Method for data transmission / reception in wireless communication system, and wireless communication terminal using same

Abstract

An operating method of a wireless communication terminal, and a device are disclosed. Particularly, a first STA according to the present invention can receive, from a second STA, a trigger frame for instructing the first STA to transmit a frame, and can transmit a multi-STA block acknowledgement frame as a response to the trigger frame. Afterward, the first STA can receive a physical layer protocol data unit (PPDU) from the second STA on the basis of the multi-STA block response frame. At this time, an access category (AC) used for transmission of the trigger frame can be the same as an AC corresponding to a TID of a medium access control protocol data unit (MPDU) included in the PDU.

Description

Method for transmitting and receiving data in a wireless communication system and a wireless communication terminal using the same

[0001] The present invention relates to a method and procedure for performing communication while taking into account interference caused by coexistence of wireless communication interfaces within a device.

[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, IEEE (Institute of Electrical and Electronics Engineers) 802.11 has been commercializing or developing various technology standards. First, IEEE 802.11b supports a communication speed 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 (orthogonal frequency division multiplexing) technology to increase the communication speed to up to 54 Mbps. However, IEEE 802.11a has the disadvantage of a shorter communication range than IEEE 802.11b. And IEEE 802.11g, like IEEE 802.11b, uses the 2.4GHz band to achieve a communication speed of up to 54Mbps and satisfies backward compatibility, which has garnered considerable attention. It is also superior to IEEE 802.11a in terms of communication distance.

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

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

[0007] Meanwhile, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard, which follows 802.11ac and 802.11ad as a wireless LAN standard, is nearing completion 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] Recently, discussions have begun on Ultra High Reliability (UHR) wireless LAN communication technology, a successor to the 802.11be standard, to overcome reliability issues that have been identified as limitations of wireless LAN. The UHR standard is currently under development with the goal of supporting low latency and low jitter in wireless LAN traffic with a high probability (e.g., greater than 99.9999%).

[0010]

[0011] The purpose of the present invention is to provide a method for efficiently performing wireless LAN communication while taking into account interference between wireless communication interfaces when a terminal includes a plurality of wireless communication interfaces.

[0012] In addition, the purpose is to provide a method for efficiently performing wireless LAN communication by limiting transmission and reception of a specific wireless interface when interference occurs between multiple interfaces.

[0013] 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.

[0014]

[0015] In a non-AP (Access Point) multi-link device (MLD) including a plurality of stations according to the present invention, a processor includes a transceiver; a processor, wherein the processor receives a trigger frame from a second STA instructing the first STA to transmit a frame, and transmits a multi-STA block acknowledgment frame in response to the trigger frame, and receives a physical layer protocol data unit (PPDU) from the second STA based on the multi-STA block acknowledgment frame, and an access category (AC) used for transmission of the trigger frame is identical to an AC corresponding to a TID of a medium access control protocol data unit (MPDU) included in the PPDU.

[0016] Additionally, in the present invention, the first STA supports a specific operation mode in which transmission and reception are restricted due to communication of another communication interface.

[0017] In addition, in the present invention, the multi-STA block response frame includes a Per AID TID information subfield including an Association Identifier (AID) Traffic Identifier (TID) information subfield and a Block Acknowledgement bitmap subfield, and when the AID TID subfield is set to a preset value indicating that i) start time information of a section in which transmission and reception is restricted due to the specific operation mode and ii) duration information of the section in which transmission and reception is restricted due to the specific operation mode are included in the block response bitmap subfield, the block response bitmap subfield includes the start time information and the duration information.

[0018] In addition, in the present invention, when a transmission opportunity (TXOP) is set by the trigger frame and the duration of the TXOP and the period of the specific operation mode overlap, transmission and reception of the first STA are not performed in the overlapping period.

[0019] In addition, in the present invention, when TXOP is set by the trigger frame, the end point of the duration of the TXOP is i) the same as the end point of the section in which transmission and reception by the specific operation mode is restricted, or ii) within the duration of the specific operation mode, the end point of the duration of the TXOP is the same as or reduced to before the start point of the specific operation mode.

[0020] Additionally, in the present invention, when the specific operation mode is applied, the timer for channel sensing is started after the period in which transmission and reception are restricted by the specific operation mode ends.

[0021] Additionally, in the present invention, when the specific operation mode is applied, the processor receives a frame for setting a network allocation vector (NAV) from the second STA, and sets the NAV based on the received frame.

[0022] Additionally, in the present invention, the processor transmits a first management frame to the second STA, wherein the first management frame includes an UL MU (uplink multi-user) disabled subfield indicating whether uplink transmission for a trigger frame is possible.

[0023] In addition, in the present invention, when the value of the UL MU disabled subfield is set to a value indicating impossibility of the uplink transmission for the trigger frame, the trigger frame indicates a format of a PPDU including the multi-STA block response frame as a non-HT (high throughput) PPDU format, and when the value of the UL MU disabled subfield is set to a value indicating possibility of the uplink transmission for the trigger frame, the trigger frame indicates a format of the PPDU including the multi-STA block response frame as a TB PPDU format or the non-HT (high throughput) PPDU format.

[0024] In addition, in the present invention, the processor transmits to the second STA a first management frame including i) a UL MU (uplink multi-user) disabled subfield indicating whether uplink transmission for a trigger frame is possible, and ii) a second management frame including a specific subfield indicating whether the specific operation mode is supported, wherein if a value of the specific subfield indicates support of the specific operation mode, a value of the UL MU disabled subfield is set to a value indicating the possibility of the uplink transmission.

[0025] In addition, the present invention provides a method including the steps of: receiving a trigger frame from a second STA, which instructs the first STA to transmit a frame; transmitting a multi-STA block acknowledgment frame in response to the trigger frame; and receiving a physical layer protocol data unit (PPDU) from the second STA based on the multi-STA block acknowledgment frame, wherein an access category (AC) used for transmitting the trigger frame is the same as an AC corresponding to a TID of a medium access control protocol data unit (MPDU) included in the PPDU.

[0026] In addition, the present invention includes a transceiver; and a processor, wherein the processor transmits a trigger frame to an access point (AP), and receives a block acknowledgement frame in response to the trigger frame, and when there is no QoS data frame transmitted by the non-AP STA within a TXOP by the trigger frame after the trigger frame, the trigger frame provides the non-AP STA with one of a plurality of access categories (ACs) to transmit the trigger frame to the AP.

[0027]

[0028] One embodiment of the present invention has the effect that a wireless LAN terminal (hereinafter referred to as STA) can instruct a counterpart STA on information related to an interference problem within the device that the STA is experiencing.

[0029] In addition, according to the present invention, an STA that has received information related to an interference problem within a device from a counterpart STA has the effect of being able to adjust a frame exchange procedure based on the received information.

[0030] Additionally, according to one embodiment of the present invention, an STA experiencing an interference problem within the device can effectively perform a procedure for MediumSync recovery when the interference problem within the device is removed / resolved.

[0031] 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.

[0032]

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

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

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

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

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

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

[0039] FIG. 7 shows various standard generation-specific physical layer protocol data unit (PPDU) formats according to an embodiment of the present invention.

[0040] Figure 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0041] FIG. 9 shows a transmission / TXOP protection method using an RTS frame and a CTS frame according to an embodiment of the present invention.

[0042] FIG. 10 illustrates an embodiment of a transmission / TXOP protection method using an MU-RTS frame and a CTS frame according to an embodiment of the present invention.

[0043] Figure 11 shows a mapping table of user priority and access category.

[0044] Figure 12 shows an example of a channel connection procedure through a secondary channel when the state of the primary channel is busy.

[0045] FIG. 13 illustrates an example of a method in which an STA performs a Virtual CS for an area including Secondary channels by utilizing a Basic NAV and multiple timers according to one embodiment of the present invention.

[0046] FIG. 14 illustrates an example of a method in which an STA, according to one embodiment of the present invention, manages Basic NAV and BW information together to perform Virtual CS of a band including a Primary channel.

[0047] FIG. 15 illustrates an example of a Virtual CS failure problem that occurs when an STA according to one embodiment of the present invention manages BW information only when updating Basic NAV.

[0048] FIG. 16 illustrates an example of a method for managing Basic NAV and Bandwidth information for a Virtual CS according to one embodiment of the present invention.

[0049] FIG. 17 illustrates an example of a state in which an AP MLD and a non-AP MLD are connected through multiple links according to an embodiment of the present invention.

[0050] FIG. 18 illustrates an example of a situation in which interference occurs between different wireless communication interfaces within a device according to an embodiment of the present invention.

[0051] FIG. 19 illustrates an example of a method for an STA that experiences interference between different wireless communication interfaces to perform a medium access recovery procedure, according to one embodiment of the present invention.

[0052] Figure 20 illustrates an example of a situation in which information related to interference between different wireless communication interfaces occurring on the non-AP STA side is not properly transmitted to the AP side.

[0053] FIG. 21 illustrates an example of a method in which a non-AP STA instructs an AP about occurrence and indicative conditions of Aperiodic IDC related to interference between different wireless communication interfaces, and the AP adjusts a frame exchange procedure accordingly, according to an embodiment of the present invention.

[0054] FIG. 22 illustrates an example of a frame exchange procedure between a non-AP STA and an AP due to an IDC-related problem occurring in the AP according to one embodiment of the present invention.

[0055] FIG. 23 illustrates an example of a frame exchange procedure in which a BSRP trigger frame and an M-BA frame are exchanged and initiated according to one embodiment of the present invention.

[0056] FIG. 24 illustrates an example of a channel access procedure of an AP transmitting a BSRP trigger frame according to one embodiment of the present invention.

[0057] FIG. 25 illustrates an example of a method for an STA that fails to receive a beacon frame due to an IDC problem to obtain information through a subsequent procedure, according to one embodiment of the present invention.

[0058] FIG. 26 illustrates an example in which a non-AP STA initiating a TXOP transmits a BSRP trigger frame including IDC related information, according to one embodiment of the present invention.

[0059] FIG. 27 illustrates an example of a method for determining an Access Category (AC) used when a non-AP STA initiating a TXOP transmits an Individually addressed BSRP trigger frame, according to one embodiment of the present invention.

[0060] FIG. 28 is a flowchart showing an example of a frame exchange procedure performed by a terminal according to an embodiment of the present invention.

[0061]

[0062] 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.

[0063] Throughout the specification, when a component is said to be "connected" to another component, this includes not only the case where the component is "directly connected," but also the case where the component is "electrically connected" with another component intervening therebetween. Furthermore, when a component is said to "include" a particular component, this does not exclude the other component, 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 value may be appropriately replaced with "more than" or "less than", respectively, depending on the embodiment.

[0064] Hereinafter, in the present invention, fields and subfields may be used interchangeably.

[0065] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0066] 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.

[0067] 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).

[0068] 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).

[0069] 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 an 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.

[0070] 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).

[0071] FIG. 2 illustrates an independent BSS, a wireless LAN system, according to another embodiment of the present invention. In the embodiment of FIG. 2, portions identical or corresponding to those in the embodiment of FIG. 1 will be omitted for duplicative description.

[0072] BSS3, illustrated in Figure 2, is an independent BSS and does not include an AP. Therefore, all stations (STA6, STA7) are not connected to an AP. An independent BSS does not allow access to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) can be directly connected to one another.

[0073] 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).

[0074] First, the communication unit (120) transmits and receives wireless signals such as wireless LAN packets, and may be built into or externally installed in the station (100). According to an embodiment, the communication unit (120) may include at least one communication module using different frequency bands. For example, the communication unit (120) may include communication modules of different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to one embodiment, the station (100) may include a communication module using a frequency band of 7.125 GHz or higher and a communication module using a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with an AP or an external station according to the wireless LAN standard of the frequency band supported by the corresponding communication module. The communication unit (120) may operate only one communication module at a time or may operate multiple communication modules simultaneously, depending on the performance and requirements of the station (100). When the station (100) includes multiple communication modules, each communication module may be provided in an independent form, or the multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit (120) may represent an RF (Radio Frequency) communication module that processes RF (Radio Frequency) signals.

[0075] 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.

[0076] 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.

[0077] 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 wireless signal transmission and reception of the station (100) according to an embodiment of the present invention. A specific embodiment thereof will be described later.

[0078] 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).

[0079] 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.

[0080] 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.

[0081] 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.

[0082] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0083] 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).

[0084] 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.

[0085] 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.

[0086] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0087] 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.

[0088] When the channel is determined to be idle, each terminal with data to transmit performs a backoff procedure after an IFS (Inter Frame Space) time, such as AIFS (Arbitration IFS) or PIFS (PCF IFS), 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 idle interval of the channel, 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. At this time, the random number may be referred to as a backoff counter. That is, the initial value of the backoff counter is set by an integer, which is a random number obtained by the terminal. If the terminal detects that the channel is idle during the slot time, the terminal may decrease the backoff counter by 1. Additionally, if the backoff counter reaches 0, the terminal may be permitted to perform channel access on the channel. Accordingly, transmission by the terminal may be permitted if the channel is idle during the AIFS time and the slot time of the backoff counter.

[0089] 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.

[0090] <Various PPDU format examples>

[0091] FIG. 7 shows various standard generation-specific physical layer protocol data unit (PPDU) formats according to an embodiment of the present invention.

[0092] 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 a detailed field configuration of L-SIG and RL-SIG commonly used in the above PPDU formats.

[0093] 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.

[0094] 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.

[0095] 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 / UHR-SIG-A (Extremely High Throughput / Ultra High Reliability Signal A field), an EHT / UHR-SIG-A (Extremely High Throughput / Ultra High Reliability 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 can only be used in some of the EHT PPDU formats.

[0096] In this way, the PPDU used in the UHR standard may have a format similar to the PPDU format used in the EHT standard. This is because the EHT PPDU format defined in 802.11be includes a U-SIG field that multiple wireless LAN generations have agreed to use in common. At this time, the value of the PHY Version Identifier field of the U-SIG field included in the EHT PPDU may be 0, and the value of the PHY Version identifier field of the U-SIG field included in the UHR PPDU may have a non-zero value, such as 1. The EHT PPDU includes an EHT-STF (Extremely High Throughput Short Training field) field in the STF field, and an EHT-LTF (Extremely High Throughput Long Training field) field in the LTF field. The UHR PPDU includes a UHR-STF (Ultra High Reliability Short Training field) field in the STF field, and a UHR-LTF (Ultra High Reliability Long Training field) field in the LTF field.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101]

[0102] 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.

[0103]

[0104] 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.

[0105]

[0106] 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.

[0107] Referring to Fig. 7(e), the U-SIG (Universal SIG) field continues to exist in EHT / UHR PPDUs and subsequent generation wireless LAN PPDUs, and serves to distinguish which generation of PPDU it is, including EHT / UHR. In addition, the U-SIG field can serve to facilitate spatial reuse of EHT / UHR and subsequent generation wireless LANs. 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.

[0108] The VI bit will maintain its current bit configuration in the future so that even if a subsequent generation PPDU is defined, current EHT / UHR 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 ID field is 3 bits and sequentially distinguishes EHT / UHR and subsequent generation wireless LAN standards by version. The PHY version ID field of the EHT (11be) PPDU has a value of 000b, and the PHY version ID field of the UHR PPDU has a value other than 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 stands for Transmit Opportunity Duration transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP containing the PPDU can be inferred without having to decode the MPDU, and has a value of 7 bits or more.

[0109] The VD field of EHT 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.

[0110] The BW field largely signals five basic PPDU BW options of 20, 40, 80, 160 (80+80), and 320 (160+160) MHz (a BW that can be expressed in the form of an exponential of 20*2 can be called the basic BW), and various remaining PPDU BWs configured through Preamble Puncturing. In addition, some 80 MHz can be signaled in a punctured form after being signaled at 320 MHz. In addition, the punctured and modified channel form can be signaled directly in the BW field, or by using the BW field together with a field that appears after the BW field (for example, a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signaling is possible, so only a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signaling is possible, so the puncturing mode can signal up to 11.

[0111] The VD field of the UHR is a field that indicates signaling information that is only useful for the UHR PPDU. However, the information indicated by each field included in the VD field of the UHR PPDU may be identical to or more extended than the information indicated by the field that plays the same role as the VD field of the EHT (11be). For example, the field indicating the puncturing pattern included in the VD field of the UHR PPDU may indicate a wider variety of patterns than the field indicating the puncturing pattern included in the VD field of the EHT PPDU. Alternatively, the field indicating the puncturing pattern included in the VD field of the UHR PPDU may be interpreted in conjunction with the BW field. This allows for indicating a wider variety of puncturing patterns.

[0112]

[0113] Figure 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0114] The EHT / UHR PPDU format can be indicated by the PPDU Format field of the U-SIG field of the PPDU. Fig. 8 (a) shows an EHT / UHR SU PPDU according to an embodiment of the present invention. The EHT / UHR SU PPDU is a PPDU used for single-user transmission between an AP and a single station, and may include an EHT-SIG-A field for additional signaling after the U-SIG.

[0115] FIG. 8(b) illustrates an EHT / UHR Trigger-based PPDU according to an embodiment of the present invention. An EHT / UHR Trigger-based PPDU is an uplink PPDU used for transmission in response to a trigger frame, and may not have a separate EHT / UHR-SIG-A field after the U-SIG.

[0116] Figure 8(c) illustrates an EHT / UHR MU PPDU according to an embodiment of the present invention. An EHT / UHR MU PPDU is a PPDU used for transmission to one or more terminals. The EHT / UHR MU PPDU format may include a HE-SIG-B field after the U-SIG field.

[0117] Figure 8(d) illustrates an EHT / UHR ER SU PPDU according to an embodiment of the present invention. The EHT / UHR ER SU PPDU is used for single-user transmission to stations in an extended range. The EHT / UHR ER SU PPDU format allows the U-SIG to be repeated along the time axis.

[0118] The EHT / UHR MU PPDU described through (c) of FIG. 8 can be used by an AP to perform downlink transmission to multiple stations. At this time, the EHT / UHR MU PPDU can include scheduling information for multiple stations to simultaneously receive the PPDU. At this time, the EHT / UHR MU PPDU can convey AID information of the receiver or transmitter of the corresponding PPDU through the user specific field of EHT / UHR-SIG-B. A station that receives the EHT / UHR MU PPDU can perform a spatial reuse operation based on the AID information obtained from the preamble of the PPDU. More specifically, the resource unit allocation (RA) field of EHT / UHR-SIG-B can include information on a resource unit (RU) partitioning form in a specific bandwidth (e.g., 20 MHz) in the frequency domain. Additionally, information about the station assigned to each partitioned resource unit may be conveyed via a user-specific field of EHT / UHR-SIG-B. The user-specific field may include one or more user fields corresponding to each partitioned resource unit.

[0119] Among the multiple resource units divided, the AID of the receiver or sender may be inserted into the user field corresponding to the resource unit in which data transmission is performed. A pre-specified null STA ID may be inserted into the user field corresponding to the remaining resource units in which data transmission is not performed.

[0120] Two or more PPDUs described through FIG. 8 may be indicated by the same PPDU format. For example, the value of the U-SIG PPDU format subfield indicating an EHT / UHR SU PPDU and the value of the U-SIG PPDU format subfield indicating an EHT / UHR MU PPDU may be the same.

[0121] Some fields or some information within a field included in the format of the PPDU described above may be omitted. This may be referred to as compression mode or compressed mode.

[0122]

[0123] <Wi-Fi 단말의 채널 액세스 방법>

[0124] Wi-Fi terminals (APs, non-AP STAs, etc.) perform communication using unlicensed bands, so before transmitting a frame, they check whether the channel they want to transmit is in use by another device. CSMA (Carrier Sense Multiple Access) is a channel access method in which a terminal that wants to transmit a packet performs carrier sense to check whether the channel is in use by another device, and transmits only if the channel is determined to be idle. Since a terminal using CSMA can perform an action of not attempting transmission at least when it is determined that another device is using the medium (channel) (when it is determined to be busy), the transmission that was initiated first can be protected from other devices.

[0125] However, multiple terminals that recognize that the medium is occupied by another device experience a transmission collision by simultaneously attempting to transmit packets when it is confirmed that the medium occupation from the other device has ended (the medium has changed to Idle). That is, as multiple other terminals simultaneously attempt to transmit packets when a specific terminal attempts to transmit a packet, a terminal that is supposed to receive the packet transmitted by the specific terminal is unable to properly receive and decode the packet that it is supposed to receive due to interference caused by the transmissions performed by the multiple other terminals.

[0126] CSMA / CA (CSMA with collision avoidance) is a channel access mechanism that prevents multiple terminals from simultaneously attempting packet transmission when the medium has changed to Idle, as described above. Terminals accessing the medium (channel) using CSMA / CA attempt to transmit after waiting for a random amount of time when the state of the medium they observe changes to Idle. The random amount of time may be an aslottime (typically 9 microseconds) equal to a random number (random backoff counter) generated by each terminal attempting to transmit. In other words, terminals accessing the medium using CSMA / CA attempt to transmit after waiting for different random amounts of time, so they attempt to transmit at different times, unlike when CSMA alone is used. In this case, when a specific terminal that waited for the shortest random amount of time after the medium changed to Idle attempts to transmit first, other terminals can recognize that the medium has been occupied (changed to busy) by the specific terminal and abort the channel access procedure. At this time, the specific terminal may perform an operation of decreasing the backoff counter maintained by it by 1 every aslottime while the medium is maintained as Idle, and may attempt transmission when the backoff counter becomes 0, or when the aslottime has passed after the backoff counter becomes 0. At this time, the specific terminal that performed the transmission may generate a new random number (new backoff counter) after the transmission is finished, and may attempt transmission when the new random number becomes 0 again, or after it becomes 0.

[0127] The CSMA / CA and random backoff procedures briefly explained above are applied to DCF (Distributed coordination function) and EDCAF (Enhanced distributed channel access), which are the basic functions used by Wi-Fi terminals when attempting to access a channel. Since these are well-known and widely used unlicensed band channel access methods, a more detailed explanation will be omitted.

[0128]

[0129] The DCF and EDCAF utilized by the MAC of the Wi-Fi terminal evaluate the channel status by considering not only the channel status (idle / busy) confirmed by each terminal performing its own physical CS (Carrier Sense) but also the results of a virtual CS. In more detail, even if the result of the physical CS performed on the channel is idle, if the result of the virtual CS is busy, the Wi-Fi terminal considers the channel status to be busy. At this time, the Virtual CS is a channel evaluation method that determines the channel to be busy if the NAV (Network allocation vector) is not 0. The NAV may be a value maintained for future traffic that is predicted to occupy the medium. To explain in more detail, when the MAC of Wi-Fi receives an RTS / CTS frame, it can set the NAV (NAV count) based on the duration information of the received frame, for example, the value of the duration field, and maintain the NAV as a non-zero value for the expected time that the medium will be occupied after the RTS / CTS frame exchange. In other words, the value maintained as NAV decreases over time. If the NAV value of a specific MAC is 0, it can be interpreted that the future traffic recognized by the specific MAC is no longer occupying the medium. If the NAV is 0, the MAC can determine the virtual CS result as Idle. At this time, the MAC of Wi-Fi can also set the NAV based on the duration value obtained from not only the RTS / CTS frame but also other received MAC frames.

[0130] The channel estimation method (determine the state of the medium) that considers the results of the physical CS and virtual CS briefly described above is also one of the well-known Wi-Fi MAC functions, so a detailed explanation is omitted.

[0131]

[0132] <EDCA와 TXOP>

[0133] EDCA provides a mechanism to differentiate and manage traffic into four types of ACs (access categories) according to the characteristics of the traffic. The four types of ACs are AC_VO (AC Voice), AC_VI (AC Video), AC_BE (AC Best Effort), and AC_BK (AC Background), and each AC can have different CW (contention window), TXOP (transmit opportunity), and AIFSN parameters. Simply put, EDCA is a mechanism that differentiates the CW, TXOP, and AIFSN parameters for the four types of ACs and controls the transmission priority of traffic transmitted using each AC. To this end, EDCA can map traffic (MSDU) that the MAC must service to one of the four ACs according to the TC (traffic category) or TS (traffic stream). At this time, the traffic mapped to one of the four ACs by EDCA is divided and managed into four queues for each AC. At this time, the four queues may be logically separated rather than physically separated.

[0134] AC_VO is an AC that can be utilized for traffic that is vulnerable to transmission delays, although the absolute volume of traffic, such as voice traffic, is not large. It has relatively small CW and AIFSN parameter values ​​to increase the probability of being serviced preferentially over traffic from other ACs. The TXOP parameter of AC_VO is limited to a relatively small value compared to the TXOP parameters of other ACs, ensuring only a shorter transmission time than other ACs.

[0135] AC_VI is an AC that is more delay-tolerant than voice traffic, but can still be utilized for traffic such as video that requires low-latency transmission and high traffic volume. AC_VI has larger CW and AIFSN parameter values ​​than AC_VO but smaller than other ACs, and its TXOP is approximately twice as long as AC_VI.

[0136] AC_BE is an AC that can be utilized for traffic that is robust to transmission delays, and most general traffic, excluding voice data and streaming video data, can be classified as AC_BE. AC_BE uses CW and AIFSN parameters with values ​​greater than AC_VO and AC_VI. In addition, AC_BE does not have a separate TXOP. Therefore, traffic corresponding to AC_BE cannot be utilized in the TXOP transmission sequence, which transmits a PPDU, receives an ACK in response, and then transmits a PPDU again after SIFS.

[0137] AC_BK, similar to AC_BE, is a delay-tolerant traffic, but can be utilized for lower-priority traffic than BE traffic. AC_BK utilizes the same CW parameter values ​​as AC_BE, and the AIFSN parameter values ​​are larger than those of AC_BE. In addition, traffic corresponding to AC_BK does not have a separate TXOP like AC_BE, so it cannot be utilized in the TXOP transmission sequence.

[0138] The four types of EDCA AC described above are mapped to the UP (user-priority) of 802.1D, and the EDCA AC is determined based on the UP value of the traffic received through the wire or the TID of the MSDU indicated from the upper layer. At this time, if the TID of the MSDU indicates a value between 0 and 7, the value indicated by the TID can correspond one-to-one with the UP.

