Apparatus and method for fast error recovery in wireless LAN system

Abstract

A method for operating an access point (AP) in a wireless LAN system for fast error recovery in the wireless LAN system comprises the steps of: receiving multiple frames from an STA; detecting an error of at least one frame among the multiple frames; transmitting a retransmission request on the basis of a frame in which the error is detected; and receiving a retransmission frame on the basis of the retransmission request, wherein the retransmission frame includes the frame in which the error is detected, and the retransmission frame is received in a link in which the retransmission request is transmitted.

Description

Device and method for rapid error recovery in wireless LAN systems

[0001] The present disclosure relates to a wireless local area network (WLAN) system. More specifically, it relates to a device and method for rapid error recovery 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] Standards for wireless LAN technology are primarily being developed by the Institute of Electrical and Electronics Engineers (IEEE) as the IEEE 802.11 standard. As the aforementioned wireless LAN technology has developed and become widespread, applications utilizing it have diversified, creating a demand for wireless LAN technology that supports higher reliability.

[0004] As applications requiring higher reliability emerge, the IEEE 802.11bn standard, an Ultra High Reliability (UHR) wireless LAN technology, is being developed for single Basic Service Set (BSS) and / or redundant BSS environments. The goals of the IEEE 802.11bn standard may include supporting increased data transmission rates, improved latency performance, and lower data error rates. Furthermore, the IEEE 802.11bn standard can support low-power operation and peer-to-peer communication.

[0005] Improvements may be needed in the method of recovering from frame errors in wireless LANs. When transmitting multiple frames, some frames with errors can be recovered after all frames have been transmitted and a acknowledgment of the error has been received. Because acknowledgments for frames with errors can only be received after all frames have been transmitted, errors may not be recovered quickly. In other words, the requirements for low-latency communication may not be met.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] The present disclosure provides a method and device for an AP and an STA using a non-simultaneous transmit receive (NSTR) link pair in a wireless LAN system to report and recover frame errors using at least one link.

[0010] The present disclosure provides a method and device for transmitting a frame for requesting retransmission of a frame in which an error is detected in a wireless LAN system.

[0011] 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 can be clearly understood by a person having ordinary skill in the technical field to which the present disclosure belongs from the description below.

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

[0013] A method for operation of an STA (station) in a wireless LAN system comprises the steps of: transmitting a plurality of frames to an AP; receiving a retransmission request based on a frame in which an error is detected among the plurality of frames; and transmitting a retransmission frame based on the retransmission request, wherein the retransmission frame includes the frame in which the error is detected, and the retransmission frame is transmitted on a link in which the retransmission request is received.

[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 from an STA, detect an error in at least one frame among the plurality of frames, transmit a retransmission request based on the frame in which the error is detected, and receive a retransmission frame based on the retransmission request, wherein the retransmission frame includes the frame in which the error is detected, and the retransmission frame is received on a link through which the retransmission request is transmitted.

[0015] 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 to an AP, receive a retransmission request based on a frame in which an error is detected among the plurality of frames, and transmit a retransmission frame based on the retransmission request, wherein the retransmission frame includes the frame in which the error is detected, and the retransmission frame is transmitted on a link in which the retransmission request is received.

[0016] 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.

[0017] According to the present disclosure, an MPDU including previous MPDU and next MPDU information can be transmitted.

[0018] According to the present disclosure, an AP can identify a frame in which an error is detected and transmit a feedback frame.

[0019] 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.

[0020] FIG. 1 is a block diagram illustrating a first embodiment of a communication node constituting a wireless LAN system.

[0021] Figure 2 illustrates a first embodiment of a negotiation procedure for multi-link operation in a wireless LAN system.

[0022] Figure 3 illustrates a first embodiment of a rapid error recovery method.

[0023] Figure 4 illustrates a second embodiment of a rapid error recovery method.

[0024] Figure 5 illustrates a third embodiment of a rapid error recovery method.

[0025] Figure 6 illustrates a fourth embodiment of a rapid error recovery method.

[0026] Figure 7 illustrates a fifth embodiment of a rapid error recovery method.

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

[0028] FIG. 9 illustrates a flowchart of an error recovery procedure according to one embodiment of the present disclosure.

[0029] This disclosure may be subject to various modifications and various embodiments. Specific embodiments are illustrated and described in detail in the drawings. However, this is not intended to limit the disclosure to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the disclosure.

[0030] 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 disclosure, a first component could be referred to as a "second component," and similarly, a second component could 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.

[0031] 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.

[0032] The terminology used in this disclosure is only used to describe specific embodiments and is not intended to limit the present disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this disclosure, it should be understood that the terms "comprises" or "has" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0033] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which this disclosure 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 shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0034] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the attached drawings. In order to facilitate an overall understanding in describing the present disclosure, identical reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted.

[0035] Below, a wireless communication system to which embodiments according to the present disclosure are applied will be described. The wireless communication system to which embodiments according to the present disclosure are applied is not limited to the description below, and the embodiments according to the present disclosure can be applied to various wireless communication systems. The wireless communication system may be referred to as a "wireless communication network."

[0036] Figure 1 is a block diagram illustrating a first embodiment of a communication node constituting a wireless LAN system.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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 disclosure 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).

[0041] FIG. 2 is a flowchart illustrating a first embodiment of a negotiation procedure for multi-link operation in a wireless LAN system.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

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

[0052] Referring to FIG. 3, AP 1-1 (301) and AP 1-2 (303) affiliated with AP MLD 1 can operate, and AP 1-1 (301) can operate in a first link, and AP 1-2 (303) can operate in a second link. STA 1-1 (311) and STA 1-2 (313) affiliated with STA MLD 1 can operate, and STA 1-1 (311) can operate in a first link, and STA 1-2 (313) can operate in a second link. The first link and the second link can be a NonSimultaneous Transmit and Receive (NSTR) link pair. STA 1-1 (311) can perform a channel access operation (e.g., an EDCA backoff operation) to obtain a TXOP. Within the TXOP acquired by STA 1-1 (311), STA 1-1 (311) can transmit at least one frame (e.g., Physical Layer Protocol Data Unit (PPDU), Medium Access Control Layer Protocol Data Unit (MPDU), Aggregated MPDU (A-MPDU)). The PPDU transmitted by STA 1-1 (311) can include at least one MPDU or A-MPDU.

