WO2025147182A1 - Method and apparatus for multi-link time division communication synchronization in wireless lan - Google Patents

Abstract

An operating method of a first AP MLD comprising a first AP associated with a first link and a second AP associated with a second link in a wireless LAN system may comprise the steps of: receiving, by the first AP MLD, a multi-link resource allocation request from a first station (STA) of a STA MLD in a first link for the first AP of the first AP MLD; transmitting, by the first AP MLD, a first frame in a second link for the second AP of the first AP MLD on the basis of the multi-link resource allocation request so as to obtain a transmit opportunity (TXOP) in the second link; and allocating, on the basis of the first frame, a time division communication interval to another wireless LAN terminal within the TXOP, and receiving a second frame in response to the first frame.

Description

Method and device for synchronizing multi-link time division communication in wireless LAN

The present disclosure relates to a method and device for synchronizing multi-link time division communication in a Wireless Local Area Network (WLAN). Specifically, the present disclosure relates to a method and device for performing communication by overcoming asynchronization by allocating time division communication sections according to resource information requested by a wireless LAN terminal based on artificial intelligence in a wireless LAN.

The present disclosure relates to a method and device for determining whether communication is possible with a wireless access point that is a target of roaming when performing roaming in a wireless LAN.

Recently, as the spread of mobile devices has expanded, wireless LAN (Wireless Local Area Network) technology that can provide fast wireless communication services to mobile devices has been receiving a lot of attention. Wireless LAN technology can be a technology that allows mobile devices such as smart phones, smart pads, laptop computers, portable multimedia players, and embedded devices to wirelessly access the Internet based on wireless communication technology in a short distance.

The standard for using wireless LAN technology is mainly developed by the Institute of Electrical and Electronics Engineers (IEEE) as the IEEE 802.11 standard. As the above-mentioned wireless LAN technology is developed and distributed, applications utilizing wireless LAN technology are diversifying, and demand for wireless LAN technology supporting higher reliability has arisen.

As applications requiring higher reliability arise, the IEEE 802.11bn standard, which is an ultra-high reliability (UHR) wireless LAN technology in a single BSS (Basic Service Set) environment and/or redundant BSS environments, is being developed. The goals of the IEEE 802.11bn standard may be to support improved data transmission speed, improved delay performance, and improved data error rate. In addition, the IEEE 802.11bn standard may support low-power operation, peer-to-peer communication, operation for increased channel utilization, coordinated time division multiple access (C-TDMA) operation of multiple APs, multi-link operation, and multi-link resource allocation request operation.

However, in a multi-link, a resource allocation request made by a terminal may not be received by an AP (access point) due to interference from other communication terminals in a redundant BSS environment. Therefore, the resource allocation operation in a multi-link may not be performed, and the performance of a wireless LAN network in a redundant BSS environment may be reduced.

In addition, a wireless LAN terminal in a wireless LAN network may support roaming. However, detailed operations during roaming may not be defined. For example, a method for checking whether a new AP connected through roaming can communicate may not be defined. It may take a long time to check whether a new AP connected through roaming can communicate. Therefore, communication errors and communication delays may occur during roaming, and the roaming operation may operate inefficiently. In other words, the performance of the wireless LAN network may decrease.

Meanwhile, the technology that serves as the background for the invention was written to promote understanding of the background for the invention, and may include content that is not a prior art already known to a person with ordinary knowledge in the field to which the technology belongs.

The present disclosure relates to a method and device for synchronizing multi-link time division communication in a wireless LAN.

The present disclosure relates to a method and device for receiving a multi-link resource request and allocating resources from another link by a multi-link device (MLD) in a wireless LAN while considering an interference situation.

The present disclosure relates to a method and device for releasing a synchronization delay timer by receiving a multi-link resource request by taking into account an interference situation in a wireless LAN.

The present disclosure relates to a method and device for checking the communication capability of a newly connected AP in a roaming operation in a wireless LAN.

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

According to one example of the present disclosure, a method for operating a first AP multi-link device (MLD) including a first access point (AP) associated with a first link and a second AP associated with a second link in a wireless LAN system may include: a step in which the first AP MLD receives a multi-link resource allocation request from a first STA of a station (STA) MLD for a first AP of the first AP MLD on the first link; a step in which the first AP MLD transmits a first frame on the second link for the second AP of the first AP MLD based on the multi-link resource allocation request to obtain a transmit opportunity (TXOP) on the second link; and a step in which the first frame is allocated to another wireless LAN terminal within the TXOP and the second frame is received in response to the first frame.

In addition, according to one example of the present disclosure, in a first access point (AP) multi link device (MLD), the multi link device includes a first AP of a first AP MLD associated with a first link, a second AP of a first AP MLD associated with a second link, at least one transceiver for transmitting and receiving a signal, at least one processor for controlling at least one of the first AP, the second AP and the at least one transceiver, and a memory for storing instructions for causing the first AP MLD to perform a specific operation, wherein the specific operation comprises: receiving a multi-link resource allocation request from a first STA of a station (STA) MLD in the first link for a first AP of the first AP MLD, transmitting a first frame in the second link for a second AP of the first AP MLD based on the multi-link resource allocation request to obtain a TXOP (transmit opportunity) in the second link, and allocating a time-division communication section to another wireless LAN terminal within the TXOP based on the first frame, and A second frame may be received in response.

Additionally, the following may be applied in common:

In addition, according to an example of the present disclosure, the multi-link resource allocation request is included in a data frame that the STA MLD transmits to the second AP MLD for the first STA, wherein the first AP MLD and the second AP MLD are included in the same multi-AP group, and the data frame including the multi-link resource allocation request is not received by the second AP MLD, and the first AP MLD can receive the data frame including the multi-link resource allocation request for the first AP of the first AP MLD in an overhearing manner on the first link.

Additionally, according to one example of the present disclosure, the multi-link resource allocation request includes an instruction requesting resources for a STA MLD on a second link, and the first AP MLD can allocate a time-division communication interval by transmitting a first frame on the second link for a second AP of the first AP MLD.

Additionally, according to an example of the present disclosure, the first AP MLD may transmit the first frame on the second link to allocate a time-division communication section in the TXOP if no reception of a data frame from the second AP MLD is detected during a waiting time after receiving the data frame including the multi-link resource allocation request.

In addition, according to an example of the present disclosure, if the first AP MLD does not detect the reception of a data frame from the second AP MLD during a waiting time and an additional time after receiving a data frame including a multi-link resource allocation request, the first AP MLD transmits a first frame from the second link to allocate a time-division communication section in the TXOP, wherein the additional time can be set based on the retransmission of the STA MLD.

In addition, according to an example of the present disclosure, the first AP MLD performs a channel access operation to transmit the first frame, and if the backoff counter reaches 0 before the waiting time according to the channel access operation, the first AP MLD transmits the first frame for the second AP of the first A MLD after the waiting time, and if the backoff counter reaches 0 after the waiting time according to the channel access operation, the first AP MLD can transmit the first frame for the second AP of the first AP MLD at the slot boundary at which the backoff counter reaches 0.

Additionally, according to an example of the present disclosure, the first frame may include at least one of information for allocating a time-division communication interval to the second AP MLD and information for allocating a time-division communication interval to the STA MLD, and the user information field of the first frame may include at least one of information for indicating the second AP MLD and information for indicating the STA MLD.

In addition, according to an example of the present disclosure, when the first AP MLD allocates a time-division communication interval to the second AP MLD according to information for allocating a time-division communication interval to the second AP MLD included in the first frame, the first AP MLD receives a second frame from the second AP MLD on the second link in response to the first frame, wherein the time-division communication interval may be an interval in which communication is performed by the second AP MLD and the STA MLD on the second link.

In addition, according to an example of the present disclosure, when a time-division communication section allocated to a second AP MLD ends and a remaining TXOP remains in the first AP MLD, the first AP MLD can re-allocate the time-division communication section to another wireless LAN terminal or directly communicate with a wireless LAN terminal connected to the first AP MLD in the remaining TXOP.

In addition, according to an example of the present disclosure, when the first AP MLD allocates a time-division communication interval to the STA MLD according to information for allocating a time-division communication interval to the STA MLD included in the first frame, the first AP MLD receives a second frame from the STA MLD on the second link in response to the first frame, wherein the time-division communication interval may be an interval during which uplink transmission is performed from the STA MLD to the second AP MLD on the second link.

Additionally, according to an example of the present disclosure, the first frame further includes bandwidth information based on orthogonal frequency division multiple access together with at least one of information for allocating a time division communication interval to a second AP MLD and information for allocating a time division communication interval to a STA MLD, and the user information field of the first frame may include at least one of information indicating the second AP MLD and information indicating the STA MLD.

In addition, according to an example of the present disclosure, a time-division communication section is allocated after a preset time from the time at which the first AP MLD receives the second frame in response to the first frame, and the first AP MLD performs communication with a wireless LAN terminal connected to the first AP MLD at a first bandwidth based on bandwidth information within the time-division communication section, but communication between the second AP MLD and the STA MLD can be further performed at the second bandwidth within the time-division communication section.

Additionally, according to one example of the present disclosure, the synchronization delay timer is started when the transmission of the data frame of the STA MLD is terminated, and the synchronization delay timer can be cleared based on at least one of the transmission of the first frame, the reception of the second frame, and the transmission of the third frame based on the second frame.

Additionally, according to an example of the present disclosure, the synchronization delay timer starts when the data frame transmission of the STA MLD ends, but the first frame transmitted by the first AP MLD for the second AP of the first AP MLD is a frame that releases the synchronization delay timer, and the TXOP may not be allocated to the first AP MLD by the first frame.

The present disclosure can provide a multi-link time division communication synchronization method in a wireless LAN.

The present disclosure can provide a method for a multi-link device (MLD) in a wireless LAN to receive a multi-link resource request and allocate resources from another link while considering an interference situation.

The present disclosure can provide a method for releasing a synchronization delay timer by receiving a multi-link resource request by taking into account interference conditions in a wireless LAN.

The present disclosure may provide a method for checking the communication capability of a newly connected AP in a roaming operation in a wireless LAN.

The effects obtainable from the present disclosure are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by a person having ordinary skill in the art to which the present disclosure belongs from the description below.

Figure 1 is a diagram showing a communication node within a wireless LAN system to which the present disclosure is applied.

Figure 2 is a diagram showing a wireless LAN system to which the present disclosure is applied.

FIG. 3 is a diagram illustrating a machine learning unit to which the present disclosure is applied.

FIG. 4 is a flowchart illustrating a method for performing communication based on a machine learning unit to which the present disclosure is applied.

FIGS. 5A to 5C are diagrams illustrating a method for allocating an adjusted time-division communication section in a multi-link wireless LAN network to which the present disclosure is applied.

FIG. 6 is a diagram illustrating a method for allocating coordinated orthogonal frequency division multiple access resources in a multi-link wireless LAN network to which the present disclosure is applied.

FIG. 7 is a diagram illustrating a method for eliminating communication delay of a wireless LAN terminal in a multi-link wireless LAN network to which the present disclosure is applied.

Figure 8 is a method showing a method for checking whether communication is possible during wireless LAN roaming to which the present disclosure is applied.

Figure 9 is a drawing showing a method for checking whether communication is possible during wireless LAN roaming applied to the present disclosure.

FIG. 10a and FIG. 10b are diagrams illustrating a method for confirming whether communication is possible during wireless LAN roaming to which the present disclosure is applied.

Figure 11 is a drawing showing a method for checking whether communication is possible during wireless LAN roaming applied to the present disclosure.

FIG. 12 is a flowchart illustrating a method for eliminating communication delay of a wireless LAN terminal in a multi-link wireless LAN network to which the present disclosure is applied.

The present disclosure may have various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present disclosure to specific embodiments, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present disclosure.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are only used to distinguish one component from another. E.g., without departing from the scope of the present disclosure, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and/or includes any combination of a plurality of related described items or any item among a plurality of related described items.

When it is said that a component is "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components in between. On the other hand, when it is said that a component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

The terminology used in this disclosure is only used to describe specific embodiments and is not intended to limit the present disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this disclosure, it should be understood that the terms "comprises" or "has" and the like are intended to specify that a feature, number, step, operation, component, part or combination thereof described in the specification is present, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and will not be interpreted in an idealized or overly formal sense unless expressly defined in this disclosure.

Hereinafter, with reference to the attached drawings, preferred embodiments of the present disclosure will be described in more detail. In order to facilitate an overall understanding in describing the present disclosure, the same reference numerals are used for the same components in the drawings, and redundant descriptions of the same components are omitted.

Below, a wireless communication system to which embodiments according to the present disclosure are applied will be described. The wireless communication system to which embodiments according to the present disclosure are applied is not limited to the contents described below, and the embodiments according to the present disclosure can be applied to various wireless communication systems. The wireless communication system can be referred to as a "wireless communication network."

FIG. 1 is a diagram illustrating a communication node in a wireless LAN system to which the present disclosure is applied. Referring to FIG. 1, a communication node (100) may include at least one of a processor (110), a memory (120), a transceiver (130), an input/output interface (140), a storage device (150), and a bus (160). For example, the communication node (100) may be an access point (AP), a station (STA), an AP (access point) multi-link device (MLD), or a non-AP MLD. However, the communication node may not be limited thereto, and may be a node that performs communication with another node or device based on the above-described configuration. For example, an operating channel width supported by an AP may be 20 MHz (megahertz), 80 MHz, 160 MHz, etc. An operating channel width supported by a station may be 20 MHz, 80 MHz, etc. However, the present disclosure may not be limited thereto.

The processor (110) in the communication node (100) can control at least one of the memory (120), the transceiver (130), the input/output interface (140), and the storage device (150) as each component in the communication node. The memory (120) in the communication node (100) can store information on commands and instructions executed by the processor (110), and the transceiver (130) can refer to a transceiver, an RF (radio frequency) unit, an RF module, or other components that perform signal transmission and reception. The input/output interface (140) in the communication node (100) is an interface for input and output and can be linked with other interfaces, and can further include a separate storage device (150). The respective components in the communication node (100) can be connected by a bus (160) and communicate with each other.

However, as an example, each component included in the communication node (100) may be connected through an individual interface or individual bus centered around the processor (110), rather than a common bus (160). The processor (1110) may be connected to at least one of the memory (120), the transmission/reception device (130), the input/output interface device (140), and the storage device (150) through a dedicated interface.

