Method and apparatus for measuring channel based on cooperation in wireless local area network system

Abstract

The purpose of the present invention is to measure a channel on the basis of cooperation within a wireless LAN network. According to an embodiment of the present invention, a method for operating a station (STA) in a wireless LAN system comprises the steps of: receiving information on a time at which a frame is transmitted from a first AP; receiving a scan response message generated based on information on a time at which the frame is transmitted; receiving a frame from the second AP based on the scan response message; measuring a channel based on a frame received from the second AP; and transmitting the measurement report message to the first AP, in which the information on the time at which the frame is transmitted includes the time at which the frame is transmitted by at least one AP including the second AP.

Description

Technical Field

[0001] The following description relates to a wireless local area network (WLAN) system, and more specifically, to a method and apparatus for a WLAN terminal to measure a channel based on cooperation within a WLAN system. Background Technology

[0002] Recently, with the widespread adoption of mobile devices, wireless LAN technology, which provides fast wireless communication services to mobile devices, has attracted attention. Wireless LAN technology is a technology that uses wireless communication to enable mobile devices (such as smartphones, tablets, laptops, portable multimedia players, embedded devices, etc.) to wirelessly access the internet.

[0003] As applications requiring higher throughput and / or real-time transmission emerge, extended frequency bandwidth and / or efficient retransmission operations can be supported in wireless LANs. Furthermore, simultaneous use of multiple channels or multiple links can be supported.

[0004] On the other hand, the techniques described in the background section are written to improve the understanding of the background of the present invention, and may include content that is not yet known to those skilled in the art to which the present invention pertains. Summary of the Invention

[0005] Technical issues This invention aims to provide a method and apparatus for a terminal to change the association between multiple access points in a wireless local area network system.

[0006] This invention aims to provide a method and apparatus for a terminal to perform efficient roaming in a wireless local area network system.

[0007] This invention aims to provide a method and apparatus for rapidly transmitting data stored in a terminal and requiring low latency in a wireless local area network system.

[0008] This invention aims to provide a method and apparatus for a terminal to change the operating link used for channel scanning in a wireless local area network system.

[0009] This invention aims to provide a method and apparatus for reducing latency in the channel scanning process in a wireless local area network system.

[0010] This invention aims to provide a method and apparatus for multiple access points (APs) to collaboratively support channel access for wireless terminals in a wireless local area network (WLAN) system.

[0011] The technical objectives to be achieved in this invention are not limited to those described above, and those skilled in the art who apply the technical configuration of this invention may consider other technical objectives not mentioned herein from the embodiments of the invention described below.

[0012] Technical solution According to an embodiment of the present invention, a method for use as an operator station (STA) in a wireless local area network includes: receiving information about the time of transmission of a frame from a first access point (AP); receiving a scan response message generated based on the information about the time of transmission of the frame; receiving a frame from a second AP based on the scan response message; measuring a channel based on the frame received from the second AP; and sending a measurement report message to the first AP, wherein the information about the time of transmission of the frame includes the time when the frame was transmitted by at least one AP including the second AP.

[0013] According to an embodiment of the present invention, a method for operating a first access point (AP) in a wireless local area network includes: obtaining information about the time of transmission of a frame; sending the information about the time of transmission of the frame to a station (STA); sending a scan response message generated based on the information about the time of transmission of the frame; and receiving a measurement report message from the STA, wherein the information about the time of transmission of the frame includes information about the time when the frame was transmitted by at least one AP, and the measurement report message includes channel measurement results for a second AP, which is one of the at least one AP.

[0014] According to an embodiment of the present invention, a station (STA) in a wireless local area network includes a transceiver and a processor connected to the transceiver, wherein the processor is configured to: receive information about the time of transmission of a frame from a first access point (AP); receive a scan response message generated based on the information about the time of transmission of the frame; receive a frame from a second AP based on the scan response message; measure a channel based on the frame received from the second AP; and send a measurement report message to the first AP, wherein the information about the time of transmission of the frame includes the time when the frame was transmitted by at least one AP including the second AP.

[0015] According to an embodiment of the present invention, a first access point (AP) in a wireless local area network includes a transceiver and a processor connected to the transceiver, wherein the processor is configured to: obtain information about the time of transmission of a frame; send the information about the time of transmission of the frame to a station (STA); send a scan response message generated based on the information about the time of transmission of the frame; and receive a measurement report message from the STA, wherein the information about the time of transmission of the frame includes information about the time when the frame was transmitted by at least one AP, and the measurement report message includes channel measurement results for a second AP, which is one of the at least one AP.

[0016] Beneficial effects According to the present invention, when the main channel of a wireless local area network system is busy, the wireless local area network terminal can operate in a sub-channel.

[0017] According to the present invention, when a wireless local area network (WLAN) terminal in a WLAN system determines that decoding is impossible in the main channel but detects that the energy exceeds a threshold, the WLAN can operate in a sub-channel.

[0018] According to the present invention, a wireless local area network (WLAN) terminal in a wireless local area network (WLAN) system can request channel information from another currently associated WLAN terminal and perform a channel scanning process based on the provided channel information.

[0019] According to the present invention, a wireless local area network terminal in a wireless local area network channel can perform a fast channel scan.

[0020] According to the present invention, roaming operations of wireless local area network terminals can be performed smoothly in a wireless local area network system.

[0021] The effects obtained in this invention are not limited to those described above, and those skilled in the art of applying the technical configurations of this invention can clearly deduce and understand other effects not mentioned above from the following description of the embodiments of this invention. That is, those skilled in the art can also deduce unintended effects in implementing the configurations described in this invention from the embodiments of this invention. Attached Figure Description

[0022] Figure 1 This is a block diagram illustrating a first embodiment of a communication node constituting a wireless local area network system.

[0023] Figure 2 This is a conceptual diagram illustrating a first embodiment of multiple links configured between multi-link devices (MLDs).

[0024] Figure 3 A first embodiment of a cooperative channel measurement method in a wireless local area network system is shown.

[0025] Figure 4 A second embodiment of a cooperative channel measurement method in a wireless local area network system is shown.

[0026] Figure 5 A third embodiment of a cooperative channel measurement method in a wireless local area network system is shown.

[0027] Figure 6 A fourth embodiment of a cooperative channel measurement method in a wireless local area network system is shown.

[0028] Figure 7A fifth embodiment of a cooperative channel measurement method in a wireless local area network system is shown.

[0029] Figure 8 A flowchart illustrating the process of measuring a channel according to an embodiment of the present invention is shown.

[0030] Figure 9 A flowchart illustrating a method for receiving channel measurement reports according to an embodiment of the present invention is shown. Detailed Implementation

[0031] This invention can have various modifications and embodiments, and specific embodiments are shown in the accompanying drawings and described in detail in the specification. However, this is not intended to limit the invention to the specific embodiments, but should be understood to include all modifications, equivalents, or alternatives contained within the spirit and technical scope of the invention.

[0032] The terms "first," "second," etc., can be used to describe various components, but components should not be limited by the terms. Terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the invention, a first component may be referred to as a second component, and similarly, a second component may be referred to as a first component. Terms and / or include combinations of multiple related descriptive terms or any one of multiple related descriptive terms.

[0033] When it is said that a component is "joined to" or "connected to" another component, it should be understood that one component is connected to the other component directly or through any other component in between. On the other hand, when it is said that a component is "directly connected to" or "directly joined to" another component, it should be understood that there are no other components between the components.

[0034] The terminology used in this invention is for describing particular embodiments only and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this invention, terms such as “comprising” or “having” are intended to specify the presence of features, quantities, steps, operations, components, parts or combinations thereof described in the specification, but should be understood not to preclude the possibility of the presence or addition of one or more other features, quantities, steps, operations, components, parts or combinations thereof.

[0035] Unless otherwise defined, all terms used herein (including technical or scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in general dictionaries shall be interpreted as having a meaning consistent with their meaning in the context of the relevant art and shall not be interpreted as having an ideal or overly formal meaning unless expressly defined herein.

[0036] In the following description, various exemplary embodiments of the invention will be described in more detail with reference to the accompanying drawings. In describing the invention, for ease of overall understanding, the same reference numerals are used for the same components in the drawings, and repeated descriptions of the same components are omitted.

[0037] The following describes a wireless communication system applying embodiments of the present invention. The wireless communication system applying embodiments of the present invention is not limited to the following description, and the embodiments of the present invention can be applied to various wireless communication systems. The wireless communication system may be referred to as a "wireless communication network".

[0038] Figure 1 A block diagram of a communication node in a wireless local area network system is shown.

[0039] refer to Figure 1 Communication node 100 can be an access point (AP), a station (STA), an AP multi-link device (MLD), or a non-AP MLD. STAs can be non-AP STAs. The operating channel width supported by the AP can be 20 MHz, 80 MHz, or 160 MHz, etc. The operating channel width supported by the STA can be 20 MHz or 80 MHz.

[0040] Communication node 100 may include at least one processor 110, memory 120, and at least one transmitting / receiving device 130 connected to a network and performing communication. Transmitting / receiving device 130 may also be referred to as a transceiver, radio frequency (RF) unit, or RF module. Additionally, communication node 100 may further include an input interface device 140, an output interface device 150, and a storage device 160. Components included in communication node 100 can be connected via bus 170 and perform communication between them.

[0041] However, each component included in communication node 100 may be connected not via common bus 170, but via a separate interface or separate bus around processor 110. For example, processor 110 may be connected via a dedicated interface to at least one of memory 120, transmitting / receiving device 130, input interface device 140, output interface device 150, and storage device 160.

[0042] Processor 110 can execute program instructions stored in at least one of memory 120 and storage device 160. Processor 110 can be a central processing unit (CPU), graphics processing unit (GPU), or dedicated processor that performs methods according to embodiments of the present invention. Memory 120 and storage device 160 can each be configured as at least one volatile storage medium and at least one non-volatile storage medium. For example, memory 120 can be configured as at least one read-only memory (ROM) and random access memory (RAM).

[0043] Figure 2 The concept of multiple links set up between multiple link devices (MLDs) in a wireless local area network system is illustrated.

[0044] refer to Figure 2 An MLD can have a medium access control (MAC) address. In an implementation, the MLD can be an AP MLD and / or a non-AP MLD. The MAC address of the MLD can be used in the multi-link establishment process between the non-AP MLD and the AP MLD. The MAC address of the AP MLD can be different from the MAC address of the non-AP MLD. APs associated with an AP MLD can have different MAC addresses, and STAs associated with a non-AP MLD can have different MAC addresses. An AP existing in an AP MLD and having a different MAC address can be responsible for the corresponding link and act as an independent AP.

[0045] A STA residing in a non-AP MLD and having a different MAC address can be responsible for the corresponding link and act as an independent STA. A non-AP MLD can be referred to as a STA MLD. An MLD can support simultaneous transmit and receive (STR) operations. For example, an MLD can perform a transmit operation on link 1 and a receive operation on link 2. An MLD that supports STR operations can be referred to as a STR MLD (e.g., a STR AP MLD or a STR non-AP MLD). In implementations, a link can be a channel or a frequency band. A device that does not support STR operations can be referred to as a non-STR (NSTR) AP MLD or an NSTR non-AP MLD (or an NSTR STA MLD).

[0046] MLDs can utilize discontinuous bandwidth extension schemes (e.g., 80 MHz + 80 MHz) to send and receive frames on multiple links. Multi-link operation can include multi-band transmission. An AP MLD can include multiple APs, and these APs can operate on different links. Each AP can perform lower-level MAC layer functions. Each AP can be referred to as a "communication node" or a "lower-level entity." A communication node (i.e., an AP) can be configured according to the upper layer (or...) Figure 1 The processor 110 shown is operated under the control of the processor. A non-AP MLD may include multiple STAs, and these STAs may operate on different links. Each STA may be referred to as a "communication node" or a "lower-level entity." A communication node (e.g., an STA) can operate according to the control of an upper layer (or...). Figure 1 The processor 110 shown is operated under its control.

