WO2025005764A1 - Low-latency communication method and device in wireless lan system - Google Patents

Abstract

A low-latency communication method and device in a wireless LAN system are provided. Provided is a method performed by a station (STA) in a wireless LAN system, the method comprising the steps of: performing at least one of transmission and reception by using a first chain in a first link; performing at least one of transmission and reception by using a second chain in a second link; receiving an initial frame for starting an enhanced multi-link multi radio (EMLMR) operation in the first link; switching the second chain from the second link to the first link on the basis of the initial frame; transmitting information for transmitting a data frame in the second link; switching the second chain from the first link to the second link on the basis of the information; receiving a trigger frame in the second link; and transmitting the data frame in the second link on the basis of at least one of the information and the trigger frame.

Description

Low-latency communication method and device in wireless LAN system

The present invention relates to a wireless LAN system, and more specifically, to a low-latency communication method and device in a wireless LAN system.

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.

As applications requiring higher throughput and real-time transmission emerge, wireless LANs may support expanded frequency bandwidths and/or efficient retransmission operations. In addition, operations utilizing multiple channels or links simultaneously may be supported.

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 skill in the field to which the technology belongs.

The present disclosure provides a method and device for quickly transmitting data stored in a wireless LAN terminal while the terminal is receiving data from another wireless LAN terminal in a wireless LAN system.

The present disclosure provides a method and device for quickly transmitting data requiring low delay stored in a terminal in a wireless LAN system.

The present disclosure provides a method and device for requesting scheduling so that data can be transmitted while receiving data in a wireless LAN system.

The present disclosure provides a method and device for a terminal performing a multi-link radio operation in a wireless LAN system to quickly transmit data requiring low delay.

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 embodiment of the present disclosure, a method performed by a station (STA) in a wireless LAN system may include the steps of performing at least one of transmission and reception using a first chain in a first link, performing at least one of transmission and reception using a second chain in a second link, receiving an initial frame for starting an enhanced multi-link multi radio (EMLMR) operation in the first link, switching the second chain from the second link to the first link based on the initial frame, transmitting information for transmission of a data frame in the second link, switching the second chain from the first link to the second link based on the information, and receiving a trigger frame in the second link, and transmitting the data frame in the second link based on at least one of the information and the trigger frame.

A method performed by an access point (AP) in a wireless LAN system may include a step of transmitting an initial frame for starting an enhanced multi-link multi radio (EMLMR) operation in a first link, a step of transmitting information for transmission of a data frame in a second link, a step of receiving information for approving use of the second link, and a step of transmitting the data frame in the second link.

According to another embodiment of the present disclosure, a method performed by an access point (AP) in a wireless LAN system may include the steps of transmitting an initial frame for starting an enhanced multi-link multi radio (EMLMR) operation in a first link, receiving information for transmission of a data frame in a second link, transmitting a trigger frame in the second link, and receiving the data frame in the second link based on the information.

According to another embodiment of the present disclosure, a method performed by a station (STA) in a wireless LAN system includes the steps of performing at least one of transmission and reception using a first chain in a first link, performing at least one of transmission and reception using a second chain in a second link, receiving an initial frame for starting an enhanced multi-link multi radio (EMLMR) operation in the first link, switching the second chain (radio chain) of the second link to the first link based on the initial frame, receiving information for transmission of a data frame in the second link, switching the second chain from the first link to the second link based on the information, transmitting information approving use of the second link, and receiving the delay-sensitive data in the second link based on the information.

According to another embodiment of the present disclosure, in a wireless LAN system, a station (STA) includes a transceiver, and a processor connected to the transceiver, wherein the processor is configured to perform at least one of transmission and reception using a first chain in a first link, perform at least one of transmission and reception using a second chain in a second link, receive an initial frame for starting an enhanced multi-link multi radio (EMLMR) operation in the first link, switch the second chain (radio chain) to the first link based on the initial frame and the first information, transmit information for transmission of a data frame in the second link, switch the second chain from the first link to the second link based on the information, receive a trigger frame in the second link, and transmit the data frame in the second link based on at least one of the information and the trigger frame.

According to another embodiment of the present disclosure, in a wireless LAN system, an access point (AP) includes a transceiver, and a processor connected to the transceiver, wherein the processor is configured to transmit an initial frame for starting an enhanced multi-link multi radio (EMLMR) operation in a first link, transmit information for transmission of a data frame in a second link, receive information for approving use of the second link, and transmit the data frame in the second link.

According to the present disclosure, a wireless LAN terminal and a communication method can be provided for requesting another wireless LAN terminal to share a TXOP (transmit opportunity) acquired by the other wireless LAN terminal in order to quickly transmit data requiring low-latency transmission when communication is in progress in a wireless LAN system.

According to the present disclosure, a wireless LAN terminal and a communication method capable of quickly transmitting data requiring low-latency transmission and reducing transmission delay of data in a wireless LAN system can be provided.

According to the present disclosure, a wireless LAN terminal and communication method capable of rapidly transmitting data using multiple links can be provided.

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 skilled in the art to which the present disclosure belongs from the description below.

Figure 1 illustrates a block diagram of a communication node constituting a wireless LAN system.

Figure 2 illustrates the concept of multiple links established between multi-link devices (MLDs).

FIG. 3a illustrates a first embodiment of a wireless LAN EMLMR (enhanced multi-link multiple radio) low-latency transmission method.

Fig. 3b illustrates a second embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 4a illustrates a third embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 4b illustrates a fourth embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 5a illustrates a fifth embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 5b illustrates a sixth embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 6a illustrates a seventh embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 6b illustrates an eighth embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 7 illustrates a ninth embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 8 illustrates a tenth embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 9 illustrates an eleventh embodiment of a wireless LAN EMLMR low-latency transmission method.

FIG. 10a illustrates a twelfth embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 10b illustrates a 13th embodiment of a wireless LAN EMLMR low-latency transmission method.

FIG. 11 illustrates a flowchart of an operation method of an STA according to one embodiment of the present disclosure.

FIG. 12 illustrates a flowchart of an operation method of an AP according to one embodiment of the present disclosure.

FIG. 13 illustrates a flowchart of an operation method of an AP according to one embodiment of the present disclosure.

FIG. 14 illustrates a flowchart of an operation method of an STA according to one embodiment of the present disclosure.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present disclosure. However, the present disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

In describing embodiments of the present disclosure, if it is determined that a specific description of a known configuration or function may obscure the gist of the present disclosure, a detailed description thereof will be omitted. In addition, parts in the drawings that are not related to the description of the present disclosure have been omitted, and similar parts have been given similar drawing reference numerals.

In the present disclosure, when a component is said to be "connected," "coupled," or "connected" to another component, this may include not only a direct connection relationship, but also an indirect connection relationship in which another component exists in between. In addition, when a component is said to "include" or "have" another component, this does not exclude the other component unless specifically stated otherwise, but rather means that the other component may be included.

In this disclosure, the terms first, second, etc. are used only for the purpose of distinguishing one component from another component, and do not limit the order or importance between the components unless specifically stated. Accordingly, within the scope of this disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

In the present disclosure, the components that are distinguished from each other are intended to clearly explain the characteristics of each, and do not necessarily mean that the components are separated. That is, a plurality of components may be integrated to form a single hardware or software unit, or a single component may be distributed to form a plurality of hardware or software units. Accordingly, even if not mentioned separately, such integrated or distributed embodiments are also included in the scope of the present disclosure.

In the present disclosure, the components described in various embodiments do not necessarily mean essential components, and some may be optional components. Accordingly, an embodiment that consists of a subset of the components described in one embodiment is also included in the scope of the present disclosure. In addition, an embodiment that includes other components in addition to the components described in various embodiments is also included in the scope of the present disclosure.

In the present disclosure, expressions of positional relationships used in the present specification, such as top, bottom, left, right, etc., are described for convenience of explanation, and when the drawings illustrated in the present specification are viewed in reverse, the positional relationships described in the specification may be interpreted in the opposite way.

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

Figure 1 is a block diagram illustrating a first embodiment of a communication node constituting a wireless LAN system.

Referring to FIG. 1, a communication node (100) may be an access point, a station, an access point (AP), a multi-link device (MLD), or a non-AP MLD. The access point may mean an AP, and the station may mean an STA or a non-AP STA. An operating channel width supported by the access point may be 20 MHz (megahertz), 80 MHz, 160 MHz, etc. An operating channel width supported by the station may be 20 MHz, 80 MHz, etc.

The communication node (100) may include at least one processor (110), a memory (120), and at least one transceiver (130) that is connected to a network and performs communication. The transceiver (130) may be referred to as a transceiver, an RF (radio frequency) unit, an RF module, etc. In addition, the communication node (100) may further include an input interface device (140), an output interface device (150), a storage device (160), etc. Each component included in the communication node (100) may be connected by a bus (170) and communicate with each other.

However, 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 (170). For example, the processor (110) may be connected to at least one of the memory (120), the transmission/reception device (130), the input interface device (140), the output interface device (150), and the storage device (160) 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 (160). The processor (110) may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor in which methods according to embodiments of the present invention are performed. Each of the memory (120) and the storage device (160) may be configured with at least one of a volatile storage medium and a nonvolatile storage medium. For example, the memory (120) may be configured with at least one of a read only memory (ROM) and a random access memory (RAM).

FIG. 2 is a conceptual diagram illustrating a first embodiment of a multi-link established between MLDs (multi-link devices).

Referring to FIG. 2, an MLD may have one MAC (medium access control) address. In embodiments, the MLD may refer to an AP MLD and/or a non-AP MLD. The MAC address of the MLD may be used in a multi-link setup procedure between the non-AP MLD and the AP MLD. The MAC address of the AP MLD may be different from the MAC address of the non-AP MLD. Access point(s) associated with the AP MLD may have different MAC addresses, and station(s) associated with the non-AP MLD may have different MAC addresses. Access points within the AP MLD having different MAC addresses may be responsible for each link and may function as independent access points (APs).

Stations in a non-AP MLD with different MAC addresses can be in charge of each link and can perform the role of independent stations (STAs). The non-AP MLD may also be referred to as a STA MLD. The MLD can support STR (simultaneous transmit and receive) operation. In this case, the MLD can perform a transmission operation on link 1 and a reception operation on link 2. An MLD supporting the STR operation may be referred to as a STR MLD (e.g., STR AP MLD, STR non-AP MLD). In the embodiments, a link may mean a channel or a band. A device that does not support the STR operation may be referred to as an NSTR (non-STR) AP MLD or an NSTR non-AP MLD (or, NSTR STA MLD).

The MLD can transmit and receive frames in multiple links by using a non-continuous bandwidth expansion scheme (e.g., 80MHz + 80MHz). The multi-link operation can include multi-band transmission. The AP MLD can include multiple access points, and the multiple access points can operate on different links. Each of the multiple access points can perform the function(s) of the lower MAC layer. Each of the multiple access points can be referred to as a "communication node" or a "subordinate entity." The communication node (i.e., the access point) can operate under the control of a higher layer (or, the processor (110) illustrated in FIG. 1). The non-AP MLD can include multiple stations, and the multiple stations can operate on different links. Each of the multiple stations can be referred to as a "communication node" or a "subordinate entity." The communication node (i.e., the station) can operate under the control of a higher layer (or, the processor (110) illustrated in FIG. 1).

The MLD can perform communications in multi-band. For example, the MLD can perform communications using a 40MHz bandwidth in a 2.4GHz band according to a channel expansion method (e.g., a bandwidth expansion method), and can perform communications using a 160MHz bandwidth in a 5GHz band according to a channel expansion method. The MLD can perform communications using a 160MHz bandwidth in a 5GHz band, and can perform communications using a 160MHz bandwidth in a 6GHz band. One frequency band (e.g., one channel) used by the MLD can be defined as one link. Alternatively, multiple links can be established in one frequency band used by the MLD. For example, the MLD can establish one link in a 2.4GHz band, and two links in a 6GHz band. Each link can be referred to as a first link, a second link, a third link, etc. Alternatively, each link can be referred to as link 1, link 2, link 3, etc. Link numbers can be set by the access point, and each link can be assigned an ID (identifier).

An MLD (e.g., an AP MLD and/or a non-AP MLD) can establish multiple links by performing an access procedure and/or a negotiation procedure for multi-link operation. In this case, the number of links and/or a link to be used among multiple links can be established. A non-AP MLD (e.g., a station) can check information on a band that can communicate with the AP MLD. In the negotiation procedure for multi-link operation between the non-AP MLD and the AP MLD, the non-AP MLD can establish one or more links among the links supported by the AP MLD to be used for the multi-link operation. A station that does not support multi-link operation (e.g., an IEEE 802.11a/b/g/n/ac/ax station) can be connected to one or more links among the multiple links supported by the AP MLD.

When the bandwidth gap between multiple links (for example, the bandwidth gap between link 1 and link 2 in the frequency domain) is sufficient, the MLD can perform the STR operation. For example, the MLD can transmit PPDU (PLCP (physical layer convergence procedure) protocol data unit) 1 using link 1 among the multiple links, and receive PPDU 2 using link 2 among the multiple links. On the other hand, when the bandwidth gap between the multiple links is insufficient and the MLD performs the STR operation, IDC (in-device coexistence) interference, which is interference between the multiple links, may occur. Therefore, when the bandwidth gap between the multiple links is insufficient, the MLD may not perform the STR operation. The link pair having the above-described interference relationship may be a Non Simultaneous Transmit and Receive (NSTR) limited link pair. Here, the MLD may be an NSTR AP MLD or an NSTR non-AP MLD.

For example, multiple links including link 1, link 2, and link 3 can be established between the AP MLD and the non-AP MLD 1. If the bandwidth gap between link 1 and link 3 is sufficient, the AP MLD can perform the STR operation using link 1 and link 3. That is, the AP MLD can transmit a frame using link 1 and receive a frame using link 3. If the bandwidth gap between link 1 and link 2 is not sufficient, the AP MLD may not perform the STR operation using link 1 and link 2. If the bandwidth gap between link 2 and link 3 is not sufficient, the AP MLD may not perform the STR operation using link 2 and link 3.