[0053] STA 1-1 (311) can transmit UL PPDU 1 (320) as the first frame of TXOP. STA MLD 1 can establish a BA session with AP MLD 1 for each TID. That is, a BA session can be established for each MLD. For example, STA 1-1 (311) can establish a BA session corresponding to a specific TID with AP 1-1 (301) on the first link, and STA 1-1 (311) of STA MLD 1 can act as an Originator and AP 1-1 (301) of AP MLD 1 can act as a Recipient. AP 1-1 (301) can record the SN of the MPDU or / and MSDU included in the received UL PPDU 1 (320) in the Scoreboard and store the received frame in the Reorder Buffer. If AP 1-1 (301) does not correctly receive UL PPDU 1 (320), a specific SN may be missing in the Scoreboard, and the MSDU corresponding to the SN following the missing SN may not be delivered to the upper layer. AP 1-1 (301) may request recovery of the missing MPDU or / and MSDU from STA 1-1 (311). Recovery of MPDU or / and MSDU may have a priority. AP 1-1 (301) may request STA 1-1 (311) to recover the missing MPDU or / and MSDU with priority. For example, AP 1-1 (301) may request recovery of the missing MPDU or / and MSDU based on the priority of TID. Here, TID is mapped to AC, and in this case, the priority of TID is the priority of AC. Alternatively, AP 1-1 (301) may request that missing MPDUs or / and MSDUs be recovered based on the priority of the frame according to Delay Bound information.

[0054] When the AP MLD identifies a missing MPDU or / and MSDU, it may perform a channel access operation (e.g., an EDCA backoff operation) on a link other than the first link (e.g., a second link) on which UL PPDU 1 (320) is being transmitted. The channel access operation may include a backoff operation. According to one embodiment of the present disclosure, initiating the backoff operation may be initiating a channel access operation. That is, the backoff operation may be initiated on the second link as soon as an error is identified on the first link. Alternatively, when frame transmission is initiated on the first link, a backoff operation may be initiated on the second link, and when the backoff operation on the second link is completed (e.g., when the backoff counter reaches 0), and when STA 1-1 (311) has finished transmission on the first link and is in a receiving state, i.e., when reception is also possible on the second link, AP 1-2 (303) may transmit a frame (e.g., a Trigger Frame (TF), 340) to STA 1-2 (313) instructing STA 1-1 (311) to transmit a frame in which an error occurred among the frames transmitted. A frame (340) indicating transmission of a frame in which an error has occurred may be transmitted at the same time as a BA (BlockAck) frame (330) transmitted on the first link, and may indicate resources (e.g., uplink transmission time) that can transmit a frame in which an error has occurred, and may include an AID (Association ID), which is an identifier that the AP MLD assigns to each connected STA MLD as a terminal identifier. The frame indicating transmission of a frame in which an error has occurred may indicate the AID of STA MLD1 1. The AID of STA MLD 1 may be the same as those of STA 1-1 (311) and STA 1-2 (313). When the backoff operation is completed, if STA 1-1 (311) is transmitting on the first link, AP 1-2 (303) may maintain the backoff counter at 0 and wait without transmitting a frame.AP 1-2 (303) may transmit a frame (340) indicating transmission of an erroneous frame when it is expected that STA 1-1 (311) has terminated transmission on the first link and is waiting to receive. A packet (e.g., MSDU) to be transmitted to another STA other than STA 1-2 (313) associated with STA MLD 1 may occur in the queue of EDCAF associated with an AC (Access Category) for which the backoff counter of AP 1-2 (303) is maintained as 0. AP 1-2 (303) of AP MLD 1 may consider the buffer of the AC for which the backoff counter is maintained as 0 as empty until the transmission of the erroneous frame is terminated, and may delay transmission of the generated packet. In another way, even if the backoff operation is finished when 'STA 1-1 (311) is transmitting on the first link', a new backoff operation can be performed again until STA 1-1 (311) ends transmission on the first link. AP 1-1 (301) can transmit a BA frame (330) a certain time (e.g., SIFS time) after the end time of transmission of UL PPDU 1 (320) transmitted by STA 1-1 (311). The AP MLD can transmit a frame indicating frame transmission in which an error occurred on the second link rather than the first link on which the BA frame (330) is transmitted at the same time as transmitting the BA frame (330). Alternatively, the transmission start time of the BA frame (330) of AP 1-1 (301) and AP 1-2 (303) of AP MLD 1 and the transmission start time of the frame (340) indicating frame transmission in which an error occurred may be different.The frame (340) indicating transmission of a frame in which an error has occurred may be padded to simultaneously transmit the frame in which an error has occurred along with the transmission of the first link so that the transmission end time of the frame (340) in which an error has occurred can be aligned with the transmission start time of the frame (340) in which an error has occurred so that the transmission end time of the frame in which an error has occurred can coincide with the end time of the BA frame (330) transmitted by STA 1-1 (311) in the first link. The BA frame (330) may be padded to simultaneously transmit subsequent frames so that the transmission end time of the frame (340) in which an error has occurred can be aligned. Padding includes a padding field and a padding bit. Padding may be performed in a MAC frame or a PHY PPDU. The frame (340) indicating transmission of a frame in which an error has occurred may include TID information of an MPDU or / and MSDU that was not correctly received in various forms such as a field, a subfield, and an indication bit. STA MLD 1 may place MPDUs or / and MSDUs requiring rapid recovery at the front of UL PPDU 2 and transmit them first by referring to the parameters (e.g., information on MPDUs or / and MSDUs that are not correctly received) included in the received BA frame (330) and the frame (340) indicating transmission of an errored frame. Alternatively, STA MLD 1 may transmit MPDUs or / and MSDUs requiring rapid recovery in the form of separate UL PPDUs on a second link other than the first link on which UL PPDU 1 (320) is transmitted. Alternatively, STA MLD 1 may transmit MPDUs or / and MSDUs requiring rapid recovery on both the first link and the second link.