[0047] MLDs can perform communication across multiple frequency bands. For example, an MLD can perform communication using a 40 MHz bandwidth in the 2.4 GHz band, and a 160 MHz bandwidth in the 5 GHz band, depending on a channel extension scheme (e.g., a bandwidth extension scheme). An MLD can also perform communication using a 160 MHz bandwidth in the 5 GHz band and a 160 MHz bandwidth in the 6 GHz band. A single frequency band (e.g., a single channel) used by an MLD can be defined as a single link. Alternatively, multiple links can be configured within a single frequency band used by an MLD. For example, an MLD can configure one link in the 2.4 GHz band and two links in the 6 GHz band. The links can be referred to as Link 1, Link 2, and Link 3, respectively. Alternatively, the links can be referred to as Link 1, Link 2, and Link 3, respectively. Link numbers can be set by the AP, and an identifier (ID) can be assigned to each link.

[0048] A Multi-Link Ledger (MLD) (e.g., an AP MLD and / or a non-AP MLD) can configure multiple links by performing access and / or negotiation procedures for multi-link operation. For example, the number of links and / or the links to be used among multiple links can be configured. A non-AP MLD (e.g., a STA) can identify information about the frequency bands that can communicate with the AP MLD. In the multi-link operation negotiation procedure between the non-AP MLD and the AP MLD, the non-AP MLD can configure one or more links supported by the AP MLD for multi-link operation. A STA that does not support multi-link operation (e.g., a STA according to IEEE 802.11 a / b / g / n / ac / ax) can access one or more links supported by the AP MLD.

[0049] When the frequency band gaps between multiple links (e.g., the frequency band gap between link 1 and link 2 in the frequency domain) are sufficient, the MLD can perform STR operations. For example, the MLD can use link 1 to transmit Physical Layer Convergence Procedure (PLCP) Protocol Data Unit (PPDU) 1 and can use link 2 to receive PPDU 2. On the other hand, when the frequency band gaps between multiple links are insufficient and the MLD performs STR operations, in-device coexistence (IDC) interference may occur, that is, interference between multiple links. Accordingly, when the frequency band gaps between multiple links are insufficient, the MLD may not be able to perform STR operations. The link pairs in the above interference relationship can be link pairs restricted to non-simultaneous transmit and receive (NSTR). Here, the MLD can be an NSTR AP MLD or an NSTR non-AP MLD.

[0050] For example, multiple links, including Link 1, Link 2, and Link 3, can be set up between the AP MLD and the non-AP MLD 1. When the band gap between Link 1 and Link 3 is sufficient, the AP MLD can perform STR operations using Link 1 and Link 3. That is, the AP MLD can use Link 1 to send frames and use Link 3 to receive frames. When the band gap between Link 1 and Link 2 is insufficient, the AP MLD may not be able to perform STR operations using Link 1 and Link 2. When the band gap between Link 2 and Link 3 is insufficient, the AP MLD may not be able to perform STR operations using Link 2 and Link 3.

[0051] On the other hand, in a wireless LAN system, a negotiation process for multi-link operation can be performed during the access process between the STA and the AP.

[0052] A device that supports multiple links (e.g., an AP or a STA) can be called a multi-link device (MLD). An AP that supports multiple links can be called an AP MLD, and an STA that supports multiple links can be called a non-AP MLD or a STA MLD. An AP MLD can have a physical address (e.g., a MAC address) for each link. An AP MLD can be implemented as if an AP were independently responsible for each link. Multiple APs can be managed within a single AP MLD. Accordingly, multiple APs belonging to the same AP MLD can cooperate. A STA MLD can have a physical address (e.g., a MAC address) for each link. A STA MLD can be implemented as if an STA were independently responsible for each link. Multiple STAs can be managed within a single STA MLD. Accordingly, multiple STAs belonging to the same STA MLD can cooperate.

[0053] For example, AP 1 of the AP MLD and STA 1 of the STA MLD can each be responsible for the first link and perform communication using the first link. AP 2 of the AP MLD and STA 2 of the STA MLD can each be responsible for the second link and perform communication using the second link. STA 2 can receive state change information for the first link on the second link. For example, the STA MLD can collect information received from each link (e.g., state change information) and control the operations performed by STA 1 based on the collected information.

[0054] Next, methods for transmitting and receiving data in a wireless local area network system will be described. When a method (e.g., signal transmission or reception) performed at a first communication node is described, a corresponding second communication node can perform a method (e.g., signal reception or transmission) corresponding to the method performed at the first communication node. That is, when the operation of a STA is described, its corresponding AP can perform an operation corresponding to the STA's operation. On the other hand, when the operation of an AP is described, its corresponding STA can perform an operation corresponding to the AP's operation. In the implementation, the operation of a STA can be interpreted as the operation of a STA MLD, the operation of a STA MLD can be interpreted as the operation of a STA, the operation of an AP can be interpreted as the operation of an AP MLD, and the operation of an AP MLD can be interpreted as the operation of an AP.

[0055] Figure 3 A first embodiment of a cooperative channel measurement method in a wireless local area network system is shown.

[0056] refer to Figure 3AP 1 301, AP 2 302, AP 3 305, AP 4 305, and STA 1 310 can operate in a wireless LAN. STA 1 310 can be associated with AP 1 301 and is designed to scan for neighboring APs, namely AP 2 303, AP 3 305, and AP 4 305. STA 1 310 can scan for neighboring APs to associate with one of them. The series of actions by which STA 1 310 stops communication with a previously associated AP, associates with one of the neighboring APs, and performs communication with the neighboring AP can be called roaming. AP 1 310 and AP 2 303 can operate on a first link. That is, AP 1 301 and AP 2 303 can operate on the same link. AP 3 305 can operate on a second link. AP 4 305 can operate on a third link. The operating frequencies (e.g., center frequency) of the first and second links can be different. The first and third links can operate at different frequencies. APs 1 301 to AP 4 305 can communicate with each other. For example, APs 1 301 to AP 4 305 can communicate via wired Ethernet. Alternatively, APs 1 301 to AP 4 305 can communicate via wireless LAN. Alternatively, APs 1 301 to AP 4 305 can communicate with each other according to different communication standards than wired Ethernet and wireless LAN. APs 1 301 to AP 4 305 can communicate with each other to form an MLD or some layers of an MLD. For example, APs 1 301 to AP 4 305 can form an upper MLD MAC layer. Alternatively, APs 1 301 to AP 4 305 can form a lower MLD MAC layer. Alternatively, APs 1 301 to AP 4 305 can form both an upper MLD MAC layer and a lower MLD MAC layer. As an alternative approach, APs 1 301 through AP 4 305 may not form an MLD (Multi-Level Disk) but instead exchange communication information with each other. For example, the exchange of communication information may include exchanging operational information about roaming operations of STAs associated with the AP (e.g., operational information about link usage and interruptions) or exchanging status information of STAs performing roaming operations (e.g., information about the sequence number (SN), packet number (PN), and block acknowledgment scoreboard of downlink and uplink packets for a specific STA) and downlink packets destined for the STA performing the roaming operation. As another example, the exchange of communication information may correspond to the exchange of AP operational information.

[0057] Because APs 1 301 to AP 4 305 communicate with each other, AP 1 301 can know information about its neighboring APs (APs 2 303 to AP 4 305). This information includes target beacon transmission time (TBTT) information. TBTT information can be timing information; that is, TBTT information indicates the expected time or period for beacon frame transmission for each AP. For example, AP 1 301 can know information about the timing of beacon frame transmissions from neighboring APs relative to the current time.

[0058] AP 1 301 can include and transmit TBTT information of neighboring APs in beacon frame 320. TBTT information can be transmitted via a reduced neighbor report (RNR) information element included in beacon frame 320. STA 1 310 can receive beacon frame 320 from AP 1 301. Based on the RNR information element included in beacon frame 320, STA 1 310 can know the TBTT information of neighboring APs. STA 1 310 can identify the TBTT information of neighboring APs not only through the RNR information element but also through various other methods. For example, AP 1 can transmit a beacon frame including information elements such as multi-link elements, and the multi-link elements can include operational information that includes the TBTT information of neighboring APs.

[0059] The received signal strength indication (RSSI), signal-to-noise ratio (SNR), etc., of the beacon frame 320 of AP 1 301 and / or the data frames received by STA 1 310 may be lower than the roaming threshold of STA 1 310. The roaming threshold may be a preset value, a value broadcast via beacon, or a value set through mutual negotiation. For example, the roaming threshold may be Rth, and the RSSI may be lower than Rth. When the RSSI of a frame received by STA 1 310 is lower than Rth or under other roaming initiation conditions, STA 1 310 may send a scan request frame 330. As an example, other roaming initiation conditions may include reducing the RSSI of received frames at a predetermined rate or higher. STA 1 310 may send the scan request frame 330 to AP 1 301 based on TBTT information of neighboring APs. As an alternative approach, STA 1 310 may not receive beacon frame 320, or the RNR information element may not be included in AP 1 301's beacon frame 320, thus STA 1 310 may not know the TBTT information of neighboring APs. Even when STA 1 310 does not know the TBTT information of neighboring APs, STA 1 310 may still send a scan request frame 330 to AP 1 301. The scan request frame 330 may be a management frame including action frames, a frame including information elements, a frame with specific information included in the control field (e.g., HT control field) of the MAC header, or other frames. The scan request frame 330 may include channel scan scheduling information requested by STA 1 310. The channel scan scheduling information includes at least one of the following: neighboring AP's TBTT information (or TBTT time), neighboring AP's link ID, neighboring AP's BSSID, or information about the AP's operating frequency. Channel scan scheduling information can use the list order of the link IDs or BSSIDs of neighboring APs to indicate that STA 1 310 should perform a scan at the corresponding AP's TBTT time. Alternatively, scan request frame 330 may include information requesting channel scan scheduling from AP 1 301. That is, STA 1 310 may not send channel scan scheduling information to AP 1 301. For example, even when no TBTT information for neighboring APs is identified, STA 1 310 can still receive channel scan scheduling information from AP 1 301 and scan neighboring APs.

[0060] AP 1 301 may send a scan response frame 340 to STA 1 310. The scan response frame 340 may be a response to a scan request frame 330 sent by STA 1 310. Alternatively, when AP 1 301 determines that roaming by STA 1 310 is required, it may send the scan response frame 340 without receiving the scan request frame 330. The scan response frame 340 may include a response to channel scan scheduling information included in the scan request frame 330 sent by STA 1 310. For example, the scan response frame 340 may include information indicating whether AP 1 301 acknowledges, modifies, or rejects the channel scan scheduling information sent by STA 1 310. When including information indicating rejection, the scan response frame 340 may include a code indicating the reason for rejection. Additionally, the scan response frame 340 may include channel scan scheduling information provided by AP 1 301 to STA 1 310. When AP 1301 confirms the channel scan schedule of STA 1310, the channel scan schedule information may or may not include the information sent by STA 1310. When AP 1301 modifies the channel scan schedule of STA 1310, the channel scan schedule information may include the channel scan information proposed by AP 1301. When AP 1301 rejects the channel scan schedule of STA 1310, the channel scan schedule information may not include the channel scan information proposed by AP 1301. On the other hand, the channel scan schedule information may include the channel scan information proposed by AP 1301. The channel scan schedule provided by AP 1301 to STA 1310 may include at least one of the following: TBTT information of neighboring APs from AP 2 303 to AP 4 305, link ID, BSSID, or information about the operating frequency of the AP. The TBTT of adjacent APs can be TBTT aa, TBTT bb, and TBTT cc, where TBTT aa is the TBTT of AP 2303, TBTT bb is the TBTT of AP 3305, and TBTT cc is the TBTT of AP 4305. The TBTT information included in the scan request frame 330 and scan response frame 340 can indicate the TBTT information of adjacent APs using a TU and / or a time synchronization function (TSF) offset. 1 TU is 1024 μs.

