Method and apparatus for supporting synchronization of AP mld in wireless LAN system

Abstract

The present disclosure relates to an improved wireless LAN system. A method performed by an AP in a wireless LAN system of the present disclosure comprises the steps of: transmitting, to an STA, a first frame for requesting transmission of a second frame related to medium synchronization on a first link; and receiving, from the STA, the second frame on the first link at a time when the first link is activated.

Description

Method and device for supporting synchronization of AP MLD in a wireless LAN system

[0001] The present disclosure relates to a wireless local area network (WLAN) system. Specifically, the present disclosure relates to a method and device for supporting synchronization of an access point (AP) and a multi-link device (MLD) in a WLAN system.

[0002] Wireless LAN (WLAN) systems are evolving for various purposes, such as improving transmission rates, increasing bandwidth, enhancing reliability, reducing errors, and reducing latency. The Institute of Electrical and Electronics Engineers (IEEE) publishes the 802.11 standard specification for WLAN systems, and the technology described in the 802.11 standard specification can be called WiFi (or Wi-Fi, Wireless Fidelity).

[0003] Wi-Fi technology has evolved over several generations of the 802.11 standard. For example, the 802.11ac standard addresses improvements for very high throughput (VHT), the 802.11ax standard addresses improvements for high efficiency (HE), and the 802.11be standard addresses improvements for extreme high throughput (EHT).

[0004] Meanwhile, technologies to provide a more improved wireless communication environment in wireless LAN systems are being discussed, and various technologies are being proposed and researched in response to the demand to further increase the reliability of wireless LAN systems.

[0005] The present disclosure proposes a method and device for supporting synchronization between an access point (AP) and a multi-link device (MLD) in a wireless LAN system. In particular, the present disclosure proposes procedures for an AP to request a station (STA) to transmit an assisting frame for synchronization at a specific time, and for the STA to transmit the assisting frame during link switching. The present disclosure also proposes a field structure for requesting an assisting frame.

[0006] The technical objectives to be achieved in the present disclosure are not limited to those mentioned above, and other technical tasks not mentioned can be considered by a person having ordinary skill in the art to which the present invention pertains from the embodiments of the present invention described below.

[0007] According to one embodiment of the present disclosure, a method performed by an access point (AP) of a wireless local area network (WLAN) system comprises the steps of: transmitting, to a station (STA), a first frame for requesting transmission of a second frame related to medium synchronization; and receiving, from the STA, the second frame at a time when a link is enabled based on the first frame, wherein the first frame includes an initial control frame (ICF), and the second frame includes a MAC protocol data unit (MPDU) or a physical layer protocol data unit (PPDU) having a duration of a transmission opportunity (TXOP) determined.

[0008] According to one embodiment of the present disclosure, a method performed by a station (STA) of a wireless local area network (WLAN) system comprises the steps of: receiving, from an access point (AP), a first frame for requesting transmission of a second frame related to medium synchronization; and transmitting, to the AP, the second frame at a time when a link is enabled based on the first frame, wherein the first frame includes an initial control frame (ICF), and the second frame includes a MAC protocol data unit (MPDU) or a physical layer protocol data unit (PPDU) having a duration of a transmission opportunity (TXOP).

[0009] According to one embodiment of the present disclosure, an access point (AP) of a wireless local area network (WLAN) system includes a transceiver and at least one processor connected to the transceiver, wherein the at least one processor comprises a step of transmitting a first frame to a station (STA) for requesting transmission of a second frame related to medium synchronization, and a step of receiving the second frame from the STA at a time when a link is enabled based on the first frame, wherein the first frame includes an initial control frame (ICF), and the second frame includes a MAC protocol data unit (MPDU) or a physical layer protocol data unit (PPDU) having a duration of a transmission opportunity (TXOP).

[0010] According to one embodiment of the present disclosure, a station (STA) of a wireless local area network (WLAN) system comprises a transceiver and at least one processor connected to the transceiver, wherein the at least one processor comprises a step of receiving, from an access point (AP), a first frame for requesting transmission of a second frame related to medium synchronization, and a step of transmitting, to the AP, the second frame at a time when a link is enabled based on the first frame, wherein the first frame includes an initial control frame (ICF), and the second frame includes a MAC protocol data unit (MPDU) or a physical layer protocol data unit (PPDU) having a duration of a transmission opportunity (TXOP).

[0011] According to various embodiments proposed in this disclosure, by receiving auxiliary frames in time with link switching in a wireless LAN system, an AP can quickly achieve medium synchronization. Furthermore, an STA can reduce resource waste by transmitting data along with the auxiliary frames.

[0012] FIG. 1 illustrates a configuration of a device for wireless communication according to one embodiment of the present disclosure.

[0013] FIG. 2 illustrates an exemplary structure of a wireless LAN system related to the present disclosure.

[0014] Figure 3 illustrates a link setup process related to the present disclosure.

[0015] Figure 4 illustrates a backoff operation related to the present disclosure.

[0016] FIG. 5 illustrates a frame transmission operation based on CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) in connection with the present disclosure.

[0017] FIG. 6 illustrates an exemplary format of a frame used in a wireless LAN system related to the present disclosure.

[0018] FIG. 7 illustrates an exemplary format of a physical layer protocol data unit (PPDU) of a wireless LAN system related to the present disclosure.

[0019] FIG. 8 illustrates another exemplary format of a PPDU of a wireless LAN system related to the present disclosure.

[0020] FIG. 9 illustrates multi-link operation (MLO) in connection with the present disclosure.

[0021] FIG. 10 illustrates an AP operation cycle based on target wakeup time (TWT) in connection with the present disclosure.

[0022] FIG. 11 illustrates an example of synchronization loss and recovery in a multi-link in connection with the present disclosure.

[0023] FIG. 12 illustrates an example of a synchronization acquisition method based on SAR (STA-assisted medium synchronization recovery) according to one embodiment of the present disclosure.

[0024] FIG. 13 illustrates an exemplary format of a subfield for a SAR request according to one embodiment of the present disclosure.

[0025] FIG. 14 illustrates an exemplary format of an enhanced distributed channel access (EDCA) parameter subfield according to one embodiment of the present disclosure.

[0026] FIG. 15 illustrates an exemplary format of a subfield for a SAR response according to one embodiment of the present disclosure.

[0027] FIG. 16 illustrates an example of a SAR-based synchronization acquisition method according to one embodiment of the present disclosure.

[0028] FIG. 17 illustrates an exemplary format of a subfield for a SAR request based on TWT according to one embodiment of the present disclosure.

[0029] FIG. 18 illustrates an example of a SAR-based synchronization acquisition method according to one embodiment of the present disclosure.

[0030] FIG. 19 illustrates an example of a SAR-based synchronization acquisition method according to one embodiment of the present disclosure.

[0031] FIG. 20 illustrates an exemplary format of a SAR control subfield according to one embodiment of the present disclosure.

[0032] FIG. 21 illustrates an example of a SAR-based synchronization acquisition method according to one embodiment of the present disclosure.

[0033] FIG. 22 illustrates a flowchart of a SAR-based synchronization acquisition operation in a wireless LAN system according to an embodiment of the present disclosure.

[0034] FIG. 23 illustrates a flowchart of a SAR-based synchronization acquisition operation in a wireless LAN system according to an embodiment of the present disclosure.

[0035] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the attached drawings. It should be noted that, where possible, identical components are represented by identical reference numerals throughout the attached drawings. Furthermore, detailed descriptions of well-known functions and configurations that may obscure the gist of the present disclosure will be omitted.

[0036] In describing the embodiments in this specification, descriptions of technical details that are well known in the technical field to which the present disclosure pertains and are not directly related to the present disclosure will be omitted. This is to avoid obscuring the gist of the present disclosure by omitting unnecessary explanations and to convey the gist more clearly.

[0037] For the same reason, some components in the attached drawings are exaggerated, omitted, or schematically depicted. Furthermore, the dimensions of each component do not entirely reflect its actual size.

[0038] The advantages and features of the present disclosure, and methods for achieving them, will become clearer with reference to the embodiments described below in detail with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various different forms. These embodiments are provided solely to ensure that the disclosure is complete and to fully inform those skilled in the art of the scope of the disclosure, and the present disclosure is defined solely by the scope of the claims.

[0039] At this time, it will be understood that each block of the flowchart drawings and combinations of the flowchart drawings can be performed by computer program instructions. These computer program instructions can be installed in a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing equipment, so that the instructions executed by the processor of the computer or other programmable data processing equipment create a means for performing the functions described in the flowchart block(s). These computer program instructions can also be stored in a computer-available or computer-readable memory that can direct a computer or other programmable data processing equipment to implement the functions in a specific manner, so that the instructions stored in the computer-available or computer-readable memory can also produce a manufactured item that includes an instruction means for performing the functions described in the flowchart block(s). Since the computer program instructions may be installed on a computer or other programmable data processing device, a series of operational steps may be performed on the computer or other programmable data processing device to create a computer-executable process, and the instructions that cause the computer or other programmable data processing device to perform the steps for performing the functions described in the flowchart block(s) may also provide steps for performing the functions described in the flowchart block(s).

[0040] Additionally, each block may represent a module, segment, or portion of code that contains one or more executable instructions for performing a specific logical function(s). It should also be noted that in some alternative implementation examples, the functions described in the blocks may occur out of order. For example, two blocks depicted in succession may actually be executed substantially concurrently, or the blocks may sometimes be executed in reverse order, depending on their respective functions.

[0041] Here, the term '~ unit' used in the present embodiment means a software or hardware component such as an FPGA or ASIC, and the '~ unit' performs certain roles. However, the '~ unit' is not limited to software or hardware. The '~ unit' may be configured to be on an addressable storage medium and may be configured to play one or more processors. Accordingly, as an example, the '~ unit' includes components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and '~ units' may be combined into a smaller number of components and '~ units' or further separated into additional components and '~ units'. Additionally, components and '~parts' may be implemented to regenerate one or more CPUs within a device or secure multimedia card.

[0042] In the present disclosure, when a component is said to be "connected," "coupled," or "connected" to another component, this may include not only a direct connection but also an indirect connection in which another component exists between them. Furthermore, the terms "comprises" or "has" in the present disclosure specify the presence of the mentioned features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0043] In this disclosure, terms such as “first,” “second,” etc. are used only to distinguish one component from another, are not used to limit the components, and do not limit the order or importance of the components unless specifically stated otherwise. Accordingly, within the scope of this disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

[0044] The terminology used herein is for the purpose of describing particular embodiments and is not intended to limit the scope of the claims. As used in the description of the embodiments and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. The term "and / or" as used herein may refer to any one of the associated enumerated items, or is meant to refer to and encompass any and all possible combinations of two or more of them. Furthermore, the use of " / " between words in this disclosure has the same meaning as "and / or" unless otherwise stated.

[0045] The examples of the present disclosure can be applied to various wireless communication systems. For example, the examples of the present disclosure can be applied to a wireless LAN system. For example, the examples of the present disclosure can be applied to a wireless LAN system based on the IEEE 802.11a / g / n / ac / ax / be standards. Furthermore, the examples of the present disclosure can be applied to a wireless LAN system based on the newly discussed IEEE 802.11bn (or UHR (ultra high reliability)) standards. Furthermore, the examples of the present disclosure can be applied to a wireless LAN system based on the next-generation standards after IEEE 802.11bn.

[0046] Additionally, examples of the present disclosure may be applied to cellular wireless communication systems. For example, examples of the present disclosure may be applied to cellular wireless communication systems based on Long Term Evolution (LTE), LTE-Advanced (LTE-A), and New Radio (NR) technologies based on 3rd Generation Partnership Project (3GPP) standard documents.

[0047] FIG. 1 illustrates a configuration of a device for wireless communication according to one embodiment of the present disclosure.

[0048] The first device (100) and the second device (200) of FIG. 1 may be replaced with various terms such as terminal, wireless device, WTRU (Wireless Transmit and Receive Unit), UE (User Equipment), MS (Mobile Station), UT (user terminal), MSS (Mobile Subscriber Station), MSS (Mobile Subscriber Unit), SS (Subscriber Station), AMS (Advanced Mobile Station), WT (Wireless terminal), client terminal, or simply user.

