Roaming method and apparatus based on multi-link devices in a wireless LAN system

Abstract

A roaming method and apparatus based on a multi-link device (MLD) in a wireless LAN system are disclosed. According to an embodiment of the present disclosure, a method performed by a first STA in the wireless LAN system may include transmitting a first roaming request frame to a first access point (AP) included in a first group, the first roaming request frame including a link identifier of a second AP and a group ID associated with a second group to which the second AP belongs, receiving a first roaming response frame from the first AP, the first roaming response frame including a first traffic indication map (TIM) field associated with the second AP, and receiving first downlink (DL) data from the second AP based on the first TIM field.

Description

[Technical Field]

[0001] The present disclosure relates to a method and apparatus for roaming based on a multi-link device (MLD) in a wireless local area network (WLAN) system. [Background technology]

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

[0003] To provide a more improved wireless communication environment, improved technologies for Extremely High Throughput (EHT) are being discussed. For example, technologies for increased bandwidth, efficient use of multiple bands, Multiple Input Multiple Output (MIMO) that supports increased spatial streams, and multiple access point (AP) coordination are being researched. In particular, various technologies for supporting traffic with low latency or real-time characteristics are being researched. In addition, new technologies for supporting ultra-high reliability (UHR), including improvements or extensions to EHT technology, are being discussed. Summary of the Invention [Problem to be solved by the invention]

[0004] The technical problem of the present disclosure is to provide a roaming method and apparatus based on a multi-link device (MLD) in a wireless LAN system.

[0005] A further technical object of the present disclosure is to provide a method and apparatus for supporting or performing roaming of a station (STA) between different access points (APs) belonging to a common MLD in a wireless LAN system.

[0006] A further technical object of the present disclosure is to provide a method and apparatus for performing communication by adding / deleting temporary links during an MLD-based roaming procedure in a wireless LAN system.

[0007] The technical problems to be solved by the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by a person having ordinary skill in the art to which the present disclosure pertains from the following description. [Means for solving the problem]

[0008] A method performed by a first station (STA) in a wireless LAN system according to one embodiment of the present disclosure may include (may comprise; may configure; may establish; may configure; may include; may contain; may have) the steps of: sending a first roaming request frame to a first access point (AP) included in a first group, the first roaming request frame including a link identifier of a second AP and a group ID associated with a second group to which the second AP belongs; receiving a first roaming response frame from the first AP, the first roaming response frame including a first traffic indication map (TIM) field associated with the second AP; and receiving first downlink (DL) data from the second AP based on the first TIM field.

[0009] A method performed by a first access point (AP) included in a first group in a wireless LAN system according to yet another aspect of the present disclosure includes receiving a first roaming request frame from a first station (STA), the first roaming request frame including a link identifier of a second AP and a group ID associated with a second group to which the second AP belongs, and transmitting a first roaming response frame to the first STA, the first roaming response frame including a first traffic indication map (TIM) field associated with the second AP, wherein first downlink (DL) data may be transmitted from the second AP to the first STA based on the first TIM field. [Effects of the Invention]

[0010] According to the present disclosure, a roaming method and apparatus based on Multi-Link Device (MLD) in a wireless LAN system can be provided.

[0011] According to the present disclosure, it is possible to provide a method and apparatus for supporting or performing roaming of a station (STA) between different access points (APs) belonging to a common MLD in a wireless LAN system.

[0012] According to the present disclosure, a method and apparatus for performing communication by adding / removing temporary links during an MLD-based roaming procedure in a wireless LAN system can be provided.

[0013] The effects obtained from the present disclosure are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those having ordinary skill in the art to which the present disclosure pertains from the following description. [Brief explanation of the drawings]

[0014] The accompanying drawings, which are included as part of the detailed description to aid in understanding the present disclosure, provide examples for the present disclosure and, together with the detailed description, explain the technical features of the present disclosure. [Figure 1] FIG. 1 is a block diagram illustrating a wireless communication device according to an embodiment of the present disclosure. [Figure 2] FIG. 1 is a diagram illustrating an exemplary structure of a wireless LAN system to which the present disclosure can be applied. [Figure 3] FIG. 1 is a diagram illustrating a link setup process to which the present disclosure can be applied. [Figure 4] FIG. 10 is a diagram illustrating a backoff process to which the present disclosure can be applied. [Figure 5] 10A and 10B are diagrams for explaining a CSMA / CA base frame transmission operation to which the present disclosure can be applied. [Figure 6] 1 is a diagram illustrating an example of a frame structure used in a wireless LAN system to which the present disclosure can be applied. [Figure 7] FIG. 1 illustrates an example of a PPDU defined in the IEEE 802.11 standard to which the present disclosure is applicable. [Figure 8] FIG. 10 is a diagram illustrating the structure of an ML element to which the present disclosure can be applied. [Figure 9] FIG. 10 is a diagram illustrating an example of a high-level structure for AP MLD to which the present disclosure can be applied. [Figure 10] FIG. 1 is a diagram for explaining BSS transition in an existing wireless LAN system. [Figure 11] 1 is a diagram illustrating an example of a method for performing MLD-based roaming by a STA according to the present disclosure. [Figure 12] 1 is a diagram illustrating an example of a method in which an AP according to the present disclosure supports MLD-based roaming of a STA. FIG. [Figure 13] FIG. 1 is a diagram illustrating an example of the structure and procedure of MLD-based roaming according to the present disclosure. [Figure 14] FIG. 1 is a diagram illustrating an example of an element including publicly known information according to the present disclosure. [Figure 15-17] FIG. 10 is a diagram for explaining an example of a reset ML element according to the present disclosure. [Figure 18-19]FIG. 1 is a diagram illustrating an example of the structure and procedure of MLD-based roaming according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the present disclosure will be described in detail below 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 embodiments in which the present disclosure can be implemented. The detailed description below includes specific details to provide a complete understanding of the present disclosure. However, it will be understood by those skilled in the art that the present disclosure can be implemented without such specific details.

[0016] In some cases, in order to avoid obscuring the concepts of the present disclosure, known structures and devices may be omitted or shown in block diagram form, focusing on the core functions of each structure and device.

[0017] In this disclosure, when a component is "coupled," "coupled," or "connected" to another component, this may include a direct connection as well as an indirect connection where there is another component between them. Also, in this disclosure, the terms "comprise" or "have" specify the presence of stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0018] In this disclosure, terms such as "first" and "second" are used only to distinguish one component from another, and are not used to limit the components, and do not limit the order or importance of the components unless otherwise specified. Therefore, within the scope of this disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

[0019] The terms used in this disclosure are for the purpose of describing particular embodiments and are not intended to limit the scope of the claims. As used in the description of the embodiments and the appended claims, the singular is intended to include the plural unless the context clearly dictates otherwise. The term "and / or" as used in this disclosure means that one of the associated listed items may be included, or that any and all possible combinations of two or more of them are included. Also, in this disclosure, " / " between words has the same meaning as "and / or" unless otherwise specified.

[0020] The examples of the present disclosure may be applied to various wireless communication systems. For example, the examples of the present disclosure may be applied to a wireless LAN system. For example, the examples of the present disclosure may be applied to a wireless LAN based on the IEEE 802.11a / g / n / ac / ax standard. Note that the examples of the present disclosure may be applied to a wireless LAN based on the newly proposed IEEE 802.11bn (or UHR) standard. Furthermore, the examples of the present disclosure may be applied to a wireless LAN based on a next-generation standard after IEEE 802.11bn. Furthermore, the examples of the present disclosure may be applied to a cellular wireless communication system. For example, the examples of the present disclosure may be applied to a cellular wireless communication system based on the LTE (Long Term Evolution) series technology and the 5G NR (New Radio) series technology of the 3GPP (3rd Generation Partnership Project: registered trademark; the same applies hereinafter) standard.

[0021] Below, technical features to which the examples of the present disclosure can be applied will be described.

[0022] FIG. 1 is a block diagram illustrating a wireless communication device according to an embodiment of the present disclosure.

[0023] 1 may be referred to by various terms such as a terminal, a wireless device, a wireless transmit receive unit (WTRU), a user equipment (UE), a mobile station (MS), a user terminal (UT), a mobile subscriber station (MSS), a mobile subscriber unit (MSS), a subscriber station (SS), an advanced mobile station (AMS), a wireless terminal (WT), or simply a user. In addition, the first device 100 and the second device 200 may be referred to by various terms such as an access point (AP), a base station (BS), a fixed station, a Node B, a base transceiver system (BTS), a network, an artificial intelligence (AI) system, a road side unit (RSU), a repeater, a router, a relay, a gateway, etc.

[0024] The devices 100 and 200 illustrated in FIG. 1 may also be referred to as stations (STAs). For example, the devices 100 and 200 illustrated 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 STAs 110 and 200 may serve as an access point (AP) or a non-AP. That is, in the present disclosure, the STAs 110 and 200 may have AP and / or non-AP functionality. When the STAs 110 and 200 have AP functionality, they may simply be referred to as APs, and when the STAs 110 and 200 have non-AP functionality, they may simply be referred to as STAs. Also, in the present disclosure, an AP may be referred to as an AP STA.

[0025] 1, a first device 100 and a second device 200 may transmit and receive wireless signals using various wireless LAN technologies (e.g., the IEEE 802.11 family). The first device 100 and the second device 200 may include interfaces for a medium access control (MAC) layer and a physical layer (PHY) in accordance with the IEEE 802.11 standard.

[0026] In addition, the first device 100 and the second device 200 may further support various communication standards (e.g., 3GPP LTE series, 5G NR series standards, etc.) other than WLAN technology. Furthermore, the devices of the present disclosure may be embodied as various devices such as mobile phones, vehicles, personal computers, augmented reality (AR) equipment, and virtual reality (VR) equipment. Furthermore, the STAs of the present disclosure may support various communication services such as voice calls, video calls, data communications, autonomous driving, machine-type communication (MTC), machine-to-machine (M2M), device-to-device (D2D), and Internet-of-Things (IoT).

[0027] 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 may be configured to control the memory 104 and / or the transceiver 106 to implement the descriptions, functions, procedures, suggestions, methods, and / or operational flowcharts of the present disclosure. For example, the processor 102 may process information in the memory 104 to generate first information / signals, and then transmit a wireless signal including the first information / signals via the transceiver 106. The processor 102 may also receive a wireless signal including second information / signals via the transceiver 106, and then store information obtained from signal processing of the second information / signals in the memory 104. The memory 104 may be coupled to the processor 102 and may store various information related to the operation of the processor 102. For example, the memory 104 may store software code including instructions for executing some or all of the processes controlled by the processor 102 or for implementing the descriptions, functions, procedures, suggestions, methods, and / or operational flowcharts in this disclosure. Here, the processor 102 and the memory 104 may be part of a communications modem / circuit / chip designed to implement wireless LAN technology (e.g., the IEEE 802.11 series). The transceiver 106 may be coupled to the processor 102 and may transmit and / or receive wireless signals via one or more antennas 108. The transceiver 106 may include a transmitter and / or a receiver. The transceiver 106 may be used interchangeably with an RF (Radio Frequency) unit. In this disclosure, a device may also refer to a communications modem / circuit / chip.

[0028] The second device 200 includes one or more processors 202, one or more memories 204, and may additionally include one or more transceivers 206 and / or one or more antennas 208. The processor 202 may be configured to control the memory 204 and / or the transceiver 206 to implement the descriptions, functions, procedures, suggestions, methods, and / or operational flowcharts disclosed in this disclosure. For example, the processor 202 may process information in the memory 204 to generate third information / signal, and then transmit a wireless signal including the third information / signal via the transceiver 206. The processor 202 may also receive a wireless signal including fourth information / signal via the transceiver 206, and then store information obtained from signal processing of the fourth information / signal in the memory 204. The memory 204 may be coupled 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 including instructions for executing some or all of the processes controlled by the processor 202 or for implementing the descriptions, functions, procedures, suggestions, methods, and / or operational flowcharts disclosed in this disclosure. Here, the processor 202 and the memory 204 may be part of a communications modem / circuit / chip designed to implement wireless LAN technology (e.g., the IEEE 802.11 series). The transceiver 206 may be coupled to the processor 202 and may transmit and / or receive wireless signals via one or more antennas 208. The transceiver 206 may include a transmitter and / or a receiver. The transceiver 206 may be used interchangeably with an RF unit. In this disclosure, a device may also refer to a communications modem / circuit / chip.

[0029] The hardware elements of the devices 100, 200 are described in more detail below. Without limitation, 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 and MAC). The one or more processors 102, 202 may generate one or more protocol data units (PDUs) and / or one or more service data units (SDUs) according to the descriptions, functions, procedures, suggestions, methods, and / or operational flow diagrams in this disclosure. The one or more processors 102, 202 may generate messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods, and / or operational flow diagrams in this disclosure. The one or more processors 102, 202 can generate and provide signals (e.g., baseband signals) including PDUs, SDUs, messages, control information, data, or information according to the functions, procedures, suggestions, and / or methods of this disclosure to the one or more transceivers 106, 206. The one or more processors 102, 202 can receive signals (e.g., baseband signals) from the one or more transceivers 106, 206 and obtain the PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods, and / or operational flowcharts of this disclosure.

[0030] The one or more processors 102, 202 may be referred to as a controller, microcontroller, microprocessor, or microcomputer. The one or more processors 102, 202 may be implemented using hardware, firmware, software, or a combination thereof. As an example, the one or more processors 102, 202 may include 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). The descriptions, functions, procedures, suggestions, methods, and / or operational flowcharts disclosed in this disclosure may be implemented using firmware or software, and the firmware or software may be implemented to include modules, procedures, functions, etc. Firmware or software configured to execute the descriptions, functions, procedures, suggestions, methods, and / or operational flow diagrams disclosed in this disclosure may be included in one or more processors 102, 202 or stored in one or more memories 104, 204 and executed by one or more processors 102, 202. The descriptions, functions, procedures, suggestions, methods, and / or operational flow diagrams disclosed in this disclosure may be embodied by firmware or software in the form of code, instructions, and / or collections of instructions.

[0031] One or more memories 104, 204 may be coupled to one or more processors 102, 202 and may store various types of data, signals, messages, information, programs, code, instructions, and / or instructions. The one or more memories 104, 204 may be comprised of ROM, RAM, EPROM, flash memory, hard drives, registers, cache memory, computer-readable storage media, and / or combinations thereof. The one or more memories 104, 204 may be located internal and / or external to the one or more processors 102, 202. Additionally, the one or more memories 104, 204 may be coupled to the one or more processors 102, 202 via various techniques, such as wired or wireless connections.