[0055] The PPDUs transmitted by AP MLD 1 on the first and second links may be self-decodable. To correct errors in the PPDUs, a channel coding combining method (e.g., Chase combining) may be used to attempt decoding by combining the original packet in which an error occurred and the retransmitted packet. In this embodiment, the channel coding combining method is referred to as the 'CC combining method'. When the decoding of the PPDU received on the first link fails (e.g., when an error occurs in the MPDU included in the PPDU received on the first link or when error correction of the PPDU received on the first link fails), STA MLD 1 combines the PPDU received on the first link with the PPDU received on the second link and then performs decoding to decode a correct frame. Combining of the PPDUs is performed after the PPDUs are demodulated in the physical layers of STA 1 and STA 2 of STA MLD 1. Combining of PPDUs and decoding of the combined PPDU may be performed in one of the physical layers of STA 1 or STA 2. Alternatively, combining of PPDUs and decoding of the combined PPDU may be performed by a separate entity existing in STA MLD 1. When CC combining is used, the PPDU transmitted by AP MLD 1 on the first link and the PPDU transmitted on the second link may use the same redundancy (e.g., redundancy bits, channel coding bits). For example, the PPDU transmitted on the first link and the PPDU transmitted on the second link may use the same channel coding and may be the same PPDU having the same codeword (e.g., bits including data bits and redundancy bits for error correction). Even when the channel coding combining is used and STA MLD 1 combines a PPDU received on the first link and a PPDU received on the second link, decoding may fail.STA MLD 1 can request additional retransmission PPDU (e.g., PPDU N) from AP MLD 1, and the PPDUs can be combined. STA MLD 1 can perform frame decoding based on the combined PPDU. As a method different from the channel coding combining method, a channel coding combining method (e.g., incremental redundancy) can be used to gradually increase the channel coding gain for each retransmission. In the present disclosure, the channel coding combining method is referred to as the 'IR combining method'. When the IR combining method is used, STA MLD 1 can decode a correct PPDU using a PPDU received from the second link when the PPDU received from the first link fails to be decoded. The codewords of the PPDU transmitted by AP MLD 1 from the first link and the PPDU transmitted from the second link include the same data bits, but have different redundancies (e.g., redundancy bits, channel coding bits). That is, the two PPDUs are PPDUs with different codewords. STA MLD 1 can combine PPDUs received on the first link and PPDUs received on the second link, and obtain additional redundancy to correct errors in the PPDUs. Since the PPDUs received on the first link and the PPDUs received on the second link have different redundancies, the code rate of the combined PPDU is lowered. As the code rate is lowered, the redundancy bits for the data bits increase, and errors can be recovered well. For example, if the code rate of the PPDU received on the first link is 3 / 4 and the code rate of the PPDU received on the second link is 3 / 4, the code rate of the PPDUs combined from the PPDUs received on the first and second links can be 3 / 5. If three PPDUs with code rates of 3 / 4 are combined, the code rate of the combined PPDU can be 1 / 2.STA MLD 1 can correct and decode PPDU errors using the combined PPDU.

[0056] In the two channel coding combining methods (CC combining and IR combining), the transmitted PPDUs may be self-decoding capable. Therefore, PPDU combining may not be used if the retransmitted PPDU (e.g., PPDU transmitted on the secondary link) is self-decoding capable without errors.

[0057] In two channel coding combining methods (CC combining and IR combining), decoding errors can be detected on an MPDU basis. For example, an error may occur in the second MPDU included in a PPDU transmitted by AP MLD 1 on the first link, while no errors may occur in the remaining MPDUs. Instead of retransmitting the entire PPDU on the second link for channel coding combining, AP MLD 1 can transmit a PPDU containing only the second MPDU. STA MLD 1 can combine a portion of the PPDU received on the first link (e.g., a portion of the PPDU containing the second MPDU) with a PPDU received on the second link, and decode the combined PPDU. Based on the combined PPDU, STA MLD 1 can correctly receive the second MPDU in which an error occurred.

[0058] AP 1-1 (301) can transmit a BA frame after a certain period of time (e.g., SIFS time) from the end of UL PPDU 2 transmission. When the AP MLD receives recovered MPDUs or / and MSDUs, it can reorder the MPDUs or / and MSDUs waiting in the reordering buffer and forward them to the upper layer.

[0059] Figure 4 illustrates a second embodiment of a rapid error recovery method.

[0060] Referring to FIG. 4, AP 1-1 (401) and AP 1-2 (403) affiliated with AP MLD 1 can operate, and AP 1-1 (401) can operate in a first link, and AP 1-2 (403) can operate in a second link. STA 1-1 (411) and STA 1-2 (413) affiliated with STA MLD 1 can operate, and STA 1-1 (411) can operate in a first link, and STA 1-2 (413) can operate in a second link. The first link and the second link can be a Non-Simultaneous Transmit and Receive (NSTR) link pair. STA 1-1 (411) can acquire a TXOP by performing a channel access operation (e.g., EDCA backoff operation). Within the TXOP acquired by STA 1-1 (411), STA 1-1 (411) can transmit at least one frame (e.g., Physical Layer Protocol Data Unit (PPDU), Medium Access Control Layer Protocol Data Unit (MPDU), Aggregated MPDU (A-MPDU)). The PPDU transmitted by STA 1-1 (411) can include at least one MPDU or A-MPDU.

[0061] STA 1-1 (411) can transmit UL PPDU (420) as the first frame of TXOP. STA MLD 1 can establish a BA session with AP MLD 1 for each TID. That is, a BA session can be established for each MLD. For example, STA 1-1 (411) can establish a BA session corresponding to a specific TID with AP 1-1 (401) on the first link, and STA 1-1 (411) of STA MLD 1 can act as an Originator and AP 1-1 (401) of AP MLD 1 can act as a Recipient. AP 1-1 (401) can record the SN of the MPDU or / and MSDU included in the received UL PPDU (420) in the Scoreboard and store the received frame in the Reorder Buffer. If AP 1-1 (401) does not correctly receive UL PPDU (420), a specific SN may be missing in the Scoreboard, and the MSDU corresponding to the SN following the missing SN may not be delivered to the upper layer. AP 1-1 (401) may request recovery of the missing MPDU or / and MSDU from STA 1-1 (411). Recovery of MPDU or / and MSDU may have a priority. AP 1-1 (401) may request STA 1-1 (411) to recover the missing MPDU or / and MSDU with priority. For example, AP 1-1 (401) may request recovery of the missing MPDU or / and MSDU based on the priority of TID. Here, TID is mapped to AC, and in this case, the priority of TID is the priority of AC. Alternatively, AP 1-1 (401) may request that missing MPDUs or / and MSDUs be recovered based on the priority of the frame according to Delay Bound information.