[0139] In addition, the four types of EDCA AC described above have default CW (CWmin, CWmax), AIFSN, and TXOP parameters defined in the standard, and the parameter values ​​of each AC can be changed by the AP, so that different values ​​can be used for each BSS.

[0140]

[0141] Using the EDCA mechanism, Wi-Fi traffic is stored in one of four queues corresponding to four ACs, and can be transmitted to the destination device only if the AC containing the traffic wins the channel access competition with other ACs. At this time, in the channel access competition between ACs, each AC competes using its assigned access parameters (CW[AC], AIFSN[AC]), and the channel access competition operation performed by each AC is identical to DCF. At this time, if a specific AC does not have any traffic to transmit in its queue, the specific AC may not participate in the competition.

[0142] However, as described above, since the CW and AIFSN parameter values ​​utilized by each AC are different, the AC_VO with the smallest CW and AIFSN parameters is more likely to win the channel access competition with other ACs, and thus the traffic of AC_VO is more likely to be serviced with priority over the traffic of other ACs.

[0143] In addition, the EDCA mechanism stipulates internal competition rules such as when an (internal) collision occurs between ACs, the AC with a higher priority wins, and increases the CW of the other AC that caused the collision, and rules for composing a PPDU including traffic from an AC other than the AC that won the competition (primary AC), but a detailed description is omitted because it is not closely related to the proposal of the present invention.

[0144] As described above, EDCA provides the EDCA TXOP (EDCA Transmission Opportunity) function along with the function of operating differentiated ACs according to the type of traffic (frames, packets, etc.) to enhance QoS. EDCA TXOP refers to the time during which the EDCAF (EDCA Function) of a specific AC can control the medium without being disturbed by other devices during the TXOP period (duration) when it obtains a channel access opportunity, i.e., becomes a TXOP holder. At this time, the EDCA TXOP may be limited by the TXOP limit advertised by the AP. The TXOP holder must ensure that its own transmission and the transmission of the response frame responded to by its own transmission can be terminated within the TXOP limit.

[0145] A TXOP holder can transmit multiple frames (multiple PPDUs) during an EDCA TXOP period. If the transmission of each frame is performed within the acquired TXOP period, the TXOP holder can transmit multiple frames continuously without performing a separate channel access procedure, such as a backoff procedure, between transmissions of each frame. At this time, if the multiple frames are MPDUs or A-MPDUs (Aggregated MAC protocol data units) that do not request an immediate ack, the transmission of the multiple frames can be performed at an interval of a short interframe space (SIFS) or a reduced interframe space (RIFS). At this time, if there is an MPDU or A-MPDU requesting an immediate ack among the multiple frames, the TXOP holder can transmit a frame requesting an immediate ack, receive the ack, and transmit the next frame after an SIFS.

[0146] At this time, traffic (packets, frames, etc.) of other ACs other than the specific AC that is the TXOP holder may also be transmitted together within the TXOP acquired by the TXOP holder (specific AC) when certain conditions are satisfied. The transmission of traffic of other ACs other than the TXOP holder within the TXOP may be an operation due to TXOP sharing between ACs, and detailed information regarding the above-mentioned certain conditions is omitted because it is not related to the present invention.

[0147]

[0148] As described above, a TXOP holder can perform continuous frame transmission without performing a separate channel access procedure within the TXOP. This may be an operation that can be achieved when other terminals understand and protect the TXOP section acquired by the TXOP holder. In other words, in order for the TXOP holder to acquire medium control authority for the EDCA TXOP section, a procedure may be required to notify other terminals so that they can recognize the acquired TXOP section.

[0149] To this end, a terminal (AC) that becomes a TXOP holder or initiates transmission after completing a channel access procedure may attempt to allow other terminals to recognize the TXOP section by transmitting an RTS frame. At this time, the RTS frame means a frame in which the Type subfield (the fourth bit (B3), the third bit (B2) of the Frame Control field) of the Frame Control field of the MAC frame header is set to 01b (Type = Control frame) and the Subtype subfield (the eighth bit (B7), the seventh bit (B6), the sixth bit (B5), the fifth bit (B4) of the Frame Control field) is set to 1011b. Another terminal that receives an RTS frame from a TXOP holder may set an NAV based on information related to the duration included in the RTS frame, for example, the value of the Duration field. The set NAV may be maintained as a non-zero value for a time corresponding to the TXOP of the TXOP holder. However, the terminal indicated as the destination device of the RTS frame must respond with a CTS frame instead of setting the NAV based on the information in the RTS frame. At this time, the destination device of the RTS frame transmitted to start TXOP is a TXOP responder and must transmit a CTS frame in response to the RTS (SIFS after the RTS frame is received). At this time, the Duration field of the responding CTS frame is set to a value calculated as the value indicated in the Duration field of the received RTS frame - the CTS frame transmission time - SIFS. The terminals receiving the CTS frame can set the NAV based on information related to the duration included in the CTS frame (e.g., the value of the Duration field).

[0150] Therefore, the NAV of the terminal that received the RTS frame from the TXOP holder and the terminal that received the CTS frame from the TXOP responder are set to 0 after the TXOP acquired by the TXOP holder ends. This allows the Wi-Fi MAC mechanism to protect the TXOP holder and the TXOP responder from exchanging multiple frames without interruption during the TXOP.

[0151] However, if the TXOP holder transmits an RTS frame as a non-HT duplicate PPDU over the primary 80 MHz band, but the CTS frame (non-HT duplicate PPDU) responded to by the TXOP responder is responded to only in the primary 40 MHz band, the TXOP holder may use only the bandwidth of the primary 40 MHz or less than the primary 40 MHz, for example, the primary 20 MHz, for frame exchange during the acquired TXOP. The CH_BANDWIDTH (a type of TXVECTOR parameter) of the PPDU transmitted by the TXOP holder shall be set to a value equal to or smaller than the CH_BANDWIDTH_IN-NON_HT (a type of RXVECTOR parameter) of the received CTS frame. In this case, the RTS frame may be an RTS frame that allows the CTS frame to be responded to in a BW smaller than the BW in which the RTS frame was transmitted. An RTS frame may be an RTS frame transmitted with DYN_BANDWIDTH_IN_NON_HT (a type of TXVECTOR parameter) set to Dynamic. If DYN_BANDWIDTH_IN_NON_HT is set to Static and the RTS frame is transmitted from a TXOP holder, the TXOP responder may have to respond with a CTS frame with the same BW as the BW in which the RTS frame was received.

[0152]

[0153] FIG. 9 shows a transmission / TXOP protection method using an RTS frame and a CTS frame according to an embodiment of the present invention.

[0154] Before transmitting a PPDU, the first station (STA1) transmits an RTS frame to the second station (STA2), which is the destination of the PPDU, and the second station (STA2) recognizes that the received RTS frame is an RTS frame destined for itself and responds with a CTS frame after SIFS.

[0155] STA1_Neighbor, a neighbor station of the first station (STA1), sets the NAV based on the value indicated by the Duration field of the RTS frame after receiving the RTS frame transmitted by the first station (STA1). STA2_Neighbor, a neighbor station of the second station (STA2), sets the NAV based on the information indicated by the Duration field of the CTS frame after receiving the CTS frame transmitted by the second station (STA2). STA1_Neighbor and STA2_Neighbor determine that the virtual CS is busy while the set NAV (counter) is maintained at a non-zero value after receiving the RTS / CTS frame, and perform actions such as not decreasing the backoff counter. As a result, the neighboring terminals that received the RTS / CTS frame do not attempt transmission during the period in which the NAV is maintained at a non-zero value. Therefore, the first station (STA1) and the second station (STA2) may not be disturbed by surrounding terminals while exchanging PPDU and Ack frames.

[0156] Even if the first station (STA1) and STA2_Neighbor are in a relationship where signals due to each other's transmissions are not detected (hidden), STA2_Neighbor can perform an operation that takes into account that the channel (channel, WM, Wireless medium) is in use while the first station (STA1) transmits a PPDU.

[0157] Meanwhile, a Wi-Fi terminal (non-AP STA) can transmit an UL PPDU to the AP without directly acquiring a TXOP or performing channel access through DCF and EDCAF. More specifically, a non-AP STA can transmit an UL PPDU using its assigned RU after receiving a trigger frame transmitted by the AP. In this case, the UL PPDU is a TB (trigger-based) PPDU.

[0158] An STA that responds with a UL PPDU after receiving a trigger frame can obtain more transmission opportunities than an STA that does not transmit a UL PPDU based on the trigger frame because it can perform transmission without obtaining direct channel access opportunities through DCF and EDCAF. Therefore, an STA that transmits a UL PPDU through the trigger frame may cause a fairness issue in terms of channel access. To address this fairness issue, 11ax defines a constraint that requires an HE non-AP STA to perform EDCAF using the MU (Multi-user)-EDCA parameter when it successfully transmits at least one MPDU through the UL PPDU transmitted after receiving the trigger frame. Accordingly, an STA that transmits a UL PPDU through the trigger frame must perform channel access using the MU-EDCA parameter, not the EDCA parameter. MU-EDCA parameters include the size of the contention window for each of AC_VO, AC_VI, AC_BE, and AC_BK and parameters related to the MU EDCA timer, and the contention window included in MU-EDCA can be set to be larger than the parameters of EDCA. An STA that transmits a TB PPDU through a trigger frame and successfully transmits at least one MPDU performs channel access within the time period corresponding to the MU EDCA timer by performing channel access using the MU EDCA parameters rather than the EDCA parameters, thereby succeeding in channel access with a lower probability than an STA that uses the EDCA parameters.In this way, by lowering the channel accessibility of an STA that transmits a UL PPDU (TB PPDU) based on a trigger frame, the fairness problem in channel accessibility between an STA that transmits a UL PPDU without performing direct channel access and an STA that does not transmit a UL PPDU based on a trigger frame can be resolved / alleviated.

[0159] <MU-RTS 트리거 프레임을 이용한 TXOP 보호>

[0160] 11ax (6th generation Wi-Fi, Wi-Fi6, HEW, High Efficiency WLAN) defines the MU-RTS Trigger / CTS frame exchange procedure, and adds a function that enables the AP to start TXOP and protect the TXOP frame exchange procedure using the MU-RTS trigger frame (hereinafter referred to as MU-RTS, MU-RTS frame). The MU-RTS frame is a type of trigger frame. When the MU-RTS frame is received, the station whose AID12 (the LSB 12 bits of the Association ID) is indicated in the User field included in the MU-RTS frame simultaneously responds with a CTS frame. When the AP protects the TXOP using the MU-RTS frame, since multiple stations respond with CTS frames, the TXOP can be protected from the peripheral devices of each of the multiple stations that are the destination devices of the DL MU PPDU (Down link multi-user PPDU). In addition, the MU-RTS frame can be used to protect the UL MU PPDU. In more detail, before requesting a TB (Trigger based) PPDU from multiple stations through a trigger frame, the AP can transmit an MU-RTS frame to cause multiple stations that will respond to the TB PPDU to respond with a CTS frame. At this time, the CTS frames responded to by the multiple stations induce the surrounding stations of each station to set a NAV that protects the TB PPDU and the Ack frame (Ack, Block Ack, etc.) to be transmitted after the TB PPDU, and through this, legacy stations STAs that cannot recognize (interpret, decode) the trigger frame and TB PPDU may not perform channel access during the packet exchange sequence period (or TXOP) initiated through the trigger frame.

[0161]

[0162] FIG. 10 shows a transmission / TXOP protection method using an MU-RTS frame and a CTS frame according to an embodiment of the present invention.

[0163] In the embodiment of FIG. 10, before transmitting an MU PPDU, the AP transmits an MU-RTS frame to the first station (STA1) and the second station (STA2), which are the destination devices of the MU PPDU, and the first station (STA1) and the second station (STA2) receive the MU-RTS frame and, after SIFS, each respond to the MU-RTS frame with a CTS frame.

[0164]

[0165] STA1_Neighbor, a neighboring station of the first station (STA1), sets its NAV based on the information indicated by the Duration field of the CTS frame after receiving the CTS frame transmitted by the first station (STA1). STA2_Neighbor, a neighboring station of the second station (STA2), sets its NAV based on the information indicated by the Duration field of the CTS frame after receiving the CTS frame transmitted by the second station (STA2). STA1_Neighbor and STA2_Neighbor perform operations such as not decreasing the back-off counter, assuming that the Virtual CS (Virtual Carrier Sense) is busy while the NAV (counter) set after receiving the CTS frame remains at a non-zero value. Therefore, neighboring terminals that have received the CTS frame do not attempt to transmit during the period in which the NAV remains at a non-zero value. This allows the AP to transmit MU PPDUs and the first station (STA1) and the second station (STA2) to transmit Ack frames without being interrupted by surrounding terminals.

[0166] The trigger frame described above is a frame type defined in 11ax, and is a frame type in which the Type (fourth bit (B3) and third bit (B2)) and Subtype (eighth bit (B7), seventh bit (B6), sixth bit (B5), and fifth bit (B4)) subfields of the Frame Control field are set to 01b and 0010b, respectively. A trigger frame is a frame of Control Type in which the Type subfield of the Frame Control field is 01b, and the Subtype value 0010 indicates that it is a Trigger frame type. In 11ax, a trigger frame is defined so that an AP can request a response frame for multiple stations at once, and an MU-RTS frame is used so that an AP can request a CTS frame for multiple stations (non-AP STAs). Trigger Types other than the MU-RTS frame include the Basic Tigger frame requesting UL MU PPDU, the Beamforming Report Poll Tigger frame requesting Beamforming Report, the MU-BAR Tigger frame (BlockAck request), the BSRP trigger frame requesting Buffer Status Report, the GCR MU-BAR trigger frame, the Bandwidth Query Report Poll (BQRP) trigger frame, and the NDP Feedback Report Poll trigger frame. Trigger Types other than the MU-RTS frame are not related to the content of the present invention, so a detailed description thereof is omitted.

[0167] <Multi-link Device (MLD)>

[0168] MLD is defined in EHT (Extremely High Throughput) of Wi-Fi 7. MLD means a logical entity that includes one or more STAs. One or more APs (AP STAs) can be affiliated to an AP MLD, and one or more non-AP STAs can be affiliated to a non-AP (STA) MLD.

[0169] Each AP belonging to an AP MLD can operate an independent Basic Service Set (BSS), and the operating bandwidth (OS) and operating channel (Operating BW) of the BSSs operated by the APs can be different. When an AP MLD and a non-AP MLD are associated, setup can be performed between multiple APs belonging to a single AP MLD and multiple non-AP STAs belonging to a single non-AP MLD. At this time, since each AP belonging to the AP MLD operates a BSS on its own Link (Operating Channel), the non-AP MLD associated with each of the multiple APs belonging to the single AP MLD is considered to have performed a Multi-Link setup. In other words, the AP MLD and non-AP MLD defined in Wi-Fi 7 can perform a Multi-Link setup connected on multiple Links.

[0170] Each MLD can have up to 15 STAs (AP STAs, non-AP STAs). That is, 15 APs can belong to an AP MLD, and the 15 APs each operate an independent BSS. At this time, each AP belonging to the AP MLD provides a service equivalent to a conventional Wi-Fi AP. That is, each AP belonging to the AP MLD can function as an independent AP and provide services to non-AP STAs (e.g., legacy non-AP STAs) that do not belong to the MLD. At this time, each AP belonging to the AP MLD operates in an independent Link, and the meaning of the Link only refers to the operating channel on which each AP operates, and does not mean a Link that distinguishes 2.4 / 5 / 6 GHz. That is, the first AP belonging to the AP MLD can operate in the first Link, and the second AP can operate in the second Link. At this time, it is possible for both the first link in which the first AP operates and the second link in which the second AP operates to be located in the 6 GHz band.

[0171] In addition, AP MLD and non-AP MLD can complete setup on multiple links through a Multi-Link setup procedure performed on a specific link. In this case, the Multi-Link setup procedure refers to the exchange of Multi-Link Probe Request / Response and Multi-Link Association Request / Response frames performed to establish a connection for one or more links. In the present invention, the procedure for performing Multi-Link setup between AP MLD and non-AP MLD is not important, so a detailed description thereof will be omitted.

[0172] When two MLDs are connected via multiple Links, the two MLDs can operate the traffic to be transmitted / received via each Link separately. This can be achieved by TID-to-Link mapping negotiation between the two MLDs or by applying the TID-to-Link mapping status indicated by the AP MLD. At this time, the TID-to-Link mapping status that the AP MLD indicates to the non-AP MLDs is indicated by the Management frame (e.g., Beacon, Probe Response frame) transmitted by the AP MLD, and the non-AP MLDs associated with the AP MLD via at least one Link must operate each Link according to the TID-to-Link mapping indicated by the AP MLD. However, if a new TID-to-Link mapping negotiation is performed between the AP MLD and the non-AP MLD, the Traffic (MPDU) of each TID can be transmitted / received via different Links according to the method determined by the new TID-to-Link mapping negotiation. For example, if an AP MLD and a non-AP MLD are connected through two Links, and TIDs 0 to 3 are mapped to Link 1 and TIDs 4 to 7 are mapped to Link 2, the AP MLD and the non-AP MLD must transmit / receive only MPDUs with TIDs 0 to 3 through Link 1, and must transmit / receive MPDUs with TIDs 4 to 7 through Link 2.

[0173] If the AP MLD does not indicate a separate TID-to-Link mapping state and there is no TID-to-Link mapping performed between the AP MLD and the non-AP MLD, the AP MLD and the non-AP MLD have the Default TID-to-Link mapping state. The Default TID-to-Link mapping state means that all TIDs are mapped to each Link, and in this case, the AP MLD and the non-AP MLD transmit / receive MPDUs of all TIDs (TID = 0 to 7) on each Link.

[0174] The fact that a multi-link setup has been performed between MLDs means that two MLDs, for example, an AP MLD and a non-AP MLD, are connected (associated) through multiple STAs. At this time, each STA included in the MLD has a different operating channel, and the operating channel on which each STA operates is called a link. That is, the AP MLD operates an AP STA on each of the multiple links (each AP STA operates a BSS on each link), and the non-AP MLD can maintain a connection state between the APs and its non-AP STAs through one or more links.

[0175] As briefly mentioned above, each link on which an MLD STA operates has a different operating channel. This is a self-evident limitation, considering that the number of STAs that can communicate at a given point in time among STAs operating on the same channel is limited to one, so a detailed explanation is omitted. Furthermore, if the frequency spacing between the operating channels of each STA included in the same MLD is narrow, a signal transmitted by a specific STA included in the MLD may interfere with the transmission / reception operations of another STA included in the MLD. This means that even if two STAs have different operating channels, adjacent channel interference issues may arise depending on the frequency separation between their operating channels.

[0176] Since Wi-Fi 8 (UHR, Ultra High Reliability) is expected to be developed based on Wi-Fi 7, the MLD concept, the connection procedure between MLDs, and the link operation method through TID-to-Link mapping will still be inherited in Wi-Fi 8. In other words, it is possible for an AP belonging to an AP MLD to be a UHR STA, and it is also possible for a non-AP STA belonging to a non-AP MLD to be a UHR STA.

[0177] <MLD의 채널 접속>

[0178] Figure 11 shows a mapping table of user priority and access category.

[0179] Each STA belonging to the MLD performs channel access in the same manner as a conventional Wi-Fi terminal. More specifically, each STA performs channel access using Enhanced Distributed Channel Access (EDCA).

[0180] Channel access mechanism using EDCA is a commonly used method for channel access in unlicensed bands.

[0181] EDCA provides a mechanism to differentiate and manage traffic into four types of ACs (access categories) according to their characteristics. The four types of ACs are AC_VO (AC Voice), AC_VI (AC Video), AC_BE (AC Best effort), and AC_BK (AC Background), and each AC can have different CW (contention window), TXOP (transmit opportunity), and AIFSN parameters. Simply put, EDCA is a mechanism to control the transmission priority of traffic transmitted using each AC by differentiating the CW, TXOP, and AIFSN parameters for the four types of ACs. To this end, EDCA can map traffic (MSDU) that the MAC must service to one of the four ACs according to the TC (traffic category) or TS (traffic stream). At this time, the traffic mapped to one of the four ACs by EDCA is divided and managed into four queues for each AC. At this time, the above four queues may not be physically separated, but rather logically separated. At this time, packets mapped to each AC and stored in the Transmission queue are transmitted when each AC completes the backoff procedure and obtains channel access. Since the method by which an AC performs the backoff procedure to obtain channel access has already been described in Figure 6, a detailed description is omitted.

[0182] AC_VO is an AC that can be utilized for traffic vulnerable to transmission delays, although the absolute volume of traffic, such as voice traffic, is not large. It has relatively small CW and AIFSN parameter values ​​to increase the probability of being serviced preferentially over traffic from other ACs. However, the TXOP parameter of AC_VO is limited to a relatively small value compared to the TXOP parameters of other ACs, ensuring only a shorter transmission time than other ACs.

[0183] AC_VI is an AC that is more delay-tolerant than voice traffic, but can still be used for low-latency transmission and high-volume traffic, such as video. AC_VI has larger CW and AIFSN parameters than AC_VO but smaller than other ACs. However, its TXOP is about twice as long as AC_VI's.

[0184] AC_BE is an AC that can be utilized for traffic that is robust to transmission delays, and most general traffic, except for voice data and streaming video data, can be classified as AC_BE. AC_BE uses CW and AIFSN parameters with values ​​larger than AC_VO and AC_VI. In addition, AC_BE does not have a separate TXOP, and therefore cannot utilize the TXOP transmission sequence that transmits a PPDU, receives an ACK in response, and then transmits a PPDU again after SIFS.

[0185] AC_BK, similar to AC_BE, is a delay-tolerant traffic, but can be utilized for lower-priority traffic than BE traffic. AC_BK utilizes the same CW parameter values ​​as AC_BE, and the AIFSN parameter values ​​are larger than those of AC_BE. Additionally, AC_BK, like AC_BE, does not have a separate TXOP, so it cannot utilize the TXOP transmission sequence.

[0186] The four types of EDCA AC described above are mapped to the UP (user-priority) of 802.1D, and the EDCA AC is determined based on the UP value of the traffic received through the wire or the TID of the MSDU indicated from the upper layer. At this time, if the TID of the MSDU indicates a value between 0 and 7, the value indicated by the TID can correspond one-to-one with the UP.

[0187] The rules for mapping 802.1D UP and EDCA AC are described in the UP-to-AC mappings table shown in Figure 43.

[0188] In addition, the four types of EDCA AC described above have default CW (CWmin, CWmax), AIFSN, and TXOP parameters defined in the standard, and the parameter values ​​of each AC can be changed by the AP, so that different values ​​can be used for each BSS.

[0189] Using the EDCA mechanism, Wi-Fi traffic is stored in one of four queues corresponding to four ACs, and can be transmitted to the destination device only when the AC it is included in wins the channel access competition with another AC. At this time, in the channel access competition between the ACs, each AC competes using the access parameters (CW[AC], AIFSN[AC]) assigned to it, and the channel access competition operation performed by each AC is identical to DCF. At this time, if a specific AC does not have any traffic to transmit in its queue, the specific AC may not participate in the competition.

[0190] However, as described above, since the CW and AIFSN parameter values ​​utilized by each AC are different, the AC_VO with the smallest CW and AIFSN parameters is more likely to win the channel access competition with other ACs, and thus the traffic of AC_VO is more likely to be serviced with priority over the traffic of other ACs.

[0191] In addition, the EDCA mechanism stipulates internal competition rules, such as when an (internal) collision occurs between ACs, the AC with a higher priority (see Fig. 11) wins, and increases the CW of the other AC that caused the collision, and rules for composing a PPDU including traffic from an AC other than the AC that won the competition (primary AC), but a detailed description is omitted because it is not closely related to the proposal of the present invention.

[0192] As described above, each STA belonging to an MLD performs channel access in the same manner as a conventional Wi-Fi terminal. That is, when observing each STA belonging to an MLD on each link, each STA belonging to an MLD performs channel access in the same manner as a non-MLD STA (QoS STA) that does not belong to an MLD performs channel access. This can be said to be a rule defined during the development of Wi-Fi 7, taking into account fairness with the existing non-MLD STAs operating on each link.

[0193] However, there is an exception defined for MLDs operating on Nonsimultaneous Transmit and Receive (NSTR) Link pairs. More specifically, STAs of MLDs operating on Nonsimultaneous Transmit and Receive (NSTR) Link pairs are allowed to defer transmission initiation after the backoff procedure has been completed in order to synchronize the transmission initiation timing with transmissions performed on other Links.

[0194] An NSTR link pair refers to a link pair that causes strong interference to the remaining links when the MLD performs transmission on a specific link among the link pairs on which the STA of the MLD operates. For example, if Link1 and Link2 are an NSTR link pair of a non-AP MLD, when non-AP STA1 of the non-AP MLD operating on Link1 performs transmission, non-AP STA2 of the non-AP MLD operating on Link2 experiences strong interference. Accordingly, non-AP STA2 cannot determine whether Link2 is IDLE / BUSY or normally receive the received PPDU while non-AP STA1 is performing transmission. In this case, the non-AP MLD has a problem that normal operation of the other link is impossible when transmission is performed on one link even though it operates STAs on two links. To alleviate this problem, Wi-Fi 7 introduced a mechanism that allows non-AP MLDs to initiate simultaneous transmission on an NSTR link pair. Briefly, the mechanism that can initiate simultaneous transmission is a mechanism that allows transmission to be initiated simultaneously on the first and second links by suspending transmission until the backoff procedure performed on the second link is completed, even if the non-AP MLD has completed the backoff procedure on the first link.

[0195] Additionally, an exception rule is defined that allows a PPDU to be received on one Link of an NSTR link pair, and a response frame (e.g., a CTS frame) may not be responded to even if a frame requesting a response (e.g., an RTS frame) is received on the other Link of the NSTR link pair.

[0196] As described above, since an NSTR link pair is characterized by interference caused by transmissions performed by STAs operating on a specific Link that makes it impossible for STAs operating on other Links to operate normally (CCA and / or PPDU reception is impossible), the same Link pair may be an NSTR link pair for a specific MLD and an STR link pair (Simultaneous transmit and receive) for another MLD. In this case, an STR link pair means a Link pair in which transmissions performed by each STA operating on each Link of the STR link pair do not affect STAs operating on other Links, and thus PPDU reception is possible on another Link while PPDU transmission is performed on a specific Link.