Meanwhile, in a wireless LAN system, a negotiation procedure for multi-link operation can be performed in the access procedure between a station and an access point.

A device (e.g., an access point, a station) supporting multiple links may be referred to as a multi-link device (MLD). An access point supporting multiple links may be referred to as an AP MLD, and a station supporting multiple links may be referred to as a non-AP MLD or a STA MLD. An AP MLD may have a physical address (e.g., a MAC address) for each link. An AP MLD may be implemented as if there are separate APs responsible for each link. Multiple APs may be managed within one AP MLD. Therefore, coordination between multiple APs belonging to the same AP MLD may be possible. An STA MLD may have a physical address (e.g., a MAC address) for each link. An STA MLD may be implemented as if there are separate STAs responsible for each link. Multiple STAs may be managed within one STA MLD. Therefore, coordination between multiple STAs belonging to the same STA MLD may be possible.

For example, each of AP1 of the AP MLD and STA1 of the STA MLD can be in charge of the first link and can communicate using the first link. Each of AP2 of the AP MLD and STA2 of the STA MLD can be in charge of the second link and can communicate using the second link. STA2 can receive state change information about the first link from the second link. In this case, the STA MLD can collect information (e.g., state change information) received from each link and control an operation performed by STA1 based on the collected information.

Next, methods of transmitting and receiving data in a wireless LAN system will be described. Even if a method (e.g., transmitting or receiving a signal) performed by a first communication node among communication nodes is described, a second communication node corresponding thereto can perform a method (e.g., receiving or transmitting a signal) corresponding to the method performed by the first communication node. That is, when an operation of an STA is described, an AP corresponding thereto can perform an operation corresponding to the operation of the STA. Conversely, when an operation of an AP is described, an STA corresponding thereto can perform an operation corresponding to the operation of the AP. In an embodiment, an operation of an STA can be interpreted as an operation of an STA MLD, an operation of an STA MLD can be interpreted as an operation of an STA, an operation of an AP can be interpreted as an operation of an AP MLD, and an operation of an AP MLD can be interpreted as an operation of an AP.

Fig. 3a illustrates a first embodiment of a wireless LAN EMLMR low-latency transmission method.

Fig. 3b illustrates a second embodiment of a wireless LAN EMLMR low-latency transmission method.

Referring to FIGS. 3A and 3B, AP 1 (101) and STA 1 (103) may operate in the first link, and AP 2 (105) and STA 2 (107) may operate in the second link. AP 1 (101) and AP 2 (105) may be APs affiliated with AP MLD 1. STA 1 (103) and STA 2 (107) may be STAs affiliated with STA MLD 1. That is, the AP and STA where AP MLD 1 and STA MLD 1 operate in the first link may be AP 1 (101) and STA 1 (103), and the AP and STA where AP MLD 1 and STA MLD 1 operate in the second link may be AP 2 (105) and STA 2 (107).

STA MLD 1 may be an MLD supporting enhanced multi-link multi-radio (EMLMR) operation. STA MLD 1 may perform EMLMR operation on the first link and the second link. That is, the first link and the second link may be referred to as EMLMR links. In the EMLMR operation, after an STA MLD having multiple radios receives an initial frame (300) from an AP through a determined number of spatial streams (NSS) according to per-link spatial stream capabilities on each link of the multi-link, receive chains and transmit chains are switched to the link that received the initial frame (300). The receive chains and transmit chains may be referred to as radio chains. The radio chains may be referred to as radio modules. After the STA MLD receives the initial frame (300), it may communicate with the AP MLD through the switched radio chain using the NSS set in the EMLMR setup process. In order for the STA MLD to perform the EMLMR operation, the STA MLD can transmit an EML OMN (enhanced multi-link operating mode notification) frame to the AP MLD. The EML OMN frame can include MCS and NSS (number of spatial streams) information to be used in the EMLMR operation. The EML OMN frame is an action frame including an EML control field (EML (enhanced multi-link) control field). When frame reception is terminated, the STA MLD can switch the radio chain to an EMLMR link from which the initial frame (300) was not received. The STA MLD cannot receive from an EMLMR link from which the initial frame (300) was not received until frame reception is terminated. The AP MLD does not transmit data from an EMLMR link from which the initial frame (300) was not transmitted until frame transmission is terminated. When an STA MLD performs an EMLMR operation on an EMLMR link and wants to transmit to an AP MLD, an STA of the STA MLD can switch the radio chain and transmit to an AP of the AP MLD using the MCS and NSS to be used in the EMLMR operation. After an STA of the STA MLD completes frame transmission, the STA MLD can operate on each link of the multi-links according to the spatial stream capability of each link. When an STA of the STA MLD transmits to an AP of the AP MLD, the AP MLD cannot transmit frames to STAs other than the STA to which the STA MLD is transmitting.

In the first link, AP 1 (101) may perform a channel access procedure to transmit a frame to STA 1 (103). The channel access procedure may be an EDCA backoff procedure. If the EDCA backoff procedure is successful, AP 1 (101) obtains a TXOP, which is a section in which multiple frames can be transmitted. That is, AP 1 (101) is a TXOP holder. AP 1 (101) may transmit an initial frame (300) to STA 1 (103). The link-specific spatial stream capability of STA 1 (103) may be NSS = 2. Therefore, AP 1 (101) may transmit a frame to STA 1 (103) using two spatial streams. STA 1 (103) may respond to the frame of AP 1 (101) with a BA (BlockAck) frame. STA MLD 1 can switch the radio chain to the first link after receiving the initial frame (300) of AP 1 (101). STA MLD 1 can transmit and receive through four spatial streams in EMLMR operation. In other words, the spatial stream capability used in EMLMR operation exchanged in EML OMN frame can be NSS = 4. Therefore, after STA MLD 1 switches the radio chain to the first link, STA 1 (103) can transmit or receive a frame using four spatial streams. AP 1 (101) can transmit a data frame (302) to STA 1 (103) using four spatial streams. STA 2 (107) cannot transmit a frame. While STA MLD 1 receives a data frame (302) in the first link, STA MLD 1 may have data to be sent in the second link. The data to be transmitted on the second link may be data that needs to be transmitted quickly. Therefore, STA 1 (103) of STA MLD 1 may indicate a request to transmit and receive a frame on another EMLMR link that is not currently being received in a BA frame (304) transmitted to AP 1 (101). This request may be referred to as EMLMR rapid transmission request information. The EMLMR rapid transmission request information may include at least one of information from among 'link bitmap', 'trigger frame request information', 'MCS-NSS information to be used on the indicated link', 'MCS-NSS information to be used on the current link', and 'delay boundary information'. The link bitmap may indicate a link that STA MLD 1 further intends to use. For example, STA MLD 1 may indicate the second link. 'Trigger frame request information' is information that requests that STA MLD 1 requires a trigger frame (306) on the link indicated in the link bitmap. For example, since STA MLD 1 indicates a second link in the link bitmap, AP 2 (105) of AP MLD 1 can transmit a trigger frame to STA 2 (107) of STA MLD 1 in the second link. The MCS-NSS information to be used in the indicated link indicates MCS and NSS information supported in the link indicated by STA MLD 1 in the link bitmap. STA MLD 1 and AP MLD 1 perform communication in the link indicated by STA MLD 1 in the link bitmap according to the MCS-NSS information. The MCS-NSS information to be used in the current link indicates MCS and NSS information supported in the link on which initial frames (300) were exchanged. STA MLD 1 and AP MLD 1 perform communication in the link on which initial frames (300) were exchanged according to the MCS-NSS information. Alternatively, STA MLD 1 and AP MLD 1 may operate according to link-specific spatial stream capabilities. Delay boundary information is information indicating until when STA MLD 1 should transmit data to AP MLD 1. For example, if STA indicates delay boundary information as 1ms, it indicates that STA wants to share TXOP from TXOP Holder within 1ms. Delay boundary information may further include time information per AC or per TID. For example, STA may indicate delay boundary information per AC, such as 1ms for AC_VO and 5ms for AC_BE. Or, STA may indicate delay boundary information per TID, such as 1ms for TID 1 and 3ms for TID 3. AC and TID-specific delay boundary information indications may be used simultaneously. Depending on the delay boundary information, AP MLD 1 may change channel access parameters (e.g., EDCA parameters) used for transmission of a trigger frame or a downlink frame in a link indicated by STA MLD 1 as a link bitmap. The EMLMR expedited transmission request information transmitted by STA 1 (103) to AP 1 (101) may be transmitted in the form of a BA frame and A-MPDU by being included in the MAC header of a QoS Null frame in the form of A-Control. The EMLMR expedited transmission request information may be AAR+ information, which is extended AAR (Assisted AP Request) information. Alternatively, the EMLMR expedited transmission request information may be information configured in the form of A-Control, or may be included in a frame transmitted by STA 1 (103) to AP 1 (101) in the form of an instruction bit, a subfield, an information element, and other forms.

STA 1 (103) may transmit an EMLMR rapid transmission request to AP 1 (101), which may request transmission of a trigger frame (306) on the second link. AP 1 (101) of AP MLD 1 may include an indicator for confirming the use of the second link in a downlink frame (308) transmitted after receiving a BA frame (304) including EMLMR rapid transmission request information transmitted by STA 1 (103). The indicator for confirming the use of the second link may indicate whether STA 2 (107) and AP 2 (105) can communicate on the second link. The indicator for confirming the use of the second link may be configured in the form of at least one of an A-Control, a field, a subfield, an indication bit, and an information element included in a MAC header or a MAC data frame. Alternatively, the indicator for confirming the use of the second link may be indicated by a PHY preamble. For example, an indicator for checking the use of the second link may be indicated by a change in NSS, which is the number of spatial streams over which a PPDU is transmitted (for example, Nss decreases compared to the previous frame reception), and the change in NSS may be notified through the PHY preamble. Alternatively, an indicator for checking the use of the second link may be indicated based on a change in the values of the NSS and MCS fields of the user field of the EHT (extremely high throughput)-SIG or the UHR (ultra high reliability)-SIG included in the PHY preamble. AP 2 (105) of AP MLD 1 may perform a channel access procedure (for example, an EDCA backoff operation) and transmit a trigger frame (306) to STA 2 (107) when the backoff counter reaches 0. The channel access procedure of AP 2 (105) may also be performed more quickly based on the delay boundary information of the EMLMR expedited transmission request information transmitted by STA 1 (103) to AP 1 (101). Alternatively, even if the backoff counter reaches 0, if the EMLMR Delay has not elapsed from the end time of transmission of the BA frame (304) including the EMLMR rapid transmission request of STA 1 (103), the trigger frame (306) may not be transmitted and the backoff counter may be maintained at 0. If the EMLMR Delay has elapsed, AP 2 (105) may transmit the trigger frame (306) to STA 2 (107). The EMLMR Delay is the time taken for the STA MLD performing the EMLMR operation to switch the radio chain. Since STA 2 (107) has not detected the channel for a certain period of time or longer on the second link, the MediumSyncDelay timer may be set on the second link. The length of the MediumSyncDelay timer can be set to a preset value, for example, aPPDUMaxTime, which is the maximum length of a PPDU, and while the MediumSyncDelay timer is operating, STA 2 (107) must perform CCA (Clear Channel Assessment) to determine whether the channel is occupied. CCA is a channel detection operation. When STA 2 (107) receives a trigger frame (306) of AP 2 (105), the MediumSyncDelay timer is initialized and frame transmission and reception can be performed. The trigger frame (306) that AP 2 (105) transmits to STA 2 (107) can indicate the length of the resource according to the EMLMR expedited transmission request information that STA 1 (103) transmits to AP 1 (101). STA 2 (107) can transmit a frame (310) requiring expedited transmission to AP 2 (105). In the first link, AP 1 (101) and STA 1 (103) can transmit and receive a frame (310) using two spatial streams according to EMLMR rapid transmission request information indicated by STA 1 (103). In the second link, AP 2 (105) and STA 2 (107) can transmit and receive a frame (310) using two spatial streams according to EMLMR rapid transmission request information indicated by STA 1 (103).

Referring to FIG. 3b, if the EMLMR Delay time has elapsed after aSIFSTime + aSlotTime + aRxPHYStartDelay time from the time point at which communication between AP 2 (105) and STA 2 (107) in the second link is terminated, AP 1 (101) and STA 1 (103) in the first link can perform a communication operation according to the EMLMR operation space-time stream capability exchanged through the EML OMN frame in the first link of STA MLD 1. For example, AP 1 (101) and STA 1 (103) can perform frame transmission and reception operations using four space streams.

FIG. 4a and FIG. 4b are timing diagrams illustrating a third and fourth embodiment of a wireless LAN EMLMR low-latency transmission method.

Referring to FIGS. 4A and 4B, AP 1 (101) and STA 1 (103) may operate in the first link, and AP 2 (105) and STA 2 (107) may operate in the second link. AP 1 (101) and AP 2 (105) may be APs affiliated with AP MLD 1. STA 1 (103) and STA 2 (107) may be STAs affiliated with STA MLD 1. That is, the AP and STA where AP MLD 1 and STA MLD 1 operate in the first link may be AP 1 (101) and STA 1 (103), and the AP and STA where AP MLD 1 and STA MLD 1 operate in the second link may be AP 2 (105) and STA 2 (107).

STA MLD 1 may be an MLD supporting enhanced multi-link multi-radio (EMLMR) operation. STA MLD 1 may perform EMLMR operation on the first link and the second link. That is, the first link and the second link may be referred to as EMLMR links. In the EMLMR operation, after an STA MLD having multiple radios receives an initial frame (400) from an AP through a determined number of spatial streams (NSS) according to per-link spatial stream capabilities on each link of the multi-link, receive chains and transmit chains are switched to the link that received the initial frame (400). The receive chains and transmit chains may be referred to as radio chains. After the STA MLD receives the initial frame (400), it may communicate with the AP MLD through the switched radio chain using the NSS set in the EMLMR setup process. In order for the STA MLD to perform the EMLMR operation, the STA MLD can transmit an EML OMN (enhanced multi-link operating mode notification) frame to the AP MLD. The EML OMN frame can include MCS and NSS (number of spatial streams) information to be used in the EMLMR operation. The EML OMN frame is an action frame including an EML control field. When frame reception is terminated, the STA MLD can switch the radio chain to an EMLMR link from which the initial frame (400) was not received. The STA MLD cannot receive from an EMLMR link from which the initial frame (400) was not received until frame reception is terminated. The AP MLD does not transmit from an EMLMR link from which the initial frame (400) was not transmitted until frame transmission is terminated. When an STA MLD performs an EMLMR operation on an EMLMR link and wants to transmit to an AP MLD, an STA of the STA MLD can switch the radio chain and transmit to an AP of the AP MLD using the MCS and NSS to be used in the EMLMR operation. After an STA of the STA MLD completes frame transmission, the STA MLD can operate on each link of the multi-links according to the spatial stream capability of each link. When an STA of the STA MLD transmits to an AP of the AP MLD, the AP MLD cannot transmit frames to STAs other than the STA to which the STA MLD is transmitting.