[0032] One or more transceivers 106, 206 may transmit user data, control information, wireless signals / channels, etc., as referred to in the methods and / or operational flowcharts 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 referred to in the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts of the present disclosure, from one or more other devices. For example, one or more transceivers 106, 206 may be coupled 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. Also, 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. Furthermore, one or more transceivers 106, 206 may be coupled to one or more antennas 108, 208, and the one or more transceivers 106, 206 may be configured to transmit and receive user data, control information, wireless signals / channels, etc., referred to in the descriptions, functions, procedures, suggestions, methods, and / or operational flowcharts disclosed in this disclosure, via the one or more antennas 108, 208. In this disclosure, the one or more antennas may be multiple physical antennas or multiple logical antennas (e.g., antenna ports). The one or more transceivers 106, 206 may convert the received user data, control information, wireless signals / channels, etc., from RF band signals to baseband signals for processing using one or more processors 102, 202. The one or more transceivers 106, 206 may convert the user data, control information, wireless signals / channels, etc., processed using one or more processors 102, 202, from baseband signals to RF band signals. To that end, one or more of the transceivers 106, 206 may include (analog) oscillators and / or filters.

[0033] For example, one of the STAs 100 and 200 may perform operations intended for an AP, and the other of the STAs 100 and 200 may perform operations intended for a non-AP STA. For example, the transceivers 106 and 206 in FIG. 1 may perform operations for transmitting and receiving signals (e.g., packets or PPDUs (Physical Layer Protocol Data Units) conforming to IEEE 802.11a / b / g / n / ac / ax / be / bn, etc.). In addition, in the present disclosure, operations for various STAs to generate transmission / reception signals or to perform data processing or calculations in advance for transmission / reception signals may be performed by the processors 102 and 202 in FIG. 1. For example, examples of operations for generating transmission / reception signals or performing data processing or calculations in advance for transmission / reception signals may include: 1) operations for determining / obtaining / configuring / calculating / decoding / encoding bit information of fields included in a PPDU (SIG (signal), STF (short training field), LTF (long training field), Data, etc.); 2) operations for determining / configuring / obtaining time resources and frequency resources (e.g., subcarrier resources) to be used for fields included in a PPDU (SIG, STF, LTF, Data, etc.); 3) operations for determining / configuring / obtaining specific sequences (e.g., pilot sequences, STF / LTF sequences, extra sequences applied to SIG) to be used for fields included in a PPDU (SIG, STF, LTF, Data, etc.); 4) power control operations and / or power saving operations applied to STAs; and 5) operations related to determining / obtaining / configuring / calculating / decoding / encoding ACK signals, etc. In addition, in the following example, various information (e.g., information regarding fields / subfields / control fields / parameters / power, etc.) used by various STAs for determining / acquiring / configuring / calculating / decoding / encoding transmitted / received signals may be stored in memories 104, 204 of FIG. 1.

[0034] Hereinafter, downlink (DL) refers to a link for communication from an AP STA to a non-AP STA, and downlink PPDUs / packets / signals, etc. may be transmitted and received via 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. Uplink (UL) refers to a link for communication from a non-AP STA to an AP STA, and uplink PPDUs / packets / signals, etc. may be transmitted and received via 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.

[0035] FIG. 2 is a diagram showing an exemplary structure of a wireless LAN system to which the present disclosure can be applied.

[0036] The structure of a WLAN system may be composed of multiple components. The interaction of these components may provide a WLAN that supports STA mobility transparent to higher layers. A Basic Service Set (BSS) is a basic building block of a WLAN. FIG. 2 illustrates two BSSs (BSS1 and BSS2), each including two STAs as members (STA1 and STA2 are included in BSS1, and STA3 and STA4 are included in BSS2). The ellipses representing BSSs in FIG. 2 may be understood to represent coverage areas where STAs included in the BSSs maintain communication. This area may be referred to as a Basic Service Area (BSA). If a STA moves outside a BSA, it will no longer be able to directly communicate with other STAs within the BSA.

[0037] Ignoring the DS shown in FIG. 2, the most basic type of BSS in a WLAN is the Independent BSS (IBSS). For example, an IBSS may have a minimal configuration consisting of only two STAs. For example, assuming that other components are omitted, BSS1 consisting of only STA1 and STA2, or BSS2 consisting of only STA3 and STA4, are representative examples of an IBSS. Such a configuration is possible when STAs can communicate directly without an AP. Furthermore, in such a WLAN, a BSS may be configured when needed by the LAN, rather than being configured in advance. This can also be called an ad-hoc network. Since an IBSS does not include an AP, there is no centralized management entity. That is, in an IBSS, STAs are managed in a distributed manner. In an IBSS, all STAs may be mobile, and connection to a distributed system (DS) is not permitted, forming a self-contained network.

[0038] The membership of STAs in a BSS may change dynamically as STAs join and leave the BSS area, etc. To become a member of a BSS, a STA may join the BSS using a synchronization process. To access all the services of the BSS-based architecture, a STA must be associated with the BSS. Such association may be dynamically configured and may include the use of a Distribution System Service (DSS).

[0039] In a wireless LAN, direct STA-to-STA distance may be limited by PHY performance. While such distance limits are sufficient in some cases, other situations may require communication between STAs over longer distances. To support extended coverage, a distributed system (DS) may be configured.

[0040] A DS refers to a structure in which BSSs are interconnected. Specifically, as shown in FIG. 2, a BSS may exist as a component of an expanded network composed of multiple BSSs. A DS is a logical concept and may be specified by the characteristics of a distributed system medium (DSM). In this regard, a wireless medium (WM) and a DSM may be logically distinguished. Each logical medium is used for different purposes and by different components. These media are neither limited to being the same nor limited to being different. The flexibility of a WLAN structure (DS structure or other network structure) can be explained by the fact that multiple media are logically distinct from one another. That is, a WLAN structure may be embodied in various ways, and the WLAN structure may be independently specified according to the physical characteristics of each implementation.

[0041] The DS can support mobile devices by providing seamless integration of multiple BSSs and logical services necessary for addressing destinations. The DS may also include a portal component that acts as a bridge between the wireless LAN and other networks (e.g., IEEE 802.X).

[0042] An AP is an entity that allows associated non-AP STAs to access the DS through the WM and also has the functionality of an STA. Data can be transferred between a BSS and a DS via the AP. For example, STA2 and STA3 shown in FIG. 2 have the functionality of an STA and provide the function of allowing associated non-AP STAs (STA1 and STA4) to access the DS. Furthermore, since all APs essentially correspond to STAs, all APs are addressable entities. The address used by an AP for communication on the WM does not necessarily have to be the same as the address used by the AP for communication on the DSM. A BSS consisting of an AP and one or more STAs can be called an infrastructure BSS.

[0043] Data transmitted from one of the STAs associated with an AP to the STA address of that AP is always received on the uncontrolled port and may be processed by the IEEE 802.1X port access entity, and once the controlled port is authenticated, the transmitted data (or frame) may be delivered to the DS.

[0044] In the above-described DS structure, an Extended Service Set (ESS) may be configured to provide wider coverage.

[0045] An ESS is a network of arbitrary size and complexity composed of a DS and a BSS. An ESS can be a collection of BSSs connected to one DS. However, an ESS does not include a DS. An ESS network is characterized by appearing as an IBSS at the Logical Link Control (LLC) layer. STAs 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 one ESS may have the same service set identification (SSID). An SSID is distinct from a BSSID, which is an identifier for a BSS.

[0046] A WLAN system does not make any assumptions about the relative physical locations of BSSs and can have any of the following configurations: BSSs may partially overlap, which is a configuration commonly used to provide continuous coverage; BSSs may not be physically connected, and there is no logical limit to the distance between BSSs; BSSs may be physically located in the same location, which may be used to provide redundancy; and 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 configurations when an ad-hoc network operates in the location where the ESS network exists, when physically overlapping wireless networks are formed by different organizations, or when two or more different access and security policies are required in the same location.

[0047] FIG. 3 is a diagram illustrating a link setup process to which the present disclosure can be applied.

[0048] In order for an STA to set up a link to a network and transmit and receive data, it must first discover the network, perform authentication, establish an association, and perform authentication procedures for security. The link setup process can also be called a session initiation process or a session setup process. In addition, the discovery, authentication, association, and security configuration processes of the link setup process can also be collectively called the association process.

[0049] In step S310, the STA may perform a network discovery operation. The network discovery operation may include a scanning operation of the STA. That is, in order for the STA to access a network, the STA must search for a joinable network. Before joining a wireless network, the STA must identify a compatible network. The process of identifying networks present in a specific area is called scanning.

[0050] Scanning methods include active scanning and passive scanning. FIG. 3 illustrates an example of a network discovery operation including an active scanning process. In active scanning, a scanning STA changes channels and transmits a probe request frame to search for nearby APs, and waits for a response. A responder transmits a probe response frame to the STA that transmitted the probe request frame in response to the probe request frame. Here, the responder may be the STA that last transmitted a beacon frame in the BSS of the channel being scanned. In a BSS, the AP transmits beacon frames, so the AP is the responder. In an IBSS, the STAs in the IBSS transmit beacon frames alternately, so the responder is not constant. For example, an STA that transmits a probe request frame on channel 1 and receives a probe response frame on channel 1 can store the BSS-related information contained in the received probe response frame, move to the next channel (e.g., channel 2), and perform scanning in the same manner (i.e., send and receive probe requests / responses on channel 2).

[0051] Although not shown in FIG. 3, the scanning operation may be performed in a passive scanning manner. In passive scanning, a scanning STA waits for a beacon frame while changing channels. A beacon frame is a management frame defined in IEEE 802.11 and is periodically transmitted to announce the existence of a wireless network and allow a scanning STA to search for and join the wireless network. In a BSS, the AP is responsible for periodically transmitting beacon frames, while in an IBSS, STAs within the IBSS transmit beacon frames in turn. When a scanning STA receives a beacon frame, it saves the BSS-related information included in the beacon frame and records the beacon frame information on each channel as it moves to other channels. A STA that receives a beacon frame saves the BSS-related information included in the received beacon frame, moves to the next channel, and scans the next channel in the same manner. Comparing active scanning with passive scanning, active scanning has the advantage of having a smaller delay and power consumption than passive scanning.

[0052] After the STA discovers the network, an authentication process may be performed in step S320. This authentication process may be called a first authentication process to clearly distinguish it from the security setup operation in step S340, which will be described later.

[0053] The authentication process involves a STA sending an authentication request frame to an AP, and the AP responding by sending an authentication response frame to the STA. The authentication frame used for the authentication request / response corresponds to a management frame.

[0054] The authentication frame may include information such as an authentication algorithm number, an authentication transaction sequence number, a status code, a challenge text, a Robust Security Network (RSN), a Finite Cyclic Group, etc. These are only examples of information that may be included in an authentication request / response frame, and other information may be substituted or additional information may be included.

[0055] The STA can send an authentication request frame to the AP. The AP can determine whether to allow authentication for the STA based on the information contained in the received authentication request frame. The AP can provide the STA with the result of the authentication process using an authentication response frame.

[0056] After the STA is successfully authenticated, an association process may be performed in step S330. The association process includes a process in which the STA transmits an association request frame to the AP, and in response, the AP transmits an association response frame to the STA.

[0057] For example, the association request frame may include information on various capabilities, a beacon listen interval, a service set identifier (SSID), supported rates, supported channels, an RSN, a mobility domain, supported operating classes, a Traffic Indication Map Broadcast request, interworking service capabilities, etc. For example, the association response frame may include information on various capabilities, a status code, an association ID (AID), supported rates, an Enhanced Distributed Channel Access (EDCA) parameter set, a Received Channel Power Indicator (RCPI), a Received Signal to Noise Indicator (RSNI), a mobility domain, a timeout interval (e.g., an association comeback time), overlapping BSS scan parameters, a TIM broadcast response, a Quality of Service (QoS) map, etc. This corresponds to only a partial example of information that may be included in the association request / response frame, and other information may be substituted or additional information may be included.

[0058] After the STA is successfully connected to the network, a security setup process may be performed in step S340. The security setup process in step S340 may also be referred to as an authentication process using a Robust Security Network Association (RSNA) request / response, and the authentication process in step S320 may be referred to as a first authentication process, and the security setup process in step S340 may simply be referred to as an authentication process.

[0059] The security setup process of step S340 may include a process of performing private key setup using, for example, four-way handshaking using an Extensible Authentication Protocol over LAN (EAPOL) frame, and may also be performed using a security method not defined in the IEEE 802.11 standard.

[0060] FIG. 4 is a diagram illustrating a backoff process to which the present disclosure can be applied.

[0061] In wireless LAN systems, the basic access mechanism of MAC (Medium Access Control) is the Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) mechanism, also known as the Distributed Coordination Function (DCF) of IEEE 802.11 MAC, which basically employs a "listen before talk" access mechanism. According to this type of access mechanism, the AP and / or STA can perform a Clear Channel Assessment (CCA) to sense the wireless channel or medium for a predetermined time period (e.g., a DCF Inter-Frame Space (DIFS)) before starting transmission. If the sensing result indicates that the medium is in an idle status, the AP and / or STA can start transmitting a frame over the medium. On the other hand, if the medium is detected as occupied or busy, the AP and / or STA can wait for a delay period (e.g., a random backoff period) for medium access without starting its own transmission, and then attempt to transmit a frame. By applying the random backoff period, multiple STAs are expected to wait for different periods of time before attempting to transmit a frame, thereby minimizing collisions.

[0062] The IEEE 802.11 MAC protocol also provides a Hybrid Coordination Function (HCF). HCF is based on the DCF and Point Coordination Function (PCF). PCF is a polling-based synchronous access method that periodically polls all receiving APs and / or STAs to ensure that they can receive data frames. HCF also includes Enhanced Distributed Channel Access (EDCA) and HCF Controlled Channel Access (HCCA). EDCA is a contention-based access method for a provider to provide data frames to multiple users, while HCCA is a non-contention-based channel access method using a polling mechanism. HCF also includes a medium access mechanism for improving the Quality of Service (QoS) of wireless LANs, and can transmit QoS data in both a contention period (CP) and a contention-free period (CFP).

