Method and apparatus for supporting power saving mode in multi-AP operation in wireless LAN system

Abstract

The present disclosure discloses a method and an apparatus for supporting a power saving mode in a multi-AP operation in a wireless LAN system. A method performed by a first AP in a wireless LAN system, according to one embodiment of the present disclosure, may comprise the steps of: receiving, from a second AP, a polling frame for identifying whether to participate in a multi-AP operation; transmitting, to the second AP, a frame including information indicating participation in the multi-AP operation in response to the polling frame, on the basis of the first AP being configured to maintain an awake state related to a power saving mode in a time interval for the multi-AP operation; receiving, from the second AP, a control frame including information related to initiation of the multi-AP operation; and performing frame exchange that is based on the multi-AP operation, on the basis of the information.

Description

Method and device for supporting power reduction mode in multi-AP operation in wireless LAN system

[0001] The present disclosure relates to a method and device for supporting a power saving mode in multi-AP operation in a wireless local area network (WLAN) system.

[0002] New technologies have been introduced for wireless local area networks (WLANs) to improve transmission rates, increase bandwidth, enhance reliability, reduce errors, and reduce latency. Among WLAN technologies, the IEEE (Institute of Electrical and Electronics Engineers) 802.11 series of standards can be referred to as Wi-Fi. For example, recently introduced technologies for WLANs include enhancements for Very High Throughput (VHT) in the 802.11ac standard and enhancements for High Efficiency (HE) in the IEEE 802.11ax standard.

[0003] To provide a more advanced wireless communication environment, improved technologies for Extremely High Throughput (EHT) are being discussed. For example, technologies for Multiple Input Multiple Output (MIMO), which supports increased bandwidth, efficient utilization of multiple bands, and increased spatial streams, and for coordination of multiple access points (APs), are being studied. In particular, various technologies are being studied to support low latency or real-time traffic. Furthermore, new technologies are being discussed to support ultra-high reliability (UHR), including improvements or extensions of EHT technology.

[0004] The technical problem of the present disclosure is to provide a method and device for supporting a power saving mode in a multi-AP operation in a wireless local area network (WLAN) system.

[0005] The technical problems to be achieved in the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by a person having ordinary skill in the technical field to which the present disclosure belongs from the description below.

[0006] A method performed by a first access point (AP) in a wireless LAN system according to one aspect of the present disclosure may include: receiving a polling frame from a second AP for checking whether to participate in a multi-AP operation; transmitting, in response to the polling frame, a frame including information indicating participation in the multi-AP operation to the second AP based on the first AP being set to maintain an awake state associated with a power reduction mode during a duration for the multi-AP operation; receiving, from the second AP, a control frame including information associated with initiation of the multi-AP operation; and performing frame exchange based on the multi-AP operation based on the information.

[0007] In accordance with an additional aspect of the present disclosure, a method performed by a first access point (AP) in a wireless LAN system may include: transmitting a target-wake time (TWT) request frame to a second AP for requesting participation in a multi-AP operation; receiving a TWT response frame from the second AP for indicating whether the requested participation is granted; and performing frame exchange based on the multi-AP operation during a TWT service period (SP) in which the first AP is configured to maintain an awake state associated with a power reduction mode during the TWT service period in which the multi-AP operation is to be performed, based on the participation being granted.

[0008] According to the present disclosure, a method and device for supporting a power saving mode in a multi-AP operation in a wireless local area network (WLAN) system can be provided.

[0009] According to the present disclosure, there is an advantage in that the technical effects of multi-AP operation can be obtained even for AP(s) operating in power reduction mode.

[0010] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects that are not mentioned will be clearly understood by a person having ordinary skill in the art to which the present disclosure pertains from the description below.

[0011] The accompanying drawings, which are incorporated in and are part of the detailed description to aid in understanding the present disclosure, provide embodiments of the present disclosure and, together with the detailed description, describe the technical features of the present disclosure.

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

[0013] FIG. 2 is a diagram showing an exemplary structure of a wireless LAN system to which the present disclosure can be applied.

[0014] FIG. 3 is a diagram for explaining a link setup process to which the present disclosure can be applied.

[0015] FIG. 4 is a diagram for explaining a backoff process to which the present disclosure can be applied.

[0016] FIG. 5 is a diagram for explaining a CSMA / CA-based frame transmission operation to which the present disclosure can be applied.

[0017] FIG. 6 is a drawing for explaining an example of a frame structure used in a wireless LAN system to which the present disclosure can be applied.

[0018] FIG. 7 is a diagram illustrating examples of PPDUs defined in the IEEE 802.11 standard to which the present disclosure can be applied.

[0019] FIG. 8 is a diagram showing examples of multi-AP techniques to which the present disclosure can be applied.

[0020] FIG. 9 illustrates an example of the operation of a first AP performing multi-AP operation considering a power reduction mode according to an embodiment of the present disclosure.

[0021] FIG. 10 illustrates an example of the operation of a second AP performing multi-AP operation considering a power reduction mode according to an embodiment of the present disclosure.

[0022] FIG. 11 illustrates another example of the operation of a first AP performing multi-AP operation considering a power reduction mode according to an embodiment of the present disclosure.

[0023] FIG. 12 illustrates another example of the operation of a second AP performing multi-AP operation considering a power reduction mode according to an embodiment of the present disclosure.

[0024] FIG. 13 illustrates an example of a polling-based method according to an embodiment of the present disclosure.

[0025] FIG. 14 illustrates another example of a polling-based method according to an embodiment of the present disclosure.

[0026] FIG. 15 illustrates an example of a TWT-based method according to an embodiment of the present disclosure.

[0027] FIG. 16 illustrates a specific example of multi-AP operation in a TWT-based scheme according to an embodiment of the present disclosure.

[0028] FIG. 17 illustrates another specific example of multi-AP operation in a TWT-based scheme according to an embodiment of the present disclosure.

[0029] FIG. 18 illustrates a pre-cooperation-based multi-AP operation method according to an embodiment of the present disclosure.

[0030] FIG. 19 is an example of applying a multi-AP operation method according to an embodiment of the present disclosure to multi-link.

[0031] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The detailed description set forth below, together with the accompanying drawings, is intended to explain exemplary embodiments of the present disclosure and is not intended to represent the only embodiments in which the present disclosure may be practiced. The following detailed description includes specific details to provide a thorough understanding of the present disclosure. However, one of ordinary skill in the art will appreciate that the present disclosure may be practiced without these specific details.

[0032] In some cases, to avoid obscuring the concepts of the present disclosure, known structures and devices may be omitted or illustrated in block diagram form focusing on the core functions of each structure and device.

[0033] 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.

[0034] In this disclosure, terms such as “first,” “second,” etc. are used only to distinguish one component from another and are not used to limit the components, and do not limit the order or importance between 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.

[0035] 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.

[0036] 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 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 based on the newly proposed IEEE 802.11bn (or UHR) standard. Additionally, the examples of the present disclosure can be applied to a wireless LAN based on the next-generation standard after IEEE 802.11bn. Furthermore, the examples of the present disclosure can be applied to a cellular wireless communication system. For example, the examples of the present disclosure can be applied to a cellular wireless communication system based on the LTE (Long Term Evolution) series of technologies and the 5G NR (New Radio) series of technologies of the 3rd Generation Partnership Project (3GPP) standard.

[0037] Below, technical features to which examples of the present disclosure can be applied are described.

[0038] FIG. 1 illustrates a block diagram of a wireless communication device according to one embodiment of the present disclosure.

[0039] The first device (100) and the second device (200) illustrated in FIG. 1 may be replaced with various terms such as a terminal, a wireless device, a WTRU (Wireless Transmit Receive Unit), a UE (User Equipment), an MS (Mobile Station), a UT (user terminal), an MSS (Mobile Subscriber Station), an MSS (Mobile Subscriber Unit), an SS (Subscriber Station), an AMS (Advanced Mobile Station), a WT (Wireless terminal), or simply a user. In addition, the first device (100) and the second device (200) may be replaced with various terms such as an access point (AP), a BS (Base Station), a fixed station, a Node B, a BTS (Base Transceiver System), a network, an AI (Artificial Intelligence) system, an RSU (road side unit), a repeater, a router, a relay, a gateway, etc.

[0040] 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.

[0041] Referring to FIG. 1, the first device (100) and the second device (200) can transmit and receive wireless signals through various wireless LAN technologies (e.g., IEEE 802.11 series). The first device (100) and the second device (200) can include interfaces for a medium access control (MAC) layer and a physical layer (PHY) that follow the provisions of the IEEE 802.11 standard.

[0042] In addition, the first device (100) and the second device (200) may additionally support various communication standards (e.g., 3GPP LTE series, 5G NR series standards, etc.) other than wireless LAN technology. In addition, the device of the present disclosure may be implemented as various devices such as a mobile phone, a vehicle, a personal computer, an AR (Augmented Reality) device, a VR (Virtual Reality) device, 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).

[0043] A first device (100) includes one or more processors (102) and one or more memories (104), and may further include one or more 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 / signals, and then transmit a wireless signal including the first information / signals via the transceivers (106). Furthermore, the processor (102) may receive a wireless signal including second information / signals via the transceivers (106), and then store information obtained from signal processing of the second information / signals 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., IEEE 802.11 series). The 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. In the present disclosure, a device may also mean a communication modem / circuit / chip.

[0044] The second device (200) includes one or more processors (202), one or more memories (204), and may further include one or more transceivers (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 memory (204) to generate third information / signals, and then transmit a wireless signal including the third information / signals via the transceivers (206). Furthermore, the processor (202) may receive a wireless signal including fourth information / signals via the transceivers (206), and then store information obtained from signal processing of the fourth information / signals 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 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 (202) and the memory (204) may be part of a communication modem / circuit / chip designed to implement a wireless LAN technology (e.g., IEEE 802.11 series). The 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. In the present disclosure, a device may also mean a communication modem / circuit / chip.

[0045] Hereinafter, the hardware elements of the device (100, 200) will be described in more detail. Although not limited thereto, 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 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 operational 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 operational 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 or information according to the functions, procedures, proposals and / or methods disclosed in the present 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 or information according to the descriptions, functions, procedures, proposals, methods and / or operational flowcharts disclosed in the present disclosure.

