the STA in the BLIND state operates. Therefore, the non-STR MLD can utilize a special channel access mechanism to prevent STAs operating on a link pair of a non-STR relationship from becoming BLIND due to each other's transmission operations.

[0161] In order to prevent STAs operating on a link pair of a non-STR relationship from becoming BLIND due to each other's transmission operations, MLD can reserve (delay) the start of transmission on a specific link even after the channel access procedure of the specific link is terminated.

[0162] Thereafter, the start of transmission on the specific link can be performed at the time when the channel access procedure of a link other than the specific link is completed, and as a result, transmission can be performed simultaneously on the specific link and the link other than the specific link. To this end, the MLD may be allowed a mechanism that can delay the channel access procedure rather than immediately starting transmission even after the channel access procedure is completed. In this case, the mechanism that can delay the channel access procedure may be one that allows transmission to be reserved while maintaining the backoff counter (BO) at 0.

[0163] That is, even if a channel access procedure is terminated on one of the multiple links of the MLD and the value of the back-off counter reaches '0', if the value of the back-off counter on another link has not reached '0', the STA of the MLD may not perform uplink transmission on the link and may maintain the value of the back-off counter as '0'. In other words, the STA of the MLD may choose not to perform uplink transmission on a specific link and to maintain the value of the back-off counter as '0' if the value of the back-off counter on another link of the MLD has not reached '0'.

[0164] For example, a multi-link of an MLD may be composed of a first link and a second link, and a back-off procedure for channel access in the first link may be performed by a first back-off counter, while a back-off procedure for channel access in the second link may be performed by a second back-off counter. In this case, the back-off procedure may be individually performed through each of the first link and the second link included in the multi-link.

[0165] In this case, if one back-off counter among the first back-off counter and the second back-off counter reaches '0' before the remaining back-off counters, a specific link among the first link and the second link that uses the one back-off counter does not perform the uplink transmission, and the one back-off counter may maintain a value of '0' until the remaining back-off counter reaches a value of '0'. Alternatively, the one back-off counter may continue to maintain a value of '0' even after the remaining back-off counter reaches a value of '0'.

[0166] At this time, the time at which transmission is performed simultaneously on the specific link and a link other than the specific link may be a slot boundary at which a channel access procedure is completed on a link other than the specific link or a slot following a slot at which a channel access procedure is completed on the other link. Alternatively, the time at which transmission is performed simultaneously on the specific link and a link other than the specific link may be a specific slot boundary after a channel access procedure is completed on a link other than the specific link. In this case, the specific slot boundary may be a slot boundary of the specific link immediately after a channel access procedure is completed on the other link.

[0167] That is, since the slot settings in each link may be different, the boundaries of slots between links may not match. Therefore, the boundaries of slots between links may not match in each slot where the backoff counter is decreased, and if all backoff counters by the backoff procedure reach '0' through the reservation operation described above in each of the multiple links of the MLD, the slot boundaries in each link may not match. Since the slots in each link can be set individually, the slot boundaries in each link may not match. Therefore, even if the values ​​of the backoff counters in each link are all '0', the slot boundaries may be different. In this case, simultaneous transmission can be performed according to the slot boundary of a specific link when the value of the backoff counter of a specific link among the multiple links is '0'. In other words, each link can perform uplink transmission simultaneously by delaying or shortening the transmission time of uplink transmission according to the slot boundary of a specific link, rather than performing uplink transmission according to the slot boundary of the respective links.

[0168] For example, if the multi-link of the MLD is composed of a first link and a second link, and one of the first back-off counter of the first link and the second back-off counter of the second link reaches '0' before the remaining back-off counter, the slot boundaries of the first link and the second link may not match when the remaining back-off counter reaches '0'. In this case, the transmission time of the uplink transmission in the second link can be shortened or delayed to control the slot boundary of the slot in which the first back-off counter of the first link is '0' or the slot boundary of the first slot which is the next slot of the slot.

[0169] At this time, the uplink transmission time on the first link and the uplink transmission time on the second link may be within a certain time period. For example, the uplink transmission time on the second link may be within 4 microseconds of the uplink transmission time on the first link.

[0170] In this way, uplink transmission can be performed simultaneously in the first link and the second link by performing uplink transmission at a time other than the slot boundary of the slot in which the second back-off counter of the second link is '0' or the slot boundary of the second slot which is the next slot of the slot.

[0171] At this time, simultaneous transmission may mean a case where transmission is performed on each link within a certain period of time.

[0172] The operation of a multi-link device accessing a channel in multiple links is described through FIGS. 12 to 24. In this case, the multiple links may be NSTR link pairs.

[0173] FIG. 12 shows that a multi-link device according to an embodiment of the present invention postpones transmission on a link when the multi-link device succeeds in channel access on one link first.

[0174] For convenience of explanation, it is assumed that the first station of the multi-link device operates on the first link and the second station operates on the second link. At this time, if the second station succeeds in channel access and the first station does not succeed in channel access, the second station can wait while maintaining the value of the backoff counter as 0 until the first station succeeds in channel access. When the first station succeeds in channel access, the first and second stations can start synchronized transmission. The synchronized transmission may be a transmission that starts within a predetermined time. The second station can perform channel sensing while maintaining the value of the backoff counter. At this time, the channel sensing may include at least one of energy detection (ED), preamble detection (PD), and network allocation (NAV) check. The second station can start synchronized transmission when the first station succeeds in channel access and the sensing result is idle.

[0175] In the embodiment of FIG. 12, a first station (STA1) of a multi-link device is connected to a first AP (AP1) in a first link (Link 1). A second station (STA2) is connected to a second AP (AP) in a second link (Link2). The second station (STA2) succeeds in channel access first, and the second station (STA2) does not perform transmission while maintaining the value of the backoff counter as 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) start synchronized transmission.

[0176] While the second station delays transmission, the channel accessed by the first station may be detected as busy. At this time, the second station (STA2) may initiate unsynchronized transmission. Additional specific embodiments are described with reference to FIGS. 13 and 14.

[0177] FIG. 13 illustrates the operation of a multi-link device when the channel of the second link is detected as occupied when the multi-link device postpones transmission on the first link after first successfully accessing the channel on the first link according to an embodiment of the present invention.

[0178] If the channel accessed by the second station is detected as busy while the first station delays transmission, the first station may acquire a new backoff 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 for the newly acquired backoff counter x slot duration. That is, the operation of detecting whether the channel is idle during AIFS in general channel access may be omitted. In another specific embodiment, if the channel is idle during AIFS as in general channel access, the first station may perform channel sensing for the newly acquired backoff counter x slot duration. When the second station acquires a new backoff 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.

[0179] In the embodiment of FIG. 13, a first station (STA1) of a multi-link device is connected to a first AP (AP1) in a first link (Link 1). A second station (STA2) is connected to a second AP (AP) in a second link (Link2). When the first station (STA1) succeeds in channel access first, the first station (STA1) does not transmit while keeping the value of the backoff counter at 0 until the second station (STA2) succeeds in channel access. At this time, the channel of the second link is detected to be busy. The first station (STA1) acquires a new backoff counter and performs channel sensing for a number of slots equal to the number of the backoff counter. When the first station (STA1) succeeds in channel access, the first station (STA2) starts unsynchronized transmission.

[0180] FIG. 14 illustrates the operation of a multi-link device when the channel of the second link is detected as occupied when the multi-link device postpones transmission on the first link after first successfully accessing the channel on the first link according to another embodiment of the present invention.

[0181] Even if the channel accessed by the second station is detected as busy while the first station delays transmission, the first station may delay transmission until the second station successfully accesses the channel. In this case, the first station may perform channel sensing until the second station successfully accesses the channel.

[0182] In the embodiment of FIG. 14, a first station (STA1) of a multi-link device is connected to a first AP (AP1) in a first link (Link 1). A second station (STA2) is connected to a second AP (AP) in a second link (Link2). The first station (STA1) succeeds in channel access first, and the first station (STA1) does not transmit while maintaining the value of the backoff counter as 0 until the second station (STA2) succeeds in channel access. At this time, the channel of the second link is detected to be 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.

[0183] In the embodiments described with reference to FIGS. 13 and 14, the first station can determine whether to perform synchronized transmission based on the duration of time during which the channel of the second link remains occupied. For example, if the duration of time during which the channel of the second link remains occupied is greater than a predetermined value, the first station can perform unsynchronized transmission. At this time, the first station can acquire a new backoff counter and perform channel access based on the acquired backoff counter. If the first station successfully accesses the channel, the first station can perform unsynchronized transmission.

[0184] If the duration of time that the channel of the second link remains occupied is equal to or less than a predefined value, the first station can perform synchronized transmission. The first station can delay transmission until the second station successfully accesses the channel. At this time, the first station can perform channel sensing until the second station successfully accesses the channel.

[0185]

[0186] In the embodiments described above, if a multi-link device excessively delays transmission on one link, the probability of transmission collisions may increase. This is explained in FIG. 15.

[0187] FIG. 15 illustrates an operation in a plurality of multi-link devices when the multi-link devices postpone transmission in a first link after the multi-link devices first succeed in channel access in the first link according to an embodiment of the present invention.

[0188] When multiple multi-link devices are all operating on the first link and the second link, and the multiple multi-link devices perform synchronized transmissions 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.

[0189] In the embodiment of FIG. 15, both the first multi-link device (STA MLD1) and the second multi-link device (STA MLD2) operate on the first link (Link 1) and the second link (Link 2). Both the first multi-link device (STA MLD1) and the second multi-link device (STA MLD2) succeed in channel access on the second link (Link 2) and delay transmission on the second link (Link 2) until the channel access on the first link (Link 1) succeeds. When the first multi-link device (STA MLD1) and the second multi-link device (STA MLD2) succeed in channel access on the first link (Link 1) at the same time, a transmission collision occurs on both the first link (Link 1) and the second link (Link 2).

[0190] The behavior of a multi-link device when a link is detected to be occupied while the multi-link device delays transmission on that link is described in FIG. 17.

[0191]

[0192] FIGS. 16 and 17 illustrate the operation of a multi-link device according to an embodiment of the present invention when the multi-link device first succeeds in channel access on the first link, and then postpones transmission on the first link and the channel of the first link is detected to be busy.

[0193] If the channel accessed by the first station is detected as busy while the first station delays transmission, the first station may acquire a new backoff counter and perform a channel access procedure. At this time, the first station may maintain the value of the CW at the value of the previously used CW.

