Method and apparatus for performing multi-AP operation in wireless LAN system

Abstract

Disclosed are a method and apparatus for operating in a wireless LAN system. The method according to an embodiment of the present disclosure comprises the steps of: receiving, by a first station (STA), a first null data physical layer protocol data unit (NDP) from a first access point (AP); and on the basis that a failure of second NDP transmission of a second AP is detected on the basis of the first NDP, transmitting, by the first STA to the first AP, a first frame including first information related to the failure of the second NDP transmission, wherein the first NDP may include second information related to whether the first NDP is used for joint sounding.

Description

Method and device for performing multi-AP operation in a wireless LAN system

[0001] The present disclosure relates to communication operations in a Wireless Local Area Network (WLAN) system, and more specifically, to a method and apparatus for performing multi-access point (AP) operations in a next-generation wireless LAN system.

[0002] New technologies have been introduced for wireless LANs (WLANs) to improve transmission rates, increase bandwidth, enhance reliability, reduce errors, and reduce latency. Among wireless LAN technologies, the IEEE (Institute of Electrical and Electronics Engineers) 802.11 series of standards can be referred to as Wi-Fi. For example, technologies recently introduced to wireless LANs 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 an improved wireless communication environment, advanced technologies for Extremely High Throughput (EHT) are being discussed. For example, technologies for Multiple Input Multiple Output (MIMO) supporting increased bandwidth, efficient utilization of multiple bands, and increased spatial streams, as well as technologies for multiple access points (AP) coordination, are being researched. In particular, various technologies are being studied to support traffic with low latency or real-time characteristics. Furthermore, new technologies to support ultra-high reliability (UHR), including improvements or extensions of EHT technology, are being discussed.

[0004] The technical problem of the present disclosure is to provide a method and apparatus for performing multi-AP operation in a wireless LAN system.

[0005] The technical problem of the present disclosure is to provide a method and apparatus for transmitting and receiving a physical layer protocol data unit (PPDU) for coordinated beamforming (CoBF).

[0006] The technical problem of the present disclosure is to provide a method and apparatus for performing a procedure when the loss of NDP occurs during a joint sounding situation.

[0007] The technical problems to be solved in this disclosure are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which this disclosure belongs from the description below.

[0008] A method according to one embodiment of the present disclosure comprises: receiving a first null data physical layer protocol data unit (NDP) from a first access point (AP) by a first station (STA); and transmitting a first frame containing first information related to the failure of the second NDP transmission by the first STA to the first AP based on the detection of the failure of the second NDP transmission by the second AP based on the first NDP, wherein the first NDP may include second information related to whether the first NDP is used for joint sounding.

[0009] A method according to one embodiment of the present disclosure comprises: transmitting a first null data physical layer protocol data unit (NDP) to a first station (STA) by a first access point (AP); transmitting a Beamforming Report Poll (BFRP) trigger frame to the first STA by the first AP; and receiving a first frame from the first STA by the first AP containing first information related to the failure of the second NDP transmission based on the detection of the failure of the second NDP transmission by the second AP, wherein the first NDP may include second information related to whether the first NDP is used for joint sounding.

[0010] By various embodiments of the present disclosure, a method and apparatus for performing multi-AP operation in a wireless LAN system may be provided.

[0011] By various embodiments of the present disclosure, a method and apparatus for transmitting and receiving PPDU for CoBF may be provided.

[0012] By various embodiments of the present disclosure, a method and apparatus for performing a procedure when loss of NDP occurs in a joint sounding situation may be provided.

[0013] The effects obtainable from the present disclosure are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present disclosure belongs from the description below.

[0014] The accompanying drawings, which are included as part of the detailed description to aid in understanding the present disclosure, provide embodiments of the present disclosure and explain the technical features of the present disclosure together with the detailed description.

[0015] FIG. 1 illustrates a block diagram of a wireless communication device according to one embodiment of the present disclosure.

[0016] FIG. 2 is a drawing showing an exemplary structure of a wireless LAN system to which the present disclosure can be applied.

[0017] FIG. 3 is a diagram illustrating a link setup process to which the present disclosure can be applied.

[0018] FIG. 4 is a drawing illustrating a backoff process to which the present disclosure may be applied.

[0019] FIG. 5 is a diagram illustrating a CSMA / CA-based frame transmission operation to which the present disclosure may be applied.

[0020] FIG. 6 is a drawing illustrating an example of a frame structure used in a wireless LAN system to which the present disclosure may be applied.

[0021] FIG. 7 is a drawing illustrating examples of PPDUs defined in the IEEE 802.11 standard to which the present disclosure may be applied.

[0022] FIG. 8 is a drawing showing an exemplary format of a trigger frame to which the present disclosure can be applied.

[0023] FIG. 9 shows an exemplary format of an NDP notice frame to which the present disclosure may be applied.

[0024] FIG. 10 is a flowchart for explaining a method performed by a first STA according to one embodiment of the present disclosure.

[0025] FIG. 11 is a flowchart for explaining a method performed by a first AP according to one embodiment of the present disclosure.

[0026] FIG. 12 is a drawing for explaining a joint sounding procedure according to one embodiment of the present disclosure.

[0027] FIG. 13 is a drawing for explaining the configuration of a UHR NDP according to one embodiment of the present disclosure.

[0028] FIG. 14 illustrates a UHR MIMO control field of a UHR compressed beamforming / CQI frame according to one embodiment of the present disclosure.

[0029] FIG. 15 is a drawing for explaining a recovery procedure according to one embodiment of the present disclosure.

[0030] FIG. 16 is a diagram illustrating a PPDU transmission and reception procedure between a transmitting STA and a receiving STA according to one embodiment of the present disclosure.

[0031] Hereinafter, preferred embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. The detailed description disclosed below, together with the accompanying drawings, is intended to describe exemplary embodiments of the present disclosure and is not intended to represent the only embodiment in which the present disclosure may be practiced. The following detailed description includes specific details to provide a complete understanding of the present disclosure. However, those skilled in the art will know that the present disclosure may be practiced without such specific details.

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

[0033] In the present disclosure, when a component is described as being “connected,” “combined,” or “joined” with another component, this may include not only a direct connection but also an indirect connection in which another component exists between them. Furthermore, in the present disclosure, the terms “comprising” or “having” specify the presence of the mentioned features, steps, actions, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, actions, elements, components, and / or groups thereof.

[0034] In the present disclosure, terms such as "first," "second," etc. are used solely for the purpose of distinguishing one component from another and are not used to limit the components, nor do they limit the order or importance of the components unless specifically stated otherwise. Accordingly, within the scope of the present disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and likewise, a second component in one embodiment may be referred to as a first component in another embodiment.

[0035] The terms used in this disclosure are for the description of specific embodiments and are not intended to limit the claims. As used in the description of embodiments and in the appended claims, the singular form is intended to include the plural form unless the context clearly indicates otherwise. The term "and / or" as used in this disclosure may refer to any one of the related enumerated items, or refers to and includes any and all possible combinations of two or more of them. Additionally, the " / " between words in this disclosure has the same meaning as "and / or" unless otherwise noted.

[0036] The embodiments of the present disclosure may be applied to various wireless communication systems. For example, the embodiments of the present disclosure may be applied to wireless LAN systems. For example, the embodiments of the present disclosure may be applied to wireless LANs based on IEEE 802.11a / g / n / ac / ax / be standards. Furthermore, the embodiments of the present disclosure may be applied to wireless LANs based on newly proposed IEEE 802.11bn (or UHR) standards. Additionally, the embodiments of the present disclosure may be applied to wireless LANs based on next-generation standards following IEEE 802.11bn. Furthermore, the embodiments of the present disclosure may be applied to cellular wireless communication systems. For example, they may be applied to cellular wireless communication systems based on LTE (Long Term Evolution) series technologies and 5G NR (New Radio) series technologies of 3GPP (3rd Generation Partnership Project) standards.

[0037] The following describes the technical features to which the examples of the present disclosure may be applied.

[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) exemplified in FIG. 1 may be replaced with various terms such as terminal, wireless device, WTRU (Wireless Transmit Receive Unit), UE (User Equipment), MS (Mobile Station), UT (user terminal), MSS (Mobile Subscriber Station), MSS (Mobile Subscriber Unit), SS (Subscriber Station), AMS (Advanced Mobile Station), WT (Wireless terminal), or simply user. Additionally, the first device (100) and the second device (200) may be replaced with various terms such as access point (AP), base station (BS), fixed station, Node B, base transceiver system (BTS), network, artificial intelligence (AI) system, road side unit (RSU), repeater, router, relay, gateway, etc.

[0040] The device (100, 200) exemplified in FIG. 1 may be referred to as a station (STA). For example, the device (100, 200) exemplified in FIG. 1 may be referred to by various terms such as a transmitting device, a receiving device, a transmitting STA, or a receiving STA. For example, the STA (110, 200) may perform the role of an access point (AP) or a non-AP. That is, in the present disclosure, the STA (110, 200) may perform the functions of an AP and / or a non-AP. If the STA (110, 200) performs the AP function, it may simply be referred to as an AP, and if the STA (110, 200) performs the non-AP function, it may simply be referred to as a STA. Additionally, in the present disclosure, the AP may also be indicated as an AP STA.

[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) may include interfaces for the medium access control (MAC) layer and the physical layer (PHY) that comply with the specifications of the IEEE 802.11 standard.

[0042] In addition, the first device (100) and the second device (200) may additionally support various communication standards other than wireless LAN technology (e.g., 3GPP LTE series, 5G NR series standards, etc.). In addition, the device of the present disclosure may be implemented as various devices such as mobile phones, vehicles, personal computers, AR (Augmented Reality) equipment, VR (Virtual Reality) equipment, etc. Furthermore, the STA of the present specification may support various communication services such as voice calls, video calls, data communication, autonomous driving, MTC (Machine-Type Communication), M2M (Machine-to-Machine), D2D (Device-to-Device), and IoT (Internet-of-Things).

[0043] The first device (100) includes one or more processors (102) and one or more memories (104), and may additionally include one or more transceivers (106) and / or one or more antennas (108). The processor (102) controls the memory (104) and / or transceivers (106) and may be configured to implement the descriptions, functions, procedures, proposals, methods and / or sequences of operation disclosed in this disclosure. For example, the processor (102) may process information within the memory (104) to generate a first information / signal and then transmit a wireless signal containing the first information / signal through the transceiver (106). Additionally, the processor (102) may receive a wireless signal containing a second information / signal through the transceiver (106) and then store information obtained from the signal processing of the second information / signal in the memory (104). Memory (104) may be connected to the processor (102) and may store various information related to the operation of the processor (102). For example, memory (104) may store software code including instructions for performing some or all of the processes controlled by the processor (102) or for performing the descriptions, functions, procedures, proposals, methods, and / or sequences of operation disclosed in this disclosure. Here, the processor (102) and memory (104) may be part of a communication modem / circuit / chip designed to implement wireless LAN technology (e.g., IEEE 802.11 series). A transceiver (106) may be connected to the processor (102) and may transmit and / or receive wireless signals through one or more antennas (108). The transceiver (106) may include a transmitter and / or receiver. The transceiver (106) may be combined with an RF (Radio Frequency) unit. In the present disclosure, the device may refer to a communication modem / circuit / chip.