The processor (110) can execute a program command stored in at least one of the memory (120) and the storage device (150). The processor (110) may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present disclosure are performed. Each of the memory (120) and the storage device (150) may be configured with at least one of a volatile storage medium or a nonvolatile storage medium. For example, the memory (120) may be configured with at least one of a read only memory (ROM) or a random access memory (RAM).

FIG. 2 is a diagram showing a wireless LAN system to which the present disclosure is applied. Referring to FIG. 2, a basic service set (BSS) of a wireless LAN system may include one AP (210) and multiple STAs (221, 222, 223, 224), and the multiple STAs (221, 222, 223, 224) may be controlled by the AP (210). However, the wireless LAN system is not limited to the BSS, and an environment composed only of STAs without a confirmed service set or AP may also be considered, and is not limited to a specific form. Each wireless device in the wireless LAN system may include a MAC (medium access control) layer and a physical (PHY) layer, and communication may be performed between the wireless devices. For convenience of explanation, the following description focuses on APs and STAs, but may not be limited thereto. As an example, the following may equally be applied to other communication nodes or devices and are not limited to a specific form.

FIG. 3 is a diagram showing a machine learning unit to which the present disclosure is applied. Each of the wireless devices within the wireless LAN system may be connected to a machine learning unit (300). However, this may not be limited, and it may also be possible for a wireless device not connected to the machine learning unit (300) to operate.

For example, the processor (110) of the communication node (100) of FIG. 1 may be connected to the machine learning unit (300). The machine learning unit (900) may be connected to the processor (110) through the input/output interface device (140) of the communication node (100) to communicate. As another example, the machine learning unit (300) may be connected to the processor (110) through the bus (160) of the communication node (100) to communicate. As another example, the machine learning unit (300) may be connected to the processor (110) of the communication node (100) through a separate interface or a dedicated bus to communicate. The machine learning unit (300) may be connected to the memory (120), the transceiver (130), and the storage device (140) through the input/output interface device (140), the bus (160), or the dedicated bus to communicate, but may not be limited to a specific form.

For example, the machine learning unit (300) may include at least one ML (Machine Learning) processor (310), an ML memory (320), an ML input/output interface (330), and an ML bus (340). The ML processor (310), the ML memory (320), and the ML input/output interface (330) may be connected to and communicate with each other through the ML bus (340). As another example, the ML processor (310) may be connected to and communicate with at least one of the ML memory (320) and the ML input/output interface (330) through a dedicated bus or interface. The ML processor (310) may be a central processing unit, a graphic processing unit, a dedicated processor on which methods according to embodiments of the present disclosure are performed, or a processor in which at least one of the central processing unit and the dedicated processor is combined. The ML processor (310) may include at least one of a training unit (311), a verification unit (312), a performing unit (313), and an updating unit (313). The training unit (311), the verification unit (312), the performing unit (313), and the updating unit (313) may be a logical entity configured by software or a hardware processing device. As an example, the ML processor (310) may perform at least one of training, verifying, performing, and updating a machine learning model. The machine learning model may be in the form of a plurality of matrices and vectors. As a specific example, the machine learning model may include weights, a transition matrix, and hyperparameters that implement and learn a single or a plurality of combined machine learning algorithms (e.g., a deep neural network (DNN), a convolutional neural network (CNN), a recurrent neural network (RNN), a deep reinforcement learning (DRL) algorithm). The machine learning model may include an input layer, at least one hidden layer, and an output layer to implement the DNN algorithm. Each of the input layer, the hidden layer, and the output layer may include at least one perceptron (e.g., an artificial neuron). The perceptron includes an activation function, an input weight, and a bias. A plurality of perceptrons may be connected to inputs and outputs to form an input layer, a hidden layer, and an output layer. The machine learning model may include a convolution algorithm and the DNN algorithm to implement the CNN algorithm. The convolution algorithm is an algorithm that convolves a kernel matrix with input data in the form of a matrix, and may be performed at least once on the input data. When the convolution algorithm is performed on the input data, the size of the data may be increased by concatenation or reduced by pooling. The input data on which the convolution algorithm has been performed at least once is used as input data of the DNN algorithm. For example, the machine learning model may include a DNN algorithm and a cell structure to implement an RNN algorithm. The cell structure may be a structure that remembers previous input data and inputs it by itself, and may be used for at least one perceptron of the DNN algorithm. The machine learning model may include an agent, an environment structure, and a DNN algorithm to implement a DRL algorithm. In the DRL algorithm, the agent may observe the environment and perform an optimal action based on the environment. The environment may feed back a reward to the agent based on the action of the agent. Based on the above, the agent may learn a policy for taking an optimal action. The agent may use a DNN algorithm to learn the optimal action.

As another example, the machine learning unit (300) may be designed to additionally implement other machine learning algorithms in addition to the machine learning algorithm. To this end, the machine learning unit (300) may include additional components for implementing other machine learning algorithms. The ML memory (320) within the machine learning unit (300) may store the machine learning model and the machine learning algorithm. The implementation of the machine learning algorithm may be performed by the ML processor (310) based on the machine learning model.

As another example, all or part of the functions of the machine learning unit (300) may be integrated into the processor (110) and the memory (120) of the communication node (100). That is, the processor (110) of the communication node (100) may perform all or part of the functions of the ML processor (310), and the memory (120) may perform all or part of the functions of the ML memory (320). When the processor (110) and the memory (120) of the communication node (100) perform all of the functions of the machine learning unit (300), the machine learning unit (300) may not be connected by the input/output interface (140), and the processor (110) and the memory (120) may operate as the machine learning unit (300).

As another example, the machine learning unit (300) may be connected not through the input/output interface (140) of the communication node (100), but through a bus (160) or a dedicated bus or interface centered around the processor (110) of the communication node (100), but may not be limited to this embodiment.

FIG. 4 is a flowchart illustrating a method for performing communication based on a machine learning unit to which the present disclosure is applied. Referring to FIG. 4, the machine learning unit (300) may be connected to a communication node (100) to collect communication data and perform a prediction based on a machine learning model (S410). As an example, the above-described prediction may be performed by the execution unit (313) of the machine learning unit (300), but is not limited thereto. Here, the communication data collected by the machine learning unit (300) may include at least one of channel noise status, channel congestion, reception strength, collision frequency, and other information obtained from a physical layer. In addition, the communication data may include information obtained from a MAC layer, and is not limited to a specific form. The communication data collected by the machine learning unit (300) may be provided as an input of the machine learning model as it is. As another example, the communication data collected by the machine learning unit (300) may be provided as an input of the machine learning model after being operated or processed. For example, the prediction result of the machine learning unit (300) may be at least one of a physical layer and MAC parameter (e.g., a modulation and coding scheme (MCS) parameter, a beamforming parameter, an enhanced distributed coordination function (EDCA) parameter, etc.). As another example, the prediction result of the machine learning unit (300) may be information for packet scheduling, multi-AP operation scheduling, and other scheduling, but is not limited to a specific form. As another example, the communication node (100) may receive all or part of the machine learning model from another communication node. All or part of the machine learning model may be collected by the machine learning unit (300) and is not limited to a specific form. For example, the communication node (100) can perform communication based on the prediction of the machine learning unit (300). (S420) In addition, the machine learning unit (300) can collect communication data based on the performed communication, and machine learning model verification can be performed based on this (S430) or machine learning model training (S440). In addition, as an example, the machine learning model can be exchanged with other communication nodes (S450), and the exchanged machine learning model information can be used for machine learning model verification or machine learning model training. For example, when the machine learning model verification is performed, it can be verified whether the communication operation performed by the prediction of the machine learning unit (300) is appropriate. As a specific example, the machine learning model verification can be performed based on at least one of the frame collision frequency, the transmission error frequency, and the packet transmission delay of the communication node (100), and an operation of determining whether the communication performance of the communication node (100) has been improved can be performed.

In addition, as an example, if it is determined that training of a machine learning model is necessary (e.g., if communication performance is not improved, if it is determined that the performance of a machine learning model of another communication node (e.g., all or part of the machine learning models) is superior to that of the current communication node (100), the communication node (100) may perform machine learning model training. As another example, the communication node (100) may exchange the machine learning model with other communication nodes without performing machine learning model verification or machine learning model training. In addition, as an example, if it is determined that training of a machine learning model is not necessary, the communication node (100) may exchange the machine learning model with other communication nodes without performing machine learning model training.

Here, the training of the machine learning model can be trained (or learned) based on at least one of the collected communication data, all or part of the machine learning model of the other communication node. The training of the machine learning model can be performed by the training unit (311), and can be performed based on at least one of the collected communication data, the machine learning model of the other communication node, and the output of the machine learning model of the communication node (100).

As another example, part or all of the machine learning model of the communication node (1000) may be replaced with part or all of the machine learning model of another communication node by the updating unit (314) of the machine learning unit (300). As another example, the machine learning model (e.g. part or all of the machine learning model) of the communication node (100) may be shared with another communication node. Alternatively, the communication node (100) may operate only based on machine learning model verification and learning without exchanging the machine learning model with other communication nodes, and is not limited to a specific form. As an example, at least one of the steps of the flowchart in the present disclosure may be performed among a change in order, an addition or removal of a step, and a repetition of a specific step. That is, the flowchart is one example explaining the operation of the machine learning unit (300) of the wireless communication node (100), and the procedure and operation thereof may be variously modified. For example, after training a machine learning model, it may be possible to perform a machine learning model validation step again to validate the trained machine learning model, and it may not be limited to a specific form.

FIGS. 5A to 5C are diagrams illustrating a method for allocating an adjusted time-division communication section in a multi-link wireless LAN network to which the present disclosure is applied.

Referring to FIGS. 5A to 5C, a multi-link operation may be performed in a wireless LAN network. FIGS. 5A to 5C are merely examples for convenience of explanation and may not be limited thereto, and may be equally applied to other situations. For example, a first link and a second link may exist, and an MLD (multi-link device) supporting a multi-link operation may operate in the first link and the second link. A plurality of AP MLDs (e.g., AP MLD 1, AP MLD 2) may operate in the first link and the second link. In addition, a STA MLD (e.g., STA MLD 1) may operate in the first link and the second link. Here, the STA MLD may be referred to as a non-AP MLD. For example, an MLD may have independent medium access control (MAC) (e.g. lower MAC layer) and PHY entities per link, and may have an upper MAC (e.g. upper MAC layer) entity that integrates the independent MAC layers per link. For example, an MLD including independent MAC and PHY per link may include independent communication modules per link.

In the following, the AP operating in the first link with AP MLD 1 may be AP 1-1 of AP MLD 1, and the AP operating in the second link with AP MLD 1 may be AP 1-2 of AP MLD 1. In addition, the AP operating in the first link with AP MLD 2 may be AP 2-1 of AP MLD 2, and the AP operating in the second link with AP MLD 2 may be AP 2-2 of AP MLD 2. In addition, the STA (non-AP STA) operating in the first link with STA MLD 1 may be STA 1 of STA MLD 1, and the STA operating in the second link with STA MLD 1 may be STA 2 of STA MLD 1. As an example, STA MLD 1 may be connected (or associated) with AP MLD 1. In addition, STA MLD 1 may be a non-simultaneous transmit and receive (NSTR) terminal. When STA MLD 1 performs transmission on one link (e.g. the first link) among the NSTR link pairs (e.g. the first link and the second link) of STA MLD 1, STA MLD 1 may not perform channel detection and frame reception operations on the link (e.g. the second link) on which transmission is not performed, and may also not be able to set a Network Allocation Vector (NAV). Accordingly, medium synchronization of the link on which STA MLD 1 does not perform transmission may be released. For example, when STA MLD 1 performs a medium synchronization recovery operation, STA MLD 1 may not perform transmission on the link (e.g. the second link) on which transmission is not performed for a certain period of time. Alternatively, when STA MLD 1 performs a medium synchronization recovery operation, a medium synchronization delay timer (MediumSyncDelay timer) that restricts transmission in STA MLD 1 may operate. That is, STA 2 of STA MLD 1 cannot transmit a frame for a certain period of time, which may cause a transmission delay. For example, if STA MLD 1 normally receives a frame while the medium synchronization delay timer is operating and can decode the received frame to normally set the NAV, the medium synchronization delay timer may be released in STA MLD 1.

STA 1 (530) of STA MLD 1 may transmit a multi-link resource allocation request to AP 1-1 (520) of AP MLD 1 in a data frame from the first link. The multi-link resource allocation request may be an AP assistance request (AAR). For example, the AAR may be transmitted in the form of A-control in the HT control field of the MAC header of the data frame, but may not be limited thereto. The AAR may include an indicator (e.g., a link bitmap) requesting resource allocation in the second link. The AAR may request the release of a medium synchronization delay timer in the multi-link and may be used for rapid uplink transmission. The resource allocation may include uplink transmission resource allocation. The uplink resource allocation may be allocated through a trigger frame or other frames.

For example, AP 1-1 (520) of AP MLD 1 may not receive a data frame transmitted by STA 1 (530) of STA MLD 1 to AP 1-1 (520) of AP MLD 1 due to communication interference occurring in AP 1-1 (520) of AP MLD 1. The communication interference occurring in AP 1-1 (520) of AP MLD 1 may be caused by internal communication of AP 1-1 (520) of AP MLD 1 (e.g. heterogeneous communication or P2P (Peer-to-Peer) communication of AP 1-1 (520) of AP MLD 1) or communication of OBSS (overlapping BSS) within the communication range of AP 1-1 (520) of AP MLD 1. However, the reason for the communication interference is not specific, and the cause of the communication interference of AP 1-1 (520) of AP MLD 1 may be in various forms other than the cause mentioned above.

If AP 1-1 (520) of AP MLD 1 fails to receive the data frame transmitted by STA 1 (530) of STA MLD 1 due to communication interference, AP 1-1 (520) of AP MLD 1 may also fail to receive AAR transmitted by STA 1 (530) of STA MLD 1. On the other hand, AP 2-1 (510) of AP MLD 2 may be able to receive the data frame transmitted by STA 1 (530) of STA MLD 1 and AAR included in the data frame since it operates in the first link, which is the same link as AP 1-1 (520) of AP MLD 1 and STA 1 (530) of STA MLD 1. Here, the APs of AP MLD 1 and the APs of AP MLD 2 may be APs included in the same multi-AP group (Multi-AP, MAP). In addition, as an example, STA 1 of STA MLD 1 may not be an STA associated with AP MLD 2. Therefore, AP 2-1 (510) of AP MLD 2 can receive based on a method of overhearing a data frame transmitted by STA 1 (530) of STA MLD 1 and an AAR included in the data frame. That is, AP MLD 2 can receive a frame of STA MLD 1 that is not associated with AP MLD 2 and check its contents. AP MLD 2 can check an indicator included in the AAR transmitted by STA 1 (530) of STA MLD 1 (e.g. an indicator requesting a resource from a second link).