[0194] When the channel accessed by the first station is detected as busy while the first station delays transmission, the second station may successfully access the channel. At this time, the second station may delay transmission until the first station successfully accesses the channel. In another specific embodiment, the second station may perform unsynchronized transmission without delaying transmission.

[0195] In the embodiments of FIGS. 16 and 17, a first station (STA1) of a multi-link device is connected to a first AP (AP1) in a first link (Link 1). A second station (STA2) is connected to a second AP (AP) in a second link (Link2). The first station (STA1) succeeds in channel access first, and delays transmission. At this time, the first station (STA1) determines that the channel of the first link (Link 1) is occupied. The first station (STA1) acquires a new backoff 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, the second station (STA2) first succeeds in channel access and performs unsynchronized transmission without delaying transmission.

[0196]

[0197] As in the previously described embodiments, for synchronized transmission, channels on different links must be successfully accessed and simultaneously idle. Therefore, the timing at which a multi-link device can perform synchronized transmission is limited, and transmissions by the multi-link device may be excessively delayed. This is explained in detail in Figure 19.

[0198] FIG. 18 shows that a transmission is delayed when a multi-link device according to an embodiment of the present invention performs channel access for synchronized transmission.

[0199] A first station (STA1) of a multi-link device connects to a first AP (AP1) on a first link (Link 1). A second station (STA2) connects to a second AP (AP) on a second link (Link2). The first station (STA1) succeeds in channel access first, and delays transmission. Before the second station (STA2) succeeds in channel access, the first station (STA1) detects that the channel of the first link (Link 1) is busy. Therefore, the first station (STA1) acquires a new backoff counter and starts the channel access procedure again. The second station (STA2) succeeds in channel access, and delays transmission because the first station (STA1) is performing channel access. Before the first station (STA1) succeeds in channel access, the second station (STA2) detects that the channel of the second link (Link 2) is busy. Therefore, the second station (STA2) acquires a new backoff counter and starts the channel access procedure again. Ultimately, both the first station (STA1) and the second station (STA2) succeeded in channel access, but did not transmit.

[0200] Unconditional repetition of transmission delay and channel access procedures like this can result in excessive transmission delay. A method for a station in a multi-link device to determine whether to perform a new backoff procedure during a transmission delay is described in Figure 20.

[0201]

[0202] FIGS. 19 and 20 illustrate an operating method when a station of a multi-link device according to an embodiment of the present invention detects that a channel is busy during transmission.

[0203] A station of a multi-link device may detect that a channel is occupied during a transmission delay. At this time, the station may determine whether to restart the channel access procedure based on the channel access status of other stations of the multi-link device at the time when the channel is determined to be idle again. Specifically, the station may determine whether to perform channel access by acquiring a new backoff counter based on the channel access status of other stations of the multi-link device at the time when the channel is determined to be idle again. If the first station is continuing the backoff procedure of the second station at the time when the first station determines the channel is idle again, the first station may delay transmission. In addition, if the second station succeeds in channel access at the time when the first station determines the channel is idle again, the first station may acquire a new backoff counter and perform the channel access procedure.

[0204] At this time, if the station detects that the channel is idle for a predetermined period of time, the station may determine that the channel is idle. The predetermined period of time may be the AIFS. In another specific embodiment, the predetermined period of time may be the AIFS, excluding the time required for reception / transmission switching.

[0205] In the embodiments of FIGS. 19 and 20, a first station (STA1) of a multi-link device is connected to a first AP (AP1) in a first link (Link 1). A second station (STA2) is connected to a second AP (AP) in 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) detects that the channel of the first link (Link 1) is busy. In the embodiment of FIG. 20, when the first station (STA1) detects that the channel is idle again, the second station (STA2) is performing a channel access procedure. Therefore, the first station (STA1) only performs channel sensing without acquiring a new backoff counter. When the second station (STA2) succeeds in channel access, the first station (STA1) and the second station (STA2) perform synchronized transmission.

[0206] In the embodiment of FIG. 20, when the first station (STA1) detects that the channel is idle again, the second station (STA2) succeeds in channel access and is delaying transmission. Therefore, the first station (STA1) acquires a new backoff counter and performs channel access. When the first station (STA1) succeeds in channel access, the first station (STA1) and the second station (STA2) perform synchronized transmission.

[0207]

[0208] FIG. 21 illustrates a method for obtaining a new backoff counter value when a station of a multi-link device according to an embodiment of the present invention detects that a channel is busy during a transmission delay.

[0209] In the embodiments described above, when a station of a multi-link device acquires a backoff counter again after detecting that the channel during transmission is busy, the station may set the value of CW to a value smaller than the previously used CW value. For example, the station may set the value of CW to half of the previously used CW value. In another specific embodiment, the station may set the value of CW to a floor value of half of the previously used CW value. Immediately after a successful channel access procedure using the newly acquired backoff counter, the station may transmit only a pre-designated type of frame. In this case, the pre-designated frame may be an RTS frame or an MU-RTS frame. In another specific embodiment, the pre-designated frame may be a BQRP frame.

[0210] If a transmission fails immediately after a successful channel access procedure using the newly acquired backoff counter, the station may set the value of CW to the value of CW before the adjustment x 2 -1. That is, the station may set the value of CW to the value of CW before the transmission delay x 2 -1.

[0211] In the embodiment of FIG. 21, a first station (STA1) is connected to a first AP (AP1) on a first link (Link 1). A second station (STA2) is connected to a second AP (AP) on a second link (Link 2). 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) detects that the channel of the first link (Link 1) is busy. The first station (STA1) sets the CW to half the value of the previously used CW and acquires 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.

[0212]

[0213] FIG. 22 shows an operation for determining whether a station of a multi-link device according to an embodiment of the present invention will perform synchronized transmission while delaying transmission.

[0214] For convenience of explanation, it is assumed that the first station of the multi-link device operates on the first link and the second station of the multi-link device operates on the second link. If 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 predetermined period until the second station succeeds in channel access. Specifically, if the channel of the first link is continuously idle for a predetermined period until the second station succeeds in channel access, the first station can perform synchronized transmission with the second station. In this case, the predetermined period may be DIFS. In addition, the predetermined period may be PIFS. In addition, the predetermined period may be AIFS. In this case, the value of AIFS may be determined according to the AC of the frame that the first station intends to transmit. Specifically, the value of AIFS may be an AIFS corresponding to an AC with a higher priority among the ACs of the frame that the first station intends to transmit.

[0215] In the embodiment of FIG. 22, a first station (STA1) is connected to a first AP (AP1) on a first link (Link 1). A second station (STA2) is connected to a second AP (AP) on a second link (Link2). The second station (STA2) succeeds in channel access first, and the second station (STA2) delays transmission. Before the first station (STA1) succeeds in channel access, the second station (STA2) detects that the channel of the second link (Link 2) is busy. Even though the channel of the second link (Link 2) is detected to be busy, the second station (STA2) continues to delay transmission. The second station (STA2) determines whether the channel of the second link (Link2) is continuously idle for an AIFS when the first station (STA1) succeeds in channel access. When the first station (STA1) succeeds in channel access, the channel of the second link (Link2) is idle continuously for AIFS, so the first station (STA1) and the second station (STA2) perform synchronized transmission.

[0216]

[0217] FIG. 23 and FIG. 24 illustrate the operation of a multi-link device according to an embodiment of the present invention when a station of the multi-link device detects that a channel on which transmission is being delayed is busy.

[0218] In the embodiments described through FIG. 22, when the first station is waiting for transmission and the second station successfully accesses the channel, the first station can determine that the channel of the first link is busy. At this time, the second station can obtain a new backoff counter and perform channel access. At this time, the second station can obtain the backoff counter by setting the CW to the same value as the previously used CW value. In another specific embodiment, the first station can obtain the channel access by obtaining a new backoff counter. At this time, the first station can obtain the backoff counter by setting the CW to the same value as the previously used CW value.

[0219] In the embodiments of FIGS. 23 and 24, a first station (STA1) is connected to a first AP (AP1) on a first link (Link 1). A second station (STA2) is connected to a second AP (AP) on a second link (Link 2). 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) detects that the channel of the second link (Link 2) has not been idle continuously for an AIFS.

[0220] In the embodiment of Figure 23, the first station (STA1) acquires a new backoff counter and performs channel access. The second station (STA2) delays transmission. After the first station (STA1) successfully accesses the channel, the channel of the second link (Link2) is detected as continuously idle for an AIFS. Therefore, the first station (STA1) and the second station (STA2) perform synchronized transmission.

[0221] In the embodiment of Fig. 24, the second station (STA2) acquires a new backoff counter and performs channel access. The first station (STA1) delays transmission. Subsequently, when the second station (STA2) successfully accesses the channel, the channel of the first link (Link1) is detected as continuously idle for an AIFS. Therefore, the first station (STA1) and the second station (STA2) perform synchronized transmission.

[0222] The method of applying EDCA to the synchronized transmission described above is explained through FIGS. 25 to 29.

[0223] Figure 25 shows an EDCA queue used when applying EDCA according to an embodiment of the present invention.

[0224] When EDCA is applied, the transmission processing order is determined based on the priority of the transmitted traffic. Traffic priority can be determined by traffic type or TID (Traffic ID). Traffic priority can be classified as AC_VO, AC_VI, AC_BE, or AC_BK. Each AC can be represented as follows:

[0225] 1) AC_VO: Voice

[0226] 2) AC_VI: Video

[0227] 3) AC_BE: Best Effort

[0228] 4) AC_BK: Background

[0229] Among the four ACs, AC_VO, AC_VI, AC_BE, and AC_BK can have higher priorities in that order. Specifically, ACs can influence the channel access procedure as follows:

[0230] In the embodiments described above, AIFS can be defined as SIFS + AIFSN[AC] * aSlotTime. Here, aSlotTime is the time of one slot, which is the unit used when a station performs a backoff operation for frame transmission. aSlotTime can be defined as 9μ when the bandwidth of the basic signal used in the BSS is 20 MHz. In addition, the minimum value of CW (CWmin) and the maximum value of the contention window (CWmax) can be different for each AC. The default AIFSN and CWmax values ​​for each AC can be set as shown in Table 1 below.

[0231]

[0232] An independent EDCA queue can be established for each AC. When a station receives traffic to be transmitted from a higher layer, the station can store the received traffic in the EDCA queue corresponding to the AC of the received traffic. At this time, independent EDCAF operations can be performed in each EDCA queue. Figure 25 illustrates this process, where a station receives traffic to be transmitted from a higher layer and stores the received traffic in the EDCA queue corresponding to the AC of the received traffic.