[0061] STA 1 310 can receive scan response frame 340 from AP 1 301 and perform channel scanning based on channel scan scheduling information provided by AP 1 301. At TBTT aa, STA 1 310 can scan AP 2 303, which operates at the same frequency as AP 1 301. STA 1 310 receives beacon frame 351 from AP 2 303 without modifying its operating frequency. AP 1 301 can complete frame transmission to STA 1 310 before TBTT aa, which is AP 2 303's TBTT. STA 1 310 can complete frame transmission to AP 1 301 before TBTT aa. When AP 1 301 and STA 1 310 complete transmission before their respective TBTTs, it can be indicated that the transmission was completed before Ts, where Ts is the time used to switch links at each TBTT. Completing transmission before a specific time can include ending the transmission opportunity (TXOP) before a specific time. At TBTT bb and TBTT cc, STA 1 310 can scan for AP 3305 and AP 4 305 operating at frequencies different from AP 1 301, and modify its operating frequency to receive beacon frames 353 and 355 from AP 3 305 and AP 4 305, respectively. For example, STA 1 310 modifies its operating frequency for the second and third links. After completing the scan, STA 1 310 modifies its operating frequency again to operate on the first link. The length of the time during which STA 1 310 modifies its operating frequency at TBTT bb and TBTT cc and then operates on the first link can be greater than or equal to 2 × Ts + (the beacon transmission period of the AP), and STA 1 310 cannot receive frames from AP 1 310 during this time period. Ts is the time required for STA 1 310 to switch its operating frequency. When STA 1 310 operates after returning to the first link from the second or third link, frame transmission may be infeasible or limited during the duration of Tm, which is the MediumSyncDelay timer or NAVSyncDelay time. AP 1 301 can complete frame transmission to STA 1 310 before TBTT bb and TBTT cc, which are the times when STA 1 310 scans AP 3 305 and AP 4 305, respectively. STA 1 310 can complete frame transmission to AP 1 301 before TBTT bb and TBTT cc. When AP 1 301 and STA 1 310 complete transmission before the corresponding TBTT, it can be indicated that the transmission was completed before Ts, which is the time used to switch links at each TBTT.Completing a transmission before a specific time can include ending a transmission opportunity (TXOP) before a specific time. When AP 1 301 and STA 1 310 complete a channel access operation (e.g., EDCA backoff operation) near each TBTT (e.g., when the backoff counter reaches 0), AP 1 301 may not transmit a frame to STA 1 310, and STA 1 310 may not transmit a frame to AP 1 301. That is, the backoff counter of AP 1 301 and / or the backoff counter of STA 1 310 may remain at 0. On the other hand, even when the backoff counter of AP 1 301 reaches 0, AP 1 301 may select a new backoff counter to continuously perform backoff operations. Alternatively, AP 1 301 may determine that a frame destined for STA 1 310 does not exist in AP 1 301's transmission queue. When a frame is destined for a different STA than STA 1 310, AP 1 301 may transmit the frame to that STA. After STA 1 310's channel scan operation is complete, AP 1 301 and / or STA 1 310 may transmit the frame. During a time period greater than or equal to 2 × Ts + (AP's beacon transmission period), AP 1 301 does not transmit frames to STA 1 310 at TBTT bb and TBTT cc. That is, AP 1 301 does not transmit frames to STA 1 310 while STA 1 310 is performing a series of operations for performing a channel scan. STA 1 310 cannot communicate with AP 1 301 while STA 1 310 is performing a series of operations for performing a channel scan. For example, AP 1301 may delay transmission to STA 1310 for channel access operations or not transmit frames to STA 1310, and may wait even when the EDCA backoff counter reaches 0 (e.g., keeping the backoff counter at 0 or reselecting the backoff counter). AP 1301 may transmit frames to STA 1310 after this time period. Frames transmitted from AP 1301 to STA 1310 may be trigger frames. For example, a trigger frame transmitted from AP 1301 to STA 1310 may be a frame used to release the MediumSyncDelay timer or NAVSyncDelay timer of STA 1310, which limits frame transmission for the duration of Tm, and may trigger uplink data transmission to STA 1310. Alternatively, frames transmitted from AP 1301 to STA 1310 may be downlink frames.

[0062] STA 1 310 can perform a scan based on scan scheduling information provided by AP 1 301. For example, STA 1 310 can collect information from AP 2 303 to AP 4 305. STA 1 310 sends a measurement report frame 360 ​​to AP 1 301. The measurement report frame 360 ​​is a frame that transmits information (e.g., signal strength, SNR, link congestion) of neighboring APs from AP 2 303 to AP 4 305. AP 1 301 can respond to STA 1 310's measurement report frame 360 ​​with a response frame (e.g., an ACK frame or a block acknowledgment frame). AP 1 301 can determine whether to roam and the roaming target based on the information from neighboring APs of STA 1 310.

[0063] In the implementation scheme, in order to obtain information about neighboring APs, STA 1 310 can send a probe request frame and then receive a probe response frame, instead of receiving beacon frames 351, 353 and 355 from the APs.

[0064] Figure 4 A second embodiment of a cooperative channel measurement method in a wireless local area network system is shown.

[0065] refer to Figure 4AP MLD 1 401, AP MLD 2 403, AP MLD 3 405, AP MLD 3 405, and STA MLD1 410 can operate in a wireless LAN. Associated AP 1-1 401-1 and AP 1-2 401-2 operate in AP MLD 1 401. AP 1-1 401-1 can operate on the first link, and AP 1-2 401-2 can operate on the second link. Associated AP 2-1 403-1 and AP 2-2 403-2 operate in AP MLD 2 403. AP 2-1 403-1 can operate on the third link, and AP 2-2 403-2 can operate on the fourth link. Associated AP 3-1 405-1 and AP 3-2 405-2 operate in AP MLD 3 405. AP 3-1 405-1 can operate on the first link, and AP 3-2 405-2 can operate on the fifth link. Associated STA 1-1 410-1 and STA 1-2 410-2 operate in STA MLD 1 410. STAMLD 1 410 can be associated with AP MLD 1 401 and is designed to scan neighboring AP MLDs, namely AP MLD 2403 and AP MLD 3 405. In other words, STA MLD 410 can be designed to scan APs associated with neighboring AP MLDs. STAMLD 410 can scan APs associated with neighboring AP MLDs to perform an association with one of the neighboring APs. STA MLD 410's actions of ceasing communication with previously associated AP MLDs, as well as its association with one of the APs associated with neighboring AP MLDs, and performing a series of actions related to communication with neighboring APs, can be termed roaming operations. The operating frequencies (e.g., center frequencies) of the first through fifth links can be different. APs MLD 1 401 to AP MLD 3 407 can communicate with each other. For example, APs MLD 1 401 to AP MLD 3 405 can communicate via wired Ethernet. Alternatively, APs MLD 1 401 to AP MLD 3 405 can communicate via wireless LAN. Alternatively, APs MLD 1 401 to AP MLD 3 405 can communicate with each other using different communication standards than wired Ethernet and wireless LAN. Slave APs of APs MLD 1 401 to AP MLD 3 405, or APs MLD 1 401 to AP MLD 3 405, can communicate with each other to form a new MLD layer. For example, APs MLD 1 401 to AP MLD 3 405 can form a new MLD MAC upper layer or a new MLD MAC lower layer.Alternatively, AP MLD 1 401 to AP MLD 3405 can form both an upper MLD MAC layer and a lower MLD MAC layer. As another approach, AP MLD 1 401 to AP MLD 3405 may not form an MLD, but instead exchange communication information with each other. As an example, the exchange of communication information may include exchanging operational information about roaming operations of STAs associated with the AP (e.g., operational information about link usage and interruptions) or exchanging status information of STAs performing roaming operations (e.g., information about the sequence number (SN), packet number (PN), and block acknowledgment scoreboard of downlink and uplink packets for a specific STA) and downlink packets destined for the STA performing the roaming operation. As yet another example, the exchange of communication information may correspond to the exchange of operational information of the APs.

[0066] Because AP MLD 1 401 to AP MLD 3 405 communicate with each other, AP MLD 1 401 can know information about neighboring AP MLDs and subordinate APs (e.g., AP MLD 2 403, AP 2-1 403-1, and AP 2-2 403-2). The information about neighboring AP MLDs includes the TBTT information of the subordinate APs. TBTT information can be timing information. That is, TBTT information indicates the expected time or interval for beacon frame transmission for each AP. For example, AP MLD 1 401 can know information about the timing of beacon frames 451, 453, 455, and 457 transmitted relative to the current time for neighboring AP MLDs.

[0067] AP 1-1 401-1 of AP MLD 1 401 can include and transmit TBTT information of neighboring APs in beacon frame 420. TBTT information can be transmitted via the Simplified Neighbor Report (RNR) information element included in beacon frame 420. STA 1-1 410-1 can receive beacon frame 420 from AP 1-1 401-1. Based on the RNR information element included in beacon frame 420, STA 1-1 410-1 can know the TBTT information of neighboring APs (e.g., the TBTT information of AP MLD 2 403, AP 2-1 403-1, and AP 2-2 403-2).

[0068] The RSSI, SNR, etc., of the beacon frame 420 of AP 1-1 401-1 and / or the data frames received by STA 1-1 401-1 may be lower than the roaming threshold of STA 1-1 410-1. For example, the roaming threshold may be Rth, and the RSSI may be lower than Rth. When the RSSI of a frame received by STA 1-1 410-1 is lower than Rth or under other roaming initiation conditions, STA 1-1 410-1 may send a scan request frame 430. As an example, other roaming initiation conditions may include reducing the RSSI of received frames at a predetermined rate or higher. STA 1-1 410-1 may send the scan request frame 430 to AP 1-1 401-1 based on TBTT information of neighboring APs. As an alternative, STA 1-1 410-1 may not receive beacon frame 420, or the RNR information element may not be included in AP 1-1 401-1's beacon frame 420, therefore STA 1-1 410-1 may not know the TBTT information of the neighboring AP. Even when STA 1-1 410-1 does not know the TBTT information of the neighboring AP, STA 1-1 410-1 can still send a scan request frame 430 to AP 1-1 401-1. The scan request frame 430 can be a management frame including action frames, a frame including information elements, a frame with specific information included in the control field (e.g., HT control field) of the MAC header, or other frames. The scan request frame 430 can include channel scan scheduling information requested by STA 1-1 410-1. The channel scan scheduling information includes at least one of the following: the TBTT information (or TBTT time) of the neighboring AP, the link ID of the neighboring AP, the BSSID of the neighboring AP, or information about the operating frequency of the AP. The scheduling information can use the list order of the link IDs or BSSIDs of neighboring APs to indicate the time to perform a scan at the corresponding AP's TBTT. Alternatively, the scan request frame 430 can include information requesting channel scan scheduling from AP 1-1 401-1. That is, STA 1-1 410-1 may not transmit channel scan scheduling information to AP 1-1 401-1. For example, even when no TBTT information for neighboring APs is identified, STA 1-1 410-1 can still receive channel scan scheduling information from AP 1-1 410-1 and scan neighboring APs.

[0069] AP 1-1 410-1 can send a scan response frame to STA 1-1 410-1. Scan response frame 440 can be AP 1-1 401-1's response to a scan request frame sent by STA 1-1 410-1. Alternatively, when AP 1-1 401-1 determines that roaming by STA 1-1 410-1 or STA MLD 1 410 is required, it can send scan response frame 440 without receiving scan request frame 430. Scan response frame 440 can include a response to channel scan scheduling information included in scan request frame 430 sent by STA 1-1 410-1. For example, scan response frame 440 can include information indicating whether AP 1-1 401-1 acknowledges, modifies, or rejects the channel scan scheduling information sent by STA 1-1 410-1. Additionally, the scan response frame 440 may include channel scan scheduling information provided by AP 1-1 401-1 to STA 1-1 410-1. When AP 1-1 401-1 confirms the channel scan scheduling of STA 1-1 410-1, the channel scan scheduling information may or may not include information transmitted by STA 1-1 410-1 without modification. When AP 1-1 401-1 modifies the channel scan scheduling of STA 1-1 410-1, the channel scan scheduling information may include channel scan information proposed by AP 1-1 410-1. When AP 1-1 401-1 rejects the channel scan scheduling of STA 1-1 410-1, the channel scan scheduling information may not include the channel scan information proposed by AP 1-1 401-1. Alternatively, the channel scan scheduling information may include the channel scan information proposed by AP 1-1 401-1. The channel scan scheduling provided by AP 1-1 401-1 to STA 1-1 401-1 includes TBTT information and the link IDs and / or operating frequency information of neighboring APs, including subordinate APs from AP MLD2 403 to AP MLD3 405. The TBTT of a neighboring AP can be TBTT aa, TBTT bb, TBTT cc, and TBTT dd. Here, TBTT aa is the TBTT of AP 2-1 403-1, TBTT bb is the TBTT of AP 2-2 403-2, TBTT cc is the TBTT of AP 3-1 405-1, and TBTT dd is the TBTT of AP 3-2 405-2. The TBTT information included in the scan request frame 430 and scan response frame 440 can indicate the TBTT information of neighboring APs in terms of TU and / or Time Synchronization Function (TSF) offsets. 1 TU is 1024 μs.