[0049] In addition, the first device (100) and the second device (200) may be replaced with various terms such as access point (AP), base station (BS), fixed station, Node B, base transceiver system (BTS), network, artificial intelligence (AI) system, road side unit (RSU), repeater, router, relay, gateway, etc.

[0050] The devices (100, 200) illustrated in FIG. 1 may also be referred to as stations (STAs). For example, the devices (100, 200) illustrated in FIG. 1 may be referred to by various terms such as transmitting device, receiving device, transmitting STA, and receiving STA. For example, the STAs (110, 200) may perform an AP (access point) role or a non-AP role. That is, in the present disclosure, the STAs (110, 200) may perform the functions of an AP and / or a non-AP. When the STAs (110, 200) perform an AP function, they may simply be referred to as APs, and when the STAs (110, 200) perform a non-AP function, they may simply be referred to as STAs. In addition, in the present disclosure, the APs may also be referred to as AP STAs.

[0051] Referring to FIG. 1, the first device (100) and the second device (200) can transmit and / or receive wireless signals through various wireless LAN technologies (e.g., technologies based on the IEEE 802.11 standard document). The first device (100) and the second device (200) can include interfaces for a medium access control (MAC) layer and a physical (PHY) layer that follow the regulations of the IEEE 802.11 standard document.

[0052] In addition, the first device (100) and the second device (200) may additionally support various wireless communication technologies other than wireless LAN technology (for example, technologies based on 3GPP LTE, LTE-A, or NR standard documents). In addition, the devices of the present disclosure may be implemented as various devices such as mobile phones, vehicles, personal computers, AR (Augmented Reality) equipment, VR (Virtual Reality) equipment, etc. In addition, the STA of the present specification may support various communication services such as voice calls, video calls, data communications, autonomous driving, MTC (Machine-Type Communication), M2M (Machine-to-Machine), D2D (Device-to-Device), and IoT (Internet-of-Things).

[0053] A first device (100) includes one or more processors (102) and one or more memories (104), and may further include one or more transceivers (or transceivers) (106) and / or one or more antennas (108). The processor (102) controls the memories (104) and / or the transceivers (106), and may be configured to implement the descriptions, functions, procedures, proposals, methods, and / or operational flowcharts disclosed in the present disclosure. For example, the processor (102) may process information in the memories (104) to generate first information and / or a first signal, and then transmit a wireless signal including the first information and / or the first signal via the transceivers (106). In addition, the processor (102) may receive a wireless signal including second information and / or a second signal through the transceiver (106), and then store information obtained through signal processing of the second information and / or the second signal in the memory (104). The memory (104) may be connected to the processor (102) and may store various information related to the operation of the processor (102). For example, the memory (104) may perform some or all of the processes controlled by the processor (102), or may store software code including instructions for performing the descriptions, functions, procedures, proposals, methods, and / or operation flowcharts disclosed in the present disclosure. Here, the processor (102) and the memory (104) may be part of a communication modem / circuit / chip designed to implement a wireless LAN technology (e.g., a technology based on the IEEE 802.11 document). A transceiver (106) may be connected to the processor (102) and may transmit and / or receive wireless signals via one or more antennas (108). The transceiver (106) may include a transmitter and / or a receiver. The transceiver (106) may be used interchangeably with an RF (Radio Frequency) unit.

[0054] The second device (200) includes one or more processors (202) and one or more memories (204), and may further include one or more transceivers (or transceiver units) (206) and / or one or more antennas (208). The processor (202) controls the memories (204) and / or the transceivers (206), and may be configured to implement the descriptions, functions, procedures, proposals, methods, and / or operational flowcharts disclosed in the present disclosure. For example, the processor (202) may process information in the memories (204) to generate third information and / or a third signal, and then transmit a wireless signal including the third information and / or the third signal via the transceivers (206). In addition, the processor (202) may receive a wireless signal including the fourth information and / or the fourth signal through the transceiver (206), and then store information obtained through signal processing of the fourth information and / or the fourth signal in the memory (204). The memory (204) may be connected to the processor (202) and may store various information related to the operation of the processor (202). For example, the memory (204) may perform some or all of the processes controlled by the processor (202), or store software code including instructions for performing the descriptions, functions, procedures, proposals, methods, and / or operation flowcharts disclosed in the present disclosure. Here, the processor (202) and the memory (204) may be part of a communication modem / circuit / chip designed to implement a wireless LAN technology (e.g., a technology based on the IEEE 802.11 document). A transceiver (206) may be connected to the processor (202) and may transmit and / or receive wireless signals via one or more antennas (208). The transceiver (206) may include a transmitter and / or a receiver. The transceiver (206) may be used interchangeably with an RF unit.

[0055] Hereinafter, hardware elements of the device (100, 200) will be described in more detail. Although not limited to the following, operations of one or more protocol layers may be implemented by one or more processors (102, 202). For example, one or more processors (102, 202) may implement operations of one or more layers (e.g., functional layers such as PHY, MAC). One or more processors (102, 202) may generate one or more Protocol Data Units (PDUs) and / or one or more Service Data Units (SDUs) according to the descriptions, functions, procedures, proposals, methods, and / or operation flowcharts disclosed in the present disclosure. One or more processors (102, 202) may generate messages, control information, data, or information according to the descriptions, functions, procedures, proposals, methods, and / or operation flowcharts disclosed in the present disclosure. One or more processors (102, 202) can generate signals (e.g., baseband signals) including PDUs, SDUs, messages, control information, data, traffic or information according to the functions, procedures, proposals and / or methods disclosed in this disclosure, and provide the signals to one or more transceivers (106, 206). One or more processors (102, 202) can receive signals (e.g., baseband signals) from one or more transceivers (106, 206) and obtain PDUs, SDUs, messages, control information, data, traffic or information according to the descriptions, functions, procedures, proposals, methods and / or operational flowcharts disclosed in this disclosure.

[0056] One or more memories (104, 204) may be coupled to one or more processors (102, 202) and may store various forms of data, signals, messages, information, programs, codes, instructions, and / or commands. The one or more memories (104, 204) may be configured as read only memory (ROM), random access memory (RAM), erasable programmable ROM (EPROM), electronically EPROM (EEPROM), flash memory, hard drives, registers, cache memory, computer readable storage media, and / or combinations thereof. The one or more memories (104, 204) may be located internally and / or externally to the one or more processors (102, 202). Additionally, the one or more memories (104, 204) may be coupled to the one or more processors (102, 202) via various technologies, such as wired or wireless connections.

[0057] One or more transceivers (106, 206) can transmit user data, control information, data, traffic, wireless signals, and / or channels, etc., as described in the methods and / or flowcharts of the present disclosure, to one or more other devices. One or more transceivers (106, 206) can receive user data, control information, data, traffic, wireless signals, and / or channels, etc., as described in the descriptions, functions, procedures, proposals, methods, and / or flowcharts of the present disclosure, from one or more other devices. For example, one or more transceivers (106, 206) can be coupled to one or more processors (102, 202) and can transmit and receive wireless signals. For example, one or more processors (102, 202) can control one or more transceivers (106, 206) to transmit user data, control information, traffic, wireless signals, and / or channels, etc., to one or more other devices. Additionally, one or more processors (102, 202) may control one or more transceivers (106, 206) to receive user data, control information, traffic, wireless signals, and / or channels from one or more other devices. Additionally, one or more transceivers (106, 206) may be coupled to one or more antennas (108, 208), and one or more transceivers (106, 206) may be configured to transmit and receive user data, control information, traffic, wireless signals, and / or channels, etc., as described in the descriptions, functions, procedures, proposals, methods, and / or operational flowcharts disclosed in the present disclosure, via one or more antennas (108, 208). In the present disclosure, one or more antennas (108, 208) may be multiple physical antennas or multiple logical antennas (e.g., antenna ports).One or more transceivers (106, 206) may convert received user data, control information, wireless signals / channels, etc. from RF band signals to baseband signals in order to process the received user data, control information, wireless signals / channels, etc. using one or more processors (102, 202). One or more transceivers (106, 206) may convert processed user data, control information, wireless signals / channels, etc. from baseband signals to RF band signals using one or more processors (102, 202). For this purpose, one or more transceivers (106, 206) may include an (analog) oscillator and / or a filter.

[0058] In one example, one of the devices (100, 200) may perform the intended operation of an AP, and the other of the devices (100, 200) may perform the intended operation of a non-AP STA. In another example, the transceiver (106, 206) of FIG. 1 may perform transmission and / or reception operations of signals (e.g., packets or PPDUs (physical layer protocol data units) according to IEEE 802.11a / b / g / n / ac / ax / be / bn, etc.).

[0059] Additionally, in the present disclosure, the operations of various STAs generating transmission / reception signals or performing data processing or calculations in advance for transmission / reception signals can be performed in the processor (102, 202) of FIG. 1. For example, an example of an operation of generating a transmission / reception signal or performing data processing or operation in advance for a transmission / reception signal is an operation of determining / obtaining / configuring / computing / decoding / encoding bit information of a field included in a PPDU (e.g., SIG (signal), STF (short training field), LTF (long training field), Data, etc.), 2) determining / configuring / obtaining time resources or frequency resources (e.g., subcarrier resources) used for a field included in a PPDU (e.g., SIG, STF, LTF, Data, etc.), 3) determining / configuring / obtaining a specific sequence (e.g., pilot sequence, STF / LTF sequence, extra sequence applied to SIG) used for a field included in a PPDU (e.g., SIG, STF, LTF, Data, etc.), 4) power control operation and / or power saving operation applied to an STA, 5) ACK (acknowledgement) signal It may include operations related to decision / acquisition / configuration / computation / decoding / encoding, etc. In addition, in the example below, various information (e.g., information related to fields / subfields / control fields / parameters / power, etc.) used by various STAs for decision / acquisition / configuration / computation / decoding / encoding of transmission / reception signals may be stored in the memory (104, 204) of FIG. 1.

[0060] Hereinafter, downlink (DL) refers to a link for communication from an AP STA to a non-AP STA, and downlink PPDUs / packets / signals, etc. can be transmitted and received through the downlink. In downlink communication, the transmitter may be part of an AP STA, and the receiver may be part of a non-AP STA. Uplink (UL) refers to a link for communication from a non-AP STA to an AP STA, and uplink PPDUs / packets / signals, etc. can be transmitted and received through the uplink. In uplink communication, the transmitter may be part of a non-AP STA, and the receiver may be part of an AP STA.

[0061] FIG. 2 illustrates an exemplary structure of a wireless LAN system related to the present disclosure.

[0062] A wireless LAN system may have a structure composed of multiple components. The wireless LAN system can support transparent STA mobility to the upper layer through the interaction of the multiple components. A Basic Service Set (BSS) corresponds to a basic building block of a wireless LAN. FIG. 2 illustrates, by way of example, the existence of two BSSs (BSS 1 and BSS 2), and the inclusion of two STAs as members of each BSS (STA 1 and STA 2 are included in BSS 1, and STA 3 and STA 4 are included in BSS 2). The oval representing a BSS in FIG. 2 can also be understood as representing a coverage area in which STAs included in the corresponding BSS maintain communication. This area can be referred to as a Basic Service Area (BSA). When an STA moves outside of the BSA, it cannot directly communicate with other STAs within the BSA.

[0063] If we do not consider the distributed system (DS) illustrated in Fig. 2, the most basic type of BSS in a wireless LAN is an Independent BSS (IBSS). For example, an IBSS can have a minimal form consisting of only two STAs. For example, assuming other components are omitted, BSS 1 consisting of only STA 1 and STA 2, or BSS 2 consisting of only STA 3 and STA 4, can be representative examples of an IBSS, respectively. Such a configuration is possible when the STAs can communicate directly without an AP. Furthermore, this type of WLAN is not planned in advance but can be configured when a local area network (LAN) is required, and can also be called an ad-hoc network. Since an IBSS does not include an AP, there is no centralized management entity. That is, in an IBSS, STAs are managed in a distributed manner. In IBSS, all STAs can be mobile STAs, and access to the DS is not permitted, forming a self-contained network.