[0044] The second device (200) includes one or more processors (202) and one or more memories (204), and may additionally include one or more transceivers (206) and / or one or more antennas (208). The processor (202) controls the memory (204) and / or transceivers (206) and may be configured to implement the descriptions, functions, procedures, proposals, methods and / or sequences of operation disclosed in this disclosure. For example, the processor (202) may process information within the memory (204) to generate a third information / signal and then transmit a wireless signal containing the third information / signal through the transceiver (206). Additionally, the processor (202) may receive a wireless signal containing a fourth information / signal through the transceiver (206) and then store information obtained from the signal processing of the fourth information / signal in the memory (204). The memory (204) may be connected to the processor (202) and may store various information related to the operation of the processor (202). For example, the memory (204) may store software code containing instructions for performing some or all of the processes controlled by the processor (202) or for performing the descriptions, functions, procedures, proposals, methods, and / or sequences of operation disclosed in this disclosure. Here, the processor (202) and the memory (204) may be part of a communication modem / circuit / chip designed to implement 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 through one or more antennas (208). The transceiver (206) may include a transmitter and / or receiver. The transceiver (206) may be used in combination with an RF unit. In the present disclosure, the device may refer to a communication modem / circuit / chip.

[0045] Hereinafter, 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 Service Data Units (SDUs) according to the descriptions, functions, procedures, proposals, methods, and / or flowcharts of operation disclosed in this 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 flowcharts of operation disclosed in this disclosure. One or more processors (102, 202) may generate a signal (e.g., a baseband signal) including a PDU, SDU, message, control information, data, or information according to the functions, procedures, proposals, and / or methods disclosed in this disclosure and provide it to one or more transceivers (106, 206). One or more processors (102, 202) may receive a signal (e.g., a baseband signal) from one or more transceivers (106, 206) and may obtain a PDU, SDU, message, control information, data, or information according to the descriptions, functions, procedures, proposals, methods, and / or flowcharts disclosed in this disclosure.

[0046] One or more processors (102, 202) may be referred to as a controller, microcontroller, microprocessor, or 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 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. Firmware or software configured to perform the descriptions, functions, procedures, proposals, methods, and / or operation sequences disclosed in this disclosure may be included in 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 sequences disclosed in this disclosure may be implemented using firmware or software in the form of code, instructions, and / or sets of instructions.

[0047] One or more memories (104, 204) may be connected to one or more processors (102, 202) and may store various forms of data, signals, messages, information, programs, codes, instructions, and / or commands. One or more memories (104, 204) may be composed of ROM, RAM, EPROM, flash memory, hard drive, registers, cache memory, computer read storage media, and / or combinations thereof. One or more memories (104, 204) may be located inside and / or outside of one or more processors (102, 202). Additionally, one or more memories (104, 204) may be connected to one or more processors (102, 202) through various technologies such as wired or wireless connections.

[0048] One or more transceivers (106, 206) may transmit user data, control information, wireless signals / channels, etc., as mentioned in the methods and / or operation flowcharts, etc., of the present disclosure to one or more other devices. One or more transceivers (106, 206) may receive user data, control information, wireless signals / channels, etc., as mentioned in the descriptions, functions, procedures, proposals, methods and / or operation flowcharts, etc., disclosed in the present disclosure from one or more other devices. For example, one or more transceivers (106, 206) may be connected to one or more processors (102, 202) and may transmit and receive wireless signals. For example, one or more processors (102, 202) may 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 connected 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, etc., as described in the descriptions, functions, procedures, proposals, methods, and / or flowcharts of operation disclosed in this disclosure through one or more antennas (108, 208). In this disclosure, one or more antennas may be a plurality of physical antennas or a plurality of logical antennas (e.g., antenna ports). One or more transceivers (106, 206) can convert the received wireless signal / channel, etc. from an RF band signal to a baseband signal in order to process the received user data, control information, wireless signal / channel, etc. using one or more processors (102, 202).One or more transceivers (106, 206) can convert user data, control information, wireless signals / channels, etc. processed using one or more processors (102, 202) from baseband signals to RF band signals. To this end, one or more transceivers (106, 206) may include (analog) oscillators and / or filters.

[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 transceiver (106, 206) of FIG. 1 may perform the operation of transmitting and receiving signals (e.g., packets or PPDU (Physical Layer Protocol Data Unit) according to IEEE 802.11a / b / g / n / ac / ax / be / bn, etc.). Additionally, the operation of generating transmission and reception signals or performing data processing or calculations in advance for transmission and reception signals by various STAs in the present disclosure may be performed by the processor (102, 202) of FIG. 1. For example, an example of an operation to generate a transmission and reception signal or to perform data processing or operations in advance for a transmission and reception signal may include: 1) an operation to determine / acquire / configure / operate / decode / encode bit information of fields (SIG (signal), STF (short training field), LTF (long training field), Data, etc.) included in the PPDU; 2) an operation to determine / configure / acquire time resources or frequency resources (e.g., subcarrier resources) used for fields (SIG, STF, LTF, Data, etc.) included in the PPDU; 3) an operation to determine / configure / acquire specific sequences (e.g., pilot sequence, STF / LTF sequence, extra sequence applied to SIG) used for fields (SIG, STF, LTF, Data, etc.) included in the PPDU; 4) power control operations and / or power saving operations applied to the STA; and 5) operations related to determining / acquiring / configuring / operating / decoding / encoding of an ACK signal. In addition, various information (e.g., information related to fields, subfields, control fields, parameters, power, etc.) used by various STAs for determining / acquiring / configuring / calculating / decoding / encoding transmission and reception signals in the following example can be stored in the memory (104, 204) of FIG. 1.

[0050] In the following, the 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 the AP STA, and the receiver may be part of the non-AP STA. The 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 the non-AP STA, and the receiver may be part of the AP STA.

[0051] FIG. 2 is a drawing 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 STA mobility transparent to the upper layer can be provided. A Basic Service Set (BSS) corresponds to the basic building block of a wireless LAN. Figure 2 exemplarily illustrates 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). In Figure 2, the ellipse representing the BSS can also be understood as representing the coverage area where the STAs included in the corresponding BSS maintain communication. This area can be referred to as a Basic Service Area (BSA). If a STA moves outside the BSA, it becomes unable to communicate directly with other STAs within that BSA.

[0053] Excluding the DS illustrated in Fig. 2, the most basic type of BSS in a wireless LAN is the Independent BSS (IBSS). For example, an IBSS can have a minimal form consisting of only two STAs. For instance, assuming other components are omitted, a BSS1 composed of only STA1 and STA2, or a BSS2 composed of only STA3 and STA4, can each be considered a representative example of an IBSS. Such a configuration is possible when the STAs can communicate directly without an AP. Furthermore, this type of wireless LAN is not configured through pre-planning but can be configured when a LAN is needed, and this can be referred to as an ad-hoc network. Since an IBSS does not include an AP, there is no centralized management entity. In other words, in an IBSS, STAs are managed in a distributed manner. In IBSS, all STAs can be mobile STAs, and since connections to distributed systems (DS) are not allowed, they form a self-contained network.

[0054] The membership of an STA in a BSS can be dynamically changed by the STA being turned on or off, or by the STA entering or leaving the BSS area. To become a member of a BSS, an STA can join the BSS using a synchronization process. To access all services of the BSS infrastructure, an STA must be associated with the BSS. This association can be configured dynamically and may include the use of a Distribution System Service (DSS).

[0055] In a wireless LAN, the direct STA-to-STA distance may be limited by PHY performance. In some cases, this distance limit may be sufficient, but in others, communication between STAs over longer distances may be required. To support extended coverage, a distributed system (DS) may be configured.

[0056] DS refers to a structure in which BSSs are interconnected. Specifically, as shown in FIG. 2, a BSS may exist as a component in an extended form of a network composed of multiple BSSs. DS is a logical concept and can be specified by the characteristics of the Distributed System Medium (DSM). In this regard, the Wireless Medium (WM) and the DSM can be logically distinguished. Each logical medium is used for a different purpose and is utilized by different components. These media are not limited to being identical or different. The flexibility of the wireless LAN structure (DS structure or other network structure) can be explained by the fact that multiple media are logically distinct in this way. That is, the wireless LAN structure can be implemented in various ways, and the corresponding wireless LAN structure can be specified independently by the physical characteristics of each implementation.

[0057] DS can support mobile devices by providing seamless integration of multiple BSSs and providing logical services necessary for handling addresses to destinations. Additionally, DS may include a component called a portal that acts as a bridge for connecting the wireless LAN with another network (e.g., IEEE 802.X).

[0058] An AP refers to an entity that enables access to the DS via the WM for combined non-AP STAs and also possesses the functionality of an STA. Data movement between the BSS and the DS can be performed through the AP. For example, STA2 and STA3 shown in FIG. 2 possess the functionality of an STA and provide the ability for combined non-AP STAs (STA1 and STA4) to access the DS. Furthermore, since all APs fundamentally correspond to STAs, all APs are addressable entities. The address used by the AP for communication on the WM and the address used by the AP for communication on the DSM do not necessarily have to be the same. A BSS composed 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) coupled to the AP to the STA address of the AP can always be received at an uncontrolled port and processed by an IEEE 802.1X port access entity. Additionally, if the controlled port is authenticated, the transmitted data (or frame) can be forwarded to the DS.

[0060] In addition to the structure of the aforementioned DS, an Extended Service Set (ESS) may be configured to provide wider coverage.

[0061] An ESS refers to a network of arbitrary size and complexity composed of DSs and BSSs. An ESS can correspond to a set of BSSs connected to a single DS. However, an ESS does not contain a DS. An ESS network is characterized by appearing as an IBSS at the Logical Link Control (LLC) layer. STAs included in 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 included in a single ESS can have the same Service Set Identification (SSID). The SSID is distinct from the BSSID, which is the identifier for the BSS.

[0062] In wireless LAN systems, no assumptions are made regarding the relative physical locations of BSSs, and all of the following forms are possible. BSSs may partially overlap, which is a form commonly used to provide continuous coverage. Additionally, BSSs may not be physically connected, and logically, there is no limit to the distance between BSSs. Furthermore, BSSs may be located in the same physical location, which can be used to provide redundancy. Also, one (or more) IBSS or ESS networks may physically exist in the same space as one (or more) ESS networks. This may apply to ESS network forms such as when an ad-hoc network operates at a location where an ESS network exists, when wireless networks that physically overlap are configured by different organizations, or when two or more different access and security policies are required at the same location.

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

[0064] In order 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 go through authentication procedures for security. The link setup process can also be referred to as the session initiation process or the session setup process. Additionally, the processes of discovery, authentication, association, and security setup in 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. The network discovery operation may include the STA's scanning operation. That is, in order for the STA to access a network, it must find a network it can join. Before joining a wireless network, the STA must identify a compatible network, and the process of identifying networks existing in a specific area is called scanning.

[0066] Scanning methods include active scanning and passive scanning. Figure 3 illustrates a network discovery operation that includes an active scanning process as an example. In active scanning, the STA performing the scanning moves between channels to search for nearby APs, transmits a probe request frame, and waits for a response. The responder transmits a probe response frame as a response to the probe request frame to the STA that transmitted the probe request frame. Here, the responder may be the STA that last transmitted a beacon frame from the BSS of the channel being scanned. In a BSS, the AP becomes the responder because it transmits the beacon frame; however, in an IBSS, the responder is not constant because STAs within the IBSS take turns transmitting the beacon frame. 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 in the same way (i.e., transmit and receive probe request / response on channel 2).