[0070] The exchange of scan request frames 430 and scan response frames 440 can be performed over multiple links. For example, STAMLD 1 410 can receive a beacon frame 420 from AP MLD 1 401 on at least one of the first or second links and request the transmission of scan request frame 430. The exchange of scan request frames 430 and scan response frames 440 can be performed on each link. For example, AP 1-1 401-1 and STA 1-1 410-1 operating on the first link can exchange scan request frames 430 and scan response frames 440 to scan AP 2-1 403-1 and AP 3-1 405-1. For example, AP 1-2 401-2 and STA 1-2 410-2 operating on the second link can exchange scan request frames and scan response frames to scan AP 2-2 403-2 and AP 3-2 405-2.

[0071] STA 1-1 410-1 or STA MLD 1 410 can receive scan response frame 440 from AP 1-1 401-1 or AP MLD 1 401, and STA MLD 1 410 performs channel scanning based on channel scan scheduling information provided by AP MLD 1 401. At TBTT aa, STA 1-1 410-1 can scan AP 2-1403-1, which operates at a different frequency than AP 1-1 401-1. STA 1-1 410-1 can modify its operating frequency to receive beacon frame 451 from AP 2-1 403-1. For example, STA 1-1 410-1 modifies its operating frequency to the third link. After completing the scan, STA 1-1 410-1 modifies its operating frequency again to operate on the first link. The length of the time period during which STA 1-1 410-1 modifies its operating frequency at TBTT aa and then operates on the first link can be greater than or equal to 2 × Ts + (the beacon transmission period of the AP), and STA 1-1 410-1 cannot receive frames from AP 1-1 401-1 during this time period. Ts is the time required for STA 1-1 410-1 to switch its operating frequency. When STA 1-1 410-1 operates after returning from the third link to the first link, frame transmission may be infeasible or restricted for the duration of Tm, which is the MediumSyncDelay timer or NAVSyncDelay time. AP 1-1 401-1 can complete the transmission of frames to STA 1-1 410-1 before TBTT aa, which is the time when STA 1-1 410-1 scans AP 2-1 403-1. STA 1-1 410-1 may transmit a frame to AP 1-1 401-1 before TBTT aa. When AP 1-1 401-1 and STA 1-1 410-1 complete transmission before their respective TBTTs, it can be indicated that the transmission was completed before Ts, where Ts is the time used to switch links at each TBTT. Completing transmission before a specific time can include ending the transmission opportunity (TXOP) before a specific time. When AP 1-1 401-1 and STA 1-1 410-1 complete a channel access operation (e.g., EDCA backoff operation) near each TBTT (e.g., when the backoff counter reaches 0), AP 1-1 401-1 may not transmit a frame to STA 1-1 410-1, and STA 1-1 410-1 may not transmit a frame to AP 1-1 401-1. The backoff counter of AP1-1 401-1 and / or the backoff counter of STA 1-1 410-1 can be kept at 0.Alternatively, even when the backoff counter of AP 1-1 401-1 reaches 0, AP 1-1 401-1 can select a new backoff counter to continuously perform backoff operations. Alternatively, AP 1-1 401-1 can determine that a frame destined for STA 1-1 410-1 does not exist in AP1's transmission queue. For example, when a frame exists destined for a STA different from STA 1-1 410-1, AP 1-1 401-1 can transmit the frame to the STA different from STA 1-1 410-1. After STA 1-1 410-1's channel scan operation is completed, AP 1-1 401-1 and / or STA 1-1 410-1 can transmit the frame. During a time period of length greater than or equal to 2×Ts+ (the beacon transmission period of the AP), AP 1-1 401-1 does not transmit frames to STA 1-1 410-1 at TBTT aa. For example, AP 1-1 401-1 delays transmission for channel access operations to STA 1-1 410-1 or does not transmit frames to STA 1-1 410-1, and waits even when the EDCA backoff counter reaches 0 (e.g., keeping the backoff counter at 0 or reselecting the backoff counter). AP 1-1 401-1 may transmit frames to STA 1-1 410-1 after this time period. Frames transmitted from AP 1-1 410-1 to STA 1-1 410-1 can be trigger frames. For example, a trigger frame transmitted from AP 1-1 410-1 to STA 1-1 410-1 can be a frame used to release the MediumSyncDelay timer or NAVSyncDelay of STA 1-1 410-1, which limits frame transmission for the duration of Tm, and can trigger uplink data for STA 1-1 410-1. Alternatively, a frame transmitted from AP 1-1 401-1 to STA 1-1 410-1 can be a downlink frame. At TBTT cc, STA 1-1 410-1 can scan AP 3-1 405-1, which operates at the same frequency as AP 1-1 401-1. AP 1-1 401-1 completes its frame transmission to STA 1-1 410-1 before TBTT cc, which is AP 3-1 405-1's TBTT. STA 1-1 410-1 can complete the frame transmission to AP 1-1 401-1 before TBTT cc.

[0072] At TBTT bb and TBTT dd, STA 1-2 410-2 can scan for AP 2-2 403-2 and AP 3-2 405-2, which operate at frequencies different from AP 1-2 401-2. STA 1-2 410-2 modifies its operating frequency to receive beacon frames 453 and 457 from AP 2-2 403-2 and AP 3-2 405-2. For example, STA 1-2 410-2 modifies its operating frequency for the fourth and fifth links. After completing the scan, STA 1-2 410-2 modifies its operating frequency again to operate on the second link. The length of the time period during which STA 1-2410-2 modifies its operating frequency at TBTT bb and TBTT dd and then operates on the second link can be greater than or equal to 2 × Ts + (the beacon transmission period of the AP), and STA 1-2 410-2 cannot receive frames from AP 1-2 410-2 during this time period. Ts is the time required for STA 1-2 410-2 to switch its operating frequency. When STA 1-2 410-2 operates after returning from the fourth or fifth link to the second link, frame transmission may be infeasible or limited for the duration of Tm, which is the MediumSyncDelay timer or NAVSyncDelay time. AP 1-2 401-2 can complete the transmission of frames to STA 1-2 410-2 before TBTT bb and TBTT cc, which are the times when STA 1-2410-2 scans AP 2-2 403-2 and AP 3-2 405-2. STA 1-2 410-2 may complete frame transmission to AP 1-2 401-2 before TBTT bb and TBTT dd. When AP 1-2 401-2 and STA 1-2 410-2 complete transmission before their respective TBTTs, it can be indicated that the transmission was completed before Ts, where Ts is the time used to switch links at each TBTT. Completing transmission before a specific time can include ending the transmission opportunity (TXOP) before a specific time. When AP 1-2 401-2 and STA 1-2 410-2 complete a channel access operation (e.g., EDCA backoff operation) near each TBTT (e.g., when the backoff counter reaches 0), AP 1-2 401-2 may not transmit frames to STA 1-2 410-2, and STA 1-2 410-2 may not transmit frames to AP 1-2 401-2. The backoff counter of AP 1-2 401-2 and / or the backoff counter of STA 1-2 410-2 can be kept at 0. Alternatively, even when the backoff counter of AP 1-2 401-2 reaches 0, AP 1-2 401-2 can select a new backoff counter to continuously perform backoff operations.Alternatively, AP 1-1 401-1 can determine that a frame destined for STA 1-2410-2 does not exist in AP 1-2 410-2's transmission queue. For example, when a frame exists destined for a different STA than STA 1-2 410-2, AP 1-1 401-1 can transmit the frame to the different STA. After STA 1-2410-2's channel scan operation is complete, AP 1-2 401-2 and / or STA 1-2 410-2 can transmit the frame. During a time period of length greater than or equal to 2×Ts+ (AP's beacon transmission period), AP 1-2 401-2 does not transmit frames to STA 1-2 410-2 at TBTT bb and TBTT cc. For example, AP 1-1 401-1 delays transmission to STA 1-2 410-2 for channel access operations or does not transmit frames to STA 1-2 410-2, and waits even when the EDCA backoff counter reaches 0 (e.g., keeping the backoff counter at 0 or reselecting the backoff counter). AP 1-2 401-2 may transmit frames to STA 1-2 410-2 after this time period. Frames sent from AP 1-2 401-2 to STA 1-2 410-2 can be trigger frames. For example, a trigger frame sent from AP 1-2 401-2 to STA 1-2 410-2 can be a frame used to release the MediumSyncDelay timer or NAVSyncDelay timer of STA 1-2 410-2, which limits frame transmission for the duration of Tm, and can trigger uplink data transmission from STA 1-2 410-2. Alternatively, the frame sent from AP 1-2 401-2 to STA 1-2 410-2 can be a downlink frame.

[0073] STA MLD 1 410 can perform a scan based on scan scheduling information provided by AP MLD 1 401. Through scanning, STA MLD 1 410 can obtain information about the APs. For example, STA MLD 1 410 can collect information from AP MLD 2 403 to AP MLD 3 405 (e.g., information about subordinate APs from AP MLD 2 403 to AP MLD 3 405). STA MLD 1 410 sends a measurement report frame 460 to AP MLD 1 401. The measurement report frame 460 is a frame used to transmit information about neighboring AP MLDs (that is, AP MLD 2 403 to AP MLD 3 405) (e.g., signal strength, SNR, and link congestion of APs operating under AP MLD 2 403 to AP MLD 3 405). AP MLD 1 401 can use response frames (e.g., ACK frames or block acknowledgment frames) to respond to measurement report frames 460 from STA MLD 1 410. AP MLD 1 401 can determine whether to roam and the roaming target based on information from neighboring AP MLDs of STA MLD 1 410.

[0074] In the implementation, in order to obtain information about neighboring AP MLDs, STA MLD 1 410 can send a probe request frame and then receive a probe response frame, instead of receiving beacon frames 451, 453, 455 and 457 from the APs.

[0075] Figure 5 A third embodiment of a cooperative channel measurement method in a wireless local area network system is shown.

[0076] refer to Figure 5AP 1 501, AP 2 503, AP 3 505, and STA 1 510 can operate in a wireless LAN. STA 1 510 can be associated with AP 1 501 and is designed to scan for neighboring APs, namely AP 2 503 and AP 3 505. STA 1 510 can scan for neighboring APs to associate with one of them. The series of actions by which STA 1 510 stops communication with a previously associated AP, associates with one of the neighboring APs, and performs communication with the neighboring AP can be called roaming. AP 1 501 can operate on a first link. AP 2 503 can operate on a second link. AP 3 505 can operate on a third link. The operating frequencies (e.g., center frequency) of the first and second links can be different. The first and third links can have different operating frequencies. AP 1 501 to AP 3 505 can communicate interconnectedly. For example, AP 1501 to AP 3505 can communicate via wired Ethernet. Alternatively, AP 1501 to AP 3505 can communicate via wireless LAN. Alternatively, AP 1501 to AP 3505 can communicate with each other according to different communication standards than wired Ethernet and wireless LAN. AP 1501 to AP 3505 can communicate with each other to form an MLD or some layers of an MLD. For example, AP 1501 to AP 3505 can form an upper MLD MAC layer. Alternatively, AP 1501 to AP 3505 can form a lower MLD MAC layer. Alternatively, AP 1501 to AP 3505 can form both an upper MLD MAC layer and a lower MLD MAC layer. As another method, AP 1501 to AP 3505 can exchange communication information with each other without forming an MLD. As an example, the exchange of communication information may include exchanging operational information about roaming operations of STAs associated with the AP (e.g., operational information about link usage and interruptions) or exchanging status information of STAs performing roaming operations (e.g., information about the sequence number (SN), packet number (PN), and block acknowledgment (BACK) scoreboard of downlink and uplink packets for a particular STA) and downlink packets destined for the STA performing the roaming operation. As another example, the exchange of communication information may correspond to the exchange of operational information of the AP.