[0062] When the AP MLD identifies a missing MPDU or / and MSDU, it may perform a channel access operation (e.g., an EDCA backoff operation) on a link other than the first link (e.g., a second link) on which the UL PPDU (420) is being transmitted. The channel access operation may include a backoff operation. According to one embodiment of the present disclosure, initiating the backoff operation may be initiating a channel access operation. That is, the backoff operation may be initiated on the second link as soon as an error is identified on the first link. Alternatively, the backoff operation may be initiated on the second link when frame transmission is initiated on the first link. When the backoff operation is completed on the second link (e.g., when the backoff count reaches 0) and STA 1-1 (411) finishes transmission on the first link and is in a receiving state, i.e., when reception is also possible on the second link, AP 1-2 (403) can transmit a frame (e.g., a Trigger Frame (TF) 440) to STA 1-2 (413) for instructing transmission of a frame in which an error occurred among the frames transmitted by STA 1-1 (411). The frame (440) for instructing transmission of a frame in which an error occurred can be transmitted at the same time as a BA frame (430) transmitted on the first link, and can indicate resources (e.g., an uplink transmission time) that can transmit a frame in which an error occurred, and can indicate information (e.g., an association identifier (AID)) that can specify STA MLD 1. The AID of STA MLD 1 is the same for STA 1-1 (411) and STA 1-2 (413). When the backoff operation is completed, if STA 1-1 (411) is transmitting on the first link, AP 1-2 (403) can keep the backoff counter at 0 and wait without transmitting a frame.AP 1-2 (403) may transmit a frame (440) indicating transmission of an erroneous frame when it is expected that STA 1-1 (411) has terminated transmission on the first link and is waiting to receive. An MSDU to be transmitted to an STA MLD having an AID different from the AID of STA MLD 1 in an EDCAF associated with an AC (Access Category) with a backoff counter of 0 may be generated or input. That is, an MSDU destined for a STA MLD other than STA MLD 1 and STAs linked under STA MLD 1 or another STA may be generated or input. AP MLD 1 may regard the buffer of the AC with a backoff counter of 0 as Empty until transmission of the erroneous frame is terminated, and may postpone transmission of the generated MSDU. In another way, even if the backoff operation is finished when 'STA 1-1 (411) is transmitting on the first link', a new backoff operation can be performed again until STA 1-1 (411) ends transmission on the first link. AP 1-1 (401) can transmit a BA frame (430) a certain time (e.g., SIFS time) after the end time of transmission of the UL PPDU (420) transmitted by STA 1-1 (411). The AP MLD can transmit a frame (e.g., Trigger Frame (TF) 440) indicating frame transmission in which an error has occurred on the second link rather than the first link on which the BA frame (430) is transmitted, while transmitting the BA frame (430). Alternatively, the start time of transmission of the BA frame of AP 1-1 (401) and AP 1-2 (403) of AP MLD 1 and the start time of transmission of the frame (440) indicating frame transmission in which an error has occurred may be different.The frame (440) indicating transmission of a frame in which an error has occurred may be padded to simultaneously transmit the frame in which an error has occurred along with the transmission of the first link so that the transmission end time of the frame (440) in which an error has occurred can be aligned with the transmission start time of the frame (440) in which an error has occurred so that the transmission end time of the frame (440) in which an error has occurred can be aligned with the end time of the BA frame (430) transmitted by STA 1-1 (411) in the first link. The BA frame (430) may be padded to simultaneously transmit subsequent frames so that the transmission end time of the frame (440) in which an error has occurred can be aligned. Padding includes a padding field and a padding bit. Padding may be performed in a MAC frame or a PHY PPDU. The frame (440) indicating transmission of a frame in which an error has occurred may include TID information of an MPDU or / and MSDU that was not correctly received in various forms such as a field, a subfield, and an indication bit. Padding is a frame that extends the end point of frame transmission.

[0063] AP 1-2 (403) of AP MLD can transmit a control frame (e.g., a trigger frame) on the second link to obtain a new TXOP for rapid recovery of a missing MPDU or / and MSDU when the Original TXOP of STA 1-1 (411) obtained through the initially transmitted UL PPDU (420) is expected to end with the transmission of a BA frame (430) (e.g., when the Original TXOP of STA 1-1 (411) is expected to end soon). The control frame transmitted by AP MLD includes an indicator (e.g., an indicator of at least one of a field, a subfield, an information element, and an indicator bit) indicating recovery of a missing MPDU or / and MSDU. The AP MLD may instruct (e.g., trigger) transmission of a UL PPDU including retransmission data (e.g., recovered MPDU or / and MSDU, 450) for retransmitting an erroneous frame in a newly acquired new TXOP, and the transmission of the UL PPDU may be transmitted on a different link (e.g., a second link) from the initially transmitted UL PPDU. The AP MLD, which has received the UL PPDU including the retransmission data (450), may transmit a BA frame after a certain amount of time (e.g., SIFS time) from the end of transmission of the UL PPDU frame including the retransmission data (450). When the AP MLD receives the recovered MPDU or / and MSDU, it may reorder the MPDUs or / and MSDUs waiting in the reordering buffer and forward them to the upper layer.

[0064] Figure 5 illustrates a third embodiment of a rapid error recovery method.

[0065] Referring to FIG. 5, AP 1-1 (501) and AP 1-2 (503) affiliated with AP MLD 1 can operate, and AP 1-1 (501) can operate in a first link, and AP 1-2 (503) can operate in a second link. STA 1-1 (511) and STA 1-2 (513) affiliated with STA MLD 1 can operate, and STA 1-1 (511) can operate in a first link, and STA 1-2 (513) can operate in a second link. The first link and the second link can be an Enhanced Multi-Link Single Radio (EMLSR) link performing EMLSR operation or / and a Non-Simultaneous Transmit and Receive (NSTR) link pair. STA 1-1 (511) can acquire a TXOP by performing a channel access operation (e.g., EDCA backoff operation). Within the TXOP acquired by STA 1-1 (511), STA 1-1 (511) can transmit at least one frame (e.g., PPDU (Physical Layer Protocol Data Unit), MPDU (Medium Access Control Layer Protocol Data Unit), A-MPDU (Aggregated MPDU)). The PPDU transmitted by STA 1-1 (511) can include at least one MPDU or A-MPDU.