[0046] One or more processors (102, 202) may be referred to as a controller, a microcontroller, a microprocessor, or a microcomputer. One or more processors (102, 202) may be implemented by hardware, firmware, software, or a combination thereof. For example, one or more Application Specific Integrated Circuits (ASICs), one or more Digital Signal Processors (DSPs), one or more Digital Signal Processing Devices (DSPDs), one or more Programmable Logic Devices (PLDs), or one or more Field Programmable Gate Arrays (FPGAs) may be included in one or more processors (102, 202). The descriptions, functions, procedures, proposals, methods, and / or operational flowcharts disclosed in this disclosure may be implemented using firmware or software, and the firmware or software may be implemented to include modules, procedures, functions, etc. The descriptions, functions, procedures, proposals, methods and / or operation flowcharts disclosed in this disclosure may be implemented using firmware or software configured to perform one or more processors (102, 202) or stored in one or more memories (104, 204) and driven by one or more processors (102, 202). The descriptions, functions, procedures, proposals, methods and / or operation flowcharts disclosed in this disclosure may be implemented using firmware or software in the form of codes, instructions and / or sets of instructions.

[0047] 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 ROM, RAM, EPROM, 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.

[0048] One or more transceivers (106, 206) can transmit user data, control information, wireless signals / channels, etc., as mentioned 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, wireless signals / channels, etc., as mentioned 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, or wireless signals 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, or wireless signals 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, wireless signals / channels, or the like, as referred to 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 may be multiple physical antennas or multiple logical antennas (e.g., antenna ports). One or more transceivers (106, 206) can 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 user data, control information, wireless signals / channels, etc. processed by one or more processors (102, 202) from baseband signals to RF band signals. For this purpose, one or more transceivers (106, 206) may include an (analog) oscillator and / or filter.

[0049] For example, one of the STAs (100, 200) may perform the intended operation of an AP, and the other of the STAs (100, 200) may perform the intended operation of a non-AP STA. For example, the transceivers (106, 206) of FIG. 1 may perform transmission and 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.). In addition, in the present disclosure, operations in which various STAs generate transmission and reception signals or perform data processing or calculations in advance for transmission and reception signals may be performed in the processors (102, 202) of FIG. 1. For example, an example of an operation for generating a transmission / reception signal or performing data processing or operation in advance for a transmission / reception signal may include 1) an operation for determining / obtaining / configuring / computing / decoding / encoding bit information of a field (SIG (signal), STF (short training field), LTF (long training field), Data, etc.) included in a PPDU, 2) an operation for determining / configuring / obtaining time resources or frequency resources (e.g., subcarrier resources) used for a field (SIG, STF, LTF, Data, etc.) included in a PPDU, 3) an operation for determining / configuring / obtaining a specific sequence (e.g., a pilot sequence, an STF / LTF sequence, an extra sequence applied to SIG) used for a field (SIG, STF, LTF, Data, etc.) included in a PPDU, 4) a power control operation and / or a power saving operation applied to an STA, 5) an operation related to determining / obtaining / configuring / computing / decoding / encoding an ACK signal, etc. Additionally, in the examples below, various information (e.g., information related to fields / subfields / control fields / parameters / power, etc.) used by various STAs for determining / acquiring / configuring / computing / decoding / encoding transmission / reception signals can be stored in the memory (104, 204) of FIG. 1.

[0050] 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.

[0051] FIG. 2 is a diagram showing an exemplary structure of a wireless LAN system to which the present disclosure can be applied.

[0052] The structure of a wireless LAN system can be composed of multiple components. Through the interaction of multiple components, a wireless LAN that supports transparent STA mobility to the upper layer can be provided. 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 (BSS1 and BSS2) and the inclusion of two STAs as members of each BSS (STA1 and STA2 are included in BSS1, and STA3 and STA4 are included in BSS2). 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 a BSA, it cannot directly communicate with other STAs within the BSA.

[0053] If we do not consider the DS illustrated in Figure 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, BSS1 consisting of only STA1 and STA2, or BSS2 consisting of only STA3 and STA4, can be representative examples of an IBSS, respectively. Such a configuration is possible when the STAs can communicate directly without an AP. Furthermore, in this type of WLAN, a LAN can be configured when needed rather than being planned in advance, and this can 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 distributed systems (DS) is not permitted, forming a self-contained network.

[0054] 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).

[0055] In a wireless LAN, the direct STA-to-STA distance can 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 distributed system (DS) can be configured.

[0056] 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 a distributed system medium (DSM). 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.

[0057] 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).

[0058] An AP is an entity that enables access to a DS through a WM for associated non-AP STAs and also has the functionality of an STA. Data movement between a BSS and a DS can be performed through an AP. For example, STA2 and STA3 illustrated in FIG. 2 have the functionality of an STA and provide the function of allowing associated non-AP STAs (STA1 and STA4) 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 a WM and the address used by an AP for communication on a DSM do not necessarily have to be the same. A BSS consisting of an AP and one or more STAs can be referred to as an infrastructure BSS.

[0059] Data transmitted from one of the STA(s) associated with an AP to the STA address of that AP may always be received on an uncontrolled port and processed by an IEEE 802.1X port access entity. In addition, if the controlled port is authenticated, the transmitted data (or frame) may be forwarded to the DS.

[0060] In addition to the structure of the DS described above, an extended service set (ESS) may be established to provide wider coverage.

[0061] An ESS is a network of arbitrary size and complexity, consisting of DSs and BSSs. An ESS 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 Logical Link Control (LLC) layer. STAs within an ESS can communicate with each other, and mobile STAs can move from one BSS to another (within the same ESS) transparently to the LLC. APs within an ESS may have the same SSID (service set identification). The SSID is distinct from the BSSID, which is the identifier of the BSS.

[0062] 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 limit 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 with one (or more) ESS networks. This can occur in cases where an ad-hoc network operates at 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.

[0063] FIG. 3 is a diagram for explaining a link setup process to which the present disclosure can be applied.

[0064] For an STA to set up a link and transmit and receive data on a network, it must first discover the network, perform authentication, establish an association, and complete security authentication procedures. 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.

[0065] In step S310, 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.

[0066] Scanning methods include active scanning and passive scanning. Figure 3 illustrates a network discovery operation including 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.

[0067] 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 so that the STA performing the scanning can 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.

[0068] After the STA discovers the network, an authentication process may be performed in step S320. This authentication process may be referred to as the first authentication process to clearly distinguish it from the security setup operation of step S340 described below.

[0069] 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 frame used for the authentication request / response corresponds to a management frame.

[0070] 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.

[0071] An STA can send 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.

[0072] After the STA is successfully authenticated, an association process may be performed in step S330. 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.

[0073] For example, the association request frame may include information about various capabilities, a beacon listen interval, a service set identifier (SSID), supported rates, supported channels, an 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 may be replaced by other information or include additional information.

[0074] After the STA successfully joins the network, a security setup process may be performed in step S340. The security setup process in step S340 may be referred to as an authentication process through a Robust Security Network Association (RSNA) request / response, the authentication process in step S320 may be referred to as a first authentication process, and the security setup process in step S340 may also be referred to simply as an authentication process.

[0075] The security setup process of step S340 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.

[0076] FIG. 4 is a diagram for explaining a backoff process to which the present disclosure can be applied.

[0077] In wireless LAN systems, the basic access mechanism of MAC (Medium Access Control) is Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA). The CSMA / CA mechanism, 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 may perform a Clear Channel Assessment (CCA) to sense the wireless channel or medium for a predetermined time period (e.g., a DCF Inter-Frame Space (DIFS)) before starting transmission. If the sensing result determines that the medium is in an idle state, the AP and / or STA may start 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 delay period (e.g., a random backoff period) for medium access before attempting to transmit frames. By applying a random backoff period, multiple STAs are expected to attempt to transmit frames after waiting for different periods of time, thereby minimizing collisions.

[0078] 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 that periodically polls all receiving APs and / or STAs to ensure that they receive data frames. In addition, the HCF has the Enhanced Distributed Channel Access (EDCA) and the HCF Controlled Channel Access (HCCA). The EDCA is a contention-based access method for a provider to provide data frames to multiple users, while the HCCA uses a non-contention-based 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 the wireless LAN, and can transmit QoS data in both the Contention Period (CP) and the Contention Free Period (CFP).

[0079] Referring to Fig. 4, an operation based on a random backoff period is described. When a medium that was occupied / busy changes to an idle state, multiple STAs can attempt to transmit data (or frames). To minimize collisions, each STA can 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 can 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 given an initial value of CWmin, but can take a value doubled in case of transmission failure (e.g., when an ACK for a transmitted frame is not received). When the CW parameter value becomes CWmax, data transmission can be attempted while maintaining the CWmax value until data transmission is successful, and if data transmission is successful, it is reset to the CWmin value. The CW, CWmin, and CWmax values ​​are 2. n It is desirable to set it to -1 (n=0, 1, 2, ...).

[0080] 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.

[0081] In the example of FIG. 4, when a packet to be transmitted reaches the MAC of STA3, STA3 can immediately transmit a 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 a random backoff count value selected by each STA after waiting for DIFS if the medium is monitored as 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, they 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. From STA4's perspective, when the medium becomes idle, it waits for DIFS, counts down according to its selected random backoff count value, and then starts transmitting frames. In the example of Figure 4, 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.

[0082] As in the example of Fig. 4, a data frame is a frame used for transmitting data forwarded to a higher 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 that is not forwarded to a higher layer, and is transmitted after a backoff performed after an IFS elapses, such as DIFS or PIFS (Point coordination function IFS). Subtype frames of a management frame include a beacon, an association request / response, a re-association request / response, a probe request / response, and an authentication request / response. A control frame is a frame used to control access to the medium. The subtype frames of the control frame include Request-To-Send (RTS), Clear-To-Send (CTS), Acknowledgment (ACK), Power Save-Poll (PS-Poll), Block ACK (BlockAck), Block ACK Request (BlockACKReq), Null Data Packet Announcement (NDP), and Trigger. 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). The type and subtype of the frame can be identified by the type field and subtype field in the Frame Control (FC) field.