In the first link, AP 1 (101) may perform a channel access procedure to transmit a frame to STA 1 (103). The channel access procedure may be an EDCA backoff procedure. If the EDCA backoff procedure is successful, AP 1 (101) obtains a TXOP, which is a section in which multiple frames can be transmitted. That is, AP 1 (101) is a TXOP holder. AP 1 (101) may transmit an initial frame (400) to STA 1 (103). The link-specific spatial stream capability of STA 1 (103) may be NSS = 2. Therefore, AP 1 (101) may transmit a frame to STA 1 (103) using two spatial streams. STA 1 (103) may respond to the frame of AP 1 (101) with a BA (BlockAck) frame. STA MLD 1 can switch the radio chain to the first link after receiving the initial frame (400) of AP 1 (101). STA MLD 1 can transmit and receive through four spatial streams in EMLMR operation. In other words, the spatial stream capability used in EMLMR operation exchanged in EML OMN frame can be NSS = 4. Therefore, after STA MLD 1 switches the radio chain to the first link, STA 1 (103) can transmit or receive a frame using four spatial streams. AP 1 (101) can transmit a data frame (402) to STA 1 (103) using four spatial streams. STA 2 (107) cannot transmit a frame. While STA MLD 1 receives a frame in the first link, STA MLD 1 may have data to be transmitted in the second link. The data to be transmitted in the second link may be data that needs to be transmitted quickly. Accordingly, STA 1 (103) of STA MLD 1 may indicate a request to transmit and receive a frame on another EMLMR link that is not currently being received in the BA frame (404) transmitted to AP 1 (101). This request may be referred to as EMLMR rapid transmission request information. The EMLMR rapid transmission request information may include at least one of the following information: 'link bitmap', 'trigger frame request information', 'MCS-NSS information to be used on the indicated link', 'MCS-NSS information to be used on the current link', and 'delay boundary information'. The link bitmap may indicate a link that STA MLD 1 further intends to use. For example, STA MLD 1 may indicate a second link. The 'trigger frame request information' is information that STA MLD 1 requests that a trigger frame (406) is needed on the link indicated in the link bitmap. For example, since STA MLD 1 indicates the second link in the link bitmap, AP 2 (105) of AP MLD 1 can transmit a trigger frame (406) to STA 2 (107) of STA MLD 1 in the second link. The MCS-NSS information to be used in the indicated link indicates MCS and NSS information supported in the link indicated by STA MLD 1 in the link bitmap. STA MLD 1 and AP MLD 1 perform communication in the link indicated by STA MLD 1 in the link bitmap according to the MCS-NSS information. The MCS-NSS information to be used in the current link indicates MCS and NSS information supported in the link on which the initial frame (400) was exchanged. STA MLD 1 and AP MLD 1 perform communication in the link on which the initial frame (400) was exchanged according to the MCS-NSS information. Alternatively, STA MLD 1 and AP MLD 1 may operate according to the spatial stream capability per link. Delay boundary information is information indicating until when STA MLD 1 should transmit data to AP MLD 1. For example, if STA indicates delay boundary information as 1ms, it indicates that STA wants to share TXOP from TXOP Holder within 1ms. Delay boundary information may further include time information per AC or per TID. For example, STA may indicate delay boundary information per AC, such as AC_VO is 1ms and AC_BE is 5ms. Or, STA may indicate delay boundary information per TID, such as TID 1 is 1ms and TID 3 is 3ms. AC and TID-specific delay boundary information indications may be used simultaneously. Depending on the delay boundary information, AP MLD 1 may change channel access parameters (e.g., EDCA parameters) used for transmission of a trigger frame (406) or a downlink frame in a link indicated by STA MLD 1 as a link bitmap. The EMLMR expedited transmission request information transmitted by STA 1 (103) to AP 1 (101) may be transmitted in the form of a BA frame and A-MPDU by being included in the MAC header of a QoS Null frame in the form of A-Control. The EMLMR expedited transmission request information may be AAR+ information, which is extended AAR (Assisted AP Request) information. Alternatively, the EMLMR expedited transmission request information may be information configured in the form of A-Control, or may be included in a frame transmitted by STA 1 (103) to AP 1 (101) in the form of an instruction bit, a subfield, an information element, and other forms.

STA 1 (103) may transmit an EMLMR rapid transmission request to AP 1 (101), which may request transmission of a trigger frame (406) on the second link. AP 1 (101) of AP MLD 1 may include an indicator for confirming the use of the second link in a downlink frame (408) transmitted after receiving a BA frame (404) including EMLMR rapid transmission request information transmitted by STA 1 (103). The indicator for confirming the use of the second link may indicate whether STA 2 (107) and AP 2 (105) can communicate on the second link. The indicator for confirming the use of the second link may be configured in the form of at least one of an A-Control, a field, a subfield, an indication bit, and an information element included in a MAC header or a MAC data frame. Alternatively, the indicator for confirming the use of the second link may be indicated by a PHY preamble. For example, an indication of secondary link usage can be indicated by a change in NSS, which is the number of spatial streams over which a PPDU is transmitted (e.g., a decrease in NSS compared to a previous frame reception), and the change in NSS can be indicated through the PHY preamble. Alternatively, an indication of secondary link usage can be indicated based on a change in the values of NSS and MCS fields of the user field of EHT (extremely high throughput)-SIG or UHR (ultra high reliability)-SIG included in the PHY preamble. For example, the NSS of the downlink frame (402) transmitted by AP 1 (101) of AP MLD 1 before receiving the expedited transmission request information of STA MLD 1 may be 4 (i.e., the NSS used in the EMLMR operation), but if the indicator that AP MLD 1 confirms the second link use of STA MLD 1 confirms the second link use of STA MLD 1, the NSS of the downlink frame (408) transmitted by AP 1 (101) of AP MLD 1 after receiving the expedited transmission request information of STA MLD 1 may be reduced from 4 (e.g., reduced from 4 to 2). That is, the downlink frame (408) may be reduced and transmitted within the spatial stream capability per link. If the indicator that confirms the second link use of AP MLD 1 does not confirm the second link use of STA MLD 1, the NSS of the downlink frame transmitted thirdly by AP 1 (101) of AP MLD 1 may not be reduced and may use 4. AP MLD 1 does not confirm the use of the second link by STA MLD 1 if the second link requested by STA MLD 1 is busy. Alternatively, AP MLD 1 may not confirm the use of the second link if at least one or more of MCS-NSS information requested by STA MLD 1 (e.g., 'MCS-NSS information to be used in the current link' and 'MCS-NSS information to be used in the indicated link'), delay boundary, and 'trigger frame request information' is not satisfied.

STA MLD 1 checks the indicator for confirming the use of the second link of AP MLD 1. If AP MLD 1 does not confirm the use of the second link, STA MLD 1 continues to communicate on the first link. If AP MLD 1 confirms the use of the second link, STA MLD 1 operates based on MCS-NSS information (e.g., 'MCS-NSS information to be used in the current link' and 'MCS-NSS information to be used in the indicated link') requested to AP 1 (101) on the first link and the second link. STA MLD 1 may not operate immediately based on 'MCS-NSS information to be used in the indicated link' or link-specific spatial stream capability on the second link. For example, STA 2 (107) of STA MLD 1 may be capable of operating after EMLMR delay from the time point of 'confirming the indicator for checking the use of the second link' (for example, the time point at which AP 1 (101) of AP MLD 1 first decodes the MAC header and/or MAC frame body included in the frame transmitted to STA 1 (103) of STA MLD 1 by AP 1 (101), or the time point at which STA 1 (103) of STA MLD 1 decodes the PHY preamble of the frame (408) transmitted by AP 1 (101) and confirms the NSS). If the 'indicator for checking the use of the second link' is indicated in the form of a PHY preamble, 'the operation of STA 1 (103) of STA MLD 1 decoding the PHY preamble of the frame (408) transmitted by AP 1 (101) and confirming the NSS' may be performed as follows. The PHY layer of STA 1 (103) decodes the PHY preamble included in the frame (408) of AP 1 (101). The PHY layer verifies the NSS of the frame (408) transmitted by AP 1 (101) based on the preamble and generates a primitive (e.g., PHY-RXSTART.indication primitive including RXVECTOR information). The RXVECTOR information is physical layer information that can directly or indirectly indicate the NSS. The PHY layer of STA 1 (103) transmits the PHY primitive to the MAC layer (i.e., MLD lower MAC sublayer) of STA 1 (103). The MAC layer of STA 1 (103) can verify the NSS of the frame (408) transmitted by AP 1 (101). Alternatively, instead of the MAC layer of STA 1 (103) checking the NSS, the MAC layer of STA 1 (103) may transmit PHY primitive information to the MAC layer of STA MLD 1 (i.e., MLD upper MAC sublayer), and the MAC layer of STA MLD 1 may check the NSS.

After AP 1 (101) of AP MLD 1 transmits an indicator for confirming the use of the second link, or after AP 1 (101) receives EMLMR expedited transmission request information of STA 1 (103), AP 2 (105) of AP MLD 1 may perform a channel access procedure (e.g., EDCA backoff operation) and transmit a trigger frame (406) to STA 2 (107) when the backoff counter reaches 0. The channel access procedure of AP 2 (105) may be performed more quickly based on the delay boundary information of the EMLMR expedited transmission request information that STA 1 (103) transmitted to AP 1 (101). Alternatively, even when the backoff counter reaches 0, if the EMLMR Delay has not elapsed since the 'time point at which the indicator for confirming the use of the second link is first confirmed', the trigger frame (406) may not be transmitted and the backoff counter may be maintained at 0. If the EMLMR Delay has elapsed after the 'point in time when the indicator for checking the use of the second link is confirmed', AP 2 (105) can transmit a trigger frame (406) to STA 2 (107). The EMLMR Delay is the time taken for the STA MLD performing the EMLMR operation to switch the radio chain. Since STA 2 (107) has not detected the channel in the second link for a certain period of time, the STA 2 (107) can set the MediumSyncDelay timer in the second link. The length of the MediumSyncDelay timer can be set to a preset value, for example, aPPDUMaxTime, which is the maximum length of a PPDU, and while the MediumSyncDelay timer is operating, STA 2 (107) must perform CCA (Clear Channel Assessment) to determine whether the channel is occupied. CCA is a channel detection operation. When STA 2 (107) receives the trigger frame (406) of AP 2 (105), the MediumSyncDelay timer is initialized, and frame transmission and reception can be performed. The trigger frame (406) that AP 2 (105) transmits to STA 2 (107) can indicate the length of the resource according to the EMLMR rapid transmission request information that STA 1 (103) transmits to AP 1 (101). STA 2 (107) can transmit a frame (410) that requires rapid transmission to AP 2 (105). In the first link, AP 1 (101) and STA 1 (103) can transmit and receive the frame (410) using two spatial streams according to the EMLMR rapid transmission request information that STA 1 (103) indicates. In the second link, AP 2 (105) and STA 2 (107) can transmit and receive frames (410) using two spatial streams according to EMLMR rapid transmission request information indicated by STA 1 (103).

Referring to FIG. 4b, if the EMLMR Delay time has elapsed after aSIFSTime + aSlotTime + aRxPHYStartDelay time from the time point at which communication between AP 2 (105) and STA 2 (107) in the second link is terminated, AP 1 (101) and STA 1 (103) in the first link can perform a communication operation according to the EMLMR operation space-time stream capability exchanged through the EML OMN frame in the first link of STA MLD 1. For example, AP 1 (101) and STA 1 (103) can perform frame transmission and reception operations using four space streams.

FIG. 5a and FIG. 5b are timing diagrams illustrating a fifth and sixth embodiment of a wireless LAN EMLMR low-latency transmission method.

Referring to FIGS. 5A and 5B, AP 1 (101) and STA 1 (103) may operate in the first link, and AP 2 (105) and STA 2 (107) may operate in the second link. AP 1 (101) and AP 2 (105) may be APs affiliated with AP MLD 1. STA 1 (103) and STA 2 (107) may be STAs affiliated with STA MLD 1. That is, the AP and STA where AP MLD 1 and STA MLD 1 operate in the first link may be AP 1 (101) and STA 1 (103), and the AP and STA where AP MLD 1 and STA MLD 1 operate in the second link may be AP 2 (105) and STA 2 (107).

STA MLD 1 may be an MLD supporting enhanced multi-link multi-radio (EMLMR) operation. STA MLD 1 may perform EMLMR operation on the first link and the second link. That is, the first link and the second link may be referred to as EMLMR links. In the EMLMR operation, after an STA MLD having multiple radios receives an initial frame (500) from an AP through a set NSS according to per-link spatial stream capabilities on each link of the multi-link, receive chains and transmit chains are switched to the link that received the initial frame (500). The receive chains and transmit chains may be referred to as radio chains. After the STA MLD receives the initial frame (500), it may communicate with the AP MLD through the switched radio chain using the NSS set in the EMLMR setup process. In order for the STA MLD to perform the EMLMR operation, the STA MLD can transmit an EML OMN (enhanced multi-link operating mode notification) frame to the AP MLD. The EML OMN frame can include MCS and NSS (number of spatial streams) information to be used in the EMLMR operation. The EML OMN frame is an action frame including an EML control field. When frame reception is terminated, the STA MLD can switch the radio chain to an EMLMR link from which the initial frame (500) was not received. The STA MLD cannot receive from an EMLMR link from which the initial frame (500) was not received until frame reception is terminated. The AP MLD does not transmit from an EMLMR link from which the initial frame (500) was not transmitted until frame transmission is terminated. When an STA MLD performs an EMLMR operation on an EMLMR link and wants to transmit to an AP MLD, an STA of the STA MLD can switch the radio chain and transmit to an AP of the AP MLD using the MCS and NSS to be used in the EMLMR operation. After an STA of the STA MLD completes frame transmission, the STA MLD can operate on each link of the multi-links according to the spatial stream capability of each link. When an STA of the STA MLD transmits to an AP of the AP MLD, the AP MLD cannot transmit frames to STAs other than the STA to which the STA MLD is transmitting.

