Apparatus and method for fast error reporting in wireless LAN system

Abstract

For fast error reporting in a wireless LAN system, this method for an operation of a station (STA) in a wireless LAN system comprises the steps of: transmitting a plurality of frames in a first link; receiving an error report of a frame in which an error is detected among the plurality of frames, in a second link; and transmitting a retransmission frame including the frame in which the error is detected on the basis of the error report, wherein each of the plurality of frames includes a delimiter, and the delimiter includes information for distinguishing each of the plurality of frames.

Description

Device and method for rapid error reporting in wireless LAN systems

[0001] The present invention relates to a wireless local area network (WLAN) system. More specifically, it relates to a device and method for rapid error reporting in a WLAN system.

[0002] With the recent proliferation of mobile devices, Wireless Local Area Network (WLAN) technology, which can provide fast wireless communication services to these devices, is attracting significant attention. WLAN technology utilizes short-range wireless communication technology to enable mobile devices such as smartphones, tablets, laptops, portable multimedia players, and embedded devices to wirelessly access the Internet.

[0003] As applications requiring higher throughput and real-time transmission arise, the IEEE 802.11be standard, an Extreme High Throughput (EHT) wireless LAN technology, is being developed. The goal of the IEEE 802.11be standard may support a high throughput of 30 Gbps. The IEEE 802.11be standard may support technologies to reduce transmission delay. In addition, the IEEE 802.11be standard may support a wider frequency bandwidth (e.g., 320 MHz bandwidth), multi-link transmission and aggregation operation including operation using multiple bands, multi-AP (Access Point) transmission operation, and / or efficient retransmission operation (e.g., Hybrid Automatic Repeat Request (HARQ) operation).

[0004] Meanwhile, the technology that serves as the background for the invention is 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.

[0005] The present disclosure provides a method and device for detecting and reporting an error in a frame received by an AP (access point) in a wireless LAN system.

[0006] The present disclosure provides a method and device for a STA (station) to quickly recover a frame in which an error is detected in a wireless LAN system.

[0007] The present disclosure provides a method and device for an AP and an STA using a STR (simultaneous transmit receive) link pair in a wireless LAN system to report and recover frame errors using multiple links.

[0008] The present disclosure provides a method and device for identifying a frame for recovering an error frame in a wireless LAN system.

[0009] The present disclosure provides a method and apparatus for exchanging information for identifying a frame in a wireless LAN system.

[0010] 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.

[0011] According to one embodiment of the present disclosure, a method for operation of a station (STA) in a wireless LAN system includes the steps of: transmitting a plurality of frames in a first link; receiving an error report of a frame in which an error is detected among the plurality of frames in a second link; and transmitting a retransmission frame including the frame in which an error is detected based on the error report, wherein each of the plurality of frames includes a delimiter, and the delimiter includes information for distinguishing each of the plurality of frames.

[0012] A method for operating an access point (AP) in a wireless LAN system comprises the steps of: receiving a plurality of frames in a first link; detecting an error in at least one frame among the plurality of frames; transmitting an error report based on the frame in which the error is detected; and receiving a retransmission frame transmitted based on the error report, wherein each of the plurality of frames includes a delimiter, and the delimiter includes information for distinguishing each of the plurality of frames.

[0013] In a wireless LAN system, a STA (station) includes a transceiver; and a processor connected to the transceiver, wherein the processor is configured to transmit a plurality of frames in a first link, receive an error report of a frame in which an error is detected among the plurality of frames in a second link, and transmit a retransmission frame including the frame in which an error is detected based on the error report, wherein each of the plurality of frames includes a delimiter, and the delimiter includes information for distinguishing each of the plurality of frames.

[0014] 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 receive a plurality of frames in a first link, detect an error in at least one frame among the plurality of frames, transmit an error report based on the frame in which the error is detected, and receive a retransmission frame transmitted based on the error report, wherein each of the plurality of frames includes a delimiter, and the delimiter includes information for distinguishing each of the plurality of frames.

[0015] According to the present disclosure, a feedback frame including time information capable of identifying a frame in which an error is detected in a wireless LAN system can be transmitted.

[0016] According to the present disclosure, an MPDU including previous MPDU and next MPDU information can be transmitted.

[0017] According to the present disclosure, an AP can identify a frame in which an error is detected and transmit a feedback frame.

[0018] The effects that can be obtained from the embodiments of the present disclosure are not limited to the effects mentioned above, and other effects not mentioned can be clearly derived and understood by those skilled in the art to which the technical configuration of the present disclosure is applied, from the description of the embodiments of the present disclosure below. In other words, unintended effects resulting from implementing the configuration described in the present disclosure can also be derived from the embodiments of the present disclosure by those skilled in the art.

[0019] FIG. 1 is a block diagram illustrating a first embodiment of a communication node constituting a wireless LAN system.

[0020] Figure 2 illustrates a first embodiment of a negotiation procedure for multi-link operation in a wireless LAN system.

[0021] Figure 3 illustrates a first embodiment of a rapid error feedback method.

[0022] Figure 4a illustrates a second embodiment of a rapid error feedback method.

[0023] Figure 4b illustrates a third embodiment of a fast error feedback method.

[0024] Figure 5 illustrates a fourth embodiment of a rapid error feedback method.

[0025] Figure 6 illustrates a fifth embodiment of a rapid error feedback method.

[0026] FIG. 7 illustrates a flowchart of an error recovery procedure according to one embodiment of the present disclosure.

[0027] FIG. 8 illustrates a flowchart of an error reporting procedure according to one embodiment of the present disclosure.

[0028] The present invention is susceptible to various modifications and embodiments. Specific embodiments are illustrated and described in detail in the drawings. However, this is not intended to limit the present invention to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0029] While terms such as "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a "second component," and similarly, a second component may also be referred to as a "first component." The term "and / or" includes a combination of multiple related items described herein or any of multiple related items described herein.

[0030] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0031] The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0032] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0033] Hereinafter, with reference to the attached drawings, preferred embodiments of the present invention will be described in more detail. In order to facilitate an overall understanding in describing the present invention, identical reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted.

[0034] Below, a wireless communication system to which embodiments of the present invention are applied will be described. The wireless communication system to which embodiments of the present invention are applied is not limited to the descriptions below, and embodiments of the present invention can be applied to various wireless communication systems. The wireless communication system may be referred to as a "wireless communication network."

[0035] Figure 1 is a block diagram illustrating a first embodiment of a communication node constituting a wireless LAN system.

[0036] 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. An access point may refer to an AP, and a station may refer to an STA or a non-AP STA. The operating channel width supported by the access point may be 20 MHz (megahertz), 80 MHz, 160 MHz, etc. The operating channel width supported by the station may be 20 MHz, 80 MHz, etc.

[0037] A communication node (100) may include at least one processor (110), a memory (120), and a plurality of transmitting and receiving devices (130) that are connected to a network and perform communication. The transmitting and receiving device (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.

[0038] 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 a memory (120), a transmission / reception device (130), an input interface device (140), an output interface device (150), and a storage device (160) through a dedicated interface.

[0039] The processor (110) can execute program commands stored in at least one of the memory (120) and the storage device (160). The processor (110) may refer to 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 non-volatile 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).

[0040] FIG. 2 is a flowchart illustrating a first embodiment of a negotiation procedure for multi-link operation in a wireless LAN system.

[0041] Referring to FIG. 2, the connection procedure between a station (STA) and an access point (AP) in an infrastructure basic service set (BSS) may include a probe step of the access point, an authentication step between the station and the detected access point, and an association step between the station and the authenticated access point.

[0042] In the detection phase, the station can detect one or more access points using either a passive scanning method or an active scanning method. When the passive scanning method is used, the station can detect one or more access points by overhearing beacon frames transmitted by one or more access points. When the active scanning method is used, the station can detect one or more access points by transmitting a probe request frame and receiving a probe response frame, which is a response to the probe request frame, from one or more access points.

[0043] If more than one access point is detected, the station can perform an authentication step with the detected access point(s). In this case, the station can perform the authentication step with multiple access points. Authentication algorithms according to the IEEE 802.11 standard can be classified into open system algorithms that exchange two authentication frames and shared key algorithms that exchange four authentication frames.

[0044] The station can transmit an authentication request frame based on an authentication algorithm according to the IEEE 802.11 standard, and complete authentication with the access point by receiving an authentication response frame, which is a response to the authentication request frame, from the access point.

[0045] When authentication with an access point is completed, the station can perform an association step with the access point. In this case, the station can select one of the access points with which it has performed the authentication step, and perform an association step with the selected access point. That is, the station can transmit an association request frame to the selected access point, and complete the association with the selected access point by receiving an association response frame, which is a response to the association request frame, from the selected access point.