[0064] An STA's membership in a BSS can dynamically change, for example, when an STA is turned on or off, or when an STA enters or leaves a BSS area. To become a member of a BSS, an STA can join the BSS using a synchronization process. To access all services in the BSS infrastructure, an STA must be associated with the BSS. This association can be dynamically established and may involve the use of a Distribution System Service (DSS).

[0065] In a wireless LAN, the direct STA-to-STA distance may be limited by PHY performance. While this distance limit may be sufficient in some cases, communication between STAs over longer distances may be required in other cases. To support extended coverage, a DS can be configured.

[0066] DS refers to a structure in which BSSs are interconnected. Specifically, a BSS may exist as an extended component of a network composed of multiple BSSs, as illustrated in Figure 2. DS is a logical concept and can be specified by the characteristics of the distributed system medium (DSM, DS medium). In this regard, the Wireless Medium (WM) and DSM can be logically distinguished. Each logical medium is used for a different purpose and by different components. These media are neither limited to being identical nor limited to being different. This logical difference between multiple media explains the flexibility of the WLAN architecture (DS architecture or other network architectures). In other words, the WLAN architecture can be implemented in various ways, and the physical characteristics of each implementation can independently specify the WLAN architecture.

[0067] A DS can support mobile devices by providing seamless integration of multiple BSSs and the logical services necessary to handle addresses to destinations. Additionally, a DS may further include a component called a portal, which acts as a bridge for connecting wireless LANs to other networks (e.g., IEEE 802.X).

[0068] An AP enables non-AP STAs associated with it to access the DS through the WM. An AP may refer to an entity that also has the functionality of an STA, and data movement between the BSS and the DS may be performed through the AP. For example, STA 2 and STA 3 illustrated in FIG. 2 have the functionality of an STA and provide the function of allowing associated non-AP STAs (STA 1 and STA 4) to access the DS. In addition, since all APs are basically STAs, all APs are addressable entities. The address used by an AP for communication on the WM and the address used by an AP for communication on the DSM do not necessarily have to be the same. A BSS consisting of an AP and one or more STAs may be referred to as an infrastructure BSS.

[0069] Data transmitted from one of the STA(s) associated with an AP to the STA address of that AP is always received on an uncontrolled port and can be processed by an IEEE 802.1X port access entity. In addition, if the controlled port is authenticated, the transmitted data (or frame) can be forwarded to the DS.

[0070] In addition to the structure of the DS described above, an extended service set (ESS) may be established to provide wider coverage.

[0071] An ESS is a network of arbitrary size and complexity, and may correspond to a set of BSSs connected to a DS. However, an ESS does not include a DS. An ESS network is characterized by appearing as an IBSS at the LLC (Logical Link Control) layer. STAs included in an ESS can communicate with each other, and mobile STAs can move from one BSS to another (i.e., within the same ESS) transparently to the LLC. APs included in an ESS may have the same SSID (service set identifier). The SSID is distinct from the BSS ID (BSS SSID), which is the identifier of the BSS.

[0072] In a wireless LAN system, no assumptions are made about the relative physical locations of BSSs, and all of the following configurations are possible: BSSs can be partially overlapping, which is commonly used to provide continuous coverage. BSSs can also be physically disconnected, and there is no logical distance restriction between them. BSSs can also be physically co-located, which can be used to provide redundancy. Furthermore, one or more IBSS or ESS networks can physically co-exist in the same space as one (or more) ESS networks. This can occur in cases where an ad-hoc network operates in the same location as an ESS network, where physically overlapping wireless networks are configured by different organizations, or where two or more different access and security policies are required at the same location.

[0073] Figure 3 illustrates a link setup process related to the present disclosure.

[0074] For an STA to set up a link and transmit and receive data on a network, it must discover the network via an AP, perform authentication, establish an association, and establish security. The link setup process can also be referred to as the session initiation process or session setup process. Furthermore, the discovery, authentication, association, and security setup processes of the link setup process can be collectively referred to as the association process.

[0075] At step 310, the STA may perform a network discovery operation. This network discovery operation may include scanning operations by the STA. That is, for the STA to access a network, it must search for available networks. Before joining a wireless network, the STA must identify compatible networks. The process of identifying networks in a specific area is called scanning.

[0076] Scanning methods include active scanning and passive scanning. Figure 3 illustrates a network discovery operation that includes an active scanning process as an example. In active scanning, an STA performing scanning transmits a probe request frame to discover any APs in the vicinity while moving between channels and waits for a response. The responder transmits a probe response frame in response to the STA that transmitted the probe request frame. Here, the responder may be the STA that last transmitted a beacon frame in the BSS of the channel being scanned. In the BSS, the AP transmits the beacon frame, so the AP becomes the responder. In the IBSS, the STAs within the IBSS take turns transmitting beacon frames, so the responder is not fixed. For example, an STA that transmits a probe request frame on channel 1 and receives a probe response frame on channel 1 can store BSS-related information included in the received probe response frame and move to the next channel (e.g., channel 2) to perform scanning (i.e., transmitting and receiving probe requests / responses on channel 2) in the same manner.

[0077] Although not shown in Figure 3, the scanning operation can also be performed in a passive scanning manner. In passive scanning, the STA performing the scanning moves between channels and waits for a beacon frame. A beacon frame is one of the management frames defined in IEEE 802.11. It announces the existence of a wireless network and is periodically transmitted to enable the STA performing the scanning to find the wireless network and participate in the wireless network. In the BSS, the AP performs the role of periodically transmitting the beacon frame, and in the IBSS, the STAs within the IBSS take turns transmitting the beacon frame. When the STA performing the scanning receives a beacon frame, it stores the information about the BSS included in the beacon frame and moves to another channel, recording the beacon frame information on each channel. The STA receiving the beacon frame stores the BSS-related information included in the received beacon frame and moves to the next channel to perform scanning on the next channel in the same manner. Comparing active scanning and passive scanning, active scanning has the advantage of lower delay and power consumption than passive scanning.

[0078] After the STA discovers the network, an authentication process may be performed at step 320. This authentication process may be referred to as the first authentication process to clearly distinguish it from the security setup operation of step 340 described below.

[0079] The authentication process involves the STA sending an authentication request frame to the AP, and the AP responding by sending an authentication response frame to the STA. The authentication request frame and the authorization response frame used in the authentication process belong to management frames.

[0080] The authentication frame may include information such as an authentication algorithm number, an authentication transaction sequence number, a status code, a challenge text, a Robust Security Network (RSN), and a Finite Cyclic Group. These are just some examples of information that may be included in an authentication request / response frame, and may be replaced with other information or include additional information.

[0081] An STA can transmit an authentication request frame to an AP. The AP can determine whether to grant authentication to the STA based on the information contained in the received authentication request frame. The AP can provide the result of the authentication process to the STA via an authentication response frame.

[0082] After the STA is successfully authenticated, an association process may be performed at step 330. The association process includes a process in which the STA transmits an association request frame to the AP, and in response, the AP transmits an association response frame to the STA.

[0083] The association request frame may include information about various capabilities, a beacon listen interval, a service set identifier (SSID), supported rates, supported channels, a robust security network (RSN), a mobility domain, supported operating classes, a Traffic Indication Map Broadcast request, interworking service capabilities, etc. For example, the association response frame may include information about various capabilities, a status code, an Association ID (AID), supported rates, an Enhanced Distributed Channel Access (EDCA) parameter set, a Received Channel Power Indicator (RCPI), a Received Signal to Noise Indicator (RSNI), a mobility domain, a timeout interval (e.g., an association comeback time), overlapping BSS scan parameters, a TIM broadcast response, a Quality of Service (QoS) map, etc. These are just some examples of information that may be included in a combined request / response frame, and the combined request / response frame may further include additional information.

[0084] After the STA successfully joins the network via the AP, a security setup process may be performed at step 340. The security setup process of step 340 may include an authentication process via a Robust Security Network Association (RSNA) request / response. Furthermore, if the authentication process of step 320 is referred to as the first authentication process, the security setup process of step 340 may also be referred to simply as the authentication process.

[0085] The security setup process of step 340 may include, for example, a process of establishing a private key through a four-way handshaking using an Extensible Authentication Protocol over LAN (EAPOL) frame. Furthermore, the security setup process may be performed according to a security method not defined in the IEEE 802.11 standard.

[0086] Figure 4 illustrates a backoff operation related to the present disclosure.

[0087] In wireless LAN systems, the basic MAC access mechanism is Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA). CSMA / CA, also known as the Distributed Coordination Function (DCF) of the IEEE 802.11 MAC, essentially employs a "listen before talk" access mechanism. According to this type of access mechanism, the AP and / or STA performs Clear Channel Assessment (CCA) to sense the wireless channel or medium for a predetermined time period (e.g., DIFS (DCF Inter-Frame Space)) before starting transmission. If the sensing result determines that the medium is in an idle state, the AP and / or STA starts transmitting frames through the medium. On the other hand, if the medium is detected to be occupied or busy, the AP and / or STA may not start its own transmission, but may wait for a predetermined delay period (e.g., a random backoff period) for medium access before attempting to transmit frames. By applying the random backoff period, multiple STAs may attempt to transmit frames after waiting for different periods of time, thereby minimizing collisions.

[0088] In addition, the IEEE 802.11 MAC protocol provides the Hybrid Coordination Function (HCF). The HCF is based on the DCF and the Point Coordination Function (PCF). The PCF is a polling-based synchronous access method, which refers to a method in which all receiving APs and / or STAs periodically poll to ensure that they can receive data frames. The HCF also includes EDCA and HCCA (HCF Controlled Channel Access). EDCA is a contention-based access method in which a provider provides data frames to multiple users, while HCCA is a contention-free channel access method that utilizes a polling mechanism. In addition, the HCF includes a medium access mechanism to improve the Quality of Service (QoS) of a wireless LAN, and can transmit QoS data in both a contention period (CP) and a contention-free period (CFP).

[0089] Referring to Fig. 4, an operation based on a random backoff period is described. When an occupied / busy medium changes to an idle state, multiple STAs may attempt to transmit data (or frames). To minimize collisions, each STA may select a random backoff count, wait for the corresponding slot time, and then attempt transmission. The random backoff count has a pseudo-random integer value and may be determined as one of the values ​​in the range of 0 to CW. Here, CW is a contention window parameter value. The CW parameter is initially given a value of CWmin, but in case of a transmission failure (e.g., if an ACK for a transmitted frame is not received), the STA may increase the CW by a factor of two. When the CW parameter value reaches CWmax, the STA may attempt data transmission while maintaining the CWmax value until the data transmission is successful, and if the data transmission is successful, the CW is reset to the CWmin value. The values ​​of CW, CWmin and CWmax can be set to 2n-1 (n=0, 1, 2, ...).

[0090] Once the random backoff process begins, the STA continues to monitor the medium while counting down the backoff slots according to the determined backoff count value. If the medium is monitored as occupied, the countdown stops and waits. When the medium becomes idle, the remaining countdown resumes.

[0091] In the example of FIG. 4, when a packet to be transmitted reaches the MAC of STA3, STA3 can immediately transmit the frame if it confirms that the medium is idle for DIFS. The remaining STAs monitor the medium for occupied / busy states and wait. In the meantime, data to be transmitted may also occur in each of STA1, STA2, and STA5, and each STA can count down the backoff slot according to the random backoff count value selected by each STA after waiting for DIFS if it confirms that the medium is idle. Assume that STA2 selects the smallest backoff count value and STA1 selects the largest backoff count value. In other words, this example shows a case where the remaining backoff time of STA5 is shorter than the remaining backoff time of STA1 when STA2 finishes the backoff count and starts frame transmission. STA1 and STA5 briefly stop counting down and wait while STA2 occupies the medium. When STA2's occupation ends and the medium becomes idle again, STA1 and STA5 wait for DIFS and then resume the backoff count that they had stopped. That is, STA1 and STA5 can start transmitting frames after counting down the remaining backoff slots equal to the remaining backoff time. Since STA5's remaining backoff time is shorter than STA1's, STA5 starts transmitting frames. While STA2 occupies the medium, STA4 may also have data to transmit. When the medium becomes idle, STA4 waits for DIFS, counts down according to a random backoff count value of its choice, and then starts transmitting frames. The example of FIG. 4 illustrates a case where the remaining backoff time of STA5 coincidentally matches the random backoff count value of STA4, in which case a collision may occur between STA4 and STA5. If a collision occurs, neither STA4 nor STA5 will receive an ACK, resulting in a failure in data transmission.In this case, STA4 and STA5 can select a random backoff count value and perform a countdown after doubling the CW value. STA1 waits while the medium is occupied by transmissions from STA4 and STA5, and when the medium becomes idle, it waits for DIFS and can start transmitting frames after the remaining backoff time elapses.