[0066] STA 1-1 (511) can transmit UL PPDU (520) as the first frame of TXOP. STA MLD 1 can establish a BA session with AP MLD 1 for each TID. That is, a BA session can be established for each MLD. For example, STA 1-1 (511) can establish a BA session corresponding to a specific TID with AP 1-1 (501) on the first link, and STA 1-1 (511) of STA MLD 1 can act as an Originator and AP 1-1 (501) of AP MLD 1 can act as a Recipient. AP 1-1 (501) can record the SN of the MPDU or / and MSDU included in the received UL PPDU (520) in the Scoreboard and store the received frame in the reordering buffer. If AP 1-1 (501) does not correctly receive UL PPDU (520), a specific SN may be missing in the Scoreboard, and the MSDU corresponding to the SN following the missing SN may not be delivered to the upper layer. AP 1-1 (501) may request recovery of the missing MPDU or / and MSDU from STA 1-1 (511). Recovery of MPDU or / and MSDU may have a priority. AP 1-1 (501) may request STA 1-1 (511) to recover the missing MPDU or / and MSDU with priority. For example, AP 1-1 (501) may request recovery of the missing MPDU or / and MSDU based on the priority of TID. Here, TID is mapped to AC, and in this case, the priority of TID is the priority of AC. Alternatively, AP 1-1 (501) may request that missing MPDUs or / and MSDUs be recovered based on the priority of the frame according to Delay Bound information.

[0067] AP 1-1 (501) may transmit a BA frame (530) a certain amount of time (e.g., SIFS time) after the end of transmission of a UL PPDU (520) transmitted by STA 1-1 (511). AP 1-1 (501) may transmit an indicator to cause STA 1-1 (511), which is a TXOP holder, to extend the TXOP limit in order to retransmit missing MPDUs or / and MSDUs. In a specific embodiment, AP 1-1 (501) may include the indicator in the BA frame (530) in the form of a field, a subfield, or an information element. In another embodiment, AP 1-1 (501) may configure the indicator as a separate MPDU and transmit it to STA 1-1 (511) in the form of an MPDU or A-MPDU including the BA frame (530). In another embodiment, AP 1-1 (501) may include the indicator in a QoS frame (e.g., a QoS Null frame and a QoS Data frame) or an Action frame. The QoS frame or the Action frame may be a QoS frame that does not request an immediate response (e.g., a frame with an Ack policy set to No Ack) or an Action No Ack frame. STA 1-1 (511) may use an extended TXOP according to the TXOP limit extension indicator in the BA frame sent by AP 1-1 (501). STA MLD 1 may be an EMLSR MLD, and STA 1-1 (511) and STA 1-2 (513) may perform EMLSR operations. STA 1-1 (511) may extend the TXOP when it receives a BA frame (530) including a TXOP extension indicator. STA 1-1 (511) can transmit frames within the extended TXOP without returning to Listening Operation in EMLSR operation using the extended TXOP.The listening operation is a state in which the STA MLD can receive only initial control frames. The initial control frames are MU-RTS trigger frames and BSRP (buffer status report poll) trigger frames. Since STA 1-1 (511) does not return to the listening operation and performs communication using an extended TXOP, there is no need to perform additional channel access procedures (e.g., EDCA backoff operation and EMLSR initial control frame transmission procedure), and since the transition delay that occurs during the EMLSR operation (e.g., EMLSR transition delay that occurs when transitioning to the listening operation) does not occur, additional delay can be prevented. STA 1-1 (511) can transmit a UL PPDU including retransmission data (540) to AP 1-1 (501) on the first link on which the initial UL PPDU was transmitted. AP 1-1 (501), which has received a UL PPDU including retransmission data (540), can transmit a BA frame after a certain period of time (e.g., SIFS time) from the end of the UL PPDU transmission. When the AP MLD receives the recovered MPDU or / and MSDU, it can sort the MPDU or / and MSDU waiting in the reordering buffer in order and forward them to the upper layer.

[0068] Figure 6 illustrates a fourth embodiment of a rapid error recovery method.

[0069] Referring to FIG. 6, AP 1-1 (601) and AP 1-2 (603) affiliated with AP MLD 1 can operate, and AP 1-1 (601) can operate in a first link, and AP 1-2 (603) can operate in a second link. STA 1-1 (611) and STA 1-2 (613) affiliated with STA MLD 1 can operate, and STA 1-1 (611) can operate in a first link, and STA 1-2 (613) can operate in a second link. The first link and the second link can be an Enhanced Multi-Link Single Radio (EMLSR) link performing EMLSR operation or / and a Non-Simultaneous Transmit and Receive (NSTR) link pair. STA 1-1 (611) can acquire a TXOP by performing a channel access operation (e.g., EDCA backoff operation). Within the TXOP acquired by STA 1-1 (611), STA 1-1 (611) can transmit at least one frame (e.g., Physical Layer Protocol Data Unit (PPDU), Medium Access Control Layer Protocol Data Unit (MPDU), Aggregated MPDU (A-MPDU)). The PPDU transmitted by STA 1-1 (611) can include at least one MPDU or A-MPDU.

[0070] STA 1-1 (611) can transmit UL PPDU (620) as the first frame of TXOP. STA MLD 1 can establish a BA session with AP MLD 1 for each TID. That is, a BA session can be established for each MLD. For example, STA 1-1 (611) can establish a BA session corresponding to a specific TID with AP 1-1 (601) on the first link, and STA 1-1 (611) of STA MLD 1 can act as an Originator and AP 1-1 (601) of AP MLD 1 can act as a Recipient. AP 1-1 (601) can record the SN of the MPDU or / and MSDU included in the received UL PPDU (620) in the Scoreboard and store the received frame in the reordering buffer. If AP 1-1 (601) does not correctly receive UL PPDU (620), a specific SN may be missing in the Scoreboard, and the MSDU corresponding to the SN following the missing SN may not be delivered to the upper layer. AP 1-1 (601) may request recovery of the missing MPDU or / and MSDU from STA 1-1 (611). Recovery of MPDU or / and MSDU may have a priority. AP 1-1 (601) may request STA 1-1 (611) to recover the missing MPDU or / and MSDU with priority. For example, AP 1-1 (601) may request recovery of the missing MPDU or / and MSDU based on the priority of TID. Here, TID is mapped to AC, and in this case, the priority of TID is the priority of AC. Alternatively, AP 1-1 (601) may request that missing MPDUs or / and MSDUs be recovered based on the priority of the frame according to Delay Bound information.