[0077] Because APs 1 501 to AP 3 505 communicate with each other, AP 1 501 can know information about neighboring APs (e.g., APs 2 503 to AP 3 505). This information includes Target Beacon Transmission Time (TBTT) information. TBTT information can be timing information. That is, TBTT indicates the expected time or interval for beacon frame transmission for each AP. For example, AP 1 501 can know information about the timing of beacon frames 551 and 553 transmitted by neighboring APs relative to the current time.

[0078] AP 1 501 can include and transmit TBTT information of neighboring APs in beacon frame 520. TBTT information can be transmitted via the Simplified Neighbor Report (RNR) information element included in beacon frame 520. STA 1 510 can receive beacon frame 520 from AP 1 501. Based on the RNR information element included in beacon frame 520, STA 1 510 can know the TBTT information of neighboring APs. STA 1 510 can identify the TBTT information of neighboring APs not only through the RNR information element but also through various other methods. For example, AP 1 can transmit beacon frames that include information elements such as multi-link elements, and these multi-link elements can include operational information that includes the TBTT information of neighboring APs.

[0079] The received signal strength indication (RSSI), signal-to-noise ratio (SNR), etc., of the beacon frame 520 of AP 1 501 and / or the data frames received by STA 1 510 may be lower than the roaming threshold of STA 1 510. For example, the roaming threshold may be Rth, and the RSSI may be lower than Rth. If the RSSI of a frame received by STA 1 510 is lower than Rth, or based on other roaming initiation conditions, STA 1 510 may send a scan request frame 530. As an example, other roaming initiation conditions may include reducing the RSSI of received frames at a predetermined rate or higher. STA 1 510 may send the scan request frame 530 to AP 1 501 based on TBTT information of neighboring APs. On the other hand, STA 1 510 may not receive beacon frames, or the RNR information element may not be included in the beacon frame 520 of AP 1 501, therefore STA 1 510 may not know the TBTT information of neighboring APs. Even when STA 1 510 does not know the TBTT information of neighboring APs, STA 1 510 can still send a scan request frame 530 to AP 1 501. The scan request frame 530 can be a management frame including action frames, a frame including information elements, a frame with specific information included in the control field (e.g., HT control field) of the MAC header, or other frames. The scan request frame 530 can include channel scan scheduling information requested by STA 1 510. The channel scan scheduling information includes at least one of the following: the TBTT information or TBTT time of neighboring APs, the link ID of neighboring APs, the BSSID of neighboring APs, or information about the operating frequency of APs. STA 1 510 can provide scheduling information indicating that STA 1 510 plans to perform a scan at the TBTT of the corresponding AP based on the list order of the link IDs or BSSIDs of neighboring APs. Alternatively, the scan request frame 530 may include information requesting channel scan scheduling from AP 1 501. That is, STA 1 510 may not send channel scan scheduling information to AP 1 510. For example, even when TBTT information of neighboring APs is not identified, STA 1 510 can still receive channel scan scheduling information from AP 1 501 and scan neighboring APs.

[0080] AP 1 501 may send a scan response frame 540 to STA 1 510. The scan response frame 540 may be a response to a scan request frame 540 sent by STA 1 510. Alternatively, when AP 1 501 determines that roaming by STA 1 510 is required, it may send the scan response frame 540 without receiving the scan request frame 530. The scan response frame 540 may include a response to channel scan scheduling information included in the scan request frame 530 sent by STA 1 510. For example, the scan response frame 540 may include information indicating whether AP 1 501 acknowledges, modifies, or rejects the channel scan scheduling information sent by STA 1 510. Additionally, the scan response frame 540 may include channel scan scheduling information provided by AP 1 501 to STA 1 510. When AP 1 501 acknowledges the channel scan scheduling of STA 1 510, the channel scan scheduling information may or may not include the information transmitted by STA 1 510 without modification. When AP 1 501 modifies the channel scan schedule of STA 1 510, the channel scan schedule information may include the channel scan information proposed by AP 1 501. When AP 1 501 rejects the channel scan schedule of STA 1 510, the channel scan schedule information may not be included in the scan response frame 540. On the other hand, even when AP 1 501 rejects the channel scan schedule of STA 1 510, the scan response frame 540 may still include the channel scan information proposed by AP 1 501. The channel scan schedule provided by AP 1 501 to STA 1 510 includes TBTT information and the link IDs and / or operating frequency information of neighboring APs, including AP 2 503 to AP 3 505. The TBTTs of neighboring APs can be TBTT aa and TBTT bb, where TBTT aa is the TBTT of AP 2 503 and TBTT bb is the TBTT of AP 3 505. The TBTT information included in the scan request frame 530 and scan response frame 540 can indicate the TBTT information of adjacent APs in terms of TU and / or time synchronization function (TSF) offset. 1 TU is 1024 μs.

[0081] STA 1 510 can receive scan response frames 540 from AP 1 501 and perform channel scanning based on channel scan scheduling information provided by AP 1 501. At TBTT aa and TBTT bb, STA 1 510 can scan AP 2 503 and AP 3 505, which operate at frequencies different from AP 1 501, and modify its operating frequency to receive beacon frames 551 and 553 from AP 2 503 and AP 3 505. For example, STA 1 510 modifies its operating frequency to the second and third links. STA 1 510 transmits scan initiation frames 561 and 563 to AP 1 501 before changing its operating frequency. After completing the scan, STA 1 510 again modifies its operating frequency to operate on the first link. When operating on the first link again, STA 1 510 transmits scan completion frames 571 and 573 to AP 1 501. The length of the time period during which STA 1 510 modifies its operating frequency at TBTT aa and TBTT bb and then operates on the first link can be greater than or equal to 2 × Ts + (the beacon transmission period of the AP), and STA 1 510 cannot receive frames from AP 1 510 during this time period. Ts is the time required for STA 1 510 to switch its operating frequency. When STA 1 510 operates after returning from the second or third link to the first link, frame transmission may be infeasible or limited during the duration of Tm, which is the MediumSyncDelay timer or NAVSyncDelay time. Accordingly, scan completion frames 571 and 573 of STA 1 510 may not be transmitted immediately. Accordingly, STA 1 510 may not transmit scan completion frames 571 and 573, transmit scan completion frames 571 and 573 within Tm, or transmit scan completion frame 571 within Tm when transmitting an RTS frame to AP 1 501 and typically receiving a CTS frame in response. AP 1 501 can complete frame transmission to STA 1 510 before TBTT aa and TBTT bb, where TBTT aa and TBTT bb are the times when STA 1 510 scans AP 2 503 and AP3 505. STA 1 510 can complete frame transmission to AP 1 501 before TBTT aa and TBTT bb. When AP 1501 and STA 1 510 complete transmission before their respective TBTTs, it can be indicated that the transmission was completed before Ts, where Ts is the time used to switch links at each TBTT. Completing transmission before a specific time can include ending a transmission opportunity (TXOP) before a specific time.When AP 1 501 and STA 1 510 complete a channel access operation (e.g., EDCA backoff operation) near each TBTT (e.g., when the backoff counter reaches 0), AP 1 501 may not transmit a frame to STA 1 510, and STA 1 510 may not transmit a frame to AP 1 501. The backoff counter of AP 1 501 and / or the backoff counter of STA 1 510 may remain at 0. Alternatively, even when the backoff counter of AP 1 501 reaches 0, AP 1 501 may select a new backoff counter to continuously perform backoff operations. Alternatively, AP 1 501 may determine that a frame destined for STA 1 510 does not exist in AP 1 501's transmission queue. For example, when a frame is present destined for a STA different from STA 1 510, AP 1 301 may transmit the frame to the STA different from STA 1 510. After the channel scan operation of STA 1 510 is completed, AP 1 501 and / or STA 1 510 may transmit frames. AP 1 501 does not transmit frames to STA 1510 for a period of length greater than or equal to 2 × Ts + (AP's transmission period), starting from the moment it receives scan initiation frames 561 and 563 from STA 1 510 or from TBTT aa and TBTT bb. For example, AP 1 501 delays the channel access operation to STA 1 510 or does not transmit frames to STA 1 510, and waits even when the EDCA backoff counter reaches 0 (e.g., keeping the backoff counter at 0 or reselecting the backoff counter). AP 1 501 may transmit frames to STA 1 510 after this period. Frames sent from AP 1 501 to STA 1 510 may be trigger frames. For example, a trigger frame sent from AP 1 501 to STA 1 510 could be a frame used to release the MediumSyncDelay timer or NAVSyncDelay timer of STA 1 510, which limits frame transmission for a duration of Tm, and could trigger uplink data or a scan completion frame from STA 1 510. Alternatively, the frame sent from AP 1 501 to STA 1 510 could be a downlink frame. In a different method than AP 1 501 transmitting the frame to STA 1 510 after this time period, AP 1 501 could transmit the frame to STA 1 510 after receiving the scan completion frame from STA 1 510. STA 1 510 cannot communicate with AP 1 501 while STA 1 510 performs a series of operations for performing a channel scan (e.g., during the time period when STA 1 sends a scan initiation frame to AP 1 and then sends a scan completion frame to AP 1).

[0082] STA 1 510 can perform a scan based on scan scheduling information provided by AP 1 501. For example, STA 1 510 can collect information from AP 2 503 to AP 3 505. STA 1 510 sends a measurement report frame 580 to AP 1 501. The measurement report frame 580 is a frame that transmits information (e.g., signal strength, SNR, link congestion) of neighboring APs from AP 2 503 to AP 3 505. AP 1 501 can respond to STA 1 510's measurement report frame 580 using a response frame (e.g., an ACK frame or a block acknowledgment frame). AP 1 501 can determine whether to roam and the roaming target based on the information of STA 1 510's neighboring APs.

[0083] In the implementation, in order to obtain information about neighboring APs, STA 1 510 can send a probe request frame and then receive a probe response frame, instead of receiving beacon frames 551 and 553 from the APs.

[0084] Figure 6 A fourth embodiment of a cooperative channel measurement method in a wireless local area network system is shown.

[0085] refer to Figure 6AP 1 601, AP 2 603, AP 3 605, and STA 1 610 can operate in a wireless LAN. STA 1 610 can be associated with AP 1 601 and is designed to scan for neighboring APs, namely AP 2 603 and AP 3 605. AP 1 601 can operate on a first link. AP 2 603 can operate on a second link. AP 3 605 can operate on a third link. STA 1 610 can scan for neighboring APs to associate with one of them. The series of actions performed by STA 1 610—stopping communication with a previously associated AP, associating with a neighboring AP, and communicating with the neighboring AP—can be called roaming. The operating frequencies (e.g., center frequencies) of the first and second links can be different. The first and third links can have different operating frequencies. AP 1 601 to AP 3 605 can communicate interconnectedly. For example, AP1 601 to AP3 605 can communicate via wired Ethernet. Alternatively, AP1 601 to AP3 605 can communicate via wireless LAN. Alternatively, AP1 601 to AP3 605 can communicate with each other according to different communication standards than wired Ethernet and wireless LAN. AP1 601 to AP3 605 can communicate with each other to form an MLD or some layers of an MLD. For example, AP1 601 to AP3 605 can form an upper MLD MAC layer. Alternatively, AP1 601 to AP3 605 can form a lower MLD MAC layer. Alternatively, AP1 601 to AP3 605 can form both an upper MLD MAC layer and a lower MLD MAC layer. As another method, AP1 601 to AP3 605 can exchange communication information with each other without forming an MLD.

[0086] As an example, the exchange of communication information may include exchanging operational information about roaming operations of STAs associated with the AP (e.g., operational information about link usage and interruptions) or exchanging status information of STAs performing roaming operations (e.g., information about the sequence number (SN), packet number (PN), and block acknowledgment (BACK) scoreboard of downlink and uplink packets for a particular STA) and downlink packets destined for the STA performing the roaming operation. As another example, the exchange of communication information may correspond to the exchange of operational information of the AP.