[0092] As shown in the example of Fig. 4, a data frame is a frame used for transmitting data to an upper layer, and can be transmitted after a backoff performed after DIFS elapses from when the medium becomes idle. Additionally, a management frame is a frame used for exchanging management information without being transmitted to an upper layer, and is transmitted after a backoff performed after an IFS such as DIFS or PIFS (Point coordination function IFS) elapses. A management frame may include a beacon, an association request / response, a re-association request / response, a probe request / response, an authentication request / response, etc. as a subtype frame. A control frame is a frame used to control access to the medium. Control frames can include RTS (Request-To-Send), CTS (Clear-To-Send), ACK (Acknowledgment), PS-Poll (Power Save-Poll), Block ACK (B-ACK or BlockAck), Block ACK Request (BlockACKReq), NDP announcement (null data packet announcement), Trigger, etc. as subtype frames. If the control frame is not a response frame to the previous frame, it is transmitted after a backoff performed after the DIFS (Direct Inverse Frame Stop) has elapsed, and if it is a response frame to the previous frame, it is transmitted without a backoff performed after the SIFS (short IFS) has elapsed. The type and subtype of a frame can be identified by the type field and subtype field in the frame control (FC) field.

[0093] A QoS (Quality of Service) STA can transmit a frame after a backoff performed after the AIFS (arbitration IFS) for the access category (AC) to which the frame belongs, i.e., AIFS[i] (where i is a value determined by the AC), has elapsed. Here, the frames for which AIFS[i] can be used can be data frames, management frames, and also control frames that are not response frames.

[0094] FIG. 5 illustrates a frame transmission operation based on CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) in connection with the present disclosure.

[0095] As mentioned above, the CSMA / CA mechanism includes virtual carrier sensing in addition to physical carrier sensing, in which STAs directly sense the medium. Virtual carrier sensing is intended to address potential issues in medium access, such as the hidden node problem. For virtual carrier sensing, the MAC of an STA can utilize a Network Allocation Vector (NAV). The NAV is a value that an STA that is currently using or has the right to use the medium indicates to other STAs the remaining time until the medium becomes available. Therefore, the value set as NAV corresponds to the period during which the STA transmitting the frame is scheduled to use the medium, and an STA that receives the NAV value is prohibited from accessing the medium during that period. For example, the NAV can be set based on the value of the "duration" field in the MAC header of the frame.

[0096] In the example of FIG. 5, STA1 wants to transmit data to STA2, and STA3 is in a position to overhear part or all of the frames transmitted and received between STA1 and STA2.

[0097] In order to reduce the possibility of collisions in transmissions of multiple STAs in a CSMA / CA-based frame transmission operation, a mechanism using RTS / CTS frames may be applied. In the example of FIG. 5, while STA1 is transmitting, STA3 may determine that the medium is idle based on carrier sensing. That is, STA1 may correspond to a hidden node for STA3. Alternatively, in the example of FIG. 5, while STA2 is transmitting, STA3 may determine that the medium is idle based on carrier sensing. That is, STA2 may correspond to a hidden node for STA3. By exchanging RTS / CTS frames before performing data transmission and reception between STA1 and STA2, STAs outside the transmission range of either STA1 or STA2, or STAs outside the carrier sensing range for transmissions from STA1 or STA3, may not attempt to occupy the channel during data transmission and reception between STA1 and STA2.

[0098] Specifically, STA1 can determine whether a channel is occupied through carrier sensing. In terms of physical carrier sensing, STA1 can determine channel occupancy idleness based on the energy level or signal correlation detected in the channel. Furthermore, in terms of virtual carrier sensing, STA1 can determine the channel occupancy status using the NAV timer.

[0099] STA1 can transmit an RTS frame to STA2 after performing a backoff if the channel is idle during the DIFS. STA2 can transmit a CTS frame, which is a response to the RTS frame, to STA1 after an SIFS if it receives the RTS frame.

[0100] If STA3 cannot overhear a CTS frame from STA2 but can overhear an RTS frame from STA1, STA3 can use the duration information contained in the RTS frame to set a NAV timer for the subsequent consecutively transmitted frame transmission period (e.g., SIFS + CTS frame + SIFS + data frame + SIFS + ACK frame). Alternatively, if STA3 cannot overhear an RTS frame from STA1 but can overhear a CTS frame from STA2, STA3 can use the duration information contained in the CTS frame to set a NAV timer for the subsequent consecutively transmitted frame transmission period (e.g., SIFS + data frame + SIFS + ACK frame). That is, if STA3 can overhear one or more of the RTS or CTS frames from one or more of STA1 or STA2, it can set a NAV accordingly. If STA3 receives a new frame before the NAV timer expires, it can update the NAV timer using the duration information contained in the new frame. STA3 does not attempt channel access until the NAV timer expires.

[0101] If STA1 receives a CTS frame from STA2, it can transmit a data frame to STA2 after SIFS from the time when the CTS frame is completely received. If STA2 successfully receives the data frame, it can transmit an ACK frame in response to the data frame to STA1 after SIFS. STA3 can determine whether the channel is in use through carrier sensing if the NAV timer expires. If STA3 determines that the channel is not in use by another terminal during the DIFS after the NAV timer expires, it can attempt channel access after a contention window (CW) based on a random backoff has elapsed.

[0102] FIG. 6 illustrates an exemplary format of a frame used in a wireless LAN system related to the present disclosure.

[0103] Based on an instruction or primitive (meaning a set of instructions or parameters) from the MAC layer, the PHY layer can prepare an MPDU (MAC PDU) to be transmitted. When the PHY layer receives a command requesting the start of transmission from the MAC layer, the PHY layer can switch to transmission mode and transmit the information (e.g., data) provided by the MAC layer in the form of a frame. In addition, when the PHY layer detects a valid preamble of the received frame, it can monitor the header of the preamble and send a command to the MAC layer notifying the start of reception by the PHY layer.

[0104] In this way, information transmission / reception in a wireless LAN system is done in the form of frames, and for this purpose, the PHY layer Protocol Data Unit (PPDU) frame format is defined.

[0105] A basic PPDU frame may include a short training field (STF), a long training field (LTF), a SIGNAL (SIG) field, and a data field. The most basic (e.g., non-HT (high throughput)) PPDU frame format may consist of only L-STF (Legacy-STF), L-LTF (Legacy-LTF), a SIG field, and a data field. In addition, depending on the type of PPDU frame format (e.g., HT-mixed format PPDU, HT-greenfield format PPDU, VHT (very high throughput) PPDU, etc.), additional (or different types of) STF, LTF, and SIG fields may be included between the SIG field and the data field. Specific types of frame formats are described later in FIG. 7.

[0106] STF is a signal for signal detection, AGC (automatic gain control), diversity selection, precise time synchronization, etc., and LTF is a signal for channel estimation, frequency error estimation, etc. STF and LTF are signals for synchronization and channel estimation of the OFDM (orthogonal frequency division multiplexing) physical layer.

[0107] The SIG field may include a RATE field and a LENGTH field, among others. The RATE field may include information about the modulation and coding rate of the data. The LENGTH field may include information about the length of the data. Additionally, the SIG field may include a parity bit, a SIG TAIL bit, among others.

[0108] The data field may include a SERVICE field, a physical layer service data unit (PSDU), a PPDU TAIL bit, and, if necessary, padding bits. Some bits of the SERVICE field may be used to synchronize the descrambler at the receiving end. The PSDU corresponds to a MAC PDU defined at the MAC layer and may contain data generated / used by upper layers. The PPDU TAIL bit may be used to return the encoder to a 0 state. The padding bit may be used to adjust the length of the data field to a predetermined unit.

[0109] MAC PDUs are defined according to various MAC frame formats, and a basic MAC frame consists of a MAC header, a frame body, and a frame check sequence (FCS). A MAC frame is composed of MAC PDUs and can be transmitted / received through the PSDU in the data portion of the PPDU frame format.

[0110] The MAC header includes a frame control field, a duration / ID field, an address field, etc. The frame control field may include control information necessary for frame transmission / reception. The duration / ID field may be set to the time for transmitting the corresponding frame, etc. The specific contents of the Sequence Control, QoS Control, and HT Control subfields of the MAC header are omitted.

[0111] Although not shown in FIG. 6, the null data packet (NDP) frame format refers to a frame format that does not include a data packet. That is, the NDP frame refers to a frame format that includes the PLCP (physical layer convergence procedure) header portion (i.e., STF, LTF, and SIG fields) of the general PPDU frame format, but does not include the remaining portion (i.e., data field). The NDP frame may also be referred to as a short frame format.

[0112] FIG. 7 illustrates an exemplary format of a physical layer protocol data unit (PPDU) of a wireless LAN system related to the present disclosure.

[0113] Standards such as IEEE 802.11a / g / n / ac / ax / be use various PPDU formats. The basic PPDU format (IEEE 802.11a / g format) includes L-LTF, L-STF, L-SIG, and Data fields. The basic PPDU format can also be referred to as the non-HT PPDU format.

[0114] The HT PPDU format (IEEE 802.11n format) additionally includes HT-SIG, HT-STF, and HT-LFT(s) fields in addition to the basic PPDU format. The HT PPDU format illustrated in Fig. 7 may be referred to as an HT-mixed format. Although not illustrated, an HT-greenfield format PPDU may be defined, which corresponds to a format that does not include L-STF, L-LTF, and L-SIG, and is composed of HT-GF-STF, HT-LTF1, HT-SIG, one or more HT-LTF, and Data fields.

[0115] The VHT PPDU format (IEEE 802.11ac format) includes VHT SIG-A, VHT-STF, VHT-LTF, and VHT-SIG-B fields in addition to the basic PPDU format.

[0116] The HE PPDU format (IEEE 802.11ax format) additionally includes RL-SIG (Repeated L-SIG), HE-SIG-A, HE-SIG-B, HE-STF, HE-LTF(s), and PE (Packet Extension) fields in addition to the basic PPDU format. Depending on specific examples of the HE PPDU format, some fields may be excluded or their lengths may vary. For example, the HE-SIG-B field is included in the HE PPDU format for multi-users (MUs), but the HE PPDU format for single-users (SUs) does not include the HE-SIG-B. In addition, the HE trigger-based (TB) PPDU format does not include the HE-SIG-B, and the length of the HE-STF field may vary to 8 μs. The HE ER (Extended Range) SU PPDU format does not include the HE-SIG-B field, and the length of the HE-SIG-A field can vary up to 16 μs.

[0117] FIG. 8 illustrates another exemplary format of a PPDU of a wireless LAN system related to the present disclosure.

[0118] The EHT PPDU format (IEEE 802.11be format) of FIG. 8 may include an EHT MU PPDU format and an EHT TB PPDU format. The EHT MU PPDU format corresponds to a PPDU that carries one or more data (or PSDU) for one or more users. The EHT MU PPDU can be used for both SU transmission and MU transmission, and the EHT MU PPDU may correspond to a PPDU for one receiving STA or multiple receiving STAs. The EHT TB PPDU omits the EHT-SIG compared to the EHT MU PPDU. An STA that receives a trigger for UL MU transmission (e.g., a trigger frame or an RTS frame) can perform UL transmission based on the EHT TB PPDU format.

[0119] The EHT PPDU format includes RL-SIG, U-SIG (Universal SIG), EHT-SIG, EHT-STF, EHT-LTF(s), and PE fields in addition to the basic PPDU format. Depending on the specific examples of the EHT PPDU format, some fields may be excluded or their lengths may vary. For example, depending on the EHT MU PPDU format and EHT TB PPDU format described above, some fields of the EHT PPDU format may or may not be included, or the lengths of specific fields may vary.