[0046] Meanwhile, multi-link operation may be supported in a wireless LAN system. An MLD may include one or more STAs associated with the MLD. An MLD may be a logical entity. An MLD may be classified into an AP MLD and a non-AP MLD. Each STA associated with an AP MLD may be an AP, and each STA associated with a non-AP MLD may be a non-AP STA. To configure multiple links, a multi-link discovery procedure, a multi-link setup procedure, etc. may be performed. The multi-link discovery procedure may be performed during the detection phase between a station and an access point. In this case, a multi-link information element (ML IE) may be included in a beacon frame, a probe request frame, and / or a probe response frame.

[0047] For example, in order to perform multi-link operation, information indicating whether multi-link operation is available and information about available links may be exchanged between an access point (e.g., an AP associated with an MLD) and a station (e.g., a non-AP STA associated with the MLD) during a detection phase. In a negotiation procedure for multi-link operation (e.g., a multi-link setup procedure), the access point and / or the station may transmit information about links to be used for multi-link operation. The negotiation procedure for multi-link operation may be performed during an association procedure (e.g., an association phase) between a station and an access point, and information element(s) required for multi-link operation may be set or changed by an action frame during the negotiation procedure.

[0048] Additionally, during the connection procedure between a station and an access point (e.g., the association phase), available link(s) of the access point may be established, and each link may be assigned an identifier (ID). Subsequently, during the negotiation and / or change procedures for multi-link operation, information indicating whether each link is active may be transmitted, and this information may be expressed using a link ID.

[0049] Information indicating whether multi-link operation is available may be transmitted and received in a capability information element (e.g., an extremely high throughput (EHT) capability information element) exchange procedure between a station and an access point. The capability information element may include information on a supporting band, information on a supporting link (e.g., an ID and / or number of supporting links), information on links capable of STR operation (e.g., band information of links, spacing information of links), etc. In addition, the capability information element may include information individually indicating links capable of STR operation.

[0050]

[0051] Figure 3 illustrates a first embodiment of a rapid error feedback method.

[0052] Referring to FIG. 3, AP MLD 1 and STA MLD 1 may operate in a wireless LAN network. The AP in which AP MLD 1 operates in the first link is AP 1 (301), and the AP in which AP MLD 1 operates in the second link is AP 2 (303). That is, AP 1 (301) and AP 2 (303) may be affiliated to AP MLD 1. Similarly, the STA in which STA MLD 1 operates in the first link may be STA 1 (311), and the STA in which STA MLD 1 operates in the second link may be STA 2 (313). That is, STA 1 (311) and STA 2 (313) may be affiliated to STA MLD 1. In the second link, STA Y (320) associated with STA MLD X may operate. X and Y can be natural numbers. For example, STA MLD X may or may not be STA MLD 1. STA Y (320) may or may not be STA 2 (313). The first link and the second link of STA MLD 1 may be links capable of simultaneous transmission and reception (STR link pair). Alternatively, the first link and the second link of STA MLD 1 may be links capable of simultaneous transmission and reception (NSTR link pair), but may be conditional STR or conditional NSTR link pairs that can be received when STA MLD 1 receives a frame transmitted by an AP with strong transmission power or / and low MCS (Modulation and Coding Scheme) on another link while transmitting on one link.

[0053] STA 1 (311) can acquire a transmit opportunity (TXOP) on the first link. TXOP acquisition is achieved when the EDCAF of STA 1 (311) determines to transmit through a channel access procedure (e.g., EDCA backoff operation). STA 1 (311) can transmit frames (e.g., PPDU (physical layer protocol data unit), MPDU (MAC layer protocol data unit), A-MPDU (aggregated MPDU)) within the TXOP. STA 1 (311) can transmit A-MPDU to AP 1 (301), and the A-MPDU includes multiple MPDUs. A delimiter can be included between MPDUs to distinguish MPDUs. A delimiter can be composed of 32 bits and can include at least one of an MPDU length indicator (e.g., 14 bits), a CRC (Cyclic Redundancy Check) (e.g., 8 bits), and a delimiter signature (e.g., 8 bits). When AP 1 (301) receives MPDUs transmitted by STA 1 (311), MPDU #1, MPDU #2 (330), and MPDU #3 (340) can be received sequentially. Among the MPDUs received by AP 1 (301), MPDU #2 (330) may have an error (e.g., cannot be decoded, FCS (Frame Check Sequence) error) and may not be properly received. Due to MPDU #2 (330) not being properly received, AP 1 (301) may not be able to transmit data in the queue to an upper layer. Alternatively, MPDU #2 (330) may be a frame that must be urgently transmitted to the upper layer. Since MPDU #2 (330) was not properly received, MPDU #2 (330) is not transmitted to the upper layer.In order to transmit a feedback frame (350) for recovering MPDU #2 (330), AP 2 (303) on the second link may perform a channel access procedure (e.g., an EDCA backoff operation). The channel access procedure may be newly started for AP 2 (303) to transmit a feedback frame (350) for recovering MPDU #2 (330). Alternatively, instead of starting the channel access procedure anew, the channel access procedure that AP 2 (303) was previously performing may continue to be performed. The channel access procedure of AP 2 (303) may succeed (e.g., the EDCA backoff counter reaches 0). AP 2 (303) transmits a feedback frame (350) to STA 2 (313) indicating that MPDU #2 (330) was not properly received. The channel access procedure of AP 2 (303) may be performed for each AC (access category). The above feedback frame (350) can be transmitted by any AC's channel access procedure (e.g., by the EDCAF of the AC whose channel access procedure ends the fastest). Alternatively, if AP 2 (303) performs a channel access procedure successfully (e.g., the EDCA backoff counter reaches 0) and there is an EDCAF of any AC that remains at 0, the feedback frame (350) can be transmitted immediately.

[0054] Alternatively, the feedback frame (350) may be transmitted by a channel access procedure related to the AC of the MPDU of the frame that STA 1 (311) of the first link transmits to AP 1 (301) (e.g., by AC_VO EDCAF of the second link when the AC of the MPDU that STA 1 (311) transmits to AP 1 (301) is AC_VO). For example, the AC-specific channel access procedure of AP 2 (303) may end AC_VO before AC_VI and other ACs (e.g., AC_BE and AC_BK). AP 2 (303) may obtain AC_VO TXOP from the second link, and AP 2 (303) transmits a feedback frame (350) indicating to STA 2 (313) that MPDU #2 (330) was not properly received. In the remaining AC_VO TXOP of AP 2 (303), AP 2 (303) can transmit a data frame to STA Y (320).

[0055] A frame error of the first link can be detected while a channel access procedure is being performed when a frame to be transmitted is generated in the transmission queue of the second link. A frame of an AC to be transmitted in the second link can be generated and a channel access procedure (e.g., a backoff procedure) can be performed, and an error can be detected in the MPDU received in the first link before the backoff counter becomes 0. The AC of the MPDU in which an error occurred in the first link can be a different AC from or the same AC as the AC for which a backoff is being performed to be transmitted in the second link. If the channel access procedure in the second link is successful (e.g., if the backoff is successful and the counter becomes 0), a TXOP including the feedback transmission time for the MPDU generated in the first link is set. That is, the duration included in the MAC header of the feedback frame (350) can be set to a time including the data frame transmission time of the AC to be transmitted. The receiving STA of the feedback frame (350) and the data frame can be different. The feedback frame (350) can be transmitted first and then the data frame can be transmitted. Alternatively, the feedback frame (350) and the data frame may be transmitted together using a downlink OFDMA (Orthogonal Frequency Division Multiple Access) method that simultaneously transmits them using different subchannels. The feedback may be restricted to be transmitted only when the priority of the AC of the data for which a channel access procedure is performed to be transmitted in the second link is lower than the AC of the MPDU that failed to be transmitted in the first link. Alternatively, the feedback of the MPDU that failed to be transmitted in the first link may be assumed to be higher than any AC. Accordingly, if channel access for data transmission is successful in the second link regardless of the AC, the feedback frame (350) may be transmitted together with the data transmission.

[0056] STA MLD 1 can receive the feedback frame (350) of AP MLD 1, and STA MLD 1 can know that MPDU #2 (330) is not properly transmitted in the frame that STA 1 (311) of the first link transmits to AP 1 (301). STA MLD 1 may or may not transmit a response frame (e.g., an ACK frame) to the feedback frame (350) of AP MLD 1. STA MLD 1 can retransmit MPDU #2 (330) in a frame that is already being transmitted. For example, MPDU #2 (330) can be retransmitted after MPDU #3 (340), which is the next MPDU after MPDU #2 (330). Alternatively, STA MLD 1 can transmit MPDU #2 (330) to AP 1 (301) through a separate frame. If AP MLD 1 normally receives the retransmitted MPDU #2 (330), it can transmit the data in the queue to the upper layer. If the retransmitted MPDU #2 (330) causes an error again, the retransmission operation of the above-described MPDU #2 (330) can be performed again. As another method for STA MLD 1 to perform retransmission, STA 1 (311) of STA MLD 1 can retransmit the frame transmitted after MPDU #2 (330) (e.g., MPDU #3 (340)) together with MPDU #2 (330), instead of retransmitting only MPDU #2 (330). That is, STA 1 (311) can transmit the frame again starting from MPDU #2 (330).