Referring to FIG. 5a, AP 2-1 (510) of AP MLD 2 may wait to determine whether AP 1-1 (520) of AP MLD 1 responds to the data frame transmitted by STA 1 (530) of STA MLD 1. For example, the waiting time for determining that AP 2-1 (510) of AP MLD 2 is waiting may be a time longer than a short interframe space (SIFS) time. As a specific example, the waiting time may be a priority interframe space (PIFS), but may not be limited thereto. For example, the waiting time may be a time for AP 1-1 (520) of AP MLD 1 to wait for transmission of a response frame to a frame transmitted by STA 1 (530) of STA MLD 1. Alternatively, the waiting time may be the time that STA 1 (530) of STA MLD 1 waits to retransmit a frame when it fails to transmit a frame to AP 1-1 (520) of AP MLD 1. If AP 1-1 (520) of AP MLD 1 does not respond to STA 1 (530) of STA MLD 1 until the waiting time (e.g. PIFS) elapses, or if STA 1 (530) of STA MLD 1 does not retransmit a data frame to AP 1-1 (520) of AP MLD 1, AP MLD 2 may transmit a frame to allocate resources to the second link. Here, AP 2-1 (540) of AP MLD 2 can recognize whether STA 1 (530) of STA MLD 1 has set TXOP before transmitting the data frame transmitted by STA 1 (530) of STA MLD 1. That is, AP 2-1 (540) of AP MLD 2 can wait for PIFS time if the data frame transmitted by STA 1 (530) of STA MLD 1 is the first frame transmitted after contention.

AP 2-2 (540) of AP MLD 2 may perform a channel access operation (e.g., EDCA (enhanced distributed channel access) backoff operation and EDCA TXOP (transmit opportunity) acquisition procedure) to transmit a frame. For example, the EDCA backoff counter of AP 2-2 (540) of AP MLD 2 may have already reached 0 before transmitting a frame for allocating resources. Here, AP 2-2 (540) of AP MLD 2 may wait without transmitting a frame for allocating resources until the PIFS time from the end time of a data frame transmitted by STA 1 (530) of STA MLD 1 in the first link even though the backoff counter has reached 0. When PIFS time or more has elapsed from the end time of a data frame transmitted by STA 1 (530) of STA MLD 1, AP 2-2 (540) of AP MLD 2 may transmit a frame (501) for allocating resources. As another example, when the EDCA backoff counter is not 0, AP 2-2 (540) of AP MLD 2 may perform a channel access operation until the EDCA backoff counter reaches 0. AP 2-2 (540) of AP MLD 2 may transmit a frame for allocating resources at a slot boundary where the EDCA backoff counter reaches 0. The frame transmitted by AP 2-2 (540) of AP MLD 2 to allocate resources in the second link may be a MU-RTS (multi user-request to send) trigger frame (MU-RTS frame, 501). AP 2-2 (540) of AP MLD 2 can obtain a transmit opportunity (TXOP) in the second link by transmitting an MU-RTS frame (501) in the second link. In addition, as an example, AP 2-2 (540) of AP MLD 2 can transmit an MU-RTS frame (501) after SIFS time after transmitting a CTS-to-Self frame, which is a CTS frame in which a Receiver Address (RA) is set to AP 2-2 (540) of AP MLD 2, to obtain a TXOP. The MU-RTS frame (501) transmitted by AP 2-2 (540) of AP MLD 2 can be a frame for allocating a communication section in a coordinated time division multiple access (C-TDMA) operation. AP 2-2 (540) of AP MLD 2 can allocate a C-TDMA communication section to another AP within TXOP. The MU-RTS frame (501) transmitted by AP 2-2 (540) of AP MLD 2 may include information for allocating a C-TDMA communication section to AP 1-2 (560) of AP MLD 1 (e.g. all or part of the MAC address that can identify AP MLD 1 or a lower AP, Multi-AP group ID, a predetermined AID (association identifier)). Alternatively, the MU-RTS frame (501) described above may include information for instructing resource allocation to STA 2 (570) of STA MLD 1 (e.g. all or part of the AID or MAC address that can identify STA MLD 1 and a lower STA). That is, the MU-RTS frame (501) allocates resources to AP 1-2 (560) of AP MLD 1 through a coordinated time division communication operation, and AP 1-2 (560) of AP MLD 1 must allocate resources to STA 2 (570) of STA MLD 1. Information indicating AP 1-2 (560) of AP MLD 1 or STA 2 (570) of STA MLD 1 may be included in the user info field of the MU-RTS frame (501). That is, the MU-RTS frame (501) may instruct to allocate a C-TDMA communication section to AP 1-2 (560) of AP MLD 1. It may instruct that the communication section allocated to AP 1-2 (560) of AP MLD 1 should be used for uplink resource allocation of STA 2 (570) of STA MLD 1. AP 1-2 (560) of AP MLD 1 can receive an MU-RTS frame (501) transmitted from AP 2-2 (540) of AP MLD 2, and transmit a CTS (clear to send, 502) frame in response after a short interframe space (SIFS) time. AP 1-2 (560) of AP MLD 1 can transmit a trigger frame (TF, 503) after a SIFS time after transmitting the CTS frame (502). The trigger frame (503) can include at least one user info field, and the user info field can include information that can identify STA 2 (570) of STA MLD 1 (e.g. AID of STA MLD 1). The trigger frame is a frame that allocates uplink resources. That is, STA 2 (570) of STA MLD 1 operating in the second link as STA MLD 1 can be allocated uplink resources based on the adjusted time division communication operation. STA 2 (570) of STA MLD 1 can receive a trigger frame (502) of AP 1-2 (560) of AP MLD 1 and check allocated resource information (e.g. uplink transmission bandwidth, transmission length, etc.) in the trigger frame (502). Thereafter, STA 2 (570) of STA MLD 1 can transmit an uplink frame to AP 1-2 (560) of AP MLD 1 based on the allocated resource information in the trigger frame (502). AP 1-2 (560) of AP MLD 1 can transmit a response frame (e.g. BlockAck frame) to the uplink frame transmitted by STA 2 (570) of STA MLD 1. After that, the C-TDMA section allocated by AP 2-2 (540) of AP MLD 2 to AP 1-2 (560) of AP MLD 1 may be terminated. Here, the TXOP of AP 2-2 (540) of AP MLD 2 may remain, and AP 2-2 (540) of AP MLD 2 may allocate the remaining TXOP to another AP as a C-TDMA section, or use it for communication with an STA (e.g. STA X (550)) connected to AP 2-2 (540) of AP MLD 2. The medium synchronization delay timer of STA 2 (570) of STA MLD 1 may be terminated early if at least one frame among the MU-RTS frame (501) of AP 2-2 (540) of AP MLD 2, the CTS frame (502) of AP 1-2 (560) of AP MLD 1, and the trigger frame (503) of AP 1-2 (560) of AP MLD 1 is normally received.

Referring to FIG. 5b, AP 2-1 (510) of AP MLD 2 may wait to determine whether AP 1-1 (520) of AP MLD 1 responds to the data frame transmitted by STA 1 (530) of STA MLD 1. For example, the waiting time for determining that AP 2-1 (510) of AP MLD 2 is waiting may be a time longer than SIFS (short interframe space) time. As a specific example, the waiting time may be PIFS (priority interframe space), but may not be limited thereto. The waiting time is the time for AP 1-1 (520) of AP MLD 1 to wait for transmission of a response frame to the frame transmitted by STA 1 (530) of STA MLD 1. Alternatively, the waiting time may be the time that STA 1 (530) of STA MLD 1 waits to retransmit a frame to AP 1-1 (520) of AP MLD 1 when frame transmission to AP 1-1 (520) of AP MLD 1 fails. If AP 1-1 (520) of AP MLD 1 does not respond to STA 1 (530) of STA MLD 1 until the waiting time (e.g. PIFS) elapses, or if STA 1 (530) of STA MLD 1 does not retransmit a data frame to AP 1-1 (520) of AP MLD 1, AP MLD 2 may transmit a frame to allocate resources to the second link. Here, AP 2-1 (540) of AP MLD 2 can recognize whether STA 1 (530) of STA MLD 1 has set TXOP before transmitting the data frame transmitted by STA 1 (530) of STA MLD 1. That is, AP 2-1 (540) of AP MLD 2 can wait for PIFS time if the data frame transmitted by STA 1 (530) of STA MLD 1 is the first frame transmitted after contention.

AP 2-2 (540) of AP MLD 2 may perform a channel access operation (e.g., EDCA (enhanced distributed channel access) backoff operation and EDCA TXOP (transmit opportunity) acquisition procedure) to transmit a frame. For example, the EDCA backoff counter of AP 2-2 (540) of AP MLD 2 may have already reached 0 before transmitting a frame for allocating resources. Here, AP 2-2 (540) of AP MLD 2 may wait without transmitting a frame for allocating resources until the PIFS time from the end time of a data frame transmitted by STA 1 (530) of STA MLD 1 in the first link even though the backoff counter has reached 0. When PIFS time or more has elapsed from the end time of a data frame transmitted by STA 1 (530) of STA MLD 1, AP 2-2 (540) of AP MLD 2 may transmit a frame (504) for allocating resources. As another example, when the EDCA backoff counter is not 0, AP 2-2 (540) of AP MLD 2 may perform a channel access operation until the EDCA backoff counter reaches 0. AP 2-2 (540) of AP MLD 2 may transmit a frame for allocating resources at a slot boundary where the EDCA backoff counter reaches 0. The frame transmitted by AP 2-2 (540) of AP MLD 2 to allocate resources in the second link may be a MU-RTS (multi user-request to send) trigger frame (MU-RTS frame, 504). AP 2-2 (540) of AP MLD 2 can obtain a transmit opportunity (TXOP) in the second link by transmitting an MU-RTS frame (504) in the second link. In addition, as an example, AP 2-2 (540) of AP MLD 2 can transmit an MU-RTS frame (504) after SIFS time after transmitting a CTS-to-Self frame, which is a CTS frame in which a Receiver Address (RA) is set to AP 2-2 (540) of AP MLD 2, to obtain a TXOP. The MU-RTS frame (504) transmitted by AP 2-2 (540) of AP MLD 2 can be a frame for allocating a communication section in a coordinated time division multiple access (C-TDMA) operation. AP 2-2 (540) of AP MLD 2 can allocate the C-TDMA communication section to another STA within the TXOP.

The MU-RTS frame (504) transmitted by AP 2-2 (540) of AP MLD 2 may include information for allocating a C-TDMA communication section to STA 2 (570) of STA MLD 1 (e.g. all or part of a MAC address that can identify STA MLD 1 or a lower STA, AID (association identifier)). That is, the MU-RTS frame (504) allocates resources to AP 1-2 (560) of AP MLD 1 through a coordinated time division communication operation, and AP 1-2 (560) of AP MLD 1 must allocate resources to STA 2 (570) of STA MLD 1. Information indicating STA 2 (570) of STA MLD 1 may be included in a user info field of the MU-RTS frame (504). That is, the MU-RTS frame (504) can instruct to allocate a C-TDMA communication section to STA 2 (570) of STA MLD 1. The MU-RTS trigger frame (504) is a frame that allocates uplink resources. That is, STA 2 (570) of STA MLD 1, which operates on the second link as STA MLD 1, can be allocated uplink resources based on the adjusted time division communication operation. STA 2 (570) of STA MLD 1 can receive the MU-RTS frame (504) transmitted by AP 2-2 (540) of AP MLD 2, and can transmit a CTS (clear to send) frame (505) as a response after a SIFS (short interframe space) time. STA 2 (570) of STA MLD 1 can transmit an uplink data frame to AP 1-2 (560) of AP MLD 1 within the allocated C-TDMA communication interval after SIFS time after transmitting the CTS frame (505). The C-TDMA interval allocated by AP 2-2 (540) of AP MLD 2 to STA 2 (570) of STA MLD 1 may be terminated.

Here, the TXOP of AP 2-2 (540) of AP MLD 2 may remain, and AP 2-2 (540) of AP MLD 2 may allocate the remaining TXOP to another AP as a C-TDMA section, or use it for communication with an STA (e.g. STA X (550)) connected to AP 2-2 (540) of AP MLD 2. The medium synchronization delay timer of STA 2 (570) of STA MLD 1 may be terminated early by a normally received MU-RTS frame (505) of AP 2-2 (540) of AP MLD 2.

Referring to FIG. 5c, AP 2-1 (510) of AP MLD 2 may wait to check whether AP 1-1 (520) of AP MLD 1 responds to the data frame transmitted by STA 1 (530) of STA MLD 1. For example, the waiting time for checking that AP 2-1 (510) of AP MLD 2 is waiting may be a time longer than SIFS (short interframe space) time. As a specific example, the waiting time may be PIFS (priority interframe space), but may not be limited thereto. The waiting time is the time for AP 1-1 (520) of AP MLD 1 to wait for transmission of a response frame to the frame transmitted by STA 1 (530) of STA MLD 1. Alternatively, the waiting time may be the time that STA 1 (530) of STA MLD 1 waits to retransmit a frame when it fails to transmit a frame to AP 1-1 (520) of AP MLD 1. If AP 1-1 (520) of AP MLD 1 does not respond to STA 1 (530) of STA MLD 1 until the waiting time (e.g. PIFS) elapses, or if STA 1 (530) of STA MLD 1 does not retransmit a data frame to AP 1-1 (520) of AP MLD 1, AP MLD 2 may transmit a frame to allocate resources to the second link. Here, AP 2-1 (540) of AP MLD 2 can recognize whether STA 1 (530) of STA MLD 1 sets TXOP before transmitting the data frame transmitted by STA 1 (530) of STA MLD 1. That is, AP 2-1 (510) of AP MLD 2 needs to consider whether STA 1 (530) of STA MLD 1 performs retransmission if the data frame transmitted by STA 1 (530) of STA MLD 1 is not the first frame transmitted after contention. Alternatively, AP 2-1 (510) of AP MLD 2 can consider whether STA 1 (530) of STA MLD 1 performs retransmission even if the data frame transmitted by STA 1 (530) of STA MLD 1 is the first frame transmitted after contention. The retransmission of STA 1 (530) of STA MLD 1 may be performed PIFS time after the end time of data frame transmission of STA 1 (530) of STA MLD 1. AP 2-1 (510) of AP MLD 2 may wait for an additional time, 'a' time, after the PIFS time from the end time of data frame transmission of STA 1 (530) of STA MLD 1 in consideration of the retransmission of STA 1 (530) of STA MLD 1. For example, 'a' time may be aSlotTime or a longer time. If AP 2-1 (510) of AP MLD 2 detects the retransmission of STA 1 (530) of STA MLD 1 during PIFS + 'a' time, AP MLD 2 may not transmit a frame for allocating resources to the second link. Alternatively, AP MLD 2 may transmit a frame allocating resources to the second link PIFS or PIFS + 'a' time after the retransmission of STA 1 (530) of STA MLD 1 is completed. If AP 2-1 (510) of AP MLD 2 does not detect the retransmission of STA 1 (530) of STA MLD 1 for PIFS + 'a' time, AP MLD 2 may transmit a frame allocating resources to the second link.

