Method and apparatus for joint communication of multiple aps in wireless LAN system

Abstract

This operating method of an access point (AP) for joint communication of multiple APs in a wireless LAN system comprises the steps of: negotiating for joint transmission with other APs; transmitting information for the joint transmission on the basis of negotiation results; and transmitting a frame on the basis of the negotiation results, wherein the negotiation includes a frequency for the joint transmission, and the frame is transmitted using the frequency for the joint transmission.

Description

Method and device for cooperative communication of multiple APs in a wireless LAN system

[0001] The present disclosure relates to a wireless local area network (WLAN) system. More specifically, it relates to a method and device for cooperative communication between multiple APs 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] In a wireless LAN, a method may be necessary for multiple access points (APs) to perform cooperative communication. Multiple APs can establish a cooperative communication schedule and change their operating frequencies to facilitate cooperative communication. However, if APs change their operating frequencies, communication between WLAN devices connected to the APs may become impossible, resulting in reduced communication efficiency and increased latency. Consequently, the reliability of the WLAN network is compromised.

[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 performing joint transmission by multiple APs (access points) in a wireless LAN system.

[0008] The present disclosure provides a method and device for performing negotiations between multiple APs to perform cooperative transmission in a wireless LAN system.

[0009] The present disclosure provides a method and device for performing scheduling for a plurality of APs to perform cooperative transmission in a wireless LAN system.

[0010] The present disclosure provides a method and device for setting a transmission prohibition period for an STA (station) that does not participate in cooperative transmission in a wireless LAN system.

[0011] The present disclosure provides a method and device for enabling STAs that do not participate in cooperative transmission in a wireless LAN system to communicate directly with each other.

[0012] The present disclosure provides a method and device for performing media synchronization after cooperative transmission is terminated in a wireless LAN system.

[0013] 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.

[0014] A method of operating an access point (AP) in a wireless LAN system includes a step of negotiating with another AP for joint transmission, a step of transmitting information for joint transmission based on a result of the negotiation, and a step of transmitting a frame based on a result of the negotiation, wherein the result of the negotiation includes a frequency for the joint transmission, and the frame is transmitted using the frequency for the joint transmission.

[0015] A method of operating an STA (station) in a wireless LAN system includes the steps of receiving information for joint transmission from a connected AP, and performing at least one of a transmission prohibition operation, a frame reception operation, or a direct communication operation in a section of the joint transmission based on the information for the joint transmission, wherein the information for the joint transmission includes at least one of information on the section of the joint transmission or information on a frequency for the joint transmission.

[0016] 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 negotiate with another AP for joint transmission, transmit information for joint transmission based on a result of the negotiation, and transmit a frame based on a result of the negotiation, wherein the result of the negotiation includes a frequency for the joint transmission, and the frame is transmitted using the frequency for the joint transmission.

[0017] In a wireless LAN system, a STA (station) includes a transceiver and a processor connected to the transceiver, wherein the processor is configured to receive information for joint transmission from a connected AP, and perform at least one of a transmission prohibition operation, a frame reception operation, or a direct communication operation in a section of the joint transmission based on the information for the joint transmission, wherein the information for the joint transmission includes at least one of information on a section of the joint transmission or information on a frequency for the joint transmission.

[0018] According to the present disclosure, scheduling for cooperative communication can be performed at a specific frequency.

[0019] According to the present disclosure, a direct communication section can be set for STAs, which are wireless LAN terminals connected to APs.

[0020] According to the present disclosure, transmission efficiency can be increased by performing direct communication between STAs even when communication with APs is impossible.

[0021] 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.

[0022] Figure 1 is a block diagram illustrating a first embodiment of a communication node constituting a wireless LAN system.

[0023] Figure 2 illustrates a first embodiment of a multi-AP cooperative transmission method.

[0024] Figure 3 illustrates a second embodiment of a multi-AP cooperative transmission method.

[0025] Figure 4 illustrates a third embodiment of a multi-AP cooperative transmission method.

[0026] Figure 5 illustrates a first embodiment of a multi-AP frequency change communication method.

[0027] FIG. 6 illustrates a flowchart of a negotiation and communication procedure for cooperative transmission according to one embodiment of the present disclosure.

[0028] FIG. 7 illustrates a flowchart of a communication execution procedure for cooperative transmission 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] Figure 2 illustrates a first embodiment of a multi-AP cooperative transmission method.

[0042] Referring to FIG. 2, AP 1 (201) operates in the first link, AP 2 (203) operates in the second link, and AP 3 (205) operates in the third link. Here, 'link' may refer to a specific operating frequency of a wireless LAN network. The operating frequencies of the first link to the third link may be different from each other or may be the same. When the operating frequencies of AP 1 (201) to AP 3 (205) are the same, the OBSS (overlapping basic service set) of AP 1 (201) is the BSSs (basic service sets) of AP 2 (203) and AP 3 (205), the OBSS of AP 2 (203) is the BSSs of AP 1 (201) and AP 3 (205), and the OBSS of AP 3 (205) is the BSSs of AP 1 (201) and AP 2 (203). AP 1 (201) to AP 3 (205) can synchronize TSF (time synchronization function) with each other. That is, AP 1 (201) to AP 3 (205) have the same TSF value at the same time. The synchronization of TSF may be for synchronizing the cooperative transmission schedules (e.g., R-TWT (restricted target wake time) SP) of AP 1 (201) to AP 3 (205) with each other. In addition, when the operating frequencies of AP 1 (201) to AP 3 (205) are the same, synchronizing the TSF may be for synchronizing the cooperative transmission schedules (e.g., R-TWT SP) of the OBSS with each other. AP 1 (201) to AP 3 (205) may perform schedule negotiation (210) for cooperative transmission. Schedule negotiation (210) for cooperative transmission may be SST (subchannel selective transmission) TWT (target wake time) negotiation, another type of TWT negotiation other than SST, or transmission interval negotiation.SST TWT negotiation is a negotiation that establishes whether communication will proceed on a different channel within the TWT period. For example, SST TWT negotiation may be a negotiation that establishes that AP 2 (203) operating on a second link and AP 3 (205) operating on a third link operate on a first link within the TWT SP. As a result of the schedule negotiation (210) for the cooperative transmission, AP 1 (201) to AP 3 (205) may establish a cooperative transmission period. The cooperative transmission period may be a TWT SP (service period). AP 1 (201) may be a master AP that initiates the cooperative transmission schedule negotiation (210), and AP 1 (201) to AP 3 (205) communicate on the operating frequency of AP 1 (201) (i.e., the first link or the first channel) within the cooperative transmission period. That is, AP 2 (203) and AP 3 (205) must change their operating frequencies (i.e., link or channel). Since AP 1 (201) to AP 3 (205) have synchronized their TSFs, the start time of the cooperative transmission intervals of AP 1 (201) to AP 3 (205) can be the same, and AP 1 (201) to AP 3 (205) can know exactly when the cooperative transmission interval starts.