[0057] In the above embodiment, when STA MLD 1 has a conditional NSTR link pair or a conditional STR link pair (e.g., when the first link and the second link are a conditional NSTR link pair), when STA MLD 1 transmits a frame to AP MLD 1 on the first link, AP MLD 1 transmits a frame to STA MLD 1 with strong transmission power and / or low MCS on the second link. In the conditional NSTR link pair or conditional STR link pair, the STA MLD may be able to receive a frame that satisfies a specific condition (e.g.) during frame transmission on one link on the other link. For example, the STA MLD may receive a frame that satisfies an MCS lower than or equal to a certain value and a reception power higher than or equal to a certain value on the first link on the second link. The feedback frame (350) of the above embodiment may be a frame in various forms. For example, the feedback frame (350) may be one of the control frames including the BlockAck frame, the action frame, and the QoS frames having a control field (e.g., an HT Control field). The feedback frame (350) includes at least one of the Sequence Number (SN) and TID of the MPDU or / and MSDU, information that can identify the MPDU or MSDU (e.g., time information that can identify the MPDU or MSDU, and the MPDU identified by the MPDU order within the A-MPDU).

[0058]

[0059] Figure 4a illustrates a second embodiment of a fast error feedback method. Figure 4b illustrates a third embodiment of a fast error feedback method.

[0060] Referring to FIGS. 4A and 4B, AP MLD 1 and STA MLD 1 may operate in a wireless LAN network. An AP in which AP MLD 1 operates on a first link is AP 1 (401), and an AP in which AP MLD 1 operates on a second link is AP 2 (403). That is, AP 1 (401) and AP 2 (403) may be affiliated to AP MLD 1. Similarly, an STA in which STA MLD 1 operates on a first link may be STA 1 (411), and an STA in which STA MLD 1 operates on a second link may be STA 2 (413). That is, STA 1 (411) and STA 2 (413) may be affiliated to STA MLD 1. In the second link, STA Y (420) associated with STA MLD X may operate. X can be a natural number. Y can be a natural number. For example, STA MLD X may or may not be STA MLD 1. STA Y (420) may or may not be STA 2 (413). The first link and the second link of STA MLD 1 may be links capable of simultaneous transmission and reception (STR link pair). Alternatively, the first link and the second link of STA MLD 1 may be links capable of simultaneous transmission and reception (NSTR link pair), but may be conditional STR or conditional NSTR link pairs that can be received when STA MLD 1 receives a frame transmitted by an AP with strong transmission power or / and low MCS (Modulation and Coding Scheme) on another link while transmitting on one link.

[0061] STA 1 (411) can acquire a TXOP from the first link. TXOP acquisition is achieved when the EDCAF of STA 1 (411) determines to transmit through a channel access procedure (e.g., EDCA backoff operation). STA 1 (411) can transmit frames (e.g., PPDU (physical layer protocol data unit), MPDU (MAC layer protocol data unit), A-MPDU (aggregated MPDU)) within the TXOP. STA 1 (411) can transmit an A-MPDU to AP 1 (401), and the A-MPDU includes multiple MPDUs. A delimiter can be included between the MPDUs to distinguish the MPDUs. A delimiter can be composed of 32 bits and can include at least one of an MPDU length indicator (e.g., 14 bits), a CRC (Cyclic Redundancy Check) (e.g., 8 bits), and a delimiter signature (e.g., 8 bits). When AP 1 (401) receives MPDUs transmitted by STA 1 (411), MPDU #1, MPDU #2 (430), and MPDU #3 (440) can be received sequentially. Among the MPDUs received by AP 1 (401), MPDU #2 (430) may have an error (e.g., cannot be decoded, FCS error) and may not be properly received. Due to MPDU #2 (430) not being properly received, AP 1 (401) may not be able to transmit data in the queue to the upper layer. Alternatively, MPDU #2 (430) may be a frame that must be urgently transmitted to the upper layer. Because MPDU #2 (430) was not properly received, MPDU #2 (430) is not transmitted to the upper layer.

[0062] Referring to FIG. 4A, AP MLD 1 is transmitting a frame to STA Y (420) on the second link while receiving a frame from STA 1 (411) on the first link. That is, AP MLD 1 is already transmitting a frame within the TXOP that AP MLD 1 acquired on the second link. AP 2 (403) of AP MLD 1 may stop transmitting a frame (460) that it was transmitting to STA Y (420) in order to transmit a feedback frame (450) indicating that MPDU #2 (430) was not properly received by STA 2 (413). The frame (460) transmitted to STA Y (420) may include an indicator (e.g., CS required) that STA Y (420) must perform channel sensing (CS) before transmitting a response frame (e.g., BlockAck frame) to AP 2 (403) and transmit the response frame only when the channel is idle for a certain period of time as a result of channel sensing. The frame (460) transmitted to STA Y (420) may include a Long or Short channel sensing time indicator. The Long or Short channel sensing time indicator may be included only when a channel sensing request indicator is included. The Long channel sensing indicator indicates to perform channel sensing for the PIFS time, and the Short channel sensing indicator indicates to perform channel sensing for the SIFS time. Alternatively, when the channel sensing time indicator is set, it may be interpreted as the Long channel sensing indicator, and when the channel sensing time indicator is not set, it may be interpreted as the Short channel sensing indicator. Alternatively, if a channel sensing request indicator is included, it may be considered that the Long Channel Sensing indicator is included, which indicates channel sensing for a PIFS time rather than a SIFS time, without including the channel time sensing indicator. The channel sensing request indicator (CS required) may be included in the MAC header.When the feedback frame (450) is transmitted after a RIFS time shorter than the SIFS time, the channel detection time indicator may not be included, and when the channel detection request indicator is included, the STA that receives it transmits a response frame only when the channel is idle after performing channel detection during the SIFS time. The frame transmission that AP 2 (403) was transmitting to STA Y (420) may be stopped in MPDU units. For example, the frame that AP 2 (403) wants to transmit to STA Y (420) may include MPDU #A, MPDU #B, and MPDU #C, and the frame transmission may be stopped after MPDU #A and MPDU #B are completely transmitted. That is, MPDU #A and MPDU #B are not lost. Alternatively, the frame (460) that AP 2 (403) was transmitting to STA Y (420) may be stopped immediately. For example, a frame that AP 2 (403) wants to transmit to STA Y (420) may include MPDU #A, MPDU #B, and MPDU #C, and frame transmission may be interrupted while MPDU #A is being transmitted and MPDU #B is being transmitted. In this case, MPDU #A is not lost, but MPDU #B is lost. Transmission interruption may be determined by considering the importance of the MPDU to be transmitted (e.g., priority of AC, delay bound). If the priority of the AC of the frame in which an error is detected in the first link is higher than the AC priority of the frame to be transmitted in the second link, transmission may be interrupted immediately even if a loss occurs. Alternatively, transmission interruption may be determined by considering the delay bound of the frame to be transmitted. Even if the frame to be transmitted in the second link is immediately interrupted and retransmitted, transmission may be interrupted immediately if the delay bound can be met.When AP 2 (403) stops transmitting frames, and after a certain period of time (e.g., short interframe space (SIFS) or reduced interframe space (RIFS)), AP 2 (403) can transmit a feedback frame (450) to STA 2 (413) indicating that MPDU #2 (430) was not properly received. The feedback frame (450) can be transmitted using OFDMA (Orthogonal Frequency Division Multiple Access). For example, a feedback frame (450) whose recipient is STA 2 (413) and a data frame whose recipient is STA Y (420) can be transmitted together using different subchannels using OFDMA. When STA Y (420) detects that a data frame being received from AP 2 (403) has been transmitted and includes a channel detection request indicator in the received data frame, STA Y (420) performs channel detection and then transmits a response frame to AP 2 (403). If the channel becomes busy due to a frame (e.g., a feedback frame (450)) transmitted by AP 2 (403) while performing channel sensing, a response frame is not transmitted after a certain period of time (e.g., SIFS or PIFS).