[0120] FIG. 9 illustrates a multi-link operation (MLO) related to the present disclosure.

[0121] As wireless LAN systems have evolved, a function has been introduced that allows a single device to communicate with other devices through multiple links. The operation of a device based on this function is called multi-link operation (MLO). A device that supports multi-link operation is called a multi-link device (MLD), and an MLD can mean a logical entity. For example, an MLD can mean a device that has one or more affiliated STAs (i.e., non-APs or APs) and a single MAC data service and a single MAC service access point for logical link control (LLC). In particular, a non-AP STA that supports multi-link operation is called a non-AP MLD, and an AP that supports multi-link operation is called an AP MLD.

[0122] Multi-link operation requires mapping a traffic identifier (TID) for specific traffic to one or more of the multi-links. This process is called TID to link mapping (TTLM). A TID can refer to an identifier used by upper-layer entities to distinguish between MAC entities and MAC SDUs (MSDUs) to support quality of service (QoS) among MAC data services.

[0123] For example, any one of up to 16 or more values ​​may be assigned to a particular TID. Furthermore, eight of the 16 TID values ​​may identify traffic categories (TCs), and the other eight may identify parameterized traffic streams (TSs).

[0124] The mechanism for mapping TIDs to links, i.e., the TTLM process, may refer to a process for determining the correspondence between TIDs during setup or association (or after performing setup or association) for downlink and uplink established through setup or association between a non-AP MLD and an AP MLD. If at least one TID is mapped to a specific link through the TTLM process, the link is defined as enabled, and if no TID is mapped to a specific link, the link can be defined as disabled. A TID must always be mapped to at least one set-up link unless admission control is applied. By default, a TID is mapped to all set-up links, so all set-up links can be activated.

[0125] According to the example of FIG. 9, TIDs 0 to 6 are mapped to link 1 set up between a non-AP MLD (STA-1) and an AP MLD (AP-1) (i.e., an enabled link), TID 7 is mapped to link 2 set up between a non-AP MLD (STA-2) and an AP MLD (AP-2) (i.e., an enabled link), and no TID is mapped to link 3 set up between a non-AP MLD (STA-3) and an AP MLD (AP-3) (i.e., a disabled link).

[0126] When a specific link is enabled (i.e., has a TID mapped to it), the link can be used for frame exchange, depending on the power state of the non-AP MLD operating on that link. Conversely, when a specific link is disabled (i.e., has no TID mapped to it), the link may not be used for frame exchange, either on the downlink or uplink.

[0127] The TTLM process described above can be performed through default mapping mode or negotiation mapping mode. Default mapping mode refers to a mode in which all TIDs are mapped to all links by the AP MLD, and since all TIDs are mapped to all links, all established links can be activated. Non-AP MLDs and AP MLDs that have performed multi-link setups can operate in this default mapping mode if negotiation for TTLM to other mappings is not performed, fails, or is torn down.

[0128] Negotiated mapping mode refers to a mode in which mapping is performed through a process in which a non-AP MLD transmits mapping information between a TID and a link to the AP MLD through a TTLM element included in a binding request frame or a TTLM request frame, and the AP MLD approves or rejects the request. If TTLM is negotiated between a non-AP MLD and an AP MLD, the non-AP MLD or the AP MLD can tear down or release the negotiated TTLM by sending a TTLM teardown frame. If TTLM is teardown, the non-AP MLD and the AP MLD can operate in the default mapping mode.

[0129] Meanwhile, TWT (target wakeup time) is a power saving (PS) technology that can improve the energy efficiency of non-AP STAs by defining a predetermined service period (SP) and sharing information about the SP among devices to reduce contention of the medium. An STA that performs a request / suggest / demand in the TWT setup phase can be called a TWT requesting STA. In addition, an AP that responds with acceptance / rejection to the request / suggest / demand of the TWT requesting STA can be called a TWT responding AP (or TWT responding STA). TWT operation can be divided into a TWT operation based on individual TWT and a TWT operation based on broadcast TWT.

[0130] FIG. 10 illustrates a TWT-based AP operation cycle related to the present disclosure.

[0131] Referring to Fig. 10, an example of a scheduled AP PS as a candidate AP PS mode is described based on the TWT for PS described above. For example, Fig. 10 illustrates AP operation related to TWT-based ON-OFF duty cycling. This may correspond to a medium-term change (e.g., a scheduled doze service period within a beacon interval) that affects all STAs operating on the link. For example, an AP may have a scheduled time window (1020) for only a portion of a beacon interval, and may remain in an awake state (1010) for the rest of the time. Within a given time interval or count, the AP may include scheduled time windows (1030, 1040) per beacon interval, and may include an awake state (1010) between each scheduled time window. Accordingly, within the time interval or count, the AP may not change to an OFF state, but may be scheduled for a specific action or may remain in an awake state.

[0132] Additionally, in addition to scheduled AP PS, dynamic AP PS and unscheduled AP PS are also being discussed. For example, dynamic AP PS may include an operation to activate a higher bandwidths / number of spatial streams (BW / NSS) mode by exchanging initial control frames. Unscheduled AP PS may include an operation to wake up other associated APs operating in PS mode by sending a wakeup request over the link of an associated AP operating in active mode with a non-AP MLD.

[0133] The TWT-based AP operation described with reference to FIG. 10 is an example for explaining one embodiment of the present disclosure, and is specifically described in FIGS. 17 and 18 below.

[0134] Meanwhile, current MLO may include two types: (e)MLSR ((enhanced) multi-link single-radio) and MLMR (multi-link multi-radio). MLSR may only be able to transmit and / or receive on a single channel at a given time (requiring antenna switching). On the other hand, eMLSR may include an AP supporting multiple radio links that can communicate with a single radio over multiple spatially multiplexed channels (e.g., at least 2×2 MIMO (multiple-input and multiple-output) for a single radio STA). eMLSR can reserve one of the channels to ensure reliability and minimize latency for high-priority applications, while servicing lower-priority but high-throughput applications on the other channel. MLMR may include cases where both the AP and the STA have simultaneous dual-radio capabilities, allowing the AP and the STA to connect and communicate simultaneously over two spatially multiplexed channels. In addition. MLMR can ensure higher reliability and lower latency when used to redundantly share data across two channels or provide higher throughput through aggregation. In the present disclosure, an AP may be an MLD supporting a single radio, and a non-AP STA may be a device supporting a single link or multiple links (e.g., an (e)MLSR or MLMR device), also referred to as an STA. However, the present disclosure is not limited to the above examples and is not limited to a specific device.

[0135] FIG. 11 illustrates an example of synchronization loss and recovery in a multi-link in connection with the present disclosure.

[0136] Referring to FIG. 11, an operation for reacquiring (or recovering) sync when the AP MLD loses synchronization is described. Hereinafter, synchronization refers to medium synchronization and can be used interchangeably with medium synchronization. At this time, the AP MLD may include a mobile AP that supports multi-links based on a single radio. Therefore, simultaneous transmission and reception cannot be performed on two links at the same time, and the AP can operate on only one link. For example, the AP MLD cannot receive a signal transmitted from an STA on link 1 during a duration in which link 1 (L1) is OFF and link 2 (L2) is ON. In addition, the AP MLD cannot receive a signal transmitted from an STA on link 2 during a duration in which link 1 is ON and link 2 is OFF. Accordingly, an AP MLD may be considered (or identified) as having lost synchronization (1110) if it cannot perform CCA for a certain period of time while operating on another MLSR link that includes a delay due to a link switch. In this case, a link switch may mean that one of the active links in MLO is deactivated and another inactive link is activated. Meanwhile, although FIG. 11 illustrates a loss of synchronization (1110) due to link switching during MLO operation, this is only one embodiment. For example, the loss of synchronization in the present disclosure may include a case where a mobile AP loses synchronization on a specific link due to coexistence with another wireless technology (e.g., Bluetooth, etc.). And an STA that has lost synchronization may start a MediumSyncDelay timer (1120).Additionally, if the MediumSyncDelay timer (1120) does not expire and the operation duration is greater than MediumSyncThreshold, the STA may start a countdown from the time when the operation ends.

[0137] At this time, the AP MLD that has lost synchronization may experience limitations in its operation until the MediumSyncDelay timer expires. Therefore, the present disclosure describes a method for more quickly restoring synchronization when a link is switched.

[0138] FIG. 12 illustrates an example of a synchronization acquisition method based on SAR (STA-assisted medium synchronization recovery) according to one embodiment of the present disclosure.

[0139] Referring to FIG. 12, SAR may refer to a method for STA-based synchronization recovery. In one embodiment, the AP MLD may transmit a request frame to STAs within the BSS (e.g., STA 1 to STA 3 that do not support multi-link). At this time, STA 1 to STA 3 may operate in link 1 (hereinafter, L1), link 2 (hereinafter, L2), and link 3 (hereinafter, L3), respectively. In the present disclosure, the request frame may refer to a frame that explicitly or implicitly indicates a request for information (or fields) for fast synchronization recovery, and such a frame may be a management frame, an action frame, or a control frame. Alternatively, the request frame transmitted by the AP MLD to the STA may refer to a frame including a subfield for an SAR request (hereinafter, SAR request subfield or SAR request subelement) and may refer to a MAC header including a subfield for an SAR request. For convenience of explanation, a transmission object according to at least one of the various forms described above may be referred to as a request frame.

[0140] If the STA allows the request of the AP MLD, the STA may transmit a response frame to the AP MLD, and thereafter, when a link transition (or switch) is negotiated, the STA may transmit an assisting frame to the AP MLD. In addition, in the following disclosure, a response frame may mean a frame that explicitly or implicitly indicates a response to a request for transmission of an assisting frame of the AP MLD, and such a frame may be a management frame, an action frame, or a control frame. Alternatively, the response frame that the STA transmits to the AP MLD may mean a frame including a subfield for a SAR response (hereinafter, a SAR response subelement), and may mean a MAC header including a subfield for a SAR response. For the convenience of explanation, a transmission object according to at least one of the various forms described above may be referred to as a response frame. Additionally, an auxiliary frame may be an example of a frame format that includes an MPDU (MAC PDU), or a PPDU with a specified receive vector (RXVECTOR) parameter (e.g., the duration of a TXOP (transmission opportunity) (TXOP_DURATION)). Accordingly, an auxiliary frame may be a management frame, an action frame, or a control frame. Additionally, an auxiliary frame is only a name used for convenience of explanation below and is not limited to a frame name.

[0141] More specifically, the AP MLD may transmit an initial control frame (ICF) (1205) including a SAR request to STA 1 within the on-duration on L1. At this time, the ICF may be a control frame for initiating a TXOP or a sequence. Hereinafter, the SAR request may refer to an SAR request subfield for requesting transmission of an auxiliary frame. The SAR request may indicate a request to transmit necessary information (e.g., an auxiliary frame) at the time when negotiation of the AP MLD between the AP MLD and the STA is initiated in the case where synchronization between the AP MLD and the STA is lost. In one embodiment, when the on-duration of the AP MLD on L1 is periodic, the AP MLD may request STA 1 to periodically transmit an auxiliary frame at the time when the link is switched to L1 through a single SAR request.

[0142] STA 1, which receives an ICF (1205) including a SAR request, may transmit an initial control response (ICR) (1210) including a response to the SAR request to the AP MLD on L1. At this time, the ICR may be a control frame for confirming a TXOP or a sequence. The SAR response may refer to a SAR response subfield for transmitting a response to the SAR request. It may include an acknowledgment of the SAR request of the AP MLD. In one embodiment, when the SAR request requests transmission of a periodic auxiliary frame, STA 1 may indicate that it will allow (or agree to) transmission of the periodic auxiliary frame or allow (or agree to) transmission of one or more auxiliary frames less than the requested number of times.

[0143] If STA 1 accepts the SAR request of AP MLD, it may transmit an auxiliary frame (1225) to AP MLD on L1 at the time when the link is switched to L1 according to the information included in the SAR request. In one embodiment, if the SAR request includes a request for transmitting a periodic auxiliary frame, STA 1 may also periodically transmit at least one auxiliary frame (1225, 1245) at the time when the link is switched to L1 according to the SAR response. Meanwhile, STA 1 may need to perform EDCA contention on an anchor channel. Accordingly, AP MLD may include parameters related to EDCA (or EDCA parameters) in the SAR request so that STA 1 can smoothly transmit the auxiliary frame at the time when the link is switched.