AP 2-2 (540) of AP MLD 2 may perform a channel access operation (e.g., EDCA (enhanced distributed channel access) backoff operation and EDCA TXOP (transmit opportunity) acquisition procedure) to transmit a frame. For example, the EDCA backoff counter of AP 2-2 (540) of AP MLD 2 may have already reached 0 before transmitting a frame for allocating resources. Here, AP 2-2 (540) of AP MLD 2 may wait without transmitting a frame for allocating resources until the PIFS time from the end time of a data frame transmitted by STA 1 (530) of STA MLD 1 in the first link even though the backoff counter has reached 0. When PIFS time or more has elapsed from the end time of the data frame transmitted by STA 1 (530) of STA MLD 1, AP 2-2 (540) of AP MLD 2 may transmit a frame (506) for allocating resources. As another example, when the EDCA backoff counter is not 0, AP 2-2 (540) of AP MLD 2 may perform a channel access operation until the EDCA backoff counter reaches 0. AP 2-2 (540) of AP MLD 2 may transmit a frame (506) for allocating resources at the slot boundary where the EDCA backoff counter reaches 0. For example, the frame (506) allocating resources transmitted by AP 2-2 (540) of AP MLD 2 in FIG. 3c may be a frame allocating resources to AP 2-1 (510) of AP MLD 2 as in FIG. 3a, or may be a frame allocating resources to STA 2 (570) of STA MLD 1 as in FIG. 3b, and may not be limited to a specific form.

In FIGS. 5A to 5C, the machine learning algorithm and the machine learning unit illustrated in FIGS. 1 to 4 may be used for the AP 2-2 (540) of the AP MLD 2 to allocate a C-TDMA communication section. For example, the machine learning unit of the AP 2-2 (540) of the AP MLD 2 may use the signal strengths of the AP 2-1 (510) of the AP MLD 2 and the STA 2 and the maximum TXOP length of the AP 2-2 (540) of the AP MLD 2 to allocate a C-TDMA communication section. The machine learning unit of the AP 2-2 (540) of the AP MLD 2 may determine whether to allocate a C-TDMA resource to the AP 2-1 (510) of the AP MLD 2 or to allocate a C-TDMA resource to the STA 2 (570) of the STA MLD 1. The machine learning unit of AP 2-2 (540) of AP MLD 2 can further determine the length of the C-TDMA communication interval allocation. The AP 2-2 (540) of AP MLD 2 can determine an AP or STA as an optimal C-TDMA communication interval allocation target based on the judgment of the machine learning unit and determine the communication interval. Therefore, the C-TDMA operation can proceed efficiently. If the AP 2-2 (540) of AP MLD 2 determines that C-TDMA communication interval allocation is unnecessary, it can perform a frame transmission operation to release only the medium synchronization delay timer of the STA MLD without separately allocating a communication interval and resources as in the embodiment related to FIG. 7 described below, and is not limited to a specific form.

FIG. 6 is a diagram illustrating a method for allocating coordinated orthogonal frequency division multiple access resources in a multi-link wireless LAN network to which the present disclosure is applied.

Referring to FIG. 6, a multi-link operation may be performed in a wireless LAN network. FIG. 6 is merely an example for convenience of explanation and may not be limited thereto, and may be equally applied to other situations. For example, a first link and a second link may exist, and an MLD (multi-link device) supporting a multi-link operation may operate in the first link and the second link. A plurality of AP MLDs (e.g. AP MLD 1, AP MLD 2) may operate in the first link and the second link. In addition, a STA MLD (e.g. STA MLD 1) may operate in the first link and the second link. Here, the STA MLD may be referred to as a non-AP MLD. For example, an MLD may have independent medium access control (MAC) (e.g. lower MAC layer) and PHY entities per link, and may have an upper MAC (e.g. upper MAC layer) entity that integrates the independent MAC layers per link. For example, an MLD including independent MAC and PHY per link may include independent communication modules per link.

In the following, the AP operating in the first link with AP MLD 1 may be AP 1-1 of AP MLD 1, and the AP operating in the second link with AP MLD 1 may be AP 1-2 of AP MLD 1. In addition, the AP operating in the first link with AP MLD 2 may be AP 2-1 of AP MLD 2, and the AP operating in the second link with AP MLD 2 may be AP 2-2 of AP MLD 2. In addition, the STA (non-AP STA) operating in the first link with STA MLD 1 may be STA 1 of STA MLD 1, and the STA operating in the second link with STA MLD 1 may be STA 2 of STA MLD 1. As an example, STA MLD 1 may be connected (or associated) with AP MLD 1. In addition, STA MLD 1 may be a non-simultaneous transmit and receive (NSTR) terminal. When STA MLD 1 performs transmission on one link (e.g. the first link) among the NSTR link pairs (e.g. the first link and the second link) of STA MLD 1, STA MLD 1 may not perform channel detection and frame reception operations on the link (e.g. the second link) on which transmission is not performed, and may also not be able to set a Network Allocation Vector (NAV). Accordingly, medium synchronization of the link on which STA MLD 1 does not perform transmission may be released. For example, when STA MLD 1 performs a medium synchronization recovery operation, STA MLD 1 may not perform transmission on the link (e.g. the second link) on which transmission is not performed for a certain period of time. Alternatively, when STA MLD 1 performs a medium synchronization recovery operation, a medium synchronization delay timer (MediumSyncDelay timer) that restricts transmission in STA MLD 1 may operate. That is, STA 2 of STA MLD 1 cannot transmit a frame for a certain period of time, which may cause a transmission delay. For example, if STA MLD 1 normally receives a frame while the medium synchronization delay timer is operating and can decode the received frame to normally set the NAV, the medium synchronization delay timer may be released in STA MLD 1.

STA 1 (630) of STA MLD 1 may transmit a multi-link resource allocation request to AP 1-1 (620) of AP MLD 1 in a first link by including it in a data frame. The multi-link resource allocation request may be an AP assistance request (AAR). For example, the AAR may be transmitted in the form of an A-control in the HT control field of the MAC header of the data frame, but may not be limited thereto. The AAR may include an indicator (e.g., a link bitmap) requesting resource allocation in the second link. The AAR may request the release of a medium synchronization delay timer in the multi-link and may be used for rapid uplink transmission. The resource allocation may include uplink transmission resource allocation. The uplink resource allocation may be allocated through a trigger frame or other frames.

For example, AP 1-1 (620) of AP MLD 1 may not receive a data frame transmitted by STA 1 (630) of STA MLD 1 to AP 1-1 (620) of AP MLD 1 due to communication interference occurring in AP 1-1 (620) of AP MLD 1. The communication interference occurring in AP 1-1 (620) of AP MLD 1 may be caused by internal communication of AP 1-1 (620) of AP MLD 1 (e.g. heterogeneous communication or P2P (Peer-to-Peer) communication of AP 1-1 (620) of AP MLD 1) or communication of OBSS (overlapping BSS) within the communication range of AP 1-1 (620) of AP MLD 1. However, the reason for the communication interference is not specific, and the cause of the communication interference of AP 1-1 (620) of AP MLD 1 may be in various forms other than the cause mentioned above.

If AP 1-1 (620) of AP MLD 1 fails to receive the data frame transmitted by STA 1 (630) of STA MLD 1 due to communication interference, AP 1-1 (620) of AP MLD 1 may also fail to receive AAR transmitted by STA 1 (630) of STA MLD 1. On the other hand, AP 2-1 (610) of AP MLD 2 may be able to receive the data frame transmitted by STA 1 (630) of STA MLD 1 and AAR included in the data frame since it operates on the first link, which is the same link as AP 1-1 (620) of AP MLD 1 and STA 1 (630) of STA MLD 1. Here, the APs of AP MLD 1 and the APs of AP MLD 2 may be APs included in the same multi-AP group (Multi-AP, MAP). In addition, as an example, STA 1 of STA MLD 1 may not be an STA associated with AP MLD 2. Therefore, AP 2-1 (610) of AP MLD 2 can receive a data frame transmitted by STA 1 (630) of STA MLD 1 and an AAR included in the data frame based on a method of overhearing. That is, AP MLD 2 can receive a frame of STA MLD 1 that is not associated with AP MLD 2 and check its contents. AP MLD 2 can check an indicator included in the AAR transmitted by STA 1 (630) of STA MLD 1 (e.g. an indicator requesting a resource from a second link).

AP 2-1 (610) of AP MLD 2 may wait to determine whether AP 1-1 (620) of AP MLD 1 responds to the data frame transmitted by STA 1 (630) of STA MLD 1. For example, the waiting time for determining that AP 2-1 (610) of AP MLD 2 is waiting may be longer than SIFS (short interframe space) time. As a specific example, the waiting time may be PIFS (priority interframe space), but may not be limited thereto. The waiting time is the time for AP 1-1 (620) of AP MLD 1 to wait for transmission of a response frame to the frame transmitted by STA 1 (630) of STA MLD 1. Alternatively, the waiting time may be the time that STA 1 (630) of STA MLD 1 waits to retransmit a frame when it fails to transmit a frame to AP 1-1 (620) of AP MLD 1. If AP 1-1 (620) of AP MLD 1 does not respond to STA 1 (630) of STA MLD 1 until the waiting time (e.g. PIFS) elapses, or if STA 1 (630) of STA MLD 1 does not retransmit a data frame to AP 1-1 (620) of AP MLD 1, AP MLD 2 may transmit a frame to allocate resources to the second link.

The AP 2-1 (610) of the AP MLD 2 may wait for an additional time, 'a' time, after the PIFS time from the end time of the data frame transmission of the STA 1 (630) of the STA MLD 1 in consideration of the retransmission of the STA 1 (630) of the STA MLD 1. For example, the 'a' time may be aSlotTime or a longer time. If the AP 2-1 (510) of the AP MLD 2 detects the retransmission of the STA 1 (630) of the STA MLD 1 during the PIFS + 'a' time, the AP MLD 2 may not transmit a frame allocating resources to the second link. Alternatively, the AP MLD 2 may transmit the frame allocating resources to the second link after the PIFS or PIFS + 'a' time after the retransmission of the STA 1 (630) of the STA MLD 1 is completed. If AP 2-1 (610) of AP MLD 2 does not detect a retransmission of STA 1 (630) of STA MLD 1 for PIFS +'a' time, AP MLD 2 may transmit a frame allocating resources to the secondary link.

AP 2-2 (640) of AP MLD 2 may perform a channel access operation (e.g., EDCA (enhanced distributed channel access) backoff operation and EDCA TXOP (transmit opportunity) acquisition procedure) to transmit a frame. For example, the EDCA backoff counter of AP 2-2 (640) of AP MLD 2 may have already reached 0 before transmitting a frame for allocating resources. Here, AP 2-2 (640) of AP MLD 2 may wait without transmitting a frame for allocating resources until the PIFS time from the end time of a data frame transmitted by STA 1 (630) of STA MLD 1 in the first link even though the backoff counter has reached 0. When PIFS time or more has elapsed from the end time of the data frame transmitted by STA 1 (630) of STA MLD 1, AP 2-2 (640) of AP MLD 2 may transmit a frame for allocating resources. As another example, when the EDCA backoff counter is not 0, AP 2-2 (640) of AP MLD 2 may perform a channel access operation until the EDCA backoff counter reaches 0. AP 2-2 (640) of AP MLD 2 may transmit a frame for allocating resources at the slot boundary where the EDCA backoff counter reaches 0.

A frame for allocating resources transmitted by AP 2-2 (640) of AP MLD 2 in the second link may be an MU-RTS trigger frame (MU-RTS frame, 601) or various types of trigger frames. AP 2-2 (640) of AP MLD 2 may obtain a transmit opportunity (TXOP) in the second link by transmitting the MU-RTS frame (601) in the second link. For example, the MU-RTS frame (601) transmitted by AP 2-2 (640) of AP MLD 2 may be a frame for allocating communication resources (e.g., communication frequency and time interval) in a coordinated orthogonal frequency division multiple access (C-OFDMA) operation. That is, AP 2-2 (640) of AP MLD 2 may allocate C-OFDMA communication resources to another AP within the TXOP. The MU-RTS frame (601) transmitted by AP 2-2 (640) of AP MLD 2 may include information for allocating C-OFDMA communication resources to AP 1-2 (660) of AP MLD 2 (e.g. all or part of the MAC address that can identify AP MLD 1 or a lower AP, Multi-AP group ID, a predetermined AID (association identifier)). In addition, the MU-RTS frame (601) may further include bandwidth information that is a C-OFDMA communication resource. In addition, as an example, the MU-RTS frame (601) may include information for instructing resource allocation to STA 2 (570) of STA MLD 1 (e.g. all or part of the AID or MAC address that can identify STA MLD 1 and a lower STA). That is, the C-OFDMA communication resources included in the MU-RTS frame (601) may be instructed to be allocated to AP 1-2 (660) of AP MLD 2, and the communication resources allocated to AP 1-2 (660) of AP MLD 2 may be instructed to be used for uplink resource allocation of STA 2 (570) of STA MLD 1. AP 1-2 (660) of AP MLD 2 may receive the MU-RTS frame (601) from AP 2-2 (640) of AP MLD 2, and may transmit a CTS (clear to send) frame (602) as a response after a short interframe space (SIFS) time. After that, AP 1-2 (660) of AP MLD 2 and AP 2-2 (640) of AP MLD 2 can transmit trigger frames (TF, 603-1, 603-2). Here, AP 1-2 (660) of AP MLD 2 and AP 2-2 (640) of AP MLD 2 can transmit trigger frames (603-1, 603-2) with a designated communication resource (frequency). As a specific example, when the second link has a bandwidth of 160 MHz, the trigger frames (603-1, 603-2) of AP 1-2 (660) of AP MLD 2 and AP 2-2 (640) of AP MLD 2 can be transmitted at 80 MHz, respectively. At least one user info field of a trigger frame (603-2) transmitted by AP 1-2 (660) of AP MLD 2 may include information (e.g. AID of STA MLD 1) that can identify STA 2 (570) of STA MLD 1. STA 2 (570) of STA MLD 1 may receive the trigger frame (603-2) of AP 1-2 (660) of AP MLD 2, and may check resource information (e.g. uplink transmission bandwidth, transmission length, etc.) allocated in the trigger frame (603-2). STA 2 (570) of STA MLD 1 may transmit an uplink frame to AP 1-2 (660) of AP MLD 2 through the resource information allocated in the trigger frame (603-2). AP 1-2 (660) of AP MLD 2 can transmit a response frame (e.g. BlockAck frame) to the uplink frame transmitted by STA 2 (570) of STA MLD 1. In addition, a trigger frame (603-1) transmitted by AP 2-2 (640) of AP MLD 2 can include a user information field of STA X (650) connected to AP 2-2 (640) of AP MLD 2. STA X (650) transmits an uplink frame to AP 2-2 (640) of AP MLD 2, and AP 2-2 (640) of AP MLD 2 can transmit a response frame to STA X (660). That is, the trigger frame (603-2) is a frame that allocates uplink resources. That is, STA 2 (670) of STA MLD 1 operating on the second link as STA MLD 1 can be allocated uplink resources based on the adjusted time division communication operation.