In the first link, AP 1 (101) may perform a channel access procedure to transmit a frame to STA 1 (103). The channel access procedure may be an EDCA backoff procedure. If the EDCA backoff procedure is successful, AP 1 (101) obtains a TXOP, which is a section in which multiple frames can be transmitted. That is, AP 1 (101) is a TXOP holder. AP 1 (101) may transmit an initial frame (500) to STA 1 (103). The link-specific spatial stream capability of STA 1 (103) may be NSS = 2. Therefore, AP 1 (101) may transmit a frame to STA 1 (103) using two spatial streams. STA 1 (103) may respond to the frame of AP 1 (101) with a BA (BlockAck) frame. STA MLD 1 can switch the radio chain to the first link after receiving the initial frame (500) of AP 1 (101). STA MLD 1 can transmit and receive through four spatial streams in EMLMR operation. In other words, the spatial stream capability used in EMLMR operation exchanged in EML OMN frame can be NSS = 4. Therefore, after STA MLD 1 switches the radio chain to the first link, STA 1 (103) can transmit or receive a frame using four spatial streams. AP 1 (101) can transmit a data frame (502) to STA 1 (103) using four spatial streams. STA 2 (107) cannot transmit a frame. AP 2 (105) does not transmit a frame to STA 2 (107). When AP MLD 1 transmits a frame on the first link, data may occur that needs to be transmitted to STA 2 (107) on the second link. The data to be transmitted on the second link may be data that needs to be transmitted quickly. Therefore, AP 1 (101) of AP MLD 1 may instruct STA 1 (103) to receive a frame on another EMLMR link that is not currently being received in the data frame (502) transmitted. This request may be referred to as radio switching request information. The radio switching request information may include at least one of information from a 'link bitmap', 'MCS-NSS information to be used on the indicated link', and 'MCS-NSS information to be used on the current link'. The link bitmap may indicate a link that AP MLD 1 intends to further use. For example, AP MLD 1 may indicate a second link. The MCS-NSS information to be used on the indicated link indicates MCS and NSS information supported on the link indicated by AP MLD 1 with the link bitmap. STA MLD 1 and AP MLD 1 perform communication on the link indicated by AP MLD 1 in the link bitmap according to MCS-NSS information. The MCS-NSS information to be used in the current link indicates MCS and NSS information supported on the link on which the initial frame (500) was exchanged. STA MLD 1 and AP MLD 1 perform communication on the link on which the initial frame (500) was exchanged according to MCS-NSS information. Alternatively, STA MLD 1 and AP MLD 1 may operate according to spatial stream capability per link. Radio switching request information transmitted by AP 1 (101) to STA 1 (103) may be transmitted in the form of A-Control, included in the MAC header of a data frame. The radio switching request information may be AAR+ information, which is extended AAR (Assisted AP Request) information. Alternatively, the radio switching request information may be information structured in the form of A-Control, or may be included in a frame transmitted from AP 1 (101) to STA 1 (103) in the form of instruction bits, subfields, information elements, and other forms.

AP 1 (101) of AP MLD 1 may transmit a data frame (502) including radio switching request information to STA 1 (103), and then perform a channel access procedure in AP 2 (105) of the second link. The radio switching request information is information requesting that STA MLD 1 be able to receive a frame in the second link. The channel access procedure may be an EDCA backoff operation. AP 2 (105) of AP MLD 1 may perform a channel access procedure (e.g., an EDCA backoff operation) and transmit a downlink frame (506) to STA 2 (107) when the backoff counter reaches 0. Even when the backoff counter reaches 0, if the EMLMR Delay has not elapsed from the time of the end of transmission of the data frame (502) including radio switching request information of AP 1 (101), the downlink data frame (506) may not be transmitted and the backoff counter may be maintained at 0. When the EMLMR Delay has elapsed, AP 2 (105) can transmit a downlink data frame (506) to STA 2 (107). The EMLMR Delay is the time taken for the STA MLD performing the EMLMR operation to switch the radio chain.

Alternatively, the transmission of the data frame (506) of AP 2 (105) may be performed based on information included in the BA frame (504) that STA 1 (103) transmits to AP 1 (101). STA 1 (103) may respond to the data frame (502) transmitted by AP 1 (101) with a BA frame (504). The BA frame (504) may further include information for accepting or rejecting the radio switching request that AP 1 (101) transmits to STA 1 (103). If STA 1 (103) accepts the radio switching request transmitted by AP 1 (101) in the BA frame (504), AP MLD 1 may perform a channel access procedure on AP 2 (105) of the second link. The channel access procedure may be an EDCA backoff operation. AP 2 (105) of AP MLD 1 can perform a channel access procedure (e.g., EDCA backoff operation) and transmit a downlink frame (506) to STA 2 (107) when the backoff counter reaches 0. Even when the backoff counter reaches 0, if the EMLMR Delay has not elapsed from the transmission end time of the BA frame (504) of STA 1 (103), the downlink data frame (506) may not be transmitted and the backoff counter may be maintained at 0. If the EMLMR Delay has elapsed, AP 2 (105) can transmit a downlink data frame (506) to STA 2 (107). The EMLMR Delay is the time taken when the STA MLD performing the EMLMR operation switches the radio chain. In the first link, AP 1 (101) and STA 1 (103) can transmit and receive frames using two spatial streams according to radio switching request information indicated by AP 1 (101). In the second link, AP 2 (105) and STA 2 (107) can transmit and receive frames (506) using two spatial streams according to radio switching request information indicated by AP 1 (101).

Referring to FIG. 5b, if the EMLMR Delay time has elapsed after aSIFSTime + aSlotTime + aRxPHYStartDelay time from the time point at which communication between AP 2 (105) and STA 2 (107) in the second link is terminated, AP 1 (101) and STA 1 (103) in the first link can perform communication operations according to the spatial stream capability during EMLMR operation exchanged through the EML OMN frame in the first link of STA MLD 1. For example, AP 1 (101) and STA 1 (103) can perform frame transmission and reception operations using four spatial streams.

FIG. 6a and FIG. 6b are timing diagrams illustrating the seventh and eighth embodiments of a wireless LAN EMLMR low-latency transmission method.

Referring to FIGS. 6A and 6B, AP 1 (101) and STA 1 (103) may operate in the first link, and AP 2 (105) and STA 2 (107) may operate in the second link. AP 1 (101) and AP 2 (105) may be APs affiliated with AP MLD 1. STA 1 (103) and STA 2 (107) may be STAs affiliated with STA MLD 1. That is, the AP and STA where AP MLD 1 and STA MLD 1 operate in the first link may be AP 1 (101) and STA 1 (103), and the AP and STA where AP MLD 1 and STA MLD 1 operate in the second link may be AP 2 (105) and STA 2 (107).

STA MLD 1 may be an MLD supporting enhanced multi-link multi-radio (EMLMR) operation. STA MLD 1 may perform EMLMR operation on the first link and the second link. That is, the first link and the second link may be referred to as EMLMR links. In the EMLMR operation, after an STA MLD having multiple radios receives an initial frame from an AP through a set NSS according to per-link spatial stream capabilities on each link of the multi-link, receive chains and transmit chains are switched to the link that received the initial frame. The receive chains and transmit chains may be referred to as radio chains. After the STA MLD receives the initial frame, it may communicate with the AP MLD through the switched radio chain using the NSS set in the EMLMR setup process. In order for the STA MLD to perform the EMLMR operation, the STA MLD can transmit an EML OMN (enhanced multi-link operating mode notification) frame to the AP MLD. The EML OMN frame can include MCS and NSS (number of spatial streams) information to be used in the EMLMR operation. The EML OMN frame is an action frame including an EML control field. When the STA MLD terminates frame reception, the STA MLD can switch the radio chain to an EMLMR link from which the initial frame has not been received. The STA MLD cannot receive on an EMLMR link from which the initial frame has not been received until the frame reception is terminated. The AP MLD does not transmit on an EMLMR link from which the initial frame has not been transmitted until the frame transmission is terminated. When the STA MLD performs the EMLMR operation on the EMLMR link and wants to transmit to the AP MLD, the STA of the STA MLD can switch the radio chain and transmit to the AP of the AP MLD using the MCS and NSS to be used in the EMLMR operation. After the STA of the STA MLD completes frame transmission, the STA MLD can operate according to the spatial stream capability of each link of the multi-link. When the STA of the STA MLD transmits to the AP of the AP MLD, the AP MLD cannot transmit the frame to STAs other than the STA to which the STA MLD is transmitting.

In the first link, STA 1 (103) may perform a channel access procedure to transmit a frame to AP 1 (101). The channel access procedure may be an EDCA backoff procedure. If the EDCA backoff procedure is successful, STA 1 (103) acquires a TXOP, which is an interval in which multiple frames can be transmitted. That is, STA 1 (103) is a TXOP holder. STA 1 (103) may transmit a frame to AP 1 (101). STA MLD 1 may transmit or receive using four spatial streams in EMLMR operation, and therefore, STA 1 (103) may transmit a frame to AP 1 (101) using four spatial streams. In other words, the spatial stream capability used in EMLMR operation exchanged in EML OMN frame may be NSS = 4. AP 1 (101) may respond to the frame of STA 1 (103) with a BA (BlockAck, 600) frame. AP 1 (101) may transmit a data frame to STA 1 (103) using four spatial streams. STA 2 (107) cannot transmit a frame. AP 2 (105) does not transmit a frame to STA 2 (107). While AP MLD 1 receives a frame on the first link, data may occur that needs to be transmitted to STA 2 (107) on the second link. The data to be transmitted on the second link may be data that needs to be transmitted quickly. Therefore, AP 1 (101) of AP MLD 1 may instruct STA 1 (103) to receive a frame on another EMLMR link that is not currently being transmitted or received in the BA frame (600). This request may be referred to as radio switching request information. The radio switching request information may include at least one of a 'link bitmap', 'MCS-NSS information to be used in the indicated link', and 'MCS-NSS information to be used in the current link'. The link bitmap may indicate a link that AP MLD 1 intends to further use. For example, AP MLD 1 may indicate a second link. The MCS-NSS information to be used in the indicated link indicates MCS and NSS information supported in the link indicated by AP MLD 1 with the link bitmap. STA MLD 1 and AP MLD 1 perform communication on the link indicated by AP MLD 1 with the link bitmap according to the MCS-NSS information. The MCS-NSS information to be used in the current link indicates MCS and NSS information supported in the link on which initial frames were exchanged. STA MLD 1 and AP MLD 1 perform communication according to the MCS-NSS information in the link on which initial frames were exchanged. Alternatively, STA MLD 1 and AP MLD 1 may operate according to link-specific spatial stream capabilities. The radio switching request information transmitted by AP 1 (101) to STA 1 (103) may be transmitted in the form of a BA frame and A-MPDU, included in the MAC header of a QoS Null frame in the form of A-Control. The radio switching request information may be AAR+ information, which is extended AAR (Assisted AP Request) information. Alternatively, the radio switching request information may be information configured in the form of A-Control, or may be included in a frame transmitted by AP 1 (101) to STA 1 (103) in the form of an instruction bit, a subfield, an information element, and other forms.

AP 1 (101) of AP MLD 1 may transmit a BA frame (600) including radio switching request information to STA 1 (103), and then perform a channel access procedure in AP 2 (105) of the second link. The radio switching request information is information requesting that STA MLD 1 can receive a frame (602) in the second link. The channel access procedure may be an EDCA backoff operation. AP 2 (105) of AP MLD 1 may perform a channel access procedure (e.g., an EDCA backoff operation) and, when the backoff counter reaches 0, may transmit a downlink frame (602) to STA 2 (107). Even if the backoff counter reaches 0, if the EMLMR Delay has not elapsed from the transmission end time of the BA frame (600) including the radio switching request information of AP 1 (101), the downlink data frame (602) may not be transmitted and the backoff counter may be maintained at 0. If the EMLMR Delay has elapsed, AP 2 (105) may transmit the downlink data frame (602) to STA 2 (107). The EMLMR Delay is the time taken when the STA MLD performing the EMLMR operation switches the radio chain. In the first link, AP 1 (101) and STA 1 (103) may transmit and receive frames using two spatial streams according to the radio switching request information indicated by AP 1 (101). In the second link, AP 2 (105) and STA 2 (107) can transmit and receive frames using two spatial streams according to the radio switching request information indicated by AP 1 (101).

Referring to FIG. 6b, if the EMLMR Delay time has elapsed after aSIFSTime + aSlotTime + aRxPHYStartDelay time from the time point at which communication between AP 2 (105) and STA 2 (107) in the second link is terminated, AP 1 (101) and STA 1 (103) in the first link can perform a communication operation according to the EMLMR operation space-time stream capability exchanged through the EML OMN frame in the first link of STA MLD 1. For example, AP 1 (101) and STA 1 (103) can perform frame transmission and reception operations using four spatial streams.

Fig. 7 is a timing diagram illustrating a ninth embodiment of a wireless LAN EMLMR low-latency transmission method.

Referring to FIG. 7, AP 1 (101) and STA 1 (103) may operate in the first link, and AP 2 (105) and STA 2 (107) may operate in the second link. AP 1 (101) and AP 2 (105) may be APs affiliated with AP MLD 1. STA 1 (103) and STA 2 (107) may be STAs affiliated with STA MLD 1. That is, the AP and STA where AP MLD 1 and STA MLD 1 operate in the first link may be AP 1 (101) and STA 1 (103), and the AP and STA where AP MLD 1 and STA MLD 1 operate in the second link may be AP 2 (105) and STA 2 (107).