[0233] FIG. 26 illustrates a method for performing channel access based on slot boundaries according to an embodiment of the present invention.

[0234] In a backoff procedure, slot boundaries can be defined as at least one of the following:

[0235] 1) If the channel occupancy situation is caused by a frame transmitted by another terminal and no frame reception error situation occurs, if the channel status is in an idle state for the AIFSN[AC]*SlotTime-aRxTxTurnaroundTime time after the SIFS time after the completion of the occupancy time, then the time elapses.

[0236] 2) If the channel occupancy situation is caused by a frame transmitted by another station and a frame reception error situation occurs, if the channel status is a channel idle state for the time (EIFS - DIFS + AIFSN[AC] * aSlotTime + aSIFSTime - aRxTxTurnaroundTime) from the time of completion of the channel occupancy state by physical detection, then the time when that time has passed

[0237] 3) After transmitting a frame requesting transmission of a response frame (e.g., an ACK frame or a BlockAck frame), whichever of the following two points in time comes first:

[0238] A) If the channel state is idle for the time period AIFSN[AC] * aSlotTime + aSIFSTime - aRxTxTurnaroundTime after the reception expiration time for receiving a response frame after the transmission completion time of the PPDU including the frame, the time period AIFSN[AC] * aSlotTime + aSIFSTime - aRxTxTurnaroundTime elapses after the reception expiration time.

[0239] B) When a response frame is received, if the channel state is idle for AIFSN[AC]*aSlotTime - aRxTxTurnaroundTime after SIFS time from the time of completion of reception of the PPDU including the response frame, when AIFSN[AC]*SlotTime - aRxTxTurnaroundTime has elapsed after SIFS time from the time of completion of reception of the PPDU.

[0240] 4) When the channel state is idle for the time AIFSN[AC]*SlotTime - aRxTxTurnaroundTime after the SIFS time at which the PPDU transmission is completed, including a frame that does not require transmission of a response frame, the time AIFSN[AC]*aSlotTime - aRxTxTurnaroundTime elapses after the SIFS time at which the PPDU transmission is completed.

[0241] If the channel state is a channel idle state for the time period of AIFSN[AC] * aSlotTime + aSIFSTime - aRxTxTurnaroundTime after any channel occupancy time that does not meet conditions 1-4, the time period of AIFSN[AC] * aSlotTime + aSIFSTime - aRxTxTurnaroundTime elapses.

[0242] If the channel state is idle for aSlotTime time since the previous slot boundary time, the end point of aSlotTime

[0243]

[0244] aRxTxTurnaroundTime may be referred to as the time required for the station's transceiver to switch from receive mode to transmit mode. The transition time may be 4 us.

[0245] Meanwhile, at each slot boundary point, the station's EDCAF can perform one of the following actions:

[0246] 1) Decrease the backoff value by 1

[0247] 2) Perform frame transmission operation

[0248] 3) Generate a new backoff value and perform a backoff operation due to an internal conflict.

[0249] 4) Do not perform any action

[0250]

[0251] At a slot boundary, if there is a frame to be transmitted in the station's EDCA queue, the backoff value is 0, and no frame belonging to an AC with a higher priority than the EDCA queue is being transmitted (i.e., there is no internal collision), the station transmits the frame stored in the EDCA queue at the slot boundary.

[0252] Meanwhile, the EDCAF operating at the station may need to perform a backoff operation when one or more of the following situations occur:

[0253] 1) When a frame to be transmitted is generated at a station, if the frame is the first frame stored in the EDCA queue and the channel is occupied at the time of frame generation.

[0254] 2) When the station's frame transmission operation is completed or the TXOP acquired by the station for frame transmission has expired.

[0255] 3) If a frame is transmitted by acquiring a TXOP according to the EDCAF operation, but the first frame transmitted within the acquired TXOP fails to be transmitted.

[0256] 4) When a frame collision occurs within the EDCA queue and the AC of the frame causing the collision has a higher priority than the AC of the frame to be transmitted.

[0257]

[0258] In the situation 1) above, the operation of determining the channel status of the channel can be performed through a physical CS (Carrier Sensing) in which the station measures the received energy level, a virtual CS in which the station recognizes the signal length of the corresponding signal through the preamble including the received frame, and an operation of checking 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 status can be additionally checked by checking the NAV value.

[0259] Meanwhile, the EDCAF operating at the station can perform a backoff operation when one of the following situations occurs:

[0260] 1) If the frame transmission operation of a frame other than the first frame in the acquired TXOP fails.

[0261] 2) When a frame is to be transmitted using the 40 MHz / 80 MHz / 160 MHz / 320 MHz bandwidth through channel extension operation, but the channel access operation is to be performed again because the channel status of the sub-channel is determined to be channel occupied.

[0262] As previously explained, if a station has a frame to transmit in its 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 can recognize that an internal collision has occurred. At this time, the station obtains a new backoff value for the EDCA queue and performs the backoff operation again.

[0263] 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 busy at the time of frame generation, the station can generate a backoff value and perform a backoff operation. At this time, the backoff value can be set to a random number from 0 to (contention window value - 1) as the backoff value. For example, when a frame to be transmitted by the station is generated, the channel may be busy at that time, and a backoff value of 3 may be obtained according to the backoff operation. After the channel occupancy time, according to the definition 1) of the slot boundary, the next slot boundary may be a time when AIFS-aRxTxTurnaroundTime has passed after the channel occupancy time has expired. If the channel continues to be idle after the channel occupancy time, the next slot boundary may arrive whenever aSlotTime has passed. If the backoff value is not 0 at each slot boundary, the backoff value for transmitting the frame may be reduced by 1. Meanwhile, if the backoff value is 0 at the slot boundary, except for the internal collision situation described above, the station can switch the transceiver to the transmission mode to transmit the frame, and then the station can transmit the frame.

[0264] The EDCAF operation for performing synchronized transmission is described in Fig. 28.

[0265]

[0266] Figures 27 and 28 show an operation in which a multi-link device performs synchronized transmission according to an EDCAF operation according to an embodiment of the present invention.

[0267] The point in time when a station can transmit a frame may be the point in time when the station completes the channel access procedure according to the 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. At this time, 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 as 0 and delays frame transmission, the station may not be allowed to transmit a frame at any slot boundary. If a frame to be transmitted is generated with the backoff value as 0, the slot boundary immediately after the backoff value becomes 0 may be the first slot boundary after the frame is generated. If the 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.

[0268] Additionally, if a transmission is delayed on one link, a synchronized transmission can be performed on the boundary of the slot immediately after the backoff value becomes 0 on the other link. Consequently, the station can perform a synchronized transmission at the following point in time.

[0269] 1) The slot boundary point immediately after the backoff value becomes 0 on the link where the station is operating.

[0270] 2) When a station is already delaying transmission by maintaining the backoff value as 0 on the link it is operating on, at the slot boundary point immediately after another station in the multi-link has its backoff value set to 0 on another link.

[0271] At this time, referring to the definition of slot boundary point, the slot boundary immediately after the backoff value for transmitting a frame becomes 0 may include the meaning that the CCA (channel state check) result is idle (or not busy) from the slot boundary where it becomes 0 to the next slot boundary.

[0272] In the embodiments of FIGS. 27 and 28, a first station (STA1) is connected to a first AP (AP1) on a first link (Link 1). A second station (STA2) is connected to a second AP (AP) on a second link (Link2). In the embodiment of FIG. 28, 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 first station (STA1) and the second station (STA2) perform synchronized transmission. Specifically, from the time when the backoff counter value of the first station (STA1) becomes 0, the first station (STA1) and the second station (STA2) perform synchronized transmission at the next slot boundary. Therefore, the actual transmission starts after the transceiver switches to transmission mode from the time when the backoff counter value of the first station (STA1) becomes 0, and then synchronized transmission begins at the next slot boundary.

[0273] In the embodiment of Fig. 28, the first station (STA1) succeeds in channel access first, and the first station (STA1) delays transmission. When the second station (STA2) succeeds in channel access, the first station (STA1) and the second station (STA2) perform synchronized transmission. Specifically, from the time when the backoff counter value of the second station (STA2) becomes 0, the first station (STA1) and the second station (STA2) perform synchronized transmission at the next slot boundary. Therefore, the actual transmission begins after the transceiver switches to transmission mode from the time when the backoff counter value of the second station (STA2) becomes 0, and synchronized transmission begins at the next slot boundary.

[0274]

[0275] A station can transmit frames at slot boundaries where the backoff value becomes 0. This simplifies synchronized transmission.

[0276] FIG. 29 shows an operation in which a multi-link device performs synchronized transmission according to an EDCAF operation according to another embodiment of the present invention.

[0277] Slot boundary points can be:

[0278] 1) If the channel occupancy situation is caused by a frame transmitted by another station and no frame reception error situation occurs, if the channel status is in an idle state for (AIFSN[AC] + 1)*aSlotTime - aRxTxTurnaroundTime time after the SIFS time after the completion of the occupancy time, then the time elapses.

[0279] 2) If the channel occupancy situation is caused by a frame transmitted by another terminal and a frame reception error situation occurs, if the channel status is a channel idle state for {EIFS - DIFS + (AIFSN[AC] + 1) * aSlotTime + aSIFSTime - aRxTxTurnaroundTime} time from the time of completion of the channel occupancy state by physical detection, the time when that time has passed.

[0280] 3) After transmitting a frame requesting transmission of a response frame (e.g., an ACK frame or a BlockAck frame), whichever of the following two points in time comes first:

[0281] A) If the channel state is channel idle for the time (AIFSN[AC] + 1) * aSlotTime + aSIFSTime - aRxTxTurnaroundTime) after the completion of transmission of the PPDU including the frame and after the expiration of reception for receiving the response frame, the time (AIFSN[AC] + 1) * aSlotTime + aSIFSTime - aRxTxTurnaroundTime) elapses.

[0282] B) When a response frame is received, if the channel state is idle for a period of (AIFSN[AC] + 1) * SlotTime - aRxTxTurnaroundTime after the SIFS time from the time of completion of reception of the PPDU including the response frame, then the time when AIFSN[AC] + 1) * aSlotTime - aRxTxTurnaroundTime has elapsed.

[0283] 4) When the channel state is idle for the time period AIFSN[AC]*aSlotTime - aRxTxTurnaroundTime after the SIFS time when the transmission of the PPDU including the frame that does not require the transmission of the response frame is completed, the time period AIFSN[AC]*SlotTime - aRxTxTurnaroundTime has elapsed.