[0071] AP 1-1 (601) can transmit a BA frame after a certain period of time (e.g., SIFS time) from the end time of the UL PPDU transmission transmitted by STA 1-1 (611). If AP 1-1 (601) fails to correctly receive the initially transmitted UL PPDU (620), the BA frame (630) can include an indicator in the form of a field, subfield, or information element, which instructs STA MLD 1 to perform a normal transmission and reception operation (e.g., retransmit a frame in which an error occurred) on the second link to recover a frame in which an error occurred. STA MLD 1, which has received a frame including an indicator instructing to perform a normal transmission and reception operation (e.g., retransmit a frame in which an error occurred) on the second link, can perform a normal transmission and reception operation (e.g., retransmit a frame in which an error occurred) on the second link after the EMLSR Transition Delay time from immediately after receiving the frame including the indicator. AP 1-2 (603) may perform a backoff operation in advance to trigger transmission of a UL PPDU including retransmission data (650) on the second link, and may wait until a time (e.g., after the EMLSR Transition Delay time from the time of completion of transmission of a frame including an indicator of AP 1-1 (601)) at which STA 1-2 (613) is expected to perform a normal transmission / reception operation (e.g., retransmit a frame in which an error occurred) while the backoff counter reaches 0. Alternatively, AP 1-2 (603) may repeat the backoff operation until a time (e.g., after the EMLSR Transition Delay time from the time of completion of transmission of a frame including an indicator of AP 1-1 (601)) at which STA 1-2 (613) is expected to perform a normal transmission / reception operation (e.g., retransmit a frame in which an error occurred).AP 1-2 (603) may wait for transmission of a trigger frame (640) in the second link until after the EMLSR Transition Delay time from the time of completion of transmission of the BA frame (630) in the first link. AP 1-2 (603) may trigger a UL PPDU including retransmission data (650) by transmitting a trigger frame to STA 1-2 (613) after the EMLSR Transition Delay time from the time of completion of transmission of the BA frame (630) in the first link. STA 1-2 (613) may transmit retransmission data (650) indicated by the trigger frame (640) to AP 1-2 (603). AP 1-2 (603) may transmit a BA frame after a certain period of time (e.g., SIFS time) from the time of termination of transmission of the UL PPDU including retransmission data (650) transmitted by STA 1-2 (613). When the AP MLD receives recovered MPDUs or / and MSDUs, it can reorder the MPDUs or / and MSDUs waiting in the reordering buffer and forward them to the upper layer.

[0072] Figure 7 illustrates a fourth embodiment of a rapid error recovery method.

[0073] Referring to FIG. 7, AP 1-1 (701) and AP 1-2 (703) affiliated with AP MLD 1 can operate, and AP 1-1 (701) can operate in a first link, and AP 1-2 (703) can operate in a second link. STA 1-1 (711) and STA 1-2 (713) affiliated with STA MLD 1 can operate, and STA 1-1 (711) can operate in a first link, and STA 1-2 (713) can operate in a second link. The first link and the second link can be an Enhanced Multi-Link Single Radio (EMLSR) link performing EMLSR operation or / and a Non-Simultaneous Transmit and Receive (NSTR) link pair. STA 1-1 (711) can acquire a TXOP by performing a channel access operation (e.g., EDCA backoff operation). Within the TXOP acquired by STA 1-1 (711), STA 1-1 (711) can transmit at least one frame (e.g., Physical Layer Protocol Data Unit (PPDU), Medium Access Control Layer Protocol Data Unit (MPDU), Aggregated MPDU (A-MPDU)). The PPDU transmitted by STA 1-1 (711) can include at least one MPDU or A-MPDU.

[0074] STA 1-1 (711) can transmit UL PPDU (720) as the first frame of TXOP. STA MLD 1 can establish a BA session with AP MLD 1 for each TID. That is, a BA session can be established for each MLD. For example, STA 1-1 (711) can establish a BA session corresponding to a specific TID with AP 1-1 (701) on the first link, and STA 1-1 (711) of STA MLD 1 can act as an Originator and AP 1-1 (701) of AP MLD 1 can act as a Recipient. AP 1-1 (701) can record the SN of the MPDU or / and MSDU included in the received UL PPDU (720) in the Scoreboard and store the received frame in the reordering buffer. If AP 1-1 (701) does not correctly receive UL PPDU (720), a specific SN may be missing in the Scoreboard, and the MSDU corresponding to the SN following the missing SN may not be delivered to the upper layer. AP 1-1 (701) may request recovery of the missing MPDU or / and MSDU from STA 1-1 (711). Recovery of MPDU or / and MSDU may have a priority. AP 1-1 (701) may request STA 1-1 (711) to recover the missing MPDU or / and MSDU with priority. For example, AP 1-1 (701) may request recovery of the missing MPDU or / and MSDU based on the priority of TID. Here, TID is mapped to AC, and in this case, the priority of TID is the priority of AC. Alternatively, AP 1-1 (701) may request that missing MPDUs or / and MSDUs be recovered based on the priority of the frame according to Delay Bound information.

[0075] AP 1-1 (701) may transmit a BA frame (730) after a certain period of time (e.g., SIFS time) from the end time of transmission of UL PPDU (720) transmitted by STA 1-1 (711). STA MLD 1 may switch STA 1-1 (711) of the first link and STA 1-2 (713) of the second link to EMLSR Listening Operation after the EMLSR Transition Delay time, and may wait for reception of an initial control frame from the first link or / and the second link. The initial control frame is an MU-RTS trigger frame (750) or a BSRP trigger frame.