STA MLD 1 may be an MLD supporting enhanced multi-link multi-radio (EMLMR) operation. STA MLD 1 may perform EMLMR operation on the first link and the second link. That is, the first link and the second link may be referred to as EMLMR links. In the EMLMR operation, after an STA MLD having multiple radios receives an initial frame (700) from an AP through a set NSS according to per-link spatial stream capabilities on each link of the multi-link, receive chains and transmit chains are switched to the link that received the initial frame (700). The receive chains and transmit chains may be referred to as radio chains. After the STA MLD receives the initial frame (700), it may communicate with the AP MLD through the switched radio chain using the NSS set in the EMLMR setup process. In order for the STA MLD to perform the EMLMR operation, the STA MLD can transmit an EML OMN (enhanced multi-link operating mode notification) frame to the AP MLD. The EML OMN frame can include MCS and NSS (number of spatial streams) information to be used in the EMLMR operation. The EML OMN frame is an action frame including an EML control field. When frame reception is terminated, the STA MLD can switch the radio chain to an EMLMR link from which the initial frame (700) was not received. The STA MLD cannot receive from an EMLMR link from which the initial frame (700) was not received until frame reception is terminated. The AP MLD does not transmit from an EMLMR link from which the initial frame (700) was not transmitted until frame transmission is terminated. When an STA MLD performs an EMLMR operation on an EMLMR link and wants to transmit to an AP MLD, an STA of the STA MLD can switch the radio chain and transmit to an AP of the AP MLD using the MCS and NSS to be used in the EMLMR operation. After an STA of the STA MLD completes frame transmission, the STA MLD can operate on each link of the multi-links according to the spatial stream capability of each link. When an STA of the STA MLD transmits to an AP of the AP MLD, the AP MLD cannot transmit frames to STAs other than the STA to which the STA MLD is transmitting.

In the first link, AP 1 (101) may perform a channel access procedure to transmit a frame to STA 1 (103). The channel access procedure may be an EDCA backoff procedure. If the EDCA backoff procedure is successful, AP 1 (101) obtains a TXOP, which is a section in which multiple frames can be transmitted. That is, AP 1 (101) is a TXOP holder. AP 1 (101) may transmit an initial frame (700) to STA 1 (103). The link-specific spatial stream capability of STA 1 (103) may be NSS = 2. Therefore, AP 1 (101) may transmit a frame to STA 1 (103) using two spatial streams. STA MLD 1 may switch the radio chain to the first link after receiving the initial frame (700) of AP 1 (101). STA MLD 1 can transmit and receive through four spatial streams in EMLMR operation. In other words, the spatial stream capability used in EMLMR operation exchanged in EML OMN frame can be NSS = 4. Therefore, after STA MLD 1 switches the radio chain to the first link, STA 1 (103) can transmit or receive frames using four spatial streams. AP 1 (101) can transmit data frames to STA 1 (103) using four spatial streams. AP 1 (101) can transmit downlink frames to STA 1 (103) consecutively at XIFS intervals. The XIFS interval can be shorter than or equal to SIFS. Alternatively, the XIFS interval can be longer than SIFS (e.g., PIFS interval). In the XIFS interval between frames transmitted by AP 1 (101), STA 1 (103) may transmit a frame to AP 1 (101). STA 2 (107) cannot transmit a frame. While STA MLD 1 is receiving a frame on the first link, STA MLD 1 may have data to transmit on the second link. The data to be transmitted on the second link may be data that needs to be transmitted quickly. Therefore, STA 1 (103) of STA MLD 1 may transmit a frame (702) in which there is a request to transmit or receive a frame on another EMLMR link that is not currently being received in the XIFS interval between frames transmitted to AP 1 (101). This request may be referred to as EMLMR expedited transmission request information, and may be included in various forms, such as a MAC header of a QoS Null frame, a BA frame, or other frames that STA 1 (103) transmits to AP 1 (101). The EMLMR expedited transmission request information may include at least one of the following information: 'link bitmap', 'trigger frame request information', 'MCS-NSS information to be used in the indicated link', 'MCS-NSS information to be used in the current link', and 'delay boundary information'. The link bitmap may indicate a link that STA MLD 1 further wishes to use. For example, STA MLD 1 may indicate a second link. The 'trigger frame request information' is information that requests that a trigger frame (704) is needed in the link indicated by STA MLD 1 in the link bitmap. For example, since STA MLD 1 indicates the second link in the link bitmap, AP 2 (105) of AP MLD 1 may transmit a trigger frame (704) to STA 2 (107) of STA MLD 1 in the second link. The MCS-NSS information to be used in the indicated link indicates the MCS and NSS information supported in the link indicated by the link bitmap by STA MLD 1. STA MLD 1 and AP MLD 1 perform communication in the link indicated by the link bitmap by STA MLD 1 according to the MCS-NSS information. The MCS-NSS information to be used in the current link indicates the MCS and NSS information supported in the link on which the initial frame (700) was exchanged. STA MLD 1 and AP MLD 1 perform communication in the link on which the initial frame (700) was exchanged according to the MCS-NSS information. Alternatively, STA MLD 1 and AP MLD 1 may operate according to the spatial stream capability of each link. The delay boundary information is information indicating until when STA MLD 1 should transmit data to AP MLD 1. For example, if STA indicates the delay boundary information as 1ms, it indicates that the STA wants to share the TXOP from the TXOP Holder within 1ms. The delay boundary information may further include time information per AC or per TID. For example, the STA may indicate the delay boundary information per AC, such as AC_VO is 1ms and AC_BE is 5ms. Or, the STA may indicate the delay boundary information per TID, such as TID 1 is 1ms and TID 3 is 3ms. The AC and TID-specific delay boundary information indications may be used simultaneously. According to the delay boundary information, the AP MLD 1 may change the channel access parameters (e.g., EDCA parameters) used for transmission of the trigger frame (704) or the downlink frame (706) in the link indicated by the link bitmap by the STA MLD 1. The EMLMR expedited transmission request information transmitted by the STA 1 (103) to the AP 1 (101) may be included in the MAC header of the QoS Null frame in the form of A-Control and transmitted in the form of a BA frame and an A-MPDU. The EMLMR expedited transmission request information may be AAR+ information, which is extended AAR (Assisted AP Request) information. Alternatively, the EMLMR expedited transmission request information may be information configured in the form of A-Control, or may be included in a frame transmitted from STA 1 (103) to AP 1 (101) in the form of instruction bits, subfields, information elements, and other forms.

STA 1 (103) may transmit an EMLMR rapid transmission request to AP 1 (101), which may request transmission of a trigger frame (704) on the second link. AP 1 (101) of AP MLD 1 may include an indicator for confirming the use of the second link in a downlink frame (706) transmitted after receiving a BA frame (702) including EMLMR rapid transmission request information transmitted by STA 1 (103). The indicator for confirming the use of the second link may indicate whether STA 2 (107) and AP 2 (105) can communicate on the second link. The indicator for confirming the use of the second link may be configured in the form of at least one of A-Control, field, subfield, indication bit, and information element. AP 2 (105) of AP MLD 1 can perform a channel access procedure (e.g., EDCA backoff operation) and transmit a trigger frame (704) to STA 2 (107) when the backoff counter reaches 0. The channel access procedure of AP 2 (105) can also be performed more quickly based on the delay boundary information of the EMLMR expedited transmission request information transmitted by STA 1 (103) to AP 1 (101). Alternatively, even when the backoff counter reaches 0, if the EMLMR Delay has not elapsed from the transmission end time of the BA frame (702) including the EMLMR expedited transmission request of STA 1 (103), the trigger frame (704) can be maintained at 0 without transmitting the backoff counter. If the EMLMR Delay has elapsed, AP 2 (105) can transmit the trigger frame (704) to STA 2 (107). STA 2 (107) can set the MediumSyncDelay timer in the second link because it has not detected the channel for a certain period of time on the second link. The length of the MediumSyncDelay timer can be set to aPPDUMaxTime, which is the maximum length of a preset PPDU, and STA 2 (107) must perform CCA while the MediumSyncDelay timer is operating. CCA is a channel detection operation. When STA 2 (107) receives a trigger frame (704) of AP 2 (105), the MediumSyncDelay timer is initialized and frame transmission and reception can be performed. The trigger frame (704) that AP 2 (105) transmits to STA 2 (107) can indicate the length of the resource according to the EMLMR expedited transmission request information that STA 1 (103) transmits to AP 1 (101). STA 2 (107) can transmit a frame (706) requiring rapid transmission to AP 2 (105). In the first link, AP 1 (101) and STA 1 (103) can transmit and receive a frame using two spatial streams according to EMLMR rapid transmission request information indicated by STA 1 (103). In the second link, AP 2 (105) and STA 2 (107) can transmit and receive a frame (706) using two spatial streams according to EMLMR rapid transmission request information indicated by STA 1 (103).

If the EMLMR Delay time has elapsed after aSIFSTime + aSlotTime + aRxPHYStartDelay time from the time point at which communication between AP 2 (105) and STA 2 (107) in the second link is terminated, AP 1 (101) and STA 1 (103) in the first link can perform a communication operation according to the EMLMR operation space-time stream capability exchanged through the EML OMN frame in the first link of STA MLD 1. For example, AP 1 (101) and STA 1 (103) can perform frame transmission and reception operations using four space streams.

Fig. 8 is a timing diagram illustrating a tenth embodiment of a wireless LAN EMLMR low-latency transmission method.

Referring to FIG. 8, AP 1 (101) and STA 1 (103) may operate in the first link, and AP 2 (105) and STA 2 (107) may operate in the second link. AP 1 (101) and AP 2 (105) may be APs affiliated with AP MLD 1. STA 1 (103) and STA 2 (107) may be STAs affiliated with STA MLD 1. That is, the AP and STA where AP MLD 1 and STA MLD 1 operate in the first link may be AP 1 (101) and STA 1 (103), and the AP and STA where AP MLD 1 and STA MLD 1 operate in the second link may be AP 2 (105) and STA 2 (107).

STA MLD 1 may be an MLD supporting enhanced multi-link multi-radio (EMLMR) operation. STA MLD 1 may perform EMLMR operation on the first link and the second link. That is, the first link and the second link may be referred to as EMLMR links. In the EMLMR operation, after an STA MLD having multiple radios receives an initial frame (800) from an AP through a set NSS according to per-link spatial stream capabilities on each link of the multi-link, receive chains and transmit chains are switched to the link that received the initial frame (800). The receive chains and transmit chains may be referred to as radio chains. After the STA MLD receives the initial frame (800), it may communicate with the AP MLD through the switched radio chain using the NSS set in the EMLMR setup process. In order for the STA MLD to perform the EMLMR operation, the STA MLD can transmit an EML OMN (enhanced multi-link operating mode notification) frame to the AP MLD. The EML OMN frame can include MCS and NSS (number of spatial streams) information to be used in the EMLMR operation. The EML OMN frame is an action frame including an EML control field. When frame reception is terminated, the STA MLD can switch the radio chain to an EMLMR link from which the initial frame (800) was not received. The STA MLD cannot receive from an EMLMR link from which the initial frame (800) was not received until frame reception is terminated. The AP MLD does not transmit from an EMLMR link from which the initial frame (800) was not transmitted until frame transmission is terminated. When an STA MLD performs an EMLMR operation on an EMLMR link and wants to transmit to an AP MLD, an STA of the STA MLD can switch the radio chain and transmit to an AP of the AP MLD using the MCS and NSS to be used in the EMLMR operation. After an STA of the STA MLD completes frame transmission, the STA MLD can operate on each link of the multi-links according to the spatial stream capability of each link. When an STA of the STA MLD transmits to an AP of the AP MLD, the AP MLD cannot transmit frames to STAs other than the STA to which the STA MLD is transmitting.

In the first link, AP 1 (101) may perform a channel access procedure to transmit a frame to STA 1 (103). The channel access procedure may be an EDCA backoff procedure. If the EDCA backoff procedure is successful, AP 1 (101) obtains a TXOP, which is a section in which multiple frames can be transmitted. That is, AP 1 (101) is a TXOP holder. AP 1 (101) may transmit an initial frame (800) to STA 1 (103). The link-specific spatial stream capability of STA 1 (103) may be NSS = 2. Therefore, AP 1 (101) may transmit a frame to STA 1 (103) using two spatial streams. STA MLD 1 may switch the radio chain to the first link after receiving the initial frame (800) of AP 1 (101). STA MLD 1 can transmit and receive through four spatial streams in EMLMR operation. In other words, the spatial stream capability used in EMLMR operation exchanged in EML OMN frame can be NSS = 4. Therefore, after STA MLD 1 switches the radio chain to the first link, STA 1 (103) can transmit or receive frames using four spatial streams. AP 1 (101) can transmit data frames to STA 1 (103) using four spatial streams. AP 1 (101) can transmit downlink frames to STA 1 (103) consecutively at XIFS intervals. The XIFS interval can be shorter than or equal to SIFS. Alternatively, the XIFS interval can be longer than SIFS (e.g., PIFS interval). During the XIFS interval between frames transmitted by AP 1 (101), STA 1 (103) may transmit a frame to AP 1 (101). STA 2 (107) cannot transmit a frame. AP 2 (105) does not transmit a frame to STA 2 (107). While AP MLD 1 transmits a frame on the first link, data to be transmitted to STA 2 (107) on the second link may occur. The data to be transmitted on the second link may be data that needs to be transmitted quickly. Therefore, AP 1 (101) of AP MLD 1 may instruct STA 1 (103) to receive a frame on another EMLMR link that is not currently being received in the data frame (802) transmitted. This request may be referred to as radio switching request information. The radio switching request information may include at least one of a 'link bitmap', 'MCS-NSS information to be used in the indicated link', and 'MCS-NSS information to be used in the current link'. The link bitmap may indicate a link that AP MLD 1 intends to further use. For example, AP MLD 1 may indicate a second link. The MCS-NSS information to be used in the indicated link indicates MCS and NSS information supported in the link indicated by AP MLD 1 with the link bitmap. STA MLD 1 and AP MLD 1 perform communication on the link indicated by AP MLD 1 with the link bitmap according to the MCS-NSS information. The MCS-NSS information to be used in the current link indicates MCS and NSS information supported in the link on which initial frames (800) were exchanged. STA MLD 1 and AP MLD 1 perform communication according to the MCS-NSS information in the link on which initial frames (800) were exchanged. Alternatively, STA MLD 1 and AP MLD 1 may operate according to the spatial stream capability per link. The radio switching request information transmitted by AP 1 (101) to STA 1 (103) may be transmitted in the form of A-Control, included in the MAC header of a data frame. The radio switching request information may be AAR+ information, which is extended AAR (Assisted AP Request) information. Alternatively, the radio switching request information may be information configured in the form of A-Control, or may be included in a frame transmitted by AP 1 (101) to STA 1 (103) in the form of instruction bits, subfields, information elements, and other forms.