[0284] 5) If the channel state is channel idle for the time (AIFSN[AC] + 1) * aSlotTime + aSIFSTime - aRxTxTurnaroundTime) after any channel occupancy time that does not meet conditions 1-4, then the time when (AIFSN[AC] + 1) * aSlotTime + aSIFSTime - aRxTxTurnaroundTime has elapsed.

[0285] 6) If the channel status is idle for aSlotTime time after the previous slot boundary point, the time when aSlotTime has elapsed.

[0286]

[0287] The point at which a station on each link can switch its transceiver into transmit mode to transmit a frame can be adjusted as follows:

[0288] 1) The multi-link slot boundary point where the backoff value becomes 0 on the link.

[0289] 2) At the multi-link slot boundary point where the backoff value on the other link becomes 0 while the link is already maintaining the backoff value as 0 and suspending frame transmission operation.

[0290] In the embodiment of FIG. 30, a first station (STA1) is connected to a first AP (AP1) on a first link (Link 1). A second station (STA2) is connected to a second AP (AP) on 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 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 a slot boundary when the backoff counter value of the first station (STA1) becomes 0. Therefore, actual transmission begins after the transceiver switches to transmission mode from the slot boundary when the backoff counter value of the first station (STA1) becomes 0, and then synchronized transmission begins.

[0291] FIG. 30 illustrates an embodiment in which MLD performs PPDU transmission simultaneously on two links by delaying a channel access procedure of a specific channel according to an embodiment of the present invention.

[0292] Referring to FIG. 30, an MLD including multiple links can adjust the value of the back-off counter of each link to perform multiple transmissions simultaneously when performing multiple transmissions on each link.

[0293] Specifically, as illustrated in FIG. 30, MLD may include STA1 and STA2. The links on which STA1 and STA2 operate may be a non-STR link pair, and MLD may attempt to perform simultaneous transmission using the non-STR link pair. In this case, MLD may not initiate PPDU2 transmission using STA2 even after the channel access procedure of STA2 is completed (i.e., BO becomes 0 by the backoff procedure), and may choose to postpone transmission of PPDU2. In this case, the point in time at which the channel access procedure is completed may mean a slot boundary at which BO becomes 0 when DCF is used, and may mean a slot boundary next to the slot boundary at which BO0 becomes 0 when EDCA is used. During the transmission grace period of the above PPDU2, STA1, another STA of the MLD, has completed the channel access procedure, and the MLD can simultaneously start transmitting PPDU1 and PPDU2 using STA1, which has just completed the channel access procedure, and STA2, which has been waiting (in transmission grace period) after completing the channel access procedure. In the present invention, a PPDU may include a frame. In addition, an operation of transmitting or not transmitting a PPDU may mean an operation of transmitting or not transmitting a frame.

[0294] That is, the EDCA rule on each link can allow channel access on all links, and for this purpose, even if the channel access procedure is terminated on one of the multiple links of the MLD and the value of the back-off counter reaches '0', if the value of the back-off counter on another link has not reached '0', the STA of the MLD can choose not to perform uplink transmission on that link and keep the value of the back-off counter as '0'. In other words, the STA of the MLD can choose not to perform uplink transmission and keep the value of the back-off counter as '0' if the value of the back-off counter on a specific link has reached '0' and the value of the back-off counter on another link of the MLD has not reached '0'.

[0295] If, after the channel access procedure of STA 2 in FIG. 30 is terminated and STA 2 immediately starts transmitting PPDU when the value of the back-off counter reaches '0', interference (or interruption) may occur in the channel access procedure of STA 1 due to the PPDU transmission of STA 2. However, as described above, by controlling the start time of PPDU transmission in the link of the STA whose channel access procedure is terminated among STA 1 and STA 2, MLD can simultaneously transmit PPDU using a link pair in a non-STR relationship.

[0296] Accordingly, STAs of an MLD may initiate PPDU transmission immediately or may not perform a new channel access procedure even if the channel access procedure is completed when the MLD intends to perform simultaneous transmission. In other words, STAs of an MLD may perform an operation of maintaining BO as 0 after the channel access procedure is completed. However, as described above, the operation of maintaining BO as 0 after a specific STA completes the channel access procedure may be limited to the case where the specific STA is an STA of the MLD. In this case, the link on which the specific STA operates may be limited to a link pair that is in a non-STR relationship with another STA of the MLD. In this case, the operation of maintaining BO as 0 after the specific STA completes the channel access procedure may be allowed only when the MLD including the specific STA intends to perform simultaneous transmission (Start time synchronous).

[0297] That is, if the links for the STAs of the MLD are link pairs in a non-STR relationship, the MLD may reserve the PPDU transmission of other links according to the link whose channel access procedure is completed latest if the channel access procedures of the STAs are completed at different times. For example, if the first link of STA 1 and the second link of STA 2 included in the MLD are non-STR link pairs, the value of the first back-off counter in the back-off procedure by the channel access procedure of the first link of STA 1 may reach '0' earlier than the value of the second back-off counter in the back-off procedure by the channel access procedure of the second link of STA 2. In this case, STA 1 may choose not to transmit the PPDU on the first link and to keep the value of the back-off counter at '0'. <Mismatch of slot boundaries when performing simultaneous transmission> As described above, MLD may perform simultaneous transmission by utilizing two or more links, and the meaning of 'simultaneous' used in the simultaneous transmission may not mean exactly the same time physically. More specifically, the simultaneous transmission performed by MLD may mean that the start times of transmissions performed on two or more links have a difference within a specific time interval. For example, if the specific time interval is aSlotTime, if MLD starts transmitting PPDU at time 't' on Link1, and starts transmitting on another Link, Link2, 'after t-aSlotTime and before t+aSlotTime', then the MLD may be considered to have performed simultaneous transmission by utilizing Link1 and Link2. At this time, aSlotTime used as an example of the specific time interval above is for illustration purposes only, and the time interval that MLD must consider / observe in order to perform simultaneous transmission may be a time value other than aSlotTime (1 us, 2 us, 3 us… x us, etc.).At this time, the time interval to be considered for performing the above simultaneous transmission may be a value indicated by the AP of the BSS. For example, the AP MLD may indicate the time value to be considered when performing simultaneous transmission by the STA MLDs associated with it through the OM (Operating Mode) element.

[0298] At this time, the aSlotTime refers to the 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 that reduces the BO (Backoff counter) by 1. At this time, the channel access procedure may be DCF or EDCA, and since it is a well-known channel access procedure of conventional Wi-Fi, a detailed description is omitted. For example, in the case of 11ax, aSlotTime is 9 us.

[0299] Thus, the reason why simultaneous transmissions performed by MLD do not strictly mean transmissions initiated "simultaneously" in the strict sense, but rather include transmissions initiated with a difference in a specific time interval, may be because the slot boundaries of each link utilized in simultaneous transmissions are not aligned. A more detailed explanation of slot boundaries is provided through an example embodiment of FIG. 31.

[0300] FIG. 31 illustrates an embodiment in which STAs of an MLD operate based on different slot boundaries according to an embodiment of the present invention.

[0301] Referring to FIG. 31, different links of STAs constituting the MLD can operate with different slot boundaries.

[0302] When a Wi-Fi device's primary channel is occupied by another device, it determines (calculates) slot boundaries based on the point in time when the primary channel ceases to be occupied. These slot boundaries serve as criteria for distinguishing between slots during channel access procedures. After a Wi-Fi device completes the channel access procedure, transmissions must be performed at a point in time aligned with the slot boundaries.

[0303] Therefore, as illustrated in FIG. 31, when medium occupation ends at different times on Link 1 and Link 2, STAs STA1 and STA2 of the MLD 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 occupation status of the respective links on which they operate, and therefore, it may be impossible to initiate transmissions "simultaneously" in the strict sense on two or more links intended for simultaneous transmission.

[0304] Additionally, although MLD may attempt to initiate transmission simultaneously on two or more links at a given point in time, the processing for PPDU transmission may not be completed at exactly the same point in time (strictly 'simultaneous') because each of the two or more links is handled through separate MACs and PHYs and different PPDU BWs will be transmitted on different links. Therefore, even if MLD attempts simultaneous transmission (strictly 'simultaneous' transmission) while ignoring different Slot boundaries of different links, the points in time at which transmissions start on the different links may still be different.

[0305] Therefore, in order for multiple STAs constituting the MLD to perform simultaneous transmissions through each link, a regulation regarding the transmission start time of the transmissions performed on each link is required. At this time, the regulation that the MLD must follow in order to perform simultaneous transmission may be that the transmission start time of a specific link performed for the purpose of simultaneous transmission must start within the aRxTxTurnaroundTime (time period within aSlotTime) period of another link performing simultaneous transmission. Alternatively, the regulation that the MLD must follow in order to perform simultaneous transmission may be that the transmission start time of a specific link performed for the purpose of simultaneous transmission must be after the CCADel (or CCATime) period within aSlotTime of another link performing simultaneous transmission. At this time, the aRxTxTurnaroundTime is the time required by the PHY performing the channel access procedure to perform PPDU transmission (the time that must actually perform Carrier Sensing and PD for CCA within aSlotTime), and the time actually required by each device may vary depending on the implementation. aRxTxTurnaroundTime is mainly considered to be 4 us in the present invention, and the specific value of the aRxTxTurnaroundTime may be changed. The CCATime may be understood as a period within aSlotTime during which each STA must perform CCA (CS), and the time period may be determined depending on the implementation. CCADel is a period value adjusted to take into account the delay of CCATime, and may vary depending on the implementation.

[0306] That is, since the slot settings in each link may be different, the boundaries of slots between links may not match. Therefore, the boundaries of slots between links may not match in each slot where the back-off counter is decreased, and if all back-off counters by the back-off procedure reach '0' through the reservation operation described above in each of the multiple links of the MLD, the slot boundaries in each link may not match. Since the slots in each link can be configured individually, the slot boundaries in each link may not match. Therefore, even if the values ​​of all back-off counters in each link are '0', the slot boundaries may be different. In this case, simultaneous transmission can be performed according to the slot boundary for the slot or the slot following the slot in which the back-off counter of a specific link among the multiple links has the value '0'. That is, if a specific link is a reference link for multiple transmissions among multiple links of a non-AP MLD, and the value of the back-off counter is reduced to '0' in slot 1 of the specific link, other links can 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.

[0307] That is, each link can perform uplink transmission simultaneously by delaying or shortening uplink transmission according to the slot boundary of a specific link, rather than performing uplink transmission according to the slot boundary of the respective links.