[0063] The operation based on the random backoff period will be described with reference to FIG. 4. When an occupied / busy medium changes to an idle state, multiple STAs can attempt to transmit data (or frames). As a method for minimizing collisions, each STA can 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 may be determined to be one of the values ​​in the range of 0 to CW. Here, CW is the contention window parameter value. The CW parameter is given a CWmin as its initial value, but can be doubled in the event of a transmission failure (e.g., if an ACK for a transmitted frame is not received). When the CW parameter value reaches CWmax, data transmission can be attempted while maintaining the CWmax value until data transmission is successful, and if data transmission is successful, it is reset to the CWmin value. The CW, CWmin, and CWmax values ​​are set to 2. n Preferably it is set to -1 (n=0,1,2,...).

[0064] When the random backoff process begins, the STA continuously monitors the medium while counting down the backoff slots according to the determined backoff count value. If the medium is monitored as occupied, the STA stops counting down and waits. If the medium becomes idle, the STA resumes the remaining countdown.

[0065] 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 a frame. The remaining STAs monitor the medium for occupied / busy status and wait. Meanwhile, STA1, STA2, and STA5 may each have data to transmit. If each STA monitors the medium as idle, it waits for DIFS and then counts down its backoff slots according to its random backoff count value. Assume that STA2 selects the smallest backoff count value and STA1 selects the largest backoff count value. That is, this example illustrates a case where, at the time STA2 finishes its backoff count and begins frame transmission, STA5's remaining backoff time is shorter than STA1's remaining backoff time. STA1 and STA5 pause their countdowns and wait while STA2 occupies the medium. When STA2's occupation ends and the medium becomes idle again, STA1 and STA5 wait for DIFS and then resume their backoff counts. That is, STA5 can start frame transmission after counting down the remaining backoff slots equal to the remaining backoff time. Because STA5's remaining backoff time is shorter than STA1's, STA5 begins frame transmission. While STA2 is occupying the medium, STA4 may also have data to transmit. From STA4's perspective, when the medium becomes idle, it waits for DIFS, then counts down the random backoff count value it selected, and can begin frame transmission. The example in FIG. 4 shows a case where STA5's remaining backoff time happens to match STA4's random backoff count value, which may result in a collision between STA4 and STA5. If a collision occurs, neither STA4 nor STA5 will receive an ACK, resulting in a failed data transmission. In this case, STA4 and STA5 can double their CW values, select a random backoff count value, and then count down.STA1 waits while the medium is occupied by transmissions from STA4 and STA5, but when the medium becomes idle, it waits for DIFS and can begin frame transmission once the remaining backoff time has elapsed.

[0066] As shown in the example of Figure 4, a data frame is a frame used for transmitting data to be forwarded to a higher layer, and may be transmitted after a backoff that occurs after a DIFS has elapsed since the medium became idle. Furthermore, a management frame is a frame used for exchanging management information that is not forwarded to a higher layer, and is transmitted after a backoff that occurs after an IFS, such as a DIFS or a PIFS (Point Coordination Function IFS). Subtype frames of management frames include a beacon, an association request / response, a re-association request / response, a probe request / response, and an authentication request / response. A control frame is a frame used to control access to a medium. Subtype frames of control frames include Request-To-Send (RTS), Clear-To-Send (CTS), Acknowledgment (ACK), Power Save-Poll (PS-Poll), BlockAck, BlockACKReq, NDP announcement (null data packet announcement), and Trigger. If a control frame is not a response frame of a previous frame, it is transmitted after a backoff that is performed after a DIFS has elapsed, and if it is a response frame of a previous frame, it is transmitted without a backoff after a short IFS (SIFS). The type and subtype of a frame may be identified by the type field and subtype field in the Frame Control (FC) field.

[0067] A Quality of Service (QoS) STA can transmit a frame after backing off after 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), has elapsed. Here, a frame that can use AIFS[i] can be a data frame, a management frame, or a control frame that is not a response frame.

[0068] FIG. 5 is a diagram for explaining a CSMA / CA base frame transmission operation to which the present disclosure can be applied.

[0069] As mentioned above, the CSMA / CA mechanism includes not only physical carrier sensing, in which a STA directly senses the medium, but also virtual carrier sensing. Virtual carrier sensing is intended to compensate for problems that may occur in medium access, such as the hidden node problem. For virtual carrier sensing, the MAC of a STA can use a network allocation vector (NAV). The NAV is a value that indicates to other STAs the time remaining until the medium becomes available for use by a STA currently using or authorized to use the medium. Therefore, the value set as the NAV corresponds to the period during which the STA transmitting the frame plans to use the medium, and STAs receiving the NAV value are prohibited from accessing the medium during that period. For example, the NAV may be set based on the value of the "duration" field in the MAC header of the frame.

[0070] In the example of FIG. 5, it is assumed that STA1 is attempting to transmit data to STA2, and STA3 is in a position where it can overhear some or all of the frames transmitted between STA1 and STA2.

[0071] In order to reduce the possibility of collisions between transmissions from multiple STAs in a CSMA / CA-based frame transmission operation, a mechanism using RTS / CTS frames may be applied. In the example of FIG. 5, while STA1 is transmitting, STA3 may determine that the medium is idle as a result of carrier sensing. That is, STA1 may be a hidden node to STA3. Alternatively, in the example of FIG. 5, while STA2 is transmitting, STA3 may determine that the medium is idle as a result of carrier sensing. That is, STA2 may be a hidden node to STA3. By exchanging RTS / CTS frames before data transmission and reception between STA1 and STA2, STAs outside the transmission range of either STA1 or STA2, or outside the carrier sensing range for transmissions from STA1 or STA3, can be prevented from attempting to occupy the channel during data transmission and reception between STA1 and STA2.

[0072] Specifically, STA1 can determine whether a channel is occupied or not using carrier sensing. In terms of physical carrier sensing, STA1 can determine whether a channel is occupied or idle based on the energy magnitude or signal correlation detected from the channel. In terms of virtual carrier sensing, STA1 can determine whether a channel is occupied or idle using a network allocation vector (NAV) timer.

[0073] When the channel is idle in DIFS, STA1 can send an RTS frame to STA2 after backing off. When STA2 receives the RTS frame, it can send a CTS frame to STA1 as a response to the RTS frame after SIFS.

[0074] If STA3 cannot overhear the CTS frame from STA2 but can overhear the RTS frame from STA1, STA3 can use the duration information included in the RTS frame to set a NAV timer for the frame transmission period (e.g., SIFS + CTS frame + SIFS + data frame + SIFS + ACK frame) that will be transmitted subsequently. Alternatively, if STA3 cannot overhear the RTS frame from STA1 but can overhear the CTS frame from STA2, STA3 can use the duration information included in the CTS frame to set a NAV timer for the frame transmission period (e.g., SIFS + data frame + SIFS + ACK frame) that will be transmitted subsequently. That is, if STA3 can overhear one or more RTS or CTS frames from at least one of STA1 and STA2, it can set a NAV based thereon. If STA3 receives a new frame before the NAV timer expires, it can update the NAV timer using the duration information included in the new frame. STA3 does not attempt channel access until the NAV timer expires.

[0075] When STA1 receives a CTS frame from STA2, it can transmit a data frame to STA2 SIFS after the completion of reception of the CTS frame. When STA2 successfully receives a data frame, it can transmit an ACK frame, which is a response to the data frame, to STA1 SIFS after the completion of reception of the CTS frame. When STA2 successfully receives a data frame, it can transmit an ACK frame, which is a response to the data frame, to STA1 SIFS after the expiration of the NAV timer. When STA3 determines that the channel is not being used by another terminal during the DIFS period after the expiration of the NAV timer, it can attempt channel access after the contention window (CW) with random backoff has elapsed.

[0076] FIG. 6 is a diagram illustrating an example of a frame structure used in a wireless LAN system to which the present disclosure can be applied.

[0077] The PHY layer can prepare an MPDU (MAC PDU) to be transmitted based on an instruction or primitive (meaning a set of instructions or parameters) from the MAC layer. For example, when the PHY layer receives a command from the MAC layer requesting the start of PHY layer transmission, the PHY layer switches to transmission mode and transmits information (e.g., data) provided by the MAC layer in the form of a frame. In addition, when the PHY layer detects a valid preamble in a received frame, it monitors the preamble header and sends a command to the MAC layer informing the start of PHY layer reception.

[0078] Thus, information transmission / reception in a wireless LAN system is performed in the form of frames, and for this purpose, a PHY layer protocol data unit (PPDU) frame format is defined.

[0079] A basic PPDU may include a Short Training Field (STF), a Long Training Field (LTF), a Signal (SIG) field, and a Data field. The most basic PPDU format (e.g., non-High Throughput (HT) shown in FIG. 7) may consist of only a Legacy-STF (L-STF), a Legacy-LTF (L-LTF), a Legacy-SIG (L-SIG) field, and a Data field. Depending on the type of PPDU format (e.g., HT-mixed format PPDU, HT-greenfield format PPDU, Very High Throughput (VHT) PPDU, etc.), an additional (or other type) RL-SIG, U-SIG, non-legacy SIG field, non-legacy STF, non-legacy LTF (i.e., xx-SIG, xx-STF, xx-LTF (e.g., xx is HT, VHT, HE, EHT, etc.)), etc. may be included between the L-SIG field and the Data field. More specific details will be described later with reference to FIG.

[0080] The STF is a signal for signal detection, AGC (Automatic Gain Control), diversity selection, precise time synchronization, etc., and the LTF is a signal for channel estimation, frequency error estimation, etc. The STF and LTF can be said to be signals for synchronization and channel estimation of the OFDM physical layer.

[0081] The SIG field may contain various information related to PPDU transmission and reception. For example, the L-SIG field may be composed 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 rate 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 PPDU. For example, for non-HT, HT, VHT, or EHT PPDU, the value of the Length field may be determined as a multiple of 3. For example, for HE PPDU, the value of the Length field may be determined as a multiple of 3 + 1 or a multiple of 3 + 2.

[0082] The data field may include a SERVICE field, a PSDU (Physical layer Service Data Unit), a PPDU TAIL bit, and, if necessary, padding bits. Some bits of the SERVICE field may be used for synchronization of a descrambler at the receiving end. The PSDU corresponds to a MAC PDU defined in the MAC layer and may contain data generated / used by a higher layer. The PPDU TAIL bit may be used to return the encoder to a 0 state. The padding bits may be used to adjust the length of the data field to a predetermined unit.

[0083] The MAC PDU is defined by various MAC frame formats, and a basic MAC frame consists of a MAC header, a frame body, and a Frame Check Sequence (FCS). The MAC frame is composed of the MAC PDU and may be transmitted / received by the PSDU in the data portion of the PPDU format.

[0084] The MAC header includes a Frame Control field, a Duration / ID field, an Address field, etc. The Frame Control field may include control information required for frame transmission / reception. The Duration / ID field may be set to the time for transmitting the frame, etc. The Address subfield may indicate the receiver address, transmitter address, destination address, or source address of the frame, and some of the Address subfields may be omitted. The MAC header includes Sequence Control, QoS Control, and HT Control subfields. For specific contents of each subfield of the MAC header, please refer to the IEEE 802.11 standard document.

[0085] The null data PPDU (NDP) format refers to a PPDU format that does not include a data field, i.e., NDP refers to a frame format that includes a PPDU preamble (i.e., L-STF, L-LTF, L-SIG fields, and, if present, non-legacy SIG, non-legacy STF, and non-legacy LTF) in a general PPDU format, but does not include the remaining part (i.e., data field).

[0086] FIG. 7 is a diagram illustrating an example of a PPDU defined in the IEEE 802.11 standard to which the present disclosure is applicable.

[0087] Various types of PPDUs are used in standards such as IEEE 802.11a / g / n / ac / ax. The basic PPDU format (IEEE 802.11a / g) includes an L-LTF, an L-STF, an L-SIG, and a Data field. The basic PPDU format can also be called a non-HT PPDU format (see FIG. 7(a)).

[0088] The HT PPDU format (IEEE 802.11n) further includes HT-SIG, HT-STF, and HT-LFT(s) fields in addition to the basic PPDU format. The HT PPDU format shown in Figure 7(b) can be referred to as an HT-mixed format. An HT-greenfield format PPDU may also be defined, which corresponds to a format that does not include L-STF, L-LTF, or L-SIG, but is composed of HT-GF-STF, HT-LTF1, HT-SIG, one or more HT-LTFs, and a Data field (not shown).

[0089] An example of a VHT PPDU format (IEEE 802.11ac) further includes VHT SIG-A, VHT-STF, VHT-LTF, and VHT-SIG-B fields in addition to the basic PPDU format (FIG. 7(c)).

[0090] An example of the HE PPDU format (IEEE 802.11ax) further includes the fields Repeated L-SIG (RL-SIG), HE-SIG-A, HE-SIG-B, HE-STF, HE-LTF(s), and Packet Extension (PE) in addition to the basic PPDU format (FIG. 7(d)). Depending on the detailed example 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 not in the HE PPDU format for single users (SU). Also, the HE trigger-based (TB) PPDU format does not include the HE-SIG-B, and the length of the HE-STF field may be 8 us. The HE Extended Range (ER) SU PPDU format does not include the HE-SIG-B field, and the length of the HE-SIG-A field may be 16 us. For example, the RL-SIG may be configured to be the same as the L-SIG. Based on the presence of the RL-SIG, the receiving STA can determine that the received PPDU is an HE PPDU or an EHT PPDU (described later).

[0091] The EHT PPDU format may include the EHT MU (multi-user) PPDU in Figure 7(e) and the EHT TB (trigger-based) PPDU in Figure 7(f). The EHT PPDU format is similar to the HE PPDU format in that it includes an RL-SIG following an L-SIG, but it may also include a U (universal)-SIG, EHT-SIG, EHT-STF, and EHT-LTF following the RL-SIG.

[0092] The EHT MU PPDU in Figure 7(e) corresponds to a PPDU that carries one or more data (or PSDUs) for one or more users. That is, the EHT MU PPDU may be used for both SU transmission and MU transmission. For example, the EHT MU PPDU may correspond to a PPDU for one receiving STA or multiple receiving STAs.

[0093] The EHT TB PPDU in Figure 7(f) omits the EHT-SIG 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.