AP 1 (101) of AP MLD 1 may transmit a data frame (802) including radio switching request information to STA 1 (103), and then perform a channel access procedure in AP 2 (105) of the second link. The radio switching request information is information requesting that STA MLD 1 be able to receive a frame in the second link. The channel access procedure may be an EDCA backoff operation. AP 2 (105) of AP MLD 1 may perform a channel access procedure (e.g., an EDCA backoff operation) and transmit a downlink frame (804) to STA 2 (107) when the backoff counter reaches 0. Even when the backoff counter reaches 0, if the EMLMR Delay has not elapsed from the time of the end of transmission of the data frame (802) including radio switching request information of AP 1 (101), the downlink data frame (804) may not be transmitted and the backoff counter may be maintained at 0. When the EMLMR Delay has elapsed, AP 2 (105) can transmit a downlink data frame (804) to STA 2 (107). The EMLMR Delay is the time required for the STA MLD performing the EMLMR operation to switch the radio chain. In the first link, AP 1 (101) and STA 1 (103) can transmit and receive frames using two spatial streams according to the radio switching request information indicated by AP 1 (101). In the second link, AP 2 (105) and STA 2 (107) can transmit and receive frames using two spatial streams according to the radio switching request information indicated by AP 1 (101).

If the EMLMR Delay time has elapsed after aSIFSTime + aSlotTime + aRxPHYStartDelay time from the time point at which communication between AP 2 (105) and STA 2 (107) in the second link is terminated, AP 1 (101) and STA 1 (103) in the first link can perform a communication operation according to the EMLMR operation space-time stream capability exchanged through the EML OMN frame in the first link of STA MLD 1. For example, AP 1 (101) and STA 1 (103) can perform frame transmission and reception operations using four space streams.

FIG. 9 is a timing diagram illustrating an 11th embodiment of a wireless LAN EMLMR low-latency transmission method.

Referring to FIG. 9, AP 1 (101) and STA 1 (103) may operate in the first link, and AP 2 (105) and STA 2 (107) may operate in the second link. AP 1 (101) and AP 2 (105) may be APs affiliated with AP MLD 1. STA 1 (103) and STA 2 (107) may be STAs affiliated with STA MLD 1. That is, the AP and STA where AP MLD 1 and STA MLD 1 operate in the first link may be AP 1 (101) and STA 1 (103), and the AP and STA where AP MLD 1 and STA MLD 1 operate in the second link may be AP 2 (105) and STA 2 (107).

STA MLD 1 may be an MLD supporting enhanced multi-link multi-radio (EMLMR) operation. STA MLD 1 may perform EMLMR operation on the first link and the second link. That is, the first link and the second link may be referred to as EMLMR links. In the EMLMR operation, after an STA MLD having multiple radios receives an initial frame from an AP through a set NSS according to per-link spatial stream capabilities on each link of the multi-link, receive chains and transmit chains are switched to the link that received the initial frame. The receive chains and transmit chains may be referred to as radio chains. After the STA MLD receives the initial frame, it may communicate with the AP MLD through the switched radio chain using the NSS set in the EMLMR setup process. In order for the STA MLD to perform the EMLMR operation, the STA MLD can transmit an EML OMN (enhanced multi-link operating mode notification) frame to the AP MLD. The EML OMN frame can include MCS and NSS (number of spatial streams) information to be used in the EMLMR operation. The EML OMN frame is an action frame including an EML control field. When the STA MLD terminates frame reception, the STA MLD can switch the radio chain to an EMLMR link from which the initial frame has not been received. The STA MLD cannot receive on an EMLMR link from which the initial frame has not been received until the frame reception is terminated. The AP MLD does not transmit on an EMLMR link from which the initial frame has not been transmitted until the frame transmission is terminated. When the STA MLD performs the EMLMR operation on the EMLMR link and wants to transmit to the AP MLD, the STA of the STA MLD can switch the radio chain and transmit to the AP of the AP MLD using the MCS and NSS to be used in the EMLMR operation. After the STA of the STA MLD completes frame transmission, the STA MLD can operate according to the spatial stream capability of each link of the multi-link. When the STA of the STA MLD transmits to the AP of the AP MLD, the AP MLD cannot transmit the frame to STAs other than the STA to which the STA MLD is transmitting.

In the first link, STA 1 (103) may perform a channel access procedure to transmit a frame to AP 1 (101). The channel access procedure may be an EDCA backoff procedure. If the EDCA backoff procedure is successful, STA 1 (103) obtains a TXOP, which is an interval in which multiple frames can be transmitted. That is, STA 1 (103) is a TXOP holder. STA 1 (103) may transmit a frame to AP 1 (101). STA MLD 1 may transmit or receive using four spatial streams in EMLMR operation. In other words, the spatial stream capability used in EMLMR operation exchanged in EML OMN frame may be NSS = 4. Therefore, STA 1 (103) may transmit a frame to AP 1 (101) using four spatial streams. AP 1 (101) can transmit data frames to STA 1 (103) using four spatial streams. STA 1 (103) can continuously transmit downlink frames to AP 1 (101) at XIFS intervals. The XIFS interval can be an interval shorter than or equal to SIFS. Alternatively, the XIFS interval can be an interval longer than SIFS (e.g., PIFS interval). In the XIFS interval between frames transmitted by STA 1 (103), AP 1 (101) can also transmit frames to STA 1 (103). STA 2 (107) cannot transmit frames. AP 2 (105) does not transmit frames to STA 2 (107). While AP MLD 1 receives frames on the first link, data to be transmitted to STA 2 (107) on the second link may occur. Data to be transmitted on the second link may be data that needs to be transmitted quickly. Therefore, AP 1 (101) of AP MLD 1 may instruct STA 1 (103) to request reception of a frame on another EMLMR link that is not currently being transmitted or received in the frame (900) transmitted. This request may be referred to as radio switching request information. The radio switching request information may include at least one of information from a 'link bitmap', 'MCS-NSS information to be used on the indicated link', and 'MCS-NSS information to be used on the current link'. The link bitmap may indicate a link that AP MLD 1 further intends to use. For example, AP MLD 1 may indicate a second link. The MCS-NSS information to be used on the indicated link indicates MCS and NSS information supported on the link indicated by AP MLD 1 with the link bitmap. STA MLD 1 and AP MLD 1 perform communication on the link indicated by AP MLD 1 in the link bitmap according to MCS-NSS information. The MCS-NSS information to be used on the current link indicates MCS and NSS information supported on the link on which the initial frames were exchanged. STA MLD 1 and AP MLD 1 perform communication on the link on which the initial frames were exchanged according to MCS-NSS information. Alternatively, STA MLD 1 and AP MLD 1 may operate according to spatial stream capability of each link. The radio switching request information transmitted by AP 1 (101) to STA 1 (103) may be included in the MAC header of the QoS Null frame in the form of A-Control and transmitted in the form of a BA frame and an A-MPDU. The radio switching request information may be AAR+ information, which is extended AAR (Assisted AP Request) information. Alternatively, the radio switching request information may be information structured in the form of A-Control, or may be included in a frame transmitted from AP 1 (101) to STA 1 (103) in the form of instruction bits, subfields, information elements, and other forms.

AP 1 (101) of AP MLD 1 may transmit a frame (900) including radio switching request information to STA 1 (103) within the XIFS interval, which is an interval between frames transmitted by STA 1 (103), and then perform a channel access procedure in AP 2 (105) of the second link. The radio switching request information is information requesting that STA MLD 1 be able to receive a frame in the second link. The channel access procedure may be an EDCA backoff operation. AP 2 (105) of AP MLD 1 may perform a channel access procedure (e.g., an EDCA backoff operation) and, when the backoff counter reaches 0, may transmit a downlink frame (902) to STA 2 (107). Even if the backoff counter reaches 0, if the EMLMR Delay has not elapsed from the transmission end time of the frame (900) including the radio switching request information of AP 1 (101), the downlink data frame (902) may not be transmitted and the backoff counter may be maintained at 0. If the EMLMR Delay has elapsed, AP 2 (105) may transmit the downlink data frame (902) to STA 2 (107). The EMLMR Delay is the time taken when the STA MLD performing the EMLMR operation switches the radio chain. In the first link, AP 1 (101) and STA 1 (103) may transmit and receive frames using two spatial streams according to the radio switching request information indicated by AP 1 (101). In the second link, AP 2 (105) and STA 2 (107) can transmit and receive frames using two spatial streams according to the radio switching request information indicated by AP 1 (101).

If the EMLMR Delay time has elapsed after aSIFSTime + aSlotTime + aRxPHYStartDelay time from the time point at which communication between AP 2 (105) and STA 2 (107) in the second link is terminated, AP 1 (101) and STA 1 (103) in the first link can perform a communication operation according to the EMLMR operation space-time stream capability exchanged through the EML OMN frame in the first link of STA MLD 1. For example, AP 1 (101) and STA 1 (103) can perform frame transmission and reception operations using four space streams.

FIG. 10a and FIG. 10b are timing diagrams illustrating the 12th and 13th embodiments of a wireless LAN EMLMR low-latency transmission method.

Referring to FIGS. 10A and 10B, AP 1 (101) and STA 1 (103) may operate in the first link, and AP 2 (105) and STA 2 (107) may operate in the second link. AP 1 (101) and AP 2 (105) may be APs affiliated with AP MLD 1. STA 1 (103) and STA 2 (107) may be STAs affiliated with STA MLD 1. That is, the AP and STA where AP MLD 1 and STA MLD 1 operate in the first link may be AP 1 (101) and STA 1 (103), and the AP and STA where AP MLD 1 and STA MLD 1 operate in the second link may be AP 2 (105) and STA 2 (107).

STA MLD 1 may be an MLD supporting enhanced multi-link multi-radio (EMLMR) operation. STA MLD 1 may perform EMLMR operation on the first link and the second link. That is, the first link and the second link may be referred to as EMLMR links. In the EMLMR operation, after an STA MLD having multiple radios receives an initial frame (1000) from an AP through a set number of spatial streams (NSS) according to per-link spatial stream capabilities on each link of the multi-link, receive chains and transmit chains are switched to the link that received the initial frame (1000). The receive chains and transmit chains may be referred to as radio chains. After the STA MLD receives the initial frame (1000), it may communicate with the AP MLD through the switched radio chain using the NSS set in the EMLMR setup process. In order for the STA MLD to perform the EMLMR operation, the STA MLD can transmit an EML OMN (enhanced multi-link operating mode notification) frame to the AP MLD. The EML OMN frame can include MCS and NSS (number of spatial streams) information to be used in the EMLMR operation. The EML OMN frame is an action frame including an EML control field. When frame reception is terminated, the STA MLD can switch the radio chain to an EMLMR link from which the initial frame (1000) has not been received. The STA MLD cannot receive from an EMLMR link from which the initial frame (1000) has not been received until frame reception is terminated. The AP MLD does not transmit from an EMLMR link from which the initial frame (1000) has not been transmitted until frame transmission is terminated. When an STA MLD performs an EMLMR operation on an EMLMR link and wants to transmit to an AP MLD, an STA of the STA MLD can switch the radio chain and transmit to an AP of the AP MLD using the MCS and NSS to be used in the EMLMR operation. After an STA of the STA MLD completes frame transmission, the STA MLD can operate on each link of the multi-links according to the spatial stream capability of each link. When an STA of the STA MLD transmits to an AP of the AP MLD, the AP MLD cannot transmit frames to STAs other than the STA to which the STA MLD is transmitting.

In the first link, AP 1 (101) may perform a channel access procedure to transmit a frame to STA 1 (103). The channel access procedure may be an EDCA backoff procedure. If the EDCA backoff procedure is successful, AP 1 (101) obtains a TXOP, which is a section in which multiple frames can be transmitted. That is, AP 1 (101) is a TXOP holder. AP 1 (101) may transmit an initial frame (1000) to STA 1 (103). The link-specific spatial stream capability of STA 1 (103) may be NSS = 2. Therefore, AP 1 (101) may transmit a frame to STA 1 (103) using two spatial streams. STA 1 (103) may respond to the frame of AP 1 (101) with a BA (BlockAck) frame. STA MLD 1 can switch the radio chain to the first link after receiving the initial frame (1000) of AP 1 (101). STA MLD 1 can transmit and receive through four spatial streams in EMLMR operation. In other words, the spatial stream capability used in EMLMR operation exchanged in EML OMN frame can be NSS = 4. Therefore, after STA MLD 1 switches the radio chain to the first link, STA 1 (103) can transmit or receive a frame using four spatial streams. AP 1 (101) can transmit a data frame to STA 1 (103) using four spatial streams. STA 2 (107) cannot transmit a frame. While STA MLD 1 receives a frame in the first link, STA MLD 1 may have data to send in the second link. The data to be transmitted in the second link may be data to be transmitted in direct communication (e.g., P2P communication) rather than data to be transmitted to the AP. The data to be transmitted in the P2P communication is not data to be transmitted to the AP MLD, but data to be transmitted to another wireless LAN terminal. Alternatively, the data to be transmitted in the second link may not be wireless LAN communication. That is, the data to be transmitted in the second link may be data transmitted in a non-802.11 protocol. Accordingly, STA 1 (103) of STA MLD 1 may indicate a request to transmit and receive a frame in another EMLMR link that is not currently being received in a BA frame (1002) transmitted to AP 1 (101). This request may be referred to as EMLMR expedited transmission request information. The EMLMR expedited transmission request information may be AAR+ information, which is extended AAR (Assisted AP Request) information. Alternatively, the EMLMR expedited transmission request information may be information configured in the form of an A-Control, or may be included in a frame that STA 1 (103) transmits to AP 1 (101) in the form of an instruction bit, a subfield, an information element, and other forms. The EMLMR expedited transmission request information may include at least one of the following information: a link bitmap, MCS-NSS information to be used in the current link, Trigger frame request information, Communication period, and Start and completion information of communication. The link bitmap may indicate a link that STA MLD 1 further wishes to use. For example, STA MLD 1 may indicate a second link. Since STA MLD 1 indicates the second link in the link bitmap, STA MLD 1 indicates that P2P communication or non-802.11 communication is performed in the second link. The MCS-NSS information to be used in the current link indicates MCS and NSS information supported in the link on which the initial frame (1000) was exchanged. STA MLD 1 and AP MLD 1 perform communication according to MCS-NSS information on the link where the initial frame (1000) is exchanged. Alternatively, STA MLD 1 and AP MLD 1 may operate according to spatial stream capability per link. The communication period indicates the period during which communication is performed on the link indicated by the STA MLD in the link bitmap, and the start and completion information of the communication may indicate whether communication is performed on the link indicated by the STA MLD in the link bitmap.