[0083] 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.

[0084] FIG. 5 is a diagram for explaining a CSMA / CA-based frame transmission operation to which the present disclosure can be applied.

[0085] 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 receiving 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.

[0086] In the example of FIG. 5, it is assumed that STA1 wants to transmit data to STA2, and STA3 is in a position to overhear some or all of the frames transmitted and received between STA1 and STA2.

[0087] 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 results. 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 results. 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.

[0088] 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 a network allocation vector (NAV) timer.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] FIG. 6 is a drawing for explaining an example of a frame structure used in a wireless LAN system to which the present disclosure can be applied.

[0093] The PHY layer can prepare an MPDU (MAC PDU) to be transmitted based on an instruction or primitive (meaning a set of instructions or parameters) from the MAC layer. For example, when a command requesting the start of transmission of the PHY layer is received 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 monitors the header of the preamble and sends a command to the MAC layer notifying the start of reception of the PHY layer.

[0094] 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) format is defined.

[0095] A basic PPDU 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) as illustrated in FIG. 7) PPDU format may consist of only the Legacy-STF (L-STF), Legacy-LTF (L-LTF), Legacy-SIG (L-SIG) fields, and a Data field. Additionally, depending on the type of PPDU format (e.g., HT-mixed format PPDU, HT-greenfield format PPDU, VHT (Very High Throughput) PPDU, etc.), additional (or different types of) RL-SIG, U-SIG, non-legacy SIG field, non-legacy STF, non-legacy LTF, (i.e., xx-SIG, xx-STF, xx-LTF (e.g., xx is HT, VHT, HE, EHT, etc.)) may be included between the L-SIG field and the data field. More specific details will be described later with reference to FIG. 7.

[0096] STF is a signal for signal detection, AGC (Automatic Gain Control), diversity selection, and precise time synchronization, while LTF is a signal for channel estimation, frequency error estimation, etc. STF and LTF can be said to be signals for synchronization and channel estimation of the OFDM physical layer.

[0097] The SIG field may include various information related to PPDU transmission and reception. For example, the L-SIG field may consist of 24 bits and may include a 4-bit Rate field, a 1-bit Reserved bit, a 12-bit Length field, a 1-bit Parity field, and a 6-bit Tail field. The RATE field may include information about the modulation and coding rate of data. For example, the 12-bit Length field may include information about the length or time duration of the PPDU. For example, the value of the 12-bit Length field may be determined based on the type of the PPDU. For example, for a non-HT, HT, VHT, or EHT PPDU, the value of the Length field may be determined as a multiple of 3. For example, for HE PPDU, the value of the Length field can be determined as a multiple of 3 + 1 or a multiple of 3 + 2.

[0098] 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.

[0099] 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 format.

[0100] The MAC header includes a Frame Control field, a Duration / ID field, an Address field, etc. The Frame Control field may include control information required for frame transmission / reception. The Duration / ID field may be set to a time for transmitting the corresponding frame, etc. The Address subfields may indicate the receiver address, transmitter address, destination address, and source address of the frame, and some Address subfields may be omitted. For specific details of each subfield of the MAC header, including the Sequence Control, QoS Control, and HT Control subfields, refer to the IEEE 802.11 standard document.

[0101] The Null-Data PPDU (NDP) format refers to a PPDU format that does not include a data field. In other words, NDP refers to a frame format that includes a PPDU preamble (i.e., L-STF, L-LTF, L-SIG fields, and, if additionally present, non-legacy SIG, non-legacy STF, and non-legacy LTF) in the general PPDU format, and does not include the remaining part (i.e., data field).

[0102] FIG. 7 is a diagram illustrating examples of PPDUs defined in the IEEE 802.11 standard to which the present disclosure can be applied.

[0103] Standards such as IEEE 802.11a / g / n / ac / ax use various PPDU formats. The basic PPDU format (IEEE 802.11a / g) 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 (Fig. 7(a)).

[0104] The HT PPDU format (IEEE 802.11n) 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(b) may be referred to as an HT-mixed format. Additionally, an HT-greenfield format PPDU may be defined, which corresponds to a format that does not include L-STF, L-LTF, and L-SIG, but consists of HT-GF-STF, HT-LTF1, HT-SIG, one or more HT-LTF, and Data fields (not illustrated).

[0105] An example of the VHT PPDU format (IEEE 802.11ac) includes VHT SIG-A, VHT-STF, VHT-LTF, and VHT-SIG-B fields in addition to the basic PPDU format (Fig. 7(c)).

[0106] An example of a HE PPDU format (IEEE 802.11ax) 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 (Fig. 7(d)). 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 8us. 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 may vary to 16us. For example, RL-SIG can be configured identically to L-SIG. The receiving STA can determine that the received PPDU is a HE PPDU or an EHT PPDU, described later, based on the presence of RL-SIG.

[0107] The EHT PPDU format may include the EHT MU (multi-user) PPDU of FIG. 7(e) and the EHT TB (trigger-based) PPDU of FIG. 7(f). The EHT PPDU format is similar to the HE PPDU format in that it includes an RL-SIG following an L-SIG, but may include a U (universal)-SIG, an EHT-SIG, an EHT-STF, and an EHT-LTF following the RL-SIG.

[0108] The EHT MU PPDU in FIG. 7(e) corresponds to a PPDU that carries one or more data (or PSDUs) for one or more users. That is, the EHT MU PPDU can be used for both SU transmission and MU transmission. For example, the EHT MU PPDU can correspond to a PPDU for one receiving STA or multiple receiving STAs.

[0109] The EHT TB PPDU of Fig. 7(f) omits the EHT-SIG compared to the EHT MU PPDU. An STA that has received a trigger for UL MU transmission (e.g., a trigger frame or TRS (triggered response scheduling)) can perform UL transmission based on the EHT TB PPDU format.

[0110] The L-STF, L-LTF, L-SIG, RL-SIG, U-SIG (Universal SIGNAL), and EHT-SIG fields can be encoded and modulated to allow legacy STAs to attempt demodulation and decoding, and mapped based on a predetermined subcarrier frequency interval (e.g., 312.5 kHz). These can be referred to as pre-EHT modulated fields. Next, the EHT-STF, EHT-LTF, Data, and PE fields can be encoded and modulated to allow STAs that have successfully decoded non-legacy SIGs (e.g., U-SIG and / or EHT-SIG) and obtained the information contained in the fields, and mapped based on a predetermined subcarrier frequency interval (e.g., 78.125 kHz). These can be referred to as EHT modulated fields.

[0111] Similarly, in the HE PPDU format, the L-STF, L-LTF, L-SIG, RL-SIG, HE-SIG-A, and HE-SIG-B fields may be referred to as pre-HE modulation fields, and the HE-STF, HE-LTF, Data, and PE fields may be referred to as HE modulation fields. Additionally, in the VHT PPDU format, the L-STF, L-LTF, L-SIG, and VHT-SIG-A fields may be referred to as pre-VHT modulation fields, and the VHT STF, VHT-LTF, VHT-SIG-B, and Data fields may be referred to as VHT modulation fields.

[0112] The U-SIG included in the EHT PPDU format of FIG. 7 can be configured based on, for example, two symbols (e.g., two consecutive OFDM symbols). Each symbol (e.g., OFDM symbol) for the U-SIG can have a duration of 4 us, and the U-SIG can have a total duration of 8 us. Each symbol of the U-SIG can be used to transmit 26 bits of information. For example, each symbol of the U-SIG can be transmitted and received based on 52 data tones and 4 pilot tones.

[0113] U-SIGs can be configured in 20MHz units. For example, when an 80MHz PPDU is configured, the same U-SIG can be duplicated in 20MHz units. That is, four identical U-SIGs can be included in an 80MHz PPDU. When the bandwidth exceeds 80MHz, for example, for a 160MHz PPDU, the U-SIGs in the first 80MHz unit and the U-SIGs in the second 80MHz unit can be different.

[0114] For example, A uncoded bits may be transmitted via U-SIG, and a first symbol of U-SIG (e.g., a U-SIG-1 symbol) may transmit the first X bits of information out of a total A bits of information, and a second symbol of U-SIG (e.g., a U-SIG-2 symbol) may transmit the remaining Y bits of information out of a total A bits of information. The A bits of information (e.g., 52 uncoded bits) may include a CRC field (e.g., a field of 4 bits in length) and a tail field (e.g., a field of 6 bits in length). The tail field may be used to terminate the trellis of the convolutional decoder and may be set to 0, for example.

[0115] The A bit information transmitted by U-SIG can be divided into version-independent bits and version-dependent bits. For example, U-SIG can be included in a new PPDU format (e.g., UHR PPDU format) not shown in FIG. 7, and in the format of the U-SIG field included in the EHT PPDU format and the format of the U-SIG field included in the UHR PPDU format, the version-independent bits can be the same, and some or all of the version-dependent bits can be different.

[0116] For example, the size of the version-independent bits of U-SIG can be fixed or variable. The version-independent bits can be assigned only to U-SIG-1 symbols, or to both U-SIG-1 symbols and U-SIG-2 symbols. The version-independent bits and the version-dependent bits can be called by various names, such as the first control bit and the second control bit.

[0117] For example, the version-independent bits of the U-SIG may include a 3-bit PHY version identifier, which may indicate the PHY version (e.g., EHT, UHR, etc.) of the transmitted and received PPDUs. The version-independent bits of the U-SIG may include a 1-bit UL / DL flag field. The first value of the 1-bit UL / DL flag field relates to UL communication, and the second value of the UL / DL flag field relates to DL communication. The version-independent bits of the U-SIG may include information about the length of a transmission opportunity (TXOP) and information about a BSS color ID.

[0118] For example, the version-dependent bits of the U-SIG may contain information that directly or indirectly indicates the type of PPDU (e.g., SU PPDU, MU PPDU, TB PPDU, etc.).

[0119] Information required for PPDU transmission and reception may be included in the U-SIG. For example, the U-SIG may further include information about bandwidth, information about the MCS technique applied to the non-legacy SIG (e.g., EHT-SIG or UHR-SIG), information indicating whether a dual carrier modulation (DCM) technique (e.g., a technique to achieve an effect similar to frequency diversity by reusing the same signal on two subcarriers) is applied to the non-legacy SIG, information about the number of symbols used for the non-legacy SIG, information about whether the non-legacy SIG is generated across the entire band, etc.