[0067] Although not illustrated in FIG. 3, the scanning operation may be performed using a passive scanning method. In passive scanning, the STA performing the scanning waits for a beacon frame while switching between channels. A beacon frame is one of the management frames defined in IEEE 802.11, which is periodically transmitted to announce the presence of a wireless network and to allow the scanning STA to find the wireless network and join it. In a BSS, the AP performs the role of periodically transmitting beacon frames, and in an IBSS, the STAs within the IBSS take turns transmitting beacon frames. When the scanning STA receives a beacon frame, it stores the information about the BSS included in the beacon frame and records the beacon frame information in each channel while moving to another channel. The STA that receives the beacon frame stores the BSS-related information included in the received beacon frame and moves to the next channel, and can perform scanning in the next channel in the same way. When 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 in step S340 described later.

[0069] The authentication process involves the STA sending an authentication request frame to the AP, and the AP sending an authentication response frame to the STA in response. The authentication frame used in the authentication request / response corresponds to a management frame.

[0070] The authentication frame may include information regarding the authentication algorithm number, authentication transaction sequence number, status code, challenge text, Robust Security Network (RSN), Finite Cyclic Group, etc. These are some examples of information that may be included in the authentication request / response frame, and they may be replaced with other information or additional information may be included.

[0071] The STA can send an authentication request frame to the AP. Based on the information contained in the received authentication request frame, the AP can determine whether to allow authentication for the STA. The AP can provide the result of the authentication process to the STA through an authentication response frame.

[0072] After the STA is successfully authenticated, the association process can be performed in step S330. The association process includes the STA transmitting an association request frame to the AP, and in response, the AP transmitting an association response frame to the STA.

[0073] For example, the association request frame may include information regarding various capabilities, beacon listen interval, service set identifier (SSID), supported rates, supported channels, RSN, mobility domain, supported operating classes, Traffic Indication Map Broadcast request, interworking service capabilities, etc. For example, the association response frame may include information regarding various capabilities, status code, Association ID (AID), supported rates, Enhanced Distributed Channel Access (EDCA) parameter set, Received Channel Power Indicator (RCPI), Received Signal to Noise Indicator (RSNI), mobility domain, timeout interval (e.g., association comeback time), overlapping BSS scan parameters, TIM broadcast response, Quality of Service (QoS) map, etc. These are some examples of information that may be included in a combined request / response frame, and may be replaced with other information or additional information may be included.

[0074] After the STA is successfully joined to the network, a security setup process can be performed in step S340. The security setup process in step S340 may be described as an authentication process through RSNA (Robust Security Network Association) requests / responses, and the authentication process in step S320 may be referred to as the first authentication process, and the security setup process in step S340 may simply be referred to as the authentication process.

[0075] The security setup process of step S340 may include, for example, a private key setup process through a 4-way handshake via an EAPOL (Extensible Authentication Protocol over LAN) frame. Additionally, 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 drawing illustrating a backoff process to which the present disclosure may be applied.

[0077] In wireless LAN systems, the basic access mechanism for MAC (Medium Access Control) is the CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) mechanism. The CSMA / CA mechanism is also known as the Distributed Coordination Function (DCF) of IEEE 802.11 MAC, and it basically employs a "listen before talk" access mechanism. According to this type of access mechanism, the AP and / or STA may perform Clear Channel Assessment (CCA) to sense the wireless channel or medium for a predetermined time interval (e.g., DIFS (DCF Inter-Frame Space)) before starting transmission. If the sensing result determines that the medium is in an idle status, it starts transmitting a frame through that 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 wait by setting a delay period for medium access (e.g., a random backoff period) before attempting to transmit a frame. 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 a Hybrid Coordination Function (HCF). The HCF is based on the aforementioned Point Coordination Function (PCF). The PCF is a polling-based synchronous access method that periodically polls to ensure all receiving APs and / or STAs can receive data frames. Furthermore, the HCF includes Enhanced Distributed Channel Access (EDCA) and Controlled Channel Access (HCCA). EDCA is a contention-based access method for a provider to offer data frames to multiple users, while HCCA uses a non-contention-based channel access method utilizing a polling mechanism. Additionally, the HCF includes a media access mechanism to improve the Quality of Service (QoS) of the wireless LAN and can transmit QoS data during both the Contention Period (CP) and the Contention-Free Period (CFP).

[0079] Referring to FIG. 4, the operation based on the random backoff period is described. When a medium in an occupied / busy state changes to an idle state, multiple STAs may attempt to transmit data (or frames). As a measure to minimize collisions, each STA may select a random backoff count and attempt transmission after waiting for the corresponding slot time. The random backoff count has a pseudo-random integer value and can be determined as one of the values ​​in the range from 0 to CW. Here, CW is the Contention Window parameter value. The CW parameter is given an initial value of CWmin, but in the case of transmission failure (e.g., failure to receive an ACK for a transmitted frame), it may take a value twice that amount. When the CW parameter value becomes CWmax, data transmission may be attempted while maintaining the CWmax value until data transmission is successful; if data transmission is successful, it is reset to the CWmin value. The values ​​of CW, CWmin, and CWmax are 2 n It is desirable to set it to -1 (n=0, 1, 2, ...).

[0080] When the random backoff process begins, the STA continues to monitor the media while counting down the backoff slots according to the determined backoff count value. When the media is monitored as occupied, it stops the countdown and waits, and when the media becomes idle, it resumes the remaining countdown.

[0081] In the example of Fig. 4, when a packet to be transmitted arrives at the MAC of STA3, STA3 confirms that the medium is idle for DIFS and can immediately transmit the frame. The remaining STAs monitor whether the medium is occupied or busy and wait. Meanwhile, data to be transmitted may also arise from each of STA1, STA2, and STA5, and each STA can perform a countdown of the backoff slot according to a random backoff count value selected by each after waiting for DIFS when the medium is monitored to be idle. Assume the case where STA2 selects the smallest backoff count value and STA1 selects the largest backoff count value. That is, this exemplifies a case where, at the point when STA2 finishes the backoff count and starts transmitting the frame, the remaining backoff time of STA5 is shorter than the remaining backoff time of STA1. STA1 and STA5 pause the countdown briefly and wait while STA2 occupies the medium. When STA2's possession ends and the medium becomes idle again, STA1 and STA5 wait for DIFS and then resume the paused backoff count. That is, they can start transmitting a frame after counting down the remaining backoff slots corresponding to the remaining backoff time. Since STA5's remaining backoff time was shorter than STA1's, STA5 starts transmitting the frame. While STA2 is occupying the medium, data to be transmitted may also be generated by STA4. From STA4's perspective, when the medium becomes idle, it waits for DIFS, performs a countdown based on a random backoff count value selected by itself, and can start transmitting a frame. The example in Figure 4 illustrates a case where STA5's remaining backoff time happens to match STA4's random backoff count value; in this case, a collision may occur between STA4 and STA5. If a collision occurs, neither STA4 nor STA5 receives an ACK, resulting in a failure to transmit data.In this case, STA4 and STA5 can double the CW value, select a random backoff count value, and perform a countdown. STA1 waits while the medium is occupied due to transmission by STA4 and STA5, and when the medium becomes idle, it waits for DIFS, and then can start transmitting frames after the remaining backoff time has passed.

[0082] As shown in the example in Fig. 4, a data frame is a frame used for transmitting data that is forwarded to an upper layer, and can be transmitted after a backoff performed after the elapsed time of DIFS from when the medium becomes idle. Additionally, a management frame is a frame used for exchanging management information that is not forwarded to an upper layer, and is transmitted after a backoff performed after the elapsed time of an IFS such as DIFS or PIFS (Point coordination function IFS). Subtypes of management frames include Beacon, Association request / response, re-association request / response, probe request / response, and authentication request / response. A control frame is a frame used to control access to the medium. Subtype frames of control frames include RTS (Request-To-Send), CTS (Clear-To-Send), ACK (Acknowledgment), PS-Poll (Power Save-Poll), Block ACK (BlockAck), Block ACK Request (BlockACKReq), NDP Announcement (null data packet announcement), and Trigger. If a control frame is not an acknowledgment frame of a previous frame, it is transmitted after a backoff performed after the elapsed DIFS; if it is an acknowledgment frame of a previous frame, it is transmitted after the elapsed SIFS (short IFS) without a backoff. The type and subtype of a frame can be identified by the type field and subtype field within the Frame Control (FC) field.

[0083] A QoS (Quality of Service) STA can transmit a frame after backoff, which is performed after the passage of the arbitration IFS (AIFS) for the access category (AC) to which the frame belongs, i.e., AIFS[i] (where i is a value determined by the AC). Here, the frame for which AIFS[i] can be used can be a data frame or a management frame, and can also be a control frame rather than a response frame.

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

[0085] As previously mentioned, the CSMA / CA mechanism includes virtual carrier sensing in addition to physical carrier sensing, where the STA directly senses the medium. Virtual carrier sensing is intended to mitigate problems that may occur in medium access, such as the hidden node problem. For virtual carrier sensing, the STA's MAC can utilize the Network Allocation Vector (NAV). The NAV is a value that indicates to other STAs the time remaining until the medium becomes available, provided that the STA currently using or authorized to use the medium is using it. Therefore, the value set as the NAV corresponds to the period during which the medium is scheduled to be used by the STA transmitting the frame, and the 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 frame's MAC header.

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

[0087] In order to reduce the possibility of collisions between multiple STAs in a CSMA / CA-based frame transmission operation, a mechanism utilizing RTS / CTS frames may be applied. In the example of FIG. 5, while STA1 is transmitting, the medium may be determined to be idle based on the carrier sensing result of STA3. That is, STA1 may be a hidden node to STA3. Alternatively, in the example of FIG. 5, while STA2 is transmitting, the medium may be determined to be idle based on the carrier sensing result of STA3. That is, STA2 may be a hidden node to STA3. By exchanging RTS / CTS frames before performing data transmission and reception between STA1 and STA2, it is possible to prevent a STA outside the transmission range of either STA1 or STA2, or a STA outside the carrier sensing range for transmission from STA1 or STA3, from attempting to occupy the channel during data transmission and reception between STA1 and STA2.

[0088] Specifically, STA1 can determine whether the channel is in use through carrier sensing. In terms of physical carrier sensing, STA1 can determine the channel occupancy idle state based on the energy magnitude or signal correlation detected in the channel. Additionally, in terms of virtual carrier sensing, STA1 can determine the channel occupancy state using a NAV (network allocation vector) timer.

[0089] If the channel is idle during DIFS, STA1 can send an RTS frame to STA2 after performing backoff. If STA2 receives the RTS frame, it can send a CTS frame to STA1 as a response to the RTS frame after SIFS.