[0063] Since AP 2 (403) transmits a feedback frame (450) to STA 2 (413) after a certain period of time (e.g., RIFS or SIFS), STA Y (420) does not transmit a response frame to AP 2 (403). After transmitting the feedback frame (450) to STA 2 (413), AP 2 (403) can transmit a data frame to STA Y (420) again, and STA Y (420) transmits a response frame to AP 2 (403). STA MLD 1 can receive the feedback frame (450) of AP MLD 1, and STA MLD 1 can know that MPDU #2 (430) is not transmitted properly in the frame that STA 1 (411) of the first link transmits to AP 1 (401). STA MLD 1 may or may not transmit a response frame (e.g., an ACK frame) to the feedback frame (450) of AP MLD 1. STA MLD 1 may retransmit MPDU #2 (430) in a frame that is already being transmitted. For example, MPDU #2 (430) may be retransmitted after MPDU #3 (440), which is the next MPDU after MPDU #2 (430). Alternatively, STA MLD 1 may transmit MPDU #2 (430) to AP 1 (401) through a separate frame. If AP MLD 1 normally receives the retransmitted MPDU #2 (430), it may transmit the data in the queue to the upper layer. If an error occurs again in the retransmitted MPDU #2 (430), the retransmission operation of MPDU #2 (430) described above may be performed again. As another way for STA MLD 1 to perform retransmission, STA 1 (411) of STA MLD 1 can retransmit frames transmitted after MPDU #2 (430) (e.g., MPDU #3 (440)) together with MPDU #2 (430), instead of retransmitting only MPDU #2 (430). That is, STA 1 (411) can transmit frames again starting from MPDU #2 (430).

[0064] In the above embodiment, when STA MLD 1 has a conditional NSTR link pair or a conditional STR link pair (e.g., when the first link and the second link are a conditional NSTR link pair), while STA MLD 1 is transmitting a frame to AP MLD 1 on the first link, AP MLD 1 transmits a frame to STA MLD 1 with strong transmit power and / or low MCS on the second link. In the conditional NSTR link pair or conditional STR link pair, STA MLD may be able to receive a frame satisfying a specific condition on one link during frame transmission. For example, STA MLD may be able to receive a frame satisfying an MCS lower than or equal to a certain value and a receive power higher than or equal to a certain value on the first link on the second link.

[0065] The feedback frame (450) of the above embodiment may be a frame of various forms. For example, the feedback frame (450) may be one of a control frame including a BlockAck frame, an action frame, and a QoS frame having a control field (e.g., an HT Control field). The feedback frame (450) includes at least one of a Sequence Number (SN) and TID of an MPDU or / and an MSDU, information that can identify an MPDU or an MSDU (e.g., time information that can identify an MPDU or an MSDU, an MPDU identified by the order of MPDUs within an A-MPDU).

[0066] Referring to FIG. 4b, when AP MLD 1 receives a frame of STA MLD 1 in the first link, it may transmit an MU-RTS frame as the first frame of the TXOP of the second link to ensure smooth transmission of the feedback frame (450). The MU-RTS frame may indicate STAs to be communicated with within the TXOP. For example, in the User Info Field included in the MU-RTS frame, AP MLD 1 may indicate AIDs to be communicated with within the TXOP. Referring to FIG. 4b, when the communication target STAs are MLD 1 and MLD X, the AIDs included in the MU-RTS frame indicate STA MLD 1 and STA MLD X. Since one AID is assigned per MLD, the AID of STA MLD X may be the same as the AID of STA Y (420). STA MLD 1 and STA MLD X can receive MU-RTS frames on the second link, and simultaneously transmit CTS frames (e.g., simultaneous CTS frames) after a certain period of time (e.g., SIFS time) after receiving MU-RTS on the second link. AP MLD 1 transmits a data frame to STA Y (420) on the second link after receiving the CTS frame on the second link. AP 2 (403) of AP MLD 1 can stop transmitting frames to STA Y (420) in order to transmit a feedback frame (450) indicating that MPDU #2 (430) was not properly received by STA 2 (413). The frame (460) transmitted to STA Y (420) may include an instruction (e.g., CS required) to perform channel sensing (CS) before STA Y (420) transmits a response frame (e.g., BlockAck frame) to AP 2 (403) and transmit the response frame only when the channel is idle as a result of channel sensing for a certain period of time.A frame (460) transmitted to STA Y (420) may include a Long or Short channel detection time indicator. The Long or Short channel detection time indicator may be included only when a channel detection request indicator is included. The Long channel detection indicator indicates to perform channel detection during the PIFS time, and the Short channel detection indicator indicates to perform channel detection during the SIFS time. Alternatively, when the channel detection time indicator is set, it may be interpreted as the Long channel detection indicator, and when the channel detection time indicator is not set, it may be interpreted as the Short channel detection indicator. Alternatively, when the channel detection request indicator is included, it may be considered as including the Long channel detection indicator, which indicates to perform channel detection during the PIFS time rather than the SIFS time, without including the channel detection time indicator. The channel detection request indicator (CS required) may be included in the MAC header. When the feedback frame (450) is transmitted after a RIFS time shorter than the SIFS time, the channel detection time indicator may not be included, and when the channel detection request indicator is included, the STA that received it transmits a response frame only when the channel is idle after performing channel detection during the SIFS time. The transmission of the frame (460) that AP 2 (403) was transmitting to STA Y (420) may be stopped in MPDU units. For example, the frame that AP 2 (403) wants to transmit to STA Y (420) may include MPDU #A, MPDU #B, and MPDU #C, and the frame transmission may be stopped after MPDU #A and MPDU #B are completely transmitted. That is, MPDU #A and MPDU #B are not lost. Alternatively, the transmission of the frame (460) that AP 2 (403) was transmitting to STA Y (420) may be stopped immediately.For example, a frame that AP 2 (403) wants to transmit to STA Y (420) may include MPDU #A, MPDU #B, and MPDU #C, and frame transmission may be interrupted while MPDU #A is being transmitted and MPDU #B is being transmitted. In this case, MPDU #A is not lost, but MPDU #B is lost. Transmission interruption may be determined by considering the importance of the MPDU to be transmitted (e.g., priority of AC, delay bound). If the priority of the AC of the frame in which an error is detected in the first link is higher than the AC priority of the frame to be transmitted in the second link, transmission may be interrupted immediately even if a loss occurs. Alternatively, transmission interruption may be determined by considering the delay bound of the frame to be transmitted. Even if the frame to be transmitted in the second link is immediately interrupted and retransmitted, transmission may be interrupted immediately if the delay bound can be met. When AP 2 (403) stops frame transmission, and after a certain period of time (e.g., SIFS (short interframe space) or RIFS (reduced interframe space)), AP 2 (403) can transmit a feedback frame (450) to STA 2 (413) indicating that MPDU #2 (430) is not properly received. The feedback frame (450) can be transmitted using OFDMA (Orthogonal Frequency Division Multiple Access). For example, a feedback frame (450) whose recipient is STA 2 (413) and a data frame whose recipient is STA Y (420) can be transmitted together using OFDMA. When STA Y (420) determines that the data frame being received from AP 2 (403) has been transmitted to completion and the received data frame includes a channel detection request indicator, STA Y (420) performs channel detection and then transmits a response frame to AP 2 (403).If the channel is busy due to a frame (e.g., a feedback frame (450)) transmitted by AP 2 (403) while performing channel sensing, a response frame is not transmitted after a certain period of time (e.g., SIFS or PIFS). Since AP 2 (403) transmits the feedback frame (450) to STA 2 (413) after a certain period of time (e.g., RIFS or SIFS), STA Y (420) does not transmit a response frame to AP 2 (403). After transmitting the feedback frame (450) to STA 2 (413), AP 2 (403) can transmit a data frame to STA Y (420) again, and STA Y (420) transmits a response frame to AP 2 (403). STA MLD 1 can receive the feedback frame (450) of AP MLD 1, and STA MLD 1 can know that MPDU #2 (430) is not properly transmitted in the frame that STA 1 (411) of the first link transmits to AP 1 (401). STA MLD 1 may or may not transmit a response frame (e.g., an ACK frame) to the feedback frame (450) of AP MLD 1. STA MLD 1 can retransmit MPDU #2 (430) in the frame that is already being transmitted. For example, MPDU #2 (430) can be retransmitted after MPDU #3 (440), which is the next MPDU after MPDU #2 (430). Alternatively, STA MLD 1 can transmit MPDU #2 (430) to AP 1 (401) through a separate frame. If AP MLD 1 normally receives the retransmitted MPDU #2 (430), it can transmit the data in the queue to the upper layer. If the retransmitted MPDU #2 (430) encounters an error again, the retransmission operation of MPDU #2 (430) described above can be performed again.As another way for STA MLD 1 to perform retransmission, STA 1 (411) of STA MLD 1 can retransmit frames transmitted after MPDU #2 (430) (e.g., MPDU #3 (440)) together with MPDU #2 (430), instead of retransmitting only MPDU #2 (430). That is, STA 1 (411) can transmit frames again starting from MPDU #2 (430).