[0308] For example, if the multi-link of MLD is composed of a first link and a second link, and the channel access procedure is terminated in one of the first link and the second link (for example, when the back-off counter of one of the first back-off counter of the first link and the second back-off counter of the second link reaches '0' before the remaining back-off counter), the slot boundaries of the first link and the second link may not match at the time when the channel access procedure of the remaining link is terminated (for example, when the remaining back-off counter reaches '0'). In this case, the uplink transmission is performed in each link according to the slot boundary of a specific link for simultaneous uplink transmission among the first link and the second link, so that the uplink transmission can be performed simultaneously in the multi-link.

[0309] That is, if the multi-link of the MLD is composed of a first link and a second link, and one of the first back-off counter of the first link and the second back-off counter of the second link reaches '0' before the remaining back-off counter, the slot boundaries of the first link and the second link may not match when the remaining back-off counter reaches '0'. In this case, the transmission time of the uplink transmission in the second link can be shortened or delayed to control the slot boundary of the slot in which the first back-off counter of the first link is '0' or the slot boundary of the first slot which is the next slot of the slot.

[0310] At this time, the uplink transmission time on the first link and the uplink transmission time on the second link may be within a certain time period. For example, the uplink transmission time on the second link may be within 4 microseconds of the uplink transmission time on the first link.

[0311] In this way, uplink transmission can be performed simultaneously in the first link and the second link by performing uplink transmission at a time other than the slot boundary of the slot in which the second back-off counter of the second link is '0' or the slot boundary of the second slot which is the next slot of the slot.

[0312] Among the STAs included in the MLD, an STA whose transmission is delayed due to a slot boundary can continue channel sensing of the corresponding slot during the delay time in the link, and if the value of the back-off counter in another link becomes '0' during channel sensing, the channel sensing can be terminated and the PPDU can be transmitted immediately. The time delayed or shortened for simultaneous transmission may be 4 us. In this case, 4 us may mean the transition time required to change to a mode for performing uplink transmission in the channel access procedure. If the delayed or shortened time exceeds 4 us, the time for switching from downlink to uplink may be exceeded, and the channel status in the corresponding slot may be changed to an occupied state (busy).

[0313] The STA operations within aSlotTime illustrated in Figure 33 are for illustrative purposes only, and the operations performed by each STA within aSlotTime corresponding to each Slot may vary. However, all Wi-Fi devices, when implemented, may be required to meet the carrier sense (CS) accuracy defined by the Wi-Fi standard.

[0314] FIG. 32 illustrates an example of a simultaneous transmission failure of MLD that may occur when there is no clear specification for the start time of simultaneous transmission according to an embodiment of the present invention.

[0315] Referring to FIG. 32, (a) and (b) of FIG. 32 show that MLD delays the start of transmission of STA1 for the purpose of performing simultaneous transmission using STA1 and STA2 even though the channel access procedure of STA1 has been completed. At this time, since the slot boundaries of STA1 and STA2 are different, MLD may try to match the transmission start time of STA1, which was delaying the channel access procedure, to a similar time point as the time point when STA2 completes the channel access procedure. At this time, MLD may match the transmission start time of STA1 to the slot boundary of STA1 that is adjacent to the slot boundary at which STA2 completes the channel access procedure (the boundary of the slot used by STA2). In this case, the start time of the transmission initiated through STA1 may be the STA1 slot boundary that exists immediately after the time point at which STA2 completes the channel access (a specific slot boundary of STA2), as in Case 1 of FIG. 14 (a). Alternatively, the start time of transmission initiated through STA1 may be the slot boundary of STA1, which exists immediately before the time point (a specific slot boundary of STA2) at which STA2 is predicted to complete channel access, as in Case 2 (b) of Fig. 14. In summary, when MLD wants to perform simultaneous transmission using two or more links, it may try to start transmission at the slot boundary of each link adjacent to the slot boundary of the link whose channel access procedure is completed last among the two or more links (the slot boundary of the STA operating on the link).

[0316] However, as explained above, since the slot boundaries of each link may be different, when a transmission is started on a specific link for the purpose of utilizing it for simultaneous transmission, the CCA operation of another link that should be utilized for simultaneous transmission may be affected, and as a result, the transmission start of the other link may not be possible. More specifically, since the transmission started on the specific link causes interference within the device, the CCA result of the other link may be determined as BUSY due to the interference within the device. Accordingly, the STA of the other link operates as if it recognizes that the WM is already occupied and channel access is restricted. As a result, the transmission of a specific link started for the purpose of simultaneous transmission may cause interference within the device of another link that was planning to transmit for the purpose of simultaneous transmission, thereby restricting the channel access of the other link. This means that, as illustrated in (a) and (b) of FIG. 14, even if STA1, which has been delaying the start of transmission after completing the channel access procedure, selects and transmits one of the two slot boundaries adjacent to the slot boundary of STA2 that has just completed or is expected to complete the channel access (the STA1 slot boundary immediately after the slot boundary where STA2 has completed the channel access procedure and the STA1 slot boundary immediately before the slot boundary where STA2 is expected to complete the channel access procedure), the transmission that started first may affect the CCA result of another link, causing simultaneous transmission to fail.

[0317] Therefore, the transmission start time of a link that has been delaying / deferring the start of transmission to perform simultaneous transmission after completing a channel access procedure cannot be specified as one of two slot boundaries (slot boundaries of a specific STA) adjacent to the time point at which the STA of another link to perform simultaneous transmission has completed or is expected to complete the channel access procedure (slot boundaries of the other STA), and must be determined by MLD at each simultaneous transmission attempt in consideration of the difference in slot boundaries between the specific link and the other link.

[0318] As described above, after completing the channel access procedure, the transmission start time of the link that has been delaying transmission for the purpose of performing simultaneous transmission should not be specified as the slot boundary (of the link that has been delaying transmission) immediately before or after the slot boundary of the link whose channel access procedure was the last to be completed among the channel access procedures of each link performing simultaneous transmission, and it should be managed so as not to affect the CCA results of other links even if two or more links that will perform simultaneous transmission each start transmission. Therefore, in order to prevent the transmission started from each link from affecting the CCA results of other links that will perform simultaneous transmission, the transmission start time of each link should be determined by considering the CCA operations performed by other links during each slot period (aSlotTime). In this case, the transmission start time of a specific link determined by considering the CCA operations of the other links may be a time point determined within aRxTxTurnaroundTime at which the other links switch from Rx mode to Tx mode after performing the CCA. In other words, an STA of a specific link performing simultaneous transmission may start transmission on the specific link in accordance with the aRxTxTurnaroundTime period of STAs of 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 STAs that have not yet started transmission.

[0319] FIG. 33 illustrates an example of a case where, when STAs of an MLD start transmissions at different slot boundaries according to an embodiment of the present invention, the transmission that starts first does not affect the CCA results of other STAs (same MLDs operating on different links).

[0320] Referring to FIG. 33, MLD operates STA1 and STA2 on Link 1 and Link 2, respectively, and may delay the transmission start time of STA1 for the purpose of performing simultaneous transmission with STA2 even though the channel access procedure of STA1 has been completed. At this time, MLD may determine that even if STA2 starts transmission at the slot boundary where STA2 has completed the channel access procedure, the Slot of STA1 including the transmission start time of STA2 (the Slot indicated by the grid, the Slot just before STA1 starts transmission) corresponds to the section where STA1 switches from Rx mode to Tx mode, so that it will not affect the CCA result of STA1. Accordingly, MLD may determine that the transmission start time of STA1, which was delaying the start of transmission after completing the channel access procedure, should start at the STA1 slot boundary after the STA2 slot boundary where STA2 started transmission after completing the channel access procedure.

[0321] At this time, the STA 1 slot boundary after the STA2 slot boundary may be the STA1 slot boundary immediately after the STA2 slot boundary. Referring again to FIG. 15 for more detailed explanation, STA1 performs an operation of switching from Rx mode to Tx mode during the last 4 us of aSlotTime corresponding to the grid-marked Slot, and may not determine the grid-marked Slot as BUSY even if interference occurs within the device during the switching period. Accordingly, since the start time of the transmission performed by STA2 exists within the aRxTxTurnaroundTime of STA1, STA1 can perform channel access without experiencing a problem due to interference within the device even after STA2 starts transmission first.

[0322] At this time, the above 4 us is used as an example of a value corresponding to aRxTxTurnaroundTime, and the above aRxTxTurnaroundTime may have different values ​​for each terminal due to the hardware characteristics of each terminal. Therefore, the difference in transmission start time of each link that must be considered when MLD performs simultaneous transmission may be applied as different time values ​​depending on the characteristics of MLD or each STA of MLD.

[0323] Meanwhile, as described above, the transmission start time of the link that started transmission first may be applied so that it starts in the section after CCADel rather than within the aRxTxTurnaroundTime section of the other link. However, in the present embodiment, the detailed description is considered because the above-described descriptions can be understood in a similar manner if the section after CCADel rather than the aRxTxTurnaroundTime section is replaced. For reference, in the embodiment of FIG. 15, the section including the M2 section illustrated before the Rx / Tx (e.g., 4us) section can be understood as the section after CCADel.

[0324] FIG. 34 illustrates an embodiment of a method for determining a time point at which to start transmission on each link based on a difference in slot boundary time points of links on which MLD wishes to perform simultaneous transmission, according to an embodiment of the present invention.

[0325] (a) of Fig. 34 illustrates a situation in which each slot boundary of STA1 precedes (is earlier in time) each slot boundary of STA2 by a period smaller than aRxTxTurnaroundTime, and (b) of Fig. 34 illustrates a situation in which each slot boundary of STA2 precedes each slot boundary of STA1 by a period smaller than aRxTxTurnaoundTime. In this case, a method for comparing slot boundary precedence relationships of the two links (STAs) may be to compare precedence relationships between slot boundaries of the two links that have a difference of less than 1 / 2 aSlotTime.

[0326] In the case of Fig. 34 (a), since each slot boundary of STA1 is ahead of each slot boundary of STA2, and even if STA1 starts transmission at its own slot boundary, since the slot boundary of STA1 is a point in time corresponding to aRxTxTurnaroundTime among the grid-patterned Slot periods (aSlotTime) of STA2, MLD can start transmission of Link1 at the slot boundary of STA1 and then perform transmission of Link2 at the slot boundary of STA2.