[0120] Some of the information required for transmitting and receiving a PPDU may be included in the U-SIG and / or the non-legacy SIG (e.g., EHT-SIG or UHR-SIG, etc.). For example, information about the type of the non-legacy LTF / STF (e.g., EHT-LTF / EHT-STF or UHR-LTF / UHR-STF, etc.), information about the length of the non-legacy LTF and the cyclic prefix (CP) length, information about the guard interval (GI) applicable to the non-legacy LTF, information about preamble puncturing applicable to the PPDU, information about resource unit (RU) allocation, etc. may be included only in the U-SIG, may be included only in the non-legacy SIG, or may be indicated by a combination of the information included in the U-SIG and the information included in the non-legacy SIG.

[0121] Preamble puncturing may refer to the transmission of a PPDU in which no signal is present in one or more frequency units within the PPDU's bandwidth. For example, the size of the frequency unit (or the resolution of the preamble puncturing) may be defined as 20 MHz, 40 MHz, etc. For example, preamble puncturing may be applied to a PPDU bandwidth greater than a certain size.

[0122] In the example of FIG. 7, non-legacy SIGs such as HE-SIG-B and EHT-SIG may include control information for the receiving STA. The non-legacy SIG may be transmitted over at least one symbol, and each symbol may have a length of 4 us. Information regarding the number of symbols used for the EHT-SIG may be included in a previous SIG (e.g., HE-SIG-A, U-SIG, etc.).

[0123] Non-legacy SIGs, such as HE-SIG-B and EHT-SIG, may contain common fields and user-specific fields. Common and user-specific fields may be coded separately.

[0124] In some cases, common fields may be omitted. For example, in a compressed mode where non-OFDMA (orthogonal frequency multiple access) is applied, common fields may be omitted, and multiple STAs may receive PPDUs (e.g., data fields of PPDUs) over the same frequency band. In a non-compressed mode where OFDMA is applied, multiple users may receive PPDUs (e.g., data fields of PPDUs) over different frequency bands.

[0125] The number of user-specific fields can be determined based on the number of users. A single user block field can contain up to two user fields. Each user field can be associated with either MU-MIMO allocation or non-MU-MIMO allocation.

[0126] The common field may include CRC bits and Tail bits, the length of the CRC bits may be determined as 4 bits, and the length of the Tail bits may be determined as 6 bits and set to 000000. The common field may include RU allocation information. The RU allocation information may include information about the location of RUs to which multiple users (i.e., multiple receiving STAs) are allocated.

[0127] An RU can contain multiple subcarriers (or tones). RUs can be used when transmitting signals to multiple STAs based on OFDMA techniques. RUs can also be defined when transmitting signals to a single STA. Resources can be allocated on an RU basis for non-legacy STFs, non-legacy LTFs, and data fields.

[0128] Depending on the PPDU bandwidth, an applicable RU size can be defined. The RU may be defined identically or differently for the applicable PPDU format (e.g., HE PPDU, EHT PPDU, UHR PPDU, etc.). For example, in the case of an 80MHz PPDU, the RU arrangements of HE PPDU and EHT PPDU may be different. The applicable RU size, RU number, RU position, DC (direct current) subcarrier position and number, null subcarrier position and number, guard subcarrier position and number, etc. for each PPDU bandwidth can be referred to as a tone plan. For example, a tone plan for a wide bandwidth can be defined in the form of multiple repetitions of a low bandwidth tone plan.

[0129] RUs of different sizes can be defined, such as 26-ton RU, 52-ton RU, 106-ton RU, 242-ton RU, 484-ton RU, 996-ton RU, 2X996-ton RU, 4X996-ton RU, etc. A multiple RU (MRU) is distinguished from multiple individual RUs and corresponds to a group of subcarriers consisting of multiple RUs. For example, one MRU can be defined as 52+26-tons, 106+26-tons, 484+242-tons, 996+484-tons, 996+484+242-tons, 2X996+484-tons, 3X996-tons, or 3X996+484-tons. Additionally, multiple RUs constituting one MRU may or may not be consecutive in the frequency domain.

[0130] The specific size of an RU may be reduced or expanded. Therefore, the specific size of each RU (i.e., the number of corresponding tones) in the present disclosure is not limited and is exemplary. Furthermore, within a given bandwidth (e.g., 20, 40, 80, 160, 320 MHz, etc.) in the present disclosure, the number of RUs may vary depending on the RU size.

[0131] The names of each field in the PPDU formats of FIG. 7 are exemplary and the scope of the present disclosure is not limited by those names. Furthermore, the examples of the present disclosure can be applied not only to the PPDU format exemplified in FIG. 7, but also to a new PPDU format in which some fields are excluded and / or some fields are added based on the PPDU formats of FIG. 7.

[0132] Multi-link operation

[0133] Below, the multi-link (ML) operation supported by the STA according to the present disclosure is described.

[0134] The STA (AP STA and / or non-AP STA) described in the present disclosure can support multi-link (ML) communication. ML communication may refer to communication that supports multiple links. Links related to ML communication may include channels (e.g., 20 / 40 / 80 / 160 / 240 / 320MHz channels) of a frequency band (e.g., 2.4GHz band, 5GHz band, 6GHz band, etc.) in which the STA operates. The multiple links used for ML communication may be configured in various ways. For example, the multiple links supported for one STA for ML communication may belong to the same frequency band or may belong to different frequency bands. In addition, each link may correspond to a frequency unit of a predetermined size (e.g., a channel, a subchannel, an RU, etc.). In addition, some or all of the multiple links may be frequency units of the same size or may be frequency units of different sizes.

[0135] When one STA supports multiple links, the transmitting and receiving devices supporting each link can operate as one logical STA. That is, an MLD is a device that has one or more affiliated STAs as a logical entity and a single MAC service access point (SAP) for one MAC data service and logical link control (LLC). A non-AP MLD refers to an MLD in which each STA affiliated with the MLD is a non-AP STA. A multi-radio non-AP MLD refers to a non-AP MLD that supports receiving or exchanging frames on more than one link at a time. An AP MLD refers to an MLD in which each STA affiliated with the MLD is an AP STA.

[0136] Multi-link operation (MLO) can enable a non-AP MLD to discover, authenticate, associate, and set up multiple links with an AP MLD. Based on the supported capabilities exchanged during the association procedure, each link can enable channel access and frame exchange between the non-AP MLD and the AP MLD. An STA affiliated with an MLD can select and manage its capabilities and operating parameters independently from other STA(s) affiliated with the same MLD.

[0137] Through the multi-link setup process, the AP MLD and / or the non-AP MLD can transmit and receive link-related information that the MLD can support. The link-related information may include one or more of information about whether the MLD supports simultaneous transmit and receive (STR) operation or non-simultaneous transmit and receive (NSTR) operation on multiple links, information about the number / upper limit of UL / DL links, information about the location / bandwidth / resource of UL / DL links, information about frame types (e.g., management, control, data, etc.) that are available or preferred on at least one UL / DL link, information about an ACK policy that is available or preferred on at least one UL / DL link, or information about a traffic identifier (TID) that is available on at least one UL / DL link.

[0138] An AP MLD (e.g., NSTR mobile AP MLD) can set one of the multiple links as the primary link. The AP MLD may transmit beacon frames, probe response frames, and group-addressed data frames only on the primary link. The remaining link(s) of the multiple links may be referred to as non-primary links. An AP MLD operating on a non-primary link may operate so as not to transmit beacon frames or probe response frames. In addition, a non-AP MLD may perform frame exchanges during authentication, (re)association, and 4-way handshaking only on the primary link.

[0139] A setup link is defined as enabled if at least one traffic identifier (TID) is mapped to the link through the multi-link setup process, and a setup link can be defined as disabled if no TID is mapped to the link. A TID must always be mapped to at least one setup link unless admission control is used. By default, a TID is mapped to all setup links, so all setup links can be enabled.

[0140] When a link is activated, it can be used for frame exchange, depending on the power state of the non-AP STAs operating on that link. Only MSDUs or A-MSDUs with TIDs mapped to the activated link can be transmitted on that link. Management frames and control frames can only be transmitted on the activated link.

[0141] When a link is disabled, that link may not be used for frame exchange, including management frames for both DL and UL.

[0142] During a multi-link setup, activation / deactivation of individual links can be directed through TID-to-Link mapping. TID-to-Link mapping can be performed in default mapping mode or / and negotiation mapping mode.

[0143] Among the STAs belonging to the MLD, one STA may provide information about one or more links other than the link on which it is located, for multi-link discovery (e.g., obtaining information about multiple links including the link on one link) or multi-link setup (e.g., simultaneous association on multiple links through exchange of association request / response frames on one link).

[0144] How multi-AP works

[0145] Multi-AP operation may correspond to a technique in which one or more APs transmit and receive information to one or more STAs.

[0146] In the case of the existing single transmission (S-Tx) method, i.e., the method in which a BSS AP transmits to a BSS STA, a problem of reduced performance may occur when the AP transmits and receives with users (e.g., STAs) at the cell edge due to interference with adjacent APs.

[0147] In contrast, multi-AP techniques can improve performance by reducing inter-symbol interference (ISI) through coordination with neighboring APs or by co-transmitting. In other words, multi-AP techniques enable information sharing and collaboration between APs.

[0148] FIG. 8 is a diagram showing examples of multi-AP techniques to which the present disclosure can be applied.

[0149] Referring to FIG. 8, as an example of a multi-AP technique, (a) of FIG. 8 illustrates coordinated OFDMA (C-OFDMA), (b) of FIG. 8 illustrates coordinated beamforming (CBF), (c) of FIG. 8 illustrates AP selection, and (d) of FIG. 8 illustrates joint transmission (J-Tx).

[0150] For example, as a multi-AP technique, coordinated TDMA (C-TDMA) technique that divides allocation between APs along the time axis, C-OFDMA technique that divides along the frequency axis, or coordinated spatial reuse (C-SR) technique that utilizes spatial reuse can be considered. As an example, referring to (a) of FIG. 8, resource allocation for AP 1 and STA 1 and resource allocation for AP 2 and STA 2 can be separated in the frequency domain.