[0090] If STA3 cannot overhear a CTS frame from STA2 but can overhear an RTS frame from STA1, STA3 can set a NAV timer for the duration of subsequently transmitted frames (e.g., SIFS + CTS frame + SIFS + data frame + SIFS + ACK frame) using the duration information included in the RTS frame. Alternatively, if STA3 cannot overhear an RTS frame from STA1 but can overhear a CTS frame from STA2, STA3 can set a NAV timer for the duration of subsequently transmitted frames (e.g., SIFS + data frame + SIFS + ACK frame) using the duration information included in the CTS 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 may transmit a data frame to STA2 after SIFS from the time the reception of the CTS frame is completed. If STA2 successfully receives the data frame, it may transmit an ACK frame to STA1 as an acknowledgment to the data frame after SIFS. STA3 may determine whether the channel is in use through carrier sensing when the NAV timer expires. If STA3 determines that the channel is not in use by another terminal during DIFS from the time the NAV timer expires, it may attempt channel access after a contention window (CW) based on random backoff has passed.

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

[0093] Based on instructions or primitives (meaning a set of instructions or parameters) from the MAC layer, the PHY layer can prepare the MPDU (MAC PDU) to be transmitted. For example, upon receiving an instruction from the MAC layer requesting the start of transmission, the PHY layer switches to transmit mode and can construct the information provided by the MAC layer (e.g., data) into a frame for transmission. Additionally, if the PHY layer detects a valid preamble of a received frame, it monitors the preamble header and sends an instruction to the MAC layer indicating the start of reception.

[0094] As such, information transmission and reception in wireless LAN systems are carried out in the form of frames, and for this purpose, the Physical 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 (SIGNAL) field, and a Data field. The most basic (e.g., the non-HT (High Throughput)) PPDU format illustrated in FIG. 7 may consist only of Legacy-STF (Legacy-STF), Legacy-LTF (Legacy-LTF), Legacy-SIG (Legacy-SIG) fields and a Data field. In addition, 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 other types of) RL-SIG, U-SIG, non-legacy SIG fields, 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 and frequency error estimation. STF and LTF can be considered signals for synchronization and channel estimation in the OFDM physical layer.

[0097] The SIG field may contain various information related to the transmission and reception of the PPDU. For example, the L-SIG field consists 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 contain information regarding the modulation and coding rates of the data. For example, the 12-bit Length field may contain information regarding 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 non-HT, HT, VHT, or EHT PPDUs, the value of the Length field may be determined as a multiple of 3. For example, for HE PPDUs, the value of the Length field may be determined as a multiple of 3 + 1 or a multiple of 3 + 2.

[0098] The data field may include a SERVICE field, a PSDU (Physical layer Service Data Unit), and PPDU TAIL bits, and may also include padding bits if necessary. Some bits of the SERVICE field may be used for synchronization of the descrambler at the receiver. The PSDU corresponds to a MAC PDU defined at the MAC layer and may contain data generated or used by the upper layer. The PPDU TAIL bits may be used to return the encoder to a 0 state. Padding bits may be used to adjust the length of the data field to a predetermined unit.

[0099] A MAC PDU is 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 a MAC PDU and can be transmitted or received through the PSDU of the data portion in 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 contain control information necessary for transmitting or receiving frames. The Duration / ID field may be set as the time for transmitting the corresponding frame. Address subfields may indicate the frame's receiver address, transmitter address, destination address, and source address, and some address subfields may be omitted. Specific details regarding each subfield of the MAC header, including Sequence Control, QoS Control, and HT Control subfields, can be found in 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 is a frame format that includes the PPDU preamble (i.e., L-STF, L-LTF, L-SIG fields, and additionally, non-legacy SIG, non-legacy STF, and non-legacy LTF if present) from a standard PPDU format, but excludes the remaining parts (i.e., the data field).

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

[0103] Various forms of PPDU have been used in standards such as IEEE 802.11a / g / n / ac / ax. The basic PPDU format (IEEE 802.11a / g) includes L-LTF, L-STF, L-SIG, and Data fields. The basic PPDU format may 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 the HT-mixed format. Additionally, an HT-greenfield format PPDU may be defined, which corresponds to a format consisting of HT-GF-STF, HT-LTF1, HT-SIG, one or more HT-LTFs, and a Data field, without including L-STF, L-LTF, and L-SIG (not shown).

[0105] An example of the VHT PPDU format (IEEE 802.11ac) includes the 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 the HE PPDU format (IEEE 802.11ax) includes the 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 the 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 multiple users (MU), but is not included in the HE PPDU format for single users (SU). Additionally, the HE trigger-based (TB) PPDU format does not include HE-SIG-B, and the length of the HE-STF field may vary to 8 µs. The HE ER (Extended Range) SU PPDU format does not include the HE-SIG-B field, and the length of the HE-SIG-A field may vary to 16 µs. For example, RL-SIG can be configured identically to L-SIG. Based on the presence of RL-SIG, the receiving STA can determine that the received PPDU is a HE PPDU or the EHT PPDU described later.

[0107] The EHT PPDU format may include the EHT MU (multi-user) 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 RL-SIG following L-SIG, but it may include U (universal)-SIG, EHT-SIG, EHT-STF, and EHT-LTF following RL-SIG.

[0108] The EHT MU PPDU of FIG. 7(e) corresponds to a PPDU that carries one or more data (or PSDU) 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-SIG is omitted in the EHT TB PPDU of FIG. 7(f) compared to the EHT MU PPDU. A STA that receives 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 so that demodulation and decoding can be attempted even on legacy STAs, and mapped based on a defined 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 so that they can be demodulated and decoded by a STA that has successfully decoded a non-legacy SIG (e.g., U-SIG and / or EHT-SIG) to obtain the information contained in the corresponding fields, and mapped based on a defined 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 can be referred to as pre-HE modulation fields, and the HE-STF, HE-LTF, Data, and PE fields can be referred to as HE modulation fields. Also, in the VHT PPDU format, the L-STF, L-LTF, L-SIG, and VHT-SIG-A fields can be referred to as pre-VHT modulation fields, and the VHT STF, VHT-LTF, VHT-SIG-B, and Data fields can be referred to as VHT modulation fields.

[0112] The U-SIG included in the EHT PPDU format of FIG. 7 can be constructed based on, for example, two symbols (e.g., two consecutive OFDM symbols). Each symbol for the U-SIG (e.g., OFDM symbol) can have a duration of 4 µs, and the U-SIG can have a total duration of 8 µs. 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 20 MHz units. For example, if an 80 MHz PPDU is configured, the same U-SIG can be duplicated in 20 MHz units. That is, four identical U-SIGs can be included within an 80 MHz PPDU. If the bandwidth exceeds 80 MHz, for example, for a 160 MHz PPDU, the U-SIG of the first 80 MHz unit and the U-SIG of the second 80 MHz unit may be different.

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

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

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

[0117] For example, the version-independent bits of U-SIG may include a 3-bit physical layer version identifier (PHY version identifier), and this information may indicate the PHY version of the transmitted / received PPDU (e.g., EHT, UHR, etc.). The version-independent bits of 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 U-SIG may include information regarding the length of the TXOP (transmission opportunity) and information regarding the BSS color ID.

[0118] For example, the version-dependent bits of 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 necessary for PPDU transmission and reception may be included in the U-SIG. For example, the U-SIG may further include information regarding bandwidth, information regarding MCS techniques applied to non-legacy SIGs (e.g., EHT-SIG or UHR-SIG, etc.), information indicating whether DCM (dual carrier modulation) techniques (e.g., techniques to achieve an effect similar to frequency diversity by reusing the same signal on two subcarriers) are applied to non-legacy SIGs, information regarding the number of symbols used for non-legacy SIGs, and information regarding whether non-legacy SIGs are generated across the entire band.

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

[0121] Preamble puncturing may refer to the transmission of a PPDU in which a signal is not present in one or more frequency units within the PPDU bandwidth. For example, the size of the frequency unit (or the resolution of preamble puncturing) may be defined as 20 MHz, 40 MHz, etc. For example, preamble puncturing may be applied to a PPDU bandwidth of a predetermined size or larger.

[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. A non-legacy SIG may be transmitted through at least one symbol, and one symbol may have a length of 4 µs. Information regarding the number of symbols used for EHT-SIG may be included in the previous SIG (e.g., HE-SIG-A, U-SIG, etc.).

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

[0124] In some cases, the common field may be omitted. For example, in a compression mode where non-OFDMA (orthogonal frequency multiple access) is applied, the common field may be omitted, and multiple STAs may receive PPDUs (e.g., the data field of the PPDU) over the same frequency band. In a non-compression mode where OFDMA is applied, multiple users may receive PPDUs (e.g., the data field of the PPDU) 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 may be related to 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 to be 4 bits, and the length of the Tail bits may be determined to be 6 bits and set to 000000. The common field may include RU allocation information. The RU allocation information may include information regarding the location of the RU to which a plurality of users (i.e., a plurality of receiving STAs) are allocated.

[0127] An RU may include multiple subcarriers (or tones). An RU may be used when transmitting signals to multiple STAs based on the OFDMA technique. Additionally, an RU may be defined when transmitting signals to a single STA. Resources may be allocated on an RU basis for non-legacy STF, non-legacy LTF, and Data fields.

[0128] Applicable RU sizes can be defined according to the PPDU bandwidth. RUs 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 80 MHz PPDU, the RU placement for HE PPDU and EHT PPDU may differ. The applicable RU sizes, number of RUs, RU locations, DC (direct current) subcarrier locations and numbers, null subcarrier locations and numbers, and guard subcarrier locations and numbers for each PPDU bandwidth can be referred to as a tone-plan. For example, a tone-plan for a wide bandwidth may be defined as a multiple repetition of a tone-plan for a low bandwidth.

[0129] RUs of various sizes can be defined as 26-ton RUs, 52-ton RUs, 106-ton RUs, 242-ton RUs, 484-ton RUs, 996-ton RUs, 2x996-ton RUs, 3x996-ton RUs, etc. An MRU (multiple RU) is distinguished from multiple individual RUs and corresponds to a group of subcarriers composed 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. In addition, multiple RUs constituting a single MRU may be continuous or non-continuous in the frequency domain.

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

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

[0132] FIG. 8 is a drawing showing an exemplary format of a trigger frame to which the present disclosure can be applied.

[0133] A trigger frame may allocate resources for one or more TB PPDU transmissions and request TB PPDU transmissions. The trigger frame may also include other information required by an STA that transmits a TB PPDU in response. The trigger frame may include common info and user info list fields in the frame body.

[0134] The common information field may include information commonly applicable to one or more TB PPDU transmissions requested by a trigger frame, such as trigger type, UL length, whether a subsequent trigger frame exists (e.g., More TF), whether a CS (channel sensing) is required, UL BW (bandwidth), etc. FIG. 8 illustrates an exemplary format for the common information field of an EHT variant.

[0135] The 4-bit trigger type subfield can have values ​​from 0 to 15. Among these, the values ​​0, 1, 2, 3, 4, 5, 6, and 7 of the trigger type subfield are defined to correspond to basic, BFRP (Beamforming Report Poll), MU-BAR (multi-user-block acknowledgement request), MU-RTS (multi-user-request to send), BSRP (Buffer Status Report Poll), GCR (groupcast with retries) MU-BAR, BQRP (Bandwidth Query Report Poll), and NFRP (NDP Feedback Report Poll), respectively, and the values ​​8 to 15 are defined as reserved.

[0136] Among the common information, the trigger-dependent common info subfield may include information that is optionally included based on the trigger type.

[0137] A special user info field may be included within the trigger frame. The special user info field does not contain user-specific information, but rather contains extended common information not provided in the common information field.