The C-OFDMA resources allocated by AP 2-2 (640) of AP MLD 2 to AP 1-2 (660) of AP MLD 2 may be terminated. The TXOP of AP 2-2 (640) of AP MLD 2 may remain, and AP 2-2 (640) of AP MLD 2 may allocate the remaining TXOP to another AP as a C-TDMA or C-OFDMA segment. Alternatively, AP 2-2 (640) of AP MLD 2 may use the remaining TXOP in communication with an STA (e.g. STA X (660)) connected to AP 2-2 (640) of AP MLD 2. The medium synchronization delay timer of STA 2 (570) of STA MLD 1 may be terminated early by at least one normally received frame among the MU-RTS frame (601) of AP 2-2 (640) of AP MLD 2, the CTS frame (602) of AP 1-2 (660) of AP MLD 2, and the trigger frame (603-2) of AP 1-2 (660) of AP MLD 2.

The machine learning algorithm and the machine learning unit illustrated in FIGS. 1 to 4 may be used by AP 2-2 (640) of AP MLD 2 to allocate C-OFDMA resources. For example, the machine learning unit of AP 2-2 (640) of AP MLD 2 may determine the maximum available channel bandwidth and the optimally allocated frequency resources and communication sections for C-OFDMA resource allocation. Based on the determined resource information, AP 2-2 (640) of AP MLD 2 may allocate the optimal frequency resources and communication sections to AP 1-2 (660) of AP MLD 2, thereby enabling efficient communication resource allocation. As another example, if AP 2-2 (640) of AP MLD 2 determines that C-OFDMA communication resource allocation is unnecessary, it may perform a frame transmission operation to release only the medium synchronization delay timer of STA MLD without separately allocating the communication section and resources as illustrated in FIG. 7 below.

FIG. 7 is a diagram illustrating a method for eliminating communication delay of a wireless LAN terminal in a multi-link wireless LAN network applied to the present disclosure.

Referring to FIG. 7, a multi-link operation may be performed in a wireless LAN network. FIG. 7 is merely an example for convenience of explanation and may not be limited thereto, and may be equally applied to other situations. For example, a first link and a second link may exist, and an MLD (multi-link device) supporting a multi-link operation may operate in the first link and the second link. A plurality of AP MLDs (e.g. AP MLD 1, AP MLD 2) may operate in the first link and the second link. In addition, a STA MLD (e.g. STA MLD 1) may operate in the first link and the second link. Here, the STA MLD may be referred to as a non-AP MLD. For example, an MLD may have independent medium access control (MAC) (e.g. lower MAC layer) and PHY entities per link, and may have an upper MAC (e.g. upper MAC layer) entity that integrates the independent MAC layers per link. For example, an MLD including independent MAC and PHY per link may include independent communication modules per link.

In the following, the AP operating in the first link with AP MLD 1 may be AP 1-1 of AP MLD 1, and the AP operating in the second link with AP MLD 1 may be AP 1-2 of AP MLD 1. In addition, the AP operating in the first link with AP MLD 2 may be AP 2-1 of AP MLD 2, and the AP operating in the second link with AP MLD 2 may be AP 2-2 of AP MLD 2. In addition, the STA (non-AP STA) operating in the first link with STA MLD 1 may be STA 1 of STA MLD 1, and the STA operating in the second link with STA MLD 1 may be STA 2 of STA MLD 1. As an example, STA MLD 1 may be connected (or associated) with AP MLD 1. In addition, STA MLD 1 may be a non-simultaneous transmit and receive (NSTR) terminal. When STA MLD 1 performs transmission on one link (e.g. the first link) among the NSTR link pairs (e.g. the first link and the second link) of STA MLD 1, STA MLD 1 may not perform channel detection on the link (e.g. the second link) on which transmission is not performed, and may also not be able to set a Network Allocation Vector (NAV). Accordingly, medium synchronization of the link on which STA MLD 1 does not perform transmission may be released. For example, when STA MLD 1 performs a medium synchronization recovery operation, STA MLD 1 may not perform transmission on the link (e.g. the second link) on which transmission is not performed for a certain period of time. Alternatively, when STA MLD 1 performs a medium synchronization recovery operation, a medium synchronization delay timer (MediumSyncDelay timer) that restricts transmission in STA MLD 1 may operate. That is, STA 2 of STA MLD 1 cannot transmit a frame for a certain period of time, which may cause a transmission delay. For example, if STA MLD 1 normally receives a frame while the medium synchronization delay timer is operating and can decode the received frame to normally set the NAV, the medium synchronization delay timer may be released in STA MLD 1.

STA 1 (730) of STA MLD 1 may transmit a multi-link resource allocation request to AP 1-1 (720) of AP MLD 1 in a data frame from the first link. The multi-link resource allocation request may be an AP assistance request (AAR). For example, the AAR may be transmitted in the form of an A-control in the HT control field of the MAC header of the data frame, but may not be limited thereto. The AAR may include an indicator (e.g., a link bitmap) requesting resource allocation in the second link. The AAR may request the release of a medium synchronization delay timer in the multi-link and may be used for rapid uplink transmission. The resource allocation may include uplink transmission resource allocation. The uplink resource allocation may be allocated through a trigger frame or other frames. Alternatively, the AAR may be used only for a request for a frame for the release of a medium synchronization delay timer in the multi-link.

For example, AP 1-1 (720) of AP MLD 1 may not receive a data frame transmitted by STA 1 (730) of STA MLD 1 to AP 1-1 (720) of AP MLD 1 due to communication interference occurring in AP 1-1 (720) of AP MLD 1. The communication interference occurring in AP 1-1 (720) of AP MLD 1 may be caused by internal communication of AP 1-1 (720) of AP MLD 1 (e.g. heterogeneous communication or P2P (Peer-to-Peer) communication of AP 1-1 (720) of AP MLD 1) or communication of OBSS (overlapping BSS) within the communication range of AP 1-1 (720) of AP MLD 1. However, the reason for the communication interference is not specific, and the cause of the communication interference of AP 1-1 (720) of AP MLD 1 may be in various forms other than the cause mentioned above.

If AP 1-1 (720) of AP MLD 1 fails to receive the data frame transmitted by STA 1 (730) of STA MLD 1 due to communication interference, AP 1-1 (720) of AP MLD 1 may also fail to receive the AAR transmitted by STA 1 (730) of STA MLD 1. On the other hand, AP 2-1 (710) of AP MLD 2 may be able to receive the data frame transmitted by STA 1 (730) of STA MLD 1 and the AAR included in the data frame since it operates on the first link, which is the same link as AP 1-1 (720) of AP MLD 1 and STA 1 (730) of STA MLD 1. Here, the APs of AP MLD 1 and the APs of AP MLD 2 may be APs included in the same multi-AP group (Multi-AP, MAP). In addition, as an example, STA 1 of STA MLD 1 may not be an STA associated with AP MLD 2. Therefore, AP 2-1 (710) of AP MLD 2 can receive a data frame transmitted by STA 1 (730) of STA MLD 1 and an AAR included in the data frame based on a method of overhearing. That is, AP MLD 2 can receive a frame of STA MLD 1 that is not associated with AP MLD 2 and check its contents. AP MLD 2 can check an indicator included in the AAR transmitted by STA 1 (730) of STA MLD 1 (e.g. an indicator requesting a resource from a second link).

AP 2-1 (710) of AP MLD 2 may wait to check whether AP 1-1 (720) of AP MLD 1 responds to the data frame transmitted by STA 1 (730) of STA MLD 1. For example, the waiting time for checking that AP 2-1 (710) of AP MLD 2 is waiting may be longer than SIFS (short interframe space) time. The waiting time is the time for which AP 1-1 (520) of AP MLD 1 waits to transmit a response frame to the frame transmitted by STA 1 (530) of STA MLD 1. Alternatively, the waiting time may be the time for which STA 1 (730) of STA MLD 1 waits to retransmit the frame when frame transmission to AP 1-1 (720) of AP MLD 1 fails. As a specific example, the waiting time may be, but is not limited to, a priority interframe space (PIFS). If AP 1-1 (720) of AP MLD 1 does not respond to STA 1 (730) of STA MLD 1 until the waiting time (e.g. PIFS) elapses, or if STA 1 (530) of STA MLD 1 does not retransmit a data frame to AP 1-1 (520) of AP MLD 1, AP MLD 2 may transmit a frame to release a medium synchronization delay timer to the second link.

Alternatively, AP 2-1 (710) of AP MLD 2 may consider a retransmission performed after PIFS time from the end time of transmission of the data frame transmitted by STA 1 (730) of STA MLD 1. AP 2-1 (710) of AP MLD 2 may wait for an additional time, 'a' time, after the PIFS time from the end time of transmission of the data frame of STA 1 (730) of STA MLD 1. 'a' time may be aSlotTime or a longer time. If AP 2-1 (710) of AP MLD 2 does not detect the retransmission of STA 1 (730) of STA MLD 1 during PIFS + 'a' time, AP MLD 2 may transmit a frame to release a medium synchronization delay timer to the second link. If AP 2-1 detects retransmission of STA 1 during PIFS + 'a' time, AP MLD 2 may not transmit a frame for releasing the medium synchronization delay timer in the second link. Alternatively, AP MLD 2 may transmit a frame for releasing the medium synchronization delay timer after PIFS or PIFS + 'a' time from the end time of the retransmission frame of STA 1 (730) of STA MLD 1.

AP 2-2 (740) of AP MLD 2 may perform a channel access operation (e.g., EDCA (enhanced distributed channel access) backoff operation and EDCA TXOP (transmit opportunity) acquisition procedure) to transmit a frame. For example, the EDCA backoff counter of AP 2-2 (740) of AP MLD 2 may have already reached 0 before transmitting a frame for releasing a synchronization delay timer. Here, AP 2-2 (740) of AP MLD 2 may wait without transmitting a frame for releasing a synchronization delay timer until PIFS time from the end time of a data frame transmitted by STA 1 (530) of STA MLD 1 in the first link even though the backoff counter has reached 0. When PIFS time or more has elapsed from the end time of a data frame transmitted by STA 1 (730) of STA MLD 1, AP 2-2 (740) of AP MLD 2 may transmit a frame for releasing a synchronization delay timer. As another example, when the EDCA backoff counter is not 0, AP 2-2 (740) of AP MLD 2 may perform a channel access operation until the EDCA backoff counter reaches 0. AP 2-2 (740) of AP MLD 2 transmits a frame for releasing a synchronization delay timer at a slot boundary where the EDCA backoff counter reaches 0. As an example, the frame for releasing a medium synchronization delay may be a data frame such as QoS (quality of service) Null or QoS data. As another example, the frame for releasing a medium synchronization delay may be various frames such as a control frame and a management frame. In Fig. 7, AP 2-2 (740) of AP MLD 2 can transmit a QoS Null frame (701) to STA 2 (770) of STA MLD 1 to release media synchronization delay, but this is only for convenience of explanation and is not limited to the embodiment.

The medium synchronization delay timer of STA 2 (770) of STA MLD 1 may be terminated when the QoS Null frame (701) of AP 2-2 (740) of AP MLD 2 is normally received. AP 2-2 (740) of AP MLD 2 may perform a channel access operation because the medium access synchronization timer is released, and if the channel access operation is successful, it may transmit an uplink frame to AP 1-2 (760) of AP MLD 2.

Figure 8 is a method showing a method for checking whether communication is possible during wireless LAN roaming to which the present disclosure is applied.

Referring to FIG. 8, a wireless LAN terminal and a plurality of APs can operate. The wireless LAN terminal may be referred to as a non-AP STA (station) or STA. The plurality of APs may configure one SMD (single mobility domain) AP MLD. The SMD AP MLD supports MLO (multi-link operation). For example, the plurality of APs may configure an SMD AP MLD (multi-link device). The plurality of APs are non-collocated APs. The plurality of APs exchange control information within the SMD AP MLD. Each of the plurality of APs may configure an MLD lower MAC sublayer of the SMD AP MLD, and a separate device or entity that configures an MLD upper MAC sublayer may exist above the plurality of APs. Alternatively, each of the plurality of APs may configure both an MLD upper MAC sublayer and an MLD lower MAC sublayer, and the SMD AP MLD may be configured in the form of a group of the plurality of APs. Each AP that configures the SMD AP MLD may configure at least one link. In the present disclosure, for ease of explanation, each AP constituting the SMD AP MLD constitutes one link. However, it should be understood that each AP may constitute more than one link. An STA that operates by connecting to the SMD AP MLD operates by connecting (associating) to at least one AP among each AP constituting the SMD AP MLD and performs communication. For ease of explanation, the SMD AP MLD may be referred to as an AP MLD. The links constituting each AP may be configured at different frequencies. That is, each AP may operate at different frequencies.