[0067] In the above embodiment, when STA MLD 1 has a conditional NSTR link pair or a conditional STR link pair (e.g., when the first link and the second link are a conditional NSTR link pair), while STA MLD 1 is transmitting a frame to AP MLD 1 on the first link, AP MLD 1 transmits a frame to STA MLD 1 with strong transmit power and / or low MCS on the second link. In the conditional NSTR link pair or conditional STR link pair, STA MLD may be able to receive a frame satisfying a specific condition on one link during frame transmission. For example, STA MLD may be able to receive a frame satisfying an MCS lower than or equal to a certain value and a receive power higher than or equal to a certain value on the first link on the second link.

[0068] The feedback frame (450) of the above embodiment may be a frame of various forms. For example, the feedback frame (450) may be one of a control frame including a BlockAck frame, an action frame, and a QoS frame having a control field (e.g., an HT Control field). The feedback frame (450) includes at least one of a Sequence Number (SN) and TID of an MPDU or / and an MSDU, information that can identify an MPDU or an MSDU (e.g., time information that can identify an MPDU or an MSDU, an MPDU identified by the order of MPDUs within an A-MPDU).

[0069]

[0070] Figure 5 illustrates a fourth embodiment of a rapid error feedback method.

[0071] Referring to FIG. 5, AP MLD 1 and STA MLD 1 may operate in a wireless LAN network. The AP in which AP MLD 1 operates in the first link is AP 1 (501), and the AP in which AP MLD 1 operates in the second link is AP 2 (503). That is, AP 1 (501) and AP 2 (503) may be affiliated to AP MLD 1. Similarly, the STA in which STA MLD 1 operates in the first link may be STA 1 (511), and the STA in which STA MLD 1 operates in the second link may be STA 2 (513). That is, STA 1 (511) and STA 2 (513) may be affiliated to STA MLD 1. In the second link, STA Y (520) associated with STA MLD X may operate. X can be a natural number. Y can be a natural number. For example, STA MLD X may or may not be STA MLD 1. STA Y (520) may or may not be STA 2 (513). The first link and the second link of STA MLD 1 may be links capable of simultaneous transmission and reception (STR link pair). Alternatively, the first link and the second link of STA MLD 1 may be links capable of simultaneous transmission and reception (NSTR link pair), but may be conditional STR or conditional NSTR link pairs capable of receiving when STA MLD 1 transmits on one link and the AP receives a frame with strong transmission power or / and low MCS (Modulation and Coding Scheme) on the other link.

[0072] STA 1 (511) can acquire a TXOP from the first link. TXOP acquisition is achieved when the EDCAF of STA 1 (511) determines to transmit by a channel access procedure (e.g., EDCA backoff operation). STA 1 (511) can transmit a frame (e.g., a physical layer protocol data unit (PPDU), a MAC layer protocol data unit (MPDU), an aggregated MPDU (A-MPDU)) within the TXOP. STA 1 (511) can transmit an A-MPDU to AP 1 (501), and the A-MPDU includes multiple MPDUs. A delimiter can be included between the MPDUs to distinguish the MPDUs. A delimiter can be composed of 32 bits and can include at least one of an MPDU length indicator (e.g., 14 bits), a CRC (Cyclic Redundancy Check) (e.g., 8 bits), and a delimiter signature (e.g., 8 bits). When AP 1 (501) receives MPDUs transmitted by STA 1 (511), MPDU #1, MPDU #2 (530), and MPDU #3 (540) can be received sequentially. Among the MPDUs received by AP 1 (501), MPDU #2 (530) may have an error (e.g., cannot be decoded, FCS error) and may not be properly received. Due to MPDU #2 (530) not being properly received, AP 1 (501) may not be able to transmit data in the queue to the upper layer. Alternatively, MPDU #2 (530) may be a frame that must be urgently transmitted to the upper layer. Because MPDU #2 (530) was not properly received, MPDU #2 (530) is not transmitted to the upper layer. Because AP 2 (503) did not properly receive MPDU #2 (530), it cannot know information about MPDU #2 (530). For example, AP 2 (503) cannot know the TID and SN of MPDU #2 (530).

[0073] All MPDUs of a frame that STA 1 (511) transmits to AP 1 (501) may be MPDUs having the same TID. For example, the TIDs of all MPDUs may be TID A. AP MLD 1 may know that MPDU #2 (530) was not received in a frame being received from STA 1 (511) on the first link after decoding MPDU #3 (540). A feedback frame (550) indicating that MPDU #2 (530) was not properly received may be transmitted after receiving MPDU #3 (540). Alternatively, the MPDUs of a frame that STA 1 (511) transmits to AP 1 (501) may be MPDUs having different TIDs. For example, all MPDUs other than MPDU #2 (530) may have TID A, and MPDU #2 (530) may have TID B. MPDU #2 (530) may be an MPDU that must be transmitted urgently, and may be transmitted among MPDUs with different TIDs. Since MPDU #2 (530) has a different TID from other MPDUs, AP MLD 1 may not know that MPDU #2 (530) was not received in the frame being received from STA 1 (511) on the first link after decoding MPDU #3 (540). Alternatively, all MPDUs in the frame that STA 1 (511) transmits to AP 1 (501) may have the same TID, but the SN order of the MPDUs may not be transmitted consistently. For example, the SNs of MPDU #1, MPDU #2 (530), and MPDU #3 (540) may be 1, 3, and 2, respectively. Therefore, if MPDU #2 (530) is not received, AP MLD 1 may not know whether MPDU #2 (530) should be retransmitted.

[0074] STA 1 (511) may include at least one of the SN (sequence number), TID information, and whether rapid recovery is required of the previous and / or next MPDU in the MAC header or / and A-MPDU delimiter of the frame transmitted to AP 1 (501). That is, STA 1 includes information that can identify the previous and / or next MPDU in each frame or / and A-MPDU delimiter transmitted to AP 1. In this case, if AP 1 (501) correctly received MPDU #1 and did not correctly receive MPDU #2 (530), AP 1 (501) can immediately know information (e.g., TID, SN) about MPDU #2 (530) in which an error occurred. If STA 1 (511) indicates that MPDU #2 (530) requires rapid recovery, AP 1 (501) may request retransmission of MPDU #2 (530).

[0075] To transmit a feedback frame (550) for recovering MPDU #2 (530), AP 2 (503) on the second link may perform a channel access procedure (e.g., an EDCA backoff operation). The channel access procedure may be newly started for AP 2 (503) to transmit a feedback frame (550) for recovering MPDU #2 (530). Alternatively, instead of starting the channel access procedure anew, the channel access procedure that AP 2 (503) was previously performing may continue to be performed. The channel access procedure of AP 2 (503) may succeed (e.g., the EDCA backoff counter reaches 0). AP 2 (503) transmits a feedback frame (550) to STA 2 (513) indicating that MPDU #2 (530) was not properly received. The channel access procedure of AP 2 (503) may be performed for each AC (access category). The feedback frame (550) may be transmitted by a channel access procedure of any AC (e.g., by an EDCAF of an AC whose channel access procedure ends the fastest). Alternatively, if there is an EDCAF of any AC that AP 2 (503) successfully performs a channel access procedure (e.g., the EDCA backoff counter reaches 0) and remains at 0, the feedback frame (550) may be transmitted immediately. Alternatively, the feedback frame (550) may be transmitted by a channel access procedure related to an AC of an MPDU of a frame that STA 1 (511) of the first link transmits to AP 1 (501) (e.g., when the AC of the MPDU that STA 1 (511) transmits to AP 1 (501) is AC_VO, by an AC_VO EDCAF of the second link). For example, the AC-specific channel access procedure of AP 2 (503) may terminate AC_VO before AC_VI and other ACs (e.g., AC_BE and AC_BK).AP 2 (503) can acquire AC_VO TXOP from the second link, and AP 2 (503) transmits a feedback frame (550) to STA 2 (513) indicating that MPDU #2 (530) was not properly received. In the remaining AC_VO TXOP of AP 2 (503), AP 2 (503) can transmit a data frame to STA Y (520).

[0076] A frame error of the first link can be detected while a channel access procedure is being performed when a frame to be transmitted is generated in the transmission queue of the second link. A frame of an AC to be transmitted in the second link can be generated and a channel access procedure (e.g., a backoff procedure) can be performed, and an error can be detected in the MPDU received in the first link before the backoff counter becomes 0. The AC of the MPDU in which an error occurred in the first link can be a different AC from or the same AC as the AC for which a backoff is being performed to be transmitted in the second link. If the channel access procedure in the second link is successful (e.g., if the backoff is successful and the counter becomes 0), a TXOP including a feedback transmission time for the MPDU generated in the first link is set. That is, the duration included in the MAC header of the feedback frame (550) can be set to a time including the data frame transmission time of the AC to be transmitted. The receiving STA of the feedback frame (550) and the data frame can be different. The feedback frame (550) can be transmitted first and then the data frame can be transmitted. Alternatively, the feedback frame (550) and the data frame may be transmitted together using a downlink OFDMA (Orthogonal Frequency Division Multiple Access) method that simultaneously transmits them using different subchannels. The feedback may be restricted to be transmitted only when the priority of the AC of the data for which a channel access procedure is performed to be transmitted in the second link is lower than the AC of the MPDU that failed to be transmitted in the first link. Alternatively, the feedback of the MPDU that failed to be transmitted in the first link may be assumed to be higher than any AC. Accordingly, if channel access for data transmission in the second link is successful regardless of the AC, the feedback frame (550) may be transmitted together with the data transmission.