[0043] AP 1 (201) to AP 3 (205) can transmit frames (221, 223, 225) indicating a cooperative transmission section before the start of the cooperative transmission section. The frames (221, 223, 225) indicating a cooperative transmission section can be frames in various forms. For example, the frames (221, 223, 225) indicating a cooperative transmission section can be beacon frames. The frames (221, 223, 225) indicating a cooperative transmission section can include information indicating a cooperative transmission section (e.g., TWT information, TWT element) and information indicating a frequency (e.g., link ID, channel number, information that can indicate a specific operating frequency). The frames (223, 225) indicating the cooperative transmission section transmitted by AP 2 (203) and AP 3 (205) may further include information indicating that transmission of STAs connected to AP 2 (203) and AP 3 (205) is prohibited within the cooperative transmission section (e.g., information indicating a section in which transmission is prohibited, quiet element). Alternatively, the information indicating that transmission is prohibited in the cooperative transmission section may be included together with the information indicating the cooperative transmission section (e.g., TWT information, TWT element). The information indicating that transmission is prohibited indicates a transmission prohibited section, which indicates a section in which the AP is unavailable, during which transmission from the STA to the AP is prohibited. The frame indicating the cooperative transmission section may include TWT information (e.g., information indicating an R-TWT SP) indicating that transmission must be terminated (e.g., TXOP (transmit opportunity) must be terminated) before the cooperative transmission section (e.g., TWT SP, R-TWT SP, SP). That is, information indicating the cooperative transmission section and frequency can indicate the R-TWT SP.The channel switching delay, which is the time it takes for an AP to change to a frequency that uses the cooperative transmission, may be included in the transmission prohibition period. The channel switching delay may be applied both when changing from the operating frequency to the frequency for cooperative transmission and when changing from the frequency for cooperative transmission to the current operating frequency. The channel switching delay may vary for each AP. APs can perform multi-AP cooperative transmission from the same point in time after the channel switching delay. If the channel switching delays of each AP are different, the length of the transmission prohibition period may vary. For example, if the channel change delay time of AP 2 (203) is longer than that of AP 1 (201), and if the channel change delay time of AP 3 (205) is longer than that of AP 2 (203), then considering the channel change delay times of each AP, the length of the transmission prohibition period of AP 3 (205) may be the longest, the length of the transmission prohibition period of AP 1 (201) may be the shortest, and the length of the transmission prohibition period of AP 2 (203) may be longer than the length of the transmission prohibition period of AP 1 (201) and shorter than the length of the transmission prohibition period of AP 3 (205). For example, the channel change delay time may be a predetermined value known to all STAs in the BSS. Alternatively, the AP may not include the channel change delay time in the transmission prohibition period. STAs can receive frames indicating cooperative transmission intervals, and when they receive a transmission prohibition instruction included in frames (223, 225) indicating cooperative transmission intervals, they can calculate and determine that the AP is unavailable from the indicated time before the AP's channel change delay time. STAs do not transmit to the AP from the calculated time. When STAs receive frames indicating cooperative transmission intervals, they can terminate transmission (e.g., terminate TXOP) before the start of the transmission prohibition interval.When the operating frequencies of AP 1 (201) to AP 3 (205) are the same, and STAs receive a frame (223, 225) indicating a cooperative transmission section of an OBSS (i.e., AP 2 (203) and AP 3 (205) when the STA is connected to AP 1 (201), AP 1 (201) and AP 3 (205) when the STA is connected to AP 2 (203), and AP 1 (201) and AP 2 (203) when the STA is connected to AP 3 (205)), transmission can be terminated before the start of the transmission prohibition section included in the frame (223, 225) indicating the cooperative transmission section of the OBSS. The frames (223, 225) indicating the cooperative transmission section transmitted by AP 2 (203) and AP 3 (205) may further include information (e.g., link ID, channel number, information capable of indicating a specific operating frequency) for indicating an operating frequency to STAs that wish to participate in the cooperative transmission section among STAs connected to AP 2 (203) and AP 3 (205). At the start of the cooperative transmission section, AP 2 (203) and AP 3 (205) may operate at the frequency for indicating the cooperative transmission, for example, the first link, and AP 1 (201) to AP 3 (205) perform cooperative communication using the frequency for performing the cooperative transmission. STAs that wish to participate in the cooperative transmission section among STAs connected to AP 2 (203) and AP 3 (205) may operate at the frequency for performing the cooperative transmission, for example, the first link, at the start of the cooperative transmission section. STAs wishing to participate in the above cooperative transmission section may need to perform a negotiation procedure with AP 2 (203) and AP 3 (205), and the negotiation procedure may be a TWT negotiation procedure (e.g., broadcast TWT negotiation, individual TWT negotiation).Among the STAs connected to AP 2 (203) and AP 3 (205), STAs that do not participate in the cooperative transmission section do not transmit frames to the corresponding APs within the cooperative transmission section based on information indicating that transmission transmitted by AP 2 (203) and AP 3 (205) is prohibited. For example, STAs that do not participate in the cooperative transmission section may regard data (e.g., data packets, MSDUs, MPDUs) destined for AP 2 (203) and AP 3 (205) as non-existent. The behavior of the STAs not transmitting frames within the cooperative transmission section may be due to NAV (network allocation vector, 251, 253). For example, STAs connected to AP 2 (203) and AP 3 (205) can set NAVs (251, 253) for the length of the cooperative transmission interval according to information indicating that transmission is prohibited, and do not perform frame transmission by considering the channel as busy during the set NAVs (251, 253). Within the cooperative transmission interval, AP 2 (203) and AP 3 (205) operate at an operating frequency (e.g., the first link) different from the original operating frequency, and since they did not perform a reception operation (i.e., a reception operation including a channel detection operation (e.g., a clear channel assessment (CCA))) at the different operating frequency before the cooperative transmission interval, medium synchronization may be lost. In addition, if the cooperative transmission interval is longer than a specific length, medium synchronization may be lost if the operating frequency is changed to the original operating frequency after the cooperative transmission interval.Therefore, AP 2 (203) and AP 3 (205) must set the MediumSyncDelay timer, which is a timer for recovering medium synchronization immediately after the start of operation on the first link, for example, the frequency for cooperative transmission at the start time of the cooperative transmission section, and frame transmission may be restricted while the MediumSyncDelay timer is operating. Restricting frame transmission while the MediumSyncDelay timer is operating may mean that, before transmitting a data frame, an RTS frame must be transmitted if the energy of the channel is below a certain level, or a CCA (clear channel assessment) operation is performed without transmitting the frame. The MediumSyncDelay timer is cleared when the frame is normally received (e.g., the MPDU is normally received without error) and successfully decoded. AP 1 (201) does not change the operating frequency and can immediately transmit the frame within the cooperative transmission section. Accordingly, AP 1 (201) can transmit an 'initial frame' (e.g., trigger frame 230) to release the MediumSyncDelay timer of AP 2 (203) and AP 3 (205) at the starting point of the cooperative transmission section and to restore medium synchronization. The initial frame includes not only the trigger frame but also all kinds of frames that AP 2 (203) and AP 3 (205) can decode and set the NAV correctly. Within the cooperative transmission frequency, i.e., the cooperative transmission section of the first link, AP 1 (201) to AP 3 (205) perform cooperative transmission. For example, AP 1 (201) to AP 3 (205) can transmit the frame (240) to STAs in the first link by performing a CO-OFDMA (coordinated orthogonal frequency division multiple access) operation or a CO-SR (coordinated spatial reuse) operation.At the end of the cooperative transmission section, AP 2 (203) and AP 3 (205) operate again on the second link and the third link.