[0197] In this way, each link pair can be an STR link pair to a specific MLD or an NSTR link pair to another MLD depending on the interference shielding capability of each MLD. However, if the operating channels of a specific link pair overlap, the specific link pair cannot help but become an NSTR link pair regardless of the characteristics / performance of the MLD. Accordingly, in Wi-Fi 7, when performing a multi-link setup in which an AP MLD and a non-AP MLD are connected through multiple links, the operating channels of the BSSs operated in each link on which the setup is performed are regulated to not overlap with each other. In other words, the operating channels of each link on which an AP MLD and a non-AP MLD perform a multi-link setup do not overlap with each other.

[0198] <Primary channel (or main channel) dependency problem in conventional Wi-Fi channel access procedures>

[0199] MLD was introduced to 1) increase throughput by utilizing multiple links, and 2) obtain channel access more quickly by performing channel access procedures across multiple links than through a single link (by quickly obtaining access through one of the multiple links). However, this method of improving channel access opportunities by simultaneously performing channel access procedures across multiple links can incur significant power consumption as the number of links performing channel access procedures increases. While MLD can perform channel access procedures across multiple links to increase the probability (frequency) of channel access, it suffers from the power consumption associated with performing channel access procedures across multiple links. Therefore, using multiple links as a solution to increase channel access probability (frequency) is considered a limited solution, and a method is needed to increase the success probability (frequency) of the channel access procedure performed on each link. For example, to obtain channel access more quickly than through a single link, the channel access procedure can be performed across more than one link, but considering power consumption, the number of links can be limited. For example, if a channel access procedure cannot be performed on a primary channel, the channel access procedure can be performed by selecting one of the idle non-primary channels (such as a non-primary channel or secondary channel) without waiting until the primary channel changes to an idle state.

[0200] Therefore, in order to support the development goal of Wi-Fi 8, which is 'Ultra High Reliability (UHR),' it is necessary to optimize the utilization of multiple links, which is a characteristic of MLD, as well as a method to support STAs operating on each link to obtain channel access opportunities in the best possible way.

[0201] In this context, it is necessary to analyze the channel accessibility issues of Wi-Fi terminals performing channel access on each link. The Wi-Fi standard has achieved significant throughput performance improvements over successive generations, and the Wi-Fi 7 standard, which is currently nearing standardization, supports throughput exceeding 30 Gbps. One of the reasons the Wi-Fi 7 standard can support extremely high throughput compared to legacy Wi-Fi standards is its wide operating bandwidth (BW). While conventional Wi-Fi terminals use a 20 MHz band as their operating bandwidth, Wi-Fi 7 operates with an operating bandwidth of up to 320 MHz. This means that the maximum throughput increase achieved solely by expanding the maximum operating bandwidth (BW) supported by the Wi-Fi standard amounts to a 16-fold increase. However, the maximum throughput of the Wi-Fi standard, which is increased by expanding the operating bandwidth, is merely a nominal figure and is unlikely to translate into actual performance improvements in Wi-Fi terminals.

[0202] In other words, despite the continuous expansion of the maximum supportable operating BW through the advancement of Wi-Fi terminals and standards, the impact on the actual performance of Wi-Fi terminals is relatively small. This is because the probability that the entire bandwidth included in the maximum operating BW will be identified as idle when the Wi-Fi terminal performs channel access is low, and the method by which the Wi-Fi terminal performs channel access has an excessively high dependency on the primary 20 MHz channel. Among these, the problem of the low probability of the entire wide bandwidth included in the operating BW being identified as idle may be an inherent problem because the frequency band in which the Wi-Fi terminal operates is an unlicensed band. In other words, it is natural for the medium to be occupied by other devices operating in the unlicensed band, and it is impossible to improve the channel access probability of the Wi-Fi terminal by improving this problem. However, the problem of excessively high Primary 20 MHz channel dependency is not a characteristic of Wi-Fi that was maintained for harmonious operation with heterogeneous devices, but rather a characteristic inherited in the process of maintaining the channel access technique traditionally used from existing Wi-Fi. To explain more specifically, the Wi-Fi standard was designed to perform channel access for a 40 MHz channel by extending the channel access technique used when the operating BW was 20 MHz.More specifically, the method for accessing a 40 MHz channel according to the method defined in the Wi-Fi standard is to perform access to the 40 MHz band (40 MHz band including the primary 20 MHz and secondary 20 MHz bands) if the secondary 20 MHz channel has been identified as IDLE for the last PIFS (Priority Inter Frame Space, aSIFSTime (16 us) + aSlotTime (9 us)) at the time when the backoff procedure on the primary 20 MHz channel is completed. Similarly, the method for accessing the 80 MHz channel according to the method defined in the Wi-Fi standard is to perform access to the 80 MHz band (80 MHz band including the Primary 20 MHz, Secondary 20 MHz, and Secondary 40 MHz bands) if the Secondary 20 MHz channel and the Secondary 40 MHz channel have been identified as IDLE for the last PIFS (Priority Inter Frame Space, aSIFSTime (16 us) + aSlotTime (9 us)) when the backoff procedure is completed on the Primary 20 MHz channel. In this way, the Wi-Fi Wide Band Operation method for accessing subchannels identified as IDLE for the PIFS when the backoff procedure is completed on the Primary 20 MHz channel is applied in the same manner when accessing the 320 MHz BW defined in Wi-Fi 7. The reason why this method has been repeatedly used is because it enables wide bandwidth access in a more energy-efficient and less hardware-implementation manner by performing backoff on only one channel (primary channel) and determining whether other subchannels are accessible within a minimum time interval.

[0203] However, this method of channel access using a primary channel has a major drawback in that when the Primary 20 MHz channel on which the Wi-Fi terminal performs the backoff procedure is determined to be busy, even if all sub-channels except the Primary 20 MHz channel are available (not occupied by other devices), the backoff procedure of the Wi-Fi terminal cannot be completed, and thus channel access to wide idle sub-channels is also impossible.

[0204] As mentioned above, the issue of channel access of Wi-Fi terminals supporting wideband operation being limited depending on the CCA results of the Primary 20 MHz subchannel is not a new issue in UHR. However, UHR, which succeeds Wi-Fi 7 and supports ultra-wideband operation up to 320 MHz, may suffer greater losses due to the dependency on the Primary 20 MHz subchannel mentioned above compared to existing WiFi standards. Moreover, next-generation standards after UHR may also experience performance degradation issues due to the dependency on the Primary 20 MHz subchannel mentioned above. Therefore, it is clear that there is a need to resolve the channel access issue related to the Primary 20 MHz subchannel mentioned above.

[0205] For this reason, the present invention provides a method and procedure for a terminal supporting wideband operation to perform communication using a subchannel other than the primary 20 MHz subchannel determined to be BUSY when the CCA result for the primary 20 MHz subchannel is BUSY.

[0206] For example, if a preamble of a PPDU is received through a Primary 20 MHz subchannel, and if CCA is performed based on the received preamble and the Primary 20 MHz subchannel is determined to be busy, a channel access procedure may be performed by selecting one of the non-Primary 20 MHz subchannels other than the Primary 20 MHz subchannel. In addition to the Primary 20 MHz subchannel, the other subchannel on which the channel access procedure is performed may be included in an operating channel that is the same as or different from the Primary 20 MHz.

[0207] Accessing channels that do not utilize the primary channel

[0208] As the simplest method to resolve the dependency problem on the aforementioned Primary 20 MHz sub-channel (hereinafter referred to as the P20 channel), a method of performing channel access using (through) a sub-channel (a non-primary channel (or sub-channel)) other than the P20 channel may be considered. At this time, performing channel access using (through) a non-primary channel means performing a backoff procedure based on whether the non-primary channel is idle / busy. At this time, there may be one or more non-primary channels on which the terminal can perform the backoff procedure. That is, the terminal can perform the backoff procedure through the P20 channel or multiple non-primary channels (e.g., the first non-primary channel or the second non-primary channel, etc.). At this time, the channels on which the terminal can perform the backoff procedure (i.e., the P20, the first non-primary channel, the second non-primary channel, the third non-primary channel, etc.) may be 20 MHz sub-channels included in different 80 MHz sub-blocks, respectively. That is, the first non-primary channel may be located in an 80 MHz subblock other than the 80 MHz subblock including the P20 channel. That is, when the terminal selects a backoff channel (non-primary channel) other than P20, the terminal must select another backoff channel (non-primary channel) from among the 20 MHz subchannels of the 80 MHz subblock (i.e., a subblock other than the Primary 80 MHz subblock) that does not include the P20 subchannel. At this time, each of the different backoff channels selected by the terminal may be located in a different 80 MHz subblock. That is, the first non-primary channel may be a subchannel located in an 80 MHz subblock other than the second non-primary channel.At this time, the selection restriction of non-primary channels related to the aforementioned 80 MHz subblock may only apply when the operating channel of the BSS is included in the 5 GHz or 6 GHz band.

[0209] At this time, channel access using a non-primary channel may be performed only during a time period in which the P20 channel is determined to be BUSY. That is, channel access using a non-primary channel (hereinafter, referred to as non-primary channel access) may be performed only when the P20 channel is determined to be busy as a result of Physical CCA (ED, Energy detection) and PD, Virtual CCA. In addition, non-primary channel access may be limitedly permitted only to STAs (AP STAs, non-AP STAs) in which the P20 channel is BUSY and the frame identified on the P20 channel is not a frame destined for itself. Accordingly, the non-primary channel access procedure may be limitedly permitted only when the preamble of a PPDU received on the P20 channel is successfully detected or the MPDU is successfully decoded. Accordingly, the non-primary channel access procedure may be limitedly permitted only to STAs that have successfully received a frame received on the P20 channel.

[0210] That is, when an MLD (AP MLD or non-AP MLD) operates on one P20 and one or more non-primary channels, one of the STAs (AP or non-AP) constituting the MLD can perform a channel access procedure on the P20 channel. In this case, the STA can receive a preamble of a PPDU on the P20 channel and perform a CCA based on the preamble. If the CCA result determines that the P20 channel is busy and the PPDU received on the P20 channel is transmitted from an overlapping BSS (OBSS), the STA can select one non-primary channel among one or more non-primary channels and perform a channel access procedure through the selected non-primary channel. The state of the non-primary channel on which the channel access procedure is performed may be an idle state.

[0211] That is, backoff and channel access procedures using subchannels other than the P20 channel may be restricted to cases where the PPDU identified on the P20 channel is an OBSS PPDU. Accordingly, backoff and channel access procedures using other subchannels may be restricted to cases where the PPDU identified on the P20 channel is a PPDU whose destination is not the device that received the PPDU.

[0212] To this end, the backoff performing and channel accessing procedures using subchannels other than the P20 channel can be initiated after confirming whether the PPDU identified on the P20 channel is the destination device or OBSS by decoding the preamble of the PPDU to confirm the BSS Color of HE-SIG and / or U-SIG, confirming the STA-ID of EHT-SIG and / or UHR-SIG, or decoding the first MAC frame of the PPDU to confirm the destination device. That is, the STA can confirm the BSS Color included in the SIG field (e.g., HE-SIG (HE-SIG-A or HE-SIG-B), or U-SIG) included in the preamble of the PPDU, or confirm the station identifier (STA-ID) included in the SIG field (e.g., HE-SIG-B, EHT-SIG, or UHR-SIG)) in order to determine whether the received PPDU was transmitted from the OBSS. Alternatively, the STA can identify the destination device by decoding the first MAC frame of the PPDU.

[0213] At this time, if the MAC addresses of the sender / receiver of a specific PPDU and the sender / receiver of the frame included in the PPDU are the APs with which it is associated, the specific PPDU can be distinguished as a PPDU (Intra-BSS PPDU) rather than an OBSS PPDU. At this time, a backoff procedure using a subchannel other than the P20 channel may need to be initiated after confirming whether the other subchannel is idle during DIFS. At this time, if the confirmed BSS Color is not its own BSS Color, the STA-ID and MAC frame decoding performed to specify the target device may be omitted. At this time, a method of confirming whether the other subchannel is idle may be to confirm by performing PHY CCA (Energy detection and / or Packet detection) performed for a preset period of time. At this time, the preset period of time may be PIFS (Priority Inter Frame Space), DIFS (Distributed Inter Frame Space), or MediumSync time. Here, MediumSync time can be a time interval with a different name, and it refers to the time that a device that intends to perform a backoff procedure on a non-primary channel (or secondary channel) must perform CCA to determine whether the medium is idle / busy. MediumSync time can be several milliseconds long and is shorter than MaxPPDU length (5.484 ms). A terminal that performs CCA using MediumSync time can set NAV using information contained in the PPDU (frame) received during the CCA.At this time, the NAV that the terminal sets based on the PPDU (frame) received on the S20 channel (a subchannel other than the primary 20 MHz channel) may be a NAV other than the two NAVs (Basic NAV, Intra-BSS NAV) used in conventional Wi-Fi. At this time, the other NAV is a timer set by the frame (PPDU) received through S20, and is a NAV used for Virtual CCA of the S20 channel when performing channel access through the S20 channel. That is, even if the other NAV is set by the frame (PPDU) received on the S20 channel and the value of the other NAV is not 0, the terminal can determine the result of the CCA performed on the P20 channel as IDLE. That is, the other NAV is a NAV for the S20 channel, not the P20 channel. At this time, the other NAV may be called a secondary NAV.

[0214] Therefore, if the terminal performing channel access via the S20 channel is an AP STA, the AP may need to manage both the basic NAV, which is set based on the frame (PPDU) received while occupying the primary 20 MHz subchannel, and the secondary NAV, which is set based on the frame (PPDU) received (i.e., received via the S20 channel) without occupying the primary 20 MHz subchannel. That is, the AP must perform a backoff procedure considering the basic NAV when performing channel access via the P20 channel, and must perform a backoff procedure considering the secondary NAV when performing channel access via the S20 channel. At this time, the secondary NAV may be a timer that is initialized to the Mediumsync time value when the terminal performing channel access via the P20 channel decides to perform channel access via the S20 channel. That is, when the AP decides to perform channel access via the S20 channel, it may need to initialize the secondary NAV to the Mediumsync time value at the same time as starting CCA for the S20 channel.

[0215] In addition, an STA that has performed frame exchange after performing channel access through a subchannel other than the Primary 20 MHz subchannel may need to perform a procedure to check whether the Primary 20 MHz subchannel is occupied by another BSS or another device when initiating a channel access procedure on the Primary 20 MHz subchannel after the frame exchange performed through the other subchannel is completed. At this time, a method for the STA to check whether the P20 channel is occupied by another BSS or another device may be to perform a CCA for the P20 channel during the MediumSync time. At this time, if the STA receives a valid PPDU (frame) while performing the CCA during the MediumSync timer, the STA may set the NAV for the P20 channel based on the information acquired through the received PPDU (frame). In this case, the STA may resume the channel access procedure performed on the Primary 20 MHz subchannel when the set NAV is released (when the NAV timer becomes 0).

[0216] At this time, the backoff procedure using another subchannel can be compensated for the delayed time for decoding the preamble of the PPDU identified in the P20 channel or decoding the MAC frame. In one embodiment, if 3-slot time (e.g., 27 us) is consumed to confirm the destination device (or BSS Color) of the PPDU identified in the P20 channel, an operation of decreasing the backoff counter used for channel access using a subchannel other than the P20 channel by 3 at once may be permitted. Alternatively, since channel access using a subchannel other than the P20 channel is an additional function that conventional devices do not utilize, the operation of decreasing the backoff counter all at once may not be permitted, but rather the backoff counter may be sequentially decremented by 1 after confirming the destination device of the PPDU identified in the P20 channel. In other words, compensation for the delayed backoff procedure may not be performed separately in the process of confirming the destination device of the PPDU identified in the P20.

[0217] In the embodiments of the present invention described below, the process of identifying the destination device of a PPDU received on the aforementioned P20 channel may be omitted for convenience of explanation. Therefore, even if not described separately, it should be understood that the channel access procedure performed using a subchannel other than the P20 channel includes the process of identifying the destination device of a PPDU received on the aforementioned P20 channel.

[0218] Figure 12 shows an example of a channel access procedure through a non-primary channel when the state of the primary channel is busy.

[0219] Referring to FIG. 12, if the CCA result of the Primary 20 MHz subchannel is determined to be busy, the terminal can perform channel access using a non-primary 20 MHz subchannel other than the Primary 20 MHz subchannel.

[0220] Specifically, an STA (AP STA, non-AP STA) constituting an MLD may perform channel access using a channel other than the P20 channel when the P20 channel is determined to be BUSY (e.g., when the P20 channel is determined to be busy based on the CCA result based on the preamble of the received PPDU). At this time, the operation of performing the channel access may be to perform a backoff according to the CCA result of the other channel. At this time, the backoff operation may be an operation of decreasing a backoff counter by 1 when the result of the CCA performed in each slot on the other channel is IDLE. In addition, the backoff operation may be an operation of maintaining the backoff counter without decreasing it when the result of the CCA performed in each slot on the other channel is BUSY.

[0221] The S20 channel that can be utilized for channel access using a 20 MHz subchannel other than the above-described P20 channel is not limited to a specific S20 channel, but multiple S20 channels can be utilized. For example, assuming that an STA performs 320 MHz operation as in the embodiment of FIG. 12, channel access may be possible not only through the S20_1 channel included in the Secondary 80 MHz subblock as illustrated in FIG. 12, but also through S20_2 and S20_3 included in the Secondary 160 MHz subblock. In this case, the number of S20 channels utilized for channel access by each STA may be determined according to the capability of each STA, or may be limited to one or two specific S20 channels. However, the STA may perform backoff only on one non-primary subchannel per 80 MHz subblock. At this time, each non-primary subchannel on which the STA performs backoff is a subchannel determined by the AP and is therefore indicated through a management frame transmitted by the AP. That is, the AP can indicate information on another subchannel (S20) on which backoff can be performed when the primary channel (P20) is busy through the management frame transmitted by the AP (e.g., Beacon, Probe Response, Association Response frame, etc.), and the other subchannel is one of the subchannels included in an 80 MHz subblock other than the Primary 80 MHz subblock.

[0222] Referring to Fig. 12 (a), the backoff counter used when performing channel access on the P20 channel and the backoff counter used when performing channel access on the S20 channel can exist and be managed separately. In this case, the backoff counter used by each channel can be changed to a new value as a backoff counter only when transmission is performed as a result of the channel access performed on each channel (when backoff is completed). In this case, changing to a new value means changing to a new backoff counter extracted using CW_min if the transmission is successful, or changing to a new backoff counter extracted using CW x 2 if the transmission fails. In other words, it does not mean an operation of decreasing the backoff counter as a result of the CCA. In this case, as described above, if there are multiple S20 channels performing channel access, the multiple S20 channels can have their own backoff counters. In this case, the backoff counter for each S20 channel may exist for each Access Category. That is, a terminal may need to manage a separate backoff counter for each AC for each S20 channel on which it can perform backoff. In other words, a terminal performing a backoff procedure through an S20 channel can internally perform a channel access procedure using four ACs.

[0223] Referring to Fig. 12 (b), all S20 channels performing channel access, including P20, can utilize a common backoff counter. As illustrated in Fig. 12 (b), as a result of the channel access operation performed on the P20 channel, the backoff counter is decreased from 5 to 3, and then changed to BUSY in the P20 channel. According to an embodiment proposed in the present invention, when the P20 channel is BUSY, the S20 channel can perform the channel access procedure, and as shown in Fig. 13 (b), the backoff counter that P20 reduced to 3 can continue to be decreased according to the CCA result performed on S20_1. If S20_1 is also determined to be BUSY while decreasing the backoff counter for channel access, the backoff counter can be maintained as is until a channel access using S20_2 is started, or until P20 to S20_1 are determined to be IDLE. At this time, if the channel connection using the above S20_2 is continued, it can be understood as an embodiment in which there are two or more S20 channels used for channel connection, and if the backoff counter is maintained until the above P20 to S20_1 are determined to be IDLE, it can be understood as an embodiment in which there is only one S20 channel used for channel connection.

[0224] <Secondary channel의 점유 정보 관리의 필요성>

[0225] Looking at the NPCA operation described above, an STA performing the NPCA operation will attempt channel access using a subchannel other than the primary 20 MHz subchannel (which may be named the NPCA primary channel) when the primary 20 MHz subchannel is switched to BUSY due to the operation of an OBSS. However, an STA performing a channel access procedure using the primary 20 MHz subchannel must check whether there is another STA performing frame exchange through the band including the NPCA primary channel before initiating a channel access procedure using the NPCA primary channel. In other words, since there may be the operation of another OBSS occupying the NPCA primary channel, an STA accessing the channel through the NPCA primary channel must perform an additional procedure to check the status of the NPCA primary channel. In this case, the additional procedure can be understood as a process of achieving medium synchronization for the NPCA primary channel. A brief description of the procedure for achieving Medium Sync for the NPCA primary channel includes evaluating the PHY CCA result by utilizing a lower value than the ED threshold used in the Primary 20 MHz channel when performing a channel access procedure on the NPCA primary channel, and transmitting a control frame of a restricted format (e.g., an RTS frame or an MU-RTS frame (allowed only to the AP)) as the first frame when the channel access procedure performed on the NPCA primary channel is completed. In this case, the number of attempts to transmit a control frame of the restricted format may also be limited.The Medium Sync achievement procedure performed by an STA operating on such an NPCA primary channel continues to be performed until the MediumSyncDelay timer of the STA for the NPCA primary channel expires or until the STA receives a valid frame on the NPCA primary channel.

[0226] This Medium Sync achievement procedure for the NPCA primary channel is performed to evaluate whether channel access using the NPCA primary channel is possible, and therefore, in a situation where it has already been confirmed that channel access using the NPCA primary channel is not possible, there is no reason for the STA to perform the aforementioned Medium Sync achievement procedure. For example, an STA that recognizes that the transmission of the OBSS occupying its primary 20 MHz subchannel is performed in a way that occupies the NPCA primary channel can know that the NPCA primary channel is not available, and therefore has no reason to initiate a channel access procedure through the NPCA primary channel even if its primary 20 MHz subchannel is occupied by the OBSS. This is because it is clear that the channel access procedure that the STA performs through its own NPCA primary channel will fail due to the transmission of the OBSS occupying its primary 20 MHz subchannel.

[0227] In this way, the STA can optimize its own operations, such as performing operations for utilizing side channels more efficiently, based on information about the bandwidth occupied by the PPDU it received.

[0228] NAV Management Techniques Including Occupied Channel Information

[0229] As described through the above-described embodiments, the conventional Wi-Fi standard has defined NAV, and can manage / recognize information related to the duration of the TXOP of another STA occupying its Primary channel based on NAV information. In addition, although not described in the above-described embodiments, an STA that receives a PPDU including a TXOP field (e.g., HE PPDU, EHT PPDU, UHR PPDU, etc.) can also set the NAV based on the information indicated through the TXOP field (included in the PHY Preamble) of the PPDU it has received. Since the method of setting / managing the NAV using the TXOP field is a NAV setting / management technique already disclosed in the conventional Wi-Fi standard, it is briefly summarized as in 1. to 4. below, and a detailed description is omitted. In this case, utilizing the information indicated through the TXOP field means utilizing the RXVECTOR parameter TXOP_DURATION generated in relation to the corresponding PPDU.

[0230] 1. If the STA that received the frame is classified as an Intra-BSS frame, if it is not the target device of the frame, or if the time length indicated through the Duration / ID field of the frame is greater than the Intra-BSS NAV it had, it updates the Intra-BSS NAV.

[0231] 2. The STA that received the frame updates the Basic-BSS NAV if the time length indicated through the Duration / ID field of the frame is greater than the Basic-BSS NAV it had, if the frame is classified as an Inter-BSS frame.

[0232] 3. An STA that receives a PPDU including a TXOP field can update its Intra-BSS NAV if the RXVECTOR generated by the PPDU is confirmed to be intra-BSS (if the value indicated by the BSS Color field of the PPDU matches the color of its own BSS) and if the time length indicated by the RXVECTOR parameter TXOP_DURATION of the PPDU is greater than its own Intra-BSS NAV. If the Duration field of the frame included in the PPDU is received, the Intra-BSS NAV is managed using the method of 1 above.

[0233] 4. An STA that receives a PPDU including a TXOP field can update its Basic NAV if the RXVECTOR generated by the PPDU is identified as inter-BSS (if the value indicated by the BSS Color field of the PPDU does not match the color of its own BSS) or if it cannot distinguish whether it is intra-BSS or inter-BSS, and if the time length indicated by the RXVECTOR parameter TXOP_DURATION of the PPDU is greater than its Basic NAV. If the Duration field of the frame included in the PPDU is received, the Basic NAV is managed using the method of 2 above.

[0234] Each STA manages the Intra-BSS NAV and Basic NAV (AP can only manage Basic NAV) through the methods 1. to 4. above, and through these, can recognize information related to the termination of transmissions performed within the BSS and transmissions performed by the OBSS. If the value of its NAV is not 0, the STA determines the Virtual CS result for its Primary channel as busy, and therefore does not access the channel even if the medium status confirmed by the PHY CS (method using Energy-Detection Threshold) is idle. This NAV management technique and the medium status evaluation method using NAV are important MAC functions of Wi-Fi that prevent collision problems that may occur between STAs in a hidden relationship, when utilized together with the protection mechanism using the (MU-)RTS / CTS frame.

[0235] However, the NAV managed by the conventional Wi-Fi STA only manages the occupation status of the Primary 20 MHz subchannel, and does not manage information related to the BW occupied by the PPDU of the OBSS occupying the Primary 20 MHz subchannel. In other words, the STA cannot distinguish whether the transmission of the OBSS occupying the Primary 20 MHz subchannel uses a 20 MHz PPDU, a 40 MHz PPDU, or an 80 MHz PPDU using the conventional NAV. Therefore, as in the NPCA operation described above, an STA that attempts to use its own secondary channel using the NPCA primary channel during the time when the Primary 20 MHz subchannel is occupied by another STA (an STA of the OBSS) does not recognize that the secondary channel is also occupied by the STA occupying the Primary 20 MHz subchannel, and only after moving to the NPCA primary channel and achieving Medium Sync does it recognize that the NPCA primary channel is unavailable. This is an inefficient subchannel occupation attempt that occurs because the NAV managed by the STA only indicates / records occupation status information for the Primary 20 MHz subchannel. In other words, if the STA can recognize that the NPCA primary channel is also occupied by the OBSS based on the BW information of the PPDU of the OBSS received on the Primary channel, the STA does not need to perform the above-mentioned inefficient subchannel occupation attempt.