[0094] The L-STF, L-LTF, L-SIG, RL-SIG, U-SIG (Universal Signal), and EHT-SIG fields may be encoded and modulated and mapped based on a predetermined subcarrier frequency interval (e.g., 312.5 kHz) so that legacy STAs can also attempt demodulation and decoding. These may be referred to as pre-EHT modulated fields. Next, the EHT-STF, EHT-LTF, Data, and PE fields may be encoded and modulated and mapped based on a predetermined subcarrier frequency interval (e.g., 78.125 kHz) so that they can be demodulated and decoded by STAs that successfully decode non-legacy SIGs (e.g., U-SIG and / or EHT-SIG) and obtain the information contained in these fields. These may be referred to as EHT modulated fields.

[0095] 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.

[0096] The U-SIG included in the EHT PPDU format of Fig. 7 may be configured based on, for example, two symbols (e.g., two consecutive OFDM symbols). Each symbol (e.g., OFDM symbol) for the U-SIG may have a duration of 4 us, and the entire U-SIG may have a duration of 8 us. Each symbol of the U-SIG may be used to transmit 26 bits of information. For example, each symbol of the U-SIG may be transmitted and received based on 52 data tones and 4 pilot tones.

[0097] U-SIGs may be configured in 20 MHz units. For example, when an 80 MHz PPDU is configured, the same U-SIG may be duplicated in 20 MHz units. That is, four identical U-SIGs may be included in an 80 MHz PPDU. When the bandwidth exceeds 80 MHz, for example, for a 160 MHz PPDU, the first U-SIG in the 80 MHz unit and the second U-SIG in the 80 MHz unit may be different from each other.

[0098] For example, a U-SIG may transmit A uncoded bits, with the first symbol of the U-SIG (e.g., U-SIG-1 symbol) transmitting the first X bits of the total A bits of information, and the second symbol of the U-SIG (e.g., U-SIG-2 symbol) transmitting the remaining Y bits of information. The A bits of information (e.g., 52 uncoded bits) may include a CRC field (e.g., a 4-bit field) and a tail field (e.g., a 6-bit field). The tail field may be used to terminate the trellis of a convolutional decoder and may be set to 0, for example.

[0099] The A-bit information transmitted by the U-SIG can be divided into version-independent bits and version-dependent bits. For example, the U-SIG may be included in a new PPDU format (e.g., a UHR PPDU format) not shown in Fig. 7. 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, but some or all of the version-dependent bits may be different.

[0100] For example, the size of the version-independent bits in a U-SIG may be fixed or variable. The version-independent bits may be assigned only to the U-SIG-1 symbol or to both the 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 first control bits and second control bits.

[0101] For example, the version independent bits of the U-SIG may include a 3-bit PHY version identifier, which may indicate the PHY version (e.g., EHT, UHR, etc.) of the transmitted and received PPDU. The version independent bits of the U-SIG may include a 1-bit UL / DL flag field. A first value of the 1-bit UL / DL flag field is associated with UL communication, and a second value of the UL / DL flag field is associated with DL communication. The version independent bits of the U-SIG may include information regarding the length of a transmission opportunity (TXOP) and information regarding a BSS color ID.

[0102] For example, the version dependent bits of the U-SIG may include information that directly or indirectly indicates the type of PPDU (eg, SU PPDU, MU PPDU, TB PPDU, etc.).

[0103] Information necessary for transmitting and receiving a PPDU may be included in the U-SIG. For example, the U-SIG may further include information about the bandwidth, information about an MCS scheme to be applied to a non-legacy SIG (e.g., an EHT-SIG or a UHR-SIG), information indicating whether a dual carrier modulation (DCM) scheme (e.g., a scheme for achieving an effect similar to frequency diversity by reusing the same signal on two subcarriers) is applied to the non-legacy SIG, information about the number of symbols used for the non-legacy SIG, information about whether the non-legacy SIG is generated across the entire band, etc.

[0104] Some of the information necessary for transmitting and receiving a PPDU may be included in the U-SIG and / or non-legacy SIG (e.g., EHT-SIG or UHR-SIG, etc.). For example, information on the type of non-legacy LTF / STF (e.g., EHT-LTF / EHT-STF or UHR-LTF / UHR-STF, etc.), information on the length of the non-legacy LTF and the cyclic prefix (CP) length, information on the guard interval (GI) applied to the non-legacy LTF, information on preamble puncturing applicable to the PPDU, information on resource unit (RU) allocation, etc. may be included only in the U-SIG, or only in the non-legacy SIG, or may be indicated by a combination of information included in the U-SIG and information included in the non-legacy SIG.

[0105] Preamble puncturing may refer to the transmission of a PPDU in which no signal is present in one or more frequency units in the bandwidth of the PPDU. For example, the size of the frequency unit (or the resolution of the preamble puncturing) may be defined as 20 MHz, 40 MHz, etc. For example, preamble puncturing may be applied to PPDU bandwidths equal to or larger than a predetermined size.

[0106] 7, non-legacy SIGs such as HE-SIG-B and EHT-SIG may contain control information for receiving STAs. Non-legacy SIGs may be transmitted in at least one symbol, and one symbol may have a length of 4 us. Information regarding the number of symbols used for the EHT-SIG may be included in previous SIGs (e.g., HE-SIG-A, U-SIG, etc.).

[0107] Non-legacy SIGs such as HE-SIG-B and EHT-SIG may include common fields and user-specific fields, which may be coded separately.

[0108] In some cases, the common field may be omitted. For example, in a compressed mode where non-OFDMA (orthogonal frequency multiple access) is applied, the common field may be omitted and multiple STAs can receive the PPDU (e.g., the data field of the PPDU) in the same frequency band. In an uncompressed mode where OFDMA is applied, multiple users can receive the PPDU (e.g., the data field of the PPDU) in separate frequency bands.

[0109] The number of user-specific fields may be determined based on the number of users. One user block field may include up to two user fields. Each user field may be associated with a MU-MIMO allocation or a non-MU-MIMO allocation.

[0110] The common field may include CRC bits and tail bits, where 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 locations of RUs to which multiple users (i.e., multiple receiving STAs) are allocated.

[0111] An RU may include multiple subcarriers (or tones). An RU may be used when transmitting signals to multiple STAs based on the OFDMA technique. An RU may also be defined when transmitting a signal to a single STA. Resources may be allocated in RU units for the non-legacy STF, non-legacy LTF, and Data field.

[0112] Applicable RU sizes may be defined depending on the PPDU bandwidth. RUs may be defined to be the same or different for applicable PPDU formats (e.g., HE PPDU, EHT PPDU, UHR PPDU, etc.). For example, in the case of an 80 MHz PPDU, the RU arrangements for HE PPDU and EHT PPDU may be different from each other. The applicable RU size, 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 may be referred to as a tone plan. For example, a tone plan for a wide bandwidth may be defined as multiple repetitions of a tone plan for a low bandwidth.

[0113] RUs of various sizes may be defined as 26-tone RUs, 52-tone RUs, 106-tone RUs, 242-tone RUs, 484-tone RUs, 996-tone RUs, 2×996-tone RUs, 4×996-tone RUs, etc. An MRU (multiple RU) is distinct from multiple individual RUs and corresponds to a group of subcarriers consisting of multiple RUs. For example, one MRU may be defined as 52+26 tones, 106+26 tones, 484+242 tones, 996+484 tones, 996+484+242 tones, 2×996+484 tones, 3×996 tones, or 3×996+484 tones. Furthermore, the multiple RUs that make up one MRU may or may not be contiguous in the frequency domain.

[0114] The specific size of an RU may be reduced or expanded. Therefore, the specific size of each RU (i.e., the number of corresponding tones) in this disclosure is illustrative and not restrictive. Also, in this disclosure, the number of RUs within a given bandwidth (e.g., 20, 40, 80, 160, 320 MHz, ...) may vary depending on the size of the RU.

[0115] The names of the fields in the PPDU format of Fig. 7 are merely examples, and the scope of the present disclosure is not limited by the names. In addition, examples of the present disclosure may be applied to a new PPDU format in which some fields are excluded and / or some fields are added based on the PPDU format of Fig. 7, in addition to the PPDU format illustrated in Fig. 7.

[0116] Multi-link operation

[0117] The following describes STA-assisted multi-link (ML) operation according to the present disclosure.

[0118] The STAs (AP STAs and / or non-AP STAs) described in this disclosure can support multi-link (ML) communication. ML communication can refer to communication supporting multiple links. Links related to ML communication may include channels (e.g., 20 / 40 / 80 / 160 / 240 / 320 MHz channels) in a frequency band (e.g., 2.4 GHz band, 5 GHz band, 6 GHz band, etc.) in which the STA operates. The multiple links used for ML communication may be configured in various ways. For example, multiple links supported by one STA for ML communication may belong to the same frequency band or different frequency bands. Furthermore, each link may correspond to a frequency unit of a predetermined size (e.g., a channel, a subchannel, an RU, etc.). Furthermore, some or all of the multiple links may correspond to frequency units of the same size or different sizes.

[0119] When one STA supports multiple links, the transceiver supporting each link may operate as one logical STA. That is, an MLD is a logical entity, has one or more affiliated STAs, and refers to a device having a single MAC Service Access Point (SAP) for one MAC data service and logical link control (LLC). Non-AP MLD refers to an MLD in which each STA belonging to the MLD is a non-AP STA. Multi-radio non-AP MLD refers to a non-AP MLD that supports frame reception or exchange on one or more links at a time. AP MLD refers to an MLD in which each STA belonging to the MLD is an AP STA.

[0120] Multi-link operation (MLO) enables non-AP MLD to discover, authenticate, associate, and set up multiple links with AP MLD. Based on the supported capabilities exchanged during the association procedure, each link can enable channel access and frame exchange between the non-AP MLD and AP MLD. STAs affiliated with an MLD can select and manage their own capabilities and operating parameters independently of other STAs belonging to the same MLD.

[0121] During the multilink setup process, the AP MLD and / or non-AP MLD can transmit and receive link-related information that the MLD supports. The link-related information may include one or more of the following: whether the MLD supports simultaneous transmit and receive (STR) operation or non-simultaneous transmit and receive (NSTR) operation on multiple links; information on the number / upper limit of UL / DL links; information on the location / bandwidth / resources of UL / DL links; information on frame types (e.g., management, control, data, etc.) available or preferred on at least one UL / DL link; information on ACK policies available or preferred on at least one UL / DL link; or information on traffic identifiers (TIDs) available on at least one UL / DL link.

[0122] AP MLD (e.g., NSTR mobile AP MLD) can configure one link among multiple links as the primary link. AP MLD can transmit beacon frames, probe response frames, and group-addressed data frames only on the primary link. The remaining links among multiple links can be configured as non-primary links. AP MLD operating on a non-primary link can also operate not to transmit beacon frames or probe response frames. Non-AP MLD can also only exchange frames during authentication, (re)association, and four-way handshaking on the primary link.

[0123] A setup link is defined as enabled (enabled, available, available, available, eligible, available) if at least one TID (traffic identifier) ​​is mapped to the link during the multilink setup process, and may be defined as deactivated (disabled, unavailable, incapable, unavailable, unavailable, eligible, available, available) if no TID is mapped to the link. A TID must always be mapped to one or more setup links unless admission control is used. Essentially, since a TID is mapped to all setup links, all setup links may be activated.

[0124] When a link is activated, it may be used for frame exchange depending on the power state of the non-AP STAs operating on that link. Only MSDUs or A-MSDUs with a TID mapped to the activated link may be transmitted on that link. Management and control frames may only be transmitted on the activated link.

[0125] When a link is deactivated, it may not be used for frame exchange, including management frames for both DL and UL.

[0126] In the multi-link setup process, activation / deactivation of each link can be instructed by TID-to-Link mapping. TID-to-Link mapping may be performed in a default mapping mode or / and a negotiation mapping mode.

[0127] One of the STAs belonging to the MLD can provide information about one or more links other than the link on which it is located for multi-link discovery (e.g., obtaining information about multiple links including the link on one link) or multi-link setup (e.g., associating simultaneously on multiple links by exchanging association request / response frames on one link). To provide such information, a multi-link (ML) element may be defined.

[0128] FIG. 8 illustrates an example of the structure of an ML element to which the present disclosure can be applied.

[0129] In an ML element, the element ID field and element ID extension field may have specific values ​​(e.g., 255 and 107) that indicate that it is an ML element, and the length field may have a value that indicates the length (e.g., in octets) of the remaining fields excluding the element ID field and length field.

[0130] The multi-link control field is defined as having a size of two octets and may include a 3-bit type subfield, a 1-bit reserved bit, and a 12-bit presence bitmap subfield. The type subfield may have a value indicating one of types such as basic, probe request, reconfiguration, tunneled direct-link setup (TDLS), and priority access. The presence bitmap subfield indicates the presence or absence of various subfields in the common info field and may be defined as different formats depending on the various variants (or types) of the ML element.

[0131] The common info field is defined as being of variable size and may include a 6-octet MLD MAC address subfield, which may have a value that identifies the MAC address of the MLD to which the STA transmitting the basic ML element belongs. Other subfields that may or may not be included in the common info field include a link ID info subfield, a BSS parameter change count subfield, a medium synchronization delay information subfield, an enhanced multi-link (EML) capability subfield, and an MLD capability subfield.

[0132] The link info field may be defined as a variable size, may contain link-specific information, and may be optionally present. If the link info field is present, it may contain one or more subelements. The format and order of the subelements may be variously defined. As an example of optional subelement IDs for a basic variant ML element, the subelement ID value 0 corresponds to the name of a per-STA profile and is extensible, the value 221 corresponds to a vendor-specific name and whether it can be extended may be determined by the vendor, and the remaining values ​​1 to 220 and 222 to 255 may be reserved.

[0133] The per-STA profile sub-element may include a 1-octet subelement ID sub-field, a 1-octet length sub-field, a 2-octet STA control sub-field, a variable-sized STA info sub-field, and a variable-sized STA profile sub-field. The STA control sub-field may include information such as a link ID, whether a complete profile is included, and whether a STA MAC address is present. The STA info sub-field may include information such as the STA MAC address. The STA profile sub-field may include information included in a probe response or probe request frame body, or information included in a (re)association response or (re)association request frame body, depending on whether the reported STA is an AP STA or a non-AP STA.