[0044] Figure 3 illustrates a second embodiment of a multi-AP cooperative transmission method.

[0045] Referring to FIG. 3, AP 1 (301) operates in the first link, AP 2 (303) operates in the second link, and AP 3 (305) operates in the third link. Here, the link may represent a specific operating frequency of a wireless LAN network. The operating frequencies of the first link to the third link may be different from each other or may be the same. When the operating frequencies of AP 1 (301) to AP 3 (305) are the same, the OBSS of AP 1 (301) is the BSSs of AP 2 (303) and AP 3 (305), the OBSS of AP 2 (303) is the BSSs of AP 1 (301) and AP 3 (305), and the OBSS of AP 3 (305) is the BSSs of AP 1 (301) and AP 2 (303). AP 1 (301) to AP 3 (305) can synchronize TSF (time synchronization function) with each other. That is, AP 1 (301) to AP 3 (303) have the same TSF value at the same time. Synchronizing TSF may be for synchronizing cooperative transmission schedules (e.g., R-TWT SP) of AP 1 (301) to AP 3 (305) with each other. In addition, when the operating frequencies of AP 1 (301) to AP 3 (305) are the same, synchronizing TSF may be for synchronizing cooperative transmission schedules (e.g., R-TWT SP) of OBSS with each other. AP 1 (301) to AP 3 (305) may perform schedule negotiation (310) for cooperative transmission. The schedule negotiation (310) for cooperative transmission may be SST (subchannel selective transmission) TWT (target wake time) negotiation, a type of TWT negotiation other than SST, or transmission interval negotiation. SST TWT negotiation is a negotiation that establishes whether communication will proceed on another channel during the TWT interval.SST TWT negotiation may be, for example, a negotiation in which AP 2 (303) operating on a second link and AP 3 (305) operating on a third link set to operate on a first link within a TWT SP. As a result of the schedule negotiation (310) for the cooperative transmission, AP 1 (301) to AP 3 (305) may set a cooperative transmission period. The cooperative transmission period may be a TWT SP (service period). AP 1 (301) may be a master AP leading the cooperative transmission schedule negotiation (310). AP 1 (301) to AP 3 (305) communicate at the operating frequency (i.e., the first link or the first channel) of AP 1 (301) within the cooperative transmission period. That is, AP 2 (303) and AP 3 (305) must change their operating frequencies (i.e., links or channels). Since AP 1 (301) to AP 3 (305) have synchronized the TSF, the start time of the cooperative transmission period of AP 1 (301) to AP 3 (305) can be the same, and AP 1 (301) to AP 3 (305) can know exactly when the cooperative transmission period starts.