[0236] According to one embodiment of the present invention, an STA can manage Network Allocation information including occupied channel information. At this time, the Network Allocation information managed together with the occupied channel information can be utilized for the Virtual CS of the Primary 20 MHz channel and other subchannels other than the Primary 20 MHz channel. For a simple example, if the STA confirms that the BW of the OBSS PPDU it received is 40 MHz, the STA sets the NAV based on the TXOP field (included in the PHY preamble) of the received PPDU or the Duration field (included in the MAC header) of the frame included in the PPDU, and records information on the occupied bandwidth occupied by the corresponding PPDU together through the Bandwidth field (included in the PHY preamble) of the OBSS PPDU or the TA / RA field (in the case of a frame to which BW signaling TA is applied) of the MAC frame. At this time, the method by which the STA obtains occupied band information through the Bandwidth field of the OBSS PPDU is to obtain information using the RXVECTOR parameters CH_BANDWIDTH and CH_BANDWIDTH_IN_NON_HT generated in relation to the OBSS PPDU. The STA can determine that the Virtual CS result for the band confirmed to be occupied by the OBSS PPDU is Busy until the NAV set by the OBSS PPDU is released.

[0237] Information about the occupied band managed by the STA may be information about BW. For example, if the BW of the received OBSS PPDU is 40 / 80 / 160 MHz, the STA can record information with values ​​related to 40 / 80 / 160 MHz and determine the Virtual CS result of the 40 / 80 / 160 MHz band including its Primary 20 MHz subchannel based on the recorded information. In this case, the STA can use the BW information together with the NAV information when performing the Virtual CS. In other words, the STA<NAV, BW> A virtual CS for each subchannel is performed using a tuple. For a simple example, if the NAV is not 0 and a specific subchannel exists within the recorded BW, the virtual CS result for the specific subchannel is<NAV, BW> It is judged to be busy by tuple.

[0238] Alternatively, information about the occupied band managed by the STA may be for each 20 MHz subchannel located within the operating BW of the BSS. For example, if the BW of the received OBSS PPDU is 40 / 80 / 160 MHz, the STA may record occupancy time information for each of two 20 MHz subchannels included in the primary 40 MHz band, four 20 MHz subchannels included in the primary 80 MHz band, and eight 20 MHz subchannels included in the primary 160 MHz band, and determine the Virtual CS result of each subchannel based on the recorded information. In this case, the STA may utilize NAV information corresponding to each subchannel when performing the Virtual CS. For example, if the value of the NAV corresponding to a specific subchannel is not 0, the STA determines that the Virtual CS result of the specific subchannel is busy. At this time, a single NAV information may correspond to one or more subchannels. This may be a subchannel-NAV response method considered to prevent the number of NAV timers from increasing according to the number of subchannels.

[0239] Detailed methods for managing information about occupied bandwidth are described in more detail through the embodiments described below.

[0240] How to use multiple timers

[0241] In the simplest way, it may be considered that multiple timers are utilized to record information related to the occupancy time of each subchannel. In this case, the Virtual CS of each subchannel can be determined based on whether the value of the timer corresponding to each subchannel is 0 or a non-zero value. At this time, the timer may be a timer that is set / managed in the same / similar way as the NAV timer is set in the conventional Wi-Fi standard. As a simple example, an STA that receives an OBSS PPDU that occupies its Primary 20 MHz subchannel and Secondary 20 MHz subchannel can set a timer for the Primary 20 MHz subchannel and a timer for the Secondary 20 MHz subchannel using the TXOP field of the OBSS PPDU or the Duration field of the MAC frame included in the PPDU. The STA may determine that the Virtual CS result for the Primary 20 MHz subchannel is busy during a time period in which the value of the timer corresponding to the Primary 20 MHz subchannel is not 0, and may determine that the Virtual CS result for the Secondary 20 MHz subchannel is busy during a time period in which the value of the timer corresponding to the Secondary 20 MHz subchannel is not 0. In this case, the timer for the Primary 20 MHz subchannel may be a timer related to the Basic NAV used by a conventional Wi-Fi STA, and the timer for the Secondary 20 MHz subchannel may be a timer newly introduced to perform the Virtual CS of the Secondary 20 MHz subchannel.The timers mentioned in the embodiments described below are different types of timers than the timers used by conventional Wi-Fi STAs to manage Intra-BSS NAV. Each timer value in the embodiments described below can be managed in a manner identical to or similar to the Basic NAV management method described above.

[0242] An STA can manage the occupancy time (timer value) of each 20 MHz subchannel within its operating BW using as many timers as the number of 20 MHz subchannels within its supported operating BW. In this case, the STA can check the Virtual CS results of each 20 MHz subchannel within its operating BW using the timers.

[0243] Alternatively, the STA can manage the occupancy time (timer value) of each 20 MHz subchannel included in the operating BW of the BSS by using as many timers as the number of 20 MHz subchannels included in the operating BW of the BSS to which it belongs (indicated by the Channel Width field of the Operation element). In this case, the STA can perform virtual CS for 20 MHz subchannels located outside its own operating BW. In this way, if the STA manages timers for subchannels located outside its own operating BW, it can perform virtual CS for each subchannel even when performing a side-channel operation that includes an operation of changing its own operating channel within the band included in the operating BW of the BSS. For example, when an STA supporting an 80 MHz operating BW performs side-channel operation and operates in the secondary 80 MHz band of the BSS, it can perform a virtual CS for the secondary 80 MHz band.

[0244] When a separate timer is used for each subchannel, as in the above methods, the STA must manage a larger number of timers as its operating BW or the operating BW of the BSS increases. This can result in increased operational complexity for the STA. Therefore, the STA can manage occupancy time information for a larger number of subchannels than the number of timers, using a limited number of timers to manage information related to the occupancy time of secondary channels.

[0245] As a simple example, an STA can manage a timer for each 40 MHz band. In this case, the STA can manage the timer so that at least one of the 20 MHz subchannels included in each 40 MHz band remains at a non-zero value during the occupied time. In this case, the STA can manage only half the number of timers compared to managing timers for each 20 MHz subchannel. Similarly, if an STA manages a timer for each 80 MHz band, the STA's timer management burden is reduced to one-quarter of that of managing timers for each 20 MHz subchannel.

[0246] As another example, the STA may manage timers applicable to the Secondary 20 MHz band, the Secondary 40 MHz band, the Secondary 80 MHz band, and the Secondary 160 MHz band. In this case, the timer managed by the STA for each band may be included in the management target only if the operating BW of the BSS includes the corresponding band. Alternatively, the timer managed by the STA for each band may be included in the management target only if the operating BW of the corresponding STA includes the corresponding band. In this way, the embodiment in which timers are respectively used for S20 / S40 / S80 / S160 is provided to show that the width of the frequency band corresponding to each timer may be different.

[0247] As described above, it is possible to manage the time information occupied by the OBSS PPDU (OBSS TXOP) on the subchannel using multiple timers in various ways. However, the occupancy time information for the Primary 20 MHz channel can always be managed using the Basic NAV.

[0248] FIG. 13 illustrates an example of a method in which an STA performs a Virtual CS for an area including Secondary channels by utilizing a Basic NAV and multiple timers according to one embodiment of the present invention.

[0249] Referring to FIG. 13, the STA receives OBSS PPDU1, and PHY-RXSTART.indication is generated from the PHY. The RXVECTOR parameter TXOP_DURATION of the PHY-RXSTART.indication is x (us), so the STA sets the Basic NAV to x. At this time, the STA confirms that the Secondary 20 MHz band (S20) is occupied by OBSS PPDU1 because the also confirmed RXVECTOR parameter CH_BANDWIDTH is CBW40. Therefore, the STA sets the timer for the Secondary 20 NAV to x. While the Basic NAV and the Secondary 20 NAV remain non-zero, the STA determines the Virtual CS of P20 and S20 to be busy.

[0250] The STA receives OBSS PPDU2, and PHY-RXSTART.indication is generated from the PHY. The RXVECTOR parameter TXOP_DURATION of PHY-RXSTART.indication is y (us), so the STA sets the Basic NAV to y. At this time, the STA confirms that the Secondary 20 MHz band (S20) and the Secondary 40 band are occupied by OBSS PPDU2 because the RXVECTOR parameter CH_BANDWIDTH also confirmed is CBW80. At this time, the STA can recognize that the subchannel corresponding to S40_1 is punctured in OBSS PPDU2, and that the region corresponding to S40_1 is not occupied by OBSS PPDU2. Therefore, the STA sets the timer for Secondary 20 NAV and the timer for Secondary 40_2 NAV to y. While the Basic NAV, Secondary 20 NAV, and Secondary 40_2 NAV remain non-zero, the STA determines the Virtual CS of P20, S20, and S40_2 as busy.

[0251] In the example of Fig. 13, it is considered that the STA manages the NAV using RXVECTOR, but it is also possible to update the NAV using the Duration ID field and TA field (to which Bandwidth Signaling TA is applied) of the MAC frame included in the PPDU.

[0252] How to use the existing Basic NAV timer

[0253] According to the method of the above-described embodiment, if the STA manages information related to the time of an OBSS PPDU (OBSS TXOP) that occupies a side channel by utilizing a separate timer, the STA must utilize a greater number of timers than the conventional Wi-Fi STA used for NAV management, thereby increasing the implementation burden of the STA. In order to reduce the implementation burden of the STA, a method of managing the occupancy time information of the side channel band by reusing an existing timer used by the conventional Wi-Fi STA may be considered, rather than a method of using a separate timer for the side channel band.

[0254] According to one embodiment of the present invention, when managing occupancy information of a subchannel band, the STA can utilize the Basic NAV. However, the STA may utilize additional information together with the Basic NAV to determine the Virtual CS result of a specific subchannel included in the subchannel band. In this case, the additional information utilized together may be BW information confirmed by a PPDU occupying a Primary 20 MHz subchannel. In this case, when the STA receives a PPDU of an OBSS on the Primary channel, the STA may set the Basic NAV according to a conventional Basic NAV management method and record information about the bandwidth occupied by the PPDU of the corresponding OBSS. That is, an STA that receives an OBSS PPDU through the Primary channel can set the Basic NAV based on the value confirmed through the TXOP field of the OBSS PPDU or the Duration field of the MAC frame included in the PPDU, and record the Bandwidth information based on the value confirmed through the Bandwidth field (included in the PHY Preamble) of the PPDU or the TA field (where Bandwidth Signaling TA is used) of the MAC frame included in the PPDU. The STA can determine the Virtual CS results of the subchannels included in the recorded Bandwidth information as Busy while the Basic NAV value remains at a value other than 0 (the value of the Basic NAV timer is 0). At this time, if the Bandwidth information is not recorded together with the Basic NAV or the recorded Bandwidth information is 20 MHz, the Basic NAV and BW information can be utilized to determine the Virtual CS results for the Primary 20 MHz subchannel in the same way that a conventional Wi-Fi STA uses the Basic NAV.

[0255] As described above, in order to perform Virtual CS for Secondary channels, the STA can receive an OBSS PPDU, use the TXOP-related information of the OBSS PPDU to set the Basic NAV, and record the Bandwidth information together. At this time, the simplest way for the STA to manage the Bandwidth information may be to record the BW information identified by the OBSS PPDU used when updating the Basic NAV (timer). In this case, the recorded BW information can be managed in a way that it is initialized together when the Basic NAV set together expires (reaches 0).

[0256] FIG. 14 illustrates an example of a method in which an STA, according to one embodiment of the present invention, manages Basic NAV and BW information together to perform Virtual CS of a band including a Primary channel.

[0257] Referring to FIG. 14, the STA receives OBSS PPDU1, and PHY-RXSTART.indication is generated from the PHY. The RXVECTOR parameter TXOP_DURATION of the PHY-RXSTART.indication is x (us), so the STA sets the Basic NAV to x. At this time, the STA records the Bandwidth information as 40 MHz (CBW40) because the RXVECTOR parameter CH_BANDWIDTH also confirmed is CBW40. The STA determines the Virtual CS of the subchannels included in the Primary 40 MHz band as busy based on the recorded Bandwidth information while the Basic NAV remains at a non-zero value.

[0258] The STA receives OBSS PPDU2, and PHY-RXSTART.indication is generated from the PHY. The RXVECTOR parameter TXOP_DURATION of PHY-RXSTART.indication is y (us), so the STA sets the Basic NAV to y. At this time, the STA records the bandwidth information as 80 MHz (CBW80) because the RXVECTOR parameter CH_BANDWIDTH confirmed together is CBW80. At this time, the STA can recognize that the subchannel corresponding to S40_1 was punctured in OBSS PPDU2, and that the area corresponding to S40_1 is not occupied by OBSS PPDU2. At this time, the STA can separately record information about the puncturing channel. While the Basic NAV remains non-zero, the STA determines the Virtual CS of the subchannels within the Primary 80 MHz band as busy based on the recorded Bandwidth information. The STA can also utilize additional information about the Puncturing channel to determine the Virtual CS of S40_1 within the Primary 80 MHz band as idle.

[0259] In the example of Fig. 14, it is considered that the STA manages Basic NAV and Bandwidth information using RXVECTOR, but it is also possible to manage Basic NAV and Bandwidth information using the Duration ID field and TA field (to which Bandwidth Signaling TA is applied) of the MAC frame included in the PPDU.

[0260] Meanwhile, an STA may receive a PPDU transmitted by another STA before the Basic NAV set by the PPDU transmitted by a specific STA expires. In this case, the STA updates the Basic NAV value only if the duration value confirmed through the PPDU transmitted by the other STA is greater than its own Basic NAV value. Therefore, when the simplest method described above (see FIG. 14) is utilized, the STA decides to maintain the Bandwidth information recorded by the PPDU transmitted by the specific STA and ignore the BW value confirmed through the PPDU transmitted by the other STA. If the BW information confirmed through the PPDU transmitted by the other STA is ignored in this way, the STA may misinterpret the Virtual CS result for a part of the band occupied by the TXOP associated with the other STA as idle.

[0261] FIG. 15 illustrates an example of a Virtual CS failure problem that occurs when an STA according to one embodiment of the present invention manages BW information only when updating Basic NAV.

[0262] In the description of Fig. 15, the contents already described in the above-described embodiments may be omitted.

[0263] Referring to FIG. 15, after receiving the PPDU of OBSS1 (the PPDU transmitted during the TXOP of OBSS1), the STA sets the Basic NAV to x (us) and the Bandwidth to 40 MHz (CBW40). Before the Basic NAV set by the PPDU of OBSS1 expires, the STA receives the PPDU of OBSS2 (the PPDU transmitted during the TXOP of OBSS2). The STA confirms that the duration information of the OBSS2 TXOP is y (us) by the PPDU of OBSS2. At this time, since the remaining value of the Basic NAV held by the STA is greater than y, the STA does not update the Basic NAV and Bandwidth information. Accordingly, the STA misunderstands that the Virtual CS for the S40 band is idle even when the OBSS2 TXOP is in progress.

[0264] Therefore, even if the value of the Basic NAV it was managing is not updated, the STA must manage the updating of the BW information, and as a result, the PPDU used to update the Basic NAV and the PPDU used to update the BW information may be different PPDUs. At this time, the STA must update the Bandwidth information regardless of whether the Basic NAV is updated if the Bandwidth information confirmed through the newly received PPDU is greater than the Bandwidth previously managed. On the other hand, the STA must manage the existing Bandwidth information in a way that it maintains the existing Bandwidth information regardless of whether the NAV is updated if the Bandwidth information confirmed through the newly received PPDU is smaller than the Bandwidth information previously managed. At this time, the STA initializes the Bandwidth information it was managing (deletes records or sets the Bandwidth information to 20 (CBW20)) when the Basic NAV expires (the timer reaches 0). Through this, the STA manages the bandwidth information by preserving the largest bandwidth information among the bandwidth information confirmed through all PPDUs received before the Basic NAV expires after the Basic NAV is set (before the updated Basic NAV expires when the Basic NAV is updated). This method of managing the bandwidth of the STA can be understood as a maximum bandwidth protection method to prevent the OBSS TXOP interference problem that may occur when a single timer (for the Basic NAV) is utilized for virtual CS for multiple subchannels.

[0265] FIG. 16 illustrates an example of a method for managing Basic NAV and Bandwidth information for a Virtual CS according to one embodiment of the present invention.

[0266] In the description of Fig. 16, the contents already described in the above-described embodiments may be omitted.

[0267] Referring to FIG. 16, after receiving the PPDU of OBSS1 (PPDU transmitted during the TXOP of OBSS1), the STA sets the Basic NAV to x (us) and sets the Bandwidth to 40 MHz (CBW40). (Phase 1) Before the Basic NAV set by the PPDU of OBSS1 expires, the STA receives the PPDU of OBSS2 (PPDU transmitted during the TXOP of OBSS2). The STA confirms that the duration information of the OBSS2 TXOP is y (us) by the PPDU of OBSS2. At this time, since the remaining value of the Basic NAV that the STA has is greater than y, the STA does not update the Basic NAV. However, the STA confirms that the RXVECTOR parameter CH_BANDWIDTH generated by the OBSS2 PPDU is larger than the Bandwidth information (40 MHz) recorded by the STA, and updates the Bandwidth information to 80 MHz (CBW80). (Phase 2) After that, the STA determines that the Virtual CS results of the subchannels included in the Primary 80 MHz are busy based on the recorded Bandwidth information until the Basic NAV expires. When the Basic NAV expires, the STA initializes the recorded Bandwidth information (sets it to 20 MHz or sets it to the default value). At this time, the STA determines the Virtual CS results for the band including the Secondary 40 as busy even though there is no OBSS occupying the Secondary 40 MHz during the time period corresponding to Phase 3. This is a kind of side effect that occurs when performing the Virtual CS using a single timer, but it may be an acceptable error to protect the TXOP of the OBSS.

[0268] How to Use Incomplete BW Information

[0269] If the received PPDU has a format that does not include a Bandwidth field, and the MAC frame included in the PPDU has a TA field that does not use Bandwidth Signaling TA, the STA cannot obtain information about the Bandwidth area occupied by the received PPDU.

[0270] In addition, there may be an ambiguity in interpretation that occurs when the BW of a PPDU received through the 6 GHz band is 320 MHz (CBW320). For reference, the 320 MHz band defined in the 6 GHz band has a form in which two different 320 MHz bands share a single 160 MHz band. For a simple example, the upper 160 MHz band of a specific 320 MHz band is the lower 160 MHz band of another 320 MHz band, and in order to distinguish the specific 320 MHz band from the other 320 MHz band, one of the two is divided into the 320 MHz-1 band and the other is divided into the 320 MHz-2 band. For this reason, there are cases in which the bandwidth-related information confirmed from the received PPDU only indicates that it is 320 MHz, and it is not possible to distinguish whether it is 320 MHz-1 or 320 MHz-2. In this case, the STA cannot distinguish whether the band occupied by the received PPDU is an area corresponding to the Primary 160 MHz of its BSS or an area corresponding to the entire 320 MHz. The reason why it is not possible to distinguish between 320 MHz-1 and 320 MHz-2 may be because the TXVECTOR and RXVECTOR of the PPDU transmitted as a non-HT duplicated PPDU do not distinguish between 320 MHz-1 and 320 MHz-2 and appear as CBW320. That is, when the RXVECTOR parameter CH_BANDWIDTH_IN_NON_HT generated by the received PPDU is CBW320, it is difficult for the STA to clearly determine information about the area occupied by the PPDU.

[0271] In cases where the bandwidth information indicated by the received PPDU is absent or uncertain, the STA must acquire / estimate the bandwidth information related to the PPDU based on the PHY CCA information performed independently, or manage the bandwidth information by making limited use of the uncertain information. The bandwidth management method described below may be applied / managed only when the bandwidth information confirmed through the methods described below indicates a larger bandwidth than the originally recorded bandwidth.

[0272] According to one embodiment of the present invention, an STA that receives a PPDU that does not include bandwidth information can manage bandwidth information using the PHY-CCA.indication primitive generated when the PPDU is received. More specifically, the STA obtains information about the bandwidth occupied by the PPDU based on the per20bitmap of the PHY-CCA.indication generated by the PHY in relation to the received PPDU. At this time, the STA records information about the minimum bandwidth (40 / 80 / 160 / 320 MHz) that includes all subchannels indicated as busy through the per20bitmap as bandwidth information. Through this, the STA can manage bandwidth information about the bandwidth including the bandwidth occupied by the received PPDU and utilize it for the Virtual CS. At this time, the method using the above-described PHY-CCA.indication is one applicable embodiment, and another method for estimating the BW of a PPDU received through Per-20 MHz CCA (for example, correcting the BW estimation result of the PPDU by examining the correlation between the signal received in the Primary 20 MHz subchannel and the signal confirmed in another subchannel) may also be applied.

[0273] According to one embodiment of the present invention, an STA whose BSS's operating channel is 320 MHz-1 records bandwidth information as 320 MHz when the RXVECTOR parameter CH_BANDWIDTH of the received PPDU is CBW320-1, and records 160 MHz as bandwidth information when the RXVECTOR parameter CH_BANDWIDTH of the received PPDU is CBW320-2. That is, the STA records bandwidth information for an area overlapping with the operating channel of its BSS among the bands occupied by the received PPDU (and the OBSS TXOP related to the PPDU) and utilizes the same for Virtual CS. Similarly, according to one embodiment of the present invention, an STA whose BSS's operating channel is 320 MHz-2 records bandwidth information as 320 MHz when the RXVECTOR parameter CH_BANDWIDTH of the received PPDU is CBW320-2, and records 160 MHz as bandwidth information when the RXVECTOR parameter CH_BANDWIDTH of the received PPDU is CBW320-1.

[0274] According to one embodiment of the present invention, an STA that receives a PPDU in which the BW is indicated to be 320 MHz and is not distinguished as 320 MHz-1 or 320 MHz-2 can record the Bandwidth information as 160 MHz. That is, if the RXVECTOR parameter CH_BANDWIDTH and the RXVECTOR parameter CH_BANDWIDTH_IN_NON_HT generated by the received PPDU are CBW320, the STA can record the Bandwidth information related to the corresponding PPDU as 160 MHz (in the form of occupying its own primary 160 MHz band) and utilize this for the Virtual CS. At this time, the reason why the STA records the Bandwidth information as 160 MHz after confirming CBW320 may be because it considers the possibility that the band occupied by the OBSS PPDU (and the OBSS TXOP related to the PPDU) does not completely overlap with the operating band of its own BSS. That is, the STA may record the Bandwidth information as a value related to 160 MHz, considering that the OBSS PPDU may not occupy its Secondary 160 MHz band, and may attempt a side-channel operation using the Secondary 160 MHz band.

[0275] Meanwhile, an STA may receive a TB PPDU transmitted by a non-AP STA of an OBSS. The Bandwidth field of the TB PPDU is not set to information about the band occupied by the TB PPDU, but to a value indicated by the AP through the Trigger frame (indicated through the UL BW subfield included in the Common Info field of the Trigger frame). Therefore, the TB PPDU transmitted by an OBSS non-AP STA may occupy only a narrower band than the value indicated by the UL BW subfield of the TB PPDU. As a simple example, there may be a situation where an AP operating an OBSS transmits a Trigger frame in which the UL BW subfield is set to a value indicating 320 MHz, and a total of four OBSS STAs respond with the TB PPDU. In this case, the TB PPDU transmitted by each OBSS STA may be transmitted in a form that occupies a different 80 MHz band (996-tone size RU). Therefore, although each TB PPDU transmitted by an OBSS STA occupies only the 80 MHz band, the Bandwidth field of the TB PPDU can be set to 320 MHz for transmission. Even if the TB PPDU received by the STA is only the TB PPDU transmitted by one of the four OBSS STAs, if the Bandwidth information must be managed for the entire band indicated through the Bandwidth field of the TB PPDU, the operation of the STA using the subchannel band is greatly restricted.

[0276] Accordingly, an STA that receives a TB PPDU of an OBSS can update the Bandwidth information it manages together with the Basic NAV using a method other than the value indicated through the Bandwidth field of the TB PPDU. At this time, the other method may be to use the per20bitmap of the PHY-CCA.indication generated by the TB PPDU. At this time, since the information for managing the Bandwidth using the per20bitmap of the PHY-CCA.indication is the same as that described in the above-described embodiment, a detailed description thereof is omitted. As a result, the STA does not utilize the RXVECTOR parameter CH_BANDWIDTH information generated by the TB PPDU transmitted by the OBSS STA when managing the Bandwidth information for the Virtual CS.

[0277] FIG. 17 illustrates an example of a state in which an AP MLD and a non-AP MLD are connected through multiple links according to an embodiment of the present invention.

[0278] Referring to FIG. 17, the AP MLD and the noon-AP MLD may each include individual APs and STAs, and each AP and STA may be connected to an individual link.

[0279] For example, as illustrated in FIG. 17, the AP MLD may have a configuration including AP1, AP2, and AP3, and the non-AP MLD may have a configuration including non-AP STA1, non-AP STA2, and non-AP STA3.

[0280] AP MLD and non-AP MLD are connected via Link1, Link2, and Link3, respectively, and AP1 and non-AP STA1, AP2 and non-AP STA2, and AP3 and non-AP STA3 connected via each Link can perform the same operations as between APs and non-AP STAs connected via conventional Wi-Fi.

[0281] In the example of Fig. 17, the frequency gap between Link 2, where Non-AP STA2 operates, and Link 3, where Non-AP STA3 operates, is narrow, so that strong interference occurs when Non-AP STA2 transmits or when Non-AP STA3 transmits. In this case, when the non-AP MLD transmits through Non-AP STA2, it cannot receive through Non-AP STA3, and when the non-AP STA3 transmits, it cannot receive through Non-AP STA2. This is because the interference generated when a non-AP STA operating on a specific Link transmits prevents STAs operating on other Links from checking the medium status (becoming BLIND). Links 2 and 3, which have these characteristics, are called the NSTR (Non-simultaneous transmission and reception) pair of the non-AP MLD.