[0077] STA MLD 1 can receive the feedback frame (550) of AP MLD 1, and STA MLD 1 can know that MPDU #2 (530) is not properly transmitted in the frame that STA 1 (511) of the first link transmits to AP 1 (501). STA MLD 1 may or may not transmit a response frame (e.g., an ACK frame) to the feedback frame (550) of AP MLD 1. STA MLD 1 can retransmit MPDU #2 (530) in the frame that is already being transmitted. For example, MPDU #2 (530) can be retransmitted after MPDU #3 (540), which is the next MPDU after MPDU #2 (530). Alternatively, STA MLD 1 can transmit MPDU #2 (530) to AP 1 (501) through a separate frame. If AP MLD 1 normally receives the retransmitted MPDU #2 (530), it can transmit the data in the queue to the upper layer. If the retransmitted MPDU #2 (530) causes an error again, the retransmission operation of the above-described MPDU #2 (530) can be performed again. As another method for STA MLD 1 to perform retransmission, STA 1 (511) of STA MLD 1 can retransmit the frame transmitted after MPDU #2 (530) (e.g., MPDU #3 (540)) together with MPDU #2 (530), instead of retransmitting only MPDU #2 (530). That is, STA 1 (511) can transmit the frame again starting from MPDU #2 (530).

[0078] In the above embodiment, when STA MLD 1 has a conditional NSTR link pair or a conditional STR link pair (e.g., when the first link and the second link are a conditional NSTR link pair), when STA MLD 1 transmits a frame to AP MLD 1 on the first link, AP MLD 1 transmits a frame with strong transmission power and / or low MCS on the second link to STA MLD 1. In the conditional NSTR link pair or conditional STR link pair, the STA MLD may be able to receive a frame satisfying a specific condition on the other link during frame transmission on one link. For example, the STA MLD may be able to receive a frame satisfying an MCS lower than or equal to a certain value and a reception power higher than or equal to a certain value on the first link on the second link.

[0079] The feedback frame (550) of the above embodiment may be a frame of various forms. For example, the feedback frame (550) may be one of a control frame including a BlockAck frame, an action frame, and a QoS frame having a control field (e.g., an HT Control field). The feedback frame (550) includes at least one of a Sequence Number (SN) and TID of an MPDU or / and an MSDU, information that can identify an MPDU or an MSDU (e.g., time information that can identify an MPDU or an MSDU, an MPDU identified by the order of MPDUs within an A-MPDU).

[0080]

[0081] Figure 6 illustrates a fifth embodiment of a rapid error feedback method.

[0082] Referring to FIG. 6, AP MLD 1 and STA MLD 1 may operate in a wireless LAN network. An AP in which AP MLD 1 operates in a first link is AP 1 (601), and an AP in which AP MLD 1 operates in a second link is AP 2 (603). That is, AP 1 (601) and AP 2 (603) may be affiliated to AP MLD 1. Similarly, an STA in which STA MLD 1 operates in a first link may be STA 1 (611), and an STA in which STA MLD 1 operates in a second link may be STA 2 (613). That is, STA 1 (611) and STA 2 (613) may be affiliated to STA MLD 1. In the second link, STA Y associated with STA MLD X may operate. X may be a natural number. Y can be a natural number. For example, STA MLD X may or may not be STA MLD 1. STA Y may or may not be STA 2 (613). The first link and the second link of STA MLD 1 may be links capable of simultaneous transmission and reception (STR link pair). Alternatively, the first link and the second link of STA MLD 1 may be links capable of simultaneous transmission and reception (NSTR link pair), but may be a conditional STR or conditional NSTR link pair that can be received when STA MLD 1 receives a frame transmitted by an AP with strong transmission power or / and low MCS (Modulation and Coding Scheme) on another link while transmitting on one link.

[0083] STA 1 (611) can acquire a TXOP from the first link. TXOP acquisition is achieved when the EDCAF of STA 1 (611) determines to transmit by a channel access procedure (e.g., EDCA backoff operation). STA 1 (611) can transmit frames (e.g., PPDU (physical layer protocol data unit), MPDU (MAC layer protocol data unit), A-MPDU (aggregated MPDU)) within the TXOP. STA 1 (611) can transmit an A-MPDU to AP 1 (601), and the A-MPDU includes multiple MPDUs. A delimiter can be included between the MPDUs to distinguish the MPDUs. A delimiter can be composed of 32 bits and can include at least one of an MPDU length indicator (e.g., 14 bits), a CRC (Cyclic Redundancy Check) (e.g., 8 bits), and a delimiter signature (e.g., 8 bits). When AP 1 (601) receives MPDUs transmitted by STA 1 (611), MPDU #1, MPDU #2 (630), and MPDU #3 (640) can be received sequentially. Among the MPDUs received by AP 1 (601), MPDU #2 (630) may have an error (e.g., cannot be decoded, FCS error) and may not be properly received. Due to MPDU #2 (630) not being properly received, AP 1 (601) may not be able to transmit data in the queue to the upper layer. Alternatively, MPDU #2 (630) may be a frame that must be urgently transmitted to the upper layer. Because MPDU #2 (630) was not properly received, MPDU #2 (630) is not transmitted to the upper layer. Because AP 2 (603) did not properly receive MPDU #2 (630), it cannot know information about MPDU #2 (630). For example, AP 2 (603) cannot know the TID and SN of MPDU #2 (630).

[0084] All MPDUs of a frame that STA 1 (611) transmits to AP 1 (601) may be MPDUs having the same TID. For example, the TIDs of all MPDUs may be TID A. AP MLD 1 may know that MPDU #2 (630) was not received in a frame being received from STA 1 (611) on the first link after decoding MPDU #3 (640). A feedback frame (650) indicating that MPDU #2 (630) was not properly received may be transmitted after receiving MPDU #3 (640). Alternatively, the MPDUs of a frame that STA 1 (611) transmits to AP 1 (601) may be MPDUs having different TIDs. For example, all MPDUs other than MPDU #2 (630) may have TID A, and MPDU #2 (630) may have TID B. MPDU #2 (630) may be an MPDU that must be transmitted urgently, and may be transmitted among MPDUs with different TIDs. Since MPDU #2 (630) has a different TID from other MPDUs, AP MLD 1 may not know that MPDU #2 (630) was not received in the frame being received from STA 1 (611) on the first link after decoding MPDU #3 (640). Alternatively, all MPDUs in the frame that STA 1 (611) transmits to AP 1 (601) may have the same TID, but the SN order of the MPDUs may not be transmitted consistently. For example, the SNs of MPDU #1, MPDU #2 (630), and MPDU #3 (640) may be 1, 3, and 2, respectively. Therefore, if MPDU #2 (630) is not received, AP MLD 1 may not know whether MPDU #2 (630) should be retransmitted.

[0085] Although AP 2 (603) cannot know the information of MPDU #2 (630), it can know when an error occurred. The error can be known when, after successfully receiving the delimiter for MPDU #1 or MPDU #2 (630), only energy is detected but not decoded, and then the delimiter transmitted before transmitting MPDU #3 (640) is received. In order to transmit a feedback frame (650) for recovering MPDU #2 (630), AP 2 (603) can perform a channel access procedure (e.g., an EDCA backoff operation) on the second link. The channel access procedure can be restarted for AP 2 (603) to transmit the feedback frame (650) for recovering MPDU #2 (630). Alternatively, instead of restarting the channel access procedure, the channel access procedure that AP 2 (603) was previously performing can be continuously performed. The channel access procedure of AP 2 (603) may succeed (e.g., the EDCA backoff counter reaches 0). AP 2 (603) transmits a feedback frame (650) to STA 2 (613) indicating that MPDU #2 (630) is not properly received. The channel access procedure of AP 2 (603) may be performed by AC (access category). The feedback frame (650) may be transmitted by the channel access procedure of any AC (e.g., by the EDCAF of the AC whose channel access procedure is completed the fastest). Alternatively, if there is an EDCAF of any type of AC that AP 2 (603) performs the channel access procedure successfully (e.g., the EDCA backoff counter reaches 0) and maintains as 0, the feedback frame (650) may be transmitted immediately.Alternatively, the feedback frame (650) may be transmitted by a channel access procedure related to the AC of the MPDU of the frame that STA 1 (611) of the first link transmits to AP 1 (601) (e.g., by AC_VO EDCAF of the second link when the AC of the MPDU that STA 1 (611) transmits to AP 1 (601) is AC_VO). For example, the AC-specific channel access procedure of AP 2 (603) may end AC_VO before AC_VI and other ACs (e.g., AC_BE and AC_BK). AP 2 (603) may obtain AC_VO TXOP from the second link, and AP 2 (603) transmits a feedback frame (650) to STA 2 (613) indicating that MPDU #2 (630) was not properly received. In the remaining AC_VO TXOP of AP 2 (603), AP 2 (603) can transmit data frames to STA Y.