STA (820) can perform communication by connecting to AP 1 (810) among AP MLDs. While communicating with AP 1 (810), it can be determined that the communication quality of AP 1 (810) is poor. STA (820) can search for APs and search for AP 2 (830) belonging to the same AP MLD as AP 1 (810). STA (820) can transmit information about APs to which STA (820) attempts to roam, for example, an identifier (e.g. link ID (identified), MAC address) of AP 2 (830), through a RAI (roaming announcement indication) frame. When AP 1 (810) receives the RAI frame of STA (820), it transmits a response frame (ACK frame, BlockAck (BA)) frame to STA (820) 1. AP 1 (810) transmits a RAR (roaming announcement response) frame to STA (820) 1. The RAR frame may include information on APs to which STA (820) 1 can roam (e.g., AP 2 (830)). The roamable AP information indicated in the RAR frame may be different from information on APs to which STA (820) attempts to roam, which is included in the RAI frame. When receiving the RAI frame of AP 1 (810), STA (820) transmits a response frame (ACK frame, BlockAck (BA)) frame to the AP. In another method of the RAI frame and the RAR frame, the RAI frame may not include information on APs to which STA (820) attempts to roam, or the RAR frame may not include information on APs to which STA (820) attempts to roam. The RAI frame may include AAR (AP assistance request) control information. A response frame to a RAR frame may include AAR control information. The AAR control information is control information included in the HT (high throughput) control field of the MAC header in the form of A-control, and includes a link bitmap corresponding to a link on which the STA (820) will attempt to roam. When the STA (820) transmits a frame including AAR control information, the STA (820) quickly requests uplink resources on a link indicated by the link bitmap included in the AAR control information. When the STA (820) transmits AAR control information, a communication delay of the STA (820) caused by the inability to communicate during roaming is compensated for. When the response frame to a RAR frame includes AAR information, the response frame may be transmitted in the form of an A-MPDU (aggregated - MAC protocol data unit) in which a QoS Null frame including AAR control information in the MAC header is concatenated to an ACK or BlockAck frame. The STA (820) may start roaming immediately after exchanging the RAI frame and the RAR frame. One of the RAI frame and the RAR frame may be omitted. If one of the RAI frame and the RAR frame is omitted, the STA (820) may start roaming immediately after transmitting the RAI frame or immediately after receiving the RAR frame. If the exchange of the RAI frame and the RAR frame is completed between AP 1 (810) and the STA (820) and the STA (820) starts roaming (or, if one of the RAI frame or the RAR frame is omitted and the STA (820) starts roaming), the STA (820) may switch the link. The time for the STA (820) to switch the link is the time required for the STA (820) to change the frequency and communication parameters so that it can receive frames from another AP (e.g., AP 2 (830)). The link switching time may be a time negotiated in advance between the STA (820) and the AP MLD. Alternatively, the link switching time may be included in the RAI frame transmitted by the STA (820). When the STA (820) performs an enhanced multi-link single radio (EMLSR) operation, the STA (820) may perform a clear channel assessment (CCA) on the link on which AP 2 (830) operates after the link switching, and may transmit and receive frames on the link when an initial control frame is received from AP 2 (830). The initial control frame may be a MU-RTS (multi-user request to send) trigger frame or a BSRP (buffer status report poll) trigger frame.

Meanwhile, AP 1 (810) can instruct the AP (AP 2 (830)) to which STA (820) is attempting to roam, of the expected roaming time when STA (820) performs roaming. If STA (820) includes AAR control information in the RAI frame or the response frame of the RAI frame, AP 1 (810) can instruct the AP that STA (820) requests uplink resources.

After switching the link, STA (820) fails to set the NAV (network allocation vector) on the link where AP 2 (830) operates, so it sets the MediumSyncDelay timer, which is a timer for correctly setting the NAV. STA (820) performs the CCA operation until the MediumSyncDelay timer expires, and frame transmission may be impossible or only transmission of an RTS (request to send) frame may be possible. STA (820) can release the MediumSyncDelay timer if it correctly receives the frame. STA (820) can perform a channel access operation even before the MediumSyncDelay timer expires. Since STA (820) is operating the MediumSyncDelay timer, if the channel access operation is successful, STA (820) can transmit an RTS frame to AP 2 (830). Alternatively, even if the MediumSyncDelay timer does not operate in STA (820), the first frame that STA (820) transmits when roaming may be an RTS frame. The receiver address of the RTS frame of STA (820) may be set to the MAC address of the AP MLD (SMD AP MLD) to which AP 2 (830) belongs, instead of being set to the MAC address of AP 2 (830). Setting the receiver address to the MAC address of the AP MLD indicates that AP 2 (830) is performing a roaming operation. When AP 2 (830) receives the RTS frame of STA (820), it responds with a CTS frame. When STA (820) receives the CTS frame of AP 2 (830), it releases MediumSyncDelay and transmits an uplink frame to AP 2 (830). The uplink frame may be a frame in various formats, such as a PS-Poll frame, a data frame (QoS data frame), and a Null frame (QoS Null frame). The uplink frame of STA (820) 1 may include context information of STA (820). The context information includes at least one of an uplink SN (sequence number) and PN (packet number) of STA (820). If AP 2 (830) responds to the RTS frame transmitted by STA (820) with a CTS frame, STA (820) and AP 2 (830) may exchange data frames. If STA (820) requests uplink resources through AAR control information, AP 2 (830) may transmit a trigger frame to STA (820) to allocate uplink resources. If AP 2 (830) does not transmit a CTS frame, STA (820) must not transmit an additional frame during the MediumSyncDelay time.

In order for STA (820) to determine whether to perform a roaming operation, the machine learning unit and machine learning algorithm of FIGS. 1 to 4 may be used. For example, the STA (820) may search for surrounding APs based on the judgment of the machine learning unit. The input of the machine learning unit may include channel status and beacon information of surrounding APs, and the machine learning unit may determine whether roaming is necessary and select the most suitable target AP.

Figure 9 is a drawing showing a method for checking whether communication is possible during wireless LAN roaming applied to the present disclosure.

Referring to FIG. 9, a wireless LAN terminal and a plurality of APs can operate. The wireless LAN terminal may be referred to as a non-AP STA (station) or STA. The plurality of APs may configure one SMD (single mobility domain) AP MLD. The SMD AP MLD supports MLO (multi-link operation). For example, the plurality of APs may configure an SMD AP MLD (multi-link device). The plurality of APs are non-collocated APs. The plurality of APs exchange control information within the SMD AP MLD. Each of the plurality of APs may configure an MLD lower MAC sublayer of the SMD AP MLD, and a separate device or entity that configures an MLD upper MAC sublayer may exist above the plurality of APs. Alternatively, each of the plurality of APs may configure both an MLD upper MAC sublayer and an MLD lower MAC sublayer, and the SMD AP MLD may be configured in the form of a group of the plurality of APs. Each AP that configures the SMD AP MLD may configure at least one link. In the present disclosure, for ease of explanation, each AP constituting the SMD AP MLD constitutes one link. However, it should be understood that each AP may constitute more than one link. An STA that operates by connecting to the SMD AP MLD operates by connecting (associating) to at least one AP among each AP constituting the SMD AP MLD and performs communication. For ease of explanation, the SMD AP MLD may be referred to as an AP MLD. The links constituting each AP may be configured at different frequencies. That is, each AP may operate at different frequencies.

STA (920) can perform communication by connecting to AP 1 (910) among AP MLDs. During communication with AP 1 (910), it can be determined that the communication quality of AP 1 (910) is poor. STA (920) can search for APs and search for AP 2 (930) and AP 3 (930) belonging to the same AP MLD as AP 1 (910). STA (920) can transmit information on APs to which STA (920) attempts to roam, for example, identifiers (e.g. link ID (identified), MAC address) of AP 2 (930) and AP 3 (930), through a RAI (roaming announcement indication) frame. When AP 1 (910) receives the RAI frame of STA (920), it transmits a response frame (ACK frame, BlockAck (BA)) frame to STA (920) 1. AP 1 (910) transmits a RAR (roaming announcement response) frame to STA (920) 1. The RAR frame may include information on APs to which STA (920) 1 can roam (e.g., AP 2 (930), AP 3 (930)). The roamable AP information indicated in the RAR frame may be different from information on APs to which STA (920) attempts to roam, which is included in the RAI frame. When receiving the RAI frame of AP 1 (910), STA (920) transmits a response frame (ACK frame, BlockAck (BA)) frame to the AP. In another method of the RAI frame and the RAR frame, the RAI frame may not include information on APs to which STA (920) attempts to roam, or the RAR frame may not include information on APs to which STA (920) attempts to roam. The RAI frame may include AAR (AP assistance request) control information. A response frame to a RAR frame may include AAR control information. The AAR control information is control information included in the HT (high throughput) control field of the MAC header in the form of A-control, and includes a link bitmap corresponding to a link on which the STA (920) will attempt to roam. When the STA (920) transmits a frame including AAR control information, the STA (920) quickly requests uplink resources on a link indicated by the link bitmap included in the AAR control information. When the STA (920) transmits AAR control information, a communication delay of the STA (920) caused by the inability to communicate during roaming is compensated. When the response frame to a RAR frame includes AAR information, the response frame may be transmitted in the form of an A-MPDU (aggregated - MAC protocol data unit) in which a QoS Null frame including AAR control information in the MAC header is concatenated to an ACK or BlockAck frame. The STA (920) may start roaming immediately after exchanging the RAI frame and the RAR frame. One of the RAI frame and the RAR frame may be omitted. If one of the RAI frame and the RAR frame is omitted, the STA (920) may start roaming immediately after transmitting the RAI frame or immediately after receiving the RAR frame. If the exchange of the RAI frame and the RAR frame is completed between AP 1 (910) and the STA (920) and the STA (920) starts roaming (or, if one of the RAI frame or the RAR frame is omitted and the STA (920) starts roaming), the STA (920) may switch the link. The time for the STA (920) to switch the link is the time required for the STA (920) to change the frequency and communication parameters so that the STA (920) can receive frames from at least one of the plurality of APs (e.g., AP 2 (930) and AP 3 (930)). The link switching time may be a time negotiated in advance between the STA (920) and the AP MLD. Alternatively, the link switching time may be included in the RAI frame transmitted by the STA (920). If the STA (920) supports MLO, the STA (920) may be able to receive frames from both AP 2 (930) and AP 3 (930) after the link switching. If the STA (920) supports MLO and performs an enhanced multi-link single radio (EMLSR) operation, the STA (920) may perform a clear channel assessment (CCA) on the links on which AP 2 (930) and AP 3 (930) operate after the link switching, and may transmit and receive frames on the corresponding link when an initial control frame is received from AP 2 (930) or AP 3 (930). The initial control frame can be a MU-RTS (multi-user request to send) trigger frame or a BSRP (buffer status report poll) trigger frame.

Meanwhile, AP 1 (910) can instruct multiple APs (AP 2 (930) and AP 3 (930)) to which STA (920) attempts to roam, of the expected roaming time when STA (920) performs roaming. If STA (920) includes AAR control information in an RAI frame or a response frame of the RAI frame, AP 1 (910) can instruct multiple APs that STA (920) requests uplink resources. AP 2 (930) and AP 3 (930) can prepare to transmit a trigger frame to confirm roaming of STA (920). The trigger frame is a frame requesting an uplink frame of STA (920). AP 2 (930) and AP 3 (930) can transmit the trigger frame to STA (920) after the expected roaming time of STA (920). The expected roaming time of the STA (920) may be after the link switching time from the roaming start time of the STA (920), or after a time longer than the link switching time from the roaming start time of the STA (920). When the STA (920) performs the EMLSR operation, the trigger frame may be an MU-RTS trigger frame.

After switching the link, STA (920) sets the MediumSyncDelay timer, which is a timer for correctly setting the NAV (network allocation vector), because it fails to set the NAV in the link where AP 2 (930) and AP 3 (930) operate. STA (920) performs the CCA operation until the MediumSyncDelay timer expires, and frame transmission may be impossible or only transmission of an RTS (request to send) frame may be possible. STA (920) may release the MediumSyncDelay timer if it correctly receives the frame. STA (920) may receive trigger frames from AP 2 (930) and AP 3 (930) after switching the link. STA (920) may select one AP (AP 2 (930)) among AP 2 (930) and AP 3 (930). When selecting one of AP 2 (930) and AP 3 (930), an AP having better reception quality of a trigger frame can be selected. Alternatively, AP 2 (930) and AP 3 (930) may use different frequencies, and STA (920) may select one of the two to select an AP. STA (920) may have received only the trigger frame of AP 2 (930) and may not have received the trigger frame of AP 3 (930). When STA (920) receives the trigger frame of AP 2 (930), it releases MediumSyncDelay and transmits a response frame to AP 2 (930). The response frame may be various types of frames, such as a PS (power save)-Poll frame, a data frame, a QoS (quality of service) data frame, a Null frame, a QoS Null frame, and a CTS frame. If the trigger frame of AP 2 (930) is an MU-RTS trigger frame, the response frame of STA (920) is a CTS frame. The response frame of STA (920) 1 may include context information of STA (920). The context information includes at least one of an uplink SN (sequence number) and PN (packet number) of STA (920). The receiver address of the response frame of STA (920) may be set to the MAC address of AP MLD (SMD AP MLD) to which AP 2 (930) belongs instead of being set to the MAC address of AP 2 (930). Setting the receiver address to the MAC address of AP MLD indicates that AP 2 (930) is performing a roaming operation. If the response frame of STA (920) is a data frame (QoS data frame) and a Null frame (QoS Null frame), STA (920) can set the More Data bit included in the MAC header of the data frame to 1 to indicate that there is data to be transmitted to the uplink by STA (920). If the response frame of STA (920) is a PS-Poll frame or a CTS frame, the Duration value included in the MAC header can indicate a longer time (e.g. adding several (1 to many) symbol times) than the transmission length of the PS-Poll frame or CTS frame to indicate that there is data to be transmitted to the uplink. If STA (920) and AP 2 (930) exchange a trigger frame and a response frame, STA (920) and AP 2 (930) can communicate data. The trigger frame of AP 2 (930) can set a TXOP (transmit opportunity), which is a communication section in which multiple frames can be transmitted. AP 2 (930) may allocate uplink resources to STA (920) through a trigger frame within TXOP or through a separate channel access procedure when the More Data bit of the MAC header of the response frame of STA (920) is set to 1, when STA (920) requests uplink resources through AAR control information transmission, or when the presence of uplink data is indicated through length information of the control frame of the response frame. AP 2 (930) may transmit downlink data within TXOP or through a separate channel access procedure.