[0282] Additionally, when the Enhanced Multi-Link Single-Radio (EMLSR) mode defined in 11be is used, an STA operating in EMLSR mode may not be able to check the medium status when an STA of another link performs frame exchange. The EMLSR mode operation is performed in a form in which multiple STAs included in the MLD share hardware resources. If one of the multiple STAs performing the EMLSR mode operation performs a data frame exchange, the remaining STAs performing the EMLSR mode operation may be in a state in which there is no available antenna, no RF chain, or the processor for 11be PPDU processing is occupied. In other words, among the STAs included in the MLD, an STA in EMLSR mode may be in a state in which it cannot observe the medium status when another EMLSR mode STA performs a data frame exchange, i.e., may fall into a state in which CCA for its primary channel is unavailable.

[0283] In 11be, an STA that has its CCA operation (clear channel assessment) interrupted by another STA's operation within the MLD is restricted to a more restricted form of channel access for a certain period of time after the CCA operation capability is restored. More specifically, an STA that has lost its CCA capability due to a transmission performed by another STA within the same MLD is forced to perform a medium access recovery procedure after the other STA's transmission has ended (after its own CCA capability has been restored). An STA performing a medium access recovery procedure must start the MediumSyncDelay timer after the CCA capability is restored, and must evaluate the CCA of the primary 20 MHz subchannel (CCA using energy detection) using the dot11MSDOFDMEDthreshold until the timer expires. That is, STAs whose MediumSyncDelay Timer is not 0 must perform CCA using dot11MSDOFDMEDthreshold (Default is -62 dBm) instead of dot11OFDMEDThreshold (Default is -62 dBm). In addition, STAs whose MediumSyncDelay timer is not 0 must transmit an RTS frame as the first frame when attempting to acquire a TXOP.

[0284] An STA whose MediumSyncDelay timer is not 0 can reset the MediumSyncDelay timer (set it to 0) if a valid frame capable of setting the NAV is received. That is, after receiving a valid frame and setting the NAV, the medium access recovery procedure is considered complete, and it is possible to perform channel access according to the conventional Wi-Fi channel access method at the time the NAV is released.

[0285] The above-described Medium Access Recovery procedure was introduced in 11be to alleviate transmission collision problems arising from frequency interference and hardware sharing issues among multiple STAs within the MLD. Since the MLD can manage the operational states of all STAs within the device, it can effectively manage the Channel Access procedure and Medium Access Recovery procedure of each STA. In more detail, the entity that performs transmission / reception through each of the multiple STAs included in the MLD is the MLD, and therefore, the MLD can manage the scheduling of transmission through a specific STA as intended according to its own operational plan. If the MLD is to perform transmission through the first STA, it will not perform the operation that triggers the Medium Access Recovery procedure of the first STA through another STA, and through this, the MLD can perform the Channel Access procedure through the first STA at the desired time.

[0286] <Operation method considering heterogeneous devices coexisting within the device>

[0287] As previously explained, multiple Wi-Fi STAs can be included in the MLD introduced in 11be. The 11be standard defines various mechanisms to support more efficient operation of multiple STAs included in MLD, as well as various restrictions to prevent potential issues. The aforementioned medium access recovery procedure can be considered one of these restrictions. These restrictions may need to be applied in a similar manner not only to STAs included in MLD but also to STAs included in non-MLD devices. One such situation could be an STA experiencing interference issues caused by heterogeneous devices coexisting within the device.

[0288] The interference problem of heterogeneous devices coexisting in a device refers to a situation in which a Wi-Fi STA cannot operate using WLAN resources or hardware due to the operation of heterogeneous devices sharing the same WLAN resources or hardware. The coexisting heterogeneous devices in a device may also be affected while the Wi-Fi STA is operating, and in this case, the interference problem of the coexisting heterogeneous devices in the device may also be considered to have occurred. For the convenience of explanation, the problem caused by the coexisting heterogeneous devices in a device will be referred to as the IDC problem. In addition, the situation in which the Wi-Fi STA cannot communicate due to the coexisting heterogeneous devices in a device will be referred to as the IDC SP (Service period) or the unavailability period of the DUO (Dynamic Unavailability Operation) mode.

[0289] For example, a terminal (non-AP STA or AP) performing Wi-Fi communication may include other communication interfaces such as 3GPP, Bluetooth, etc. in addition to Wi-Fi. In this case, if Wi-Fi and other heterogeneous communication interfaces use the same radio resources (e.g., a specific frequency band), interference may occur between them, and the period during which such interference occurs may be referred to as an unavailability period in which IDC SP or DUO mode is applied.

[0290] During these IDC SPs or unavailability periods, terminals cannot perform Wi-Fi communication smoothly due to interference from heterogeneous communication interfaces. Therefore, terminals suspend signal transmission and reception during these IDC SPs or unavailability periods and resume signal transmission and reception after the interference has ceased.

[0291] FIG. 18 illustrates an example of a situation in which interference occurs between different wireless communication interfaces within a device according to an embodiment of the present invention.

[0292] Figure 18 (a) illustrates interference in a case where a Wi-Fi (WLAN) interface, a Bluetooth interface, and an LTE interface are included in the same terminal, and Figure 18 (b) illustrates an example of a terminal including heterogeneous interfaces sharing common hardware resources.

[0293] Specifically, as illustrated in (a) of FIG. 18, a wireless communication terminal may include multiple wireless communication interfaces (e.g., Bluetooth, LTE, and Wi-Fi (WLAN) interfaces) to provide various wireless communication means. Bluetooth and LTE can operate using the same unlicensed band as Wi-Fi, and signals radiated from Bluetooth RF can be received by LTE RF and WLAN RF, respectively. In this case, the LTE RF and WLAN RF may be interfered with when receiving LTE signals or Wi-Fi signals due to Bluetooth signals radiated at close range. That is, a device having a configuration such as that of FIG. 18 (a) may experience an IDC problem in the process in which multiple wireless communication interfaces share a common frequency resource, in which case the terminal may operate in DUO mode.

[0294] Figure 18 (b) illustrates a device configured such that Wi-Fi and Bluetooth interfaces share common hardware resources. A device configured as shown in Figure 18 (b) cannot use both Wi-Fi and Bluetooth interfaces simultaneously, even if they operate using different wireless LAN resources. This is because the device has a hardware configuration that prevents support for other interfaces while the RF / Baseband Processor is utilized through a specific interface.

[0295] Meanwhile, situations in which multiple wireless communication processors utilizing the same wireless LAN resources are included in a single device (e.g., a mobile phone) already exist, even excluding the case of MLD described above.

[0296] For example, mobile phones and IoT (Internet of Things) devices support Bluetooth connectivity as well as Wi-Fi, and Wi-Fi and Bluetooth share the same unlicensed band wireless LAN resources. Furthermore, in some implementations, as illustrated in the example of FIG. 12, Bluetooth and Wi-Fi share a single baseband processor, such that when Wi-Fi is using the processor, processing support for Bluetooth is unavailable, and vice versa. Given this situation, even if a Wi-Fi STA is not included in the MLD, it may find itself unable to support Wi-Fi operations, including CCA, depending on the operation of other coexisting devices within the device.

[0297] In this case, not only is the performance of Wi-Fi communication degraded, but when a Wi-Fi STA that has recovered its performance attempts to access the channel, there is a possibility that it may interfere with the transmissions of other Wi-Fi STAs that were already in progress. Therefore, even if the Wi-Fi STA is unable to perform CCA due to an issue arising from a coexisting device within the device, it may not be able to immediately perform the normal channel access procedure and may have to perform the Medium Access Recovery procedure described above.

[0298] For example, if a terminal supports not only Wi-Fi communication but also other heterogeneous communication means (e.g., Bluetooth, 3GPP (LTE, 5G, etc.)), interference may occur between Wi-Fi and the other heterogeneous communication means if they use the same frequency band (e.g., unlicensed band). In this case, data transmission and reception using Wi-Fi may be interrupted, and later, to resume the interrupted data transmission and reception, the CCA (clear channel assessment) procedure must be performed to perform the channel access procedure again. For example, if the channel access procedure is interrupted due to interference from a heterogeneous communication means during the channel access procedure, the terminal must perform the channel access procedure again after the interference from the heterogeneous communication means has ended. In this case, the terminal must perform the Medium Access Recovery procedure instead of the general channel access procedure because there is a possibility that the terminal may interfere with the channel access procedure of another terminal that is already performing it.

[0299] In this case, the terminal can start a timer (MediumSyncDelay timer) for the medium access recovery procedure after the interference by the heterogeneous communication means ends (for example, after the unavailable period by the DUO mode ends).

[0300] Alternatively, the medium access recovery procedure can be performed by receiving a frame for setting NAV transmitted from a counterpart terminal of the terminal that has recognized that interference by the terminal's heterogeneous communication means has ended.

[0301] In summary, according to one embodiment of the present invention, a Wi-Fi STA that has lost the ability to perform CCA with respect to a heterogeneous device coexisting in the device may perform a medium access recovery procedure by starting a MediumSyncDelay timer when the ability to perform CCA is restored. At this time, the point in time when the Wi-Fi STA starts the MediumSyncDelay timer may be after the IDC SP ends. At this time, the termination of the IDC SP may mean that the Wi-Fi STA has recovered the ability to perform (ED, Energy detection) CCA for its Primary 20 MHz subchannel. At this time, a reference channel for determining whether the ability to perform CCA is lost may be the Primary 20 MHz subchannel. That is, a non-AP STA that has lost the ability to perform CCA for the Primary 20 MHz subchannel during the IDC SP is considered to have lost Medium Synchronization and must start the MediumSyncDelay timer when the IDC SP ends. On the other hand, non-AP STAs that were able to perform CCA on the Primary 20 MHz subchannel even during the IDC SP are considered not to have lost Medium Synchronization, and thus may not start the MediumSyncDelay timer after the IDC SP ends.

[0302] Meanwhile, even if an STA loses its ED CCA capability due to an IDC issue, there may be circumstances in which it is permitted not to perform the medium access recovery procedure. One such circumstance is that the time period in which the ED CCA capability is lost due to the IDC issue is shorter than a specific time interval. In other words, a Wi-Fi STA that has experienced the CCA capability loss due to an IDC issue for a shorter time period may not initiate the medium access recovery procedure when its CCA capability is restored. Another circumstance is that a Wi-Fi STA may have an unexpired NAV timer (i.e., a non-zero NAV value) when it regains its CCA capability. In this case, the Wi-Fi STA may not perform the medium access recovery procedure because it lost / restored its CCA capability while the medium was occupied by another Wi-Fi STA and the other Wi-Fi STA has not yet finished transmitting.

[0303] Meanwhile, a Wi-Fi STA that recognizes that its connected counterpart Wi-Fi STA is operating in DUO mode or experiencing an IDC problem can help the counterpart STA complete a medium access recovery procedure by transmitting a frame capable of setting a NAV to the counterpart Wi-Fi STA at a point in time when the interference of the heterogeneous network interface of the counterpart Wi-Fi STA is considered to have ended (i.e., the end of the unavailability period in DUO mode or the end of the IDC SP). At this time, the frame transmitted to the counterpart Wi-Fi STA can be an individually addressed frame targeting the counterpart Wi-Fi STA or a broadcast frame. At this time, the frame capable of setting a NAV means an MPDU (MAC Protocol Data Unit) including a Duration / ID field in the MAC header and a PPDU including a TXOP field in the Preamble (i.e., HE / EHT / UHR PPDU).

[0304] That is, a non-AP STA or AP with medium synchronization may have an IDC SP or unavailable period, which is a section where Wi-Fi communication is impossible due to interference from a heterogeneous network, when the DUO mode is supported. In this case, the non-AP STA or AP may lose medium synchronization with the counterpart non-AP STA or AP during the section. Therefore, the non-AP STA or AP may perform a medium access recovery procedure to recover medium synchronization after the section ends (i.e., after the interference from the heterogeneous network ends). In order to recover the lost medium synchronization, the non-AP STA or AP may start the MediumSyncDelay Timer after the section ends, or set the NAV based on a frame transmitted by the counterpart non-AP STA or AP that has recognized that the interference from the heterogeneous network has ended.

[0305] In addition, if an STA experiencing an IDC problem is included in an MLD, the MLD can request the opposing MLD to transmit a Trigger frame to an STA among its STAs that is performing a Medium access recovery procedure. For example, a non-AP MLD whose MediumSyncDelay time of an STA operating on a specific link is not 0 can request the AP MLD to transmit a Trigger frame through the link on which the specific STA is operating. In this case, the AP MLD can request a response of a TB PPDU by transmitting a Trigger frame to the specific STA. Through this, the specific STA can minimize the impact of the Medium access recovery procedure initiated due to the IDC problem by early terminating the Medium access recovery procedure and performing TB PPDU transmission.

[0306] FIG. 19 illustrates an example of a method for an STA that experiences interference between different wireless communication interfaces to perform a medium access recovery procedure, according to one embodiment of the present invention.

[0307] Referring to FIG. 19, when interference by a heterogeneous network ends, a non-AP STA or AP can start MediumSyncTimer to recover lost medium synchronization.

[0308] Specifically, as illustrated in FIG. 19, an STA supporting DUO mode experiences an IDC problem during IDC service period 1 and is unable to perform CCA. When IDC service period 1 ends and the STA recovers the CCA performance capability, the STA starts the MediumSyncDelay timer. While the value of the MediumSyncDelay timer remains non-zero, the STA performs ED CCA for the Primary 20 MHz subchannel by applying dot11MSDOFDMAEDthreshold. If the backoff procedure is completed (BO reaches 0) when the MediumSyncDelay timer is non-zero, the STA transmits an RTS frame as the first frame to attempt to acquire a TXOP. In the example of FIG. 19, the STA fails to acquire a TXOP because no response is received to the RTS frame transmitted by the STA. An STA experiencing IDC service period 2 starts the MediumSyncDelay timer in the same manner as in period 1. In the example of FIG. 19, the STA received the ICF before the MediumSyncDelay timer expired, and the STA that set the NAV through the ICF (Initial Control frame) resets the MediumSyncDelay timer and then responds with an ICR (Initial Control response frame).

[0309] <IDC 문제 관리 방법 및 IDC 문제와 관련한 정보 지시 방법>

[0310] The IDC problem caused by the inclusion of heterogeneous networks is not a recent problem, but has been occurring since the time when multiple independently developed wireless LAN technologies, such as Wi-Fi, Bluetooth, Zigbee, NFC, and RFID, began to function within a single device. However, devices with IDC problems have been utilizing multiple wireless LAN technologies with limited resources (radio frequency resources and hardware (processor, antenna, etc.) resources) by internally performing scheduling for each wireless LAN technology, and the counterpart devices communicating with the device have been operating without information related to the IDC problem experienced by the device.

[0311] Devices with a Wi-Fi interface, such as mobile phones, have been selectively utilizing either the Bluetooth or Wi-Fi interface based on their own decisions when communicating via Bluetooth, without interacting with the other device communicating via the Wi-Fi interface. Therefore, when an AP communicating with a non-AP STA in a device with an IDC issue confirms that the transmission of a PPDU it sent to the non-AP STA has failed, it cannot determine that the failure was due to an IDC issue. In this case, the AP may consider a collision as the cause of the PPDU transmission failure and make decisions such as doubling the contention window to generate a backoff counter, or lowering the data rate applied to the PPDU as the cause of the transmission failure. However, since transmission failure due to an IDC issue occurs regardless of the Wi-Fi channel access mechanism or data rate, the aforementioned follow-up procedures of the AP (such as doubling the contention window and adjusting the data rate) are inappropriate countermeasures that only unnecessarily degrade Wi-Fi communication performance.

[0312] In order to alleviate the Wi-Fi performance degradation caused by the aforementioned IDC problem, the 802.11bn Task Group is discussing a technique for exchanging information related to the IDC problem between APs and non-AP STAs, and adjusting the transmission timing of PPDUs and the TXOP operation method based on the exchanged information. More specifically, a non-AP STA instructs the AP on information related to the time it experiences an IDC problem, and the AP adjusts the transmission timing of PPDUs transmitted to the non-AP STA based on the instructed information. For example, if a non-AP STA instructs the AP on information related to the start time of the time it experiences an IDC problem and the duration of the IDC problem, the AP does not transmit PPDUs to the non-AP STA during the time that the non-AP STA is considered to be experiencing an IDC problem. As another example, when a non-AP STA receives a frame from an AP, it may indicate the start time and length information of the IDC problem it will experience in a response frame to the received frame, and the AP may decide to prematurely terminate the frame exchange sequence with the non-AP STA before the IDC problem starts (e.g., prematurely truncate a TXOP for which the non-AP STA is a TXOP responder).

[0313] <Periodic IDC 문제>

[0314] Some IDC issues may exhibit periodic behavior. This may be due to the scheduling behavior of the device experiencing the IDC issue. For example, a device experiencing IDC issues between Bluetooth and Wi-Fi within the device may schedule the use of both interfaces by dividing the utilization times of the Bluetooth and Wi-Fi interfaces using Time Division Multiple Access (TDMA). In this case, the Wi-Fi STA of the device will experience IDC issues while the Bluetooth interface within the same device is being utilized. Since the utilization time of the Bluetooth interface is periodic, the IDC issue also occurs periodically.

[0315] A non-AP STA experiencing such periodic IDC issues can notify the AP of recurring IDC issues all at once by indicating to the AP when the IDC issue started, how long the issue persists, and the frequency of the IDC issue recurrence. The AP can utilize the periodic IDC issue occurrence time information indicated by the non-AP STA to take actions such as adjusting the timing of the PPDU transmitted to the non-AP STA or adjusting the length of the TXOP as described above.

[0316] As a method of indicating the IDC problem with periodicity, recycling / reusing the indication method of P2P (Peer-to-Peer) TWT introduced in 11ax is being actively discussed, but since the present invention is not related to a specific signaling method, a detailed description is omitted.

[0317] <Aperiodic IDC 문제>

[0318] An aperiodic IDC problem refers to an IDC problem that occurs without periodicity. It is also possible that all IDC problems other than the aforementioned periodic IDC problem can be classified as aperiodic IDC problems. An aperiodic IDC problem is, as the name suggests, an IDC problem that occurs without periodicity. Therefore, even a device containing a Wi-Fi STA with an IDC problem does not have information about the timing and periodicity of the IDC problem. However, depending on the device's implementation, this information may be determined in advance before performing an operation using a specific interface. For example, a device may decide to communicate using a Bluetooth interface several milliseconds before it actually initiates use of the Bluetooth interface. In this case, the device may internally notify the Wi-Fi interface that it will soon experience an IDC problem.

[0319] In this case, if the information related to the IDC issue acquired on the Wi-Fi interface is transmitted to the counterpart Wi-Fi STA through the Wi-Fi STA, the counterpart Wi-Fi STA can perform actions to alleviate the IDC issue (such as the above-described PPDU transmission decision and TXOP length adjustment) during the time when the IDC issue occurs. Therefore, even in the case of the aperiodic IDC issue, it is important to establish a procedure so that the counterpart STA is notified in advance before the IDC issue occurs by the Wi-Fi STA. In this context, the 11bn Task group is discussing various methods to allow information about the aperiodic IDC issue to be exchanged between STAs. One promising method is for an STA (e.g., a non-AP STA) that receives a frame from a counterpart STA (e.g., an AP STA) to indicate the time information related to the aperiodic IDC issue that it will experience in the response frame that it transmits. Although the Multi-STA BlockAck frame is being actively discussed as a specific response frame format, the details of the specific instruction method and frame format are not closely related to the main idea of ​​the present invention, so they are omitted.

[0320] <IDC 정보의 교환을 위한 frame exchange sequence 조정 방법>

[0321] As mentioned earlier, an STA that is about to experience an aperiodic IDC problem can indicate information related to the aperiodic IDC problem to the other STA through the response frame it transmits. In this case, the other STA can adjust the frame exchange timing with the STA that is about to experience the aperiodic IDC problem based on the aperiodic IDC problem occurrence time and time interval information obtained through the response frame.

[0322] However, an STA that experiences an aperiodic IDC problem can only instruct the counterpart STA about IDC problem-related information through a Response frame if it has the opportunity to transmit a Response frame, and if it does not have the opportunity to transmit a Response frame, it is impossible to transmit the IDC problem-related information acquired on the Wi-Fi interface to the counterpart STA.

[0323] That is, in order to allow information related to an Aperiodic IDC problem acquired by a specific STA to be transmitted to an opposing STA, the specific STA must be able to transmit a Response frame at least once from the time the specific STA acquired the information related to the Aperiodic IDC problem until the Aperiodic IDC problem starts. Therefore, an STA that wishes to receive information related to an Aperiodic IDC problem from an opposing STA must continuously and not too late provide an opportunity for the opposing STA to indicate information related to the Aperiodic IDC problem. In this case, providing an information indication opportunity not too late means that the information indication opportunity must be provided before the Aperiodic IDC problem starts.

[0324] Figure 20 illustrates an example of a situation in which information related to interference between different wireless communication interfaces occurring on the non-AP STA side is not properly transmitted to the AP side.

[0325] Referring to FIG. 20, if a data transmission problem caused by interference from a heterogeneous network is not accurately conveyed to a counterpart STA (AP or non-AP STA), the counterpart STA cannot clearly recognize the data transmission problem, and as a result, the counterpart STA may not recognize that the non-AP STA or AP is in a state where it cannot receive frames in a specific period (ICD SP or unavailable period).

[0326] Specifically, as illustrated in FIG. 20, the AP transmitted an ICF to the non-AP STA for the purpose of performing a frame exchange sequence with the non-AP STA. Since the non-AP STA did not have information related to the confirmed Aperiodic IDC problem, it did not indicate information related to the Aperiodic IDC problem through the ICR. Accordingly, the AP starts transmitting a long DL PPDU to the non-AP STA. While the DL PPDU transmission is in progress by the AP, information related to the Aperiodic IDC problem is acquired by the non-AP STA. However, the non-AP STA does not have an opportunity to transmit a frame including the information related to the IDC problem to the AP, and encounters a situation where the Aperiodic IDC problem, which was previously confirmed, starts before reception of the long DL PPDU is completed. In this case, the AP and non-AP STA initiate operations assuming that there will be no Aperiodic IDC problem identified through ICF / ICR, but the non-AP STA fails to respond to the Aperiodic IDC problem identified late and fails to transmit / receive DL PPDU.

[0327] According to one embodiment of the present invention, an STA (e.g., a non-AP STA) experiencing an Aperiodic IDC problem can indicate to a counterpart STA (e.g., an AP STA) a maximum response frame interval to ensure that the STA can indicate information related to the Aperiodic IDC problem. At this time, the maximum response frame interval may be a value related to a time interval during which the STA experiencing the IDC problem can obtain information related to the Aperiodic IDC problem in advance. For example, a Wi-Fi interface configured to obtain information related to the Aperiodic IDC problem 2 ms before the onset of the Aperiodic IDC problem through information within the device can indicate to the counterpart STA (a second STA, an STA of another device) a time value determined based on 2 ms or 2 ms through the STA (a first STA). In this case, the second STA, which has been instructed with the time value, may adjust the frame exchange sequence so that the first STA can transmit a response frame at least once within the instructed time value when performing a frame exchange sequence with the first STA. At this time, the response frame transmitted at least once means a response frame (e.g., a multi-station block response frame (Multi-STA Block Acknowledgement frame or Multi-STA BlockAck frame, etc.)) that may include information related to an Aperiodic IDC problem. At this time, the time value related to the advance acquisition of information related to an Aperiodic IDC problem that the non-AP STA instructs the AP may be the minimum time for the non-AP STA to advance acquire information related to an Aperiodic IDC problem.For example, if a non-AP STA can obtain information related to an Aperiodic IDC problem in advance within a range of x ms to y ms before the Aperiodic IDC problem occurs (where y is greater than or equal to x), the non-AP STA indicates time information corresponding to x ms to the AP. That is, the minimum time during which the Aperiodic IDC information can be obtained in advance is indicated from the non-AP STA to the AP, and the AP can provide the non-AP STA with an opportunity to transmit a response frame that can include information related to the Aperiodic IDC problem based on the indicated time value.

[0328] According to one embodiment of the present invention, an STA (e.g., an AP STA) connected to an STA (e.g., a non-AP STA) experiencing an Aperiodic IDC problem must adjust a frame exchange sequence to be performed with a device experiencing an Aperiodic IDC problem based on information indicated by the STA experiencing an Aperiodic IDC problem. At this time, the STA experiencing an Aperiodic IDC problem does not mean that the STA is currently experiencing an IDC problem, but rather that the STA has a device characteristic that may cause an Aperiodic IDC problem to occur during operation. At this time, adjusting the frame exchange sequence means performing frame exchange in a form that allows the STA experiencing an Aperiodic IDC problem to transmit a response frame (a response frame in a format that may include information related to the Aperiodic IDC problem) at least once during a specific time interval. That is, if only the Multi-STA BlockAck frame is a frame configured to include information related to an Aperiodic IDC problem, the STA communicating with the STA experiencing the Aperiodic IDC problem must request a response of Multi-STA BlockAck from the STA experiencing the Aperiodic IDC problem at least once during a specific time interval. To this end, the STA communicating with the STA experiencing the Aperiodic IDC problem may need to adjust the transmission length of the PPDU it transmits based on the length of the specific time interval. In this case, the specific time interval may be a time interval specified based on a time interval during which the STA experiencing the Aperiodic IDC problem can obtain information related to the occurrence of the Aperiodic IDC problem through information within the device before the Aperiodic IDC problem starts.

[0329] Therefore, an STA experiencing an Aperiodic IDC problem may need to indicate that it has a characteristic of experiencing an Aperiodic IDC problem when performing an association with an AP, and at the same time, indicate a maximum response frame interval (same as the Aperiodic IDC problem information pre-acquisition capability or the Aperiodic IDC problem information pre-acquisition time, etc.) to ensure that it can indicate information related to the Aperiodic IDC problem. The AP, which has been instructed with the above information from a non-AP STA, must adjust the frame exchange sequence in a way that the non-AP STA can transmit a response frame (in a format that can include information related to the Aperiodic IDC problem) at least once within a time determined based on the instructed information, when performing a frame exchange sequence with the non-AP STA. At this time, even an STA that has been instructed not to experience an Aperiodic IDC problem during the association process can indicate that it has a characteristic of experiencing an Aperiodic IDC problem through a frame transmitted during the operation process. In this case, the AP should consider the STA to be in the same state as the one indicated during the association process as experiencing the aperiodic IDC problem. At this time, the STA can indicate that it is prone to the aperiodic IDC problem by transmitting a management frame, for example, a frame containing the UHR operation element. At this time, the STA can indicate that it is prone to the aperiodic IDC problem through the A-Control subfield of the frame it transmits.