[0046] AP 1 (301) to AP 3 (305) can transmit frames (321, 323, 325) indicating a cooperative transmission section before the start of the cooperative transmission section. The frames (321, 323, 325) indicating the cooperative transmission section can be frames in various forms, for example, can be beacon frames. The frames (321, 323, 325) indicating the cooperative transmission section can include information indicating the cooperative transmission section (e.g., TWT information, TWT element) and information indicating a frequency (e.g., link ID, channel number, information that can indicate a specific operating frequency). The frames (323, 325) indicating the cooperative transmission section transmitted by AP 2 (303) and AP 3 (305) may further include information (e.g., information on the section in which direct communication can be performed, information on STAs that can participate in direct communication) that instructs STAs connected to AP 2 (303) and AP 3 (305) to perform direct communication (e.g., operation of communicating between STAs without going through the AP, 350) within the cooperative transmission section. In the present embodiment, the information that instructs the performance of the direct communication (350) is referred to as a direct communication instruction. The direct communication instruction may be included together with the information indicating the cooperative transmission section (i.e., TWT element, TWT information). The direct communication instruction instructs the AP to perform direct communication (350) within the unavailable section, and transmission from the STA to the AP is prohibited during the corresponding period. The frames (321, 323, 325) indicating the cooperative transmission section may include TWT information (e.g., information indicating R-TWT SP) that requires termination of transmission (e.g., termination of TXOP (transmit opportunity)) prior to the cooperative transmission section (e.g., TWT SP, R-TWT SP, SP). That is, the information indicating the cooperative transmission section and frequency may indicate R-TWT SP.The period during which direct communication is performed within an AP's unavailable interval may be referred to as a direct communication interval. The channel switching delay, which is the time required for the AP to change to a frequency that uses the cooperative transmission, may be included in the direct communication interval. The channel switching delay may be applied to both the time when the operating frequency changes to a frequency for cooperative transmission and the time when the frequency for cooperative transmission changes to the current operating frequency. The channel switching delay may vary for each AP, and the APs may perform multi-AP cooperative transmission from the same time after the channel switching delay. If the channel switching delay times of each AP are different, the length of the transmission prohibition interval may vary. For example, if the channel change delay time of AP 2 (303) is longer than that of AP 1 (301), and if the channel change delay time of AP 3 (305) is longer than that of AP 2 (303), then considering the channel change delay times of each AP, the length of the transmission prohibition period of AP 3 (305) may be the longest, the length of the transmission prohibition period of AP 1 (301) may be the shortest, and the length of the transmission prohibition period of AP 2 (303) may be longer than the length of the transmission prohibition period of AP 1 (301) and shorter than the length of the transmission prohibition period of AP 3 (305). The channel change delay time may be a predefined value known to all STAs in the BSS. Alternatively, the AP may not include the channel change delay time in the direct communication period. STAs can receive frames (323, 325) indicating a cooperative transmission interval, and upon receiving a direct communication instruction contained within the frame indicating a cooperative transmission interval, they can calculate and determine that the AP is unavailable from the indicated time to a time period before the AP's channel change delay time. The STA does not transmit to the AP from the calculated time.When STAs receive a frame (321, 323, 325) indicating a cooperative transmission interval, they can terminate transmission (e.g., terminate TXOP) before the start of the transmission prohibition interval. When the operating frequencies of AP 1 (301) to AP 3 (305) are the same and STAs receive a frame (323, 325) indicating a cooperative transmission section of an OBSS (i.e., AP 2 (303) and AP 3 (305) when the STA is connected to AP 1 (301), AP 1 (301) and AP 3 (305) when the STA is connected to AP 2 (303), and AP 1 (301) and AP 2 (303) when the STA is connected to AP 3 (305)), transmission can be terminated before the start of the direct communication section included in the frame (323, 325) indicating the cooperative transmission section of the OBSS. Additionally, frames (323, 325) indicating cooperative transmission sections transmitted from AP 2 (303) and AP 3 (305) may further include an indicator that transmission is prohibited during the section in which the AP is unavailable (e.g., information indicating a section in which transmission is prohibited, a quiet element). The indicator that transmission is prohibited during the section in which the AP is unavailable is information that instructs STAs to set a NAV during the section in which the AP is unavailable. Within the section in which the AP is unavailable, STAs that recognize the direct communication indication and wish to perform direct communication (350) may ignore the indication that transmission is prohibited (e.g., without setting a NAV) and perform direct communication (350) (e.g., performing a channel access operation, performing a frame transmission). STAs that do not perform direct communication (350) or do not recognize the direct communication indication set a NAV during the section in which the AP is unavailable by the indication that transmission is prohibited, and do not perform a channel access operation and a frame transmission operation. Within the section where the AP is unavailable, STAs perform direct communication (350), which is communication that does not go through the AP.The frames (323, 325) indicating the cooperative transmission section transmitted by AP 2 (303) and AP 3 (305) may further include information (e.g., link ID, channel number, information capable of indicating a specific operating frequency) for indicating an operating frequency to STAs that wish to participate in the cooperative transmission section among STAs connected to AP 2 (303) and AP 3 (305). At the start of the cooperative transmission section, AP 2 (303) and AP 3 (305) may operate on the first link, and AP 1 (301) to AP 3 (305) perform cooperative communication. At the start of the cooperative transmission section, STAs that wish to participate in the cooperative transmission section among STAs connected to AP 2 (303) and AP 3 (305) may operate on the frequency for indicating the cooperative transmission, for example, the first link. STAs wishing to participate in the above cooperative transmission section may need to perform a negotiation procedure with AP 2 (303) and AP 3 (305), and the negotiation procedure may be a TWT negotiation (e.g., broadcast TWT negotiation, individual TWT negotiation) procedure. STAs connected to AP 2 (303) and AP 3 (305) that do not participate in the cooperative transmission section perform communication (e.g., direct communication, peer-to-peer communication) between STAs using the original operating frequency within the cooperative transmission section based on information instructing direct communication (350) transmitted by AP 2 (303) and AP 3 (305). STAs that do not participate in the above cooperative transmission section do not transmit frames to AP 2 (303) and AP 3 (305) within the cooperative transmission section. STAs that do not participate in the above cooperative transmission section must select a new backoff counter (e.g., EDCA backoff counter) when the cooperative transmission section and the direct communication section are terminated.STAs that do not participate in the cooperative transmission period may consider that there is no data (e.g., data packet, MSDU, MPDU) destined for AP 2 (303) and AP 3 (305) in the queue during the cooperative transmission period. Since AP 2 (303) and AP 3 (305) operate at an operating frequency (e.g., the first link) different from the original operating frequency within the cooperative transmission period and did not perform a reception operation (i.e., a reception operation including a channel sensing operation (e.g., a clear channel assessment (CCA))) at the different operating frequency before the cooperative transmission period, medium synchronization may be lost. In addition, if the cooperative transmission period is longer than a specific length, medium synchronization may be lost if the operating frequency is changed to the original operating frequency after the cooperative transmission period. Therefore, AP 2 (303) and AP 3 (305) must set the MediumSyncDelay timer, which is a timer for recovering medium synchronization immediately after the start of operation on the first link, for example, the frequency for cooperative transmission at the start time of the cooperative transmission section, and frame transmission may be restricted while the MediumSyncDelay timer is operating. Restricting frame transmission while the MediumSyncDelay timer is operating may mean that an RTS frame must be transmitted before frame transmission or a CCA (clear channel assessment) operation is performed without frame transmission. The MediumSyncDelay timer is cleared when a frame is normally received (e.g., the MPDU is normally received without error) and successfully decoded. AP 1 (301) does not change its operating frequency and can immediately transmit a frame within the cooperative transmission section.Accordingly, AP 1 (301) can transmit an 'initial frame' (e.g., trigger frame, 330) to release the MediumSyncDelay timer of AP 2 (303) and AP 3 (305) at the starting point of the cooperative transmission section and to restore medium synchronization. The initial frame can be any type of frame that AP 2 (303) and AP 3 (305) can decode and set the NAV correctly, not just the trigger frame. Within the cooperative transmission frequency, i.e., the cooperative transmission section of the first link, AP 1 (301) to AP 3 (305) perform cooperative transmission. For example, AP 1 (301) to AP 3 (305) can perform a CO-OFDMA (coordinated orthogonal frequency division multiple access) operation or a CO-SR (coordinated spatial reuse) operation to transmit the frame (340) to STAs on the first link. At the end of the cooperative transmission section, AP 2 (303) and AP 3 (305) operate again on the second link and the third link.

[0047]

[0048] Figure 4 illustrates a third embodiment of a multi-AP cooperative transmission method.