[0134] The format of the ML element in Figure 8 is exemplary, and the order, names, sizes, etc. of the fields / subfields may be changed, additional fields / subfields may be further defined, or some fields / subfields may be excluded. In short, the common information field may contain information common among STAs in the MLD, and the link information field may contain specific information about each STA / link (e.g., in a per-STA profile subelement containing the link ID corresponding to that STA).

[0135] FIG. 9 is a diagram illustrating an example of a high-level structure for AP MLD to which the present disclosure can be applied.

[0136] An AP MLD may include one or more APs. One AP MLD may have a high-level architecture as shown in FIG. 9. For example, the MLD may use the upper MAC sublayer to control various procedures / parameters that apply commonly to multiple APs. For example, authentication, association, sequence number (SN) / packet number (PN) assignment, power-saving buffering for individually addressed frames, etc. may be commonly controlled among APs belonging to one AP MLD.

[0137] Each serving AP (e.g., AP1, ..., AP n) can provide upper MAC sublayer functionality for non-MLD data frames (e.g., traffic to and from non-MLD STAs, group-addressed MLD traffic, etc.). AP MLD can provide upper MAC sublayer functionality for MLD data frames (e.g., traffic to and from MLD STAs) and provide MLD data to the lower MAC sublayer of each serving AP. Each serving AP can provide PHY functionality (e.g., PHY1, ..., PHY n). Both ML operation (MLO) and non-MLO may be performed on the links (e.g., Link 1, ..., Link n) corresponding to each PHY.

[0138] MLD-based roaming

[0139] Before describing MLD-based roaming according to the present disclosure, a procedure (for example, BSS transition) in which a non-AP STA moves or roams from one AP to another in an existing wireless LAN system will be described.

[0140] FIG. 10 is a diagram for explaining BSS transition in an existing wireless LAN system.

[0141] In the fast BSS transition (FT) method, which is a representative example of BSS transition (or roaming), various processes such as authentication request / response and re-association request / response are required between the FT originator (FTO) and the target FTR in order to move from a current FT responder (FTR) to a target FTR. That is, in the existing BSS transition method, a reassociation process is required on the same mobility domain.

[0142] 10, various operational parameters such as agreements related to BA (BlockAck) or SCS (Service Classification Service), SN, and EDCAF (EDCA function) parameters are reset. Therefore, the FTO must exchange a large number of frames for FT and must re-agree / configure with a new FTR. Therefore, the FT process is complex and requires high overhead, and data loss may occur during the FT process. As such, it is difficult for existing WLAN systems to provide seamless roaming to STAs.

[0143] This disclosure describes an example for MLD-based seamless roaming. For example, based on the AP MLD functionality described with reference to FIG. 9, when a non-AP STA moves / roams between entities belonging to one MLD, MLD-level parameters / configurations / agreements may be maintained without being reset.

[0144] In the following description, the roaming STA is referred to as RSTA, the currently associated AP is referred to as OAP (old AP) or first AP (or AP1), and the newly associated AP is referred to as NAP (new AP) or second AP (or AP2). Also, the newly proposed MLD-based roaming in this disclosure can be simply referred to as MLD roaming.

[0145] Furthermore, the RSTA, OAP, and NAP may be STAs that belong to different MLDs.

[0146] For example, an RSTA is a non-AP STA that belongs to a non-AP MLD and can also perform MLD roaming simultaneously / together with one or more other non-AP STAs.

[0147] For example, an OAP may be an AP STA that belongs to AP MLD 1, and AP MLD 1 may include APs other than the OAP.

[0148] For example, a NAP may be an AP STA that belongs to AP MLD 2, and AP MLD 2 may include other APs other than the NAP.

[0149] For example, the OAP and the NAP may belong to the same upper MLD (or roaming MLD or AP MLD 0). For example, AP MLD 1 to which the OAP belongs may belong to an upper MLD (e.g., AP MLD 0), and AP MLD 2 to which the NAP belongs may belong to the same upper MLD (e.g., AP MLD 0). Alternatively, among the APs belonging to AP MLD 1, one or more APs including the OAP may belong to an upper MLD (e.g., AP MLD 0), while the other APs may not belong to the same upper MLD (e.g., AP MLD 0), may belong to another upper MLD, or may not belong to any upper MLD. Similarly, among the APs belonging to AP MLD 2, one or more APs including the NAP may belong to an upper MLD (e.g., AP MLD 0), while the other APs may not belong to the same upper MLD (e.g., AP MLD 0), may belong to another upper MLD, or may not belong to any upper MLD.

[0150] Also, considering non-AP MLD, one or more OAPs belonging to AP MLD 1 may belong to a higher MLD, and one or more NAPs belonging to AP MLD 2 may belong to the same higher MLD. For example, MLD-based roaming may be performed from multiple OAPs to multiple NAPs.

[0151] The following describes in detail the procedure for performing MLD-based roaming of a STA.

[0152] 11 is a diagram illustrating an example of a method for performing MLD-based roaming by a first STA according to the present disclosure. In FIG. 11 and FIG. 12, the first STA may belong to a non-AP MLD. The first STA may associate with a first AP belonging to a first (AP) group to transmit and receive data.

[0153] The first STA may send a first (MLD) roaming request frame to the first AP included in the first group, the first (MLD) roaming request frame including a link identifier of the second AP and a group ID associated with the second group to which the second AP belongs (S1110).

[0154] Before step S1110, the first STA may receive announcement information from the first AP. Here, the announcement information may be included in an MLD-based roaming element or a reduced neighbor report (RNR) element included in the management frame. The MLD-based roaming element or the RNR element may include a subfield associated with at least one group ID and / or information related to whether addition of at least one link to the first STA is supported.

[0155] Also, before step S1110, the first STA may receive a beacon frame from the first AP, the beacon frame including a second TIM field indicating whether there is second DL data to be transmitted from the first AP to the first STA.

[0156] The first STA can request the first AP to roam from the first AP to the second AP using a first roaming request frame including a link identifier of the second AP and a group ID associated with the second group to which the second AP belongs.

[0157] For example, the first group and the second group may belong to the same AP MLD. To roam from a first AP included in the first group to a second AP included in the second group, a first STA may transmit a first request frame to the first AP.

[0158] As yet another example of the present disclosure, the first group and the second group may be mapped to separate AP MLDs. For example, the first group may be mapped to the first AP MLD, and the second group may be mapped to the second AP MLD. That is, in the description of the present disclosure, each group may be expressed as a separate AP MLD. The first AP MLD and the second AP MLD may belong to separate group entities (or overall AP MLDs). The group entities (or overall AP MLDs) may collectively refer to specific entities to which each AP MLD belongs.

[0159] The group entity may correspond to the (overall) AP MLD shown in Figures 9, 13, and 18. As an example, the group entity may perform the function of the upper MAC sublayer of the MLD described with reference to Figure 9.

[0160] The first STA may receive a first roaming response frame from the first AP, the first roaming response frame including a first traffic indication map field associated with the second AP (S1120).

[0161] Specifically, the first roaming response frame may include information indicating acceptance of roaming of the first STA to the second AP, information related to the second AP (e.g., a group ID associated with the second group to which the second AP belongs), roaming timer (i.e., MLD roaming timer) information associated with the time when the first DL data can be received from the second AP, and / or a first TIM field associated with the second AP (e.g., information indicating whether there is first DL data to be transmitted from the second AP to the first STA).

[0162] The information indicating acceptance of roaming of the first STA to the second AP and the first TIM field may be included in the common information field of the first roaming response frame (e.g., the basic ML element of the first roaming response frame) or the link information field (e.g., the profile subelement for each STA corresponding to the first STA included in the link information field of the first roaming response frame).

[0163] Based on the transmission of the first roaming response frame to the first STA, a link between the first STA and the second AP may be added. That is, while the link between the first STA and the first AP is connected, the link between the first STA and the second AP may be connected. Then, the first STA can exchange frames through the link connected to the first AP or the link connected to the second AP.

[0164] For example, the first STA may exchange frames through a link connected to the second AP. Specifically, the frame exchange may be performed after the first STA performs a link switch operation from the first AP to the second AP. Here, the link switch operation from the first STA to the second AP may include an operation of changing the link between the first STA and the first AP to a disabled state and the link between the first STA and the second AP to an enabled state.

[0165] That is, while the link between the first STA and the first AP is connected, the link between the first STA and the second AP may be connected. Then, when the link between the first STA and the first AP is deactivated and the link between the first STA and the second AP is activated, data frames may be exchanged between the first STA and the second AP through the activated link.

[0166] The first STA can receive the first DL data from the second AP based on the first TIM field (S1130).

[0167] As an example of the present disclosure, based on the first TIM field indicating the presence of first DL data (to be transmitted from the second AP to the first STA), the first STA may receive a power saving (PS)-poll frame for transmitting the first DL data from the second AP. However, this is only one example, and the first STA may receive the first DL data from the second AP without transmitting a PS-poll frame. At this time, the first STA may be in a state where the links between the first AP and the second AP are connected.

[0168] Based on the first DL data transmitted from the second AP to the first STA, the first STA may transmit a second roaming request frame to the second AP requesting deletion of the link connection between the first AP and the first STA. The first STA may receive a second roaming response frame from the second AP acknowledging the deletion of the link between the first AP and the first STA. This may complete the roaming procedure of the first STA from the first AP to the second AP.

[0169] The method performed by the first STA illustrated in FIG. 11 may be performed by the first device 100 of FIG. 1. For example, one or more processors 102 of the first device 100 of FIG. 1 may transmit a first roaming request frame, including a link identifier of the second AP and a group ID associated with the second group to which the second AP belongs, to a first AP included in a first group via one or more transceivers 106. The one or more processors 102 may receive a first roaming response frame, including a first TIM field associated with the second AP, from the first AP via one or more transceivers 106. The one or more processors 102 may receive first DL data from the second AP via one or more transceivers 106 based on the first TIM field.

[0170] The memory 104 may store instructions that, when executed by one or more processors 102, perform the method described in the example of FIG.

[0171] FIG. 12 is a diagram illustrating an example of a method for performing MLD-based roaming by a first AP according to the present disclosure.

[0172] The first AP belonging to the first group may receive a first roaming request frame from the first STA, the first roaming request frame including a link identifier of the second AP and a group ID associated with the second group to which the second AP belongs (S1210).

[0173] Before step S1210, the first AP may transmit, to the first STA, public information including at least one group ID, information related to whether addition of at least one link to the first STA is supported, etc. The first AP may check the roaming request information of the first STA through the first roaming request frame.

[0174] The first AP may transmit a first roaming response frame including a first TIM field associated with the second AP to the first STA (S1220).

[0175] Specifically, the first AP may transmit to the first STA a first roaming response frame including information about the second AP and a first TIM field indicating whether there is first data to be transmitted from the second AP to the first STA, thereby further strengthening the link between the first STA and the second AP, and allowing the first STA to receive first DL data from the second AP based on the first TIM field.

[0176] The method performed by the first AP illustrated in the example of Fig. 12 may be performed by the second device 200 of Fig. 1. For example, the one or more processors 202 of the second device 200 of Fig. 10 may receive a first roaming request frame from the first STA via the one or more transceivers 206, the first roaming request frame including a link identifier of the second AP and a group ID associated with a second group to which the second AP belongs. The one or more processors 202 may transmit a first roaming response frame including a first TIM field associated with the second AP to the first STA via the one or more transceivers 206.

[0177] It should be noted that the one or more memories 204 of the second device 200 may store instructions for performing the method described in the example of FIG. 12 when executed by the one or more processors 202.

[0178] 11 and 12 may correspond to some of various examples of the present disclosure. Various examples of the present disclosure, including the examples of Fig. 11 and 12, will be described in more detail below.

[0179] Example 1

[0180] A first embodiment relates to exemplary operations of a STA and an AP for MLD-based roaming. As an example of the present disclosure, Fig. 13 is a diagram for explaining an example of the structure and procedure of MLD-based roaming according to the present disclosure.

[0181] 13, AP1, AP2, and AP3 may belong to AP group 1, and AP4 and AP5 may belong to AP group 2. Each AP group does not have to be collocated, and APs belonging to each AP group may be collocated in the same or similar locations. The term "collocated" refers not only to APs belonging to the exact same device, but also to APs located in logically similar locations even if they do not belong to the exact same device.

[0182] Since the AP MLD is a logical entity, it may be implemented as a specific physical device, but it refers to an MLD that covers affiliated APs regardless of their location and executes / applies MLO. That is, all APs that belong to an AP group may include the affiliated AP of one AP MLD.

[0183] As an example of the present disclosure, assume that a non-AP MLD is set up in multilink with an AP MLD, and STA1 and STA2 are respectively associated with AP2 and AP3 included in AP group 1, as shown in FIG. 13. When the non-AP MLD moves to an area where AP group 2 exists, roaming from AP group 1 to AP group 2 may be necessary. That is, STA1 may be associated with AP4, and STA2 may be associated with AP5, due to the roaming. In this case, STA1 and STA2 may temporarily associate with AP4 and AP5, respectively, so that AP4 and AP5 can transmit frames to STA1 and STA2 during the roaming process.

[0184] Here, a non-AP MLD may include multiple associated STAs or may include only one STA. The roaming operation / architecture shown in Figure 13 may be applied to a non-AP MLD including one or more associated STAs, and the roaming operation / architecture may also be applied to non-AP STAs that are not part of an MLD.

[0185] In the description of the present disclosure, roaming may apply not only to movement between groups but also to movement between APs within a specific AP group. Furthermore, MLD-based roaming according to the present disclosure may be performed by changing a link while maintaining an existing ML setup, without tearing down the existing ML setup. For example, while maintaining the ML setup for the upper MLD of AP1 and AP2, a STA MLD can move from AP group 1 to AP group 2 by changing a link within the upper MLD. This may result in lower overhead and a reduced risk of data loss compared to existing BSS transition.

[0186] The MLD-based roaming procedure may include AP group ID setting (Example 1-1), AP announcement (Example 1-2), and frame exchange between the AP and the STA (request in Example 1-3 and response in Example 1-4).

[0187] An ID may be assigned / configured for each AP group (composed of co-located APs). In the description of the present disclosure, the ID assigned / configured for each AP group is referred to as a group ID. As an example, the group ID may be configured as a unique ID within a single AP group. As another example, the group ID may be configured as a unique ID for each AP group within the overall AP MLD.