In order for STA (920) to determine whether to perform a roaming operation, the machine learning unit and machine learning algorithm of FIGS. 1 to 4 may be used. For example, the STA (920) may search for surrounding APs based on the judgment of the machine learning unit. The input of the machine learning unit may include channel status and beacon information of surrounding APs, and the machine learning unit may determine whether roaming is necessary and select the most suitable target AP.

FIG. 10a and FIG. 10b are diagrams illustrating a method for confirming whether communication is possible during wireless LAN roaming to which the present disclosure is applied.

Referring to FIGS. 10A and 10B, a wireless LAN terminal and a plurality of APs can operate. The wireless LAN terminal may be referred to as a non-AP STA (station) or STA. The plurality of APs may configure one SMD (single mobility domain) AP MLD. The SMD AP MLD supports MLO (multi-link operation). For example, the plurality of APs may configure an SMD AP MLD (multi-link device). The plurality of APs are non-collocated APs. The plurality of APs exchange control information within the SMD AP MLD. Each of the plurality of APs may configure an MLD lower MAC sublayer of the SMD AP MLD, and a separate device or entity that configures an MLD upper MAC sublayer may exist above the plurality of APs. Alternatively, each of the plurality of APs may configure both an MLD upper MAC sublayer and an MLD lower MAC sublayer, and the SMD AP MLD may be configured in the form of a group of the plurality of APs. Each AP constituting the SMD AP MLD can configure at least one link. In the present disclosure, for ease of explanation, each AP constituting the SMD AP MLD configures one link. However, it should be understood that each AP can configure more than one link. An STA that operates by connecting to the SMD AP MLD operates by being associated with at least one AP among each AP constituting the SMD AP MLD and performs communication. For ease of explanation, the SMD AP MLD may be referred to as an AP MLD. The links configured by each AP may be configured at different frequencies. That is, each AP may operate at different frequencies.

STA (1020) can perform communication by connecting to AP 1 (1010) among AP MLDs. While communicating with AP 1 (1010), it can be determined that the communication quality of AP 1 (1010) is poor. STA (1020) can search for APs and search for AP 2 (1030) belonging to the same AP MLD as AP 1 (1010). STA (1020) can transmit information on APs to which STA (1020) attempts to roam, for example, an identifier (e.g. link ID (identified), MAC address) of AP 2 (1030), through a RAI (roaming announcement indication) frame. When AP 1 (1010) receives the RAI frame of STA (1020), it transmits a response frame (ACK frame, BlockAck (BA)) frame to STA (1020) 1. AP 1 (1010) transmits a RAR (roaming announcement response) frame to STA (1020) 1. The RAR frame may include information on APs to which STA (1020) 1 can roam (e.g., AP 2 (1030)). The roamable AP information indicated in the RAR frame may be different from information on APs to which STA (1020) attempts to roam, which is included in the RAI frame. When receiving the RAI frame of AP 1 (1010), STA (1020) transmits a response frame (ACK frame, BlockAck (BA)) frame to the AP. In another method of the RAI frame and the RAR frame, the RAI frame may not include information on APs to which STA (1020) attempts to roam, or the RAR frame may not include information on APs to which STA (1020) attempts to roam. The RAI frame may include AAR (AP assistance request) control information. A response frame to a RAR frame may include AAR control information. The AAR control information is control information included in the HT (high throughput) control field of the MAC header in the form of A-control, and includes a link bitmap corresponding to a link on which the STA (1020) will attempt to roam. When the STA (1020) transmits a frame including AAR control information, the STA (1020) quickly requests uplink resources on a link indicated by the link bitmap included in the AAR control information. When the STA (1020) transmits AAR control information, a communication delay of the STA (1020) caused by the inability to communicate during roaming is compensated for. When the response frame to a RAR frame includes AAR information, the response frame may be transmitted in the form of an A-MPDU (aggregated - MAC protocol data unit) in which a QoS Null frame including AAR control information in the MAC header is concatenated to an ACK or BlockAck frame. The STA (1020) can start roaming immediately after exchanging the RAI frame and the RAR frame. One of the RAI frame and the RAR frame may be omitted. If one of the RAI frame and the RAR frame is omitted, the STA (1020) can start roaming immediately after transmitting the RAI frame or start roaming immediately after receiving the RAR frame. If the exchange of the RAI frame and the RAR frame is completed between AP 1 (1010) and the STA (1020) and the STA (1020) starts roaming (or, if one of the RAI frame or the RAR frame is omitted and the STA (1020) starts roaming), the STA (1020) can switch the link. The time for STA (1020) to switch the link is the time required for STA (1020) to change the frequency and communication parameters so that it can receive frames from another AP (e.g. AP 2 (1030)). The link switching time may be a time negotiated in advance between STA (1020) and AP MLD. Alternatively, the link switching time may be included in the RAI frame transmitted by STA (1020).

The STA (1020) may determine that the signal strength of AP 2 (1030) is not suitable for roaming. For example, the received signal quality of AP 2 (1030) may deteriorate. Or, the received signal quality of AP 1 (1010) may improve enough to resume communication. The STA (1020) may stop the roaming operation and attempt to communicate with AP 1 (1010) again. The STA (1020) may operate again on the link on which AP 1 (1010) operates. Accordingly, the STA (1020) may ignore or be unable to receive the trigger frame of AP 2 (1030), and the STA (1020) may not respond to the trigger frame of AP 2 (1030). Or, the STA (1020) may not switch to the frequency on which AP 2 (1030) operates.

Referring to FIG. 10A, STA (1020) transmits a comeback frame to AP 1 (1010). The comeback frame is a frame that instructs STA (1020) to stop roaming and perform communication with AP 1 (1010). The comeback frame is a frame in various formats such as an action frame, a data frame, a PS-Poll frame, and an RTS frame. After transmitting the comeback frame to AP 1 (1010), STA (1020) performs data communication with AP 1 (1010) or performs a new roaming operation if a roaming condition is satisfied.

Referring to FIG. 10b, AP 1 (1010) may transmit a trigger frame including an AID (association identifier) of STA (1020) or a trigger frame to which resources are allocated in a UORA (uplink OFDMA (orthogonal frequency division multiple access) Random Access) manner after a certain period of time (e.g., link switching time + maximum transmission length of a trigger frame of AP 2 (1030) + link switching time + response frame transmission time for the trigger frame, or link switching time + maximum transmission length of the trigger frame + PIFS + link switching time) from the time when STA (1020) starts performing a roaming operation. The trigger frame transmitted by AP 1 (1010) after a certain period of time is transmitted to determine whether roaming was successful. If STA (1020) does not respond to the trigger frame of AP 1 (1010), AP 1 (1010) can determine that STA (1020) performed roaming successfully. If STA (1020) does not respond after AP 1 (1010) transmits a trigger frame, AP 1 (1010) sets a deletion timer. The start time of the deletion timer may be one of the time when AP 1 (1010) starts transmitting the trigger frame, the time when the trigger frame transmission is completed, and the time when it is confirmed that STA (1020) does not respond to the trigger frame after transmitting the trigger frame. If STA (1020) does not transmit a frame to AP 1 (1010) while the deletion timer is in progress, AP 1 (1010) deletes context information (e.g. PN, SN, BA scoreboard, transmission buffer) of STA (1020). If STA (1020) responds to the trigger frame of AP 1 (1010), AP 1 (1010) can know that STA (1020) has failed to roam and is communicating with AP 1 (1010). When STA (1020) stops roaming operation, STA (1020) transmits a response frame to the trigger frame of AP 1 (1010). The response frame transmitted by STA (1020) may be a comeback frame. The comeback frame is a frame that instructs STA (1020) to stop roaming and perform communication with AP 1 (1010). The comeback frame is a frame in various formats such as an action frame, a data frame, a PS-Poll frame, and an RTS frame. After transmitting the comeback frame to AP 1 (1010), STA (1020) performs data communication with AP 1 (1010) or performs a new roaming operation.

In order for STA (1020) to determine whether to perform a roaming operation, the machine learning unit and machine learning algorithm of FIGS. 1 to 4 may be used. For example, the STA (1020) may search for surrounding APs based on the judgment of the machine learning unit. The input of the machine learning unit may include channel status and beacon information of surrounding APs, and the machine learning unit may determine whether roaming is necessary and select the most appropriate target AP.

Figure 11 is a drawing showing a method for checking whether communication is possible during wireless LAN roaming applied to the present disclosure.

Referring to FIG. 11, a wireless LAN terminal and a plurality of APs can operate. The wireless LAN terminal may be referred to as a non-AP STA (station) or STA. The plurality of APs may configure one SMD (single mobility domain) AP MLD. The SMD AP MLD supports MLO (multi-link operation). For example, the plurality of APs may configure an SMD AP MLD (multi-link device). The plurality of APs are non-collocated APs. The plurality of APs exchange control information within the SMD AP MLD. Each of the plurality of APs may configure an MLD lower MAC sublayer of the SMD AP MLD, and a separate device or entity that configures an MLD upper MAC sublayer may exist above the plurality of APs. Alternatively, each of the plurality of APs may configure both an MLD upper MAC sublayer and an MLD lower MAC sublayer, and the SMD AP MLD may be configured in the form of a group of the plurality of APs. Each AP configuring the SMD AP MLD may configure at least one link. In the present disclosure, for ease of explanation, each AP constituting the SMD AP MLD constitutes one link. However, it should be understood that each AP may constitute more than one link. An STA that operates by connecting to the SMD AP MLD operates by connecting (associating) to at least one AP among each AP constituting the SMD AP MLD and performs communication. For ease of explanation, the SMD AP MLD may be referred to as an AP MLD. The links constituting each AP may be configured at different frequencies. That is, each AP may operate at different frequencies.

STA (1120) can perform communication by connecting to AP 1 (1110) among AP MLDs. While communicating with AP 1 (1110), it can be determined that the communication quality of AP 1 (1110) is poor. STA (1120) can search for APs and search for AP 2 belonging to the same AP MLD as AP 1 (1110). STA (1120) can transmit information on APs to which STA (1120) attempts to roam, for example, an identifier (e.g. link ID (identified), MAC address) of AP 2 (1130), through a RAI (roaming announcement indication) frame. When AP 1 (1110) receives the RAI frame of STA (1120), it transmits a response frame (ACK frame, BlockAck (BA)) frame to STA (1120) 1. AP 1 (1110) transmits a RAR (roaming announcement response) frame to STA (1120) 1. The RAR frame may include information on APs to which STA (1120) 1 can roam (e.g., AP 2 (1130)). The roamable AP information indicated in the RAR frame may be different from information on APs to which STA (1120) attempts to roam, which is included in the RAI frame. When receiving the RAI frame of AP 1 (1110), STA (1120) transmits a response frame (ACK frame, BlockAck (BA)) frame to the AP. In another method of the RAI frame and the RAR frame, the RAI frame may not include information on APs to which STA (1120) attempts to roam, or the RAR frame may not include information on APs to which STA (1120) attempts to roam. The RAI frame may include AAR (AP assistance request) control information. A response frame to a RAR frame may include AAR control information. The AAR control information is control information included in the HT (high throughput) control field of the MAC header in the form of A-control, and includes a link bitmap corresponding to a link on which the STA (1120) will attempt to roam. When the STA (1120) transmits a frame including AAR control information, the STA (1120) quickly requests uplink resources on a link indicated by the link bitmap included in the AAR control information. When the STA (1120) transmits AAR control information, a communication delay of the STA (1120) caused by the inability to communicate during roaming is compensated for. When the response frame to a RAR frame includes AAR information, the response frame may be transmitted in the form of an A-MPDU (aggregated - MAC protocol data unit) in which a QoS Null frame including AAR control information in the MAC header is concatenated to an ACK or BlockAck frame. STA (1120) can start roaming immediately after exchanging RAI frames and RAR frames. One of the RAI frames and RAR frames may be omitted. If one of the RAI frames and RAR frames is omitted, STA (1120) can start roaming immediately after transmitting the RAI frame or immediately after receiving the RAR frame. If the exchange of RAI frames and RAR frames is completed between AP 1 (1110) and STA (1120) and STA (1120) starts roaming (or, if one of the RAI frames or RAR frames is omitted and STA (1120) starts roaming), STA (1120) can switch the link. The time for STA (1120) to switch the link is the time required for STA (1120) to change the frequency and communication parameters so that it can receive frames from AP (e.g. AP 2 (1130)) that wants to perform roaming by changing the frequency. The link switching time may be a time negotiated in advance between STA (1120) and AP MLD. Alternatively, the link switching time may be included in the RAI frame transmitted by STA (1120). If STA (1120) supports MLO, STA (1120) may be able to receive all frames of AP 2 (1130) after link switching. When STA (1120) supports MLO and performs enhanced multi-link single radio (EMLSR) operation, STA (1120) can perform CCA (clear channel assessment) on links where AP 2 (1130) operates after link switching, and can transmit and receive frames on the link when it receives an initial control frame from AP 2 (1130). The initial control frame can be a MU-RTS (multi-user request to send) trigger frame or a BSRP (buffer status report poll) trigger frame.

Meanwhile, AP 1 (1110) can instruct the AP (AP 2 (1130)) to which STA (1120) attempts to roam, of the expected roaming time when STA (1120) performs roaming. If STA (1120) includes AAR control information in an RAI frame or a response frame of the RAI frame, AP 1 (1110) can instruct AP 2 (1130) that STA (1120) requests uplink resources. AP 2 (1130) can prepare to transmit a trigger frame to confirm roaming of STA (1120). The trigger frame is a frame that requests an uplink frame of STA (1120). AP 2 (1130) can transmit the trigger frame to STA (1120) after the expected roaming time of STA (1120). The expected roaming time of STA (1120) may be after the link switching time from the roaming start time of STA (1120), or after a time longer than the link switching time from the roaming start time of STA (1120). When STA (1120) performs EMLSR operation, the trigger frame may be an MU-RTS trigger frame.