[0144] Meanwhile, the AP MLD may transmit an ICF (1215) including a SAR request to STA 2 within the on-duration on L2. Accordingly, STA 2 may transmit an ICR (1220) including an acknowledgment of the SAR request to the AP MLD on L2. Furthermore, if STA 2 accepts the SAR request of the AP MLD, it may transmit an auxiliary frame (1230) to the AP MLD on L2 at the point in time when the link is switched to L2 based on the information included in the SAR request.

[0145] Additionally, if there is another STA (e.g., STA 3) associated with the AP MLD on L2 within the BSS, the AP MLD may transmit an ICF (1235) including a SAR request to STA 3 within the on-duration on L2. Accordingly, STA 3 may transmit an ICR (1240) including an acknowledgment for the SAR request to the AP MLD on L2, and if the SAR request is allowed, may transmit an auxiliary frame (1250) to the AP MLD on L2 at a time when the link is switched to L2 according to the information included in the SAR request.

[0146] The specific configuration of the (sub)field format for the above-described SAR request and SAR response is specifically described in FIGS. 13 to 15 below.

[0147] FIG. 13 illustrates an exemplary format of a subfield for a SAR request according to one embodiment of the present disclosure.

[0148] Referring to FIG. 13, an exemplary configuration of a SAR request subfield format is described. The SAR request subfield may include at least one of an Element ID (identifier) ​​subfield (1305), a Length subfield (1310), an Element ID Extension subfield (1315), a Frame Control subfield (1320), a Start Time subfield (1325), an Interval subfield (1330), a Count subfield (1335), an EDCA parameters subfield (1340), or a Multi-Link Info subfield (1345). Hereinafter, a field may be used interchangeably with an element with the same meaning, and similarly, a sub-field and a sub-element may be used interchangeably with the same meaning as sub-components constituting a field and an element, respectively.

[0149] Referring back to FIG. 13, the Element ID subfield (1305) includes 1 octet and may represent a Management element ID. For example, the Element ID subfield (1305) may have a value of 255. Of course, the value of the Element ID subfield (1305) is not limited to the above example. The Length subfield (1310) includes 1 octet and may include information about the length (e.g., in bytes) of information transmitted via the SAR request subfield format. The Element ID Extension subfield (1315) may represent an extension value of Element ID 255 and may have a value such as 111.

[0150] The Frame Control subfield (1320) may include at least one of a Time unit subfield (1350) or a Number of Multi-Link Info subfield (1355). The Time unit subfield (1350) may have a size of 4 bits and may indicate a time unit (e.g., μs or ms) of the subfields (e.g., 1325 to 1345). The Number of Multi-Link Info subfield (1355) may have a size of 4 bits and may indicate how many links information will be included when the Multi-Link Info subfield (1345) is added.

[0151] The Start Time subfield (1325) may indicate the transmission time of the first auxiliary frame. For example, the Start Time subfield (1325) may include 8 octets when given as a TSF (timing synchronization function) value, and may include 1 octet when given as an offset value.

[0152] The Interval subfield (1330) and the Count subfield (1335) may be subfields required when requesting transmission of periodic auxiliary frames. The Interval subfield (1330) may include 1 octet and may indicate a transmission cycle of the auxiliary frame. The Count subfield (1335) may include 1 octet and may indicate the number of transmissions of the auxiliary frame. In one embodiment, when the AP MLD does not request transmission of periodic auxiliary frames, the Interval subfield (1330) may have a value of 0 and the Count subfield (1335) may have a value of 1. In one embodiment, when the AP MLD wants to request to continuously transmit periodic auxiliary frames until there is separate signaling, the Count subfield (1335) may have a value of 0.

[0153] The EDCA parameters subfield (1340) may contain 4 octets and may indicate new EDCA parameters for the STA to preferentially apply instead of previously stored EDCA parameters. The specific configuration of the EDCA parameters subfield (1340) is specifically described in FIG. 14 below.

[0154] The Multi-Link Info subfield (1345) may indicate multi-link information for requesting transmission of auxiliary frames related to multiple links to an STA. Accordingly, the Multi-Link Info subfield (1345) may include subfields related to at least one other link (e.g., L2, L3, ...) in addition to the link (e.g., L1) associated with the values ​​indicated by the subfields described above. However, the octet value of the Multi-Link Info subfield (1345) is not specified (variable), which may be because, if the STA does not support multi-link, the AP MLD may request transmission of auxiliary frames for only one link to the STA, and thus there is no need to provide information about multi-links to one STA. The Multi-Link Info subfield (1345) may include at least one of a Link ID subfield (1360), a Start Time subfield (1365), an Interval subfield (1370), a Count subfield (1375), or an EDCA parameter subfield (1380). The Link ID subfield (1360) may have a size of 4 bits and may indicate an identifier of a link requesting auxiliary frame transmission. The Start Time subfield (1365) may have a size of 8 bits and may indicate a transmission time of the first auxiliary frame of an auxiliary frame in the link indicated by the Link ID subfield (1360). The Interval subfield (1370) may have a size of 8 bits and may indicate a transmission cycle on the link indicated by the Link ID subfield (1360) when requesting periodic auxiliary frame transmission. The Count subfield (1375) may have a size of 8 bits and may indicate the number of transmissions on the link indicated by the Link ID subfield (1360) when requesting periodic auxiliary frame transmission.The EDCA parameter subfield (1380) may have a size of 32 bits and may indicate a new EDCA parameter to be preferentially applied in the link indicated by the Link ID subfield (1360).

[0155] Meanwhile, the structure of the format illustrated in FIG. 13, the field names, the values ​​indicated by the fields, the number of fields to which meaningful values ​​are assigned, the order of the fields, the number of octets or bits, whether fields are included in the format, etc. are merely examples, and may of course be changed differently from the illustrated and described embodiment.

[0156] FIG. 14 illustrates an exemplary format of an EDCA parameter subfield according to one embodiment of the present disclosure.

[0157] Referring to FIG. 14, the specific configuration of the EDCA parameters subfield (1340) among the SAR request subfields described in FIG. 13 is described. The EDCA parameters subfield may include at least one of an ACI / AIFSN (access category index / arbitration interframe space number) subfield (1410), an ECWmin / ECWmax (exponent of contention window minimum and maximum) subfield (1420), or a TXOP Limit subfield (1430).

[0158] Referring back to FIG. 14, the ACI / AIFSN subfield (1410) may include 1 octet and may include at least one of the AIFSN subfield (1440), the Data Allowed subfield (1450), or the Reserved subfield (1460). The AIFSN subfield (1440) may have a size of 4 bits and may indicate the number of slots after a short interframe space (SIFS), which is an interval that an STA postpones or defers before invoking a backoff or starting a transmission. The Data Allowed subfield (1450) may have a size of 1 bit and may indicate whether to allow including data in an auxiliary frame.

[0159] The ECWmin / ECWmax subfield (1420) may include one octet, and may include an ECWmin subfield (1470) indicating a minimum value of the contention window and an ECWmax subfield (1480) indicating a maximum value of the contention window, respectively. In addition, the minimum and maximum values ​​of the contention window may each be expressed in exponential form.

[0160] The TXOP Limit subfield (1430) may include 2 octets and may represent the maximum length of the TXOP as an unsigned integer in units of time indicated in the Time unit subfield (1350) or in units of a predetermined time (e.g., 32 microseconds). For example, if the Data Allowed subfield (1450) indicates that data is allowed to be transmitted together within an auxiliary frame, the size of the data included in the auxiliary frame may be limited to the maximum length value of the TXOP indicated in the TXOP Limit subfield (1430).

[0161] Meanwhile, the structure of the format illustrated in FIG. 14, the field names, the values ​​indicated by the fields, the number of fields to which meaningful values ​​are assigned, the order of the fields, the number of octets or bits, whether fields are included in the format, etc. are merely examples and may, of course, be changed differently from the illustrated and described embodiment.

[0162] FIG. 15 illustrates an exemplary format of a subfield for a SAR response according to one embodiment of the present disclosure.

[0163] Referring to FIG. 15, an exemplary configuration of a SAR response subfield format is described in detail. The SAR response subfield may include at least one of an Element ID (identifier) ​​subfield (1510), a Length subfield (1520), an Element ID Extension subfield (1530), a Status Code subfield (1540), a Count subfield (1550), or an Accepted link Bitmap subfield (1560).

[0164] Referring back to FIG. 15, the Element ID subfield (1510) includes 1 octet and may represent a Management element ID. For example, the Element ID subfield (1510) may have a value of 255. Of course, the value of the Element ID subfield (1510) is not limited to the above example. The Length subfield (1520) includes 1 octet and may include information about the length (e.g., in bytes) of information transmitted via the SAR response subfield format. The Element ID Extension subfield (1530) may represent an extension value of Element ID 255 and may have a value of 112.

[0165] The Status Code subfield (1540) may include 2 octets and may indicate whether the requested operation of the AP MLD is successful. The Count subfield (1550) may include 1 octet and may indicate the number of times the auxiliary frame will actually be transmitted within the requested number of times when the AP MLD requests transmission of multiple auxiliary frames. The Accepted link Bitmap subfield (1560) may include 0 or 2 octets and may indicate a link among the links requested by the AP MLD to actually transmit the auxiliary frame when the AP MLD requests transmission of the auxiliary frame for multi-link.

[0166] Meanwhile, the structure of the format illustrated in FIG. 15, the field names, the values ​​indicated by the fields, the number of fields to which meaningful values ​​are assigned, the order of the fields, the number of octets or bits, whether fields are included in the format, etc. are merely examples, and may of course be changed differently from the illustrated and described embodiment.

[0167] FIG. 16 illustrates an example of a SAR-based synchronization acquisition method according to one embodiment of the present disclosure.

[0168] Referring to FIG. 16, an example of a method in which an AP MLD requests transmission of auxiliary frames for multiple links to one STA through the Multi-Link Info subfield (1345) described above when the STA supports multi-links is illustrated. Meanwhile, the embodiment of FIG. 16 may include operations overlapping with the operations of FIG. 12 described above, and information included in each transmission frame (e.g., SAR request subfield, SAR response subfield, or auxiliary frame) may be described based on FIGS. 13 to 15 described above. Therefore, descriptions of overlapping operations may be omitted.

[0169] In one embodiment, the AP MLD may transmit an ICF (1610) including a SAR request to an STA on L1. The STA may be an STA that supports multiple links (e.g., L1 and L2) (ML capable STA). The SAR request may indicate a request to transmit information (e.g., an auxiliary frame) required at the time when negotiation between the AP MLD and the STA begins in case synchronization between the AP MLD and the STA is lost. The SAR request included in the ICF (1610) may include at least one of the same SAR request subfields described in FIGS. 13 and 14. For example, the SAR request may include a Multi-Link Info subfield (1345) and may include an auxiliary frame transmission request for each of L1 and L2. For example, the SAR request may request that the AP MLD transmit an auxiliary frame (1640) at the time when link switching back to L1 occurs. Additionally, the SAR request may request that the AP MLD transmit an auxiliary frame (1630, 1650) at the time of link switching to L2. Accordingly, the SAR request subfield may include both subfields related to L1 and subfields related to L2. For example, the Number of Multi-Link Info subfield (1355) included in the SAR request subfield may have a value of 1, and the Multi-Link Info subfield (1345) may include information for requesting transmission of an auxiliary frame (1630, 1650) in L2. Meanwhile, the STA that receives the ICF (1610) including the SAR request may transmit an ICR (1610) including a response to the SAR request to the AP MLD on L1. The SAR response may include an acknowledgment of the SAR request of the AP MLD.If the SAR response includes an acknowledgment for the SAR request, the STA may transmit an auxiliary frame (1640) on L1 at the time when the link switches to L1 based on the information included in the SAR request subfield. Additionally, the STA may transmit an auxiliary frame (1630, 1650) on L2 at the time when the link switches to L2 based on the information included in the SAR request subfield (e.g., Number of Multi-Link Info subfield (1355) and Multi-Link Info subfield (1345)).