[0138] The user information list contains zero or more user info fields. Figure 8 illustrates an exemplary EHT variant user info field format.

[0139] The AID12 subfield basically indicates that it is a user information field for the STA with the corresponding AID. Additionally, if the AID12 field has a specific predetermined value, it may be utilized for other purposes, such as assigning a Random Access (RA)-RU or being configured as a special user info field. A special user info field is a user information field that does not contain user-specific information but includes extended common information not provided in the common information field. For example, a special user info field can be identified by an AID12 value of 2007, and a special user info field flag subfield within the common information field can indicate whether the special user info field is included.

[0140] The RU allocation subfield can indicate the size and location of the RU / MRU. To this end, the RU allocation subfield may be interpreted together with the PS160 (primary / secondary 160MHz) subfield of the user information field, the UL BW subfield of the common information field, etc.

[0141] FIG. 9 shows an exemplary format of an NDP notice frame to which the present disclosure may be applied.

[0142] An NDP notice frame may include one or more STA information (Info) fields. If an NDP notice frame includes only one STA Info field, the RA (receiver address) field may be set to the address of an STA capable of providing feedback. If an NDP notice frame includes multiple STA Info fields, the RA field may be set to a broadcast address.

[0143] The TA (transmitter address) field may be set to the address of the STA transmitting the NDP notice frame or to the bandwidth signaling TA of the STA transmitting the NDP notice frame. For example, in a non-HT or non-HT duplicate format, if the scrambling sequence (or scrambling sequence and service field) includes parameters for channel bandwidth, the TA field may be set to the bandwidth signaling TA.

[0144] The first two bits (B0 and B1) of the eight bits (B0-B7) of the sounding dialogue token field can be used to indicate the type / variant of the NDP notice frame. For example, for VHT or HE, B0 has a value of 0, and if the value of B1 is 0, it may indicate a VHT NDP notice frame, and if the value of B1 is 1, it may indicate an HE NDP notice frame. For example, an EHT NDP notice frame may correspond when both the values ​​of B0 and B1 are set to 1. If the value of B0 is 1 and the value of B1 is 0, it may correspond to a ranging NDP notice frame.

[0145] In the case of VHT STA, the first two bits (B0 and B1) of the sounding dialogue token field are defined as reserved, so VHT STA can recognize the sounding dialogue token number field of bits B2-B7 regardless of the values ​​of B0 and B1.

[0146] For VHT STA, the first two bits (B0 and B1) of the sounding dialogue token field are defined as reserved. Therefore, VHT STA can recognize the sounding dialogue token number field of bits B2-B7 regardless of the values ​​of B0 and B1.

[0147] For HE STA, the first bit (B0) of the sounding dialogue token field is defined as reserved, and if the value of the second bit (B1) is 0, it indicates a VHT NDP notice frame, and if the value of B1 is 1, it indicates an HE NDP notice frame. Therefore, HE STA can recognize the sounding dialogue token number field of bits B2-B7 when the value of B1 is 1, regardless of the value of B0.

[0148] The sounding dialogue token number subfield (bit positions B2-B7) may include a value for identifying an NDP notification frame selected by the beamformer.

[0149] An NDP notification frame may contain n (where n is an integer greater than or equal to 1) STA Info fields. Each STA Info field has a size of K octets, and K=2 in a VHT NDP notification frame, and K=4 in a HE NDP notification frame or an EHT NDP notification frame.

[0150] As shown in the example of FIG. 9(a), the STA Info field of the VHT NDP notification frame may include AID12, feedback type, and Nc index subfields.

[0151] The AID12 subfield contains 12 LSB (least significant bits) of the AID of the STA expected to process the subsequent NDP and prepare sounding feedback.

[0152] The feedback type subfield indicates the type of feedback required, and corresponds to SU if the value is 0 and MU if the value is 1.

[0153] The Nc index subfield indicates the value obtained by subtracting 1 from the number of columns (i.e., Nc) in the compressed beamforming feedback matrix (i.e., Nc-1) when the feedback type is MU. When it is SU, the Nc index field is reserved.

[0154] The example in Fig. 9(b) shows the format of the STA Info field of the HE NDP notification frame when the value of the AID11 field is not a specific value (e.g., 2047).

[0155] Values ​​of the AID11 subfield other than a specific value (e.g., 2047) include 11 LSB among the AIDs of the STA expected to process the subsequent NDP and prepare sounding feedback.

[0156] The partial BW Info subfield may include a 7-bit (B0-B6) RU start index and a 7-bit (B7-B13) RU end index. The RU index may be determined based on the bandwidth of the NDP notice frame, and the unit may be 26-tone RU. For example, to indicate a 26-tone RU index X, the value of the start / end RU index subfield may be set to X-1.

[0157] The feedback type and Ng subfield, in combination with the codebook size subfield, can indicate whether SU / MU / CQI feedback is requested for trigger-based (TB) sounding, Ng=4 or 16, and the quantization resolution. For non-TB sounding, the feedback type and Ng subfield and the codebook size subfield can indicate SU or CQI.

[0158] The disambiguation subfield is set to 1 to help prevent non-HE STAs (e.g., VHT STAs) from misinterpreting the field as an AID field.

[0159] The Nc subfield is set to a value of Nc-1. If the feedback type is SU or MU, Nc corresponds to the number of columns in the compressed beamforming feedback matrix, and if the feedback type is CQI, Nc may correspond to the number of space-time streams (STS). For NDP notice frames that have an AID11 subfield value other than 2047 and are individually addressed for a single STA, the Nc subfield may be reserved.

[0160] The example in Fig. 9(c) shows the format of the STA Info field of the HE NDP notification frame when the value of the AID11 field is a specific value (e.g., 2047).

[0161] The disallowed subchannel bitmap subfield indicates the 20 MHz subchannel(s) and 242-tone RU(s) present in the sounding NDPs announced by the NDP announcement frame, and the 242-tone RU(s) to be included in the requested sounding feedback. The lowest numbered bit of the disallowed subchannel bitmap corresponds to the 20 MHz subchannel located at the lowest frequency among all 20 MHz subchannels within the BSS bandwidth. Each subsequent bit in the bitmap corresponds to the next highest 20 MHz subchannel. A bit set to 1 in the bitmap may indicate that no energy is present in the sounding NDP associated with the NDP announcement frame. For each disallowed 20 MHz subchannel, the 242-tone RU that is closest in frequency to the corresponding 20 Hz subchannel may be disallowed for a PPDU using a specific tone plan. The STA(s) addressed by the NDP notice frame do not include tones from the 242-tone RU that are not allowed when determining the average SNR of STS 1 through Nc in generating the requested sounding feedback. If a 20 MHz subchannel and its corresponding 242-tone RU are allowed, the corresponding bit in the bitmap is set to 0.

[0162] The example in Fig. 9(d) shows the format of the STA Info field of the EHT NDP notification frame.

[0163] Basically, the AID11 subfield contains the identifier of the STA expected to process the subsequent NDP and prepare sounding feedback.

[0164] The partial BW subfield may include a 1-bit (B0) resolution subfield and an 8-bit (B1-B8) feedback bitmap. The resolution subfield indicates a resolution bandwidth (e.g., 20 MHz or 40 MHz) for each bit of the feedback bitmap subfield. The feedback bitmap subfield may indicate requests for each resolution bandwidth from low frequency to high frequency, and the first bit (B1) of the bitmap corresponds to the lowest resolution bandwidth. Each bit of the feedback bitmap is set to 1 when feedback for the corresponding resolution bandwidth is requested. If the bandwidth of the EHT NDP notification frame is less than 320 MHz, the value of the resolution bit (B0) may be set to 0 to indicate a resolution of 20 MHz.

[0165] If the bandwidth of the EHT NDP notification frame is 20 MHz, B1 is set to 1 to indicate that feedback for 242-tone RU is requested, and B2-B8 can be reserved and set to 0.

[0166] When the bandwidth of the EHT NDP notice frame is 40 MHz, B1 and B2 indicate that feedback is requested at each of the two 242-tone RUs from low frequency to high frequency, and B3-B8 may be reserved and set to 0.

[0167] If the bandwidth of the PPDU carrying the EHT NDP notice frame is 80 MHz, B0 can be set to 0 to indicate a resolution of 20 MHz. If B1-B4 are all set to 1, it can indicate that feedback is requested for the 996-tone RU. Otherwise, B1-B4 indicate that feedback is requested for each of the four 242-tone RUs from the low frequency to the high frequency, and B5-B8 can be reserved and set to 0.

[0168] If the bandwidth of the PPDU carrying the EHT NDP notice frame is 160 MHz, B0 can be set to 0 to indicate a resolution of 20 MHz. If B1-B4 are all set to 1, it can indicate that feedback is requested for the lower 996-tone RU; otherwise, B1-B4 can indicate that feedback is requested for each of the four 242-tone RUs from the low frequency to the high frequency in the lower 80 MHz. If B5-B8 are all set to 1, it can indicate that feedback is requested for the upper 996-tone RU; otherwise, B5-B8 can indicate that feedback is requested for each of the four 242-tone RUs from the low frequency to the high frequency in the upper 80 MHz.

[0169] If the bandwidth of the PPDU carrying the EHT NDP notice frame is 320 MHz, B0 can be set to 1 to indicate a resolution of 40 MHz. If both B1 and B2 are set to 1, it can indicate that feedback is requested for the first 996-tone RU; otherwise, B1 and B2 can indicate that feedback is requested for each of the two 484-tone RUs from low frequency to high frequency in the first 80 MHz. If both B3 and B4 are set to 1, it can indicate that feedback is requested for the second 996-tone RU; otherwise, B3 and B4 can indicate that feedback is requested for each of the two 484-tone RUs from low frequency to high frequency in the second 80 MHz. If both B5 and B6 are set to 1, it may indicate that feedback is requested for the third 996-tone RU; otherwise, B5 and B6 may indicate that feedback is requested for each of the two 484-tone RUs from low to high frequency at the third 80 MHz. If both B7 and B8 are set to 1, it may indicate that feedback is requested for the fourth 996-tone RU; otherwise, B7 and B8 may indicate that feedback is requested for each of the two 484-tone RUs from low to high frequency at the fourth 80 MHz. The feedback tone set for each 484-tone RU may consist of the feedback tone sets of two 242-tone RUs that overlap with the 484-tone RU.

[0170] The partial bandwidth subfield can have values ​​such as the example in Table 1 depending on the relevant settings.

[0171]

[0172] For TB sounding, the feedback type, Ng subfield, and codebook size subfield can be set according to the example in Table 2.

[0173]

[0174] For non-TB sounding, the feedback type and Ng subfield and codebook size subfield can be set according to the example in Table 3.

[0175]

[0176] The disambiguation subfield is set to 1 to help prevent non-EHT STAs (e.g., VHT STAs) from misinterpreting the field as an AID field.

[0177] In an EHT NDP announcement frame, RA is set to the broadcast address, and the following may apply. If the feedback type and Ng subfields and the codebook size subfield indicate SU or MU, the Nc index subfield is set to a value of Nc-1, where Nc corresponds to the number of columns in the compressed beamforming feedback matrix, and values ​​greater than 7 in the Nc index subfield are reserved. If the feedback type and Ng subfields and the codebook size subfield indicate CQI, the Nc index subfield is set to a value of Nc-1, where Nc corresponds to the number of STS (space-time streams), and values ​​greater than 7 in the Nc index subfield are reserved. One or more STA Info fields may exist.