[0327] In the case of Fig. 34 (b), since each slot boundary of STA2 is ahead of each slot boundary of STA1, and even if STA2 starts transmission at its own slot boundary, since the slot boundary of STA2 is a point in time corresponding to aRxTxTurnaroundTime among the grid-patterned Slot periods (aSlotTime) of STA1, MLD can start transmission of Link2 at the slot boundary of STA2 and then perform transmission of Link1 at the slot boundary of STA1.

[0328] As a result, MLD can perform simultaneous transmission by starting transmission first through the STA operating on the link with the earliest slot boundary when the slot boundaries of each link performing simultaneous transmission (of STAs operating on each link) have a time difference less than or equal to aRxTxTurnaroundTime. In this case, even if the time difference (aRxTxTurnaroundTime) as the reference is applied as the end point of CCADel, the aRxTxTurnaroundTime is only changed to M2 (see FIG. 33) + aRxTxTurnaroundTime, and thus it can be understood in the same way, so a detailed description thereof is omitted.

[0329] As described above, MLD can prevent the interference within the device caused by the link that starts transmission first from affecting the CCA of other links by considering the slot boundary difference of the links that perform simultaneous transmission. However, if the slot boundary difference of each link that performs simultaneous transmission has a difference within a specific value, MLD may not be able to prevent the channel access of the other link from being interrupted regardless of the order in which transmission is initiated on each link. In this case, the difference within the specific value may mean a difference of more than (or more than) 4 us and 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 of two links that MLD intends to utilize for simultaneous transmission is greater than (or equal to) 4 us and less than (or equal to) 4.5 us, then even if MLD starts transmission first through whichever of the two links, channel access (simultaneous transmission) may be limited on the other link due to interference within the device caused by the link that started transmission first.

[0330] FIG. 35 illustrates an embodiment of a case where simultaneous transmission fails when two link pairs of MLD have a difference in slot boundaries within a specific range according to an embodiment of the present invention.

[0331] Referring to FIG. 35, MLD can operate STA1 and STA2 on Link 1 and Link 2, respectively, and STA1 and STA2 can perform channel access based on slot boundaries that differ by 1 / 2 aSlotTime. At this time, STA1 has completed the channel access procedure first, and MLD can reserve the start of transmission of STA1 for the purpose of performing simultaneous transmission using STA1 and STA2. In this case, MLD may attempt to start transmission of Link 1 at the slot boundary of STA1 adjacent to the slot boundary where STA2's channel access ends, but the simultaneous transmission may not succeed due to the difference in slot boundaries between STA1 and STA2.

[0332] MLD may try to start transmission on Link1 by selecting one of two slot boundaries of STA1 adjacent to the slot boundary (T2 in FIG. 35) where STA2 has completed / is expected to complete its channel access procedure. If MLD starts transmission on Link1 at the slot boundary of STA1 (T1 in FIG. 35) that appears before the predicted channel access procedure completion time of STA2, the last backoff Slot of STA2 (indicated as 0) may be determined as BUSY due to the transmission started on Link1, and thus the channel access procedure of STA2 will not be completed at the predicted time of T2. In other words, if MLD starts transmission using STA1 at time T1, the channel access procedure of STA2 will not be completed due to the interference within the device caused by the transmission on Link1, and the simultaneous transmission will fail. Meanwhile, if MLD attempts to transmit to Link1 at the slot boundary of STA1 (T3 in FIG. 35) that appears after STA2 completes its channel access procedure, the last slot of Link1, which ends at T3, may be determined as BUSY due to the transmission of Link2 that has already started at T2, making channel access to Link1 impossible. This may be because the time difference between T1 and T2, and T2 and T3, is greater than aRxTxTurnaroundTime, respectively, and thus, regardless of which link among Link1 and Link2 initiates transmission first, the channel access procedure of the other remaining links may be interrupted.

[0333] As described above, when certain links have slot boundary differences within a certain range, it may be impossible for the links to participate in simultaneous transmission by starting transmission according to their respective slot boundaries. Assuming a situation where aSlotTime is 9 us and aRxTxTurnaroundTime is 4 us, as in the example of FIG. 35 described above, the probability that a certain link pair has a slot boundary difference that prevents simultaneous transmission can be understood as 1 / 9 through simple calculation. This may be a rather high probability, considering that a non-STR MLD may actively attempt simultaneous transmission, even if only to prevent a certain link from entering a BLIND state.

[0334] In addition, depending on the device, there may be a device with a relatively short aRxTxTurnaroundTime, and when performing simultaneous transmission using devices with such a relatively short aRxTxTurnaroundTime, the probability of simultaneous transmission limitation due to the slot boundary difference of a specific link pair may increase. For example, if STAs of a specific MLD have the characteristic of requiring an aRxTxTurnaroundTime of only 1.5 us and performing CCA during the remaining time, when performing simultaneous transmission using two links, the specific MLD may fail to access one of the two channels with a probability of (4.5-1.5) / 9 = 1 / 3.

[0335] Channel access that does not align with slot boundaries

[0336] As described above, in order to prevent the problem of simultaneous transmission (simultaneous channel access) being limited by the slot boundary difference, when the MLD is withholding the start of transmission of a specific STA for the purpose of performing simultaneous transmission (the specific STA has completed the backoff procedure (channel access procedure) (BO == 0)), the transmission started through the specific STA may be allowed to have an error below a certain level with respect to the slot boundary of the specific STA. In other words, when the MLD performs simultaneous transmission through multiple links, the non-STR link pairs of the MLD's non-STR link pairs may have their respective channel access procedures terminated at different times. In this case, the STA of the link whose backoff counter value first reaches '0' by the backoff procedure of each of the non-STR link pairs may not transmit a PPDU while maintaining the backoff counter value as '0' until the backoff counter value reaches '0' in the link of another STA. In this case, if the values ​​of the back-off counters of the STAs, which are non-STR link pairs of the MLD, all reach '0', the slot boundaries of the STAs may not match, so the STAs of the MLD may start transmission at a time other than their own slot boundaries. At this time, the error below a certain level may be a value determined in consideration of aSlotTime. For example, the error below a certain level may not exceed 10% of aSlotTime. At this time, if aSlotTime is 9 us, the transmission performed by the STA of the MLD may start within +- 0.9 us of its own slot boundary. At this time, the reason for considering aSlotTime when determining the range (error) that allows transmission to start at a time other than the slot boundary may be to prevent an error that may damage the slot boundary synchronization (Sync.) between the STAs operating on a specific link.At this time, the slot boundary synchronization may mean a level of synchronization that allows channel access to be performed according to EDCA rules when each STA performs a channel access procedure using its own slot boundary, even if each STA uses a slightly different slot boundary due to propagation delay.

[0337] That is, the error below the above-mentioned certain level may mean that it does not exceed 10% of (aSlotTime - aAirPropagationTime). At this time, the aAirPropagationTime may be a value (in us) calculated as twice the signal propagation time between the farthest STAs (slots synchronized), or a value indicated by the Coverage Class field parameter of the BSS. For example, if the aAirPropagationTime of the BSS considered by the EHT AP is 1 us or less, the start time of the transmission performed by the STAs of the BSS may be allowed to have an error of up to 0.8 us (+-10% * (9 us - 1 us)) from the slot boundary. In other words, the EHT STA may be required to ensure that its transmission start time has a difference of 0.8 us or less from the slot boundary.

[0338] That is, considering the length of aSlotTime used by the BSS and the slot boundary synchronization stability (completeness) between STAs, there is an allowable 'transmission start time - slot boundary' error, and taking this into account, an error below the above-mentioned certain level can be determined (secured). In simple terms, by using the error between the slot boundary and the transmission start time allowed by the slot boundary synchronization stability between STAs of a specific link, the STA of the MLD can start transmission at a time different from the slot boundary (within the error range).

[0339] Alternatively, the error below the above-mentioned predetermined level may be a value already determined (promised) regardless of aSlotTime, or a value indicated by the AP MLD. If a specific STA in the MLD that has completed the channel access procedure and has been holding transmission is allowed to initiate transmission regardless of its slot boundary, the allowed error level from the slot boundary can be understood as aSlotTime / 2.

[0340] FIG. 36 illustrates an embodiment of a simultaneous transmission technique performed by an STA of an MLD that has completed a channel access procedure and reserved the start of transmission, thereby initiating transmission at a time different from its own slot boundary, according to an embodiment of the present invention.

[0341] Referring to FIG. 36, MLD can operate STA1 and STA2 on Link 1 and Link 2, respectively, and STA1 and STA2 can perform channel access based on slot boundaries that differ by 1 / 2 aSlotTime. At this time, STA1 has completed the channel access procedure first, and MLD can reserve the start of transmission of STA1 for the purpose of performing simultaneous transmission using STA1 and STA2. This is the same situation considered in FIG. 17. If transmission to Link 1 is started according to the slot boundary of STA1, which is an STA of MLD, simultaneous transmission (simultaneous channel access) using STA1 and STA2 is not possible. However, in the case of STA1, since the start of transmission has been reserved for the purpose of simultaneous transmission after completing the channel access procedure, it can freely adjust the transmission start time within a certain (allowed) error from its own slot boundary.

[0342] Therefore, STA1 can start PPDU transmission at a point in time that is delayed (relative to T1) by the allowed tolerance time, rather than starting transmission at T1, which is one of its slot boundaries. As a result, STA2 operating on Link2 can determine the slot (lattice pattern) adjacent to T2, the slot boundary where the channel access procedure is completed, as IDLE, and start simultaneous transmission at T2, regardless of the interference within the device caused by the transmission performed by STA1. In short, if the transmission of STA1 had started at T1 according to its slot boundary, the simultaneous transmission may have failed because the channel access procedure of STA2 was not completed at T2. However, STA1 delayed the transmission start time by the Slot Sync budget, and started transmission on Link1 during the aRxTxTurnaroundTime period of STA2.

[0343] As described above, when a specific STA of MLD is operated for the purpose of performing simultaneous transmission, the specific STA may be allowed to start transmission at a different time (but within an allowed error range) from the slot boundary Sync that it used for its channel access procedure, and as a result, MLD can perform simultaneous transmission by managing the transmission start time in each link regardless of the difference in the slot boundaries of each link to be used for simultaneous transmission.

[0344] FIG. 37 illustrates an embodiment of signaling that may be utilized when an AP MLD indicates a Slot Sync Budget that may be utilized in a BSS using an Operation element according to an embodiment of the present invention.