[0086] A frame error of the first link can be detected while a channel access procedure is being performed when a frame to be transmitted is generated in the transmission queue of the second link. A frame of an AC to be transmitted in the second link can be generated and a channel access procedure (e.g., a backoff procedure) can be performed, and an error can be detected in an MPDU received in the first link before the backoff counter becomes 0. The AC of the MPDU in which an error occurred in the first link can be a different AC from or the same AC as the AC for which a backoff is being performed to be transmitted in the second link. If the channel access procedure in the second link is successful (e.g., if the backoff is successful and the counter becomes 0), a TXOP including a feedback transmission time for the MPDU generated in the first link is set. That is, the duration included in the MAC header of the feedback frame (650) can be set to a time including the data frame transmission time of the AC to be transmitted. The receiving STA of the feedback frame (650) and the data frame can be different. The feedback frame (650) can be transmitted first and then the data frame can be transmitted. Alternatively, the feedback frame (650) and the data frame may be transmitted together using a downlink OFDMA (Orthogonal Frequency Division Multiple Access) method that simultaneously transmits them using different subchannels. The feedback may be restricted to be transmitted only when the priority of the AC of the data for which a channel access procedure is performed to be transmitted in the second link is lower than the AC of the MPDU that failed to be transmitted in the first link. Alternatively, the feedback of the MPDU that failed to be transmitted in the first link may be assumed to be higher than any AC. Accordingly, if channel access for data transmission is successful in the second link regardless of the AC, the feedback frame (650) may be transmitted together with the data transmission.

[0087] Information indicating that MPDU #2 (630) is not properly received may be indicated as time information. For example, the time information is information including at least one of 'TSF (time synchronization function) information', 'TSF information and offset', 'time interval using multiple TSF information', and 'frame duration'. When the time information is indicated as 'TSF information', the time information may indicate 'the start or end time of the last properly received MPDU', 'the start or end time of the MPDU in which an error occurred', or 'the time during which the MPDU in which an error occurred was being transmitted'. Alternatively, the time information may be indicated as TSF information that can identify that there is an error in MPDU #2 (630). The TSF information indicated by AP MLD 1 may be based on the TSF of the first link or the second link. The TSF information indicated by AP MLD 1 may be indicated using some bits (e.g., some LSBs) of the TSF managed by AP MLD 1. When the above time information is indicated as 'TSF information and offset' information, the time information may indicate at least one of 'the transmission section of the last well-received MPDU' and 'the transmission section of the MPDU in which an error occurred'. Alternatively, the time information may be indicated as TSF information and an offset that can identify that there is an error in MPDU #2 (630). The offset information is time information indicating after or before the time indicated by the TSF information. For example, the offset information may be indicated in TU units (1 TU = 1024 us) or may be indicated using some LSBs of the TSF. Alternatively, the offset information may indicate the time length in a manner identical or similar to the duration field included in the MAC header of the MPDU. The TSF information indicated by AP MLD 1 may be based on the TSF of the first link or the second link.When the above time information is indicated as 'time interval using multiple TSF information', the time information may indicate at least one of 'transmission interval of the last well-received MPDU' and 'transmission interval of the MPDU in which an error occurred'. Alternatively, the time information may be indicated as multiple TSF information that can identify that there is an error in MPDU #2 (630). The multiple TSF information indicated by AP MLD 1 may be based on the TSF of the first link or the second link. Some or all of the multiple TSF information indicated by AP MLD 1 may be indicated using some bits (e.g., some LSBs) of the TSF managed by AP MLD 1. When the above time information is indicated as 'frame duration', the time information may indicate at least one of 'transmission length of the last well-received MPDU' and 'transmission length of the MPDU in which an error occurred'. Alternatively, the time information may be indicated as duration information that can identify that there is an error in MPDU #2 (630). The duration of a frame may indicate the length of time in the same or similar manner as the duration field included in the MAC header of the MPDU. STA MLD 1 must record timing information (e.g., TSF information when transmitting each MPDU, duration information of each MPDU) during transmission of each MPDU to properly recover from a corrupted MPDU (e.g., MPDU #2 (630)). AP MLD 1 must record timing information (e.g., TSF information when receiving each MPDU, duration information of each MPDU) during reception of each MPDU to properly recover from a corrupted MPDU (e.g., MPDU #2 (630)).

[0088] STA MLD 1 can receive the feedback frame (650) of AP MLD 1, and STA MLD 1 can identify that MPDU #2 (630) was not properly transmitted using the time information of the feedback frame (650) of AP MLD 1. STA MLD 1 may or may not transmit a response frame (e.g., an ACK frame) to the feedback frame (650) of AP MLD 1. STA MLD 1 can retransmit MPDU #2 (630), which is an MPDU in which an error occurred, in a frame that is already being transmitted. For example, MPDU #2 (630) can be retransmitted after MPDU #3 (640), which is the next MPDU after MPDU #2 (630). Alternatively, STA MLD 1 can transmit MPDU #2 (630) to AP 1 (601) through a separate frame. If AP MLD 1 receives retransmitted MPDU #2 (630) without error, it can transmit the data in the queue to the upper layer. If the retransmitted MPDU #2 (630) causes an error again, the retransmission operation of MPDU #2 (630) described above can be performed again. As another method for STA MLD 1 to perform retransmission, STA 1 (611) of STA MLD 1 can retransmit a frame transmitted after MPDU #2 (630) (e.g., MPDU #3 (640)) instead of retransmitting only MPDU #2 (630). That is, STA 1 (611) can transmit a frame again starting from MPDU #2 (630).

[0089] In the above embodiment, when STA MLD 1 has a conditional NSTR link pair or a conditional STR link pair (e.g., when the first link and the second link are a conditional NSTR link pair), when STA MLD 1 transmits a frame to AP MLD 1 on the first link, AP MLD 1 transmits a frame to STA MLD 1 with strong transmit power and / or low MCS on the second link. In the conditional NSTR link pair or conditional STR link pair, STA MLD may be able to receive a frame satisfying a specific condition on one link during frame transmission. For example, STA MLD may be able to receive a frame satisfying an MCS lower than or equal to a certain value and a receive power higher than or equal to a certain value on the first link on the second link.

[0090] The feedback frame (650) of the above embodiment may be a frame of various forms. For example, the feedback frame (650) may be one of a control frame including a BlockAck frame, an action frame, and a QoS frame having a control field (e.g., an HT Control field). The feedback frame (650) includes at least one of a Sequence Number (SN) and a TID of an MPDU or / and an MSDU, information that can identify an MPDU or an MSDU (e.g., time information that can identify an MPDU or an MSDU, an MPDU identified by the order of MPDUs within an A-MPDU).

[0091]

[0092] Below, a procedure for detecting the occurrence of a transmission error is described. The described procedure is performed by a first STA and an AP. The first STA and the AP may be connected using a first link and a second link. The first link and the second link may be a STR link pair. The AP may be connected to a second STA using the second link. That is, the first STA, the second STA, and the AP may be multi-link devices (MLDs).

[0093]

[0094] FIG. 7 illustrates a flowchart of an error recovery procedure according to one embodiment of the present disclosure. FIG. 7 illustrates a procedure performed by a first STA. The first STA (e.g., STA MLD 1 of FIG. 3 ) connects to an AP (e.g., AP MLD 1 of FIG. 3 ) using a first link and a second link.

[0095] Referring to FIG. 7, in step S701, a first STA transmits a plurality of frames (e.g., MPDU #2 (330) and MPDU #3 (340) of FIG. 3) on a first link. The plurality of frames may include at least one MPDU. Each frame may include a delimiter for distinguishing frames. The delimiter may include at least one of an MPDU length indicator, a CRC, or a delimiter signature. For example, the delimiter may have a size of 32 bits. In addition, the delimiter includes at least one of an MPDU including the delimiter or an SN (sequence number) of an MPDU to be transmitted next, TID information, or whether rapid recovery is required, so that a receiver can detect an error.