[0178] In an EHT NDP notice frame having a single STA Info field, the RA field is set to an individual address, and the Nc index subfield may be reserved.

[0179] Multi-AP operation

[0180] The MAPC (multi-AP coordination) framework may include a series of procedures such as Co-BF (coordinated beamforming), Co-SR (coordinated spatial reuse), Co-TDMA (coordinated-time division multiple access), Co-RTWT (coordinated restricted target wake time), and Co-CR (coordinated channel recommendation). Through the procedures described above, APs operating BSS on the same primary channel (e.g., 20 MHz) can reduce interference levels, thereby improving network performance such as media utilization efficiency, communication stability, and latency.

[0181] Among the methods included in the aforementioned MAPC framework, CO-BF refers to a technology that improves system performance (e.g., output volume, latency, etc.) by enabling simultaneous transmission of multiple APs through the elimination or reduction of interference directed toward the STA of an adjacent BSS. Each AP can control interference by designing and applying a precoder capable of reducing interference directed toward the OBSS STA. Additionally, CO-SR refers to a technology that enables simultaneous transmission by allowing an AP to select STAs that can cause minimal mutual interference.

[0182] CoBF transmission is a multi-AP cooperation technology that increases the transmission rate by enabling multiple APs (e.g., two APs) to transmit frames simultaneously. For example, the CoBF transmission procedure may apply full nulling, which eliminates all interference directed toward the OBSS STA, and / or partial nulling, which eliminates only some interference. When nulling operations are performed, transmission dimensions may be consumed by the dimension required for the nulling operation. If a large number of dimensions are consumed by nulling, the transmission dimensions available to obtain beamforming gain for the STA within the BSS may be reduced, which may lead to performance degradation. Therefore, system performance can be improved by reducing dimension consumption through partial nulling rather than eliminating all interference, and by using the remaining dimensions to obtain beamforming gain within the BSS.

[0183] Meanwhile, for CoBF transmission, the BSS AP must receive downlink channel information directed to the OBSS STA from the OBSS STA. Therefore, a new sounding feedback procedure for the CoBF procedure must be defined, and this sounding feedback procedure can be expressed as an OBSS sounding procedure.

[0184] At this time, to avoid the complexity of the STA having to decode all OBSS packets, a method may be applied in which the NDP notice frame and BFRP trigger frame are transmitted only to the STA within the BSS. For the above method to be performed, even if the BSS AP transmits the NDP notice frame, a situation may arise where the OBSS AP must transmit the subsequent NDP.

[0185] Sounding methods for the CoBF procedure may include sequential sounding methods and joint sounding methods. Sequential sounding is a method of performing in-BSS sounding and OBSS sounding in succession, and joint sounding is a method of performing in-BSS sounding and OBSS sounding simultaneously. Sequential sounding may be more efficient when full knurling is applied, and joint sounding may be more efficient when partial knurling is applied.

[0186] OBSS sounding may include the action of an initiating AP transmitting an NDP notice frame and a responding AP transmitting an NDP after decoding the NDP notice frame. In this case, if the responding AP fails to decode the NDP notice frame or detects the transmission of another packet via CCA, it may not be able to transmit the NDP. Consequently, the normal OBSS sounding procedure may not be performed, and a procedure to resolve this may be required.

[0187] Basically, in the case of sequential sounding, it is possible for the NDP to enter / transmit Rx mode at a scheduled time, and accordingly, the initiating AP can determine whether the responding AP's NDP has been transmitted. If the responding AP's NDP has not been transmitted, the initiating AP can re-trigger the transmission of the responding AP's NDP by retransmitting an NDP notification frame.

[0188] Meanwhile, in the case of the joint sounding method, since the initiating AP must also transmit an NDP at the time the responding AP transmits its NDP, the initiating AP may not be able to verify whether the responding AP has transmitted an NDP. If the responding AP has not transmitted an NDP normally, the STA may perform an estimation operation based on a steering matrix for invalid channels (e.g., empty channels). The STA may feed back a dummy CSI based on invalid channels, which may degrade CoBF performance.

[0189] Below, we will explain how to notify the initiating AP of the failure to transmit the NDP of the responding AP when the NDP of the responding AP is not transmitted successfully, in cases where the joint sounding method is applied.

[0190] In one example of the present disclosure, the STA can determine whether the NDP of the responding AP (e.g., UHR NDP) has been successfully transmitted. The STA can detect the presence or absence of the NDP by measuring the signal strength using the P matrix index of the responding AP. If the NDP is not present, the STA can transmit information indicating that the NDP is not present to the initiating AP via a CSI report frame. For reference, the P matrix may refer to an LTF mapping matrix to be applied to UHR-LTF symbols.

[0191] FIG. 10 is a flowchart illustrating a method performed by a first STA according to one embodiment of the present disclosure. In FIG. 10 and FIG. 11, the first STA may be a STA (e.g., a non-AP STA) associated with a first AP (or a BSS of the first AP). Also, the first AP may be an initiating AP and the second AP may be a responding AP, but is not limited thereto.

[0192] The first STA can receive the first NDP from the first AP (S1010).

[0193] Specifically, the first NDP (e.g., UHR NDP) may be configured based on an NDP notice frame (e.g., the first NDP notice frame) that the first AP transmits to the second AP. That is, after the first AP transmits the first NDP notice frame to the second AP and SIFS, the first STA may receive the first NDP based on the first NDP notice frame from the first AP. Here, the first NDP notice frame may be an NDP notice frame for CoBF. That is, the first NDP notice frame may include transmission parameter(s) for the first NDP transmission of the first STA from the first AP as well as the second NDP transmission of the first STA from the second AP.

[0194] For example, the first NDP may include at least one of i) second information related to whether the first NDP is used for joint sounding (e.g., a sounding procedure including simultaneous transmission of the first NDP and the second NDP, etc.) (e.g., second information set in a joint sounding instruction (sub)field) and ii) third information indicating the index of the first spatial stream (or, start spatial stream) among the indices of each of at least one spatial stream related to the second NDP of an LTF mapping matrix (e.g., P matrix) (e.g., third information set in a start spatial stream subfield).

[0195] That is, the first STA can identify, through the second information, the situation in which the second NDP is currently being transmitted from the second AP as well as the first NDP. Additionally, the first STA can identify, through the third information, the index of the first spatial stream associated with the second NDP among the spatial stream(s) of the LTF mapping matrix. The LTF mapping matrix may include a matrix for the configuration / mapping of LTF symbols (e.g., UHR LTF symbols) of the first NDP and / or the second NDP.

[0196] Here, each of the first information and the second information may be included in either the UHR-SIG(signal) field or the U(universal)-SIG field of the first NDP.

[0197] As an example of the present disclosure, based on the detection of a failure of the second NDP transmission of the second AP based on the first NDP, the first STA may transmit a first frame containing first information related to the failure of the second NDP transmission to the first AP (S1020).

[0198] As described above, the first STA can identify the index of the first spatial stream associated with the second NDP among the spatial stream(s) of the joint sounding procedure and LTF mapping matrix through the second information and / or third information included in the first NDP. Accordingly, the first STA can measure the signal strength associated with the second NDP (e.g., RSSI (received signal strength indicator), etc.) based on the spatial stream(s) associated with the second NDP.

[0199] Specifically, the signal strength associated with the second NDP may include the signal strength measured using the spatial stream(s) associated with the second NDP. The first STA may identify at least one spatial stream associated with the second NDP through the index of the first spatial stream associated with the second NDP in the LTF mapping matrix, and obtain a signal strength value associated with the second NDP using the identified at least one spatial stream.

[0200] In one example of the present disclosure, based on the signal strength of the second NDP being below a threshold value, the first STA may detect that the transmission of the second NDP by the second AP has failed (e.g., detect that the second NDP does not exist). Accordingly, the first STA may transmit a first frame containing first information related to the failure of the transmission of the second NDP to the first AP. In this case, the first information may be included in the MIMO (Multiple-Input Multiple-Output) control field of the first frame, but is not limited thereto.

[0201] Additionally or alternatively, the first frame (e.g., the first UHR compressed beamforming / CQI frame) may include a beamforming feedback matrix based on the first NDP. That is, the first STA may perform a (sounding) measurement operation based on the first NDP received from the first AP to obtain a beamforming feedback matrix (e.g., the first beamforming feedback matrix) and transmit the beamforming feedback matrix to the first AP through the first frame.

[0202] Subsequently, the first STA can receive a third NDP from the second AP. That is, as the first STA transmits the first information to the first AP, the first AP can transmit a separate NDP notification frame (e.g., a second NDP notification frame) to the second AP. The first STA can receive a third NDP based on the second NDP notification frame from the second AP. At this time, the second NDP notification frame may include parameter(s) for transmitting the third NDP.

[0203] The first STA may transmit a second frame (e.g., a feedback frame) related to the third NDP to the first AP. At this time, the second frame (e.g., a second UHR compressed beamforming / CQI frame) may include a beamforming feedback matrix for the third NDP (e.g., a second beamforming feedback matrix). That is, the beamforming feedback matrix for the third NDP may be a feedback matrix obtained through a measurement operation for the third NDP.

[0204] In one example of the present disclosure, at least one of the first frame or the second frame may be transmitted based on a BFRP trigger frame transmitted from the first AP. That is, when the first AP transmits BFRP trigger frame(s), the first STA may transmit the first frame or / and the second frame to the second AP based on the BFRP trigger frame. The first frame may be transmitted and received based on the first BFRP trigger frame, and the second frame may be transmitted and received based on the second BFRP trigger frame.

[0205] The method described in the example of FIG. 10 can be performed by the first device (100) of FIG. 1. For example, at least one processor (102) can receive a first NDP from a first AP through one or more transceivers (106). Based on the detection of a failure of the second NDP transmission of the second AP based on the first NDP, one or more processors (102) can transmit a first frame containing first information related to the failure of the second NDP transmission to the first AP through one or more transceivers (106).

[0206] Furthermore, one or more memories (104) of the first device (100) may store instructions for performing the method described in the example of FIG. 10 or the examples described below when executed by one or more processors (102).

[0207] FIG. 11 is a flowchart for explaining a method performed by a first AP according to one embodiment of the present disclosure.

[0208] The first AP can transmit the first NDP to the first STA (S1110).

[0209] Specifically, prior to step S1110, the first AP may transmit a first NDP notification frame to the second AP. For example, the first NDP notification frame may include the ID of the second AP participating in the CoBF, information for setting the U-SIG field of the first NDP and / or the second NDP, or parameter(s) for channel estimation. The first AP may transmit the first NDP to the first STA based on the first NDP notification frame. For example, the first AP may generate and transmit the first NDP based on P matrix row sequence(s) (e.g., spatial stream(s) associated with the first NDP) assigned to it (by the first NDP notification frame). Since the configuration of the first NDP has been described with reference to FIG. 10, a redundant description will be omitted.

[0210] The first AP can transmit a BFRP trigger frame to the first STA (S1120).

[0211] That is, the first AP can transmit a BFRP trigger frame to the first STA to receive feedback on channel information estimated by the first STA (e.g., channel information based on the first NDP and / or channel information based on the second NDP, etc.).