[0345] The AP MLD can determine and indicate a Slot Sync Budget that can be utilized when STA MLDs within a BSS perform simultaneous transmission by evaluating the completeness of slot boundary synchronization between STAs within a BSS. At this time, the Slot Sync Budget may be indicated through an Operation element. At this time, the name of the field and the indicated element may be changed at any time. The value indicated through the Slot Sync Budget may be applied as the maximum error that the transmission start time of each link may have with the slot boundary of the link when the STA MLD performs simultaneous transmission. At this time, the Slot Sync Budget is not limited to the purpose of simultaneous transmission, and may be applied as the timing error that the transmission performed by the EHT STA may have with the slot boundary.

[0346] For example, when the slot boundary synchronization between STAs within a BSS is strong (well-synchronized), the AP MLD can indicate a relatively large value through the Slot Sync Budget field of the Operation element when the slot boundary synchronization between STAs within the BSS is weak (synchronization is not good, or the slot boundary difference between STAs is predicted / estimated to be large). At this time, the value indicated through the Slot Sync Budget field can be utilized to check whether the time point at which each STA starts transmission has a certain degree of tolerance with respect to the slot boundary. When the STA MLDs of the BSS perform simultaneous transmission, the simultaneous transmission must be performed so that the time point at which each link starts transmission has a time difference that does not exceed the tolerance range confirmed based on the value indicated by the Slot Sync Budget field from the slot boundary it uses when performing the channel access procedure.

[0347] <Simultaneous transmission method considering information exchange delay between links>

[0348] The above-described simultaneous transmission operations are based on the assumption that information related to the progress of the channel access procedure can be closely shared among multiple STAs included in the MLD. For example, the operation in which a specific STA performs transmission at the time when another STA in the MLD completes the channel access procedure is an operation that assumes that the specific STA knows parameters related to the channel access procedure of the other STA (e.g., the number of remaining backoff counters and slot boundaries).

[0349] However, each STA in an MLD basically performs channel access procedures independently on the link on which it operates, and the method by which each STA shares information may not be defined. Therefore, whether STAs within an MLD can share parameters related to each other's channel access procedures in real time may vary depending on the implementation method. Furthermore, the CCA performed by each STA for channel access at each slot requires information that must be updated every aSlotTime, and whether this data needs to be exchanged every second between each STA within an MLD may vary depending on the developer's opinion.

[0350] That is, when considering the channel access procedure for simultaneous transmission, it must be kept in mind that each STA within the MLD may have a certain level of delay before obtaining information about each other's channel access procedure.

[0351] At this time, the method for each STA of the MLD to perform simultaneous transmission may be such that, as considered in the embodiments of the present invention described above, an STA that has been withholding transmission after completing a backoff procedure may 1) start transmission at a time when it is predicted that another STA in the MLD will complete a channel access procedure, or 2) start transmission after confirming that another STA in the MLD has completed a channel access procedure.

[0352] Since the simultaneous transmission operation corresponding to 1) above is explained through the embodiments of the present invention described above, a detailed description thereof will be omitted, and the simultaneous transmission operation corresponding to 2) will be explained in more detail.

[0353] According to one embodiment of the present invention, an MLD that wishes 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. At this time, the specific STA may initiate transmission after confirming that another STA of the MLD has completed the channel access procedure. At this time, the other STA may delay the start of transmission for a specific period of time after the completion of the channel access procedure, taking into account the information processing delay within the device (information exchange delay between links) required until the specific STA obtains information that it has completed the channel access procedure. At this time, the specific period of time may be a value set in consideration of the information processing delay within the device. At this time, the unit of the specific period of time may be us or a multiple of aSlotTime (1 aSlotTime or 2 aSlotTime).

[0354] Figure 38 illustrates an example of a simultaneous transmission procedure that takes into account information exchange delay between links according to one embodiment of the present invention.

[0355] Referring to FIG. 38, MLD may wish to perform simultaneous transmission using STA1 and STA2. In this case, 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 may complete the channel access procedure (BO == 0) at time T1, but may postpone transmission of PPDU1 in order to perform simultaneous transmission with STA2.

[0356] After this, STA2 completes the channel access procedure at time T2, and at time T2, STA1 may not be able to recognize that STA2 has completed the channel access procedure due to the delay in information exchange between links. Therefore, although STA2 is not waiting for STA1's channel access procedure, STA2 may postpone its transmission until time T3, taking into account the delay time (T_delay) for which information that STA2 has completed the channel access procedure is transmitted to STA1, and then initiate transmission of PPDU2.

[0357] At this time, T3 may be the time point of the slot boundary that appears after the inter-link information exchange delay time based on the time point (T2) at which STA2 completes the channel access procedure. In other words, the time difference between T3 and T2 may be greater than or equal to the inter-link information exchange delay time. At this time, the time difference between T3 and T2 may be less than or equal to (inter-link information exchange delay time + aSlotTime).

[0358] After this, STA1 can start transmitting PPDU1 at its own slot boundary adjacent to T3 after receiving information that STA2 has completed the channel access procedure. At this time, its own slot boundary adjacent to T3 may be the first slot boundary existing after T3. Alternatively, STA1 can start transmitting PPDU1 at T3 after receiving information that STA2 has completed the channel access procedure.

[0359] As a result, STA1 and STA2 performing simultaneous transmission may not perform transmission immediately even if both STAs have completed their own channel access procedures. The STA that has completed the channel access procedure first may postpone its transmission until it confirms (through information exchange between links) that the other STA has completed the channel access procedure, and the STA that has completed the channel access procedure later may postpone its transmission considering the delay time until the other STA, which had been postponing transmission until it completed the channel access procedure, obtains information that its channel access procedure has been completed.

[0360] Meanwhile, even if simultaneous transmission is performed considering the information exchange delay between links, an operation considering the slot boundary time difference between the links performing simultaneous transmission, as considered in the previous embodiments of the present invention, must be performed. That is, when performing simultaneous transmission considering the information exchange delay between links, there still exists a possibility that the channel access procedure of another link may be interrupted due to transmission initiated on a specific link. Therefore, even when the MLD performing simultaneous transmission considers the information exchange delay between links, the method provided in the above-described embodiments of the present invention must still be followed to select a slot boundary.

[0361] However, when an MLD performing simultaneous transmission performs simultaneous transmission considering the information exchange delay between links, the STA that has completed the channel access procedure first may initiate transmission by aligning it with its slot boundary, and the STA that has completed the channel access procedure later may need to determine the slot boundary at which it will initiate transmission. In this case, the method for determining the slot boundary is the same as that described in the embodiment of FIG. 34, and thus a detailed description thereof will be omitted.

[0362] Additionally, the same problem described using Figure 35 (the inability to determine appropriate slot boundaries) can also occur in simultaneous transmissions considering inter-device interference, in which case an STA that has completed the channel access procedure later may be permitted to initiate transmission at a time different from its slot boundary. In this case, the restrictions applied to transmissions initiated at a time different from the slot boundary may be the same as those described using the example of Figure 36.

[0363] FIG. 39 illustrates a simultaneous transmission technique in which an STA of an MLD, which has completed a channel access procedure and reserved the start of transmission, initiates transmission at a time different from its own slot boundary after recognizing that another STA's channel access procedure has been completed, according to one embodiment of the present invention.

[0364] Referring to FIG. 39, MLD may wish to perform simultaneous transmission using STA1 and STA2. In this case, 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 may complete the channel access procedure (BO == 0) at time T1, but may postpone transmission of PPDU1 in order to perform simultaneous transmission with STA2.

[0365] After this, STA2 completes the channel access procedure at time T2, and at time T2, STA1 may not be able to recognize that STA2 has completed the channel access procedure due to the delay in information exchange between links. Therefore, although STA2 is not waiting for STA1's channel access procedure, STA2 may postpone its transmission until time T3, taking into account the delay time (T_delay) for which information that STA2 has completed the channel access procedure is transmitted to STA1, and then initiate transmission of PPDU2.

[0366] At this time, T3 may be the time point of the slot boundary that appears after the inter-link information exchange delay time based on the time point (T2) at which STA2 completes the channel access procedure. In other words, the time difference between T3 and T2 may be greater than or equal to the inter-link information exchange delay time. At this time, the time difference between T3 and T2 may be less than or equal to (inter-link information exchange delay time + aSlotTime).

[0367] After this, STA1 can start transmission at its own slot boundary (T4) that exists after T3 after receiving the information that STA2 has completed the channel access procedure. At this time, STA2 can recognize that STA1 will start transmission at the slot boundary corresponding to T4, considering the information exchange delay between links, and can recognize that if STA2 starts transmission at the slot boundary (T3 + aSlotTime) that exists after T3, its transmission initiation will be interrupted by the transmission initiated by STA1. In addition, STA2 can recognize that if it starts transmission at the slot boundary that is chronologically the same as T3, STA1 cannot perform simultaneous transmission due to the transmission that it has initiated, and as a result, it can recognize that neither the slot boundary that is chronologically the same as T3 nor the slot boundary that exists after T3 can be used as the initiation point of simultaneous transmission.

[0368] In this case, STA2 can initiate its transmission at a time different from its slot boundary, within the limits permitted by the Slot Sync budget. Since the meaning and utilization of the Slot Sync budget have been explained through other embodiments of the present invention described above, a detailed description thereof will be omitted.

[0369] As a result, STA2 can initiate its transmission at the time when STA1 performs Rx / TxTurnaround by adjusting the time when it performs transmission initiation to the value of T3 + slot Sync budget or T4.

[0370] FIG. 40 illustrates an example of a method for a multi-link device to perform simultaneous transmissions over multiple links, according to one embodiment of the present invention.

[0371] Referring to FIG. 40, a non-AP MLD may perform a back-off procedure to perform simultaneous transmissions over multiple links (S40010). The back-off procedure may be individually performed over the first link of the first STA and the second link of the second STA included in the non-AP MLD.

[0372] The back-off procedure in the first link is performed using a first back-off counter, and the back-off procedure in the second link is performed using a second back-off counter.

[0373] Thereafter, the non-AP MLD can simultaneously perform uplink transmission to the AP MLD through each of the first link and the second link (S40020).

[0374] At this time, if both the first back-off counter and the second back-off counter have a value of '0', and the transmission time of the uplink transmission in the first link is a slot boundary of the first slot which is the next slot of the slot in which the first back-off counter is '0', the uplink transmission in the second link can be performed within a certain time from the transmission time of the first link.