[0151] Additionally or alternatively, as a multi-AP technique, a CBF technique or a coordinated nulling (CN) technique that transmits by nulling interference affecting neighbors may be considered, and an AP selection technique that sets / defines an AP with a good channel condition among neighboring APs (i.e., adjacent APs) to perform transmission may also be considered. For example, in the example of (c) of FIG. 8, since AP 2 is determined to have a better channel condition than AP 1, AP 2 can perform transmission to STA 1.

[0152] Additionally or alternatively, as a multi-AP technique, a J-Tx technique (e.g., joint beamforming, joint MU-MIMO) in which multiple APs collaborate to perform simultaneous transmission or reception may be considered. The example in (d) of Fig. 8 corresponds to a method in which multiple APs transmit data to STA 1.

[0153] In the multi-AP technique described above, the multi-AP environment may be comprised of a master AP, slave APs, and STAs. In this regard, the master AP may be referred to as a sharing AP, and the slave AP may be referred to as a shared AP.

[0154] Here, the master AP can initiate and control multi-AP operations, which are technologies for transmission and reception by multiple APs. Additionally, the master AP can group slave AP(s) and manage links with the slave AP(s) to enable information sharing between the slave AP(s). Additionally, the master AP can manage information about the BSS comprised by the slave AP(s) and information about the STA(s) associated with the BSS.

[0155] By associating with a master AP, slave APs can share control information, management information, and data traffic. Additionally, slave APs can perform essentially the same functions as APs that establish a BSS in existing wireless LAN systems.

[0156] As in a conventional wireless LAN system, an STA can form a BSS by associating with an AP (i.e., a master AP or a slave AP).

[0157] In a multi-AP environment as described above, the master AP and slave APs may be capable of direct transmission and reception between each other. Additionally or alternatively, the master AP and STA may not be capable of direct transmission and reception between each other. Additionally or alternatively, the slave AP (associated with the STA) and the STA may be capable of direct transmission and reception between each other. Additionally or alternatively, one of the slave APs may become the master AP.

[0158] Multi-AP operation considering AP power saving mode

[0159] Multi-AP operation in a wireless LAN system has technical benefits such as expanded coverage, improved reliability, and support for low-latency traffic.

[0160] Currently, interest and efforts to reduce the total carbon dioxide (CO2) footprint are rapidly increasing to prevent catastrophic human impacts caused by climate change, such as global warming. In this regard, there is a growing demand for methods to drastically reduce the contribution to global warming caused by the massive power production and consumption required to support communications infrastructure.

[0161] Considering these points, a method for applying / supporting a power reduction mode to AP(s) in the aforementioned multi-AP operating environment may be required. For example, the power reduction mode may be applied semi-statically or dynamically to one or more APs / STAs.

[0162] Conventional multi-AP operation methods do not consider power reduction modes for APs. In contrast, the present disclosure proposes a method for supporting multi-AP operation while applying power reduction modes for APs. This method allows for the combination of power reduction operations for APs and multi-AP operation, thereby efficiently achieving the technical benefits provided by both operations.

[0163] FIGS. 9 and 10 illustrate an example of a method for performing multi-AP operation considering a power reduction mode according to the present disclosure. In FIGS. 9 and 10 , with respect to multi-AP operation, the first AP may correspond to a Coordinated AP, and the second AP may correspond to a Coordinator AP. According to definitions of other technical terms, the first AP may correspond to a Shared AP, and the second AP may correspond to a Sharing AP.

[0164] For multi-AP operations in FIGS. 9 and 10 , information about the first AP may be provided in advance to the second AP. For example, the information about the first AP may include one or more of identification information, information related to the power reduction operation, or information regarding the types of multi-AP operations that can be supported.

[0165] FIG. 9 illustrates an example of the operation of a first AP performing multi-AP operation considering a power reduction mode according to an embodiment of the present disclosure.

[0166] The first AP can receive a polling frame from the second AP to determine whether to participate in multi-AP operation (S910).

[0167] In this regard, the time interval for multi-AP operation may be included within the transmission opportunity (TXOP) acquired by the second AP. At this time, the first AP may be configured to operate based on a power reduction mode within the TXOP or within the time interval for multi-AP operation. For example, in relation to the power reduction mode, the first AP in an awake state may operate to receive the corresponding polling frame.

[0168] In a time period for multi-AP operation, the first AP is set to maintain an awake state associated with a power reduction mode, and when the first AP wishes to participate in the multi-AP operation, the first AP may transmit a frame (e.g., a CTS-to-self frame) including information indicating participation in the multi-AP operation to the second AP in response to a polling frame (S920).

[0169] If the first AP is configured to enter a doze state associated with a power reduction mode prior to the time period for multi-AP operation, or if it does not wish to participate in multi-AP operation, the first AP may not transmit a response to the polling frame.

[0170] Thereafter, the first AP receives a control frame including information related to the initiation of multi-AP operation (S930), and can perform frame / data exchange based on the multi-AP operation based on the information (S940).

[0171] In this regard, the control frame may include one or more of information indicating the type of multi-AP operation or information about resources for the multi-AP operation. For example, if the type of multi-AP operation is indicated as coordinated-OFDMA (C-OFDMA), the control frame may include information about a resource unit to be used by a first AP in the multi-AP operation, etc. For another example, if the type of multi-AP operation is indicated as coordinated-TDMA (C-TDMA), the control frame may include information about a transmission order of the first AP in the multi-AP operation and an allocated time interval, etc. For another example, if the type of multi-AP operation is indicated as coordinated-SR (C-SR), the control frame may include information about APs capable of simultaneous transmission on the same resource in the multi-AP operation, information about transmission power, etc.

[0172] Additionally or alternatively, with respect to the procedure described in FIG. 9, a method of performing pre-cooperation for the multi-AP operation within a predetermined time interval may be additionally applied. Here, the predetermined time interval may be set / indicated periodically or aperiodically. In this regard, during a TXOP including the time interval for the multi-AP operation, the APs participating in the multi-AP operation through pre-cooperation may be configured to maintain an awake state associated with the power reduction mode, while the remaining APs may be configured to be in a doze state associated with the power reduction mode.

[0173] Additionally or alternatively, with respect to the procedure described in FIG. 9, multi-link operation may be applied. For example, if the first AP belongs to / is affiliated with an AP multi-link device (MLD) for multi-link operation, the first AP may transmit information indicating that frame exchange based on multi-AP operation is performed based on multi-link operation to a station (STA) belonging to / is affiliated with a non-AP MLD that is the target of the frame exchange.

[0174] The method described in the example of FIG. 9 may be performed by the first device (100) of FIG. 1. For example, one or more processors (102) of the first device (100) of FIG. 1 may be configured to receive a polling frame for checking whether to participate in a multi-AP operation, transmit a response thereto, receive a control frame including information related to the initiation of a multi-AP operation, and perform frame / data exchange based on the multi-AP operation based thereon. Furthermore, one or more memories (104) of the first device (100) may store commands for performing the method described in the example of FIG. 9 or the examples described below when executed by one or more processors (102).

[0175] FIG. 10 illustrates an example of the operation of a second AP performing multi-AP operation considering a power reduction mode according to an embodiment of the present disclosure.

[0176] The second AP may transmit a polling frame to the first AP to determine whether to participate in multi-AP operation (S1010). Thereafter, the second AP may receive a frame (e.g., a CTS-to-self frame) containing information indicating participation in multi-AP operation in response to the polling frame (S1020).

[0177] Thereafter, the first AP may receive a control frame containing information related to the initiation of multi-AP operation (S1030). Based on this, frame / data exchange based on multi-AP operation may be performed / progressed.

[0178] Specific details regarding polling frames, responses thereto, control frames, operations / settings related to awake / doze states in power reduction mode, settings / instructions related to multi-AP operations, pre-cooperation, multi-link operations, etc. are the same as those described in the example of Fig. 9, and therefore, redundant descriptions are omitted.

[0179] The method described in the example of FIG. 10 may be performed by the second device (200) of FIG. 1. For example, one or more processors (202) of the second device (200) of FIG. 1 may be configured to transmit a polling frame to determine whether to participate in a multi-AP operation, receive a response thereto, and transmit a control frame including information related to the initiation of the multi-AP operation. Furthermore, one or more memories (204) of the second device (200) may store commands for performing the method described in the example of FIG. 14 or the examples described below when executed by one or more processors (202).

[0180] Figures 11 and 12 illustrate an example of a method for performing multi-AP operation considering a power reduction mode according to the present disclosure. In Figures 11 and 12 , with respect to multi-AP operation, the first AP may correspond to a Coordinated AP, and the second AP may correspond to a Coordinator AP. According to the definition of other technical terms, the first AP may correspond to a Shared AP, and the second AP may correspond to a Sharing AP.

[0181] For multi-AP operations in FIGS. 11 and 12 , information about the first AP may be provided in advance to the second AP. For example, the information about the first AP may include one or more of identification information, information related to the power reduction operation, or information regarding the types of multi-AP operations that can be supported.

[0182] FIG. 11 illustrates another example of the operation of a first AP performing multi-AP operation considering a power reduction mode according to an embodiment of the present disclosure.

[0183] The first AP can transmit a TWT (target-wake time) request frame to the second AP to request participation in multi-AP operation (S1110).

[0184] For example, the TWT request frame may include information indicating intent to participate, and the information related thereto may be structured in the form of elements, fields, and / or subfields and transmitted through the TWT request frame.

[0185] The first AP may receive a TWT response frame from the second AP to indicate whether to grant the requested participation (S1120).

[0186] For example, the TWT response frame may include information indicating a permission status for participation, and the information related thereto may be structured in the form of elements, fields, and / or subfields and transmitted through the TWT response frame.

[0187] If participation is permitted and the first AP is set to maintain an awake state associated with a power reduction mode during the TWT service period (SP) in which multi-AP operation is to be performed, the first AP can perform frame / data exchange based on multi-AP operation during the TWT SP (S1130).