[0087] Because AP 1 601 to AP 3 605 communicate with each other, AP 1 601 can know information about neighboring APs (e.g., AP 2 603 and AP 3 605). This information includes Target Beacon Transmission Time (TBTT) information. TBTT information can be timing information. That is, TBTT information indicates the expected time or interval for beacon frame transmission for each AP. For example, AP 1 601 can know information about the timing of beacon frame transmissions from neighboring APs relative to the current time.

[0088] AP 1 601 can include and transmit TBTT information of neighboring APs in beacon frame 620. TBTT information can be transmitted via a Simplified Neighbor Report (RNR) information element included in beacon frame 620. STA 1 610 can receive beacon frame 620 from AP 1 601. Based on the RNR information element included in beacon frame 620, STA 1 610 can know the TBTT information of neighboring APs. STA 1 610 can identify the TBTT information of neighboring APs not only through the RNR information element but also through various other methods. For example, AP 1 601 can transmit beacon frames that include information elements such as multi-link elements, and these multi-link elements can include operational information that includes the TBTT information of neighboring APs.

[0089] The Received Signal Strength Indication (RSSI), Signal-to-Noise Ratio (SNR), etc., of the beacon frame 620 of AP 1 601 and / or the data frames received by STA 1 610 may be lower than the roaming threshold of STA 1 610. For example, the roaming threshold may be Rth, and the RSSI may be lower than Rth. When the RSSI of a frame received by STA 1 610 is lower than Rth, or based on other roaming initiation conditions, STA 1 610 may send a scan request frame 630. As an example, other roaming initiation conditions may include reducing the RSSI of received frames at a predetermined rate or higher. The scan request frame sent by STA 1 610 to AP 1 601 may include a list of neighboring APs obtained by STA 1 610 from the beacon frame 620 of AP 1 601. Alternatively, STA 1 610 may not know about neighboring APs, and the scan request frame 630 sent by STA 1 610 to AP 1 601 may not include information about neighboring APs.

[0090] Based on the scan request frame 630 received from STA 1 610, AP 1 601 performs cooperative scanning with neighboring APs (i.e., AP 2 603 and AP 3 605). Based on the cooperative scanning, a time-to-trigger (TTT) is set for scanning AP 2 603 and AP 3 605. The TTT for scanning AP 2 603 is TTT aa, and the TTT for scanning AP 3 605 is TTT bb. AP 1 601 may include the set TTT information in a scan response frame 640 and send the scan response frame 640 to STA 1 610. The scan response frame 640 further includes information about the links and / or operating frequencies of the neighboring APs (i.e., AP 2 603 and AP 3 605). The scan response frame 640 may be a response to the scan request frame 640 sent by STA 1 610. Even when roaming of STA 1 610 is determined to be necessary, a scan response frame 640 can be sent without receiving a scan request frame 630. The TTT information of neighboring APs (e.g., TTT aa and TTT bb) can be represented as an offset of the TU and / or Time Synchronization Function (TSF) after the scan response frame 640 is initially or completely transmitted. 1 TU is 1024 µs.

[0091] STA 1 610 can receive scan response frame 640 from AP 1 601 and perform channel scanning based on channel scan scheduling information provided by AP 1 601. At TTT aa and TTT bb, STA 1 610 can scan AP 2 603 and AP 3 605, which operate at frequencies different from AP 1 601, and modify its operating frequency to receive frames from AP 2 603 and AP 3 605. For example, STA 1 610 modifies its operating frequency to the second and third links. AP 2 603 and AP 3 605 transmit null data PPDU (NDP) frames 651 and 653 at the set TTT (that is, TTT aa and TTT bb). Because AP 1 601 negotiates TTT with AP 3 605, AP 2 603 and AP 3 605 do not send NDP announcement (NDPA) frames before sending NDP frames 651 and 653. On the other hand, even if AP 1 601 and AP 3 605 negotiate TTT, AP 2 603 and AP 3 605 can send NDPA frames before sending NDP frames 651 and 653. AP 2 603 and AP 3 605 can send probe response frames instead of sending NDP frames 651 and 653 at TTT aa and TTT bb. STA 1 610 can receive frames 651 and 653 from AP 2 603 and AP 3 605 and obtain information from AP 2 603 and AP 3 605.

[0092] After completing the scan, STA 1 610 modifies its operating frequency again to operate on the first link. When operating on the first link again, STA 1 610 sends a scan completion frame to AP 1 601. The length of the time during which STA 1 610 modifies its operating frequency at TTT aa and TTTbb respectively and then operates on the first link can be greater than or equal to 2 × Ts + (AP's NDP transmission period), and STA 1 610 cannot receive frames from AP 1 601 during this period. Ts is the time required for STA 1 610 to switch its operating frequency. When STA 1 610 operates after returning from the second or third link to the first link, frame transmission may be infeasible or limited for the duration of Tm, which is the MediumSyncDelay timer or NAVSyncDelay time. Accordingly, STA 1 610's scan completion frame may not be sent immediately. AP 1601 can complete frame transmission to STA 1610 before TTT aa and TTT bb, where TTT aa and TTT bb are the times when STA 1610 scans AP 2603 and AP 3605. STA 1610 can complete frame transmission to AP 1601 before TTT aa and TTT bb. When AP 1601 and STA 1610 complete transmission before the corresponding TTT, it can be indicated that transmission is completed before Ts, where Ts is the time used to switch links at each TTT. Completing transmission before a specific time can include ending transmission opportunity (TXOP) before a specific time. When AP 1601 and STA 1610 complete channel access operations (e.g., EDCA backoff operations) near each TTT (e.g., when the backoff counter reaches 0), AP 1601 may not transmit frames to STA 1610, and STA 1610 may not transmit frames to AP 1601. The backoff counter of AP 1601 and / or the backoff counter of STA 1610 can remain at 0. Alternatively, even when the backoff counter of AP 1601 reaches 0, AP 1601 can select a new backoff counter to continuously perform backoff operations. Alternatively, AP 1601 can determine that there are no frames in AP 1601's transmission queue destined for STA 1610, and when there are frames destined for another STA different from STA 1610, it can transmit the frames to the STA different from STA 1610. After the channel scan operation of STA 1610 is completed, AP 1601 and / or STA 1610 can transmit frames. During a time period of length greater than or equal to 2×Ts+ (AP's NDP transmission period), AP 1601 does not transmit frames to STA 1610 at TTT aa and TTT bb.For example, AP 1601 may delay transmission to STA 1610 for channel access operations or not transmit frames to STA 1610, and may wait even when the EDCA backoff counter reaches 0 (e.g., keeping the backoff counter at 0 or reselecting the backoff counter). AP 1601 may transmit frames to STA 1610 after this time period. Frames transmitted from AP 1601 to STA 1610 may be trigger frames. For example, a trigger frame transmitted from AP 1601 to STA 1610 may be a frame used to release the MediumSyncDelay timer or NAVSyncDelay timer of STA 1610, which limits frame transmission for the duration of Tm, and may trigger uplink data or scan completion frames for STA 1610. Alternatively, frames transmitted from AP 1601 to STA 1610 may be downlink frames. In a different method than that in which AP 1 601 transmits frames to STA 1 610 after this time period, AP 1 601 may transmit frames to STA 1 610 after receiving a scan completion frame from STA 1 610. STA 1 610 cannot communicate with AP 1 601 while STA 1 610 performs a series of operations for channel scanning (when STA 1 610 switches the channel to AP 2 603 and AP 3 605 to receive NDP frames).

[0093] STA 1 610 can perform a scan based on scan scheduling information provided by AP 1 601. For example, STA 1 610 can collect information from AP 2 603 to AP 3 605. STA 1 610 sends a measurement report frame 660 to AP 1 601. Measurement report frame 660 is a frame that transmits information (e.g., signal strength, SNR, link congestion) of neighboring APs from AP 2 603 to AP 3 605. AP 1 601 can respond to STA 1 610's measurement report frame 660 with a response frame (e.g., an ACK frame or a block acknowledgment frame). AP 1 601 can determine whether to roam and the roaming target based on the information of STA 1 610's neighboring APs.

[0094] Figure 7 A fifth embodiment of a cooperative channel measurement method in a wireless local area network system is shown.

[0095] refer to Figure 7AP MLD 1 701, AP MLD 2 703, AP MLD 3 705, and STA MLD 1 710 can operate in a wireless LAN. Associated AP 1-1 701-1 and AP 1-2 701-2 operate on AP MLD 1 701. AP 1-1 701-1 can operate on the first link, and AP 1-2 701-2 can operate on the second link. Associated AP 2-1 703-1 and AP 2-2 703-2 operate on AP MLD 2 703. AP 2-1 703-1 can operate on the third link, and AP 2-2 703-2 can operate on the fourth link. Associated AP 3-1 705-1 and AP 3-2 705-2 operate on AP MLD 3705. AP 3-1 705-1 can operate on the first link, and AP 3-2 705-2 can operate on the fifth link. The associated STA 1-1 710-1 and STA 1-2 710-2 operate within STA MLD 1 710. STA MLD 1 710 can be an enhanced multi-link single radio (EMLSR) MLD. That is, STA MLD 1 710 can perform EMLSR operation, and STA 1-1 710-1 and STA 1-2 710-2 under STA MLD 1 710 can also perform EMLSR operation. Because STA MLD 1 710 is an EMLSR MLD, STA 1-2 710-2 cannot receive frames and perform channel detection, while STA 1-1 710-1 transmits and receives frames. STA 1-1 710-1 cannot receive frames and performs channel detection, while STA 1-2 710-2 transmits and receives frames. STA MLD 1 710 can be associated with AP MLD 1 701 and is designed to scan neighboring AP MLDs, namely AP MLD 2 703 and AP MLD 3 705. In other words, STA MLD 710 can be designed to scan APs associated with neighboring AP MLDs. STA MLD 710 can scan APs associated with neighboring AP MLDs to perform association with one of the neighboring APs. STA MLD 710's actions of ceasing communication with previously associated AP MLDs, as well as its association with one of the APs associated with neighboring AP MLDs, and performing a series of operations to communicate with neighboring APs, can be called roaming operations. The operating frequencies (e.g., center frequencies) of the first through fifth links can be different. AP MLD 1 701 through AP MLD 3 705 can communicate interconnectedly.For example, AP MLD 1 701 to AP MLD 3 705 can communicate via wired Ethernet. Alternatively, AP MLD 1 701 to AP MLD 3 705 can communicate via wireless LAN. Alternatively, AP MLD 1 701 to AP MLD 3 705 can communicate with each other according to different communication standards than wired Ethernet and wireless LAN. Slave APs of AP MLD 1 701 to AP MLD 3 705 or AP MLD 1 701 to AP MLD 3 705 can communicate with each other to form a new MLD layer. For example, AP MLD 1 701 to AP MLD 3 705 can form a new MLD MAC upper layer or a new MLD MAC lower layer. Alternatively, AP MLD 1 701 to AP MLD 3 705 can form both an MLD MAC upper layer and an MLD MAC lower layer. As an alternative approach, AP MLDs 1 701 to 3 705 may not form an MLD, but instead exchange communication information with each other. As an example, the exchange of communication information may include exchanging operational information (e.g., operational information about link usage and interruption) for roaming operations of STA MLDs associated with the AP MLD, or exchanging status information (e.g., information about sequence numbers (SN), packet numbers (PN), and block acknowledgment scoreboards for downlink and uplink packets of a specific STA MLD) and downlink packets destined for the STA MLD performing the roaming operation. As another example, the exchange of communication information may correspond to the exchange of operational information of the AP MLDs.

[0096] Because AP MLD 1 701 to AP MLD 3 705 communicate with each other, AP MLD 1 701 can know information about neighboring AP MLDs and subordinate APs (e.g., AP MLD 2 703 and AP 2-1 703-1 and AP 2-2 703-2 under AP MLD 2 703). The information about neighboring AP MLDs includes the TBTT information of the subordinate APs. TBTT information can be timing information. That is, TBTT information indicates the expected time or interval for beacon frame transmission for each AP or AP MLD. For example, AP MLD 1 701 can know information about the time when beacon frames 751, 753, 755, and 757 of neighboring AP MLDs will be transmitted relative to the current time.