[0330] FIG. 21 illustrates an example of a method in which a non-AP STA instructs an AP about occurrence and indicative conditions of Aperiodic IDC related to interference between different wireless communication interfaces, and the AP adjusts a frame exchange procedure accordingly, according to an embodiment of the present invention.

[0331] Referring to FIG. 21, a terminal (non-AP STA or AP) supporting DUO mode, which may experience interference due to a heterogeneous network, may transmit a management frame to a counterpart terminal (AP or non-AP STA) to perform a connection, including information related to whether the terminal supports DUO mode and / or, if it supports DUO mode, at least one of the maximum values ​​of IDC SP or unavailable period that occur due to DUO mode.

[0332] Specifically, as illustrated in (a) of FIG. 21, the UHR Capabilities element is a brief example of a UHR capabilities element included in a management frame (e.g., an Association request frame, etc.) that a non-AP STA transmits to perform a connection with an AP. A non-AP STA indicates whether it is an STA experiencing an Aperiodic IDC problem (or whether it supports a DUO mode) through the Aperiodic IDC Presence field. A non-AP STA that indicates whether it supports DUO mode or experiences an Aperiodic IDC problem through the Aperiodic IDC Presence field also indicates the maximum time interval information that it should consider in order to indicate the Aperiodic IDC problem-related information that it has acquired through the Maximum IDC Indication Interval field. The value indicated through the Maximum IDC Indication Interval field is set based on how far in advance a non-AP STA can obtain IDC problem-related information through the information within the device before an actual Aperiodic IDC problem occurs. The above fields can also be indicated through the IDC Information element transmitted by the non-AP STA as illustrated in (b) of FIG. 21, which is used to allow the non-AP STA to perform Aperiodic IDC-related instructions without performing a new Association when an Aperiodic IDC problem that did not occur when the STA was associated occurs.At this time, the above element name (IDC Information element) and the names of each field are pseudonyms created for explanation, and it is possible to utilize fields with different names that have the same / similar functions.

[0333] The bottom of Figure 21 illustrates how the AP adjusts the frame exchange sequence based on information indicated through the Aperiodic IDC Presence and Maximum IDC Indication Interval fields described above.

[0334] The AP receives Aperiodic IDC-related Capability information from a non-AP STA. The received Capability information includes information that the non-AP STA is an STA experiencing an Aperiodic IDC problem and maximum response IDC indication interval information (x us) for indicating Aperiodic IDC problem-related information. Accordingly, the AP adjusts the length of the DL PPDU transmitted to the non-AP STA to ensure that the non-AP STA can transmit at least one response frame (in a format that can include Aperiodic IDC problem-related information) within x us. At this time, the DL PPDU transmitted by the AP is transmitted with an Ack Policy other than No Ack or Delayed Ack set to allow the M-BA frame response of the non-AP STA.

[0335] Meanwhile, when an AP transmits a DL MU PPDU targeting multiple non-AP STAs, multiple non-AP STAs among the target non-AP STAs may be non-AP STAs experiencing an Aperiodic IDC-related problem. In this case, the AP must ensure that it can respond with a response frame (indicating Aperiodic IDC-related information) with an interval shorter than the maximum response frame interval indicated by each of the multiple non-AP STAs experiencing an Aperiodic IDC-related problem. In other words, when the AP operates a frame exchange sequence targeting multiple non-AP STAs experiencing an Aperiodic IDC-related problem, the AP must adjust the frame exchange sequence based on the shortest maximum response frame interval among the maximum response frame intervals indicated by each non-AP STA that is a target of the frame exchange. At this time, a detailed description of the method of adjusting the frame exchange sequence based on the maximum response frame interval information indicated by the non-AP STA (considered to be indicated through the Maximum IDC Indication Interval field in the case of FIG. 15) is omitted because it has been described through the embodiments described above.

[0336] The capability for pre-acquisition of information related to an Aperiodic IDC problem indicated by a non-AP STA (the capability for how far in advance the information is acquired by the non-AP STA before an Aperiodic IDC occurs on the non-AP STA side) can be used by the AP to evaluate how long the Aperiodic IDC related information previously indicated by the non-AP STA is valid. In this case, the capability for pre-acquisition of information related to an Aperiodic IDC problem is a capability having the same / similar meaning as that indicated by the Maximum IDC Indication Interval field of FIG. 15 described above.

[0337] To be more specific, if a non-AP STA that can acquire Aperiodic IDC problem-related information at least 10 ms in advance indicates 'No Aperiodic IDC Problem', the AP can be sure that the non-AP STA will not experience an Aperiodic IDC problem for at least 10 ms. That is, the AP can use the Aperiodic IDC problem-related information pre-acquisition Capability indicated by the non-AP STA to verify the validity of the Aperiodic IDC problem-related information previously indicated by the non-AP STA. At this time, a specific validity evaluation method may be that the Aperiodic IDC problem-related information indicated by the non-AP STA is evaluated as valid during the time period indicated by the Aperiodic IDC problem-related information pre-acquisition Capability of the non-AP STA from the time at which the non-AP STA indicated the Aperiodic IDC problem-related information.

[0338] An AP can more efficiently adjust the frame exchange sequence it performs with a non-AP STA based on the validity of previously indicated Aperiodic IDC related problem information from the non-AP STA. As a specific example, if a TXOP that the AP wants to start for frame exchange with a non-AP STA ends at a time when a previously performed 'no Aperiodic IDC related problem (i.e., no indicated Aperiodic IDC information)' indication from the non-AP STA is still valid, the AP can initiate the TXOP without using an initial control frame requesting a response of Aperiodic IDC information when starting the TXOP. That is, if the AP predicts (evaluates) that the non-AP STA receiving the TXOP will not experience an Aperiodic IDC-related problem until the end of the newly started TXOP, it is possible to initiate the TXOP without using the ICF / ICR exchange procedure for acquiring IDC-related information even if the non-AP STA receiving the TXOP is a non-AP STA that has the characteristic of experiencing an Aperiodic IDC-related problem. That is, it is possible that the initial control frame of the TXOP is utilized in a frame format other than that transmitted to request Aperiodic IDC information from the counterpart non-AP STA, or that the TXOP is initiated together with a frame type other than a control frame (e.g., a frame of management or data type).At this time, if the TXOP initiated by the AP is targeted at multiple non-AP STAs, the AP can perform the ICF / ICR exchange procedure for acquiring IDC-related information only for non-AP STAs that have the characteristic of experiencing an Aperiodic IDC problem and for which the validity of the 'No Aperiodic IDC-related problem' indication previously transmitted by the non-AP STA expires before the expected end time of the TXOP. In other words, even if the TXOP is initiated through an ICF / ICR related to IDC, it is possible that a response of IDC-related information is not requested for a non-AP STA for which the 'No Aperiodic IDC-related problem' indication previously transmitted is evaluated to be valid until the end time of the TXOP.

[0339] For the sake of convenience, the explanation is based on the end time of TXOP. However, it is possible to apply whether or not to attempt to acquire IDC-related information for each non-AP STA based on the end time of frame exchange performed between each non-AP STA and the AP. For example, the AP can perform frame exchange with multiple non-AP STAs using the TXOP it has acquired, and the AP can determine the end time of frame exchange with the corresponding STA based on the IDC-related information indicated by each non-AP STA. In other words, the TXOP of the AP can continue to perform frame exchange with other non-AP STAs even after a specific non-AP STA transitions to an unavailable state due to an IDC-related problem. Therefore, the TXOP management method described above is a description for the case where the TXOP is acquired to perform frame exchange with a single non-AP STA, and the described TXOP management method should be interpreted as a method for managing frame exchange for each individual non-AP STA that performs frame exchange with the AP within the TXOP.

[0340] FIG. 22 illustrates an example of a frame exchange procedure between a non-AP STA and an AP due to an IDC-related problem occurring in the AP according to one embodiment of the present invention.

[0341] Referring to Figure 22, if a terminal (non-AP STA or AP) supports DUO mode and interference occurs due to a heterogeneous network, frame transmission may be restricted in the section where interference occurs. In this case, the terminal may not transmit information related to interference caused by the heterogeneous network to the other terminal.

[0342] Specifically, a non-AP STA supporting DUO mode may include not only Wi-Fi but also other heterogeneous network interfaces (e.g., Bluetooth, 3GPP (LTE or 5G, etc.)). In this case, if the terminal uses the same frequency band (e.g., an unlicensed band) as the heterogeneous network, interference may occur due to the heterogeneous network.

[0343] Accordingly, a non-AP STA may transmit a management frame including a subfield indicating whether it supports the DUO mode in the association procedure with the AP. In addition, if the subfield indicating whether the DUO mode is supported indicates support for the DUO mode, the UL MU disabled subfield included in the management frame, which indicates whether UL MU transmission is disabled, may always be set to a value indicating that UL MU transmission is not disabled (e.g., '0'). If the subfield indicating whether the DUO mode is supported is set to a value indicating support for the DUO mode, but the UL MU disabled subfield included in the management frame, which indicates whether UL MU transmission is disabled, is set to a value indicating that UL MU transmission is disabled, the non-AP STA may transmit a non-HT PPDU instead of a TB PPDU in response to a trigger frame transmitted by the AP. At this time, the TB PPDU and non-HT PPDU may include a Multi-STA BlockAck frame, and the Multi-STA BlockAck frame may include information related to a period (e.g., IDC SP or unavailable period) in which interference occurs due to heterogeneous networks. The information related to the period in which interference occurs may include a subfield (e.g., AID TID info subfield) set to a value indicating that the corresponding information is included in the Multi-STA BlockAck frame (or M-BA frame), and a Block Ack bitmap subfield including feedback information indicating the start time and duration of the period in which interference occurs.

[0344] Afterwards, the AP, which recognizes that the non-AP STA supports the DUO mode, transmits a trigger frame to the non-AP STA, and the non-AP STA can transmit the TB PPDU or non-HT PPDU described above in response to the trigger frame.

[0345] When an AP receives a Multi-STA BlockAck frame transmitted from a Non-AP STA and recognizes a section where interference occurs due to a heterogeneous network to a Non-AT STA through the received Multi-STA BlockAck frame, the AP can transmit a DL PPDU in a section that does not overlap with the section within the TXOP configured through a trigger frame. For example, if the end time of the TXOP duration is the same as or before the end time of the section where interference occurs, the AP can bring forward the end time of the configured TXOP so that it ends before the interference occurs, and transmit the DL PPDU to the non-AP STA before the TXOP ends. If the DL PPDU cannot be transmitted until the end time of the TXOP, the length of the DL PPDU can be adjusted based on the end time of the TXOP (for example, the length of the DL PPDU can be reduced depending on the end time of the adjusted TXOP).

[0346] At this time, when a trigger frame is transmitted as included in a PPDU, the access category of the PPDU including the trigger frame may be determined based on the access category of the PPDU transmitted after the Multi-STA BlockAck frame. For example, the access category (AC) for the PPDU of the trigger frame may be the same as the access category of the DL PPDU transmitted thereafter.

[0347] In other words, the AP receives the CRF (Multi-STA BlockAck) frame transmitted from the non-AP STA when the previous TXOP ends. At this time, the CRF transmitted by the non-AP STA indicates that there is no IDC-related problem (No IDC) that the non-AP STA is aware of. The "No IDC-related problem" report indicated by the non-AP STA is considered valid by the AP until time t based on the "Aperiodic IDC problem-related information pre-acquisition Capability" indicated by the non-AP STA. In this case, since the frame exchange sequence that the AP intends to initiate with the non-AP STA ends earlier than time t, the AP initiates the frame exchange sequence (TXOP) without requesting the IDC-related problem information of the non-AP STA when initiating the frame exchange sequence. A TXOP initiated from the AP is terminated at a point in time when the “no IDC-related problem” indicated by the non-AP STA is still valid, and the frame exchange sequence between the AP and the non-AP STA is performed without being affected by the IDC-related problem and without exchanging IDC-related problem information.

[0348] Although this embodiment has been described using the example of a case where a non-AP STA experiences interference due to a heterogeneous network, this embodiment can also be applied to a case where an AP experiences interference due to a heterogeneous network. For example, a non-AP STA can transmit a trigger frame to the AP, and the AP can transmit information related to interference caused by a heterogeneous network to the non-AP STA by including this in a BlockAck frame as described above. Thereafter, the non-AP STA can transmit a UL PPDU to the AP, and at this time, if the trigger frame transmitted by the non-AP STA is included in the PPDU and transmitted, the access category of the PPDU including the trigger frame can be determined based on the access category of the UL PPDU transmitted after the BlockAck frame. For example, the access category of the PPDU of the trigger frame can be the same as the access category of the UL PPDU transmitted thereafter.

[0349] <IDC 정보 교환을 위한 Initial Control frame 및 Initial Control 응답 프레임>

[0350] Through the embodiments of the present invention described above, it was shown that an STA experiencing an Aperiodic IDC problem can indicate information related to the Aperiodic IDC problem it is experiencing to a counterpart STA, and an STA receiving information related to the Aperiodic IDC problem from the counterpart STA can adjust the frame exchange sequence it operates, thereby alleviating the inefficiency problem caused by the Aperiodic IDC problem.

[0351] Information related to an Aperiodic IDC problem experienced by an STA that is a TXOP responder can be indicated through a response frame that the STA transmits to the TXOP holder. At this time, the response frame may be a Multi-STA BlockAck frame as considered in the embodiments of the present invention described above. More specifically, information related to the Aperiodic IDC problem can be indicated through a Per AID TID Info field in which the AID11 field is set to a pre-agreed value among the Per AID TID info fields included in the Multi-STA BlockAck frame. Accordingly, a TXOP holder that confirms that the Multi-STA BlockAck frame transmitted by the TXOP responder includes the AID11 field set to a pre-agreed value can obtain information related to whether the STA that transmitted the Multi-STA BlockAck frame is expected to experience an Aperiodic IDC problem and the time and time period in which the IDC problem occurs.

[0352] However, in the existing Wi-Fi standard, the condition for an STA that is a TXOP responder to transmit a Multi-STA BlockAck frame is limited to when it has received a BlockAck request frame or a PPDU from an STA that is a TXOP holder. Therefore, even if an STA recognizes that an Aperiodic IDC problem will occur, it cannot indicate information related to the Aperiodic IDC problem to the other STA before the opportunity to transmit a Multi-STA BlockAck frame is secured. In other words, after some time has passed since the exchange of Multi-STA BlockAck frames between two STAs, each STA is in a state where it cannot indicate the information related to the Aperiodic IDC problem that it will experience to the other STA even though it is aware of the information. Therefore, an STA that wants to initiate a frame exchange sequence with the other STA must first check whether the other STA is aware of information related to the Aperiodic IDC problem.

[0353] That is, an STA that wants to initiate a frame exchange sequence with an STA that has a characteristic of experiencing an Aperiodic IDC-related problem may need to transmit a frame in a pre-arranged format when initiating a frame exchange sequence with the counterpart STA so as to indicate Aperiodic IDC-related information that the counterpart STA is aware of. At this time, the frame in the pre-arranged format may be a BSRP (Buffer Status Report Poll) Trigger frame in which a specific subfield has a value set to a pre-arranged value. At this time, the specific subfield may be a subfield that is set to a different value depending on the purpose for which the BSRP Trigger frame is transmitted. For example, an AP may set a specific subfield of a BSRP Trigger frame transmitted to request a response to a BSR (Buffer Status Report) frame to a specific value (e.g., 0), and may set a specific subfield of a BSRP Trigger frame transmitted to request a response to Aperiodic IDC-related information to another value (e.g., 1). In this case, when the STA receiving the BSRP Trigger frame confirms that the value of the specific subfield is set to a specific value, the STA may respond with a TB PPDU including a BSR frame, and when the STA confirms that the value of the specific subfield is set to a different value, the STA may respond with Aperiodic IDC-related information that it is aware of. At this time, the Aperiodic IDC-related information may be included and indicated in a Multi-STA BlockAck frame. That is, the STA that has been requested to respond with Aperiodic IDC-related information through the BSRP Trigger frame can transmit a Multi-STA BlockAck frame in response to the BSRP Trigger frame.

[0354] FIG. 23 illustrates an example of a frame exchange procedure in which a BSRP trigger frame and an M-BA frame are exchanged and initiated according to one embodiment of the present invention.

[0355] Referring to FIG. 23, a terminal to which DUO mode is applied can transmit an element indicating that DUO mode is applied in a management frame, and then, by transmitting a BlockAck frame in response to the trigger frame, the terminal can inform the opposing terminal of the start time and duration of a section in which interference occurs due to a heterogeneous network.

[0356] Specifically, a non-AP STA transmits Capability information to the AP to indicate that it has the characteristic of experiencing an Aperiodic IDC problem. Considering that the non-AP STA is an STA experiencing an Aperiodic IDC problem, the AP initiates a frame exchange with the non-AP STA through a BSRP trigger frame requesting information related to the IDC problem. The non-AP STA confirms that the received BSRP trigger frame requests indication of information related to the IDC problem and then responds with an M-BA frame. At this time, the M-BA frame includes information related to the IDC problem and is transmitted in a Non-HT (duplicated) PPDU format. The AP can recognize that the non-AP STA experiences an IDC problem for x us from time t through the M-BA frame responded from the non-AP STA, and adjusts the frame exchange sequence. The DL PPDU and M-BA frame transmitted in the adjusted frame exchange sequence are terminated before time t. The CF-END frame can be transmitted after time t. This is because the CF-END frame is transmitted to help third-party STAs release NAV, and is not a frame intended for non-AP STAs as receivers.

[0357] As considered in the above-described embodiment of the present invention, an STA that initiates a frame exchange sequence with an STA having a characteristic of experiencing an Aperiodic IDC-related problem attempts to initiate the frame exchange sequence by transmitting a BSRP trigger frame, and the STA that receives the BSRP trigger frame can indicate the Aperiodic IDC-related information that it is aware of by responding with a Multi-STA BlockAck frame. An STA that acquires Aperiodic IDC-related information through a Multi-STA BlockAck frame received from a counterpart STA operates the frame exchange sequence in a form that is not affected by the Aperiodic IDC problem by adjusting the frame exchange sequence performed with the counterpart STA.

[0358] However, the BSRP trigger frame introduced in the existing Wi-Fi standard 802.11ax is transmitted to request a response to a TB PPDU (trigger-Based PPDU), and the STA that receives the BSRP trigger frame responds with BSR (Buffer Status Report) information using the TB PPDU format. This is no different from the fact that the format of the response PPDU for all trigger frames except the MU-RTS trigger frame is the TB PPDU. Therefore, it is possible to understand that the default operation according to the existing Wi-Fi standard is for an STA that transmits a Multi-STA BlockAck (hereinafter referred to as M-BA) frame for the purpose of indicating IDC-related information after receiving a BSRP trigger frame to respond to the PPDU in the TB PPDU format with an M-BA frame.

[0359] However, when a BSRP trigger frame and an M-BA frame are used as initial control frames for initiating a frame exchange sequence as considered in one embodiment of the present invention described above, a problem arises in that legacy STAs that have identified a TB PPDU containing an M-BA frame cannot set a NAV. To be more specific, when an STA that suffers from an Aperiodic IDC-related problem responds with an M-BA frame contained in a TB PPDU in response to a BSRP trigger frame it has received, legacy STAs that do not support reception of the TB PPDU format cannot receive the M-BA frame. In other words, legacy STAs cannot set a NAV using the TB PPDU and M-BA frame, and consequently cannot provide NAV protection for a frame exchange sequence initiated through the BSRP trigger frame / M-BA frame exchange. Therefore, the BSRP trigger frame / M-BA frame exchange must be performed using a PPDU in a format in which legacy STAs can set NAV, and specifically, it may be performed using a non-HT (duplicated) PPDU format.

[0360] According to one embodiment of the present invention, a BSRP trigger frame may include an indicator indicating the type of frame to be responded to and / or the format of a PPDU to be responded to. The indicator included in the BSRP trigger frame may be set to different values ​​when requesting a response to a frame including BSR information and when requesting a response to an M-BA frame including IDC information. That is, an STA receiving a BSRP trigger frame can determine the type of frame to be responded to based on the value of the indicator. In addition, the indicator included in the BSRP trigger frame may be set to different values ​​when requesting a response to a non-HT (duplicated) PPDU and when requesting a response to a TB PPDU. That is, an STA receiving a BSRP trigger frame can determine the format of a PPDU to be responded to based on the value of the indicator. In addition, the BSRP trigger frame may include an indicator indicating a response to both an M-BA frame including IDC-related information and a frame including BSR information. At this time, the indicator indicating to respond to both types of frames may be the same indicator as the indicator indicating the frame type and / or PPDU format. As a simple example, the indicator included in the BSRP trigger frame may be set to a first value to indicate a response to an M-BA frame (non-HT (duplicated) PPDU format), set to a second value to indicate a response to a frame including BSR information (TB PPDU format), and set to a third value to indicate a response to both an M-BA frame and a frame including BSR information (non-HT (duplicated) PPDU format).

[0361] According to one embodiment of the present invention, an STA that receives a BSRP trigger frame requesting an indication of IDC-related information can respond with an M-BA frame including the IDC-related information using a Non-HT (duplicated) PPDU format. At this time, the Non-HT (duplicated) PPDU format refers to a PPDU format in which a 20 MHz Non-HT PPDU is repeatedly transmitted on each 20 MHz subchannel in which the PPDU is transmitted. That is, an STA that receives a BSRP trigger frame can respond with a Non-HT (duplicated) PPDU format. Through this, legacy STAs that receive a Non-HT PPDU can receive an M-BA frame included in the Non-HT PPDU, and thus, legacy STAs can also set a NAV through the M-BA frame. That is, a frame exchange sequence initiated through a BSRP trigger frame / M-BA frame exchange can receive NAV protection from legacy STAs by transmitting the M-BA frame as a non-HT (duplicated) PPDU. However, the operation of responding to the BSRP trigger frame with an M-BA frame and determining the format of the response PPDU to the trigger frame as a non-HT PPDU rather than a TB PPDU is different from the response regulation for the BSRP trigger frame defined in the existing 802.11ax, and therefore must be applied according to the established procedure.

[0362] According to one embodiment of the present invention, an STA that receives a BSRP trigger frame must determine the type of frame to respond to and the format of the PPDU to respond to based on the information indicated through the BSRP trigger frame. More specifically, an STA that receives a BSRP trigger frame from a counterpart STA may respond with an M-BA frame including IDC problem-related information as a response frame to the BSRP trigger frame only when the BSRP trigger frame requests an indication of IDC problem-related information. At this time, an STA that responds with an M-BA frame to the received BSRP trigger frame must determine the format of the PPDU to be a non-HT (duplicated) PPDU format. However, an STA that receives a BSRP trigger frame requesting an indication of IDC problem-related information may be permitted to respond with a frame including BSR information instead of an M-BA frame if there is no IDC-related information to indicate to the counterpart STA. At this time, the frame including the BSR information means a frame including BSR information (e.g., Queue size) in the BSR Control (a type of A-Control subfield) of the frame's MAC Header. At this time, the frame including the BSR information means a frame including BSR information (e.g., Queue size) in the QoS Control field of the frame's MAC header. At this time, the STA that responds with a frame including BSR information after receiving the BSRP trigger frame must determine the format of the responding PPDU as TB PPDU.

[0363] Meanwhile, an STA transmitting a BSRP trigger frame can request a response regarding IDC problem information only when the receiving device of the BSRP trigger frame is a single STA. In other words, an STA transmitting a BSRP trigger frame configured with multiple STAs as receiving devices (i.e., a BSRP trigger frame configured with a group address) must not request a response regarding IDC problems. This is a BSRP trigger frame configuration restriction to prevent multiple STAs from responding with non-HT PPDUs. In addition, an STA transmitting a BSRP trigger frame within an already initiated TXOP must not transmit a BSRP trigger frame requesting a response regarding IDC problems. In this case, the already initiated TXOP refers to a TXOP in which another frame has already been transmitted / received before the BSRP trigger frame is transmitted.

[0364] According to one embodiment of the present invention described above, an STA experiencing an Aperiodic IDC related problem responds to a BSRP trigger frame it has received with an M-BA frame in a non-HT (duplicated) PPDU format to indicate information related to the IDC problem it is experiencing. In this case, the STA indicating the IDC problem related information may be allowed to perform a response to the BSRP trigger frame regardless of whether it is capable of transmitting a TB PPDU.

[0365] That is, as described above, a non-AP STA can transmit a management frame to the AP during the association procedure with the AP. At this time, the management frame can include a UL MU disabled subfield indicating whether the non-AP STA can transmit UL MU in response to the trigger frame as described above. If the UL MU disabled subfield is set to a value (e.g., '1') indicating that transmission of a TB PPDU is possible in response to the trigger frame, the non-AP STA can transmit a TB PPDU in response to the trigger frame. However, if the UL MU disabled subfield is set to a value (e.g., '0') indicating that transmission of a TB PPDU is not possible in response to the trigger frame, the non-AP STA cannot transmit a TB PPDU in response to the trigger frame, and therefore the AP cannot transmit a trigger frame to the non-AP STA as a recipient. However, when supporting DUO mode, a non-AP STA must inform the AP of information related to a section where interference due to a heterogeneous network occurs. Therefore, even if the UL MU disabled subfield included in the management frame is set to a value indicating that transmission of a TB PPDU is impossible in response to a trigger frame, the AP can transmit a trigger frame to a non-AP STA supporting DUO mode (i.e., a non-AP STA where interference due to a heterogeneous network occurs) as a recipient, and the non-AP STA must transmit a PPDU to the AP in response to the trigger frame. Therefore, in this case, the non-AP STA can transmit information related to a section where interference due to a heterogeneous network occurs to the AP using a non-HT PPDU format rather than a TB PPDU format.