[0049] Referring to FIG. 4, AP 1 (401) operates in the first link, AP 2 (403) in the second link, and AP 3 (405) in the third link. The links may represent specific operating frequencies of a wireless LAN network. The operating frequencies of the first to third links may be different from each other or may be the same. When the operating frequencies of AP 1 (401) to AP 3 (405) are the same, the OBSS of AP 1 (401) is the BSSs of AP 2 (403) and AP 3 (405), the OBSS of AP 2 (403) is the BSSs of AP 1 (401) and AP 3 (405), and the OBSS of AP 3 (405) is the BSSs of AP 1 (401) and AP 2 (403). AP 1 (401) to AP 3 (405) can synchronize TSF (time synchronization function) with each other. That is, AP 1 (401) to AP 3 (405) have the same TSF value at the same time. Synchronizing TSF may be for synchronizing cooperative transmission schedules (e.g., R-TWT SP) of AP 1 (401) to AP 3 (405) with each other. In addition, when the operating frequencies of AP 1 (401) to AP 3 (405) are the same, synchronizing TSF may be for synchronizing cooperative transmission schedules (e.g., R-TWT SP) of OBSS with each other. AP 1 (401) to AP 3 (405) may perform schedule negotiation (410) for cooperative transmission. The schedule negotiation (410) for cooperative transmission may be SST (subchannel selective transmission) TWT (target wake time) negotiation, or a type of TWT negotiation other than SST, or transmission interval negotiation. SST TWT negotiation is a negotiation that establishes whether communication will proceed on another channel during the TWT interval.SST TWT negotiation may be, for example, a negotiation in which AP 2 (403) operating on a second link and AP 3 (405) operating on a third link set to operate on a first link within a TWT SP. As a result of the schedule negotiation (410) for the cooperative transmission, AP 1 (401) to AP 3 (405) may set a cooperative transmission period. The cooperative transmission period may be a TWT SP (service period). AP 1 (401) may be a master AP leading the cooperative transmission schedule negotiation (410), and AP 1 (401) to AP 3 (405) communicate at the operating frequency (i.e., the first link or the first channel) of AP 1 (401) within the cooperative transmission period. That is, AP 2 (403) and AP 3 (405) must change their operating frequencies (i.e., links or channels). Since AP 1 (401) to AP 3 (405) have synchronized the TSF, the starting point of the cooperative transmission period can be the same for AP 1 (401) to AP 3 (405), and AP 1 (401) to AP 3 (405) can know exactly when the cooperative transmission period starts.