After switching the link, STA (1120) sets the MediumSyncDelay timer, which is a timer for correctly setting the NAV (network allocation vector), because it failed to set the NAV on the link where AP 2 (1130) operates. STA (1120) performs the CCA operation until the MediumSyncDelay timer expires, and frame transmission may be impossible or only transmission of an RTS (request to send) frame may be possible. STA (1120) may release the MediumSyncDelay timer if it correctly receives the frame. STA (1120) may receive a trigger frame from AP 2 (1130) after switching the link. If STA (1120) receives the trigger frame of AP 2 (1130), it releases MediumSyncDelay and transmits a response frame to AP 2 (1130). The response frame can be various types of frames such as a PS (power save)-Poll frame, a data frame, a QoS (quality of service) data frame, a Null frame, and a QoS Null frame. If the trigger frame of AP 2 (1130) is an MU-RTS trigger frame, the response frame of STA (1120) is a CTS frame. STA (1120) can determine that the reception quality of the trigger frame of AP 2 (1130) is not good. STA (1120) can transmit a negative response frame to AP 2 (1130). The negative response frame is a response frame that instructs STA (1120) to cancel roaming. After STA (1120) transmits the negative response frame, STA (1120) can transmit a comeback frame to AP 1 (1110). Alternatively, AP 1 (1110) may retransmit the trigger frame after a certain period of time from the time when STA (1120) starts performing the roaming operation, and STA (1120) may respond to the trigger frame of AP 1 (1110) with a comeback frame. If AP 1 (1110) responds to the comeback frame, STA (1120) may perform frame exchange with AP 1 (1110). STA (1120) may perform a new roaming operation. The operation of transmitting the comeback frame may be the same as or similar to the operation of STA (1120) transmitting the comeback frame to AP 1 (1110) in FIGS. 10A and 10B. For example, the certain period of time may be the certain period of time in FIG. 10B. The comeback frame may be the comeback frame in FIGS. 10A and 10.

In order for STA (1120) to determine whether to perform a roaming operation, the machine learning unit and machine learning algorithm of FIGS. 1 to 4 may be used. For example, the STA (1120) may search for surrounding APs based on the judgment of the machine learning unit. The input of the machine learning unit may include channel status and beacon information of surrounding APs, and the machine learning unit may determine whether roaming is necessary and select the most appropriate target AP.

FIG. 12 is a flowchart illustrating a method for eliminating communication delay of a wireless LAN terminal in a multi-link wireless LAN network to which the present disclosure is applied.

Referring to FIG. 12, a method of operating a first AP MLD including a first AP associated with a first link and a second AP associated with a second link can be provided. Here, the first AP MLD can be AP MLD 2 described above with reference to FIGS. 5A to 7.

Referring to FIG. 12, a first AP MLD may receive a multi-link resource allocation request from a first STA of a STA MLD on a first link for a first AP of the first AP MLD. (S1210) Here, the STA MLD may be the STA MLD 1 described above with reference to FIGS. 5A to 7. In addition, the operation of the first AP MLD for the first AP of the first AP MLD may be an operation for a lower AP of the first AP MLD. For example, the operation of the first AP MLD for the first AP of the first AP MLD may be an operation of AP 2-1 of AP MLD 2, but may not be limited thereto. Thereafter, based on the multi-link resource allocation request, the first AP MLD can transmit the first frame on the second link for the second AP of the first AP MLD to obtain a TXOP on the second link. (S1220) For example, the operation of the first AP MLD for the second AP of the first AP MLD may be, but is not limited to, the operation of AP 2-2 of AP MLD 2. In addition, the first frame may be, but is not limited to, the MU-RTS frame or QoS null frame described above with reference to FIGS. 5A to 7. Thereafter, the first AP MLD can allocate a time-division communication section to another wireless LAN terminal within the TXOP based on the first frame (S1230), and receive a second frame in response to the first frame. (S1240) Here, the second frame may be the CTS frame described above with reference to FIGS. 5A to 7.

Additionally, as an example, the first AP MLD may include a first AP of the first AP MLD associated with the first link, a second AP of the first AP MLD associated with the second link, at least one transceiver for transmitting and receiving a signal, at least one processor for controlling at least one of the first AP, the second AP and the at least one transceiver, and a memory for storing instructions that cause the first AP MLD to perform a specific operation by the at least one processor. Here, the specific operation may include the operation described above and the operation described below.

For example, the multi-link resource allocation request may be included in a data frame that the STA MLD transmits to the second AP MLD for the first STA. The first AP MLD and the second AP MLD may be included in the same multi-AP group, and the second AP MLD may be AP MLD 1 described above with reference to FIGS. 5A to 7. The data frame including the multi-link resource allocation request may not be received by the second AP MLD, and the first AP MLD may receive the data frame including the multi-link resource allocation request for the first AP of the first AP MLD in an overhearing manner on the first link. In addition, the multi-link resource allocation request may include an indicator requesting resources for the STA MLD on the second link. The first AP MLD may transmit the first frame on the second link for the second AP of the first AP MLD to allocate a time-division communication section. Additionally, the first AP MLD may transmit the first frame on the second link to allocate a time-division communication section in the TXOP if no reception of a data frame from the second AP MLD is detected during a waiting time after receiving the data frame including the multi-link resource allocation request.

As another example, the first AP MLD may transmit the first frame on the second link to allocate a time-division communication section in the TXOP if the reception of the data frame from the second AP MLD is not detected during the waiting time and the additional time after receiving the data frame including the multi-link resource allocation request. Here, the additional time may be a time set based on the retransmission of the STA MLD, as described above.

In addition, the first AP MLD can transmit the first frame by performing a channel access operation. If the backoff counter reaches 0 before the waiting time according to the channel access operation, the first AP MLD can transmit the first frame for the second AP of the first A MLD after the waiting time. On the other hand, if the backoff counter reaches 0 after the waiting time according to the channel access operation, the first AP MLD can transmit the first frame for the second AP of the first AP MLD at the slot boundary where the backoff counter reaches 0.

In addition, the first frame may include at least one of information for allocating a time-division communication section to the second AP MLD and information for allocating a time-division communication section to the STA MLD, and the user information field of the first frame may include at least one of information for indicating the second AP MLD and information for indicating the STA MLD. Here, when the first AP MLD allocates a time-division communication section to the second AP MLD according to the information for allocating a time-division communication section to the second AP MLD included in the first frame, the first AP MLD may receive a second frame from the second AP MLD on the second link in response to the first frame. The time-division communication section may be a section in which communication is performed by the second AP MLD and the STA MLD on the second link, as described above.

In addition, when the time-division communication section allocated to the second AP MLD ends and the remaining TXOP remains in the first AP MLD, the first AP MLD can re-allocate the time-division communication section to another wireless LAN terminal or directly communicate with the wireless LAN terminal connected to the first AP MLD in the remaining TXOP, as described above.

In addition, as an example, when the first AP MLD allocates a time-division communication section to the STA MLD according to information for allocating a time-division communication section to the STA MLD included in the first frame, the first AP MLD may receive a second frame from the STA MLD on the second link in response to the first frame. Here, the time-division communication section may be a section in which uplink transmission is performed from the STA MLD to the second AP MLD on the second link.

Additionally, the first frame may further include bandwidth information based on orthogonal frequency division multiple access together with at least one of information for allocating a time-division communication section to the second AP MLD and information for allocating a time-division communication section to the STA MLD. The user information field of the first frame may include at least one of information indicating the second AP MLD and information indicating the STA MLD.

In addition, a time-division communication section is allocated after a preset time from the time point at which the first AP MLD receives the second frame in response to the first frame, and the first AP MLD can perform communication with a wireless LAN terminal connected to the first AP MLD at a first bandwidth based on bandwidth information within the time-division communication section. Here, communication between the second AP MLD and the STA MLD can be further performed at the second bandwidth within the time-division communication section, as described above.

In addition, the synchronization delay timer starts when the data frame transmission of the STA MLD ends, and the synchronization delay timer can be released based on at least one of the first frame transmission, the reception of the second frame, and the transmission of the third frame based on the second frame. As another example, the synchronization delay timer can start when the data frame transmission of the STA MLD ends. Here, the first frame that the first AP MLD transmits for the second AP of the first AP MLD is a frame that releases the synchronization delay timer, and the TXOP may not be allocated to the first AP MLD by the first frame, as described above.

The methods according to the present disclosure may be implemented in the form of program commands that can be executed through various computer means and recorded on a computer-readable medium. The computer-readable medium may include program commands, data files, data structures, etc., alone or in combination. The program commands recorded on the computer-readable medium may be those specially designed and configured for the present disclosure or may be known and available to those skilled in the art of computer software.

Examples of computer-readable media include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine language codes produced by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, and the like. The hardware devices described above may be configured to operate with at least one software module to perform the operations of the present disclosure, and vice versa.

Although the present disclosure has been described with reference to the above embodiments, it will be understood by those skilled in the art that various modifications and changes can be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the claims below.

The above may also apply to other systems.

Claims (15)

In a wireless LAN system, a method for operating a first AP multi-link device (MLD) including a first access point (AP) associated with a first link and a second AP associated with a second link, A step in which the first AP MLD receives a multi-link resource allocation request from a first STA of the STA (station) MLD on the first link for the first AP of the first AP MLD; A step for the first AP MLD to transmit a first frame on the second link for the second AP of the first AP MLD based on the multi-link resource allocation request to obtain a TXOP (transmit opportunity) on the second link; and An operating method of a first AP MLD, comprising the steps of allocating a time-division communication section to another wireless LAN terminal within the TXOP based on the first frame, and receiving a second frame in response to the first frame. In the first paragraph, The multi-link resource allocation request is included in a data frame that the STA MLD transmits to the second AP MLD for the first STA, wherein the first AP MLD and the second AP MLD are included in the same multi-AP group, and the data frame including the multi-link resource allocation request is not received by the second AP MLD. A method of operating a first AP MLD, wherein the first AP MLD receives, in an overhearing manner, the data frame including the multi-link resource allocation request for the first AP of the first AP MLD on the first link. In the second paragraph, The above multi-link resource allocation request includes an instruction requesting resources for the STA MLD on the second link, A method of operating a first AP MLD, wherein the first AP MLD allocates the time-division communication section by transmitting the first frame on the second link for the second AP of the first AP MLD. In the third paragraph, An operating method of the first AP MLD, wherein the first AP MLD transmits the first frame on the second link and allocates the time-division communication section in the TXOP if reception of a data frame from the second AP MLD is not detected during a waiting time after receiving the data frame including the multi-link resource allocation request. In the fourth paragraph, The first AP MLD transmits the first frame on the second link if the reception of the data frame from the second AP MLD is not detected during the waiting time and additional time after receiving the data frame including the multi-link resource allocation request, thereby allocating the time-division communication section in the TXOP. The above additional time is set based on the retransmission of the STA MLD, and the operation method of the first AP MLD. In the fourth paragraph, The first AP MLD transmits the first frame by performing a channel access operation, and if the backoff counter reaches 0 before the waiting time according to the channel access operation, the first AP MLD transmits the first frame after the waiting time for the second AP of the first A MLD. An operating method of a first AP MLD, wherein, when the backoff counter reaches 0 after the waiting time according to the channel access operation, the first AP MLD transmits the first frame for the second AP of the first AP MLD at the slot boundary where the backoff counter reaches 0. In the second paragraph, The first frame includes at least one of information for allocating the time-division communication section to the second AP MLD and information for allocating the time-division communication section to the STA MLD, A method of operating a first AP MLD, wherein the user information field of the first frame includes at least one of information indicating the second AP MLD and information indicating the STA MLD. In Article 7, A method of operating a first AP MLD, wherein when the first AP MLD allocates the time-division communication section to the second AP MLD according to information for allocating the time-division communication section to the second AP MLD included in the first frame, the first AP MLD receives the second frame from the second AP MLD on the second link in response to the first frame, wherein the time-division communication section is a section in which communication is performed by the second AP MLD and the STA MLD on the second link. In Article 8, An operating method of a first AP MLD, wherein when the time-division communication section allocated to the second AP MLD ends and a remaining TXOP remains in the first AP MLD, the first AP MLD re-allocates the time-division communication section to another wireless LAN terminal or directly communicates with a wireless LAN terminal connected to the first AP MLD in the remaining TXOP. In Article 7, A method of operating a first AP MLD, wherein when the first AP MLD allocates the time-division communication section to the STA MLD according to information for allocating the time-division communication section to the STA MLD included in the first frame, the first AP MLD receives the second frame from the STA MLD on the second link in response to the first frame, wherein the time-division communication section is a section in which uplink transmission is performed from the STA MLD to the second AP MLD on the second link. In the second paragraph, The first frame further includes bandwidth information based on orthogonal frequency division multiple access together with at least one of information for allocating the time division communication section to the second AP MLD and information for allocating the time division communication section to the STA MLD, A method of operating a first AP MLD, wherein the user information field of the first frame includes at least one of information indicating the second AP MLD and information indicating the STA MLD. In Article 11, The time-division communication section is allocated after a preset time from the time when the first AP MLD receives the second frame in response to the first frame, An operating method of a first AP MLD, wherein the first AP MLD performs communication with a wireless LAN terminal connected to the first AP MLD in the first bandwidth based on the bandwidth information within the time-division communication section, and communication between the second AP MLD and the STA MLD within the time-division communication section is further performed in the second bandwidth. In the second paragraph, A method of operating a first AP MLD, wherein the synchronization delay timer is started when the transmission of the data frame of the STA MLD is terminated, and the synchronization delay timer is cleared based on at least one of the transmission of the first frame, the reception of the second frame, and the transmission of the third frame based on the second frame. In the second paragraph, The synchronization delay timer starts when the above STA MLD's transmission of the above data frame ends. An operating method of a first AP MLD, wherein the first frame transmitted by the first AP MLD for the second AP of the first AP MLD is a frame for releasing the synchronization delay timer, and the TXOP is not allocated to the first AP MLD by the first frame. In the first access point (AP) multi link device (MLD), The first AP of the first AP MLD associated with the first link; Second AP of the first AP MLD associated with the second link; At least one transceiver for transmitting and receiving signals; At least one processor controlling at least one of the first AP, the second AP and the at least one transceiver; and A memory storing instructions that cause the first AP MLD to perform a specific operation by at least one processor, The above specific actions are: Receive a multi-link resource allocation request from a first STA of a STA (station) MLD on the first link for the first AP of the first AP MLD, Based on the multi-link resource allocation request, transmitting a first frame on the second link for the second AP of the first AP MLD to obtain a transmit opportunity (TXOP) on the second link, and A first AP MLD that allocates a time-division communication section to another wireless LAN terminal within the TXOP based on the first frame and receives a second frame in response to the first frame.

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