[0188] The notice may correspond to a procedure in which each AP belonging to the upper MLD notifies the STA of information such as whether it supports MLD-based roaming. Frame exchange between the STA and the AP may be performed based on this notice information.

[0189] Frame exchange may correspond to a procedure for transmitting and receiving frames that trigger / initiate MLD-based roaming between an AP and a STA. Through frame exchange, the AP and the STA negotiate information and settings required for MLD-based roaming, and MLD-based roaming can be completed based on the negotiated information / settings. As a result, the STA no longer operates with the OAP (old AP) (e.g., an AP included in AP group 1) but operates with the NAP (new AP) (e.g., an AP included in AP group 2).

[0190] Thus, in order for MLD-based roaming to be triggered / initiated, frame exchange between the STA and the AP is required. The exchanged frames may correspond to management frames (e.g., beacons, (re)association requests / responses, probe requests / responses, action frames, etc.). For example, an action frame, which is a type of management frame, may be used for frame exchange.

[0191] In the examples described below, a frame that a STA (or AP) sends to an AP (or STA) to request MLD roaming is called an MLD roaming request frame, and a frame that an AP (or STA) sends to a STA (or AP) to respond to the MLD roaming request frame is called an MLD roaming response frame.

[0192] Below, specific examples of a procedure for setting a group ID for each AP group, a procedure for requesting information about APs in each AP group, a known procedure for MLD-based roaming, and a frame exchange procedure will be described.

[0193] Furthermore, each of one or more STAs belonging to one non-AP MLD can set up multiple links using one radio resource, i.e., one STA can add or delete a link, thereby allowing two or more links to be connected to the STA.

[0194] However, while frames are exchanged over one link, frame exchange may not occur over the other links, and the other links may be in a doze state or a disabled state. To this end, non-AP MLD may transmit capabilities related to ML setup (e.g., capabilities indicating whether to support simultaneous association of multiple links) using an association request frame or the like during ML setup. For example, non-AP MLD may transmit capabilities related to ML setup using a management frame including a basic multilink element, which will be described later.

[0195] If all STAs have the capability related to the ML setup, the capability related to the ML setup may be indicated by an MLD capability and operation subfield included in the common information field of the basic multilink element. If only a specific STA has the capability related to the ML setup, the capability related to the ML setup may be indicated by a link information field corresponding to the specific STA (e.g., a per-STA profile subelement corresponding to the specific STA).

[0196] The capability information indicating that at least one STA belonging to one non-AP MLD can be set up to multiple links using one radio resource may be indicated by a single-radio ML setup enabled subfield, which may indicate that at least one STA can be connected to two or more links.

[0197] Example 1-1

[0198] Example 1-1 relates to a procedure for setting a group ID for each AP group. A moving MLD (or STA) may need to recognize the AP to roam to among at least one AP in the AP MLD to which it is connected. Also, when the MLD (or STA) requests roaming, the AP MLD can check data and management information to be transmitted from the OAP to the NAP depending on which NAP the MLD (or STA) moves to. Therefore, in Example 1-1, an identification method that takes into account belonging APs that are not co-located in the AP MLD (i.e., a method for setting an ID for roaming in the AP MLD) will be described.

[0199] An ID (i.e., group ID) may be assigned to a collocated AP group. For example, a unique group ID may be assigned within one AP group (Example 1-1-1). For another example, a unique ID may be assigned to each AP group within the overall AP MLD (Example 1-1-2).

[0200] Example 1-1-1

[0201] Example 1-1-1 relates to a method for setting a unique ID within an AP group in AP MLD, that is, the group ID may be unique within one AP group.

[0202] As an example of the present disclosure, the group ID may be set to an integer equal to or greater than 0. As one example, if the field indicating the group ID is configured with 4 bits, the group ID may be set to any one of 0 to 15. As yet another example, if the field indicating the group ID is configured with 8 bits, the group ID may be set to any one of 0 to 127.

[0203] For example, if the group ID is 0, APs having this group ID may belong to the same AP group located at the same location. That is, the MLD (or STA) can determine that APs having this group ID are located at the same location. Other group IDs may be mapped so that each group can be uniquely identified.

[0204] Additionally, other APs in the multiple BSSID set (e.g., transmitted BSSID (i.e., TxBSSID) or non-transmitted BSSID (nonTxBSSID)) to which each AP in the AP group belongs may also be assigned the same group ID since they use the same physical resources, although the AP MLD IDs of the AP MLDs to which they belong may be different.

[0205] Example 1-1-2

[0206] Example 1-1-2 relates to a method for setting a unique ID in an AP MLD, that is, a group ID may be set uniquely for each AP group in the entire AP MLD.

[0207] As described above, the group ID may be set to an integer equal to or greater than 0. As one example, if the field indicating the group ID is configured with 4 bits, the group ID may be set to any one of 0 to 15. As yet another example, if the field indicating the group ID is configured with 8 bits, the group ID may be set to any one of 0 to 127.

[0208] Additionally, a group ID of APs performing roaming may be set, i.e., an MLD roaming ID for MLD roaming may be set between APs having the group ID.

[0209] The existing MDID (mobility domain ID) field may be used to set the MLD roaming ID and / or group ID, but while the MDID field has a size of 2 octets, the MLD roaming ID and / or group ID may be set in a smaller field.

[0210] Example 1-2

[0211] Examples 1-2 relate to known procedures for MLD-based roaming based on group IDs.

[0212] Each AP included in the AP MLD may publicly announce whether MLD-based roaming described in the present disclosure is possible and its group ID. For example, each AP may transmit public information including information indicating whether roaming is possible (e.g., "MLD roaming enabled"), a group ID, an MLD roaming ID, and / or temporary link addition / deletion information. The information indicating whether roaming is possible may be configured as, but is not limited to, one bit. And, as described above, the group ID refers to the group ID of the AP group that constitutes the AP MLD. That is, APs having the same group ID may belong to the same AP group.

[0213] The public information may be transmitted in a management frame (e.g., a beacon frame, a probe frame, a (re)association response frame, etc.) As an example, the public information may be included in an included MLD roaming information element (IE) or a reduced neighbor report (RNR) IE.

[0214] For example, the RNR IE may include a target beacon transmission time (TBTT) information header, an operation class, a channel number, and a TBTT information set field. Among these, the TBTT information set may include one or more TBTT information fields. As shown in FIG. 14(a), the TBTT information field may include subfields for neighbor AP TBTT offset, BSSID, short BSSID, BSS parameters, 20 MHz PSD (Power Spectral Density), and MLD parameters. The MLD parameters may include AP MLD ID, link ID, BSS parameter change count, all update inclusion, and disabled link indication fields, as well as an MLD roaming enabled subfield corresponding to public information.

[0215] Furthermore, the TBTT information field may include MLD roaming parameters, which may include publicly known information (i.e., MLD roaming enabled information, group ID information, MLD roaming ID, and temporary link addition information, etc.). The example in Figure 14(a) corresponds to a case where the size of the MLD parameters subfield is insufficient to include the publicly known information. The size of the MLD parameters subfield may be changed, but this may cause decoding problems for IEEE 802.11be-based STAs.

[0216] In this case, since the fact that the MLD roaming parameters are included in the TBTT information field itself can mean that MLD roaming is possible, the MLD roaming enabled information may be omitted.

[0217] The subfield indicating temporary link addition information shown in (a) of Figure 14 may indicate whether a link can be temporarily added or removed for one STA. That is, the subfield indicating temporary link addition information may indicate whether one STA is supported to have two or more links for a certain period of time. As an example, the subfield indicating temporary link addition information may be configured with one bit, but is not limited to this.

[0218] As yet another example, as shown in Figure 14(b), the MLD roaming enabled information may be included in the MLD parameters subfield, and the MLD roaming ID and / or group ID may be sent in the MLD roaming parameters subfield or in a separate field.

[0219] Additionally or alternatively, the above-mentioned public information may be included in a basic multi-link IE.

[0220] Examples 1-3

[0221] Request information for triggering / starting MLD-based roaming may be included in a management frame (e.g., an MLD roaming request frame). For example, the MLD roaming request frame may have the exemplary format of Table 1. The format of Table 1 is exemplary, and some fields may be omitted, or fields not illustrated may be included.

[0222] [Table 1]

[0223] The category in order 1 may be set to a value indicating a category corresponding to the MLD roaming request frame. For example, the category may correspond to a new UHR action or a protected UHR action. This is exemplary, and the MLD roaming request frame may be defined as a category with a different name. The UHR action or protected UHR action in order 2 may be set to a value corresponding to the MLD roaming request.

[0224] The dialogue token in order 3 may be set to a value to match requests and responses.

[0225] The reconfiguration ML element in step 4 corresponds to an element containing information required for an MLD-based roaming request. This is an example, and elements / fields with other names containing information required for an MLD roaming request may be defined and used.

[0226] FIG. 15 is a diagram illustrating an example of a reset ML element including request information according to the present disclosure.

[0227] FIG. 15(a) shows an example of a presence bitmap field (e.g., the Presence Bitmap in the Multi-Link Control field of FIG. 8). The presence bitmap of a reconfigured ML element may include information regarding the presence or absence of an MLD MAC address subfield. In addition, the presence bitmap according to the present disclosure can indicate, at specific bit positions in the bitmap, whether an enhanced ML (EML) capability subfield is present in the common information field and whether an MLD capability and operation subfield is present in the common information field.

[0228] 15(b) shows an example of a common information field (e.g., the Common Info field of FIG. 8). The common information field of the Reconfigure ML element may include a common information length subfield and an MLD MAC address subfield. Additionally, the common information field of the present disclosure may include an EML capabilities subfield or both an MLD capabilities and operations subfield (depending on the value of the corresponding bit position in the presence bitmap).

[0229] When one or more STAs (especially in the case of non-AP MLD) moving to a NAP simultaneously perform MLD-based roaming, the EML capability information / MLD capability and operation information may change, and this information can be provided to the AP as MLD roaming request information.

[0230] Figure 15(c) shows an example of an STA control (e.g., STA Control in Figure 8) field included in the profile sub-element for each STA of the link information field (e.g., Link Info field in Figure 8) of the reconfiguration ML element. Figure 15(d) shows an example of an STA information (e.g., STA Info in Figure 8) field included in the profile sub-element for each STA of the link information field (e.g., Link Info field in Figure 8) of the reconfiguration ML element.

[0231] When one or more STAs simultaneously perform MLD-based roaming, one or more profile sub-elements for each STA may be included in the MLD roaming request frame.

[0232] The presence or absence of each subfield included in the STA information field may be indicated by the present subfield of that subfield in the STA control field. For example, the NSTR indication bitmap present subfield of the STA control field may indicate whether the NSTR indication bitmap subfield is present in the STA information field, and if present, the bitmap size may be indicated by the NSTR bitmap size subfield of the STA control field. For example, the MLD roaming timer present subfield of the STA control field may indicate whether the MLD roaming timer subfield is present in the STA information field.

[0233] 15(c) may be set to a link identifier value corresponding to one of the NAPs (e.g., AP2 belonging to AP MLD 2 and, if present, other APs belonging to AP MLD 2). For example, the Link ID subfield of the STA Control field of the profile sub-element for the first per STA may be set to a link identifier value corresponding to AP2 belonging to AP MLD 2, and the Link ID subfield of the STA Control field of the profile sub-element for the second per STA may be set to a link identifier value corresponding to another NAP belonging to AP MLD 2.

[0234] The complete profile in the STA control field in (c) of Figure 15 may correspond to the complete information of the STA (i.e., all information included in the (re)association request frame). In the MLD-based roaming process, a new STA does not associate with an AP belonging to a higher MLD, but an existing STA moves between APs belonging to the higher MLD, so it is possible to consider a case where the capabilities and operation parameters of the STA do not change. Considering the case where the higher MLD knows the information of the STA, the complete profile subfield in (c) of Figure 15 may be set to a value indicating that changed profile information (or partial profile information) is included.

[0235] For example, a partial profile corresponds to a case where the value of the Complete Profile subfield of the STA Control field is 0, and the STA Profile field (e.g., the STA Profile field in FIG. 8) in the Profile subelement for each STA may include only the changed information fields / elements (i.e., information that changes compared to the OAP when moving to a NAP). Alternatively, the Complete Profile subfield of the STA Control field may be renamed the Changed Profile subfield, and when the value of this subfield is 1, the STA Profile field may include only the changed information fields / elements (i.e., information that changes compared to the OAP when moving to a NAP).

[0236] Alternatively, a case where the capabilities and operation parameters of the STA are changed entirely during the MLD-based roaming process can also be considered. In this case, the value of the Complete Profile subfield in (c) of Figure 15 may be set to 1, and the STA Profile field may contain complete information (e.g., all information contained in the (re)association request frame).

[0237] When a STA moves to another AP, information regarding the STR or NSTR for each link may change from a non-AP MLD perspective, so an NSTR indication bitmap (e.g., the NSTR indication bitmap subfield in (d) of Figure 15) may be included in the MLD roaming request frame.

[0238] The MLD roaming timer subfield may include information about a roaming timer that indicates the expected / required time for the STA to switch from the currently connected AP to the roaming AP. The MLD roaming timer may be associated with the TIM (traffic indication map) field, which will be described later.

[0239] Additionally or alternatively, the MLD roaming timer information may include a value for each of one or more NAPs, or may include a value that applies commonly to one or more NAPs. For example, individual MLD roaming timer information corresponding to the number of NAPs may be included in the per-STA profile sub-element of the MLD roaming request frame. For example, one piece of MLD roaming timer information common to one or more NAPs may be included in the common information field of the MLD roaming request frame.

[0240] When the MLD roaming timer is commonly applied to all APs, information about the MLD roaming timer may be included in the common information field, and the existence or non-existence of the MLD roaming timer may be indicated in the common information field using a presence bitmap.

[0241] The group ID may be added to the reconfiguration ML element shown in Fig. 15. The group ID refers to the ID of the AP group to which the AP to which the non-AP MLD (or STA) roams belongs.

[0242] Example 1-3-1

[0243] As an example of the present disclosure, the group ID may be included in the common information field of the reconfiguration ML element. Specifically, as shown in (a) of Figure 16, a presence bitmap of the reconfiguration ML element may indicate whether the group ID is included in the common information field of the reconfiguration ML element. As shown in (b) of Figure 16, if the group ID is included only in the common information field, a MLD roaming request frame may request roaming to an AP in an AP group with the same group ID.