[0076] AP 1-2 (703) may perform a backoff operation in advance before a time point at which STA 1-2 (713) is expected to operate in a listening operation (e.g., after the EMLSR Transition Delay time from the time point at which BA frame (730) of AP 1-1 (701) is completed transmitting) to trigger transmission of a UL PPDU containing retransmission data (750) on the second link, and may wait while the backoff counter reaches 0. Alternatively, AP 1-2 (703) may repeatedly perform a backoff until a time point at which STA 1-2 (713) is expected to operate in a listening operation (e.g., after the EMLSR Transition Delay time from the time point at which BA frame (730) of AP 1-1 (701) is completed transmitting). AP 1-2 (703) may wait for transmission of an MU-RTS trigger frame (740) until after the EMLSR Transition Delay time from the end time of transmission of the BA frame (730) of the first link. AP 1-2 (703) may transmit an MU-RTS frame (740) to STA 1-2 (713) (i.e., transmit an initial control frame) after the EMLSR Transition Delay time from the end time of transmission of the BA frame (730) of the first link, so that STA MLD 1 may perform normal transmission and reception operations (e.g., retransmit a frame in which an error occurred) on the second link. STA 1-2 (713) may transmit a CTS frame after a certain time (e.g., SIFS time) from the end time of transmission of the MU-RTS frame (740). AP 1-2 (703) can trigger a UL PPDU containing retransmission data (750) by transmitting a trigger frame to STA 1-2 (713). STA 1-2 (713) can transmit retransmission data (750) indicated by the trigger frame (740) to AP 1-2 (703).AP 1-2 (703) can transmit a BA frame after a certain period of time (e.g., SIFS time) from the end of transmission of UL PPDU including retransmission data (740) transmitted by STA 1-2 (713). When AP MLD receives recovered MPDU or / and MSDU, it can sort MPDU or / and MSDU waiting in the reordering buffer in order and forward it to the upper layer.

[0077]

[0078] Hereinafter, embodiments of an error recovery procedure are described. The error recovery procedure is performed by an STA and an AP. The STA and AP may be MLDs. In other words, the STA and AP may communicate using multiple links. For example, the STA and AP may communicate using a first link and a second link. Here, the first link and the second link may be a NSTR link pair. In other words, the STA and AP cannot simultaneously transmit and receive on the first link and the second link.

[0079]

[0080] FIG. 8 illustrates a flowchart of an error recovery procedure according to one embodiment of the present disclosure. FIG. 8 illustrates a procedure performed by an AP (e.g., AP MLD of FIG. 3 ).

[0081] Referring to FIG. 8, in step S801, the AP receives a plurality of frames. The AP may receive a plurality of frames (e.g., UL PPDU 1 (320) of FIG. 3) using the first link. The plurality of frames may include at least one Physical Layer Protocol Data Unit (PPDU), Medium Access Control Layer Protocol Data Unit (MPDU), or Aggregated MPDU (A-MPDU). For example, the plurality of frames may be grouped and received as a single PPDU. The plurality of frames may include at least one of a sequence number (SN) or a traffic identifier (TID). Each of the frames may have the same TID, or alternatively, may have different TIDs. For example, at least some of the frames may have the same TID. At least some of the frames may have different TIDs. Each of the frames may have a priority for recovery. For example, each frame can have a priority based on its TID, and frames with higher priorities can be recovered or retransmitted first when errors are detected. The AP records multiple received frames in a reorder buffer and performs reordering based on the SN, etc.

[0082] In step S803, the AP detects errors among multiple frames. Errors include cases where a received frame is not decoded. The AP can detect errors based on the received frames. For example, the AP can detect errors based on the TID or SN included in the received frame. For example, in the reordering procedure, the AP can recognize that a frame containing a missing SN was not properly received and detect the error.

[0083] In step S805, the AP transmits a retransmission request. The AP may transmit a retransmission request to request retransmission of a frame in which an error has been detected. The retransmission request may be transmitted on the first link or the second link. The retransmission request may be transmitted in a trigger frame (e.g., the trigger frame (340) of FIG. 3), a response frame (e.g., the BA frame (530) of FIG. 5), or an MU-RTS frame (e.g., the MU-RTS trigger frame (740) of FIG. 7). When the retransmission request is transmitted on the second link, the frame including the retransmission request may be terminated at the same time as the response frame transmitted on the first link. To terminate transmission at the same time, the frame including the retransmission request may include padding. Alternatively, the response frame transmitted on the first link may include padding to terminate transmission at the same time. The retransmission request may include at least one of the TID, SN of the frame in which an error is detected, the resource used for retransmission of the frame in which an error is detected, or the AID of the STA retransmitting the frame. To transmit the retransmission request, the AP may perform a channel access procedure. For example, the channel access procedure may be performed from the time when an error in the frame is detected. After the channel access procedure is completed, the AP may wait without transmitting the retransmission request. For example, the AP may transmit the retransmission request after the STA completes transmitting a plurality of frames. As another example, the AP may transmit the retransmission request after the STA transmits the frames and then switches to the EMLSR listening mode. To transmit the retransmission request, the AP may obtain a TXOP from the second link.

[0084] In step S807, the AP receives a retransmission frame (e.g., retransmission data (350) of FIG. 3). The retransmission frame includes a frame in which an error was detected. For example, the retransmission frame may include a frame in which an error was detected and a frame transmitted after the frame in which the error was detected. The retransmission frame may be received using the first link or the second link. The retransmission frame may be received using the first link or the second link depending on the type of frame containing the retransmission request. For example, if the retransmission request is included in a trigger frame transmitted on the second link or an MU-RTS frame transmitted on the second link, the retransmission frame may be received using the second link. As another example, if the retransmission request is included in a response frame transmitted on the first link, the retransmission frame may be received using the first link.

[0085]

[0086] FIG. 9 illustrates a flowchart of an error recovery procedure according to one embodiment of the present disclosure. FIG. 9 illustrates a procedure performed by an STA (e.g., the STA MLD of FIG. 3 ).

[0087] Referring to FIG. 9, in step S901, an STA transmits a plurality of frames (e.g., UL PPDU 1 (320) of FIG. 3). The STA may transmit the plurality of frames using the first link. To transmit the plurality of frames, the STA may obtain a transmit opportunity (TXOP). The plurality of frames include at least one Physical Layer Protocol Data Unit (PPDU), Medium Access Control Layer Protocol Data Unit (MPDU), or Aggregated MPDU (A-MPDU). For example, the plurality of frames may be grouped and transmitted as one PPDU. The plurality of frames may include at least one of a sequence number (SN) or a traffic identifier (TID). Each of the frames may have the same TID, or alternatively, may have different TIDs. For example, at least some of the frames may have the same TID. At least some of the frames may have different TIDs. Each of the frames may have a priority for recovery. For example, each frame may have a priority based on its TID, and a frame with a higher priority may be recovered or retransmitted first when an error is detected. Multiple frames may be transmitted in SN order, or alternatively, they may be transmitted regardless of SN order.