[0170] FIG. 17 illustrates an exemplary format of a subfield for a SAR request based on TWT according to one embodiment of the present disclosure.

[0171] Referring to FIG. 17, an exemplary format of a broadcast TWT parameter set field in a TWT-based SAR request method is described. Before going into a specific description of how to use the broadcast TWT parameter set field for a SAR request, the specific configuration of the broadcast TWT parameter set field is as follows. In this case, the description of TWT may overlap with the description of TWT of FIG. 10 described above, and the overlapping description may be omitted.

[0172] Referring back to FIG. 17, the Broadcast TWT Parameter Set field may include at least one of a Request Type subfield (1710), a Target wake time subfield, a Nominal Minimum TWT Wake Duration subfield, a TWT Wake Interval Mantissa subfield, or a Broadcast TWT Info subfield. The Target Wake Time subfield may indicate the start time of a scheduled future broadcast TWT SP. The Nominal Maximum TWT Wake Duration subfield may indicate the minimum unit within which a TWT requesting STA expects to wake up to complete the exchange of frames associated with a TWT flow identifier during the TWT wake duration. The TWT Wake Interval Mantissa subfield may be expressed as a binary value of a TWT wake interval value in microseconds.

[0173] Meanwhile, the Request Type subfield (1710) may include at least one of a TWT Request subfield, a TWT setup Command subfield, a Trigger subfield, a Last broadcast parameter set subfield, a Flow type subfield (1720), a Broadcast TWT Recommendation subfield, a TWT Wake Interval Exponent subfield, or a Reserved subfield.

[0174] The TWT Request subfield (1710) may indicate whether the WT element is transmitted by a TWT requesting STA or a TWT responding AP. If the value of the TWT Request subfield is 1, it may indicate a TWT requesting STA or a TWT scheduled STA, and if the value of the TWT Request subfield is 0, it may indicate a TWT responding AP (or, a TWT responding STA) or a TWT scheduling AP.

[0175] The TWT setup Command subfield can represent commands such as request, suggest, demand, grouping, accept, alternate, dictate, and reject.

[0176] The Trigger subfield can indicate whether a trigger frame is to be used in the TWT SP. If the value of the Trigger subfield is 1, the trigger is to be used, and if the value of the Trigger subfield is 0, the trigger is not to be used.

[0177] The Last broadcast parameter set subfield may indicate whether the corresponding broadcast TWT parameter set field is the last broadcast TWT parameter set. If the value of the Last Broadcast Parameter Set subfield is 1, it may indicate that the corresponding broadcast TWT parameter set field is the last broadcast TWT parameter set within the TWT element, and if the value of the Last Broadcast Parameter Set subfield is 0, it may indicate that there are more broadcast TWT parameter sets within the TWT element.

[0178] The Flow type subfield (1720) may indicate the type of interaction between a TWT requesting STA (or, TWT scheduled STA) and a TWT responding AP (or TWT scheduling AP).

[0179] The Broadcast TWT Recommendation subfield contains 3 bits and can indicate recommendations for frame types transmitted by the AP during a broadcast TWT SP, with a value of 0 to 7.

[0180] The TWT Wake Interval Exponent subfield may contain a value representing the TWT wake interval value in binary microseconds. For an individual TWT, the TWT Wake Interval Exponent subfield may indicate the interval between individual TWT SPs. The TWT wake interval of a TWT requesting STA may be defined as TWT Wake Interval Mantissa * 2 * TWT Wake Interval Exponent.

[0181] The last 1 bit of the Request Type subfield (1710) in the Broadcast TWT Parameter Set field may be reserved.

[0182] The Broadcast TWT Info subfield may include 2 octets and may include a 3-bit Reserved subfield (1730), a Broadcast TWT ID subfield, and a Broadcast TWT Persistence subfield. At this time, the Broadcast TWT ID subfield may indicate the broadcast ID of a specific broadcast TWT in which the STA requests participation or provides TWT parameters, depending on the value of the TWT setup command subfield of the TWT element. In addition, the Broadcast TWT Persistence subfield is a value expressed as the number of TBTTs for the section in which the broadcast TWT SP corresponding to the corresponding broadcast TWT parameter set is included. For example, when the value of the broadcast TWT persistence subfield is 10, it means that the broadcast TWT SP configured with the corresponding parameters is operated during the time when 10 beacon frames are transmitted, and when the value is 255, it may indicate that the broadcast TWT SP is applied permanently.

[0183] Meanwhile, the SAR request method using the broadcast TWT parameter set field described above may use the Flow type subfield (1720) and the reserved subfield (1730). In one embodiment, if the value of the Flow type subfield (1720) is 0, the AP may indicate an announced TWT, which means that it will not perform downlink transmission until the STA transmits a PS-Poll or APSD (automatic power save delivery) trigger frame. For example, the AP MLD may transmit the broadcast TWT parameter set field ahead of a periodic service interval. At this time, if the value of the Flow type subfield (1720) included in the broadcast TWT parameter set field is 0 and the reserved subfield (1730) includes information indicating that it is a SAR request, it may indicate that the TWT is used for a SAR request. A specific operation for a SAR request using the broadcast TWT parameter set field as described above is described in FIG. 18 below.

[0184] FIG. 18 illustrates an example of a SAR-based synchronization acquisition method according to one embodiment of the present disclosure.

[0185] Referring to FIG. 18, operations in the SAR request method using the broadcast TWT parameter set field of FIG. 17 described above are described. Therefore, in the description of the operations below, any description that overlaps with the broadcast TWT parameter set field of FIG. 17 may be omitted.

[0186] In one embodiment, the AP MLD on L1 may transmit an announced TWT (1810) to the STA. At this time, the announced TWT may refer to a broadcast TWT parameter set field in which the Flow type subfield (1720) is 0 and the reserved subfield (1730) includes at least 1 bit to indicate that the TWT is for a SAR request. An STA that receives the announced TWT (1810) from the AP MLD may transmit a join request (1820) to the AP MLD if it wants to join a TWT for requesting SAR. When the join request (1820) is received from the STA, the AP MLD may transmit an ICF (1830) including the SAR request to the STA. At this time, the ICF (1830) may mean an ICF including the SAR request subfield described in FIGS. 12 to 16. And based on the information included in the announced TWT (1810), the AP MLD can transmit an auxiliary frame (1840) at the start of the service period. At this time, the auxiliary frame may refer to the auxiliary frame described in FIGS. 12 to 16.

[0187] FIG. 19 illustrates an example of a SAR-based synchronization acquisition method according to one embodiment of the present disclosure.

[0188] Referring to FIG. 19, a SAR request method based on a SAR control subfield may be described. However, any description overlapping with the SAR request subfield-based SAR request method described previously in FIGS. 12 to 16 may be omitted.

[0189] In one embodiment, the AP MLD may perform a (re)association procedure (1905, 1910) with the STA. For example, the AP MLD may identify whether the STA is an MLMR-supporting STA through the association procedure with the STA. More specifically, the STA may notify the AP MLD of a parameter (e.g., dot11SAROptionImplemented) indicating whether MLMR support is possible. For example, when dot11SAROptionImplemented has a value of true, the STA connected to a non-AP MLD may indicate that the STA supports MLMR during the connection process with the AP MLD. In addition, the STA may indicate whether the STA supports SAR through the value of the SAR Support subfield within the MLD Capability and Operation subfield included in the Basic Multi-Link element. For example, if the value of the SAR Support subfield is 1, it may indicate that SAR is supported, and if the value of the SAR Support subfield is 0, it may indicate that SAR is not supported. Of course, the meaning of each value of the SAR Support subfield is not limited to the above example.

[0190] And if STA supports SAR, AP MLD can transmit ICF (1915 or 1945) including SAR control to STA on L1. Then, STA can transmit response frame (1920 or 1950) to AP MLD, and the response frame can be ICR. And STA can transmit auxiliary frame (1940 or not shown) to AP MLD at the time of link switching to L1. Also, AP MLD can transmit ICF (1930) including SAR control to STA on L2, and STA can transmit response frame (1935) to AP MLD. And STA can transmit auxiliary frame (1955) to AP MLD at the time of link switching to L2.

[0191] In one embodiment, if the STA is an STA that supports MLMR or eMLSR, the STA can receive SAR control on all links (e.g., L1 and L2), and thus the STA can identify a request to transmit an assistive frame for all links. At this time, a subfield related to a link ID included in the SAR control subfield (e.g., an Assisting STA Link ID Bitmap subfield) can have a value of 1, and the subfield related to the link ID can indicate a link identifier of at least one other assisting AP belonging to the same AP MLD operating on at least one enabled link. Hereinafter, an assisting AP may refer to an AP other than an AP that has requested assistive frame transmission among APs belonging to the same AP MLD. In addition, an assisting STA may refer to an STA other than an STA that has received a request to transmit an assistive frame among STAs belonging to the same non-AP MLD. And, if there is no scheduled frame exchange, the secondary STA may need to schedule transmission of the secondary frame to the AP that requested the transmission of the secondary frame after another STA belonging to the same non-AP MLD receives the SAR control subfield. For example, the AP MLD may request transmission of the secondary frame even when switching to another link (e.g., L2) via ICF (1915). For example, the STA may transmit the secondary frame at the time of switching to L2 (1925) rather than the time of switching to L1 (1940), based on the SAR control included in ICF (1915). Meanwhile, FIG. 19 illustrates an example of activated links of L1 and L2, but is not limited thereto.Additionally, an STA supporting MLMR may request transmission of an assist frame at the time of switching to multiple links having a value of 1 in a subfield related to the link ID (e.g., Assisting STA Link ID Bitmap subfield).

[0192] The specific configuration of the SAR control subfield format described above is described below in Figure 20.

[0193] FIG. 20 illustrates an exemplary format of a SAR control subfield according to one embodiment of the present disclosure.

[0194] Referring to FIG. 20, the SAR control subfield may include a control information subfield. The control information subfield may have a size of 20 bits and may include at least one of the Assisting STA Link ID Bitmap subfield (2010) and the Time Offset subfield (2020). The SAR control subfield may be a subfield included in the control field.

[0195] The Assisting STA Link ID Bitmap subfield (2010) may indicate the link identifier of an auxiliary STA belonging to a non-AP MLD requested to support an AP belonging to an AP MLD belonging to a non-simultaneous transmit and receive (NSTR) link pair or (e)MLSR links. The 15th bit of the Assisting STA Link ID Bitmap subfield (2010) may be a reserved value.

[0196] The Time Offset subfield (2020) may indicate the difference from the time at which the transmission of the auxiliary frame is requested, and may include the switching delay value of the AP. In addition, the Time Offset subfield (2020) may be expressed in a predefined unit time unit (e.g., 4 us, 16 us, 32 us, etc.). Meanwhile, the Time Offset subfield (2020) may be set to a reserved value in the AAR (AP-assisted medium synchronization recovery) control subfield. Accordingly, when the STA receives an A-control field including an AAR control subfield from the AP MLD, the STA may determine or regard it as being the same as the SAR control subfield. Accordingly, when the STA receives an AAR control subfield from the AP MLD, the STA may identify the field set to a reserved value as a time offset and perform the same operation as when the SAR control subfield is received.

[0197] However, the SAR control subfield may not include additional EDCA parameters for STA contention (e.g., EDCA parameters (1340)). Therefore, when using the SAR control subfield, the additional EDCA parameters may be provided before transmission of the frame containing the SAR control subfield via another frame (e.g., a beacon, probe response, or connection response).

[0198] FIG. 21 illustrates an example of a SAR-based synchronization acquisition method according to one embodiment of the present disclosure.

[0199] Referring to Fig. 21, another example of auxiliary frame transmission based on the SAR control subfield is described. However, descriptions overlapping with Fig. 19 may be omitted.