[0050] AP 1 (401) to AP 3 (405) can transmit frames (421, 423, 425) indicating a cooperative transmission section before the cooperative transmission section starts. The frames (421, 423, 425) indicating a cooperative transmission section can be frames in various forms. For example, the frames (421, 423, 425) indicating a cooperative transmission section can be beacon frames. The frames (421, 423, 425) indicating a cooperative transmission section can include cooperative transmission section information (e.g., TWT information, TWT element) and frequency information (e.g., link ID, channel number, information that can indicate a specific operating frequency). The frames (423, 425) indicating the cooperative transmission section transmitted by AP 2 (403) and AP 3 (405) may further include information (e.g., link ID, channel number, information capable of indicating a specific operating frequency) for indicating an operating frequency to STAs that wish to participate in the cooperative transmission section among STAs connected to AP 2 (403) and AP 3 (405). Before the cooperative transmission section starts, AP 2 (403) and AP 3 (405) may transmit a frame (430) for indicating the performance of direct communication (e.g., an operation in which STAs communicate with each other without transmitting data to the AP) in the second link and the third link. The frame (430) for indicating the performance of direct communication may indicate the section in which direct communication is performed (i.e., the direct communication section) and STAs that can communicate in the direct communication section. Alternatively, the indication for the performance of direct communication may be included in the information for indicating the cooperative transmission section. For example, a TWT element may be instructed to direct communication of an STA. In this embodiment, an instruction to perform direct communication included in a frame (430) or information indicating a cooperative transmission section instructing direct communication is referred to as a direct communication instruction.The above direct communication instruction instructs the AP to perform direct communication within the unavailable section, and transmission to the AP may be prohibited during the corresponding period. The frames (421, 423, 425) indicating the cooperative transmission section may include TWT information (e.g., information indicating R-TWT SP) that requires termination of transmission (e.g., termination of TXOP (transmit opportunity)) prior to the cooperative transmission section (e.g., TWT SP, R-TWT SP, SP). That is, information indicating the cooperative transmission section and frequency may indicate R-TWT SP. The period during which direct communication is performed within the unavailable section of the AP may be referred to as a direct communication section. A channel switching delay, which is the time for the AP to change to a frequency using the cooperative transmission, may be included in the direct communication section. The channel switching delay may be applied to both the time when the operating frequency changes to the frequency for cooperative transmission and the time when the frequency for cooperative transmission changes to the current operating frequency. The channel change delay time may be different for each AP, and the APs can perform multi-AP cooperative transmission from the same point in time after the channel change delay time. If the channel change delay time of each AP is different, the length of the transmission prohibition period may be different. For example, if the channel change delay time of AP 2 (403) is longer than that of AP 1 (401), and if the channel change delay time of AP 3 (405) is longer than that of AP 2 (403), considering the channel change delay times of each AP, the length of the transmission prohibition period of AP 3 (405) may be the longest, the length of the transmission prohibition period of AP 1 (401) may be the shortest, and the length of the transmission prohibition period of AP 2 (403) may be longer than the length of the transmission prohibition period of AP 1 (401) and shorter than the length of the transmission prohibition period of AP 3 (405). The channel change delay time may be a predefined value known to all STAs in the BSS.Alternatively, the AP may not include the channel change delay time in the direct communication interval. STAs may receive frames (423, 425) indicating a cooperative transmission interval, and upon receiving a direct communication instruction contained within the frames (423, 425) indicating a cooperative transmission interval, STAs may calculate that the AP is unavailable from a time period before the indicated time, which is the AP's channel change delay time, and may not transmit to the AP from this time. STAs may terminate transmission (e.g., terminate TXOP) before the start of the transmission prohibition interval upon receiving frames (423, 425) indicating a cooperative transmission interval. When the operating frequencies of AP 1 (401) to AP 3 (405) are the same, and STAs receive a frame (423, 425) indicating a cooperative transmission section of an OBSS (i.e., AP 2 (403) and AP 3 (405) when the STA is connected to AP 1 (401), AP 1 (401) and AP 3 (405) when the STA is connected to AP 2 (403), and AP 1 (401) and AP 2 (403) when the STA is connected to AP 3 (405)), transmission can be terminated before the start of the direct communication section included in the frame (423, 425) indicating the cooperative transmission section of the OBSS. Within the section where the AP is unavailable, STAs perform direct communication, which is communication that does not go through the AP. The frame (430) instructing the execution of direct communication may be a MU-RTS (multi user-request to send) TXS (TXOP sharing) trigger frame, or various types of frames capable of instructing the direct communication section. The frame (430) instructing the execution of direct communication may set the direct communication section to be equal to or longer than the cooperative communication section.At the start of the cooperative transmission section, AP 2 (403) and AP 3 (405) may operate at a frequency that indicates the cooperative transmission, for example, the first link, and AP 1 (401) to AP 3 (405) perform cooperative communication using the frequency at which the cooperative transmission is performed. Among the STAs connected to AP 2 (403) and AP 3 (405), STAs that wish to participate in the cooperative transmission section may operate at a frequency at which the cooperative transmission is performed, for example, the first link, at the start of the cooperative transmission section. STAs that wish to participate in the cooperative transmission section may need to perform a negotiation procedure with AP 2 (403) and AP 3 (405), and the negotiation procedure may be a TWT negotiation procedure (e.g., broadcast TWT negotiation, individual TWT negotiation). Among the STAs connected to AP 2 (403) and AP 3 (405), STAs that do not participate in the cooperative transmission section perform direct communication according to the frames that instruct direct communication to be performed transmitted by AP 2 (403) and AP 3 (405). STAs that do not participate in the cooperative transmission section must select a new backoff counter (e.g., EDCA backoff counter) when the cooperative transmission section and direct communication section are terminated. STAs that do not participate in the cooperative transmission section may regard data (e.g., data packets, MSDUs, MPDUs) destined for AP 2 (403) and AP 3 (405) that exist in the queue during the cooperative transmission section as not existing. STAs that do not participate in the cooperative transmission section do not transmit frames to AP 2 (403) and AP 3 (405) within the cooperative transmission section.Within the cooperative transmission period, AP 2 (403) and AP 3 (405) may lose medium synchronization because they operate at an operating frequency (e.g., the first link) different from their original operating frequency and have not performed a reception operation (i.e., a reception operation including a channel sensing operation (e.g., a clear channel assessment (CCA))) at the different operating frequency before the cooperative transmission period. In addition, if the cooperative transmission period is longer than a specific length, medium synchronization may be lost if they change back to the original operating frequency after the cooperative transmission period. Therefore, AP 2 (403) and AP 3 (405) must set a MediumSyncDelay timer, which is a timer for restoring medium synchronization, immediately after they start operating at a frequency for cooperative transmission, e.g., the first link, at the start time of the cooperative transmission period, and frame transmission may be restricted while the MediumSyncDelay timer is operating. Restricting frame transmission while the MediumSyncDelay timer is running may mean that an RTS frame must be transmitted if the channel energy falls below a certain level before transmitting a data frame, or that a CCA (clear channel assessment) operation may be performed without transmitting the frame. The MediumSyncDelay timer is cleared when a frame is normally received (e.g., the MPDU is normally received without error) and successfully decoded. AP 1 (401) does not change its operating frequency and can immediately transmit frames within the cooperative transmission period. Therefore, AP 1 (401) can clear the MediumSyncDelay timers of AP 2 (403) and AP 3 (405) at the starting point of the cooperative transmission period and transmit an 'initial frame' (e.g., trigger frame, 440) to restore medium synchronization.The initial frame includes all kinds of frames that AP 2 (403) and AP 3 (405) can decode and correctly set the NAV, not just the trigger frame. Within the cooperative transmission frequency, i.e., the cooperative transmission period of the first link, AP 1 (401) to AP 3 (405) perform cooperative transmission. For example, AP 1 (401) to AP 3 (405) may perform a coordinated orthogonal frequency division multiple access (CO-OFDMA) operation or a coordinated spatial reuse (CO-SR) operation to transmit the frame (450) to STAs on the first link. At the end of the cooperative transmission period, AP 2 (403) and AP 3 (405) operate on the second link and the third link again. Since AP 2 (403) and AP 3 (405) operate on the first link during the cooperative transmission period, AP 2 (403) and AP 3 (405) must set the MediumSyncDelay timer, which is a timer for losing medium synchronization in the second and third links, which are the original operating frequencies, and recovering medium synchronization. Due to the setting of the MediumSyncDelay timer, the frame transmission operations of AP 2 (403) and AP 3 (405) may be restricted. STAs capable of performing direct communication indicated in the frames indicating direct communication transmitted by AP 2 (403) and AP 3 (405) transmit frames (470) simultaneously at a specific time point after the end of the cooperative transmission period (e.g., the end of the cooperative transmission period, a predetermined time point before the end of the direct communication period). The frames (470) transmitted simultaneously may be frames for recovering medium synchronization. The frame (470) transmitted simultaneously by STAs may be an S-CTS (simultaneous clear to send) frame.When the frame (470) transmitted simultaneously by STAs is an S-CTS frame, the SCRAMBLER_INITIAL_VALUE included in the TXVECTOR parameter present in the PHY preamble of the S-CTS frame is equal to the SCRAMBLER_INITIAL_VALUE of the RXVECTOR parameter obtained by receiving from the PHY preamble of the MU-RTS TXS trigger frame. Alternatively, the frame (430) indicating direct communication transmitted by AP 2 (403) and AP 3 (405) may indicate one of the STAs connected to AP 2 (403) and AP 3 (405) (e.g., indicating a specific AID, indicating a specific MAC address). Each STA instructed by AP 2 (403) and AP 3 (405) performs direct communication within the direct communication section, and after the cooperative transmission section ends, transmits a frame (e.g., a CTS frame, a QoS Null frame) to AP 2 (403) and AP 3 (405) to release the MediumSyncDelay timer of AP 2 (403) and AP 3 (405) and restore medium synchronization. The frame for restoring medium synchronization may be a simultaneously transmitted frame (470). With the above frame transmission operation, AP 2 (403) and AP 3 (405) can restore medium synchronization and release the MediumSyncDelay timer. For frame transmission to release the MediumSyncDelay timer of AP 2 (403) and AP 3 (405), the end time of the direct communication section may be later than that of the cooperative transmission section. For example, the end point of a direct communication segment may be at least a certain frame length later than the cooperative transmission segment (e.g., a CTS frame, a QoS Null frame).