STA MLD 1 and AP MLD 1 may communicate with a lower spatial stream (e.g., 2SS) than when EMLMR is set in the first link. STA MLD 1 may communicate with another STA in the second link or perform non-802.11 communication (1004). AP MLD 2 does not perform communication for the communication period indicated by STA MLD 1. Alternatively, the section in which STA MLD 1 communicates in the second link may not be determined. Therefore, instead of indicating a specific communication period, STA MLD 1 may transmit EMLMR rapid transmission request information to AP MLD 1 at the start and end of the communication, respectively, to indicate a section in which AP MLD 1 prohibits transmission to STA MLD 1 in the second link. The start and end of the communication may be indicated by start and end information of the communication present in the EMLMR rapid information request information.

Referring further to FIG. 10b, when the communication period of the second link indicated by STA MLD 1 has ended, AP MLD 1 and STA MLD 1 may communicate with the spatial stream (e.g., 4SS) set when EMLMR is set in the first link. Alternatively, when STA MLD 1 indicates to AP MLD 1 that communication has started in the second link through start and completion information of communication present in EMLMR rapid information request information, communication may be performed with a lower spatial stream (e.g., 2SS) than the spatial stream set when EMLMR is set in the first link. When STA MLD 1 indicates to AP MLD 1 that communication has ended in the second link through start and completion information of communication present in EMLMR rapid information request information, communication may be performed with the spatial stream (e.g., 4SS) set when EMLMR is set in the first link.

In FIGS. 10A and 10B, if STA MLD 1 instructs AP MLD 1 to transmit a trigger frame on the second link through trigger frame request information present in EMLMR fast information request information, AP MLD 1 may perform a TXOP Sharing operation on the second link. The TXOP Sharing operation may be a Triggered TXOP Sharing operation and may be performed through a MU-RTS TXS (TXOP sharing) frame of AP MLD 1. The MU-RTS TXS frame may include an AID of STA MLD 1, and the TXS Mode may indicate 2 or 1. STA MLD 1 may respond to the MU-RTS TXS frame on the second link with a CTS frame. If the TXS Mode is indicated as 2, STA MLD 1 may perform P2P communication or communication with the AP within the time indicated by the MU-RTS TXS frame on the second link. When TXS Mode is indicated as 1, STA MLD 1 can communicate with the AP within the time indicated by the MU-RTS TXS frame on the second link.

FIG. 11 is a flowchart illustrating an operation method of an STA according to an embodiment of the present disclosure. For example, the STA may be an MLD device. In other words, the STA may transmit or receive a frame using a plurality of links including a first link and a second link. Here, the frame may include a control frame (e.g., a BA frame), an initial frame, and a data frame (e.g., a PPDU, an MPDU, an A-MPDU). FIG. 11 illustrates an operation for the STA to transmit a data frame (e.g., low-latency data) on the second link.

Referring to FIG. 11, in step S1101, the STA receives an initial frame (e.g., the initial frame (300) of FIG. 3a). The initial frame may be received using the first link. The initial frame may include at least one of information for switching a radio chain, information for starting an EMLMR operation, and information for setting up an EMLMR. The initial frame may be a frame transmitted by an AP and may be a frame indicating the start of an EMLMR operation. The initial frame may be transmitted and received using a predefined NSS.

In step S1103, the STA transmits a frame including first information to the AP. The first information may be information related to EMLMR operation. For example, the first information may be information including at least one of an MCS and an NSS for EMLMR operation. The frame including the first information may be, for example, an EML OMN frame.

In step S1105, the STA switches the radio chain based on the initial frame and the first information. In other words, the STA performs the EMLMR operation based on the initial frame and the first information. The radio chain includes a first chain and a second chain. Before performing the EMLMR operation, the STA may communicate on the first link using the first chain. The STA may communicate on the second link using the second chain. In order to perform transmission and reception on the first link, the STA may switch the radio chain from the second link to the first link. For example, the STA may switch the second chain from the second link to the first link. Here, the first link may mean a link on which the initial frame is received. The second link may mean a link on which the initial frame is not received. In other words, the NSS of the link on which the initial frame is not received (e.g., the second link) may be used in the link on which the initial frame is received (e.g., the first link). For example, if each link has two NSSs, the STA can perform transmission and reception using four NSSs on the first link.

After switching the radio chain, the STA can communicate with the AP (e.g., AP 1 (101) in FIG. 3a) using the first link. In other words, the STA can transmit a frame to the AP using the first link, and can receive a frame from the AP using the first link.

In step S1107, the STA may transmit second information. The second information may be information indicating that there is data to be transmitted using the second link. In other words, the second information may be information indicating that there is data to be transmitted on a link on which an EMLMR operation is not performed. For example, the data transmitted using the second link may be latency sensitive data. The latency sensitive data may be transmitted using a data frame. The second information may be transmitted using the first link. For example, a data frame transmitted on the first link (e.g., a BA frame (304) of FIG. 3A) may include the second information. The second information may include information for transmitting the data frame on the second link.

The second information may include at least one of a link bitmap, trigger frame request information, MCS information for the indicated link, NSS information for the indicated link, MCS information for the current link, NSS information for the current link, and delay boundary information. The link bitmap indicates a link on which a data frame is to be transmitted. In other words, the link bitmap indicates one of the links from which an initial frame has not been received. According to one embodiment of the present disclosure, the link bitmap may indicate a second link. The trigger frame request information is information for requesting a trigger frame (e.g., the trigger frame (306) of FIG. 3A) from a link indicated by the link bitmap. The indicated link means a link indicated by the link bitmap. The current link means a link on which an EMLMR operation is performed. In other words, the current link means a link (e.g., the first link) from which an initial frame has been received. The delay boundary information is information related to a time for transmitting data or a frame. The delay boundary information may be information used to change a channel access parameter.

The second information can be expressed in various forms. For example, the second information can be included in the MAC header of the QoS Null frame in the form of A-Control. As another example, the second information can be in the form of AAR+, which is extended AAR information. As another example, the second information can be expressed in the form of one of an instruction bit, a subfield, and an information element.

In step S1109, the STA may switch the radio chain to the second link based on the second information. For example, the STA may switch the second chain to the second link based on the second information. The STA may receive information indicating use of the second link (e.g., an indicator confirming use of the second link) from the first link. The information indicating use of the second link may be information included in a control frame or a data frame (e.g., data frame (408) of FIG. 4A). For example, the STA may switch the radio chain from the first link to the second link based on at least one of the second information and the information indicating use of the second link. As another example, the STA may switch the radio chain to the second link after transmitting the second information to the AP.

At step S1111, the STA can receive a trigger frame. The STA can receive the trigger frame after switching the radio chain. The STA can receive the trigger frame using the second link.

A trigger frame may be a frame that includes information indicating the size of a resource for transmitting a data frame. Here, the size of the resource may be a value determined based on second information. For example, trigger frame request information included in the second information may include information regarding the size of a resource required for transmitting a data frame.

The STA can set the MediumSyncDelay timer before receiving the trigger frame on the second link. The STA can initialize the MediumSyncDelay timer after receiving the trigger frame on the second link. The STA can transmit and receive frames on the second link after receiving the trigger frame.

In step S1113, the STA may transmit the data frame to the AP using the second link. For example, the STA may transmit the data frame using the NSS of the second link. As another example, the STA may transmit the data frame based on the second information. For example, the STA may transmit the data frame based on at least one of the MCS information for the indicated link and the NSS information for the indicated link. As another example, the STA may transmit the data frame based on a trigger frame. The STA may transmit the data frame based on a size of a resource included in the trigger frame. In other words, the STA may transmit the data frame based on at least one of the second information and the trigger frame.

The data frame can be transmitted by being included in an uplink frame (e.g., the uplink frame (310) of FIG. 3a). After transmitting the data frame, the STA can receive a BA from the AP.

After transmitting a data frame, the STA can transmit and receive the frame using the radio chain of the second link in the first link. In other words, the STA can perform an EMLMR operation in the first link. That is, the STA can switch the radio chain. Alternatively, the STA may not perform an EMLMR operation in the first link after transmitting a data frame.

FIG. 12 is a flowchart illustrating an operation method of an AP according to an embodiment of the present disclosure. For example, the AP may be an MLD device. In other words, the AP may transmit or receive a frame using a plurality of links including a first link and a second link. Here, the frame may include a control frame (e.g., a BA frame), an initial frame, and a data frame (e.g., a PPDU, an MPDU, an A-MPDU). FIG. 12 illustrates an operation for the AP to receive a data frame (e.g., low-latency data).

Referring to FIG. 12, in step S1201, the AP transmits an initial frame (e.g., the initial frame (300) of FIG. 3a) to the STA. The initial frame can be received using the first link. The initial frame can include at least one of information for switching a radio chain, information for starting an EMLMR operation, and information for setting up an EMLMR. The initial frame can be a frame indicating the start of an EMLMR operation. The initial frame can be received using a predefined NSS.

In step S1203, the AP receives a frame including first information from the STA. The first information may be information related to EMLMR operation. For example, the first information may be information including at least one of an MCS and an NSS for EMLMR operation. The frame including the first information may be, for example, an EML OMN frame.

In step S1205, the AP may receive second information from the STA. The second information may be information indicating that there is data to be transmitted using the second link. In other words, the second information may be information indicating that there is data to be transmitted on a link on which an EMLMR operation is not performed. For example, the data to be transmitted using the second link may be latency sensitive data. The latency sensitive data may be transmitted using a data frame. The second information may be information transmitted from the STA. For example, the AP may receive a control frame (e.g., a BA frame (304) of FIG. 3A) including the second information. As another example, the AP may receive a data frame (e.g., a PPDU, an MPDU, an A-MPDU) including the second information. The second information may include information for transmitting the data frame on the second link.

The second information may include at least one of a link bitmap, trigger frame request information, MCS information for the indicated link, NSS information for the indicated link, MCS information for the current link, NSS information for the current link, and delay boundary information. The link bitmap indicates a link on which a data frame is to be transmitted. In other words, the link bitmap indicates one of the links from which an initial frame has not been received. According to one embodiment of the present disclosure, the link bitmap may indicate a second link. The trigger frame request information is information for requesting a trigger frame (e.g., the trigger frame (306) of FIG. 3A) in a link indicated by the link bitmap. The indicated link means a link indicated by the link bitmap. The current link means a link on which an EMLMR operation is performed. In other words, the current link means a link (e.g., the first link) from which an initial frame has been received. The delay boundary information is information related to a time for transmitting data or a frame. The delay boundary information may be information used to change a channel access parameter.

The second information can be expressed in various forms. For example, the second information can be included in the MAC header of the QoS Null frame in the form of A-Control. As another example, the second information can be in the form of AAR+, which is extended AAR information. As another example, the second information can be expressed in the form of one of an instruction bit, a subfield, and an information element.

In step S1207, the AP may transmit at least one of a trigger frame and information indicating use of the second link to the STA. The AP may transmit the trigger frame after acquiring the second information. The AP may transmit information indicating use of the second link (e.g., an indicator confirming use of the second link) after transmitting the trigger frame or before transmitting the trigger frame. The AP may transmit the trigger frame using the second link. The AP may transmit information indicating use of the second link using the first link. The information indicating use of the second link may be information included in a control frame or a data frame (e.g., data frame (408) of FIG. 4A). The information indicating use of the second link may be included in a frame different from the trigger frame.

A trigger frame may be a frame that includes information indicating the size of a resource for transmitting a data frame. Here, the size of the resource may be a value determined based on second information. For example, trigger frame request information included in the second information may include information regarding the size of a resource required for transmitting a data frame.

The AP may perform a backoff operation. For example, the AP may transmit a data frame to the STA when the backoff counter reaches 0. As another example, the AP may transmit a trigger frame to the STA when the backoff counter reaches 0 and a predefined time (e.g., EMLMR Delay) has elapsed from the end time of transmission of a frame including the second information. The backoff operation may be performed before the AP transmits the trigger frame. The backoff operation may be started after the information indicating the use of the second link is transmitted.

In step S1209, the AP may receive a data frame from the STA using the second link. For example, the AP may receive the data frame using the NSS of the second link. As another example, the AP may receive the data frame based on the second information. For example, the AP may receive the data frame based on at least one of the MCS information for the indicated link and the NSS information for the indicated link. For example, the data frame may be received while being included in an uplink frame (e.g., the uplink frame (310) of FIG. 3A). After receiving the data frame, the AP may transmit a BA to the STA.

After receiving the data frame, the AP can transmit and receive the frame using the radio chain of the second link on the first link. In other words, the AP can perform the EMLMR operation on the first link. Alternatively, the AP may not perform the EMLMR operation on the first link after transmitting the data frame.

FIG. 13 is a flowchart illustrating an operation method of an AP according to an embodiment of the present disclosure. For example, the AP may be an MLD device. In other words, the AP may transmit or receive a frame using a plurality of links including a first link and a second link. Here, the frame may include a control frame (e.g., a BA frame), an initial frame, and a data frame (e.g., a PPDU, an MPDU, an A-MPDU). FIG. 13 illustrates an operation for the AP to transmit a data frame (e.g., low-latency data).