[0244] That is, when a group ID is included in the common information field, a non-AP MLD (or a STA) cannot request roaming to multiple group IDs even within the same AP MLD. For example, when a group ID of a specific AP group is included in the common information field, a non-AP MLD (or a STA) cannot request roaming to an AP of the AP group to which it currently belongs or an AP belonging to an AP group other than the specific AP group. However, when roaming between groups, the method according to Example 1-3-1 can reduce overhead compared to when a group ID is included in the link information field.

[0245] Additionally, the common information field of the Reconfiguration ML element is a field for including the function of temporarily adding / removing links for MLD-based roaming, and may include a type subfield.

[0246] As an example of the present disclosure, the type subfield may be configured with 2 bits, but is not limited to this. For example, when the type subfield is configured with 2 bits, the type field may be configured as shown in Table 2. However, this is just one example, and the type corresponding to the type subfield value may be defined as another type. Also, "temporary deletion" in Table 2 may be replaced with "deletion," which corresponds to a type subfield value of 1.

[0247] [Table 2]

[0248] When the Type subfield indicates "add," this may mean that a non-AP MLD STA requests an additional link connection with a specific AP MLD AP (e.g., NAP). When the Type subfield indicates "delete," this may mean that a non-AP MLD STA requests to disconnect its current link (e.g., disconnect its link with an OAP). When the Type subfield indicates "temporary addition," this may mean that a non-AP MLD STA requests to add a link with an AP (e.g., NAP) other than the AP (e.g., OAP) to which it is currently connected. As yet another example of the present disclosure, as shown in (b) of FIG. 16, the common information field (or MLD roaming request frame body) may include a temporary subfield and a type subfield as fields for including a function for temporarily adding / deleting a link for MLD-based roaming. As an example, each of the temporary subfield and the type subfield may be configured with 1 bit, and the type subfield may indicate "add" or "delete." The temporary subfield may indicate information indicating whether the "addition" or "deletion" in the type subfield is a temporary addition or a temporary deletion.

[0249] For example, if the Type subfield indicates "addition" and the Temporary subfield indicates information indicating that the operation indicated by the Type subfield is a temporary operation, this may correspond to "Temporary addition" in Table 2.

[0250] If the Type and / or Temporary subfields are included in the common information field, the STAs included in the non-AP MLD can only perform one operation for all APs. That is, if the Type and / or Temporary subfields indicate "add," the STAs can only request each AP to add a link.

[0251] Example 1-3-2

[0252] As an example of the present disclosure, as shown in (c) of Figure 16, the Reconfiguration ML element may include a Link Information field, and the Link Information field may include one or more Per-STA Profile sub-elements. As shown in (d) of Figure 16, a roaming request to a specific AP belonging to a specific AP group may be indicated by the Link ID and Group ID included in the STA Control field of the Per-STA Profile sub-element.

[0253] Additionally or alternatively, as shown in (d) of Figure 16, the STA control field may include a Type and / or Temporary subfield (i.e., the Type and / or Temporary subfield described in Example 1-3-1). That is, a Type and / or Temporary subfield for temporarily adding / deleting a link for MLD-based roaming may be included in the STA control field format (included in the Link Information field). The configuration and function of the Type and / or Temporary subfield have been described above, and a repeated description thereof will be omitted.

[0254] When the Type and / or Temporary subfields are included in the Link Information field, a STA included in a non-AP MLD can request different actions from each AP, i.e., the STA can request "temporary addition" from one AP and "deletion" from another AP, depending on the Type and / or Temporary subfields.

[0255] One or more per-STA profile sub-elements may request roaming to one or more APs corresponding to one or more group IDs. However, when roaming based on the same group ID is requested, the overhead may be larger than that of the method according to Example 1-3-1.

[0256] Example 1-3-3

[0257] As an example of the present disclosure, as shown in (a) of Figure 17, the STA control field of the profile sub-element for each STA includes a group ID existence sub-field, and the group ID existence sub-field can indicate whether an AP group ID to which an AP corresponding to a specific link ID belongs exists. And, as shown in (b) of Figure 17, the group ID can be included in the STA information field or the STA profile field.

[0258] One or more per-STA profile sub-elements may request roaming to one or more APs corresponding to one or more group IDs. In particular, assume that this is combined with the method according to Example 1-3-1 (i.e., the method in which the group ID is included in the common information field). In this case, if roaming is requested to APs corresponding to the same group ID, the group ID does not need to be included in the STA information field or STA profile field, which can reduce overhead.

[0259] As another example, if a group ID is indicated in the common information field, it may be implicitly indicated that roaming to an AP corresponding to the same group ID is requested. Therefore, the group ID may not be included in the STA information field or the STA profile field, and the Group ID presence field may not be present.

[0260] Examples 1-4

[0261] Response information to the MLD-based roaming request may be included in a management frame (e.g., an MLD roaming response frame). For example, the MLD roaming response frame may have the exemplary format shown in Table 3. The format of Table 3 is exemplary, and some fields may be omitted, or fields not shown may be included.

[0262] [Table 3]

[0263] The MLD roaming response frame may include link-level parameters. For example, the link-level parameters may include information necessary to change links while maintaining the MLD setup. The category in order 1 may be set to a value indicating the category that corresponds to the MLD roaming response frame. For example, the category may correspond to a new UHR action or a protected UHR action. This is exemplary, and the MLD roaming response frame may be defined as a category with other names.

[0264] The UHR action of order 2 or the protected UHR action may be set to a value corresponding to the MLD roaming response.

[0265] The dialogue token in order 3 may be set to a value to match requests and responses.

[0266] The status code in step 4 may be set to one of various values ​​indicating success, failure, accept, reject, unsupported, invalid, error, etc. Among the values ​​indicated by the status code, failure, reject, unsupported, invalid, error, etc. may be defined as different values ​​depending on the cause.

[0267] The basic ML element in order 5 may include information necessary for roaming related to the upper MLD (or roaming MLD) and the roaming target AP / AP MLD (e.g., NAP or AP MLD including NAP). To this end, some fields in the existing basic ML element format may be modified or omitted, or new fields may be added.

[0268] For example, the common information field of the basic ML element may have a format similar to the example of the common information field in Figure 8. Here, the common information field of the basic ML element of the MLD roaming response frame may include information that is common to or corresponds to the NAPs where one or more STAs perform MLD-based roaming.

[0269] For example, the link information field of the basic ML element may have a format similar to the example of the link information field in Fig. 8. Here, the link information field of the basic ML element of the MLD roaming response frame may include one or more per-STA profile sub-elements for the corresponding APs when one or more STAs simultaneously perform MLD-based roaming. Thus, the STA control field, STA information field, and / or STA profile field included in the per-STA profile sub-element in the link information field of the basic ML element of the MLD roaming response frame may have the following characteristics:

[0270] The Link ID subfield of the STA Control field may be set to the Link ID value corresponding to the NAP.

[0271] The complete profile in the STA control field may correspond to the complete information of the AP (i.e., all information included in the (re)association response frame). When a STA performs MLD-based roaming between APs belonging to the same upper MLD (or roaming MLD), it is possible to consider a case where the capabilities or operating parameters of the AP do not change. In this case, the complete profile subfield may be set to a value (e.g., 0) indicating that changed profile information (or partial profile information) is included. As a result, the STA profile field in the profile subelement for each STA may include only changed information fields / elements (i.e., information changed in the NAP compared to the OAP).

[0272] Alternatively, the case where the AP's capabilities and operating parameters are changed entirely during the MLD-based roaming process can also be considered. In this case, the value of the Complete Profile subfield may be set to 1, and the STA Profile field may contain complete information (e.g., all information contained in the (re)association response frame).

[0273] Also, since the (temporary) deletion is indicated by the type or / and temporary subfield of the MLD roaming request frame, the complete profile for the AP is already known, so the complete profile subfield value may be indicated as 0.

[0274] The STA control field may include a field indicating whether an MLD roaming timer exists. If the existence of an MLD roaming timer is indicated, the STA information field may include an MLD roaming timer subfield. The MLD roaming timer subfield may indicate the point in time when MLD-based roaming is completed and the STA no longer operates with the OAP but operates with the NAP. The value of the MLD roaming timer included in the MLD roaming response frame may be set based on / using the value of the MLD roaming timer included in the MLD roaming request frame (e.g., to a changed value if the requested timer value is changed). For example, if the value of the MLD roaming timer requested by the STA is used as is and the status code value is set to a value indicating success / acceptance, the MLD roaming timer subfield may not be included in the MLD roaming response frame.

[0275] Additionally or alternatively, the MLD roaming timer information may include a value for each of one or more NAPs, or may include a value that applies commonly to one or more NAPs. For example, individual MLD roaming timer information corresponding to the number of NAPs may be included in a per-STA profile sub-element of the MLD roaming response frame. For example, one common MLD roaming timer information for one or more NAPs may be included in the common information field of the MLD roaming response frame.

[0276] Additionally, the base ML element may contain a group ID.

[0277] As an example of the present disclosure, as shown in Example 1-3-1, a group ID may be included in the common information field of the basic ML element, and the presence bitmap subfield of the basic ML element may be used to indicate whether the group ID is present in the common information field, so that the MLD roaming response frame may include information about APs that belong to the same AP group and have the group ID indicated in the common information field.

[0278] As an example of the present disclosure, when an MLD roaming response frame including a group ID (i.e., when the group ID is included in the link information field) is transmitted, as in Example 1-3-2, the group ID may be included in the link information field of the basic ML element of the MLD roaming response frame.

[0279] Specifically, the link information field of the basic ML element may include one or more per-STA profile sub-elements, and the STA control field of each of the one or more per-STA profile sub-elements may include a link ID and a group ID (i.e., the ID of the AP group).

[0280] One or more per-STA profile sub-elements may provide information about one or more APs corresponding to one or more group IDs. However, providing information about APs with the same group ID may result in larger overhead than the method according to Example 1-3-1.

[0281] As yet another example of the present disclosure, the STA control field of each per-STA profile sub-element may include information indicating whether a group ID is present in each of one or more per-STA profile sub-elements (i.e., group ID presence information).

[0282] That is, the group ID presence information of the STA control field included in the per-STA profile sub-element may indicate whether the ID of the AP group (i.e., group ID) to which the AP corresponding to the link ID included in the STA control field belongs exists in the per-STA profile sub-element. In this case, the group ID may be included in the STA information field or the STA profile field of the per-STA profile sub-element.

[0283] One or more Per-STA Profile sub-elements may provide information about one or more APs that correspond to one or more Group IDs.

[0284] Additionally or alternatively, the method of Example 1-3-1 (i.e., the method in which the group ID is included in the common information field) may be combined with the method of Example 1-3-3 (i.e., the information indicating whether the group ID is present in the STA control field).When providing only information on APs corresponding to the same group ID, it is not necessary to include the group ID in the profile sub-element for each STA, thereby reducing overhead.

[0285] As an example of the present disclosure, as described in Example 1-1-1, when a unique ID is set within an AP group in AP MLD, the group ID may be omitted if the group ID is 0. In other words, when there is no group ID, an AP that receives an MLD roaming request frame can implicitly determine that the request frame is a request for information about other APs in the group to which it belongs.

[0286] As yet another example of the present disclosure, if a group ID is included in the common information field, the STA can implicitly determine that the information included in the MLD roaming response frame is information about an AP corresponding to the same group ID, and thus the group ID presence field does not need to be included in the MLD roaming response frame.

[0287] The group key information in step 6 may be set to a value indicating group key information for the NAP. The group key may be different for each link, so group key information for the NAP needs to be provided. For example, the field corresponding to the group key information may include a subfield indicating the length of the group key information subfield and a subfield set to the value of the group key information. The group key information may include an MLO group temporal key (GTK) key data encapsulation (KDE) format, an MLO integrity group temporal key (IGTK) KDE format, an MLO beacon integrity group temporal key (BIGTK) KDE format, etc., including the link identifier of the NAP.

[0288] The AID information in order 7 can manage the AID for each group. Since the total AID space is limited, the AID can be managed in the AP group. That is, when roaming to another group, a different AID may be assigned. However, when roaming to another group and the same AID is assigned, or when the AP MLD manages the total AID space as in the past, the AID information in order 7 may not exist.

[0289] The channel switching information information and extended channel switching information information in orders 8 and 9 may be omitted from the MLD roaming response frame if all APs with MLD-based roaming enabled operate on the same channel. If MLD-based roaming occurs on another channel, channel information may be provided by the (extended) channel switching information element. Additionally or alternatively, the (extended) channel switching information element may be included in the STA information / STA profile field of the basic ML element in order 5.

[0290] The TID-to-Link mapping information of Order 10 may be used to map TIDs to newly connected links using TID-to-Link mapping in advance. If TID-to-Link mapping is not performed separately, default mapping may be applied to newly connected links. When the default mapping mode is applied, all TIDs may be mapped to links set up for both DL and UL, and all set up links may be enabled.

[0291] Furthermore, the AP MLD can include the MLD roaming timer of the above-mentioned reconfiguration ML element in the MLD roaming response frame. That is, since the AP MLD can control the MLD-based roaming procedure, it can set / instruct the MLD roaming timer. For example, assume that the STA transmits an MLD roaming request frame that does not include an MLD roaming timer, or that the information on the MLD roaming timer transmitted by the STA is determined by the AP to be inappropriate. In this case, the AP MLD can transmit an MLD roaming response frame to the STA that includes information for setting the MLD roaming timer.

[0292] Here, the expiration of the MLD roaming timer means that the STA has completed MLD-based roaming and will no longer perform various operations with the OAP, but has reached the point where it can perform various operations with the NAP. As an example, assume that the STA has sent an MLD roaming request frame including a request to add a temporary link with the NAP. In this case, if the MLD roaming timer expires, the STA can disconnect from the OAP (i.e., link "deletion" or "temporary deletion") and connect to the NAP.

[0293] When the MLD roaming timer is commonly applied to all APs, information about the MLD roaming timer may be included in the common information field of the reconfiguration / basic ML element as shown in (b) of Figure 16. Then, information indicating whether the MLD roaming timer is present in the common information field may be included in the presence bitmap subfield of the reconfiguration / basic ML element.