[0097] AP 1-1 701-1 of AP MLD 1 701 can include and transmit TBTT information of neighboring APs in beacon frame 720. TBTT information can be transmitted via the Simplified Neighbor Report (RNR) information element included in beacon frame 720. STA 1-1 710-1 can receive beacon frame 720 from AP 1. Based on the RNR information element included in beacon frame 720, STA 1-1 710-1 can know the TBTT information of neighboring APs (e.g., the TBTT information of APs under AP MLD 2 703 to AP MLD 3 705).

[0098] The RSSI, SNR, etc., of the beacon frame 720 of AP 1-1 701-1 and / or the data frames received by STA 1-1 710-1 may be lower than the roaming threshold of STA 1-1 710-1. For example, the roaming threshold may be Rth, and the RSSI may be lower than Rth. When the RSSI of a frame received by STA 1-1 710-1 is lower than Rth or under other roaming initiation conditions, STA 1-1 710-1 may send a scan request frame 730. As an example, other roaming initiation conditions may include reducing the RSSI of received frames at a predetermined rate or higher. STA 1-1 710-1 may send the scan request frame 730 to AP 1-1 701-1 based on the TBTT information of neighboring APs. As an alternative approach, STA 1-1 710-1 may not receive beacon frame 720, or the RNR information element may not be included in AP 1-1 701-1's beacon frame 720. Therefore, STA 1-1 710-1 may not know the TBTT information of the neighboring AP. Even when STA 1-1 710-1 does not know the TBTT information of the neighboring AP, STA 1-1 710-1 can still send a scan request frame 730 to AP 1-1 701-1. The scan request frame 730 can be a management frame including action frames, a frame including information elements, a frame with specific information included in the control field (e.g., HT control field) of the MAC header, or other frames. The scan request frame 730 can include channel scan scheduling information requested by STA 1-1 710-1. The channel scan scheduling information includes the TBTT information (or TBTT time) of the neighboring AP, the link ID of the neighboring AP, the BSSID of the neighboring AP, and information about the AP's operating frequency. Channel scan scheduling information can use a list of link IDs or BSSIDs of neighboring APs to instruct the STA to perform a scan at the corresponding AP's TBTT time. Alternatively, the scan request frame 730 can include information requesting channel scan scheduling from AP 1-1 701-1. That is, STA 1-1 710-1 may not send channel scan scheduling information to AP 1-1 701-1. For example, even when no TBTT information for neighboring APs is identified, STA 1-1 710-1 can still receive channel scan scheduling information from AP 1-1 701-1 and scan neighboring APs.

[0099] AP 1-1 701-1 can send a scan response frame 740 to STA 1-1 710-1. The scan response frame 740 can be a response from AP 1-1 701-1 to a scan request frame 730 sent by STA 1-1 710-1. Alternatively, even when AP 1-1 701-1 determines that roaming by STA 1-1 710-1 or STA MLD 1 710 is required, the scan response frame 740 can be sent without receiving a scan request frame. The scan response frame 740 can include a response to channel scan scheduling information included in the scan request frame 730 sent by STA 1-1 710-1. For example, the scan response frame 740 can include information indicating whether AP 1-1 701-1 acknowledges, modifies, or rejects the channel scan scheduling information sent by STA 1-1 710-1. Additionally, the scan response frame 740 may include channel scan scheduling information provided by AP 1-1 701-1 to STA 1-1 710-1. When AP1-1 701-1 confirms the channel scan scheduling of STA 1-1 710-1, the channel scan scheduling information may include information sent by STA 1-1 710-1 without modification, or may not include information sent by STA 1-1 710-1. When AP1-1 701-1 modifies the channel scan scheduling of STA 1-1 710-1, the channel scan scheduling information may include channel scan information proposed by AP 1-1 701-1. When AP 1-1 701-1 rejects the channel scan scheduling of STA 1-1 710-1, the channel response frame 740 may not include the channel scan scheduling information. Alternatively, even when AP 1-1 701-1 rejects the channel scan scheduling of STA 1-1 710-1, the scan response frame 740 may also include channel scan information proposed by AP 1. The channel scan scheduling provided by AP 1-1 701-1 to STA 1-1 710-1 includes TBTT information and the link IDs and / or operating frequency information of neighboring APs, including subordinate APs from AP MLD 2 703 to AP MLD3 705. The TBTTs of neighboring APs can be TBTT aa, TBTTbb, TBTT cc, and TBTT dd, where TBTT aa is the TBTT of AP 2-1 703-1, TBTT bb is the TBTT of AP 2-2 703-2, TBTT cc is the TBTT of AP 3-1 705-1, and TBTT dd is the TBTT of AP 3-2 705-2. The TBTT information included in the scan request frame 730 and scan response frame 740 can indicate the TBTT information of adjacent APs in terms of TU and / or Time Synchronization Function (TSF) offset. 1 TU is 1024 μs.

[0100] The exchange of scan request frames 730 and scan response frames 740 can be performed over multiple links. For example, STAMLD 1 710 can receive a beacon frame 720 from AP MLD 1 701 on at least one of the first or second links and request the transmission of a scan response frame 740. The exchange of scan request frames 730 and scan response frames 740 can be performed on each link. For example, AP 1-1 701-1 and STA 1-1 710-1 operating on the first link can exchange scan request frames 730 and scan response frames 740 to scan AP 2-1 703-1 and AP 3-1 705-1. For example, AP 1-2 701-2 and STA 1-2 710-2 operating on the second link can exchange scan request frames 730 and scan response frames 740 to scan AP 2-2 703-2 and AP 3-2 705-2.

[0101] STA 1-1 710-1 (STA MLD 1 710) can receive scan response frames 740 from AP 1-1 701-1 or MLD 1 701, and STA MLD 1 710 performs channel scanning based on channel scanning scheduling information provided by AP MLD 1 701. At TBTT aa, TBTT bb, and TBTT dd, STA 1-1 710-1 and STA 1-2 710-2 can scan AP 2-1 703-1, AP 2-2 703-2, and AP 3-2 705-2, which operate at frequencies different from AP 1-1 701-1. STA 1-1 710-1 can modify the operating frequency at TBTT aa to scan AP 2-1 703-1 (e.g., modify the operating link to a third link at TBTT aa). STA 1-2 710-2 can modify the operating frequencies at TBTT bb and TBTT dd to scan AP 2-2 703-2 and AP 3-2 705-2 respectively (e.g., modifying the operating links at TBTT bb and TBTT dd to the fourth and fifth links respectively). The time period during which STA 1-1 710-1 and STA 1-2 710-2 modify the operating frequencies at the corresponding TBTT and then operate again on the first and second links can be greater than or equal to 2×Ts+ (the beacon transmission period of the AP), and STA 1-1 710-1 and STA 1-2 710-2 cannot receive frames from AP 1-1 701-1 and AP 1-2 701-2. In other words, when STA1-1 710-1 performs a channel scan, STA1-2 710-2 cannot receive frames, and when STA1-2 710-2 performs a channel scan, STA1-1 710-1 cannot receive frames. Ts is the time required for STA1-1 710-1 and STA1-2 710-2 to switch these operating frequencies. Time Ts can be the EMLSR transition delay time or a time longer than or equal to the EMLSR transition delay time. When STA1-1 710-1 operates after returning to the first link from a different link, STA1-1 701-1 and STA1-2 710-2 cannot or are limited in transmitting frames during Tm, which corresponds to the MediumSyncDelay timer or NAVSyncDelay time. When STA 1-2 710-2 operates after returning to the second link from a link different from the second link, STA 1-1 701-1 and STA 1-2 710-2 cannot or limit the transmission of frames during the Tm period corresponding to the MediumSyncDelay timer or NAVSyncDelay time.

[0102] AP 1-1 701-1 and AP 1-2 701-2 can complete frame transmission to STA 1-1 710-1 and STA 1-2 710-2 before TBTT aa, where TBTT aa is the time when STA 1-1 710-1 scans AP 2-1 703-1. STA 1-1 710-1 and STA 1-2 710-2 can complete frame transmission to AP 1-1 701-1 and AP 1-2 701-2 before TBTT aa. AP 1-1 701-1 and AP 1-2 701-2 can transmit frames to STA 1-1 710-1 and STA 1-2 710-2 before TBTT bb and TBTT cc, where TBTT bb and TBTT cc are the times when STA 1-2 710-2 scans AP 2-2 703-2 and AP 3-2 705-2. STA 1-1 710-1 and STA 1-2 710-2 can transmit frames to AP 1-1 701-1 and AP 1-2 701-2 before TBTT bb and TBTT dd.

[0103] When AP 1-1 701-1, AP 1-2 701-2, STA 1-1 710-1, and STA 1-2 710-2 complete their transmissions before their respective TBTTs, it can be indicated that the transmission was completed before Ts, where Ts is the time used to switch links at each TBTT. Completing a transmission before a specific time can include ending a transmission opportunity (TXOP) before a specific time. When AP 1-1 701-1, AP 1-2 701-2, STA 1-1 710-1, and STA 1-2 710-2 complete a channel access operation (e.g., EDCA backoff operation) near each TBTT (e.g., when the backoff counter reaches 0), AP 1-1 701-1 and AP 1-2 701-2 may not transmit frames to STA 1-1 710-1 and STA 1-2 710-2, and STA 1-1 710-1 and STA 1-2 710-2 may also not transmit frames to AP 1-1 701-1 and AP 1-2 701-2. The backoff counters of AP 1-1 701-1 and AP 1-2 701-2, and / or the backoff counters of STA 1-1 710-1 and STA 1-2 710-2, may remain at 0. Alternatively, even when the backoff counters of AP 1-1 701-1 and AP 1-2 701-2 reach 0, AP 1-1 701-1 and AP 1-2 701-2 can select a new backoff counter to continuously perform backoff operations. Alternatively, AP 1-1 701-1 and AP 1-2 701-2 can determine that the transmission queue does not have frames destined for STA 1-1 710-1 and STA 1-2 710-2, and when frames are present destined for STAs different from STA 1-1 710-1 and STA 1-2 710-2, AP 1-1 701-1 and AP 1-2 701-2 can transmit frames to STAs different from STA 1-1 710-1 and STA 1-2 710-2. After the channel scanning operations of STA 1-1 710-1 and STA 1-2 710-2 are completed, AP 1-1 701-1 and AP 1-2 701-2 or / and STA 1-1 710-1 and STA 1-2 710-2 may transmit frames. During a time period of length greater than or equal to 2×Ts+ (the beacon transmission period of the AP), AP 1-1 701-1 and AP 1-2 701-2 do not transmit frames to STA 1-1 710-1 and STA 1-2 710-2 at TBTT aa, TBTT bb, or TBTT dd.For example, AP 1-1 701-1 and AP 1-2 701-2 delay the transmission of channel access operations to STA 1-1 710-1 and STA 1-2 710-2, or do not transmit frames to STA 1-1 710-1 and STA 1-2 710-2, and wait even when the EDCA backoff counter reaches 0 (e.g., keep the backoff counter at 0 or reselect the backoff counter). AP 1-1 701-1 and AP 1-2 701-2 may transmit frames to STA 1-1 710-1 and STA 1-2 710-2 after this time period. Frames sent from AP 1-1 701-1 and AP 1-2 701-2 to STA 1-1 710-1 and STA 1-2 710-2 can be trigger frames. For example, a trigger frame sent from AP 1-1 710-1 to STA 1-1 710-1 can be a frame used to release the MediumSyncDelay timer or NAVSyncDelay timer of STA 1-1 710-1, which limits frame transmission for the duration of Tm, and can trigger uplink data transmission for STA 1-1 710-1. Alternatively, a frame sent from AP 1-1 701-1 to STA 1-1 710-1 can be a downlink frame.

[0104] At TBTT cc, STA 1-1 710-1 can scan AP3-1 705-1, which operates at the same frequency as AP 1-1 701-1. However, when STA 1-1 710-1 scans AP 3-1 705-1, STA 1-2 710-2 may be unable to transmit / receive. AP 1-1 701-1 and AP 1-2 701-2 can complete frame transmission to STA 1-1 710-1 and STA 1-2 710-2 before TBTT cc, which is the TBTT of AP 3-1 705-1. STA 1-1 710-1 and STA 1-2 710-2 complete frame transmission to AP 1-1 701-1 and AP 1-2 701-2 before TBTT cc.