Referring to FIG. 13, in step S1301, the AP transmits an initial frame (e.g., the initial frame (500) of FIG. 5a) to the STA. The initial frame may be transmitted using the first link. The initial frame may include at least one of information for switching a radio chain, information for starting an EMLMR operation, and information for setting up an EMLMR. The initial frame may be a frame indicating the start of an EMLMR operation. The initial frame may be transmitted and received using a predefined NSS.

In step S1303, the AP receives a frame including first information from the STA. The first information may be information related to EMLMR operation. For example, the first information may be information including at least one of an MCS and an NSS for EMLMR operation. The frame including the first information may be, for example, an EML OMN frame.

In step S1305, the AP may transmit second information to the STA. The second information may be information indicating that there is data to be transmitted using the second link. In other words, the second information may be information indicating that there is data to be transmitted on a link on which an EMLMR operation is not performed. For example, the data to be transmitted using the second link may be, for example, latency sensitive data. The latency sensitive data may be transmitted using a data frame. The second information may be transmitted by being included in a control frame or a data frame (e.g., frame (502) of FIG. 5A). For example, the AP may transmit a control frame (e.g., a BA frame) including the second information. As another example, the AP may transmit a data frame (e.g., a PPDU, an MPDU, an A-MPDU) including the second information. The second information may include information for transmitting a data frame on the second link.

The second information may include at least one of a link bitmap, trigger frame request information, MCS information for the indicated link, NSS information for the indicated link, MCS information for the current link, NSS information for the current link, and delay boundary information. The link bitmap indicates a link on which a data frame is to be transmitted. In other words, the link bitmap indicates one of the links from which an initial frame has not been received. According to one embodiment of the present disclosure, the link bitmap may indicate a second link. The trigger frame request information is information for requesting a trigger frame in a link indicated by the link bitmap. The indicated link means a link indicated by the link bitmap. The current link means a link on which an EMLMR operation is performed. In other words, the current link means a link (e.g., a first link) from which an initial frame has been received. The delay boundary information is information related to a time for transmitting data or a frame. The delay boundary information may be information used to change a channel access parameter.

The second information can be expressed in various forms. For example, the second information can be included in the MAC header of the data frame in the form of A-Control. As another example, the second information can be in the form of AAR+, which is extended AAR information. As another example, the second information can be expressed in the form of one of an instruction bit, a subfield, and an information element.

According to one embodiment of the present disclosure, after transmitting the second information, the AP may receive information approving the use of the second link using the first link. The information approving the use of the second link may be information included in a control frame (e.g., BA frame (504) of FIG. 5A) or a data frame. The information indicating the use of the second link may be information transmitted in response to the second information. In other words, the information approving the use of the second link may be information transmitted by the STA in response to the second information. Alternatively, the AP may receive information rejecting the use of the second link. If the AP receives information rejecting the use of the second link, step S1307 is not performed.

In step S1307, the AP may transmit a data frame to the STA using the second link. For example, the AP may transmit the data frame using the NSS of the second link. As another example, the AP may transmit the data frame based on the second information. For example, the AP may transmit the data frame based on at least one of the MCS information for the indicated link and the NSS information for the indicated link. For example, the data frame may be transmitted while being included in a downlink frame (e.g., the downlink frame (506) of FIG. 5A). After transmitting the data frame, the AP may receive a BA from the STA.

The AP may perform a backoff operation to transmit the data frame. For example, the AP may transmit the data frame to the STA when the backoff counter reaches 0. As another example, the AP may transmit the data frame to the STA when the backoff counter reaches 0 and a predefined time (e.g., EMLMR Delay) has elapsed from the end time of transmission of the data frame including the second information. The backoff operation may be performed before the AP transmits the data frame.

After transmitting the data frame, the AP can transmit and receive the frame using the radio chain of the second link on the first link. In other words, the AP can perform the EMLMR operation on the first link. Alternatively, the AP may not perform the EMLMR operation on the first link after transmitting the data frame.

FIG. 14 is a flowchart illustrating an operation method of an STA according to an embodiment of the present disclosure. For example, the STA may be an MLD device. In other words, the STA may transmit or receive a frame using a plurality of links including a first link and a second link. Here, the frame may include a control frame (e.g., a BA frame), an initial frame, and a data frame (e.g., a PPDU, an MPDU, an A-MPDU). FIG. 14 illustrates an operation for an STA to receive a data frame (e.g., low-latency data).

Referring to FIG. 14, in step S1401, the STA receives an initial frame (e.g., the initial frame (500) of FIG. 5a) from the AP. The initial frame may be transmitted using the first link. The initial frame may include at least one of information for switching a radio chain, information for starting an EMLMR operation, and information for setting up an EMLMR. The initial frame may be a frame indicating the start of an EMLMR operation. The initial frame may be received using a predefined NSS.

In step S1403, the STA receives a frame including first information from the AP. The first information may be information related to EMLMR operation. For example, the first information may be information including at least one of an MCS and an NSS for EMLMR operation. The frame including the first information may be, for example, an EML OMN frame.

In step S1405, the STA switches the radio chain based on the initial frame and the first information. In other words, the STA performs the EMLMR operation based on the initial frame and the first information. The radio chain includes a first chain and a second chain. Before performing the EMLMR operation, the STA may communicate on the first link using the first chain. The STA may communicate on the second link using the second chain. In order to perform transmission and reception on the first link, the STA may switch the radio chain from the second link to the first link. For example, the STA may switch the second chain from the second link to the first link. Here, the first link may mean a link on which the initial frame is received. The second link may mean a link on which the initial frame is not received. In other words, the NSS of the link on which the initial frame is not received (e.g., the second link) may be used in the link on which the initial frame is received (e.g., the first link). For example, if each link has two NSSs, the STA can perform transmission and reception using four NSSs on the first link.

In step S1407, the STA may receive second information from the AP. The second information may be information indicating that there is data to be transmitted using the second link. In other words, the second information may be information indicating that there is data to be transmitted on a link on which an EMLMR operation is not performed. For example, the data to be transmitted using the second link may be latency sensitive data. The latency sensitive data may be transmitted using a data frame. The second information may be transmitted by being included in a control frame or a data frame (e.g., the data frame (502) of FIG. 5A). For example, the STA may receive a control frame (e.g., a BA frame) including the second information. As another example, the STA may receive a data frame (e.g., a PPDU, an MPDU, an A-MPDU) including the second information. The second information may include information for transmitting a data frame on the second link.

The second information may include at least one of a link bitmap, trigger frame request information, MCS information for the indicated link, NSS information for the indicated link, MCS information for the current link, NSS information for the current link, and delay boundary information. The link bitmap indicates a link on which a data frame is to be transmitted. In other words, the link bitmap indicates one of the links from which an initial frame has not been received. According to one embodiment of the present disclosure, the link bitmap may indicate a second link. The trigger frame request information is information for requesting a trigger frame from a link indicated by the link bitmap. The indicated link means a link indicated by the link bitmap. The current link means a link on which an EMLMR operation is performed. In other words, the current link means a link from which an initial frame has been received (e.g., the first link). The delay boundary information is information related to a time for transmitting data or a frame. The delay boundary information may be information used to change a channel access parameter. The information included in the second information may be expressed as a condition for transmitting a data frame using the second link. For example, if the NSS included in the NSS information for the indicated link is not available, the data frame may not be transmitted using the second link.

The second information can be expressed in various forms. For example, the second information can be included in the MAC header of the data frame in the form of A-Control. As another example, the second information can be in the form of AAR+, which is extended AAR information. As another example, the second information can be expressed in the form of one of an instruction bit, a subfield, and an information element.

According to one embodiment of the present disclosure, after receiving the second information, the STA may transmit information approving the use of the second link using the first link. The information approving the use of the second link may be information included in a control frame (e.g., BA frame (504) of FIG. 5A) or a data frame. The information indicating the use of the second link may be information transmitted in response to the second information. In other words, the information approving the use of the second link may be information transmitted by the STA in response to the second information. Alternatively, the STA may transmit information rejecting the use of the second link. For example, the STA may transmit information rejecting the use of the second link when a condition for transmitting a data frame using the second link is not satisfied. If the STA transmits information rejecting the use of the second link, step S1409 is not performed.

At step S1409, the STA may switch the radio chain to the second link based on the second information. For example, the STA may switch the radio chain from the first link to the second link based on at least one of the second information and the information approving the use of the second link. As another example, the STA may switch the radio chain to the second link after receiving the second information from the AP. For example, the STA may switch the second chain to the second link.

In step S1411, the STA may receive a data frame from the AP using the second link. For example, the STA may receive the data frame using the NSS of the second link. As another example, the STA may receive the data frame based on the second information. For example, the STA may receive the data frame based on at least one of the MCS information for the indicated link and the NSS information for the indicated link. For example, the data frame may be received while being included in a downlink frame (e.g., the downlink frame (506) of FIG. 5A). After receiving the data frame, the STA may transmit a BA to the AP.

After receiving a data frame, the STA may transmit and receive the frame using the radio chain of the second link in the first link. In other words, the STA may switch the radio chain to perform the EMLMR operation in the first link. Alternatively, the STA may not perform the EMLMR operation in the first link after transmitting the data frame.

The methods according to the present invention 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 invention 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, and flash memory. Examples of program instructions include not only machine language codes generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc. The above-described hardware devices can be configured to operate with at least one software module to perform the operations of the present invention, and vice versa.

Although the present invention 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 invention without departing from the spirit and scope of the present invention as set forth in the claims below.

The present disclosure can be used in devices and recording media in a wireless LAN system.

Claims (17)

In a method performed by a STA (station) in a wireless LAN system, A step of performing at least one of transmission and reception using a first chain in a first link; A step of performing at least one of transmission and reception using a second chain in a second link; A step of receiving an initial frame for starting an enhanced multi-link multi radio (EMLMR) operation in the first link; A step of switching the second chain from the second link to the first link based on the initial frame; A step of transmitting information for transmission of a data frame in the second link; a step of switching the second chain from the first link to the second link based on the above information; and A step of receiving a trigger frame from the second link; A method comprising the step of transmitting the data frame on the second link based on at least one of the above information and the above trigger frame. In the first paragraph, A method wherein the above information includes MCS (modulation and coding scheme) and NSS (number of spatial streams) information for the second link, and information requesting the trigger frame. In the first paragraph, The step of switching the second chain from the first link to the second link is, A step of receiving information indicating use of a second link in response to the above information; and A method comprising the step of switching the second chain based on the information and the information indicating use of the second link. In the third paragraph, If the second link is busy, the information indicating the use of the second link includes information denying the use of the second link, The above second chain is not switched to the above second link. In the third paragraph, The above information includes conditions for transmitting the data frame using the second link, If the above conditions are not satisfied, The information instructing the use of the second link includes information denying the use of the second link, The above second chain is not switched to the above second link. In the third paragraph, A method in which information indicating use of the second link is indicated using a PHY preamble. In Article 6, The above PHY preamble includes information indicating the NSS of the downlink frame transmitted on the first link, The step of switching the second chain from the first link to the second link is, A step of decoding the preamble in the PHY layer to generate a primitive; and A step of verifying the NSS based on the primitive in the MAC layer; and A method further comprising the step of obtaining information indicating use of the second link based on the NSS. In Article 7, The above primitive is a primitive containing RXVECTOR information. In a method performed by an AP (access point) in a wireless LAN system, A step of transmitting an initial frame to start enhanced multi-link multi radio (EMLMR) operation in the first link; A step of transmitting information for transmission of a data frame in a second link; A step of receiving information approving the use of the second link; A method comprising the step of transmitting the data frame over the second link. In Article 9, A method wherein the above information includes MCS and NSS information for the second link. In Article 9, A method further comprising the step of performing a channel access procedure in the second link. In Article 11, The above channel access procedure includes an operation of counting the EDCA backoff (enhanced distributed channel access backoff), A method in which the above data frame can be transmitted after the time of EMLMR Delay has elapsed from the time point of termination of transmission of the first information, when the counter of the backoff is 0. In Article 11, The above channel access procedure includes an operation of counting EDCA backoff, A method in which the above data frame can be transmitted after the time of EMLMR Delay has elapsed from the time of termination of transmission of information approving the use of the second link, when the counter of the above backoff is 0. In a method performed by an AP (access point) in a wireless LAN system, A step of transmitting an initial frame to start enhanced multi-link multi radio (EMLMR) operation on the first link; A step of receiving information for transmission of a data frame on a second link; A step of transmitting a trigger frame in the second link; A method comprising the step of receiving the data frame from the second link based on the above information. In a method performed by a STA (station) in a wireless LAN system, A step of performing at least one of transmission and reception using a first chain in a first link; A step of performing at least one of transmission and reception using a second chain in a second link; A step of receiving an initial frame for starting an enhanced multi-link multi radio (EMLMR) operation in the first link; A step of switching the second chain (radio chain) of the second link to the first link based on the initial frame; A step of receiving information for transmission of a data frame in the second link; A step of switching the second chain from the first link to the second link based on the above information; A step of transmitting information approving the use of the second link; and A method comprising the step of receiving the delay-sensitive data from the second link based on the above information. In a wireless LAN system, at STA (station), Transmitter and receiver; and Including a processor connected to the above transceiver, The above processor, At least one of transmission and reception is performed using the first chain in the first link, At least one of transmission and reception is performed using the second chain in the second link, Receive an initial frame for starting an enhanced multi-link multi radio (EMLMR) operation on the first link, Switching the second chain (radio chain) to the first link based on the initial frame and the first information; Transmitting information for transmitting data frames in the second link, Based on the above information, the second chain is switched from the first link to the second link, Receive a trigger frame from the second link above, A STA configured to transmit the data frame on the second link based on at least one of the above information and the above trigger frame. In a wireless LAN system, at the AP (access point), Transmitter and receiver; and Including a processor connected to the above transceiver, The above processor, Transmit an initial frame to start the enhanced multi-link multi radio (EMLMR) operation on the first link, Transmit information for transmission of data frames on the second link, Receive information consenting to the use of the above second link; An AP configured to transmit the data frame over the second link.

Images