[0088] In step S903, the STA receives a retransmission request. The retransmission request may be received on the first link or the second link. The retransmission request may be received in a trigger frame (e.g., the trigger frame (340) of FIG. 3), a response frame (e.g., the BA frame (530) of FIG. 5), or an MU-RTS frame (e.g., the MU-RTS trigger frame (740) of FIG. 7). If the retransmission request is received on the second link, the frame including the retransmission request may be received at the same time as the response frame received on the first link. To be received at the same time, the frame including the retransmission request may include padding. The retransmission request may include at least one of the TID of the frame in which an error is detected, the SN, the resource used for retransmission of the frame in which an error is detected, or the AID of the STA retransmitting the frame. The STA may receive the retransmission request after transmission of a plurality of frames is completed. As another example, an STA may receive a retransmission request after transmitting frames and then switching to EMLSR listening mode. The retransmission request may include an indication for extending the STA's TXOP. If the retransmission request includes an indication for extending the TXOP, the STA may extend the TXOP to transmit the retransmitted frame.

[0089] In step S905, the STA transmits a retransmission frame (e.g., retransmission data (350) of FIG. 3). The retransmission frame includes a frame in which an error was detected. For example, the retransmission frame may include a frame in which an error was detected and a frame transmitted after the frame in which the error was detected. The retransmission frame may be transmitted using the first link or the second link. The retransmission frame may be transmitted using the first link or the second link depending on the type of frame that includes the retransmission request. For example, if the retransmission request is included in a trigger frame transmitted on the second link or an MU-RTS frame transmitted on the second link, the retransmission frame may be transmitted using the second link. As another example, if the retransmission request is included in a response frame transmitted on the first link, the retransmission frame may be transmitted using the first link. To transmit the retransmission data, the STA may obtain a TXOP. The STA may obtain a TXOP on the link through which the retransmission frame is transmitted.

[0090]

[0091] The methods according to the present disclosure 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 configured for the present disclosure or may be known and available to those skilled in the computer software art.

[0092] 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 disclosure, and vice versa.

[0093] Although the present disclosure has been described with reference to the above embodiments, it will be understood by those skilled in the art that various modifications and changes can be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the claims below.

[0094] The present disclosure can be used in devices and recording media in a wireless LAN system.

Claims

1. A method for operating an AP (access point) in a wireless LAN system, A step of receiving a plurality of frames from an STA; A step of detecting an error in at least one frame among the plurality of frames; A step of transmitting a retransmission request based on a frame in which the above error is detected; A step of receiving a retransmission frame based on the above retransmission request, The above retransmitted frame includes the frame in which the error was detected, The above retransmission frame is received on the link through which the retransmission request was transmitted.

2. In paragraph 1, The above retransmission request is, A method comprising a TID of a frame in which the error is detected, an SN of the frame in which the error is detected, a resource used for transmission of the retransmitted frame, or an AID of the STA.

3. In paragraph 1, The above retransmission request is transmitted using a response frame, a trigger frame or a MU-RTS frame.

4. In paragraph 3, A method in which, when the above retransmission request is transmitted using the above trigger frame, transmission of the trigger frame is terminated at the same time as the response frame.

5. In paragraph 4, A method wherein the trigger frame includes padding for terminating transmission at the same time as the response frame.

6. In paragraph 1, Further comprising the step of performing a channel access procedure for transmitting the above retransmission request, A method in which the above retransmission request is transmitted after the channel access procedure and reception of the plurality of frames are completed.

7. In paragraph 6, The above retransmission request is transmitted after the time for which the STA switches to listening mode has elapsed.

8. In paragraph 1, Each of the above multiple frames includes a priority, A method in which the above retransmission frame is received based on the above priority.

9. A method for operation of STA (station) in a wireless LAN system, A step of transmitting multiple frames to the AP; A step of receiving a retransmission request based on a frame in which an error is detected among the plurality of frames; Including a step of transmitting a retransmission frame based on the above retransmission request, The above retransmitted frame includes the frame in which the error was detected, The above retransmission frame is transmitted on the link through which the retransmission request was received.

10. In paragraph 9, The above retransmission request is, A method comprising a TID of a frame in which the error is detected, an SN of the frame in which the error is detected, a resource used for transmission of the retransmitted frame, or an AID of the STA.

11. In paragraph 9, The above retransmission request is received using a response frame, a trigger frame or a MU-RTS frame.

12. In paragraph 11, A method in which, when the above retransmission request is received using the above trigger frame, reception of the trigger frame is terminated at the same time as the response frame.

13. In paragraph 12, A method wherein the trigger frame or the response frame includes padding for terminating reception at the same time as the response frame or the trigger frame.

14. In paragraph 9, The above retransmission request is received after transmission of the plurality of frames is completed.

15. In paragraph 14, Further comprising a step of switching to a listening mode after receiving a response frame for the above multiple frames, The above retransmission request is received after the time for switching to the listening mode has elapsed.

16. In paragraph 9, Each of the above multiple frames includes a priority, A method in which the above retransmission frame is transmitted based on the above priority.

17. 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, Receive multiple frames from STA, Detecting an error in at least one frame among the above multiple frames, A retransmission request is sent based on the frame in which the above error is detected, configured to receive a retransmission frame based on the above retransmission request, The above retransmitted frame includes the frame in which the error was detected, The above retransmission frame is received by the AP on the link through which the retransmission request was transmitted.

18. In a wireless LAN system, at STA (station), Transmitter and receiver; and Including a processor connected to the above transceiver, The above processor, To the AP, send multiple frames, Receive a retransmission request based on a frame in which an error is detected among the above multiple frames, configured to transmit a retransmission frame based on the above retransmission request, The above retransmitted frame includes the frame in which the error was detected, The above retransmission frame is transmitted by an STA on the link on which the retransmission request was received.

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