[0051]

[0052] Figure 5 illustrates a first embodiment of a multi-AP frequency change communication method.

[0053] Referring to FIG. 5, AP 1 (501) to AP 3 (505) operate at the same operating frequency. AP 1 (501) to AP 3 (505) can exchange TWT (e.g., individual TWT, broadcast TWT, restricted TWT) schedules set within each AP. As a result of the TWT schedule exchange, AP 1 (501) to AP 3 (505) can know each other's TWT schedules (e.g., TWT SP). The TWT schedules of AP 1 (501) to AP 3 (505) may overlap in time. For example, TWT SP #1, TWT SP #2, and TWT SP #3, which are TWT schedules of AP 1 (501) to AP 3 (505), may completely overlap in time or partially overlap. AP 1 (501) to AP 3 (505) perform a negotiation process (510) to separate the frequencies on which the TWT schedules operate, and negotiate frequencies to be used in overlapping TWT schedules. As a result of the negotiation (510), AP 1 (501) to AP 3 (505) can use different frequencies in the overlapping TWT schedules. For example, TWT SP #1, which is the TWT schedule of AP 1 (501), can be negotiated to use Channel 1, TWT SP #2, which is the TWT schedule of AP 2 (503), can be negotiated to use Channel 2, and TWT SP #3, which is the TWT schedule of AP 3 (505) can be negotiated to use Channel 3. AP 1 (501) to AP 3 (505) can transmit frames (e.g., frames including SST TWT information, TWT information, and TWT elements, 521, 523, 525) indicating frequencies to be used in the TWT schedules. Frames (521, 523, 525) that indicate the frequency to be used in the TWT schedule can change the existing set TWT schedule or set a new TWT schedule.The communication frequency of the TWT schedule indicated by the frames (521, 523, 525) indicating the frequency to be used in the TWT schedule transmitted by each of AP 1 (501) to AP 3 (505) may indicate the frequency negotiated by AP 1 (501) to AP 3 (505). TWT SP #1 of AP 1 (501) is performed on Channel 1, TWT SP #2 of AP 2 (503) is performed on Channel 2, and TWT SP #3 of AP 3 (505) is performed on Channel 3, and the TWT schedules of AP 1 (501) to AP 3 (505) are separated in frequency so that TWT operations can be performed without interference with each other.

[0054]

[0055] Below, the negotiation and communication procedures for cooperative transmission are described. The negotiation and communication procedures for cooperative transmission can be performed by multiple APs and STAs connected to each AP. The multiple APs may communicate with the STA using the same frequency. Alternatively, the multiple APs may communicate with the STA using different frequencies. Cooperative transmission may refer to an operation in which multiple APs transmit data or frames using the same frequency or link.

[0056]

[0057] FIG. 6 illustrates a flowchart of negotiation and communication procedures for cooperative transmission according to one embodiment of the present disclosure. The procedure illustrated in FIG. 6 is performed by one of multiple APs. The AP of the present disclosure may be a master AP. The master AP (e.g., AP 1 (201) of FIG. 2 ) may be the AP that takes the lead in negotiation. Alternatively, the AP of the present disclosure may be an AP other than the master AP (e.g., AP 2 (203) of FIG. 2 ).

[0058] Referring to FIG. 6, in step S601, the AP negotiates with at least one other AP (e.g., schedule negotiation (210) for cooperative transmission in FIG. 2). The AP may negotiate with other APs for cooperative transmission. The negotiation may be performed to schedule a cooperative transmission interval. Here, the cooperative transmission interval refers to a time interval during which cooperative transmission is performed. For example, the negotiation may include SST TWT negotiation, non-SST TWT negotiation, or transmission interval negotiation. During the negotiation process, the AP may synchronize the TSF to synchronize the cooperative transmission schedule or cooperative transmission interval.

[0059] In step S603, the AP transmits information for cooperation based on the negotiation result. The AP can transmit the information for cooperation to the STA. The information for cooperation can be generated based on the negotiation result. The information for cooperation can be carried by a beacon frame (e.g., frame (221) indicating a cooperative transmission interval in FIG. 2). The information for cooperation includes information about the cooperative transmission interval, information about the frequency, a transmission prohibition instruction, or information about direct communication. Alternatively, the information about direct communication can be carried by a frame different from the information for cooperation (e.g., frame (430) indicating the performance of direct communication in FIG. 4). For example, the information about the cooperative transmission interval includes at least one of TWT information, a channel change delay time, or a TWT element. The information about the frequency includes, for example, at least one of a link ID, a channel number, or frequency information. The transmission prohibition instruction can include at least one of information about the transmission prohibition interval or information about the STA whose transmission is prohibited. Information about direct communication includes at least one of information about whether direct communication is taking place, the section in which direct communication is performed, or the STA participating in direct communication.

[0060] In step S605, the AP performs cooperative transmission. Cooperative transmission may refer to an operation of transmitting a frame (e.g., frame (240) of FIG. 2) to STAs. Cooperative transmission may include an operation of transmitting a frame based on a CO-OFDMA operation or a CO-SR operation. To perform cooperative transmission, the AP changes its operating frequency or operating link based on information for cooperation. The primary AP may transmit an initial frame (e.g., initial frame (230) of FIG. 2) to another AP to perform cooperative transmission. Cooperative transmission may be performed within a cooperative transmission period. Within the cooperative transmission period, the AP may transmit a frame based on information for cooperation. The frame may be transmitted to an STA participating in cooperative transmission. The STA participating in cooperative transmission may be an STA that has performed a negotiation procedure with the AP. The negotiation procedure between the AP and the STA may be performed by an AP other than the primary AP. The negotiation procedure between the AP and the STA may be performed before the cooperative transmission period.

[0061]

[0062] FIG. 7 illustrates a flowchart of a communication procedure for cooperative transmission according to one embodiment of the present disclosure. FIG. 7 illustrates a procedure performed by an STA. The STA of FIG. 7 may be an STA connected to an AP. For example, the STA of the present disclosure may be an STA connected to a primary AP (e.g., AP 1 (201) of FIG. 2 ) or an AP other than the primary AP (e.g., AP 2 (203) of FIG. 2 ).