[0188] In this regard, frame exchange based on multi-AP operation can be initiated based on the exchange of trigger frames, polling frames (e.g., PS_Poll, etc.), and response frames (e.g., block-ACK (BA), etc.) between the first AP and the second AP within the corresponding TWT SP.

[0189] Additionally or alternatively, with respect to the procedure described in FIG. 11, a method of performing pre-cooperation for the multi-AP operation within a predetermined time interval may be additionally applied. Here, the predetermined time interval may be set / indicated periodically or aperiodically. In this regard, during a TXOP including the time interval for the multi-AP operation, the APs that will participate in the multi-AP operation through pre-cooperation may be configured to maintain an awake state associated with the power reduction mode, while the remaining APs may be configured to be in a doze state associated with the power reduction mode.

[0190] Additionally or alternatively, with respect to the procedure described in FIG. 11, multi-link operation may be applied. For example, if the first AP belongs to / is affiliated with an AP multi-link device (MLD) for multi-link operation, the first AP may transmit information indicating that frame exchange based on multi-AP operation is performed based on multi-link operation to a station (STA) belonging to / is affiliated with a non-AP MLD that is the target of the frame exchange.

[0191] The method described in the example of FIG. 11 may be performed by the first device (100) of FIG. 1. For example, one or more processors (102) of the first device (100) of FIG. 1 may be configured to transmit a TWT request frame for requesting participation in a multi-AP operation, receive a TWTW response frame for indicating whether to grant the requested participation, and perform frame / data exchange based on the multi-AP operation during the TWT service period based on the grant or grant status and a power reduction mode. Furthermore, one or more memories (104) of the first device (100) may store commands for performing the method described in the example of FIG. 11 or the examples described below when executed by one or more processors (102).

[0192] FIG. 12 illustrates another example of the operation of a second AP performing multi-AP operation considering a power reduction mode according to an embodiment of the present disclosure.

[0193] The second AP may receive a target-wake time (TWT) request frame from the first AP to request participation in multi-AP operation (S1210).

[0194] For example, the TWT request frame may include information indicating intent to participate, and the information related thereto may be structured in the form of elements, fields, and / or subfields and transmitted through the TWT request frame.

[0195] The second AP may transmit a TWT response frame to the first AP to indicate whether or not to grant the requested participation (S1220).

[0196] For example, the TWT response frame may include information indicating a permission status for participation, and the information related thereto may be structured in the form of elements, fields, and / or subfields and transmitted through the TWT response frame.

[0197] If participation is permitted and the first AP is configured to remain in an awake state associated with a power reduction mode during the TWT service period (SP) during which multi-AP operation is to be performed, frame / data exchange based on multi-AP operation can be performed during that TWT SP.

[0198] Specific details regarding TWT request frames, TWT response frames, frame exchange based on multi-AP operation, operations / settings related to awake / doze states in power reduction mode, pre-cooperation, multi-link operation, etc. are the same as those described in the example of Fig. 11, so redundant descriptions are omitted.

[0199] The method described in the example of FIG. 12 may be performed by the second device (200) of FIG. 1. For example, one or more processors (202) of the second device (200) of FIG. 1 may be configured to receive a TWT request frame for requesting participation in a multi-AP operation and to transmit a TWTW response frame for indicating whether to grant the requested participation. Furthermore, one or more memories (204) of the second device (200) may store commands for performing the method described in the example of FIG. 12 or the examples described below when executed by one or more processors (202).

[0200] The examples of FIGS. 9 through 12 may correspond to some of the various examples of the present disclosure. Below, various examples of the present disclosure, including the examples of FIGS. 9 through 12, will be described in more detail.

[0201] Specifically, various examples are provided to explain how AP(s) in a power-reduced state can come out of the power-reduced state and perform cooperative operations during a set / scheduled time for multi-AP operation.

[0202] In the methods described below, it may be assumed that the Coordinator AP and one or more Coordinated AP(s) perform multi-AP operation (e.g., C-OFDMA, C-TDMA, C-SR, etc.) during an acquired transmission opportunity (TXOP).

[0203] Here, the Coordinator AP may correspond to an AP that has acquired a TXOP (Transmission Control Point) during a time period that may include multi-AP operation through channel access contention. The Coordinated AP may correspond to an AP that participates in multi-AP operation during the TXOP acquired by the Coordinator AP. There may be one or more Coordinated APs.

[0204] In this regard, the Coordinated AP(s) may be in a power reduction mode (i.e., power reduction state mode) at the initiation of a TXOP or at the time of multi-AP operation during a TXOP.

[0205] Additionally, a Coordinated AP may have knowledge of Coordinated APs that will perform multi-AP operations.

[0206] For example, the information may include identification information for the AP (e.g., MAC address, BSS ID, virtual BSS ID, etc.), information related to power reduction mode-based operation, information about supportable multi-AP operation (e.g., C-OFDMA, C-TDMA, etc.), etc. Here, the information related to power reduction mode-based operation may include whether the power reduction mode is in operation, the cycle of the power reduction mode, the time interval related to the power reduction mode (e.g., awake / doze interval), etc.

[0207] Example 1

[0208] This embodiment is about a method of utilizing a polling-based method to support multi-AP operation considering power reduction mode.

[0209] At the start of a TXOP or during the TXOP, the Coordinator AP may transmit a polling frame to one or more Coordinated APs to confirm their willingness to participate in multi-AP operation. For example, the transmission of the polling frame may be transmitted to one or more Coordinated APs based on a multicast or broadcast method.

[0210] Coordinated APs that receive the polling frame can transmit a response signal to the Coordinator AP, thereby expressing their intent to participate. The response signal may correspond to a CTS-to-self frame, another type of response frame, etc.

[0211] For example, the Coordinated AP(s) that communicate their intent to participate may correspond to Coordinated AP(s) that are awake with respect to the power reduction mode (i.e., Coordinated APs in the awake interval / state). That is, only awake Coordinated APs can communicate their intent to participate, and sleeping Coordinated APs (i.e., Coordinated APs in the doze interval / state) and Coordinated APs that are awake but engaged in data transmission may not communicate their intent to participate.

[0212] Thereafter, the Coordinator AP may initiate multi-AP operations targeting the Coordinated AP(s) that have communicated their intent to participate. In this case, the initiation of multi-AP operations may be performed after a certain period of time (e.g., SIFS, PIFS, etc.) after receiving a response signal from the Coordinated AP(s).

[0213] For example, a Coordinator AP that receives a participation intent from Coordinated AP(s) can identify AP(s) that will participate in the multi-AP operation and determine the type of multi-AP operation (commonly) supportable for the AP(s). This can be performed based on information about Coordinated APs that the Coordinator AP knows in advance (i.e., that has been shared / forwarded in advance) (e.g., information about the types of multi-AP operations that can be supported by each Coordinated AP, etc.).

[0214] Initiation of multi-AP operation may begin with the transmission of a control frame by the Coordinator AP. In this regard, the control frame may include information indicating the type of multi-AP operation (e.g., C-OFDMA, C-TDMA, C-SR, etc.) and / or information regarding related resource utilization.

[0215] For example, if C-OFDMA is indicated through a control frame, the control frame may include information about resource units (RUs) to be used by the Coordinator AP(s). For another example, if C-TDMA is indicated through a control frame, the control frame may include information about the transmission order and time interval / length of each Coordinated AP. For another example, if C-SR is indicated through a control frame, the control frame may include indication information and transmission power for Coordinated AP(s) capable of simultaneous transmission on the same resource (e.g., the same time / frequency resource).

[0216] FIG. 13 illustrates an example of a polling-based method according to an embodiment of the present disclosure.

[0217] Referring to FIG. 13, a multi-AP operation within a TXOP acquired by a Coordinator AP is described assuming that there is a first Coordinated AP (i.e., Coordinated AP1) and a second Coordinated AP (i.e., Coordinated AP2).

[0218] For example, the Coordinator AP may transmit a polling frame to the first Coordinated AP and the second Coordinated AP at the start of a TXOP, wherein the polling frame may be intended to confirm their willingness to participate in multi-AP operations within the TXOP.

[0219] After transmitting and receiving the polling frame, after a certain period of time (e.g., SIFS), the second Coordinated AP may transmit a CTS-to-Self frame to the Coordinator AP as a response to the polling frame, indicating its intention to participate in multi-AP operation. In this regard, the second Coordinated AP in the awake state may transmit a response to the polling frame, and the first Coordinated AP in the doze state or the awake state but in a state in which multi-AP operation cannot be performed may not transmit a response to the polling frame.

[0220] After transmitting and receiving the CTS-to-Self frame, after a certain period of time (e.g., SIFS), the Coordinator AP can transmit a control frame to the second Coordinated AP to initiate multi-AP operation.

[0221] After transmitting and receiving the control frame, after a certain period of time (e.g., SIFS, etc.), the second Coordinated AP can perform frame exchange with the STA associated with it. For example, if multi-AP operation according to C-TDMA is indicated, the second Coordinated AP can transmit data (e.g., PPDU, etc.) to the STA associated with it within the indicated / allocated time period, and receive a response (e.g., Block-ACK (BA)) from the STA.

[0222] In relation to the frame exchange between the second Coordinated AP and the STA, the success / failure situation of the frame exchange can be considered. At this time, after the PPDU is transmitted by the second Coordinated AP, an operation to determine whether it is successful can be performed. For example, the success or failure of the frame exchange can be determined by checking whether another operation is performed within the channel during the PIFS duration, checking whether the BA received from the STA is delivered to the Coordinator AP, or checking whether the broadcast BA is received.

[0223] FIG. 14 illustrates another example of a polling-based method according to an embodiment of the present disclosure.

[0224] Referring to FIG. 14, a multi-AP operation within a TXOP acquired by a Coordinator AP is described assuming that there is a first Coordinated AP (i.e., Coordinated AP1) and a second Coordinated AP (i.e., Coordinated AP2).

[0225] For example, a coordinator AP can exchange frames with an STA associated with it within a TXOP. For example, the coordinator AP can transmit data (e.g., PPDU, etc.) to the STA and receive a response (e.g., Block-ACK (BA)) from the STA.

[0226] After such frame exchange is completed, the Coordinator AP may transmit polling frames to the first Coordinated AP and the second Coordinated AP in relation to multi-AP operations within the TXOP. That is, the Coordinator AP may transmit polling frames to confirm their willingness to participate in multi-AP operations within the TXOP at a point in time after the TXOP has been initiated.