[0096] In step S703, the first STA receives an error report from the second link. The error report includes a message transmitted from the AP when an error is detected among the frames transmitted in step S701. The error report may include information for reporting an error and requesting retransmission. The error report may be included in a feedback frame (e.g., feedback frame (350) of FIG. 3). The error report may include information about the error. The information about the error may be information directly indicating the frame in which the error was detected. Alternatively, the information about the error may be information indirectly indicating the frame in which the error was detected. The indirectly indicating information may include time information. The time information includes at least one of time synchronization function (TSF) information, TSF information and an offset, a time interval using multiple pieces of TSF information, or the duration of the frame. The first STA may recognize that an error has occurred in frame transmission based on the information about the error. For example, the first STA can recognize a frame in which an error is detected by recognizing the transmission time, transmission time interval, or transmission time length of the frame in which an error is detected based on time information.

[0097] In step S705, the first STA transmits a retransmission frame (e.g., MPDU #2 (330) of FIG. 3) on the first link. Here, the retransmission frame may include a frame in which an error is detected. For example, the retransmission frame may include at least one of a frame in which an error is detected or a frame transmitted after the frame in which an error is detected (e.g., MPDU #3 (340) of FIG. 3). The retransmission frame may be retransmitted after transmission of a frame being transmitted on the first link is completed. Alternatively, the retransmission frame may be retransmitted after transmission of a frame being transmitted on the first link is stopped.

[0098]

[0099] FIG. 8 is a flowchart illustrating an error reporting procedure according to an embodiment of the present disclosure. FIG. 8 illustrates a procedure performed by an AP. An AP (e.g., AP MLD 1 of FIG. 3 ) is connected to at least one of a first STA (e.g., STA MLD 1 of FIG. 3 ) or a second STA (e.g., STA MLD X of FIG. 3 ) using a first link and a second link.

[0100] Referring to FIG. 8, in step S801, the AP receives a plurality of frames (e.g., MPDU #2 (330) and MPDU #3 (340) of FIG. 3) from the first link. The plurality of frames may be frames for transmitting data. The plurality of frames may include an MPDU. The plurality of frames may be frames having the same TID. Alternatively, the plurality of frames may be frames having different TIDs. Each frame may include a delimiter. The delimiter may include at least one of an MPDU length indicator, a CRC, or a delimiter signature. For example, the delimiter may have a size of 32 bits. In addition, the delimiter includes at least one of an MPDU including the delimiter or an SN (sequence number) of an MPDU to be transmitted next, TID information, or whether rapid recovery is required, so that the receiver can detect an error.

[0101] In step S803, the AP detects an error among multiple frames. At least one of the frames may be undecodable, or at least one frame may have an FCS error, etc. If the TIDs of the frames are the same, the AP can detect an error in one of the frames based on the SN. If the TIDs of the frames are not the same, or if the TIDs are the same but the frames are not transmitted in the SN order, the AP can determine the point in time of error based on the delimiter. For example, if the AP receives a frame containing the delimiter and energy is detected but cannot be decoded, it can detect an error in the frame transmission.

[0102] In step S805, the AP transmits an error report on the second link. The error report is transmitted to the first STA. The error report may be included in a feedback frame (e.g., feedback frame 350 of FIG. 3). To transmit the error report, the AP may stop transmitting a frame being transmitted to the second STA on the second link. Alternatively, the AP may transmit the error report after transmission of the frame being transmitted is completed. The error report may include information about the error. The information about the error may be information directly indicating the frame in which the error was detected. Alternatively, the information about the error may be information indirectly indicating the frame in which the error was detected. The indirectly indicating information may include time information. The time information includes at least one of time synchronization function (TSF) information, TSF information and an offset, a time interval using multiple pieces of TSF information, or the duration of the frame.

[0103] In step S807, the AP receives a retransmission frame (e.g., MPDU #2 (330) in FIG. 3) from the first link. The retransmission frame may include a frame in which an error is detected. For example, the retransmission frame may include at least one of a frame in which an error is detected or a frame transmitted after the frame in which an error is detected (e.g., MPDU #3 (340) in FIG. 3). The retransmission frame may be retransmitted after transmission of a frame being transmitted on the first link is completed. Alternatively, the retransmission frame may be retransmitted after transmission of a frame being transmitted on the first link is stopped.

[0104]

[0105] A first STA or AP acquires a TXOP to transmit a frame. To acquire the TXOP, the first STA or AP performs a channel access procedure. The channel access procedure may be performed for each AC. The frames transmitted by the first STA and the error report transmitted by the AP may be transmitted based on the same AC. Alternatively, the frames transmitted by the first STA and the error report transmitted by the AP may be transmitted based on different ACs. The AP may abort a frame being transmitted to the second STA based on the AC of the frame in which an error is detected, or transmit an error report after the transmission of the frame in which the frame is being transmitted is completed. Alternatively, the frame in which an error is detected or the error report may be transmitted with a higher priority than the AC.

[0106]

[0107] The methods according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded on a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc., either singly or in combination. The program instructions recorded on the computer-readable medium may be those specifically designed and constructed for the present invention, or may be known and available to those skilled in the computer software art.

[0108] 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 hardware devices described above may be configured to operate with at least one software module to perform the operations of the present invention, and vice versa.

[0109] 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.

[0110] The present disclosure can be used in devices and recording media in a wireless LAN system.

Claims

1. A method for operation of STA (station) in a wireless LAN system, In the first link, a step of transmitting a plurality of frames; In the second link, a step of receiving an error report of a frame in which an error is detected among the plurality of frames; and Including a step of transmitting a retransmission frame including a frame in which the error is detected based on the above error report, Each of the above multiple frames includes a delimiter, A method in which the above delimiter includes information for distinguishing each of the plurality of frames.

2. In paragraph 1, A method wherein the above error report includes information directly indicating a frame in which the error was detected or information indirectly indicating a frame in which the error was detected.

3. In paragraph 2, A method wherein the above indirectly indicating information includes at least one of TSF information, an offset of TSF information, a time interval based on a plurality of TSFs, or a duration of a frame.

4. In paragraph 2, A method wherein the above directly indicating information includes at least one of a TID, SN of a frame in which an error is detected, or time information capable of identifying the frame in which an error is detected.

5. In paragraph 1, A method wherein the retransmission frame comprises at least one of a frame in which the error was detected or a frame transmitted after the frame in which the error was detected.

6. In paragraph 1, A method in which information for distinguishing each of the above frames includes at least one of a traffic identifier (TID), a sequence number (SN), or information indicating whether fast recovery is required for each of the plurality of frames.

7. In paragraph 1, A method wherein the above plurality of frames include frames having the same TID.

8. In a method for operating an AP (access point) in a wireless LAN system, In the first link, a step of receiving a plurality of frames; A step of detecting an error in at least one frame among the plurality of frames; A step of transmitting an error report based on a frame in which the above error is detected; and A step of receiving a retransmission frame transmitted based on the above error report, Each of the above multiple frames includes a delimiter, A method in which the above delimiter includes information for distinguishing each of the plurality of frames.

9. In paragraph 8, A method wherein the above error report includes information directly indicating a frame in which the error was detected or information indirectly indicating a frame in which the error was detected.

10. In paragraph 9, A method wherein the above indirectly indicating information includes at least one of TSF information, an offset of TSF information, a time interval based on a plurality of TSFs, or a duration of a frame.

11. In paragraph 9, A method wherein the above directly indicating information includes at least one of a TID, SN of a frame in which an error is detected, or time information capable of identifying the frame in which an error is detected.

12. In paragraph 8, A method in which information for distinguishing each of the above frames includes at least one of a TID, a sequence number (SN), or information indicating whether rapid recovery is required for each of the plurality of frames.

13. In paragraph 12, The steps for detecting the above errors are: A method further comprising the step of detecting an error based on the TID or the SN included in the above delimiter.

14. In paragraph 8, A method wherein the retransmission frame comprises at least one of a frame in which the error was detected or a frame transmitted after the frame in which the error was detected.

15. In paragraph 8, The steps for detecting the above errors are: A method further comprising the step of detecting an error based on a time interval until the next delimiter is received after receiving a frame including the above delimiter.

16. In paragraph 8, The steps for sending the above error report are: A step of determining whether to stop transmission of a frame being transmitted on a second link based on the AC (access category) of the frame in which the above error is detected; and A method comprising the step of transmitting the error report based on whether the transmission has been interrupted.

17. In a wireless LAN system, at STA (station), Transmitter and receiver; and Including a processor connected to the above transceiver, The above processor, In the first link, multiple frames are transmitted, In the second link, an error report of a frame in which an error is detected among the plurality of frames is received, configured to transmit a retransmission frame including a frame in which the error is detected based on the above error report, Each of the above multiple frames includes a delimiter, The above delimiter is an STA that includes information for distinguishing each of the plurality of frames.

18. 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, In the first link, multiple frames are received, Detecting an error in at least one frame among the above multiple frames, Transmit an error report based on the frame in which the above error is detected, configured to receive a retransmission frame transmitted based on the above error report, Each of the above multiple frames includes a delimiter, The above delimiter is an AP that includes information for distinguishing each of the plurality of frames.

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