[0366] In this regard, 802.11ax defines a UL MU operation using a triggering frame (i.e., a trigger frame), and the defined UL MU operation includes the method and restrictions for the AP to configure the triggering frame, the procedure and restrictions for STAs that receive the triggering frame to respond with a TB PPDU, etc. One of the restrictions that the AP receives when configuring the triggering frame is to determine the STA that responds to the trigger frame based on the information indicated in the OM Control subfield (a type of A-Control subfield) transmitted by the STA. The function of the OM Control subfield is briefly described as follows. An STA that does not want to perform a response to the triggering frame can indicate to the AP that it will not respond to the triggering frame by transmitting the UL MU Disable subfield included in the OM Control subfield of the frame that it transmits by setting it to 1. Additionally, an STA that does not want to perform a response to a Basic trigger frame can instruct the AP that it will not perform a response to a Basic trigger frame by transmitting a frame that it transmits with the UL MU Data Disable subfield included in the OM Control subfield set to 1. Therefore, the AP is restricted to not transmit a triggering frame to an STA that has set the UL MU Disable subfield to 1 through the OM Control subfield, and to not transmit a Basic trigger frame to an STA that has set the UL MU Data Disable subfield to 1.That is, an STA can use the UL MU Disable subfield and / or the UL MU Data Disable subfield included in the OM Control subfield it transmits to indicate to the counterpart STA (AP STA) whether it will participate in trigger-based UL MU transmission, and an STA transmitting a trigger frame must transmit the trigger frame only to STAs that intend to participate in UL MU transmission.

[0367] However, the BSRP trigger frame transmitted to request information related to an IDC problem is not transmitted to initiate UL MU transmission, nor is it a frame transmitted to request a response to a TB PPDU. Therefore, an STA transmitting a BSRP trigger frame may be permitted to transmit a BSRP trigger frame destined for the counterpart STA even if the UL MU Disable subfield of the OM Control subfield most recently received from the counterpart STA is set to 1. In addition, even if an STA transmits an OM Control subfield with the UL MU Disable subfield set to 1 to the counterpart STA, it may be permitted to perform a response to the BSRP trigger frame when a BSRP trigger frame requesting IDC-related information is received from the counterpart STA. That is, the BSRP trigger frame transmission and M-BA response procedure performed for requesting IDC-related information may be a frame exchange procedure that is always allowed (if the opposing STA indicates that it has a characteristic of experiencing an Aperiodic IDC problem) regardless of the value of the UL MU Disabled subfield exchanged between the two STAs. That is, it is possible that a restriction applied based on the UL MU Disabled subfield value (for example, a restriction that an AP STA cannot transmit a trigger frame to an STA that indicates the UL MU Disabled subfield as 1) may not be applied to a BSRP trigger frame transmitted to indicate a request for IDC-related information.

[0368] Alternatively, an STA experiencing the Aperiodic IDC problem may need to always set the value of the UL MU Disabled subfield it transmits to its peer STA (AP STA) to 0. In other words, an STA experiencing the Aperiodic IDC problem may need to allow its peer STA to always transmit BSRP trigger frames destined for it.

[0369] That is, if the subfield indicating whether the DUO mode is supported included in the management frame indicates support for the DUO mode, the UL MU disabled subfield indicating whether the UL MU transmission included in the management frame is disabled can always be set to a value indicating that the UL MU transmission is not disabled (e.g., '0'). Accordingly, the AP can always transmit a trigger frame to a non-AP STA that experiences interference due to a heterogeneous network, with the non-AP STA as the recipient.

[0370] Meanwhile, an AP that wants to initiate a frame exchange sequence with a non-AP STA that suffers from the Aperiodic IDC problem transmits a BSRP trigger frame targeted at the non-AP STA and initiates a TXOP. At this time, since the AP transmits a PPDU containing only the BSRP trigger frame, channel access using Any AC is allowed according to the regulations defined in the existing 802.11ax. This is because, among the regulations defined in 802.11ax, channel access is allowed using Any AC when the AP transmits a PPDU containing only the trigger frame. At this time, performing channel access using Any AC means that channel access is performed when any one of the four ACs (AC_VO, AC_VI, AC_BE, AC_BK) described above has completed the channel access procedure (completed the backoff procedure). In the 802.11ax standard, one of the reasons why an AP is allowed to transmit a trigger frame after performing channel access using Any AC is because the frame exchange sequence initiated using the trigger frame is a UL MU operation involving multiple STAs, and is not a procedure in which the AP itself performs transmission of a DL PPDU. However, an AP that transmits a BSRP trigger frame requesting information related to an IDC problem can receive an M-BA from the other STA to obtain the IDC problem-related information, and then continue the frame exchange sequence for transmitting a DL PPDU. Therefore, if the AP is allowed to perform channel access using Any AC when sending a BSRP trigger frame, the AP can operate the channel access procedure in a way that is advantageous compared to other STAs.As a simple example, it is possible for an AP to perform channel access through AC_VO, which has a relatively high channel access success probability, and then transmit a DL PPDU containing traffic corresponding to AC_BE, which results in an unreasonable situation in terms of fairness of the channel access procedure.

[0371] Therefore, an AP that initiates a frame exchange sequence that includes the transmission of a DL PPDU must perform channel access through an AC corresponding to the access category of the traffic it intends to transmit through the DL PPDU, even if the PPDU it transmits only includes a trigger frame. That is, an AP that transmits a BSRP trigger frame requesting information related to an IDC problem must perform channel access using an Access Category that matches the traffic type (Access category) of the DL PPDU to be transmitted within the frame exchange sequence (i.e., TXOP) initiated through the BSRP trigger frame. However, an AP that does not intend to transmit a DL PPDU within the frame exchange sequence initiated through the BSRP trigger frame may be permitted to perform channel access using Any AC and then transmit the BSRP trigger frame. In this case, the AC corresponding to the traffic type of the DL PPDU means the AC corresponding to the TIDs of the MPDUs included in the DL PPDU, and it is possible for traffic with a TID corresponding to an Access Category that is not used for channel access to be included in the DL PPDU according to the EDCA TXOP sharing rule. As a simple example, an AP that performs channel access through a specific AC (e.g., AC_BE) and transmits a BSRP trigger frame requesting information about an IDC issue can transmit MPDUs corresponding to the specific AC as well as MPDUs corresponding to higher priority ACs (e.g., AC_VO) within the acquired TXOP.

[0372] That is, when interference occurs due to a heterogeneous network, a non-AP STA may transmit a Multi-STA BlockAck frame including information related to the duration during which interference occurs due to the heterogeneous network (e.g., whether information related to the duration is included, the start time and length of the duration, etc.) in response to a trigger frame from the AP. Whether information related to the duration is included may be indicated through the AID TID Info subfield, and when the AID TID Info subfield is set to a preset value (e.g., when the Ack type subfield is set to '0' and the TID subfield is set to 13), it may indicate that feedback information related to the section during which interference occurs is included in the Block Ack Bitmap subfield. The feedback information related to the section during which interference occurs may include the start time and duration of the section during which interference occurs due to the heterogeneous network.

[0373] Thereafter, the AP can transmit a DL PPDU in a section where interference does not occur based on the Multi-STA BlockAck frame. At this time, if a trigger frame is transmitted by being included in the PPDU, the access category of the PPDU including the trigger frame can be determined based on the access category of the PPDU transmitted after the Multi-STA BlockAck frame. For example, the access category (AC) for the PPDU of the trigger frame can be the same as the access category of the DL PPDU transmitted thereafter.

[0374] Although this embodiment has been described using the example of a case where a non-AP STA experiences interference due to a heterogeneous network, this embodiment can also be applied to a case where an AP experiences interference due to a heterogeneous network. For example, a non-AP STA can transmit a trigger frame to the AP, and the AP can transmit information related to interference caused by a heterogeneous network to the non-AP STA by including this in a BlockAck frame as described above. Thereafter, the non-AP STA can transmit a UL PPDU to the AP, and at this time, if the trigger frame transmitted by the non-AP STA is included in the PPDU and transmitted, the access category of the PPDU including the trigger frame can be determined based on the access category of the UL PPDU transmitted after the BlockAck frame. For example, the access category of the PPDU of the trigger frame can be the same as the access category of the UL PPDU transmitted thereafter.

[0375] FIG. 24 illustrates an example of a channel access procedure of an AP transmitting a BSRP trigger frame according to one embodiment of the present invention.

[0376] Referring to FIG. 24, the AP transmits a Basic trigger frame and acquires TXOP#1. When the AP transmits the Basic trigger frame to initiate TXOP#1, it performs channel access using Any AC because it transmits a PPDU containing only the Basic trigger frame. On the other hand, when the AP transmits the BSRP trigger frame to initiate TXOP#2, it performs channel access using AC_BE. This is because TXOP#2, which is initiated through the BSRP trigger frame, is initiated for the purpose of transmitting a DL PPDU containing an MPDU corresponding to AC_BE. In other words, when the AP initiates TXOP#2, it transmits a PPDU containing only the BSRP trigger frame, but since the BSRP trigger frame is not transmitted to initiate UL MU operation but to request information related to an IDC problem, it cannot perform channel access using Any AC.

[0377] <IDC 문제를 겪는 STA의 관리 문제>

[0378] Through the above-described embodiments, it has been shown that an STA that has the characteristic of experiencing an IDC problem and an STA that initiates a frame exchange sequence can transmit a BSRP trigger frame, and IDC problem-related information can be exchanged through the responded M-BA frame. In short, periodic IDC problem-related information can be indicated to the counterpart STA in a manner similar to the P2P TWT SP, and non-periodic IDC problem-related information can be indicated to the STA that initiates the frame exchange sequence using an M-BA frame.

[0379] An STA that performs a frame exchange sequence with an STA that has a characteristic of experiencing an IDC problem can adjust the frame exchange sequence in a way that minimizes the impact of the IDC problem by using information about the IDC problem of the STA. However, information about the aperiodic IDC problem experienced by each STA is indicated through the M-BA frame transmitted by the STA when the STA participates in the frame exchange sequence, and therefore, if the STA does not have an opportunity to transmit an M-BA frame, it cannot be indicated to the other STA.

[0380] The beacon frame periodically transmitted by the AP not only includes various parameters used in the BSS operated by the AP, but also indicates the value of the TSF (Timing Synchronization Function) Timer maintained by the AP through the Timestamp field. In other words, the beacon frame contains information such as parameters that must be received by member STAs participating in the BSS, as well as information for maintaining time synchronization. Therefore, STAs that cannot receive the beacon frame transmitted by the AP of the BSS to which they belong cannot operate normally within the BSS. Additionally, when major changes are scheduled to occur, such as changing the operating channel of the BSS or changing the EDCA parameters, the AP operates so that all STAs belonging to the BSS can receive the corresponding information by indicating the change and the time of change through multiple consecutive beacon frames. The reason for repeatedly indicating the change through multiple consecutive beacon frames is to support STAs that do not receive some beacon frames in order to perform the Power Save operation to receive the beacon frame at least once before the change is applied.

[0381] An AP can use the Listen Interval of each BSS member STA to determine whether all STAs within the BSS can obtain the information when the information is indicated in several consecutive beacon frames. The Listen Interval is a value related to the maximum number of beacon intervals during which an STA performing Power Save can not receive a beacon frame, and a non-AP STA indicates its own Listen interval when associating with an AP. If the Listen interval indicated by a specific non-AP STA is a value corresponding to five times the beacon interval, the specific non-AP STA operates in a way that it receives at least one beacon frame among five consecutive beacon frames. Therefore, an AP indicating an important update status through a beacon frame repeatedly indicates the corresponding information in a beacon frame during a period in which the non-AP STA that indicated the largest Listen interval among the non-AP STAs associated with it can receive at least one beacon frame. At this time, the reflection time of the above important update can be separately indicated using a counter that decreases by 1 for each beacon frame transmission.

[0382] Meanwhile, an STA that has the characteristic of experiencing an IDC problem may fail to receive a beacon frame due to the IDC problem at the time it attempts to receive the beacon frame.

[0383] As a simple example, let's assume that a non-AP STA that has indicated a listen interval of 5 intends to receive the fifth beacon frame among five consecutive beacon frames but has not received the previous four beacon frames. In this situation, the STA may not receive the fifth beacon frame that it was scheduled to receive due to an IDC issue. In this case, the non-AP STA may fail to receive important change information (e.g., EDCA parameter set change or operating channel change (switch) information) indicated by the AP through the beacon frame, and depending on the situation, the connection with the AP may be terminated. In addition, a non-AP STA that has not received a beacon frame for a long period of time may not be able to maintain time synchronization with the AP due to issues such as clock drift of the TSF timer, and may not be able to participate in timing-based operations (e.g., TWT SP initiation timing, etc.) previously established with the AP.

[0384] As described above, due to IDC issues, an STA may not be able to receive a beacon frame at the planned time, which may cause problems in performing the planned management operations (a series of management procedures for functioning as a member STA of the BSS). To prevent such issues, a non-AP STA must successfully receive at least one beacon frame within the Listen interval it instructs the AP to receive, regardless of the IDC issues it experiences. To achieve this, a non-AP STA must set the Listen interval value it instructs the AP to receive, taking into account not only the Power Save mode operation it intends to perform but also any IDC-related issues it experiences. However, due to the nature of aperiodic IDC, an unpredictable beacon frame reception failure may still occur on the non-AP STA side when the non-AP STA determines the Listen interval value. Therefore, it is essential to devise a follow-up action method that a non-AP STA can take after failing to receive a beacon frame. Situations in which a Non-AP STA fails to receive a beacon frame due to an IDC problem may include: 1. When an IDC problem occurs during a time period including the Target Beacon Transmission Time (TBTT); 2. When an IDC problem starts while receiving a beacon frame.

[0385] According to one embodiment of the present invention, a non-AP STA that fails to receive a beacon frame due to an IDC problem can request the AP to transmit critical update information and / or a Timestamp field. That is, a non-AP STA that fails to receive a beacon frame that it should have received due to an IDC problem can request the AP to additionally transmit information that it should have received. At this time, the request can be performed using a frame in a pre-arranged format. At this time, the frame in the pre-arranged format can be a Probe request frame or another type of management frame. The AP that receives the pre-arranged frame from the non-AP STA can transmit to the non-AP STA a frame that includes information corresponding to a Critical Update (e.g., (MU) EDCA parameter set change information and (Extended) Channel Switch Announcement element) among the information included in the beacon frame that it most recently transmitted. At this time, the frame may be transmitted as an individually addressed frame targeting the non-AP STA, or as a group addressed frame (group address or broadcast address). At this time, the frame transmitted by the AP may have a configuration including a timestamp field (same as the timestamp field included in the beacon frame).

[0386] FIG. 25 illustrates an example of a method for an STA that fails to receive a beacon frame due to an IDC problem to obtain information through a subsequent procedure, according to one embodiment of the present invention.

[0387] Referring to FIG. 25, a non-AP STA fails to receive a beacon frame transmitted by an AP due to an IDC problem. At this time, the non-AP STA can determine that it failed to receive the beacon frame based on the fact that the IDC problem occurred during the time period including the TBTT corresponding to the beacon frame it attempted to receive. The non-AP STA transmits a request frame in a pre-arranged format to the AP for the purpose of updating important information that may have been included in the beacon frame it failed to receive. The AP, which receives the request frame in the pre-arranged format, can recognize that the non-AP STA failed to receive the beacon frame and can transmit a response frame after SIFS. The response frame includes important change information that should have been received via the beacon frame. At this time, the response frame has a format including a Timestamp field. The non-AP STA can update parameter values ​​or adjust the TSF timer based on the response frame received from the AP, and as a result, although it failed to receive the beacon frame, it can maintain a management state similar to that of successfully receiving the beacon frame.

[0388] <AP assisted medium synchronization recovery procedure for IDC>

[0389] Through the above-described embodiments, it was explained that a non-AP STA that was unable to perform CCA during a time when an IDC-related problem occurred (IDC Service period of FIG. 13) must initiate a procedure for recovering Medium Synchronization, such as starting the MediumSyncDelay timer, when the IDC-related problem is resolved (IDC Service period ends).

[0390] An STA that has lost Medium Synchronization is restricted in its channel access procedures while the MediumSyncDelay timer remains at a non-zero value, and the MediumSyncDelay timer is reset to 0 when an MPDU or PPDU capable of setting a NAV is received. Therefore, an STA that has lost Medium Synchronization attempts to obtain information for setting a NAV by receiving a packet (PPDU / MPDU) transmitted from a third STA, or attempts to obtain a TXOP by transmitting an RTS by performing a limited form of channel access procedure (such as using dot11MSDOFDMEDthreshold as a CCA threshold as shown in FIG. 19). For reference, when the destination device of the RTS frame transmitted by the STA responds with a CTS frame, the CTS frame functions as an MPDU capable of setting a NAV, and the STA's MediumSyncDelay timer is reset to 0 (Medium Synchronization is restored). That is, in order for the Medium synchronization of an STA that has lost Medium Synchronization to be restored, a packet transmitted by another STA that maintains Medium Synchronization must be received by the STA that has lost Medium Synchronization.

[0391] According to one embodiment of the present invention, an STA that is expected to lose Medium Synchronization due to an IDC-related problem can request a peer STA to transmit a frame for its Medium Synchronization recovery. For example, a non-AP STA that reports IDC problem-related information to an AP through a response frame (e.g., a Multi-STA BlockAck frame) can transmit a response frame including an indicator requesting that the AP transmit a frame to itself after the IDC problem (indicated by the response frame) is resolved. In this case, after the IDC problem period (Unavailable period, IDC Service period) reported by the non-AP STA ends, the AP can transmit the frame to the non-AP STA to help the non-AP STA recover Medium Synchronization. At this time, the AP can transmit a frame to help recover Medium Synchronization only when there is no operation with another non-AP STA that has already been scheduled. At this time, the frame for which the transmission is requested may be a trigger frame. When the AP is instructed to transmit IDC problem-related information through a response frame received from a non-AP STA and the response frame requests transmission of a trigger frame, the AP may transmit a trigger frame targeted at the non-AP STA after the indicated IDC problem is considered to have ended. At this time, the AP may transmit the trigger frame only when the MediumSyncDelay timer of the non-AP STA is determined to remain at a non-0 value. In other words, the AP may not transmit the trigger frame when the MediumSyncDelay timer of the non-AP STA is determined to have a value of 0.At this time, a non-AP STA can request the AP to transmit a trigger frame only if it has traffic it wants to transmit (i.e., there is queueing traffic in the transmission queue).

[0392] The procedure for recovering the medium synchronization described above, that is, the procedure for setting the MediumSyncDelay timer when a non-AP STA that has lost the CCA capability due to an IDC-related problem recovers the CCA capability, can also be performed using a timer other than the MediumSyncDelay timer. This is because the medium synchronization recovery procedure using the MediumSyncDelay timer is defined for the MLD defined in 11be, and application of a different type of timer may be considered for the medium synchronization recovery procedure of an STA that has experienced an IDC-related problem. Therefore, the method for setting the medium synchronization timer and the procedure for recovering medium synchronization described above can be equally applied using a different type of timer, and it should be understood that the medium synchronization recovery procedure of a non-AP STA that has experienced an IDC-related problem is performed according to the method provided by the present invention even if a different type of timer is used instead of the MediumSyncDelay timer considered in the present invention.

[0393] <Mobile AP의 IDC 관련 문제 정보 지시 방법 및 이를 고려한 non-AP STA의 동작>

[0394] Additionally, while general APs typically only perform wireless LAN services using the 802.11 standard and thus do not experience IDC-related issues, mobile APs may experience similar IDC-related issues to non-AP STAs. For example, if a non-AP STA that experiences IDC-related issues functions as a mobile AP, its function as a mobile AP will also be affected by the IDC-related issues. In this case, the mobile AP refers to a wireless LAN STA that performs services such as tethering (phone-as-modem (PAM)). If an STA functioning as a mobile AP loses its CCA capability due to an IDC-related issue, the mobile AP STA must also start the MediumSyncDelay timer when it has recovered from the IDC-related issue, that is, after the CCA capability has been restored.

[0395] STAs that function as mobile APs operate their own BSSs similarly to regular APs and serve other non-AP STAs. Under conventional Wi-Fi standards, non-AP STAs associated with mobile APs can communicate by performing the same operations as those associated with regular APs. However, non-AP STAs associated with mobile AP STAs that experience IDC-related issues must perform operations that take into account the IDC-related issues experienced by the mobile APs they are associated with.

[0396] A mobile AP experiencing an IDC-related issue can announce information about the periodic IDC issue it is experiencing through the management frame it transmits (e.g., a beacon frame). Specifically, the mobile AP can announce the occurrence frequency and duration of the periodic IDC issue it is experiencing (period and duration information), thereby allowing non-AP STAs to confirm the occurrence of the periodic IDC issue and the time of occurrence. The AP can use the TWT element to announce this information.

[0397] In addition, a mobile AP that experiences an aperiodic IDC-related problem can transmit information about the IDC-related problem it will experience as a broadcast addressed frame (a frame other than an individually addressed frame, i.e., a broadcast or group addressed frame) before the aperiodic IDC-related problem occurs, thereby allowing non-AP STAs to obtain information about the time of occurrence and duration of the IDC-related problem it will experience. Accordingly, when the AP with which it is associated transmits a broadcast addressed Multi-STA BlockAck frame, the non-AP STAs must obtain the IDC-related problem information after receiving the frame. At this time, the frame transmitted by the AP may be a Multi-STA BlockAck frame that includes information about the IDC problem. At this time, the method by which the IDC-related problem information of the mobile AP is indicated through the Multi-STA BlockAck frame is the same as the method by which the IDC-related problem information of the non-AP STA described above is indicated through the Multi-STA BlockAck frame. Alternatively, the mobile AP may transmit a frame format other than the Multi-STA BlockAck frame to indicate information related to the aperiodic IDC problem it will encounter. In this case, the other frame used to indicate the IDC problem-related information is a broadcast addressed frame that includes information on the IDC problem occurrence start time (TSF (time sync function) value) and the IDC problem duration.

[0398] A non-AP STA that has received information about an IDC issue from its associated (mobile) AP must not attempt to transmit UL frames to the AP during the time the AP is considered to be experiencing an IDC issue. This can be understood as a UL frame transmission restriction that is applied considering that it is self-evident that the AP will fail to receive UL frames while experiencing an IDC issue.

[0399] An AP that indicates (announces) information about an IDC-related problem that it will experience can transmit information indicating whether it wishes to receive a frame for NAV setup (Medium Synchronization recovery procedure) when the IDC problem is completed, together with the frame indicating the IDC problem. When the AP indicates a wish to receive a frame for NAV setup through the frame indicating its IDC-related problem, non-AP STAs that have confirmed this can transmit a short frame including a Duration / ID field at a time when the AP's IDC-related problem is considered to be completed. At this time, the short frame may be a PS-Poll frame, a CTS frame, or a QoS Null frame. At this time, the Duration / ID field of the short frame may be set to 0 or a preset value including an Ack frame response time. For example, a non-AP STA can help the AP configure its NAV by transmitting a QoS Null frame with the Duration / ID subfield set to a preset value (Ack response time (specifically, Ack frame time + SIFS)). The AP, upon receiving the QoS Null frame, transmits an Ack frame in response to the QoS Null frame, and other non-AP STAs receiving the Ack frame can recognize that the AP's NAV configuration is complete (the medium synchronization recovery procedure is complete). Once the completion of the AP's NAV configuration is confirmed, non-AP STAs no longer transmit short frames for NAV configuration.

[0400] When a (mobile) AP that has experienced an IDC problem receives the short frame transmitted by a non-AP STA, the medium synchronization is restored, and it is possible to initiate a frame exchange sequence with non-AP STAs, including the non-AP STA that transmitted the short frame, without additional delay related to the medium synchronization recovery procedure. Meanwhile, the above-described AP's indication of a desire to receive a frame for NAV configuration can be performed indirectly (implicitly). That is, even if the AP announces an IDC-related problem and does not include a separate frame request indicator, it can always be considered that the indication of a desire to receive a frame for NAV configuration has been performed when the AP indicates an IDC-related problem. Accordingly, a non-AP STA that has received IDC-related problem information from an associated AP may need to transmit the short frame (e.g., a QoS Null frame) to the AP at the time when it is determined that the AP's IDC-related problem has been resolved (more precisely, after that time), even if no separate indication has been performed by the AP.

[0401] A Mobile AP STA with a non-zero MediumSyncDelay timer can attempt a medium sync recovery procedure by transmitting an RTS frame or an MU-RTS trigger frame when the backoff procedure is completed using the dot11MSDOFDMEDthreshold. This means that, unlike the recovery procedure of the non-AP STA described above, where only the transmission of the RTS frame was allowed, the transmission of the MU-RTS trigger frame is additionally allowed for the Mobile AP STA. The reason why the transmission of the MU-RTS trigger frame is allowed is that the frame exchange procedure that the Mobile AP wants to perform after recovering medium synchronization may target multiple non-AP STAs.

[0402] <IDC 관련 정보를 포함하는 BSRP 트리거 프레임 활용 조건 및 제한>

[0403] As described above, an STA that receives a BSRP trigger frame requesting a response to IDC-related information can indicate the IDC-related information it is aware of through an M-BA (Multi-STA BlockAck) frame. This behavior of an STA indicating IDC information through a response frame after receiving a BSRP trigger frame is a procedure used to indicate its IDC-related information to an STA that is a TXOP holder when the STA functions as a TXOP responder.

[0404] An STA experiencing an IDC-related issue can, when it initiates a TXOP, indicate the IDC-related information it is aware of to the TXOP responder STA. That is, an STA that is aware that it will transition to an Unavailable state in the future can, when it initiates a TXOP, indicate to the other STA the Unavailable state transition time and maintenance period that it is aware of. If an STA that is a TXOP holder indicates IDC-related information to an STA that is a TXOP responder, an action can be performed that takes into account the state of the STA that was a TXOP responder when it acquired the TXOP (whether it is in an Unavailable state, etc.). As a simple example, if a non-AP STA that is a TXOP holder indicates its future Unavailable start time / time information (i.e., IDC-related information) to an AP that is a TXOP responder, the AP that later acquires the TXOP can perform its frame exchange by taking into account whether the non-AP STA is in an Unavailable state.