[0227] Since the content related to the response after transmission of the polling frame and the multi-AP operation based thereon overlaps with the content described in Fig. 13, a detailed description thereof is omitted in Fig. 14.

[0228] Example 2

[0229] This embodiment is about a method that utilizes a target-wake time (TWT) based method to support multi-AP operation considering a power reduction mode.

[0230] One or more Coordinated APs may transmit a TWT request frame to the Coordinator AP to indicate their intent to participate in multi-AP operation within a TXOP.

[0231] At this time, information indicating the intent to participate and information necessary therefor (e.g., information related to multi-AP operation that is the target of participation, etc.) may be transmitted using elements, fields, and / or subfields within the TWT request frame.

[0232] A Coordinator AP that receives the TWT request frame can transmit a TWT response frame to the Coordinated AP(s) to indicate whether or not the requested participation is permitted.

[0233] At this time, information indicating permission to participate and information necessary therefor (e.g., information related to multi-AP operation that is the target of participation, etc.) may be transmitted using elements, fields, and / or subfields within the TWT response frame. In this regard, when configuring the TWT response frame, the Coordinator AP may configure the information included in the TWT request frame identically or, if necessary, modify it.

[0234] FIG. 15 illustrates an example of a TWT-based method according to an embodiment of the present disclosure.

[0235] Referring to FIG. 15, a multi-AP operation within a TXOP acquired by a Coordinator AP is described assuming that there is a first Coordinated AP (i.e., Coordinated AP1) and a second Coordinated AP (i.e., Coordinated AP2).

[0236] At this time, the multi-AP operation can be set / defined to be performed within a TWT service period (TWT SP) according to TWT negotiation between the Coordinator AP and the first Coordinated AP and the second Coordinated AP.

[0237] For example, within the TXOP acquired by the Coordinator AP, the first Coordinated AP and the second Coordinated AP may transmit a TWT request frame to the Coordinator AP to convey their intention to participate in multi-AP operation. Thereafter, the Coordinator AP may transmit a TWT response frame to the first Coordinated AP and / or the second Coordinated AP to convey whether the requested intention to participate is permitted. Through the TWT negotiation process, a request for participation in multi-AP operation and whether the request is permitted can be negotiated / conveyed, and based on this, multi-AP operation during the TWT SP can be set / instructed.

[0238] Within the first TWT SP illustrated in FIG. 15, the Coordinator AP may transmit a trigger frame to the Coordinated AP(s) that have permitted multi-AP operation. Here, the trigger frame may be for initiating multi-AP operation.

[0239] For multi-AP operation within the first TWT SP, a case may be considered where participation is permitted for both the first Coordinated AP and the second Coordinated AP. In this case, the second Coordinated AP in the awake state may transmit a PS-Poll frame in response to the trigger frame, and the first Coordinated AP in the doze state or the awake state but in a state in which multi-AP operation cannot be performed may not transmit a response to the trigger frame. In this case, the second Coordinated AP receives a block-ACK (BA) from the Coordinator AP, and may then perform frame exchange with the STA associated with it (i.e., multi-AP operation during the first TWT SP).

[0240] Alternatively, for multi-AP operations within the first TWT SP, a case may be considered where only the second Coordinated AP is permitted to participate. In this case, the second Coordinated AP, which is in an awake state, may transmit a PS-Poll frame in response to the trigger frame. In this case, the second Coordinated AP receives a block-ACK (BA) from the Coordinator AP and may then perform frame exchange with the STA associated with it (i.e., multi-AP operation during the first TWT SP).

[0241] Additionally, within the second TWT SP illustrated in FIG. 15, the Coordinator AP may transmit a trigger frame to the Coordinated AP(s) that have permitted multi-AP operation, wherein the trigger frame may be for initiating multi-AP operation.

[0242] For multi-AP operation within the second TWT SP, if participation is permitted for both the first Coordinated AP and the second Coordinated AP, the first Coordinated AP and the second Coordinated AP in the awake state may each transmit a PS-Poll frame in response to the trigger frame. In this case, the first Coordinated AP and the second Coordinated AP receive a Block-ACK (BA) from the Coordinator AP and may then perform the negotiated multi-AP operation.

[0243] For example, the procedures illustrated in FIGS. 16 and 17 may be performed depending on the type of multi-AP operation negotiated within the second TWT SP.

[0244] FIG. 16 illustrates a specific example of multi-AP operation in a TWT-based scheme according to an embodiment of the present disclosure, and FIG. 17 illustrates another specific example of multi-AP operation in a TWT-based scheme according to an embodiment of the present disclosure.

[0245] Referring to FIG. 16, when the negotiated multi-AP operation is C-OFDMA, the first Coordinated AP and the second Coordinated AP, which have received BA from the Coordinator AP, can transmit data on different frequency resources. For example, in the same time resource and different frequency resource, the first Coordinated AP and the second Coordinated AP can each transmit data to the STA associated with them, and in response, receive a block-ACK (BA) on a preset resource. Simultaneous data transmission by the two APs can also be applied in the case of C-SR.

[0246] Referring to FIG. 17, when the negotiated multi-AP operation is C-TDMA, the first Coordinated AP and the second Coordinated AP, which have received BA from the Coordinator AP, can perform frame exchange with the STA in different time intervals. At this time, information on the time interval in which the frame exchange is to be performed can be transmitted / set / indicated through the TWT negotiation process and / or the exchange of trigger frames and PS-Poll frames within the TWT SP. For example, after receiving the BA from the Coordinator AP within the second TWT SP, the first Coordinated AP can perform frame exchange with the STA associated with it. After the completion of the frame exchange, the second Coordinated AP can perform frame exchange with the STA associated with it.

[0247] Example 3

[0248] The present embodiment relates to a method for supporting / performing pre-coordination in relation to multi-AP operation according to the present disclosure.

[0249] The pre-collaboration described below can be applied to the polling-based method according to Embodiment 1 of the present disclosure and / or the TWT-based method according to Embodiment 2.

[0250] For example, the Coordinator AP and Coordinated AP(s) can share information about the time period for pre-coordination. This time period can be set / determined periodically or aperiodic. In this case, this time period can be referred to as a multi-AP coordination period, a multi-AP setup period, etc.

[0251] In this regard, Coordinated AP(s) that have expressed / communicated their intent to participate in multi-AP operations through prior cooperation may remain awake during the TXOP during which the cooperation, i.e., multi-AP operations, will be in progress. During this time, the remaining Coordinated AP(s) may remain in a doze state.

[0252] For example, additional power reduction operations may be supported during a TXOP. As a specific example, in the case of C-TDMA, Coordinated AP(s) that are not participating in the transmission may enter a power reduction mode (e.g., enter a doze state) until their transmission time.

[0253] At this time, at the initiation of a TXOP or during a TXOP, the Coordinated AP may perform a polling procedure for Coordinated AP(s) that have indicated / communicated their intent to participate in multi-AP operation through prior cooperation.

[0254] FIG. 18 illustrates a pre-cooperation-based multi-AP operation method according to an embodiment of the present disclosure.

[0255] Referring to FIG. 18, a multi-AP operation within a TXOP acquired by a Coordinator AP is described assuming that there are a first Coordinated AP (i.e., Coordinated AP1), a second Coordinated AP (i.e., Coordinated AP2), and a third Coordinated AP (i.e., Coordinated AP3).

[0256] Pre-coordination for multi-AP operation can be performed in a multi-AP cooperation period prior to each TXOP. Alternatively, pre-coordination for multiple TXOPs can be performed in a single multi-AP cooperation period.

[0257] For example, the first Coordinated AP and the third Coordinated AP may pre-coordinate to participate in multi-AP operation in the first TXOP. In this case, the first Coordinated AP and the third Coordinated AP may remain in an awake state in the first TXOP, and the second Coordinated AP may transition to a doze state in the first TXOP. Based on this, the first Coordinated AP and the third Coordinated AP may each perform frame exchanges with the STA associated with them based on the multi-AP operation.

[0258] Additionally, the first Coordinated AP and the second Coordinated AP may pre-coordinate to participate in multi-AP operation in the second TXOP. In this case, the first Coordinated AP and the second Coordinated AP may remain awake in the second TXOP, and the third Coordinated AP may transition to a doze state in the second TXOP.

[0259] Example 4

[0260] This embodiment is about a method for extending / supporting the method proposed in the present disclosure (e.g., the method proposed in Embodiments 1 to 3) to multi-link operation (MLO).

[0261] FIG. 19 is an example of applying a multi-AP operation method according to an embodiment of the present disclosure to multi-link.

[0262] Referring to FIG. 19, it is assumed that the first Coordinated AP (i.e., Coordinated AP1) and the second Coordinated AP (i.e., Coordinated AP2) are set / configured as the first AP MLD (i.e., AP MLD 1), and the third Coordinated AP (i.e., Coordinated AP3) and the fourth Coordinated AP (i.e., Coordinated AP4) are set / configured as the second AP MLD (i.e., AP MLD 2).

[0263] In this regard, an AP MLD may be comprised of multiple APs supporting different links. For example, in the first AP MLD, a first Coordinated AP may support a link in the 2.4 GHz band, and a second Coordinated AP may support a link in the 5 GHz band.

[0264] For example, multi-AP operation between AP MLD and non-AP MLD performed during the first TXOP acquired by the Coordinator AP may be as follows.

[0265] The Coordinator AP may transmit a polling frame to confirm its willingness to participate in multi-AP operation (e.g., the polling frame described in Embodiment 1).

[0266] The first Coordinated AP belonging to the first AP MLD may transmit to the Coordinator AP a response to the polling frame, i.e., information indicating its intention to participate in multi-AP operation. At this time, the first Coordinated AP may be in an awake state, and the second Coordinated AP in a doze state may not transmit the response. Alternatively, the response may be configured / defined to be transmitted only by the first Coordinated AP associated with the primary link, regardless of whether the second Coordinated AP is in an awake / doze state.

[0267] The Coordinator AP that receives the response can transmit a control frame to the first Coordinated AP to initiate multi-AP operation.