[0200] In one embodiment, the AP MLD may transmit an ICF (2110 or 2150) including SAR control to the STA on L1. The STA may also transmit an auxiliary frame (2140 or not shown) together with the response at a time indicated by the value of the Time Offset subfield included in the SAR control subfield (e.g., the time when link switches to L1) without transmitting a separate response frame. Furthermore, the AP MLD may also transmit an ICF (2130) including SAR control to the STA on L2, and the STA may transmit an auxiliary frame (2160) together with the response at a time indicated by the value of the Time Offset subfield of the SAR control subfield included in the ICF (2130) without transmitting a separate response frame (e.g., the time when link switches to L2).

[0201] In one embodiment, the AP MLD may request transmission of auxiliary frames even when switching to another link (e.g., L2) via ICF (2110). For example, the STA may transmit auxiliary frames at the time of switching to L2 (2130, 2160) rather than at the time of switching to L1 (2140), based on the SAR control subfield included in ICF (2110).

[0202] Meanwhile, Fig. 21 illustrates, but is not limited to, the activated links of L1 and L2. In addition, an STA supporting MLMR may request transmission of an auxiliary frame for multiple links having a value of 1 in a subfield related to the link ID (e.g., the Assisting STA Link ID Bitmap subfield) at the time of switching to the corresponding links.

[0203] Meanwhile, the SAR request or SAR control for requesting transmission of the auxiliary frame above may refer to the SAR request subfield or the SAR control subfield, and similarly, the SAR response in response to the request of the AP MLD may refer to the SAR response subfield.

[0204] FIG. 22 illustrates a flowchart of a SAR-based synchronization acquisition operation in a wireless LAN system according to an embodiment of the present disclosure.

[0205] Referring to FIG. 22, the SAR operation proposed in the present disclosure is illustrated, and some or all of the various embodiments related to the AP (e.g., an AP belonging to an AP MLD) described above may be applied identically or similarly to FIG. 22.

[0206] At step 2210, the AP may transmit a first frame to the STA to request transmission of a second frame related to medium synchronization. The first frame may include an ICF, and the ICF may include a SAR request subfield or a SAR control subfield.

[0207] At step 2220, the AP may receive a second frame from the STA at a link switching time based on the first frame. At this time, the second frame may include an auxiliary frame including a PPDU with a fixed duration of MPDU or TXOP. By receiving the auxiliary frame at a fixed time (e.g., the link switching time), the AP can recover medium synchronization more quickly, and the AP's operation may not be restricted even if the MediumSyncDelay timer does not expire.

[0208] Meanwhile, the above has described one embodiment of the operation of an AP belonging to the AP MLD based on the flow chart illustrated in FIG. 22, but it is obvious that the operation of the AP may vary depending on other embodiments described above.

[0209] FIG. 23 illustrates a flowchart of a SAR-based synchronization acquisition operation in a wireless LAN system according to an embodiment of the present disclosure.

[0210] Referring to FIG. 23, the SAR operation proposed in the present disclosure is illustrated, and some or all of the various embodiments related to the STA described above (e.g., STA belonging to a non-AP MLD) may be applied identically or similarly to FIG. 22.

[0211] At step 2310, the STA may receive a first frame from the AP for requesting transmission of a second frame related to medium synchronization. This frame may include an ICF, and the ICF may include a SAR request subfield or a SAR control subfield.

[0212] At step 2320, the STA may transmit a second frame to the AP at a link switching time based on the first frame. At this time, the second frame may include an auxiliary frame including an MPDU or a PPDU with a specified duration of TXOP. By transmitting the auxiliary frame at a specified time (e.g., a link switching time) at the request of the AP, the STA may enable the AP to recover medium synchronization more quickly, and the AP's operation may not be restricted even if the MediumSyncDelay timer does not expire.

[0213] Meanwhile, in the above, one embodiment of the operation of an STA belonging to a non-AP MLD has been described based on the flowchart illustrated in FIG. 23, but it is obvious that the operation of the STA may vary depending on other embodiments described above.

[0214] Meanwhile, the present specification and drawings disclose preferred embodiments of the present disclosure, and although specific terms are used, they are used only in a general sense to easily explain the technical contents of the present disclosure and to help understand the disclosure, and are not intended to limit the scope of the present disclosure.

[0215] Furthermore, it will be apparent to those skilled in the art that, in addition to the embodiments described in this disclosure, other modifications based on the technical concepts of this disclosure are possible. For example, some or all of the contents of one embodiment described above may be combined with some or all of one or more other embodiments, and such combinations are also included in the embodiments proposed in this disclosure.

Claims

1. In a method performed by an AP (access point) of a wireless local area network (WLAN) system, A step of transmitting a first frame on a first link to request transmission of a second frame related to medium synchronization by a STA (station); and A step of receiving the second frame on the first link from the STA at a time when the first link is enabled, The first frame above includes an initial control frame (ICF), The second frame above includes an MPDU (MAC protocol data unit) or a PPDU (physical layer protocol data unit) with a fixed duration of a TXOP (transmission opportunity), and A method wherein the above AP is an AP MLD (multi-link device) that supports multi-link operation.

2. In paragraph 1, The first frame includes a SAR (STA-assisted medium synchronization recovery) request subfield or a SAR control subfield, The SAR request subfield includes at least one of a time unit subfield, an existence subfield, a transmission time subfield of the second frame, an interval subfield for indicating a repeat transmission period of the second frame, a count subfield for indicating a number of repeat transmissions of the second frame, an EDCA (enhanced distributed channel access) parameter subfield, or a multi-link information subfield for requesting transmission of the second frame on at least one link other than the link on which the first frame is transmitted when the STA supports multi-link. A method according to claim 1, wherein the SAR control subfield includes a link ID (identifier) ​​subfield for the STA when the STA supports multi-link, or a time offset subfield for indicating the transmission time of the second frame.

3. In the second paragraph, the method, Further comprising the step of receiving a third frame including a SAR response subfield from the STA on the first link, The third frame includes an initial control response (ICR), A method according to claim 1, wherein the SAR response subfield includes at least one of a status code subfield for indicating whether the request is successful, a count subfield for indicating the number of times the second frame is repeatedly transmitted, or an accepted link bitmap subfield for indicating the ID of an accepted link among the at least one link when the STA supports multi-links.

4. In paragraph 1, The first frame above includes a broadcast TWT parameter set field, The above broadcast TWT parameter set field includes a flow type sub-field and a reserved sub-field, The above flow type subfield contains a value of 0, A method wherein the reserved subfield indicates that the broadcast TWT parameter set field is a request for the second frame.

5. In a method performed by a STA (station) of a wireless local area network (WLAN) system, A step of receiving a first frame on a first link for requesting transmission of a second frame related to medium synchronization from an AP (access point); and comprising a step of transmitting the second frame on the first link at a time when the first link is enabled, with the AP; The first frame above includes an initial control frame (ICF), The second frame above includes an MPDU (MAC protocol data unit) or a PPDU (physical layer protocol data unit) with a fixed duration of a TXOP (transmission opportunity), and A method wherein the above AP is an AP MLD (multi-link device) that supports multi-link operation.

6. In paragraph 5, The first frame includes a SAR (STA-assisted medium synchronization recovery) request subfield or a SAR control subfield, The SAR request subfield includes at least one of a time unit subfield, an existence subfield, a transmission time subfield of the second frame, an interval subfield for indicating a repeat transmission period of the second frame, a count subfield for indicating a number of repeat transmissions of the second frame, an EDCA (enhanced distributed channel access) parameter subfield, or a multi-link information subfield for requesting transmission of the second frame on at least one link other than the link on which the first frame is transmitted when the STA supports multi-link. A method according to claim 1, wherein the SAR control subfield includes a link ID (identifier) ​​subfield for the STA when the STA supports multi-link, or a time offset subfield for indicating the transmission time of the second frame.

7. In the 6th paragraph, the method, The method further includes the step of transmitting a third frame containing a SAR response subfield to the AP over the first link, The third frame includes an initial control response (ICR), A method according to claim 1, wherein the SAR response subfield includes at least one of a status code subfield for indicating whether the request is successful, a count subfield for indicating the number of times the second frame is repeatedly transmitted, or an accepted link bitmap subfield for indicating the ID of an accepted link among the at least one link when the STA supports multi-links.

8. In Paragraph 5, The first frame above includes a broadcast TWT parameter set field, The above broadcast TWT parameter set field includes a flow type sub-field and a reserved sub-field, The above flow type subfield contains a value of 0, A method wherein the reserved subfield indicates that the broadcast TWT parameter set field is a request for the second frame.

9. Regarding AP (access point), At least one transceiver; At least one processor communicatively coupled to said at least one transceiver; and At least one memory communicatively coupled to said at least one processor and storing instructions, The above instructions are executed individually or in any combination by the at least one processor, so that the AP: STA (station) receives a first frame on a first link to request transmission of a second frame related to medium synchronization, and From the STA, to receive the second frame on the first link at a time when the first link is enabled, The first frame above includes an initial control frame (ICF), The second frame above includes an MPDU (MAC protocol data unit) or a PPDU (physical layer protocol data unit) with a fixed duration of a TXOP (transmission opportunity), and The above AP is an AP MLD (multi-link device) that supports multi-link operation.

10. In paragraph 9, The first frame includes a SAR (STA-assisted medium synchronization recovery) request subfield or a SAR control subfield, The SAR request subfield includes at least one of a time unit subfield, an existence subfield, a transmission time subfield of the second frame, an interval subfield for indicating a repeat transmission period of the second frame, a count subfield for indicating a number of repeat transmissions of the second frame, an EDCA (enhanced distributed channel access) parameter subfield, or a multi-link information subfield for requesting transmission of the second frame on at least one link other than the link on which the first frame is transmitted when the STA supports multi-link. AP, wherein the above SAR control subfield includes a link ID (identifier) ​​subfield for the STA if the STA supports multi-link, or a time offset subfield for indicating the transmission time of the second frame.

11. In paragraph 10, the commands are: To receive a third frame including a SAR response subfield from the STA on the first link, The third frame includes an initial control response (ICR), The AP, wherein the SAR response subfield includes at least one of a status code subfield for indicating whether the request is successful, a count subfield for indicating the number of repeated transmissions of the second frame, or an accepted link bitmap subfield for indicating the ID of an accepted link among the at least one link when the STA supports multi-links.

12. In paragraph 9, The first frame above includes a broadcast TWT parameter set field, The above broadcast TWT parameter set field includes a flow type sub-field and a reserved sub-field, The above flow type subfield contains a value of 0, The above reserved subfield is intended to indicate that the broadcast TWT parameter set field is a request for the second frame, AP.

13. In STA(station), At least one transceiver; At least one processor communicatively coupled to said at least one transceiver; and At least one memory communicatively coupled to said at least one processor and storing instructions, The above instructions are executed individually or in any combination by the above at least one processor, and the above STA: Receive a first frame on the first link from the AP (access point) to request the transmission of a second frame related to medium synchronization, and The above AP transmits the second frame on the first link at the time when the first link is enabled, and The first frame above includes an initial control frame (ICF), The second frame above includes an MPDU (MAC protocol data unit) or a PPDU (physical layer protocol data unit) with a fixed duration of a TXOP (transmission opportunity), and The above AP is an STA, which is an AP MLD (multi-link device) that supports multi-link operation.

14. In Paragraph 13, The first frame includes a SAR (STA-assisted medium synchronization recovery) request subfield or a SAR control subfield, The SAR request subfield includes at least one of a time unit subfield, an existence subfield, a transmission time subfield of the second frame, an interval subfield for indicating a repeat transmission period of the second frame, a count subfield for indicating a number of repeat transmissions of the second frame, an EDCA (enhanced distributed channel access) parameter subfield, or a multi-link information subfield for requesting transmission of the second frame on at least one link other than the link on which the first frame is transmitted when the STA supports multi-link. An STA wherein the SAR control subfield includes a link ID (identifier) ​​subfield for the STA if the STA supports multi-link, or a time offset subfield for indicating the transmission time of the second frame.

15. In paragraph 14, the commands are: To the above AP, transmit a third frame including a SAR response subfield on the first link, The third frame includes an initial control response (ICR), The STA, wherein the SAR response subfield includes at least one of a status code subfield for indicating whether the request is successful, a count subfield for indicating the number of times the second frame is repeatedly transmitted, or an accepted link bitmap subfield for indicating the ID of an allowed link among the at least one link when the STA supports multi-links.

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