[0405] According to one embodiment of the present invention, an AP initiating a TXOP can indicate information about the time point at which it transitions to an Unavailable state and the time period during which it remains in the Unavailable state through a Broadcast (Group) addressed BSRP trigger frame transmitted by the AP. At this time, the AP can transmit the BSRP trigger frame by including a User Info field having a pre-specified AID12 subfield value (e.g., 2008), thereby allowing non-AP STAs receiving the BSRP trigger frame to recognize that the User Info field includes information about the time point and time period during which the AP transitions to Unavailable. That is, among the User Info fields included in the BSRP trigger frame transmitted by the AP, the User Info field in which the AID12 subfield is set to 2008 is a User Info field transmitted to multiple non-AP STAs that have received the trigger frame, and therefore, the non-AP STAs that have confirmed the User Info field in which the AID12 subfield is indicated as 2008 must confirm (receive, decode) the Feedback information of the AP included in the User Info field (i.e., the Unavailable start time and maintenance time, etc.). At this time, if the User Info field indicating the Feedback information of the AP is included in the BSRP trigger frame, it appears in a position ahead of the User Info fields of each non-AP STA that is requested to send a TB PPDU response by the User Info field trigger frame indicating the Unavailable section.As a simple example, when an AP transmits a BSRP trigger frame requesting a TB PPDU response to two non-AP STAs and also indicates its own Unavailable interval information, the User Info field indicating the Unavailable interval information may appear first in the BSRP trigger frame, and then User Info fields corresponding to the two non-AP STAs may appear respectively. At this time, the BSRP trigger frame may additionally include a Special User Info field (a User Info field included in the trigger frame when requesting a response to an EHT / UHR TB PPDU), and when the Special User Info field is included in the trigger frame, the User Info field indicating the Unavailable interval information appears between the Special User Info field and the User Info field corresponding to each non-AP STA.

[0406] The above-mentioned pre-specified AID12 subfield value may be 2008. In this case, the above-mentioned pre-specified AID12 subfield value may be a value greater than or equal to 2008 and less than 2045. A non-AP STA that confirms that the Broadcast (Group) addressed BSRP trigger frame transmitted by the AP includes a User Info field having the above-mentioned pre-specified AID12 subfield value must perform an operation considering that the AP is Unavailable during the time period indicated through the User Info field. That is, the non-AP STA must not attempt to transmit a UL PPDU during the above-mentioned time period. The method by which the Unavailable time period of the AP is indicated through the Broadcast (Group) addressed BSRP trigger frame transmitted by the AP may be similar / identical to the method by which IDC-related information is indicated through the Per AID TID Info field of the above-mentioned M-BA frame. For example, the User Info field, in which a pre-specified value is indicated through the AID12 subfield, may have a configuration including an Unavailable Start Time field and an Unavailable Duration field. The Unavailable Start Time field indicates the TSF value at which the AP transitions to the Unavailable state, and the Unavailable Duration field indicates the length of time the AP remains in the Unavailable state. Since the indication / utilization methods for these two fields are identical to those of the fields (of the same name) included in the Per AID TID Info field of the aforementioned M-BA frame, a detailed explanation will be omitted.

[0407] According to one embodiment of the present invention, a non-AP STA initiating a TXOP can initiate the TXOP by transmitting a BSRP trigger frame including IDC-related information. At this time, an AP that receives the BSRP trigger frame transmitted by the non-AP STA must respond with a response frame (e.g., a Multi-STA BlockAck frame) with a non-HT (duplicate) PPDU. At this time, the BSRP trigger frame transmitted by the non-AP STA has the RA (receiver address) field set to the MAC address of the peer STA. That is, a non-AP STA initiating a TXOP to transmit a UL PPDU sets the RA field of the BSRP trigger frame to the MAC address of the AP with which it is associated. That is, the BSRP trigger frame transmitted by the non-AP STA to indicate IDC-related information is an individually addressed BSRP trigger frame. At this time, the BSRP trigger frame transmitted by the non-AP STA has a configuration including a User Info field indicating IDC-related information. At this time, the User Info field indicating the IDC-related information is set to a pre-specified value (e.g., 2008) in the AID12 subfield. However, a non-AP STA may be able to attempt to acquire a TXOP using a BSRP trigger frame only when there is Unavailable-related information to be indicated to the AP (i.e., the IDC-related information described above). In other words, a non-AP STA may be restricted from transmitting a BSRP trigger frame and initiating a TXOP if it does not have Unavailable-related information to be indicated through the BSRP trigger frame. This may be a BSRP trigger frame transmission restriction considering the original purpose of the BSRP trigger frame defined in 11ax.To explain in more detail, the BSRP trigger frame defined in 11ax was defined to support the AP that plans to transmit the Basic trigger frame to check the Buffer status information of peer STAs, and the basic purpose of utilizing the BSRP trigger frame is to efficiently operate the UL MU frame exchange sequence. Therefore, a non-AP STA is not allowed to transmit the BSRP trigger frame indiscriminately, and transmission may be permitted only when it initiates a TXOP while indicating its Unavailable status related information to the AP. That is, the BSRP trigger frame transmitted by a non-AP STA to the ICF always has a structure that includes Unavailable status related information (Unavailable Start Time subfield (or Unavailability Target Start Time subfield), Unavailable Duration subfield (or Unavailability Duration subfield)).

[0408] The method by which IDC-related information is indicated through the User Info field included in the BSRP trigger frame may be similar / identical to the method by which IDC-related information is indicated through the Per AID TID Info field of the aforementioned M-BA frame. For example, among the User Info fields included in the BSRP trigger frame, the User Info field including IDC-related information (e.g., the User Info field with the AID12 subfield of 2008) may have a structure including an Unavailable Start Time field and an Unavailable Duration field. The Unavailable Start Time field indicates the TSF value at the time when the IDC-related problem starts, and the Unavailable Duration field indicates the length of time the IDC-related problem persists. In this case, since the two fields are identical in indication / utilization method to the fields (of the same name) included in the Per AID TID Info field of the aforementioned M-BA frame, a detailed description thereof will be omitted.

[0409] FIG. 26 illustrates an example in which a non-AP STA initiating a TXOP transmits a BSRP trigger frame including IDC related information, according to one embodiment of the present invention.

[0410] Referring to FIG. 26, a non-AP STA transmits a BSRP trigger frame to the AP after completing a channel access procedure. The BSRP trigger frame transmitted to the AP includes IDC-related information of the non-AP STA. In the example illustrated in FIG. 20, the indicated IDC-related information is that the time point of transition to Unavailable is t and the time of remaining Unavailable is x us. The Duration field of the BSRP trigger frame transmitted by the non-AP STA is set to a value indicating T_NAV, which is a time point earlier than t, and therefore the TXOP of the non-AP STA ends before the non-AP STA transitions to Unavailable. The AP, which has acquired the Unavailable transition time point and retention time information of the non-AP STA, can recognize that the non-AP STA1 is in the Unavailable state during the TXOP it has acquired, and therefore does not transmit a frame destined for the non-AP STA.

[0411] Channel Access of non-AP STAs transmitting BSRP trigger frames>

[0412] As described above, an AP may transmit an Individually addressed BSRP trigger frame (a BSRP TF targeted at a single non-AP STA) for the purpose of requesting a response of IDC-related information, and a non-AP STA may transmit an Individually addressed BSRP trigger frame (a BSRP TF targeted at the AP) for the purpose of indicating its IDC-related information.

[0413] The BSRP trigger frame can be used to request a response to IDC-related information or to indicate IDC-related information, but it can also be used for other purposes. For example, an STA initiating a TXOP can request that the other STA respond with a type of feedback information other than IDC-related information through the BSRP trigger frame, or an STA initiating a TXOP can transmit a BSRP trigger frame for the purpose of indicating various types of feedback information to the other STA. For example, an AP transmits a BSRP trigger frame for the purpose of allowing responses with various types of feedback information, and a non-AP STA receiving this can further indicate whether it has low-latency traffic (i.e., the presence of buffered low-latency traffic) in addition to its own IDC-related information.

[0414] In addition, the BSRP trigger frame is considered as an ICF (Initial Control frame) transmitted to non-AP STAs operating in various modes such as EMLSR (Enhanced Multi-Link Single Radio), DPS (Dynamic Power Save), NPCA (Non-primary Channel Access), and DSO (Dynamic Sub-band Operation) mode, and the frame exchange sequence initiated when the AP transmits the BSRP trigger frame can proceed in a form in which the AP can transmit a DL PPDU.

[0415] Similarly, a non-AP STA performing NPCA operation transmits a BSRP trigger frame as an Initial Control frame when a channel access procedure performed on a non-primary channel (a 20 MHz subchannel other than the primary 20 MHz subchannel) is completed. In this case, the BSRP trigger frame may not include IDC-related information.

[0416] As such, in the embodiments of the present invention described above, the BSRP trigger frame is mainly considered to be used to request a response of IDC-related information or to indicate IDC-related information through the BSRP trigger frame, but the BSRP trigger frame can be transmitted for various purposes (such as requesting and indicating various feedback information or initiating various operation modes). An STA that transmits a BSRP trigger frame and initiates a TXOP must determine the Access Category to use when transmitting the BSRP trigger frame based on the nature of the scheduled operation (e.g., whether to transmit a QoS Data frame) during the TXOP (frame exchange) initiated through the BSRP trigger frame, regardless of the purpose of transmitting the BSRP trigger frame. Alternatively, an STA that obtains a TXOP by using the BSRP trigger frame as an ICF must determine the TID of the QoS Data frame to be transmitted within the TXOP based on the Access Category used when transmitting the BSRP trigger frame. At this time, the BSRP trigger frame transmitted to the ICF is transmitted alone, without being aggregated with other frames. In other words, the PPDU containing the BSRP trigger frame transmitted to the ICF does not contain any frames other than the BSRP trigger frame. Therefore, in the description below, the rules related to the Access Category applied when transmitting the BSRP trigger frame are applied to the PPDU containing the BSRP trigger frame.

[0417] For an AP, if the frame exchange sequence initiated by the BSRP trigger frame it transmits includes the transmission of a DL PPDU (containing a QoS Data frame), it must transmit the BSRP trigger frame after performing channel access through the AC corresponding to the TID of the QoS Data frame included in the DL PPDU. However, if the DL PPDU that the AP wants to transmit is intended for multiple STAs, the AP can transmit the BSRP trigger frame (i.e., the PPDU containing the BSRP trigger frame) using Any AC. Therefore, an AP that initiates a TXOP by transmitting an Individually addressed BSRP trigger frame must transmit the BSRP trigger frame using the Access Category corresponding to the TID of the QoS Data frame if there is a QoS Data frame to be transmitted within the TXOP that it initiated. If the frame exchange sequence initiated by the BSRP trigger frame does not include a QoS Data frame to be transmitted in the downlink, the AP may not be restricted by the Access Category when transmitting the BSRP trigger frame. That is, the AP can transmit a BSRP trigger frame using Any AC if the frame exchange sequence (TXOP) initiated by the BSRP trigger frame does not include a downlink QoS Data frame transmission.

[0418] When such restrictions are applied, an AP that acquires a TXOP by transmitting an individually addressed BSRP trigger frame to the ICF must restrict the types of QoS Data frames transmitted within the TXOP based on the Access Category used when transmitting the individually addressed BSRP trigger frame. The specific frame restriction method is as follows.

[0419] 1. When transmitting an individually addressed BSRP trigger frame, only the QoS Data frame of the Access Category (i.e., Primary AC) used is transmitted.

[0420] Exceptionally, for an AP transmitting a DL MU PPDU destined for multiple non-AP STAs, it can transmit QoS Data frames without AC-related restrictions (i.e., transmit frames for Any AC).

[0421] 2. If at least one frame satisfying condition 1 has been transmitted and there are no more frames satisfying condition 1, a frame of an access category (secondary AC) with a higher priority than the primary AC is transmitted. However, the TXOP limit of the primary AC must not be exceeded due to additionally transmitted frames of the secondary AC.

[0422] A non-AP STA may transmit an Individually addressed BSRP trigger frame even if it does not intend to transmit a QoS Data frame, and in this case, the transmitted Individually addressed BSRP trigger frame includes IDC-related information instructing the AP. In this case, the non-AP STA may transmit the Individually addressed BSRP trigger frame to the AP using Any AC. Alternatively, a non-AP STA that transmits an Individually addressed BSRP trigger frame even if it does not intend to transmit a QoS Data frame may be required to use a pre-designated Access Category (e.g., AC_BE or AC_VI) when transmitting the trigger frame.

[0423] When a non-AP STA is to transmit a QoS Data frame using a frame exchange sequence (TXOP) initiated by an Individually addressed BSRP trigger frame, the non-AP STA must transmit the Individually addressed BSRP trigger frame using an Access Category corresponding to the TID of the QoS Data frame that it is to transmit. That is, a non-AP STA that transmits an Individually addressed BSRP trigger frame to an ICF must select / decide an Access Category to use when transmitting the Individually addressed BSRP trigger frame based on the Access Category corresponding to the TID of the QoS Data frame that it is to transmit. In this case, a non-AP STA that transmits an Individually addressed BSRP trigger frame using a specific AC must transmit only the QoS Data frame of the specific AC (Primary AC) within the acquired TXOP (i.e., a QoS Data frame having a TID corresponding to the Primary AC). At this time, if the non-AP STA has transmitted all frames of the AC (i.e., Primary AC) used when transmitting the Individually addressed BSRP trigger frame, it is possible to transmit frames of an AC having a higher priority than the said AC (Primary AC). In addition, if the non-AP STA has transmitted all frames of the AC (i.e., Primary AC) used when transmitting the Individually addressed BSRP trigger frame and frames of an AC having a higher priority than the Primary AC, it may be permitted to additionally transmit frames of an AC having a lower priority than the Primary AC.However, non-AP STAs must ensure that the TXOP limit of the Primary AC is not exceeded by frames corresponding to ACs other than the Primary AC's frames.

[0424] FIG. 27 illustrates an example of a method for determining an Access Category (AC) used when a non-AP STA initiating a TXOP transmits an Individually addressed BSRP trigger frame, according to one embodiment of the present invention.

[0425] Referring to FIG. 27, a non-AP STA acquires TXOP twice after completing the backoff procedure.

[0426] The first TXOP (TXOP#1) acquired by a non-AP STA is a TXOP initiated to indicate IDC-related information using an individually addressed BSRP trigger, and the non-AP STA does not transmit a QoS Data frame through the first TXOP. Therefore, the non-AP STA transmits an individually addressed BSRP trigger frame using any AC (any one of AC_VO, AC_VI, AC_BE, and AC_BK).

[0427] A non-AP STA transmits a PPDU including a QoS Data frame using the second TXOP (TXOP#2) that it has confirmed. At this time, the Access Category corresponding to the TID of the QoS Data frame transmitted by the non-AP STA is AC_BE. Therefore, when the non-AP STA transmits an Individually addressed BSRP trigger frame, which is an ICF, it transmits the Individually addressed BSRP trigger frame using AC_BE, which is the Access Category corresponding to the QoS Data frame that it wants to transmit. A non-AP STA that has transmitted an Individually addressed BSRP trigger frame using AC_BE transmits the frame of AC_BE within the acquired TXOP, and although not shown in FIG. 21, after transmitting all frames of AC_BE, it can further transmit frames of AC_VO or AC_VI, which are ACs having a higher priority than AC_BE.

[0428] FIG. 28 is a flowchart showing an example of a frame exchange procedure performed by a terminal according to an embodiment of the present invention.

[0429] Referring to Figure 28, if a terminal includes a heterogeneous network interface in addition to Wi-Fi, interference from the heterogeneous network may occur. In this case, the terminal may transmit information related to the interference caused by the heterogeneous network to the counterpart terminal, and the AC of the PPDU containing the trigger frame transmitted from the counterpart terminal may be limited by the AC of the PPDU transmitted subsequently.

[0430] Specifically, the first STA may receive a trigger frame from the second STA that instructs the first STA to transmit a frame (S28010), and transmit a multi-STA block acknowledgment frame in response to the trigger frame (S28020).

[0431] Thereafter, the first STA may receive a physical layer protocol data unit (PPDU) from the second STA based on the multi-STA block response frame (S28030). At this time, the access category (AC) used for transmission of the trigger frame may be identical to the AC corresponding to the TID of the medium access control protocol data unit (MPDU) included in the PPDU.

[0432] The first STA may include a heterogeneous network interface in addition to Wi-Fi. In this case, if the first STA uses the same frequency band (e.g., an unlicensed band) as the heterogeneous network, interference may occur due to the heterogeneous network. Throughout the present invention, a mode in which data transmission and reception operations cannot be dynamically utilized due to interference from the heterogeneous network may be referred to as DUO mode. In other words, the first STA may support a specific operating mode in which transmission and reception are restricted due to communication via another communication interface.

[0433] A multi-STA block response frame may include a Per AID TID information subfield that includes an Association Identifier (AID) Traffic Identifier (TID) information subfield and a Block Acknowledgement bitmap subfield.

[0434] When the AID TID subfield is set to a preset value indicating that the block response bitmap subfield includes i) start time information of a section in which transmission and reception are restricted due to a specific operation mode and ii) duration information of the section in which transmission and reception are restricted due to a specific operation mode, the block response bitmap subfield may include start time information and duration information.

[0435] When a transmission opportunity (TXOP) is established by a trigger frame and the duration of the TXOP and the period of a specific operation mode overlap, transmission and reception of the first STA are not performed during the overlapping period.

[0436] When TXOP is set by a trigger frame, the end point of the duration of TXOP may be i) the same as the end point of the section in which transmission and reception are restricted by a specific operation mode, or ii) within the duration of the specific operation mode, the end point of the duration of the TXOP may be the same as or reduced to before the start point of the specific operation mode.

[0437] When a specific operation mode is applied, the timer for channel sensing may be started after the period in which transmission and reception are restricted by the specific operation mode has ended.

[0438] When a specific operation mode is applied, the first STA can receive a frame for setting a network allocation vector (NAV) from the second STA and set the NAV based on the received frame.

[0439] The first STA may transmit a first management frame to the second STA before transmitting the trigger frame. At this time, the first management frame may include a UL MU (uplink multi-user) disabled subfield indicating whether uplink transmission for the trigger frame is possible.

[0440] If the value of the UL MU disabled subfield is set to a value indicating impossibility of the uplink transmission for the trigger frame, the trigger frame may indicate the format of the PPDU including the multi-STA block response frame as a non-HT (high throughput) PPDU format. However, if the value of the UL MU disabled subfield is set to a value indicating possibility of the uplink transmission for the trigger frame, the trigger frame may indicate the format of the PPDU including the multi-STA block response frame as a TB PPDU format or the non-HT (high throughput) PPDU format.

[0441] Before transmitting the trigger frame, the first STA may transmit to the second STA i) a first management frame including an UL MU (uplink multi-user) disabled subfield indicating whether uplink transmission for the trigger frame is possible, and ii) a second management frame including a specific subfield indicating whether the specific operation mode is supported. In this case, if the value of the specific subfield indicates support for the specific operation mode, the value of the UL MU disabled subfield may be set to a value indicating the possibility of the uplink transmission.

[0442] In addition, when the first STA according to the present invention is a non-AP STA, the non-AP STA can transmit a trigger frame to an access point (AP) and receive a block acknowledgment frame in response to the trigger frame.

[0443] At this time, if there is no QoS data frame transmitted by the non-AP STA within the TXOP by the trigger frame after the trigger frame, the trigger frame may be transmitted to the AP using any one of a plurality of access categories (ACs).

[0444]

[0445] 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.

[0446] 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. As the first station (STA), Transmitter and receiver; and Contains a processor, The above processor, Receive a trigger frame from the second STA that instructs the first STA to transmit a frame, In response to the above trigger frame, a multi-STA Block Acknowledgement frame is transmitted, Receive a physical layer protocol data unit (PPDU) from the second STA based on the multi-STA block response frame, The access category (AC) used for transmission of the above trigger frame is the same STA as the AC corresponding to the TID of the MPDU (medium access control protocol data unit) included in the PPDU.

2. In paragraph 1, The above first STA is an STA that supports a specific operation mode in which transmission and reception are restricted due to communication of another communication interface.

3. In paragraph 2, The above multi-STA block response frame includes a Per AID TID information subfield including an Association Identifier (AID) TID (Traffic identifier) ​​information subfield and a Block Acknowledgement bitmap subfield, When the AID TID subfield is set to a preset value indicating that i) start time information of a section in which transmission and reception are restricted due to the specific operation mode and ii) duration information of the section in which transmission and reception are restricted due to the specific operation mode are included in the block response bitmap subfield, the block response bitmap subfield is an STA including the start time information and the duration information.

4. In paragraph 3, An STA in which a transmission opportunity (TXOP) is set by the trigger frame and the duration of the TXOP and the period of the specific operation mode overlap, and transmission and reception of the first STA are not performed in the overlapping period.

5. In the third paragraph, if TXOP is set by the trigger frame, An STA in which the end point of the duration of the TXOP is i) the same as the end point of the section in which transmission and reception are restricted by the specific operation mode, or ii) within the duration of the specific operation mode, the end point of the duration of the TXOP is the same as or reduced to before the start point of the specific operation mode.

6. In paragraph 3, When the above specific operation mode is applied, the timer for channel sensing is started by the STA after the period in which transmission and reception are restricted by the above specific operation mode ends.

7. In the third paragraph, the processor, When the above specific operation mode is applied, a frame for setting a network allocation vector (NAV) is received from the second STA, An STA that sets the NAV based on the received frame.

8. In the first paragraph, the processor, Transmitting a first management frame to the second STA, The above first management frame includes a UL MU (uplink multi-user) disabled subfield indicating whether uplink transmission for the trigger frame is possible.

9. In paragraph 8, If the value of the UL MU disabled subfield is set to a value indicating impossibility of the uplink transmission for the trigger frame, the trigger frame indicates the format of the PPDU including the multi-STA block response frame as a non-HT (high throughput) PPDU format, If the value of the UL MU disabled subfield is set to a value indicating the possibility of the uplink transmission for the trigger frame, the trigger frame is an STA that indicates the format of the PPDU including the multi-STA block response frame as a TB PPDU format or the non-HT (high throughput) PPDU format.

10. In the second paragraph, the processor, Transmitting to the second STA i) a first management frame including a UL MU (uplink multi-user) disabled subfield indicating whether uplink transmission for a trigger frame is possible, and ii) a second management frame including a specific subfield indicating whether the specific operation mode is supported, An STA in which the value of the UL MU disabled subfield is set to a value indicating the possibility of uplink transmission, when the value of the specific subfield indicates support of the specific operation mode.

11. In a method performed by a first station (STA), the method comprises: A step of receiving a trigger frame from a second STA that instructs the first STA to transmit a frame; A step of transmitting a multi-STA Block Acknowledgement frame in response to the trigger frame; and A step of receiving a physical layer protocol data unit (PPDU) from the second STA based on the multi-STA block response frame, The access category (AC) used for transmission of the above trigger frame is the same as the AC corresponding to the TID of the MPDU (medium access control protocol data unit) included in the PPDU.

12. In paragraph 11, A method in which the above first STA supports a specific operation mode in which transmission and reception are restricted due to communication of another communication interface.

13. In paragraph 12, The above multi-STA block response frame includes a Per AID TID information subfield including an Association Identifier (AID) TID (Traffic identifier) ​​information subfield and a Block Acknowledgement bitmap subfield, A method in which the block response bitmap subfield includes the start time information and the duration information when the AID TID subfield is set to a preset value indicating that i) start time information of a section in which transmission and reception are restricted due to the specific operation mode and ii) duration information of the section in which transmission and reception are restricted due to the specific operation mode are included in the block response bitmap subfield.

14. In paragraph 13, A method in which a transmission opportunity (TXOP) is set by the trigger frame and the duration of the TXOP and the period of the specific operation mode overlap, and transmission and reception of the first STA are not performed in the overlapping period.

15. In the third paragraph, if TXOP is set by the trigger frame, A method in which the end point of the duration of the TXOP is i) the same as the end point of the section in which transmission and reception are restricted by the specific operation mode, or ii) within the duration of the specific operation mode, the end point of the duration of the TXOP is the same as or reduced to before the start point of the specific operation mode.

16. In paragraph 13, When the above specific operation mode is applied, the timer for channel sensing is started after the section in which transmission and reception are restricted by the above specific operation mode ends.

17. In the 13th paragraph, the method, When the above specific operation mode is applied, a step of receiving a frame for setting a network allocation vector (NAV) from the second STA; and A method further comprising the step of setting the NAV based on the received frame.

18. In the 11th paragraph, the method, Further comprising a step of transmitting a first management frame to the second STA, A method wherein the first management frame includes an UL MU (uplink multi-user) disabled subfield indicating whether uplink transmission for a trigger frame is possible.

19. In paragraph 18, If the value of the UL MU disabled subfield is set to a value indicating impossibility of the uplink transmission for the trigger frame, the trigger frame indicates the format of the PPDU including the multi-STA block response frame as a non-HT (high throughput) PPDU format, A method in which, when the value of the UL MU disabled subfield is set to a value indicating the possibility of the uplink transmission for the trigger frame, the trigger frame indicates the format of the PPDU including the multi-STA block response frame as a TB (trigger based) PPDU format or the non-HT PPDU format.

20. In the 12th paragraph, the method, Further comprising the step of transmitting to the second STA i) a first management frame including a UL MU (uplink multi-user) disabled subfield indicating whether uplink transmission for a trigger frame is possible, and ii) a second management frame including a specific subfield indicating whether the specific operation mode is supported, A method in which the value of the UL MU disabled subfield is set to a value indicating the possibility of uplink transmission when the value of the specific subfield indicates support of the specific operation mode.

21. As a non-AP STA (non-access point stat), Transmitter and receiver; and Contains a processor, The above processor, Transmit a trigger frame to the AP (access point), In response to the above trigger frame, a block acknowledgment frame is received, If there is no QoS data frame transmitted by the non-AP STA within the TXOP by the trigger frame after the trigger frame, the trigger frame is transmitted to the AP by the non-AP STA using one of a plurality of access categories (AC).

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