[0063] Referring to FIG. 7, in step S701, the STA receives information for cooperation. The information for cooperation may be information generated based on negotiations between APs (e.g., schedule negotiation (210) for cooperative transmission in FIG. 2). The information for cooperation includes information on cooperative transmission intervals, information on frequencies, a transmission prohibition instruction, or information on direct communication. At least some of the information for cooperation may be carried by at least one frame. For example, the information for cooperation may be carried by a beacon frame (e.g., frame (221) indicating a cooperative transmission interval in FIG. 2). As another example, the information for cooperation may be carried by a beacon frame and an MU-RTS frame (e.g., frame (430) indicating direct communication in FIG. 4). For example, among the information for cooperation, information on direct communication may be carried by the MU-RTS frame, and the remaining information may be carried by the beacon frame. For example, information about a cooperative transmission interval includes at least one of TWT information, a channel change delay time, or a TWT element. Information about a frequency includes, for example, at least one of a link ID, a channel number, or frequency information. A transmission prohibition instruction may include at least one of information about a transmission prohibition interval or an STA whose transmission is prohibited. Information about direct communication includes at least one of information about whether direct communication is performed, an interval in which direct communication is performed, or an STA participating in direct communication.

[0064] In step S703, the STA may set a transmission prohibition interval (e.g., NAV (251) in FIG. 3) based on information for cooperation. The transmission prohibition interval refers to an interval in which frame transmission is prohibited to the AP. For example, the transmission prohibition interval may include a NAV or a silence interval. The transmission prohibition interval may be set based on a transmission prohibition instruction included in the information for cooperation. Alternatively, the STA may set the transmission prohibition interval based on information about the cooperative transmission interval and a channel change delay time. The STA may terminate frame transmission before the transmission prohibition interval. For example, the STA may terminate frame transmission by terminating TXOP before the transmission prohibition interval. If the information for cooperation includes information about direct communication, the STA may additionally set a direct communication interval (e.g., the direct communication (350) interval in FIG. 3). The direct communication interval is an interval in which the STA can transmit frames without going through the AP. If the direct communication interval is set, the transmission prohibition interval may not be set. In other words, a direct communication section can be set instead of a transmission prohibition section.

[0065] In step S705, the STA may transmit a frame based on information for cooperation. If the STA has established a direct communication section, the STA may transmit a frame to another STA. The STA may transmit a frame to another STA within the direct communication section. If the STA has not established a direct communication section, the STA may transmit a frame after the cooperative transmission section ends. After the cooperative transmission section ends, the STA with and without the direct communication section established may transmit a frame (e.g., a frame (470) transmitted simultaneously by the STAs in FIG. 4) to release a timer for medium synchronization recovery of the AP. For example, the STA may transmit an S-CTS frame or a QoS Null frame to the connected AP.

[0066]

[0067]

[0068] 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.

[0069] 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.

[0070] 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.

[0071] The present disclosure can be used in devices and recording media in a wireless LAN system.

Claims

1. In the operation method of AP (access point) in a wireless LAN system, A step of negotiating for joint transmission with at least one other AP; A step of transmitting information for cooperative transmission based on the results of the negotiation; and Including a step of transmitting a frame based on the result of the above negotiation, The result of the above negotiation includes the frequency for the above cooperative transmission, The above frame is transmitted using a frequency for the cooperative transmission.

2. In paragraph 1, A method in which the information for the cooperative transmission includes at least one of information on the section of the cooperative transmission, information on the frequency for the cooperative transmission, information on a transmission prohibited section, or direct communication instruction information.

3. In paragraph 1, The step of transmitting the above frame is: Further comprising a step of changing the operating frequency to a frequency for the above cooperative transmission, The above frame is transmitted within the interval of the cooperative transmission established by the above negotiation.

4. In paragraph 3, The above cooperative transmission section is a method including a TWT SP (service period), an R-TWT (restricted TWT) SP or SP.

5. In paragraph 1, A method further comprising the step of synchronizing a time synchronization function (TSF) for the above cooperative transmission.

6. In paragraph 1, The above frame is transmitted based on CO-OFDMA (coordinated orthogonal frequency division multiple access) or CO-SR (coordinated spatial reuse).

7. In paragraph 1, A method wherein the above frame includes an initial frame for restoring media synchronization of the other AP.

8. In paragraph 1, A method further comprising a step of performing negotiation with an STA participating in the cooperative transmission for the cooperative transmission.

9. In paragraph 1, A method wherein the above negotiation includes at least one of SST (subchannel selective transmission) TWT (target wake time) negotiation, TWT negotiation other than the SST, or transmission interval negotiation.

10. In the operation method of STA (station) in a wireless LAN system, A step of receiving information for joint transmission from a connected AP; Including a step of performing at least one of a transmission prohibition operation, a frame reception operation, or a direct communication operation in a section of the cooperative transmission based on the information for the cooperative transmission, A method wherein the information for the cooperative transmission includes at least one of information on the interval of the cooperative transmission or information on the frequency for the cooperative transmission.

11. In Article 10, A method wherein the above transmission prohibition operation includes an operation of setting a transmission prohibition period including an interval of the cooperative transmission and an operation of ignoring a frame scheduled to be transmitted to the connected AP within the transmission prohibition period.

12. In paragraph 10, A method wherein the above frame receiving operation includes an operation of receiving a frame using a frequency for the cooperative transmission within the interval of the cooperative transmission.

13. In paragraph 10, A method wherein the above direct communication operation includes an operation of communicating with another STA within the interval of the cooperative transmission.

14. In paragraph 10, A method in which the information for the cooperative transmission includes at least one of information on the section of the cooperative transmission, information on the frequency for the cooperative transmission, information on a transmission prohibited section, or direct communication instruction information.

15. In paragraph 10, A method further comprising the step of transmitting a frame for media synchronization of the connected AP to the connected AP after the above cooperative transmission section ends.

16. In paragraph 10, A method further comprising the step of negotiating with the connected AP for receiving the frame.

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, Negotiate with other APs for joint transmission, Transmit information for cooperative transmission based on the results of the above negotiation, It is configured to transmit frames based on the results of the above negotiation, The results of the above negotiations include the frequencies for the above cooperative transmissions, The above frame is transmitted by the AP using the frequency for the cooperative transmission.

18. In a wireless LAN system, at STA (station), Transmitter and receiver; and Including a processor connected to the above transceiver, The above processor, Receive information for joint transmission from the connected AP, Based on the information for the cooperative transmission, it is configured to perform at least one of a transmission prohibition operation, a frame reception operation, or a direct communication operation in the section of the cooperative transmission. A method wherein the information for the cooperative transmission includes at least one of information on the interval of the cooperative transmission or information on the frequency for the cooperative transmission.

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