[0212] Based on the detection of a failure in the second NDP transmission of the second AP, the first AP can receive a first frame containing first information related to the failure of the second NDP transmission from the first STA (S1130).

[0213] Additionally or alternatively, the first frame may include a beamforming feedback matrix based on the first NDP. Also, the first NDP and the second NDP may include (identical) channel matrices associated with the first AP and / or the second AP, and the first STA may obtain channel estimation / measurement information through the channel matrix included in the first NDP.

[0214] Accordingly, the first AP may initiate cross-BSS sounding, sequential sounding, or joint sounding procedures for the recovery procedure. For example, the first AP may transmit an additional NDP notification frame to the second AP, and the second AP may transmit a third NDP to the first STA based on the said NDP notification frame. The first AP may receive a second frame from the first STA containing channel estimation information (e.g., beamforming feedback matrix) through the third NDP.

[0215] This is merely one embodiment, and the first AP may receive information from the second AP to notify of the failure of the second NDP transmission. Accordingly, the first AP may perform the recovery procedure described above.

[0216] The method described in the example of FIG. 11 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 transmit the first NDP to the first STA through one or more transceivers (206). One or more processors (102) may transmit a BFRP trigger frame to the first STA through one or more transceivers (206). Based on the detection of a failure in the transmission of the second NDP of the second AP, one or more processors (202) may receive a first frame containing first information related to the failure of the transmission of the second NDP from the first STA through one or more transceivers (206).

[0217] Furthermore, one or more memories (204) of the second device (200) may store instructions for performing the method described in the example of FIG. 11 or the examples described below when executed by one or more processors (202).

[0218] Below, we will specifically explain the method for notifying the initiating AP of the failure to transmit the NDP of the responding AP when the NDP of the responding AP is not successfully transmitted, in cases where the joint sounding method is applied.

[0219] Example 1

[0220] Example 1 relates to a whole joint sounding procedure when the NDP of the responding AP (e.g., UHR NDP) is not successfully transmitted.

[0221] FIG. 12 is a diagram illustrating a joint sounding procedure according to one embodiment of the present disclosure. As illustrated in FIG. 12, the initiating AP may transmit an NDP notice frame (e.g., CoBF NDP notice frame) (to the responding AP). After the NDP notice frame is transmitted and SIFS, both the initiating AP and the responding AP may transmit an NDP (e.g., UHR NDP).

[0222] In this case, if the NDP notification frame is not heard, or if the NDP notification frame is heard but cannot be transmitted according to the CCA, the responding AP may not be able to transmit the NDP. In this case, STA 1 (e.g., a STA belonging to the BSS of the initiating AP) may perform a channel estimation operation in a situation where the NDP has not been successfully transmitted, and the CSI feedback matrix generated according to the channel estimation operation may contain dummy data.

[0223] In the standard PPDU transmission procedure, if the NDP is not successfully transmitted or received, the only issue is that the beamforming effect is not generated; however, in the CoBF PPDU transmission procedure, if the NDP is not successfully transmitted or received, the nulling effect may not occur. Consequently, the transmission signals of the two APs may collide, and PPDU transmission and reception itself may become impossible.

[0224] Therefore, the STA (e.g., STA 1) can detect whether the NDP of the responding AP was successfully transmitted by combining the codes for the P matrix index signal(s) transmitted from the responding AP and measuring the energy of the said signal(s). Based on the information regarding whether the NDP of the responding AP was transmitted, the STA can decide whether to perform a channel estimation operation with the responding AP. If it is determined that the NDP was lost, the STA does not perform estimation for the channel(s) corresponding to the P matrix index, but can only perform estimation for the BSS channel. Subsequently, the initiating AP can transmit a BFRP (trigger) frame (to the STA), and the STA can feed back information about the channel within the BSS to the initiating AP.

[0225] Example 2

[0226] Example 2 relates to the configuration of the signaling described in Example 1.

[0227] As an example of the present disclosure, an NDP (e.g., UHR NDP) transmitted by an initiating AP and / or a responding AP may include at least one of a joint sounding indication field or a starting spatial stream field. However, this is merely one example, and the names of each field may be expressed differently.

[0228] As an example of the present disclosure, the joint sounding indication field may indicate whether the NDP is an NDP for a joint sounding method. The STA needs to detect whether the NDP was successfully transmitted (e.g., whether the NDP transmission failed) only in a joint sounding situation. Accordingly, the joint sounding indication field may be interpreted as a field indicating whether to perform an operation to detect whether the NDP was successfully transmitted.

[0229] The start space stream field may indicate the first index among the P matrix index(s) corresponding to the NDP of the response AP (e.g., the stream corresponding to the first index among the P matrix index(s) of the NDP of the response AP). That is, the start space stream field may indicate from which P matrix index it corresponds to the NDP of the response AP. The STA may identify the index(s) of the P matrix corresponding to the NDP of the response AP through the start space stream field, perform code binding on the identified index(s) of the P matrix, and then perform an energy measurement operation. The STA may detect the presence of the NDP through the energy measurement operation described above.

[0230] For example, the first or fifth stream can be indicated using a 1-bit start space stream field. As another example, the first or eighth stream can be indicated using a 3-bit start space stream field.

[0231] As an example of the present disclosure, a BF feedback frame transmitted by STA 1 (e.g., a UHR compressed beamforming / CQI frame) may include a responding NDP failure field. The responding NDP failure field may detect a portion of the LTF of the UHR NDP to indicate whether the NDP transmission of the responding AP has failed. The size of the responding NDP failure field may be 1 bit, but is not limited thereto.

[0232] However, this is merely one embodiment, and if feedback of a smaller dimension than the feedback requested by the initiating AP is transmitted or received, the failure of the NDP transmission by the responding AP may be implicitly interpreted. In this case, the response NDP failure field may not be defined.

[0233] Example 2-1

[0234] Example 2-1 relates to the configuration of the U-SIG field of a UHR NDP. FIG. 13(a) illustrates the configuration of the U-SIG field of a UHR NDP according to one embodiment of the present disclosure. In this case, the UHR NDP may be represented as a URH sounding NDP for the STA to attempt to detect the presence of the NDP of the responding AP, but is not limited thereto. Also, the UHR NDP may be an NDP received by the STA from the initiating AP, but is not limited thereto.

[0235] As an example of the present disclosure, the U-SIG field of a UHR NDP may include a field indicating that the NDP is designed / configured for a joint sounding method (e.g., a joint sounding indication field, etc.). As illustrated in FIG. 13(a), the field may be mapped / set to the 21st bit (B20) of the U-SIG field of the UHR NDP, but is not limited thereto. An STA that decodes the field may perform a detection operation to determine whether the NDP of the responding AP is successfully transmitted.

[0236] Additionally or alternatively, the U-SIG field of the UHR NDP may include a field (e.g., a start space stream field) indicating the space stream index where the NDP transmission of the responding AP begins. As illustrated in FIG. 13(a), the start space stream field may be mapped / set to the 22nd bit (B20), but is not limited thereto. The STA can determine the presence of the NDP by detecting the energy associated with the NDP transmission (e.g., the NDP transmission of the responding AP) from the first stream (or index) indicated by the start space stream field to the last stream.

[0237] Example 2-2

[0238] Example 2-2 relates to the configuration of the UHR-SIG field of a UHR NDP. FIG. 13(b) illustrates the configuration of the UHR-SIG field according to one embodiment of the present disclosure. As an example, the UHR-SIG field of the UHR NDP may include the joint sounding indication field or / and the start space stream field described in Example 2-1.

[0239] As shown in Fig. 13(b), the joint sounding instruction field can be set / mapped to the 15th bit (B14) of the UHR-SIG field, and the start space stream field can be set / mapped to the 16th bit (B15) of the UHR-SIG field.

[0240] However, this is merely one embodiment, and at least one of the joint sounding instruction field and the start space stream field may be mapped to another bit of the UHR-SIG field. Additionally, at least one of the joint sounding instruction field and the start space stream field may be set / included in one of the U-SIG field and the UHR-SIG field.

[0241] Examples 2-3

[0242] Examples 2-3 relate to the UHR MIMO control field of a BF feedback frame (e.g., UHR compressed beamforming / CQI frame).

[0243] FIG. 14 illustrates a UHR MIMO control field of a UHR compressed beamforming / CQI frame according to one embodiment of the present disclosure. To solve the joint sounding method failure problem, a UHR MIMO control field may be included on the UHR compressed beamforming / CQI frame. The UHR MIMO control field may include information indicating whether the response NDP failed (e.g., whether the NDP transmission sent by the responding AP failed).

[0244] For example, as illustrated in FIG. 14, information indicating whether the response NDP failed (e.g., the response NDP failure field) can be set / mapped to the 15th bit (B14) of the UHR MIMO control field, but is not limited thereto.

[0245] An STA that detects a response NDP failure (e.g., failure of the responding AP's NDP transmission) can perform channel estimation as if it had received only the in-BSS sounding NDP, without performing cross-BSS sounding. Additionally, the STA can receive a BFRP (trigger) frame addressed to it from the initiating AP. At this time, instead of transmitting UHR compressed beamforming / CQI based on the joint sounding parameters requested in the NDP announcement frame, the STA can perform a feedback procedure by reducing the sounding dimension as if it had received a request for in-BSS sounding. Accordingly, the dimension of the parameter(s) of the UHR MIMO control field can be reduced.

[0246] Example 3

[0247] Example 3 relates to a recovery procedure when a lost NDP (e.g., a missing NDP) is detected. The recovery procedure may involve at least one of a method of performing an additional cross-BSS sounding procedure (Example 3-1) and a method of notifying the initiating AP that its NDP transmission has failed (Example 3-2). The methods according to Example 3-1 and Example 3-2, respectively, may be performed individually or in combination.

[0248] Example 3-1

[0249] Example 3-1 relates to a method of performing an additional cross-BSS sounding procedure.

[0250] FIG. 15(a) illustrates a cross-BSS sounding-based recovery procedure according to one embodiment of the present disclosure. During the process of performing the joint sounding method, a situation may occur where the NDP notification frame is not received and / or where the responding AP is unable to transmit the NDP due to a hidden node issue. In this case, the STA can detect that the NDP was not transmitted by the responding AP through Example 1 and / or Example 2, and can transmit information indicating that the NDP was not transmitted by the responding AP to the initiating AP. Accordingly, the initiating AP can perform a recovery procedure to estimate the cross-BSS channel that was not performed normally.

[0251] In one example of the present disclosure, the multi-AP procedure sounding procedure is set as a joint sounding procedure, but the information regarding the sounding procedure required in the recovery step may be cross-BSS sounding information (e.g., feedback / reporting information according to the sounding procedure between the responding AP and STA). Accordingly, the subsequent sounding procedure may be a cross-BSS sounding procedure which is a subsequent step of the CoBF sequential sounding procedure.

[0252] Specifically, the initiating AP can trigger the transmission of the responding AP's NDP by transmitting an NDP notice frame to the responding AP. After the NDP notice frame is transmitted and SIFS is completed, the responding AP can transmit an NDP (e.g., UHR NDP) to STA 1 (e.g., a target STA associated with the initiating AP (e.g., the initiating AP's BSS)). STA 1 can perform the estimation operation of the cross-BSS channel through the NDP. Additionally, STA 1 can transmit a beamforming feedback matrix to the initiating AP (via a feedback frame) based on the BFRP frame transmitted by the initiating AP. In this case, the feedback frame may be a UHR compressed beamforming / CQI frame, but is not limited thereto. Furthermore, the feedback frame may be overheard by the responding AP and utilized for the next Co-BF transmission.