[0268] For example, the control frame may include information indicating that multi-AP operation is to be performed based on multi-link operation. That is, even if the control frame is transmitted to one of the APs belonging / belonging to the first AP MLD, the initiated multi-AP operation may be indicated to be performed based on the APs belonging to the first AP MLD.

[0269] A first Coordinated AP, which has received a control frame from a Coordinator AP, may transmit a control frame for initiating frame exchange to a first STA belonging / belonging to a non-AP MLD associated with the first AP MLD. Here, the control frame may include information indicating that a frame exchange operation will be performed by the first Coordinated AP and the second Coordinated AP belonging to the first AP MLD.

[0270] Thereafter, the first STA can transmit a response frame to the first Coordinated AP, and frame exchange according to multi-AP operation between the first AP MLD and the combined non-AP MLD can be performed based on the multi-link operation.

[0271] For example, multi-AP operation between AP MLD and non-AP MLD performed during the second TXOP acquired by the Coordinator AP may be as follows.

[0272] The Coordinator AP may transmit a polling frame to confirm its willingness to participate in multi-AP operation (e.g., the polling frame described in Embodiment 1).

[0273] At this time, for the polling frame, the Coordinated AP in the awake state can transmit a response frame to the Coordinator AP. For example, among the two Coordinated APs belonging / belonging to the first AP MLD, the first Coordinated AP in the awake state can transmit a response frame. Additionally, among the two Coordinated APs belonging to the second AP MLD, the third Coordinated AP in the awake state can transmit a response frame.

[0274] Thereafter, the Coordinator AP may transmit a control frame to initiate multi-AP operation to the Coordinated AP(s) that transmitted the aforementioned response frame.

[0275] In this regard, the Coordinator AP can initiate multi-AP operation on an AP MLD basis. For example, the Coordinator AP can first initiate multi-AP operation (e.g., frame exchange between the first AP MLD and the associated non-AP MLD) by transmitting a control frame to the first Coordinated AP belonging to the first AP MLD. After the multi-AP operation is completed, the Coordinator AP can initiate multi-AP operation (e.g., frame exchange between the second AP MLD and the associated non-AP MLD) by transmitting a control frame to the third Coordinated AP belonging to the second AP MLD.

[0276] Multi-AP operation in existing wireless LAN systems has not considered power-saving modes for APs. In contrast, the multi-AP operation proposed in this disclosure can be supported by considering the power-saving modes of participating APs (i.e., Coordinated APs). This provides the advantage of simultaneously achieving the technical benefits of multi-AP operation and power-saving modes.

[0277] The embodiments described above are combinations of components and features of the present disclosure in a predetermined form. Each component or feature should be considered optional unless explicitly stated otherwise. Each component or feature may be implemented without being combined with other components or features. Furthermore, it is also possible to form embodiments of the present disclosure by combining some components and / or features. The order of operations described in the embodiments of the present disclosure may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is self-evident that claims that do not have an explicit citation relationship in the patent claims may be combined to form embodiments or incorporated as new claims through post-application amendments.

[0278] It will be apparent to those skilled in the art that the present disclosure may be embodied in other specific forms without departing from the essential characteristics thereof. Therefore, the above detailed description should not be construed as limiting in any respect, but rather as illustrative. The scope of the present disclosure should be determined by a reasonable interpretation of the appended claims, and all modifications within the scope of equivalents of the present disclosure are intended to be included within the scope of the present disclosure.

[0279] The scope of the present disclosure includes software or machine-executable instructions (e.g., an operating system, an application, firmware, a program, etc.) that cause operations according to the methods of various embodiments to be executed on a device or a computer, and a non-transitory computer-readable medium having such software or instructions stored thereon and executable on the device or computer. Instructions that can be used to program a processing system to perform the features described in the present disclosure can be stored on / in a storage medium or a computer-readable storage medium, and a computer program product including such a storage medium can be used to implement the features described in the present disclosure. The storage medium can include, but is not limited to, high-speed random access memory, such as DRAM, SRAM, DDR RAM, or other random access solid state memory devices, and can include non-volatile memory, such as one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, or other non-volatile solid state storage devices. The memory optionally includes one or more storage devices remotely located from the processor(s). The memory or, alternatively, the non-volatile memory device(s) within the memory comprise a non-transitory computer-readable storage medium. The features described in this disclosure may be incorporated into software and / or firmware stored on any of the machine-readable media, which may control the hardware of the processing system and allow the processing system to interact with other mechanisms that utilize results according to embodiments of the present disclosure. Such software or firmware may include, but is not limited to, application code, device drivers, operating systems, and execution environments / containers.

[0280] The method proposed in this disclosure is described with a focus on examples applied to IEEE 802.11-based systems, but can be applied to various wireless LANs or wireless communication systems in addition to IEEE 802.11-based systems.

Claims

1. In a method performed by a first access point (AP) in a wireless LAN system, the method comprises: A step of receiving a polling frame from a second AP to determine whether to participate in a multi-AP operation; A step of transmitting, in response to the polling frame, a frame including information indicating participation in the multi-AP operation to the second AP, based on the first AP being set to maintain an awake state associated with a power reduction mode during a time period for the multi-AP operation; A step of receiving a control frame including information related to the initiation of the multi-AP operation from the second AP; and A method comprising the step of performing frame exchange based on the multi-AP operation based on the above information.

2. In paragraph 1, A method wherein the time interval for the above multi-AP operation is included within a transmission opportunity (TXOP) acquired by the second AP.

3. In paragraph 2, A method wherein the first AP is configured to operate based on the power reduction mode within the TXOP or during a time period for the multi-AP operation.

4. In paragraph 1, In connection with the above multi-AP operation, information about the first AP is provided to the second AP in advance, A method wherein the information about the first AP includes one or more of identification information, information related to the power reduction operation, or information about the type of multi-AP operation that can be supported.

5. In paragraph 1, A method wherein the control frame includes at least one of information indicating the type of the multi-AP operation or information about resources for the multi-AP operation.

6. In paragraph 5, A method wherein the control frame includes information about a resource unit to be used by a first AP in the multi-AP operation, based on the type of the multi-AP operation being indicated as coordinated-OFDMA (C-OFDMA).

7. In paragraph 5, A method wherein the control frame includes information about the transmission order and allocated time interval of the first AP in the multi-AP operation, based on the type of the multi-AP operation being indicated as coordinated-TDMA (C-TDMA).

8. In paragraph 5, A method wherein the control frame includes information about APs capable of simultaneous transmission on the same resource in the multi-AP operation, based on the type of the multi-AP operation being indicated as coordinated-SR (C-SR).

9. In paragraph 1, A method wherein the first AP is configured not to transmit the response frame based on the first AP being configured to enter a doze state associated with a power reduction mode prior to a time period for the multi-AP operation.

10. In paragraph 1, Further comprising a step of performing pre-cooperation for the above multi-AP operation within a certain time interval, A method in which the above-mentioned time interval is set periodically or aperiodically.

11. In paragraph 10, During a transmission opportunity (TXOP) that includes a time interval for the above multi-AP operation, A method wherein, through the above-described prior cooperation, the APs participating in the above-described multi-AP operation are set to remain in an awake state associated with the power reduction mode, and the remaining APs are set to be in a doze state associated with the power reduction mode.

12. In paragraph 1, Based on the above first AP belonging to an AP MLD (multi-link device) for multi-link operation, A method further comprising the step of transmitting information indicating that frame exchange based on the multi-AP operation is performed based on the multi-link operation to a station (STA) belonging to a non-AP MLD that is a target of the frame exchange.

13. In a first access point (AP) device in a wireless LAN system, the device: one or more transmitters and receivers; and comprising one or more processors connected to said one or more transceivers, One or more of the above processors: Receive a polling frame from a second AP to determine whether to participate in a multi-AP operation; Based on the first AP being set to maintain an awake state associated with a power reduction mode during a time period for the multi-AP operation, in response to the polling frame, transmitting a frame including information instructing the second AP to participate in the multi-AP operation; Receive a control frame from the second AP, the control frame including information related to the initiation of the multi-AP operation; A device configured to perform frame exchange based on the multi-AP operation based on the above information.

14. In a method performed by a first access point (AP) in a wireless LAN system, the method: A step of transmitting a TWT (target-wake time) request frame to a second AP to request participation in multi-AP operation; A step of receiving a TWT response frame from a second AP to indicate whether or not to grant the requested participation; A method comprising: performing frame exchange based on the multi-AP operation during a TWT service period (SP), based on the first AP being set to maintain an awake state associated with a power reduction mode during the TWT service period (SP) in which the above participation is permitted and the multi-AP operation is to be performed.

15. In paragraph 14, A method wherein frame exchange based on the above multi-AP operation is initiated based on the exchange of trigger frames, polling frames, and response frames between the first AP and the second AP within the TWT SP.

16. In paragraph 14, Further comprising a step of performing pre-cooperation for the above multi-AP operation within a certain time interval, A method in which the above-mentioned time interval is set periodically or aperiodically.

17. In paragraph 16, During a transmission opportunity (TXOP) that includes a time interval for the above multi-AP operation, A method wherein, through the above-described prior cooperation, the APs participating in the above-described multi-AP operation are set to remain in an awake state associated with the power reduction mode, and the remaining APs are set to be in a doze state associated with the power reduction mode.

18. In paragraph 1, Based on the above first AP belonging to an AP MLD (multi-link device) for multi-link operation, A method further comprising the step of transmitting information indicating that frame exchange based on the multi-AP operation is performed based on the multi-link operation to a station (STA) belonging to a non-AP MLD that is a target of the frame exchange.

19. In a first access point (AP) device in a wireless LAN system, the device: one or more transmitters and receivers; and comprising one or more processors connected to said one or more transceivers, One or more of the above processors: Transmitting a target-wake time (TWT) request frame to the second AP to request participation in multi-AP operation; Receive a TWT response frame from the second AP to indicate whether or not to grant the requested participation; A device configured to perform frame exchange based on the multi-AP operation during the TWT service period (SP), based on the above participation being permitted and the first AP being configured to maintain an awake state associated with a power reduction mode during the TWT service period (SP) in which the multi-AP operation is to be performed.

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