[0294] Furthermore, the MLD roaming response frame may include information about the MLD roaming timer. To this end, the STA control field may include an MLD roaming timer present field, and the STA information field may include an MLD roaming timer field. The MLD roaming timer may indicate the time remaining until the STA can receive data from the roaming AP and is associated with the TIM field. The MLD roaming timer may be set based on the MLD roaming timer information sent by the STA.

[0295] MLD roaming procedure based on TIM information

[0296] As an example of the present disclosure, Figure 18 illustrates a procedure for performing MLD-based roaming. Assume that STA1, which belongs to a non-AP MLD, is currently associated with AP1 in AP group 1, and STA2, which belongs to a non-AP MLD, is currently associated with AP2 in AP group 1. In this case, STA1 and STA2 move from AP group 1 to AP group 2, so that STA1 can perform a roaming procedure to AP4 in AP group 1, and STA2 can perform a roaming procedure to AP5 in AP group 2.

[0297] For example, AP1 may exchange MLD roaming response / request frames with STA1, where the MLD roaming request frame may include a group ID associated with AP group 2 and a link ID corresponding to AP4, and the MLD roaming response frame may include a basic ML element including whether to accept MLD roaming and information about AP4.

[0298] AP2 can exchange MLD roaming response / request frames with STA2. At this time, the MLD roaming request frame may include a group ID associated with AP group 2 and a link ID corresponding to AP5, and the MLD roaming response frame may include a basic ML element including whether to accept MLD roaming and information about AP5.

[0299] After the above procedure is completed, STA1 may be temporarily connected to AP1 and AP4, and STA2 may be connected to AP2 and AP5. At this time, STA1 can exchange frames with either AP1 or AP4. That is, while STA1 is exchanging frames with AP1, it may not be able to exchange frames with AP4. In order for STA1 to completely roam from AP1 to AP4, the procedure shown in FIG. 19 may be performed.

[0300] 19, AP1 may use the TIM field in a beacon frame to indicate information regarding whether there is data to transmit to STA1. In this case, to roam from AP1 to AP4, STA1 may transmit to AP1 an MLD roaming request frame including information for adding a link connection with AP4. Although FIG. 19 only shows a procedure in which STA1 requests / executes roaming from AP1 to AP4, a procedure in which STA2 requests / executes roaming from AP2 to AP5 (e.g., a procedure in which STA2 requests addition of a link to AP5) may also be performed.

[0301] After confirming the MLD roaming request frame, AP1 can transmit an MLD roaming response frame to STA1, accepting the roaming procedure to AP4. However, STA1 may receive information from AP1's recent beacon frame that DL data is not buffered, or may be unable to receive the DL data from AP1 even if it is buffered. Therefore, AP1 can inform STA1 that AP4 or the AP MLD has DL data (e.g., DL data to be transmitted to STA1). As a result, when STA1 switches to AP4, it can transmit a power saving (PS)-poll frame to AP4 without waiting to receive a beacon frame from AP4. AP4 can then transmit DL data to STA1 in response to the PS-poll frame.

[0302] For the above procedure, a TIM field may be included in the MLD roaming response frame sent from AP1 to STA1. The TIM field may indicate that an AP (e.g., an AP to which STA1 has requested roaming) (e.g., AP4) or an AP MLD is currently buffering DL data for the requested STA. As an example, the TIM field may be configured with 1 bit, but is not limited thereto.

[0303] From the MLD level perspective, the AP MLD can indicate that it is buffering DL data for the requesting STA, and the TIM field can be included in the MLD roaming response frame body or common information field.

[0304] For example, from the AP's perspective, AP1 can indicate that AP4 has DL data before STA1 switches to AP4, and the TIM field may be included in the link information field.

[0305] Furthermore, a STA (eg, STA1) can use the MLD roaming timer in the MLD roaming response frame to set the time to switch to another AP (eg, AP4).

[0306] For example, if the time remaining for STA1 to receive DL data from a roaming AP (e.g., AP4) exceeds a predefined time before switching, STA1 can first receive DL data by transmitting a PS-Poll frame (if necessary) to the currently associated AP (e.g., AP1). Then, STA1 can perform a switching procedure to AP4. Here, STA1 performing a switching procedure to AP4 may mean that STA1 disables the existing link (i.e., the link between STA1 and AP1) and activates the link between STA1 and AP4.

[0307] As yet another example, if STA1 can switch to AP4 and directly receive DL data, STA1 can directly perform the switching procedure to AP4 and receive DL data from AP4.

[0308] The embodiments described above are combinations of the components and features of the present disclosure in a predetermined form. Each component or feature should be considered optional unless otherwise explicitly stated. Each component or feature may be implemented without being combined with other components or features. It is also possible to combine some components and / or features to form embodiments of the present disclosure. 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 clear that claims that do not have an explicit reference relationship in the claims may be combined to form embodiments, or may be included as new claims by amendment after filing.

[0309] It is obvious to those skilled in the art that the present disclosure can be embodied in other specific forms without departing from the essential features of the present disclosure. Therefore, the above detailed description should not be interpreted as limiting in any respect, but should be considered as illustrative. The scope of the present disclosure should be determined by reasonable interpretation of the appended claims, and any modifications within the equivalent scope of the present disclosure are included in the scope of the present disclosure.

[0310] The scope of the present disclosure includes software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that cause a device or computer to perform operations according to the methods of various embodiments, as well as non-transitory computer-readable media on which such software or instructions are stored and executable on a device or computer. Instructions usable for programming a processing system to perform features described in this disclosure may be stored on or in a storage medium or computer-readable storage medium, and computer program products including such storage media may be used to embody features described in this disclosure. 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. Memory optionally includes one or more storage devices located remotely from the processor. The memory, or alternatively, a non-volatile memory device within the memory, comprises a non-transitory computer-readable storage medium. The features described in this disclosure may be embodied in software and / or firmware stored on any one of a number of machine-readable media and capable of controlling the hardware of a processing system and allowing the processing system to interact with other mechanisms that utilize the results of embodiments of the present disclosure. Such software or firmware may include, but is not limited to, application code, device drivers, operating systems, and execution environments / containers.

[0311] [Industrial Applicability] The method proposed in this disclosure has been described mainly as being applied to an IEEE 802.11-based system, but it can also be applied to various wireless LANs or wireless communication systems other than the IEEE 802.11-based system.

[0312] [Claims at the time of international application] [Claim 1] A method performed by a first station (STA) in a wireless LAN system, comprising: transmitting a first roaming request frame to a first access point (AP) included in a first group, the first roaming request frame including a link identifier (ID) of a second AP and a group ID associated with a second group to which the second AP belongs; receiving a first roaming response frame from the first AP, the first roaming response frame including a first traffic indication map (TIM) field associated with the second AP; receiving first downlink (DL) data from the second AP based on the first TIM field. [Claim 2] The method of claim 1 , wherein the information indicating acceptance of roaming of the first STA to the second AP and the first TIM field are included in a common information field or a link information field of the first roaming response frame. [Claim 3] The method of claim 1 , wherein the first TIM field includes information indicating whether there is first DL data to be transmitted from the second AP to the first STA. [Claim 4] The method of claim 1 , wherein the first TIM field includes information indicating whether there is first DL data to be transmitted from the second AP to the first STA. [Claim 5] A link between the first STA and the second AP is added based on the first roaming response frame being transmitted to the first STA; The method of claim 1 , wherein frames are exchanged over a link between the first STA and the first AP or a link between the first STA and the second AP. [Claim 6] The method of claim 5, wherein a link between the first STA and the first AP is deactivated (disabled) and a link between the first STA and the second AP is activated (enabled), and data frames are exchanged between the first STA and the second AP through the activated link. [Claim 7] The method of claim 1 , wherein the first roaming response frame includes a group ID associated with a second group to which the second AP belongs. [Claim 8] The method of claim 1, wherein a beacon frame including a second TIM field indicating whether there is second DL data to be transmitted from the first AP to the first STA is transmitted from the first AP to the first STA. [Claim 9] The method of claim 1, wherein a second roaming request frame requesting deletion of a link connection between the first AP and the first STA is transmitted from the first STA to the second AP based on the first DL data being transmitted from the second AP to the first STA. [Claim 10] The method of claim 1 , wherein the first roaming response frame includes roaming timer information related to a time when the first DL data is available to be received from the second AP. [Claim 11] The method of claim 1 , wherein each of the first group and the second group is mapped to a separate AP MLD. [Claim 12] The method of claim 1 , wherein the first STA belongs to a non-AP MLD. [Claim 13] A first station (STA) in a wireless LAN system, one or more transceivers; one or more processors coupled to the one or more transceivers; the one or more processors: Transmitting a first roaming request frame to a first access point (AP) included in a first group via the one or more transceivers, the first roaming request frame including a link identifier of a second AP and a group ID (identifier) ​​associated with a second group to which the second AP belongs; receiving, from the first AP via the one or more transceivers, a first roaming response frame including a first traffic indication map (TIM) field associated with the second AP; a first STA configured to receive first downlink (DL) data from the second AP via the one or more transceivers based on the first TIM field; [Claim 14] A method performed by a first access point (AP) included in a first group in a wireless LAN system, comprising: receiving a first roaming request frame from a first station (STA), the first roaming request frame including a link identifier of a second AP and a group ID (identifier) ​​associated with a second group to which the second AP belongs; transmitting a first roaming response frame to the first STA, the first roaming response frame including a first traffic indication map (TIM) field associated with the second AP; The method further comprises transmitting first downlink (DL) data from the second AP to the first STA based on the first TIM field. [Claim 15] A first access point (AP) included in a first group in a wireless LAN system, one or more transceivers; one or more processors coupled to the one or more transceivers; the one or more processors: receiving a first roaming request frame from a first station (STA) via the one or more transceivers, the first roaming request frame including a link identifier of a second AP and a group ID associated with a second group to which the second AP belongs; transmitting, via the one or more transceivers, to the first STA, a first roaming response frame including a first traffic indication map (TIM) field associated with the second AP; A first AP transmits first downlink (DL) data from the second AP to the first STA based on the first TIM field. [Claim 16] 1. A processing device configured to control a first station (STA) in a wireless LAN system, comprising: one or more processors; and one or more computer memories operably coupled to the one or more processors and storing instructions that, when executed by the one or more processors, perform the method of claim 1. [Claim 17] one or more non-transitory computer-readable media storing one or more instructions, A non-transitory computer-readable medium, the one or more instructions being executed by one or more processors to control a first STA (station) in a wireless LAN system to perform the method of claim 1.

Claims

1. A method performed by a first station (STA) in a wireless LAN system, comprising: transmitting a first roaming request frame to a first access point (AP) included in a first group, the first roaming request frame including a link identifier (ID) of a second AP and a group ID associated with a second group to which the second AP belongs; receiving a first roaming response frame from the first AP, the first roaming response frame including a first traffic indication map (TIM) field associated with the second AP; receiving first downlink (DL) data from the second AP based on the first TIM field.

2. The method of claim 1 , wherein the information indicating acceptance of roaming of the first STA to the second AP and the first TIM field are included in a common information field or a link information field of the first roaming response frame.

3. The method of claim 1 , wherein the first TIM field includes information indicating whether there is first DL data to be transmitted from the second AP to the first STA.

4. The method of claim 1 , wherein the first TIM field includes information indicating whether there is first DL data to be transmitted from the second AP to the first STA.

5. a link between the first STA and the second AP is added based on the first roaming response frame being transmitted to the first STA; The method of claim 1 , wherein frames are exchanged over a link between the first STA and the first AP or a link between the first STA and the second AP.

6. 6. The method of claim 5, wherein a link between the first STA and the first AP is deactivated and a link between the first STA and the second AP is activated, and data frames are exchanged between the first STA and the second AP through the activated link.

7. The method of claim 1 , wherein the first roaming response frame includes a group ID associated with a second group to which the second AP belongs.

8. The method of claim 1, wherein a beacon frame including a second TIM field indicating whether there is second DL data to be transmitted from the first AP to the first STA is transmitted from the first AP to the first STA.

9. The method of claim 1, wherein a second roaming request frame requesting deletion of a link connection between the first AP and the first STA is transmitted from the first STA to the second AP based on the first DL data being transmitted from the second AP to the first STA.

10. The method of claim 1 , wherein the first roaming response frame includes roaming timer information related to a time when the first DL data is available for reception from the second AP.

11. The method of claim 1 , wherein each of the first group and the second group is mapped to a separate AP MLD.

12. The method of claim 1 , wherein the first STA belongs to a non-AP MLD.

13. A first station (STA) in a wireless LAN system, one or more transceivers; one or more processors coupled to the one or more transceivers; The one or more processors: transmit a first roaming request frame to a first access point (AP) included in a first group via the one or more transceivers, the first roaming request frame including a link identifier of a second AP and a group ID (identifier) ​​associated with a second group to which the second AP belongs; receiving, from the first AP via the one or more transceivers, a first roaming response frame including a first traffic indication map (TIM) field associated with the second AP; A first STA is configured to receive first downlink (DL) data from the second AP via the one or more transceivers based on the first TIM field.

14. A method performed by a first access point (AP) included in a first group in a wireless LAN system, comprising: receiving a first roaming request frame from a first station (STA), the first roaming request frame including a link identifier of a second AP and a group identifier (ID) associated with a second group to which the second AP belongs; transmitting a first roaming response frame to the first STA, the first roaming response frame including a first traffic indication map (TIM) field associated with the second AP; A method, wherein first downlink (DL) data is transmitted from the second AP to the first STA based on the first TIM field.

15. A first access point (AP) included in a first group in a wireless LAN system, one or more transceivers; one or more processors coupled to the one or more transceivers; The one or more processors: receiving a first roaming request frame from a first station (STA) via the one or more transceivers, the first roaming request frame including a link identifier of a second AP and a group ID associated with a second group to which the second AP belongs; transmit, to the first STA via the one or more transceivers, a first roaming response frame including a first traffic indication map (TIM) field associated with the second AP; A first AP transmits first downlink (DL) data from the second AP to the first STA based on the first TIM field.

16. 1. A processing device configured to control a first station (STA) in a wireless LAN system, comprising: one or more processors; and one or more computer memories operatively coupled to the one or more processors and storing instructions that, when executed by the one or more processors, perform the method of claim 1.

17. one or more non-transitory computer-readable media storing one or more instructions, A non-transitory computer-readable medium, the one or more instructions being executed by one or more processors to control a first STA (station) in a wireless LAN system to perform the method of claim 1.

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