[0253] Additionally or alternatively, a recovery procedure based on sequential or joint sounding methods may be used. If the NDP of the responding AP is lost while the joint sounding method is being performed, the STA may detect the loss of the NDP of the responding AP and notify the initiating AP of the loss of the NDP. The initiating AP may restart the sequential or joint sounding method for recovery purposes based on information regarding the loss of the NDP of the responding AP.

[0254] Example 3-2

[0255] Example 3-2 relates to a method in which a STA informs an initiating AP that its NDP transmission has failed.

[0256] FIG. 15(b) illustrates a recovery procedure through an operation indicating that the NDP transmission of the responding AP has failed, according to one embodiment of the present disclosure. During the process of performing the joint sounding method, a situation may occur in which the responding AP fails to transmit the NDP due to a failure to receive an NDP notification frame and / or a hidden node issue.

[0257] As the responding AP is the subject of the NDP transmission, it can recognize that the transmission of the NDP has failed. Therefore, the response AP can perform a recovery procedure by transmitting information regarding the failure of the NDP transmission to the initiating AP. In this case, since the STA does not need to detect whether the response AP's NDP has been lost, the implementation complexity of the STA can be reduced.

[0258] In addition, new versions of frames, such as UHR sounding NDP or UHR MIMO control, may not be defined, so the NDP loss problem can be resolved without increasing complexity. However, if the above method is applied, it does not resolve the issue when the responding AP decodes the NDP announcement frame, so a procedure for the STA to detect whether the NDP transmission has failed may be performed.

[0259] For the recovery procedure, the responding AP may send a specific frame containing a Failure Notification field to the initiating AP. The Failure Notification field may be a field indicating that the responding AP was unable to transmit an NDP for the joint sounding method, and the field name may be changed.

[0260] An initiating AP that detects that the NDP was not successfully transmitted through demodulation of the failure notification field may perform a separate CoBF sounding procedure for recovery. The separate CoBF sounding procedure may include a cross-BSS sounding procedure (e.g., a sounding procedure between the responding AP and STA 1), a CoBF sequential sounding procedure, or a CoBF joint sounding procedure.

[0261] FIG. 16 is a diagram illustrating a PPDU transmission and reception procedure between a transmitting STA and a receiving STA according to one embodiment of the present disclosure. Some of the step(s) shown in FIG. 16 may be omitted depending on the situation and / or settings, etc. The transmitting device and the receiving STA may be an AP and / or a non-AP STA.

[0262] The transmitting STA can obtain control information related to the tone-plan (or RU / DRU) described above (S105). The control information related to the tone-plan may include the size and location of the RU, control information related to the RU, information regarding the frequency band in which the RU is included, information regarding the STA receiving the RU, etc.

[0263] The transmitting STA can configure / generate a PPDU based on acquired control information (S110). Configuring / generating a PPDU may mean configuring / generating each field of the PPDU. That is, the step of configuring / generating a PPDU may include the step of configuring the U-SIG and UHR-SIG-A / B / C fields containing control information regarding the tone-plan.

[0264] That is, the step of configuring / generating the PPDU may include the step of configuring a field containing control information (e.g., N bitmap) indicating the size / location of the RU and / or the step of configuring a field containing an identifier (e.g., AID) of the STA receiving the RU.

[0265] Additionally, the step of configuring / generating the PPDU may include the step of generating an STF / LTF sequence transmitted through a specific RU. The STF / LTF sequence may be generated based on a preset STF generation sequence / LTF generation sequence.

[0266] Additionally, the step of configuring / generating the PPDU may include the step of generating a data field (i.e., MPDU) that is transmitted through a specific RU.

[0267] The transmitting STA can transmit the configured / generated PPDU to the receiving STA (S115).

[0268] Specifically, the transmitting STA can perform at least one of cyclic shift diversity (CSD), spatial mapping, inverse discrete Fourier transform (IDFT) / inverse fast Fourier transform (IFFT) operations, and guard interval (GI) insertion operations.

[0269] The receiving STA can decode the PPDU and obtain control information related to the tone-plan (or RU) (S120).

[0270] Specifically, the receiving STA can decode the L-SIG and U-SIG / UHR-SIG of the PPDU based on L-STF / LTF and obtain information contained in the L-SIG, U-SIG, and UHR-SIG fields. Information regarding various tone-plans (i.e., RU) of the present disclosure may be contained in U-SIG / UHR-SIG (UHR-SIG-A / B / C, etc.), and the receiving STA can obtain information regarding tone-plans (i.e., RU) through EHT-SIG.

[0271] The receiving STA can decode the remainder of the PPDU based on information regarding the acquired tone-plan (i.e., RU) (S125). For example, the receiving STA can decode the STF / LTF field of the PPDU based on information regarding the tone-plan (i.e., RU). Additionally, the receiving STA can decode the data field of the PPDU based on information regarding the tone-plan (i.e., RU) and acquire the MPDU contained in the data field.

[0272] In addition, the receiving STA can perform a processing operation to transmit the decoded data to an upper layer (e.g., MAC layer). In addition, if the generation of a signal is instructed from the upper layer to the PHY layer in response to the data transmitted to the upper layer, the receiving STA can perform a subsequent operation.

[0273] The embodiments described above are combinations of the components and features of the present disclosure in a specific form. Each component or feature should be considered optional unless otherwise explicitly stated. Each component or feature may be implemented in a form not combined with other components or features. Additionally, it is possible to construct 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 obvious that embodiments may be constructed by combining claims that are not explicitly related in the claims, or that they may be included as new claims by amendment after filing.

[0274] It is obvious to those skilled in the art that the present disclosure may be embodied in other specific forms without departing from the essential features of the present disclosure. Accordingly, the detailed description set forth above should not be interpreted restrictively in all respects and should be considered exemplary. The scope of the present disclosure shall be determined by a reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the present disclosure are included within the scope of the present disclosure.

[0275] The scope of the present disclosure includes software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that enable operations according to the methods of various embodiments to be executed on a device or computer, and a non-transitory computer-readable medium on which such software or instructions, etc. are stored and executable on a device or computer. Instructions that may be used to program a processing system to perform the features described in the present disclosure may be stored on or within a storage medium or a computer-readable storage medium, and the features described in the present disclosure may be implemented using a computer program product comprising such a storage medium. The storage medium may 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 may 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 may optionally include one or more storage devices located remotely from the processor(s). Memory or alternatively, non-volatile memory device(s) within memory comprises a non-transient computer-readable storage medium. The features described in this disclosure may be stored in any one of the machine-readable media and integrated into software and / or firmware that can control the hardware of a processing system and allow the processing system to interact with other mechanisms utilizing results according to the embodiments of this disclosure. Such software or firmware may include, but is not limited to, application code, device drivers, operating systems, and execution environments / containers.

[0276] Although the method proposed in this disclosure has been described with an example applied to an IEEE 802.11-based system, it can be applied to various wireless LANs or wireless communication systems in addition to IEEE 802.11-based systems.

Claims

1. A step of receiving a first null data physical layer protocol data unit (NDP) from a first access point (AP) by a first station (STA); and Based on the detection of a failure of the second NDP transmission of the second AP based on the first NDP, the method includes the step of transmitting a first frame containing first information related to the failure of the second NDP transmission to the first AP by the first STA. A method in which the first NDP includes second information regarding whether the first NDP is used for joint sounding.

2. In Paragraph 1, The above joint sounding is a method comprising the simultaneous transmission of the first NDP and the second NDP.

3. In Paragraph 1, A method in which the first NDP comprises third information indicating the index of the first spatial stream among the indices of each of at least one spatial stream associated with the second NDP of the LTF (long training field) mapping matrix.

4. In Paragraph 3, Through the index of the first spatial stream, the at least one spatial stream is identified by the first STA, and A method in which the signal strength value of the second NDP is obtained by the first STA using the above at least one spatial stream.

5. In Paragraph 4, A method in which the failure of the transmission of the second NDP of the second AP is detected by the first STA based on the signal strength associated with the second NDP being below a threshold value.

6. In Paragraph 1, The first frame above includes a beamforming feedback matrix based on the first NDP, and The above first information is a method included in the MIMO (Multiple-Input Multiple-Output) control field of the above first frame.

7. In Paragraph 1, A third NDP is transmitted from the second AP to the first STA, and The above third NDP is a method based on an NDP announcement frame transmitted from the first AP to the second AP.

8. In Paragraph 7, A second frame associated with the third NDP is transmitted from the first STA to the first AP, and The above second frame includes a beamforming feedback matrix for the above third NDP, a method.

9. In Paragraph 8, A method in which at least one of the first frame or the second frame is transmitted based on a Beamforming Report Poll (BFRP) trigger frame transmitted from the first AP.

10. In Paragraph 3, A method in which each of the above first information and the above second information is included in either the UHR (ultra-high reliability)-SIG (signal) field or the U (universal)-SIG field of the above first NDP.

11. In the first station (STA), the first STA is: One or more transceivers; and It includes one or more processors connected to the above one or more transmitters and receivers, and The above one or more processors are: Receiving a first null data physical layer protocol data unit (NDP) from a first access point (AP) through one or more transceivers; and Based on the detection of a failure of the second NDP transmission of the second AP based on the first NDP, a first frame containing first information related to the failure of the second NDP transmission is configured to be transmitted to the first AP through the one or more transceivers, and The first NDP comprises a first STA including second information regarding whether the first NDP is used for joint sounding.

12. A step of transmitting a first null data physical layer protocol data unit (NDP) to a first station (STA) by a first access point (AP); and A step of transmitting a BFRP (Beamforming Report Poll) trigger frame to the first STA by the first AP; and Based on the detection of a failure of a second NDP transmission by the second AP, the method includes the step of receiving a first frame containing first information related to the failure of the second NDP transmission from the first STA by the first AP. A method in which the first NDP includes second information regarding whether the first NDP is used for joint sounding.

13. In the first access point (AP), the first AP is: One or more transceivers; and It includes one or more processors connected to the above one or more transmitters and receivers, and The above one or more processors are: Transmitting a first null data physical layer protocol data unit (NDP) to a first station (STA) through one or more transceivers; and Transmitting a BFRP (Beamforming Report Poll) trigger frame to the first STA through the one or more transceivers; and Based on the detection of a failure of the second NDP transmission of the second AP, a first frame containing first information related to the failure of the second NDP transmission is configured to be received from the first STA through the one or more transceivers, and The first NDP above includes a first AP comprising second information regarding whether the first NDP is used for joint sounding.

14. A processing device configured to control a station (STA) in a wireless local area network (WLAN) system, wherein the processing device: One or more processors; and A processing device comprising one or more computer memories that are operably connected to one or more processors and store instructions for performing a method according to any one of claims 1 to 10 based on execution by one or more processors.

15. One or more non-transitory computer-readable media storing one or more instructions, A computer-readable medium in which one or more of the above commands are executed by one or more processors to control a device in a wireless LAN system to perform a method according to any one of claims 1 to 10.

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