[0375] Specifically, since the slot settings in each link may be different, the boundaries of slots between links may not match. Therefore, the boundaries of slots between links may not match in each slot where the backoff counter is decreased, and if all backoff counters by the backoff procedure reach '0' through the reservation operation described above in each of the multiple links of the MLD, the slot boundaries in each link may not match. Since the slots in each link can be set individually, the slot boundaries in each link may not match. Therefore, even if the values ​​of the backoff counters in each link are all '0', the slot boundaries may be different. In this case, simultaneous transmission can be performed according to the slot boundary of a specific link when the value of the backoff counter of a specific link among the multiple links is '0'. In other words, each link can perform uplink transmission simultaneously by delaying or shortening the transmission time of uplink transmission according to the slot boundary of a specific link, rather than performing uplink transmission according to the slot boundary of the respective links.

[0376] For example, if the multi-link of the MLD is composed of a first link and a second link, and one of the first back-off counter of the first link and the second back-off counter of the second link reaches '0' before the remaining back-off counter, the slot boundaries of the first link and the second link may not match when the remaining back-off counter reaches '0'. In this case, the transmission time of the uplink transmission in the second link can be shortened or delayed to control the slot boundary of the slot in which the first back-off counter of the first link is '0' or the slot boundary of the first slot which is the next slot of the slot.

[0377] At this time, the uplink transmission time on the first link and the uplink transmission time on the second link may be within a certain time period. For example, the uplink transmission time on the second link may be within 4 microseconds of the uplink transmission time on the first link.

[0378] In this way, uplink transmission can be performed simultaneously in the first link and the second link by performing uplink transmission at a time other than the slot boundary of the slot in which the second back-off counter of the second link is '0' or the slot boundary of the second slot which is the next slot of the slot.

[0379] At this time, when both the first back-off counter and the second back-off counter are '0', the transmission time of the upper link transmission in the second link can be adjusted to be included within the predetermined time from the slot boundary of the first slot.

[0380] At this time, when the first back off counter is '0' and the second back off counter is '0', the slot boundary of the second slot, which is the next slot of the slot in which the second back off counter of the first slot and the second link is '0', does not match, and the slot boundary of the second slot may not be included within the predetermined time.

[0381] In addition, if one of the first back off counter and the second back off counter reaches '0' before the remaining back off counters, the link using the one back off counter among the first link and the second link may not perform the uplink transmission and may maintain the one back off counter as '0' until the remaining back off counter reaches '0'.

[0382] That is, even if the channel access procedure is terminated on one of the multiple links of the MLD as described above and the value of the back-off counter reaches '0', if the value of the back-off counter on another link has not reached '0', the STA of the MLD may not perform uplink transmission on that link and may maintain the value of the back-off counter as '0'. In other words, the STA of the MLD may choose not to perform uplink transmission on a specific link and to maintain the value of the back-off counter as '0' if the value of the back-off counter on another link of the MLD has not reached '0'.

[0383] For example, a multi-link of an MLD may be composed of a first link and a second link, and a back-off procedure for channel access in the first link may be performed by a first back-off counter, while a back-off procedure for channel access in the second link may be performed by a second back-off counter. In this case, the back-off procedure may be individually performed through each of the first link and the second link included in the multi-link.

[0384] In this case, if one back-off counter among the first back-off counter and the second back-off counter reaches '0' before the remaining back-off counters, a specific link among the first link and the second link that uses the one back-off counter does not perform the uplink transmission, and the one back-off counter may maintain a value of '0' until the remaining back-off counter reaches a value of '0'. Alternatively, the one back-off counter may continue to maintain a value of '0' even after the remaining back-off counter reaches a value of '0'.

[0385] A non-AP MLD in which, when one of the first back-off counter and the second back-off counter reaches '0' before the remaining back-off counter, and when the remaining back-off counter reaches '0', the slot boundary of the first slot of the first link and the second slot which is the next slot of the second link in which the second back-off counter is '0' do not match, 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 predetermined time from the slot boundary of the first slot.

[0386] At this time, if the slot boundary of the second slot is located earlier or later on the time axis than the slot boundary of the first slot, the transmission time point of the second link may be delayed or shortened for a specific time from the slot boundary of the first slot.

[0387] At this time, the maximum value of the above-mentioned period of time is 4us, and 4us may mean a change time for performing the above-mentioned uplink transmission in the channel access procedure.

[0388] Additionally, the non-AP MLD may perform channel sensing before the transmission time of the second link, wherein the transmission time of the second link may not coincide with the slot boundary of the second slot of the second link.

[0389] At this time, the uplink transmission may be performed in the slot following the slot in which the first back-of counter and the second back-off 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).

[0390] Additionally, the non-AP MLD can sense whether the channel is idle in the first link and the second link, and the first back-off counter and the second back-off counter are decremented when the first link and the second link are idle, respectively.

[0391] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single entity may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined manner.

[0392] The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. In a non-AP (Access Point) multi-link device (MLD) of a wireless communication system, Communication module; comprising a processor controlling the above communication module; The above processor, Perform a back off procedure for performing uplink transmission through multiple links of the above non-AP MLD. The above back-off procedure is performed individually through the first link of the first STA and the second link of the second STA included in the non-AP MLD, respectively. The back-off procedure in the first link is performed using the first back-off counter, The back-off procedure in the second link is performed using a second back-off counter, The uplink transmission is performed simultaneously to the AP MLD through each of the first link and the second link, A non-AP MLD in which the uplink transmission in the second link is performed within a certain time from the transmission time of the first link when both the first back off counter and the second back off counter have a value of '0' and the transmission time of the uplink transmission in the first link is a slot boundary of the first slot which is a slot following the slot in which the first back off counter is '0'.

2. In paragraph 1. If both the first back off counter and the second back off counter are '0', A non-AP MLD in which the transmission time of the upper link transmission in the second link is adjusted to be included within the predetermined time from the slot boundary of the first slot.

3. In paragraph 2, If the first back off counter is '0' and the second back off counter is '0', the slot boundaries of the first slot and the second slot, which is the next slot of the slot where the second back off counter of the second link is '0', do not match, The slot boundary of the above second slot is a non-AP MLD that is not included within the above schedule time.

4. In paragraph 1, A non-AP MLD in which, if one of the first back off counter and the second back off counter reaches '0' before the remaining back off counters, the link using the one back off counter among the first link and the second link does not perform the uplink transmission and maintains the one back off counter as '0' until the remaining back off counter reaches '0'.

5. In paragraph 1, A non-AP MLD in which, when one of the first back off counter and the second back off counter reaches '0' before the remaining back off counters, and when the remaining back off counter reaches '0', the slot boundaries of the first slot of the first link and the second slot, which is a slot next to the slot in which the second back off counter is '0', do not coincide, 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 predetermined time from the slot boundary of the first slot.

6. In paragraph 5, A non-AP MLD in which the transmission time point of the second link is delayed or shortened for a specific time from the slot boundary of the first slot 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.

7. In paragraph 6, The maximum value for the above schedule time is non-AP MLD with 4us.

8. In paragraph 7, The above 4us is the non-AP MLD, which is a change time for performing the above uplink transmission in the channel access procedure.

9. In the 8th paragraph, the processor, Perform channel sensing before the above transmission time of the above second link, A non-AP MLD where the transmission time of the second link does not coincide with the slot boundary of the second slot of the second link.

10. In paragraph 1, The above uplink transmission is a non-AP MLD performed in the slot following the slot in which the first back-of counter and the second back-off counter reach '0'.

11. In paragraph 1, The above first link and the above second link are non-AP MLD, which is a NSTR link pair that does not support Simultaneous Transmit and Receive (STR).

12. In the first paragraph, the processor, Sensing is performed to determine whether the channel is idle in the first link and the second link, The first back off counter and the second back off counter are non-AP MLDs that are decremented when the first link and the second link are in an idle state, respectively.

13. In a method for a non-AP (Access Point) multi-link device (MLD) of a wireless communication system to perform uplink transmission, Perform a back off procedure for performing uplink transmission through multiple links of the above non-AP MLD. The above back-off procedure is performed individually through the first link of the first STA and the second link of the second STA included in the non-AP MLD, respectively. The back-off procedure in the first link is performed using the first back-off counter, The back-off procedure in the second link is performed using a second back-off counter, The uplink transmission is performed simultaneously to the AP MLD through each of the first link and the second link, A method in which, when both the first back off counter and the second back off counter have a value of '0', the transmission time of the uplink transmission in the first link is a slot boundary of a first slot that is a slot following a slot in which the first back off 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. In paragraph 13. If both the first back off counter and the second back off counter are '0', A method in which the transmission time of the upper link transmission in the second link is adjusted to be included within the predetermined time from the slot boundary of the first slot.

15. In paragraph 14, If the first back off counter is '0' and the second back off counter is '0', the slot boundaries of the first slot and the second slot, which is the next slot of the slot where the second back off counter of the second link is '0', do not match, A method wherein the slot boundary of the second slot is not included within the period of time.

16. In paragraph 13, A method of: if one back off counter among the first back off counter and the second back off counter reaches '0' before the remaining back off counters, a link using the one back off counter among the first link and the second link does not perform the uplink transmission, and maintains the one back off counter as '0' until the remaining back off counter reaches '0'.

17. In paragraph 13, A method in which, when one of the first back off counter and the second back off counter reaches '0' before the remaining back off counter, and when the remaining back off counter reaches '0', the slot boundaries of the first slot of the first link and the second slot, which is a slot next to the slot in which the second back off counter is '0', do not coincide, the transmission time point of the uplink transmission in the second link is adjusted to be before or after the slot boundary of the second slot so as to be included within the predetermined time from the slot boundary of the first slot.

18. In paragraph 17, A method in which the transmission time point of the second link is delayed or shortened for a specific time from the slot boundary of the first slot 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.

19. In paragraph 18, The maximum value of the above schedule time is 4us.

20. In paragraph 19, The above 4us is a method for changing the time for performing the uplink transmission in the channel access procedure.

21. In paragraph 20, Further comprising a step of performing channel sensing before the transmission time of the second link, A method wherein the transmission time of the second link does not coincide with the slot boundary of the second slot of the second link.

22. In paragraph 13, A method wherein the above uplink transmission is performed in a slot following a slot in which the first back-of counter and the second back-off counter reach '0'.

23. In paragraph 13, A method wherein the first link and the second link are an NSTR link pair that does not support simultaneous transmit and receive (STR).

24. In paragraph 13, Further comprising a step of performing sensing to determine whether the channel is idle in the first link and the second link, A method wherein the first back off counter and the second back off counter are decremented when the first link and the second link are in an idle state, respectively.

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