[0105] STA MLD 1 710 can perform a scan based on scan scheduling information provided by AP MLD 1 701. For example, STA MLD 1 710 can collect information from AP MLD 2 703 to AP MLD 3 705 (e.g., information about subordinate APs from AP MLD 2 703 to AP MLD 3 705). STA MLD 1 710 sends a measurement report frame 760 to AP MLD 1 701. The measurement report frame 760 is a frame used to transmit information about neighboring AP MLDs (that is, AP MLD 2 703 to AP MLD 3 705) (e.g., signal strength, SNR, and link congestion of APs operating under AP MLD 2 703 to AP MLD 3 705). AP MLD 1 701 can respond to the measurement report frame 760 from STA MLD 1 710 using a response frame (e.g., an ACK frame or a block acknowledgment frame). AP MLD 1 701 can determine whether to roam and the roaming target based on information from neighboring AP MLDs of STA MLD 1 710.

[0106] In the implementation, in order to obtain information about neighboring AP MLDs, STA MLD 1 710 can send a probe request frame and then receive a probe response frame, instead of receiving beacon frames 751, 753, 755, and 757 from the APs.

[0107] The following describes an implementation scheme for the channel measurement process. The channel measurement process can be performed between multiple APs and a single STA. The multiple APs include a first AP and the remaining APs. The first AP refers to the AP associated with the STA. The remaining APs refer to the APs other than the first AP among the multiple APs. That is, there can be at least one remaining AP. The multiple APs can be APs connected to each other. Here, "connection" includes wired connections and wireless connections, and connected APs can communicate with each other. For example, multiple APs can be connected to each other wired or wirelessly. As another example, at least some APs can be wirelessly connected to each other, and other APs can be wired to each other.

[0108] Each of the multiple APs can be an MLD. Alternatively, each of the multiple APs can not be an MLD. If the multiple APs are MLDs, the STA can be an MLD. If the multiple APs are not MLDs, the STA can not be an MLD. If the multiple APs and the STA are MLDs, the multiple APs and the STA can be an EMLSR MLD.

[0109] Each of the multiple APs can operate on a different link. For example, the first AP can operate on the first link, the second AP, which is one of the remaining APs, can operate on the second link, and another of the remaining APs can operate on the third link. Here, each link can have a different operating frequency. In the case where each of the multiple APs is an MLD (Multi-Level Display), each AP can operate on multiple links.

[0110] Figure 8 A flowchart illustrating the process of measuring a channel according to an embodiment of the present invention is shown. Figure 8 The channel measurement process is not performed by the MLD but by the STA. The STA (e.g., Figure 3 The STA 310 is connected to the first AP (e.g., Figure 3 (AP 1301). In other words, the STA's operating link is the link operated by the first AP. The link operated by the first AP can be called the first link.

[0111] refer to Figure 8 In step S801, the STA receives and transmits frames on the first link (e.g., Figure 3 Information related to the time of beacon frame 351. Here, the time of frame transmission refers to the time when the frame is transmitted by at least one remaining AP. For example, the time of frame transmission may include the time of transmission by the second AP among the remaining APs (e.g., Figure 3 The time when AP 2 (303) sends frames, and the time when another AP (e.g., ...) sends frames. Figure 3 The AP (AP 3,305) transmits the frame at a specific time. For example, the transmission time can be expressed as an absolute or relative time value relative to the information reception time. Alternatively, the time value can be expressed in time units (e.g., ps, ns, μs, or ms) or resource units (e.g., frames or time slots). The frame may include at least one beacon frame or null data PPDU (NDP) frame. Information related to the transmission time of the frame can be received from the first AP. Information related to the transmission time of the frame can be received through the beacon frame of the first AP. Information related to the transmission time of the frame can be received through the RNR information element of the beacon frame.

[0112] In step S803, the STA sends a scan request message on the first link (e.g., Figure 3The scan request frame (330) can be sent based on whether scan conditions are met. For example, scan conditions can be met if the RISS or SNR of a frame sent from the first AP is equal to or less than a threshold. Scan request messages can be sent in various types of frames. Scan request messages can include scheduling information for the STA. Scheduling information includes at least one of the following: information related to the time of frame transmission, the link ID of at least one remaining AP, the BSSID of at least one remaining AP, or the operating frequency information of at least one remaining AP. Scheduling information can be information instructing the STA on the time and order in which to perform scans. For example, the STA can perform scans according to the order of the link IDs included in the scheduling information.

[0113] In step S805, the STA receives a scan response message (e.g., Figure 3 The scan response frame 340. The scan response message can be a message sent from the first AP. The scan response message can be a message sent in response to a scan request message. Alternatively, the scan response message can be a message sent independently of the scan request message. The scan response message can include a response to scheduling information. For example, the scan response message can include approval, modification, or rejection of scheduling information. If the scan response message includes approval of scheduling information, the scheduling information sent by the STA can be included in the scan response message. If the scan response message includes modification of scheduling information, the scan response message can include scheduling information generated by the first AP. If the scan response message includes rejection of scheduling information, the scan response message may not include scheduling information, or it may include scheduling information generated by the first AP. The scheduling information generated by the first AP includes at least one of the following: the time the frame was sent, the link ID of at least one remaining AP, or the operating frequency information of at least one remaining AP.

[0114] In step S807, the STA measures the channel in the second link. The second link refers to the link operated by the second AP. The second AP refers to one of the remaining APs. For channel measurement, the STA can switch the operating link to the second link when the second AP transmits a frame. For example, the STA can switch the operating link based on the transmitted scheduling information or the scheduling information received from the first AP. Although Figure 8 Not shown in the diagram, but before switching operating links, the STA can send a scan start message to the first AP (e.g., Figure 5 The scan initiation frame 561). After switching the operational link, the STA can receive frames sent by the second AP for channel measurement (e.g., ...). Figure 3(Beacon frame 351). For example, the frame includes a beacon frame or an NDP frame. The STA can measure the channel based on the received frame. For example, the STA can measure the channel by measuring at least one of the signal strength, SNR, or link congestion of the second AP on the operational link. After performing channel measurements for the second AP, channel measurements can be repeated for the other remaining APs. For example, channel measurements can be performed for APs other than the second AP among the remaining APs. That is, channel measurements can be performed for links other than the second link.

[0115] In step S809, the STA sends a measurement report message on the first link (e.g., Figure 3 The measurement report frame 360). After the channel measurement is completed, the STA can switch the operational link to the first link. After the operational link switch is completed, the STA can send a scan completion message to the first AP (e.g., ...). Figure 5 (Scan completion frame 571). The STA can send a measurement report message to the first AP. The measurement report message can include the results of the measurement in step S807. For example, the measurement report message can include at least one of the signal strength, SNR, or link congestion of the second AP measured in step S807.

[0116] Reference Figure 8 The described implementation scheme describes performing channel measurements in a link. That is, in Figure 8 In one embodiment, a measurement report message can be sent after channel measurements are performed on one link. Alternatively, according to another embodiment, a measurement report message can be sent after channel measurements are performed on multiple links. The measurement report message can include measurement results for at least one link. For example, the measurement report message can be sent individually for each link, or alternatively, it can be sent for each group of multiple links. As another example, multiple measurement report messages including at least one measurement result can be sent. Even after sending the measurement report message, steps S807 to S809 can be repeated. For example, after sending a channel report message for at least one link, channel measurements can be performed on the remaining links, and channel report messages can be sent afterward.

[0117] Figure 9 A flowchart illustrating a method for receiving channel measurement reports according to an embodiment of the present invention is shown. This is performed by a first AP. Figure 9 The process (e.g., Figure 3 AP 1 (301). The first AP is not an MLD AP. The first AP operates in the first link. The first AP can obtain the time when the remaining APs send frames from the remaining APs.

[0118] refer to Figure 9In step S901, the first AP sends a transmission frame (e.g., ... Figure 3 The beacon frame 351 contains information about the time of transmission. The transmission time refers to the time when the frame was transmitted by at least one of the remaining APs. For example, the transmission time may include the second AP among the remaining APs (e.g., Figure 3 The time when AP 2 (303) sends frames, and the time when another AP (e.g., ...) sends frames. Figure 3 The time when AP 3 305 sends a frame. For example, the frame can be a beacon frame. The AP can be any of the remaining APs excluding the first AP. It can send a frame to the STA (e.g., Figure 3 The STA 310 sends information about the time of transmission of the frame. Information about the time of transmission of the frame can be received via the beacon frame of the first AP. Information about the time of transmission of the frame can also be received via the RNR information element of the beacon frame.

[0119] In step S903, the first AP receives a scan request message from the STA (e.g., Figure 3 The scan request frame (330) can be used. The STA can generate a scan request message based on whether scan conditions are met. For example, scan conditions can be met if the RSSI or SNR of a frame sent from the first AP is equal to or less than a threshold. The scan request message can be sent in various types of frames. The scan request message can include scheduling information for the STA. The scheduling information includes at least one of the following: information related to the scan time of at least one remaining AP, the link ID of at least one remaining AP, the BSSID of at least one remaining AP, or the operating frequency information of at least one remaining AP. The scheduling information can be information instructing the STA to perform scans in the order they occur. For example, the STA can perform scans according to the order of the link IDs included in the scheduling information.

[0120] In step S905, the first AP sends a scan response message (e.g., Figure 3(Scan response frame 340). A scan response message can be sent to the STA. A scan response message can be sent in response to a scan request message. On the other hand, a scan response message can be sent independently of a scan request message. A scan response message can include a response to scheduling information. For example, a scan response message can include approval, modification, or rejection of scheduling information. If the scan response message includes approval of scheduling information, the scheduling information sent by the STA can be included in the scan response message. If the scan response message includes modification of scheduling information, the scan response message can include scheduling information generated by the first AP. If the scan response message includes rejection of scheduling information, the scan response message may not include scheduling information, or it may include scheduling information generated by the first AP. The scheduling information generated by the first AP includes at least one of the following: the time of frame transmission, the link ID of at least one remaining AP, or the operating frequency information of at least one remaining AP. Before sending a scan response message, the first AP can share information and obtain information about at least one remaining AP by cooperating with at least one remaining AP. The first AP can send a scan response message based on the obtained information about at least one remaining AP. Based on the scheduling information in the scan response message, the first AP can stop sending frames to the STA. That is, the first AP can set a communication prohibition period based on the scan response message.

[0121] In step S907, the first AP receives a measurement report message from the STA (e.g., Figure 3 The measurement report message (360) may include information about at least one remaining AP operating link as measured by the STA. The measurement report message may include at least one of the signal strength, SNR, or link congestion of at least one remaining AP as measured by the STA. The measurement report message may be received after the STA has measured a link operating with one remaining AP. Alternatively, the measurement report message may be received after measurements have been performed for multiple remaining APs. The first AP may determine, based on the received measurement report message, whether the STA is roaming or at least one of the roaming targets.

[0122] exist Figure 8 and Figure 9 In the case where the AP and STA are MLDs, each of the STA, the first AP, and at least one remaining AP can operate on multiple links. For example, the STA can operate on one of the links operated by the first AP (e.g., Figure 4 Steps S801 to S805 are performed in the first link, and can be performed in at least one of the remaining AP operating links (e.g., Figure 4 Step S807 is executed on the third link. For example, a measurement result message can be sent on the link where step S801 was executed.

[0123] The operation of the methods according to various aspects of the present invention can be implemented as a computer-readable program or code in a computer-readable recording medium. The computer-readable recording medium may include all types of recording means for storing data that can be read by a computer system. Furthermore, the computer-readable recording medium can store and execute programs or code that can be distributed across computer systems connected via a network and read in a distributed manner by a computer.

[0124] Additionally, computer-readable recording media may include hardware devices specifically configured to store and execute program commands, such as ROM, RAM, or flash memory. Program commands may include not only machine language code created by a compiler but also high-level language code that can be executed by a computer using an interpreter.

[0125] Although the invention has been described with reference to preferred embodiments thereof, those skilled in the art will understand that various modifications and alterations may be made to the invention without departing from the scope and spirit of the invention as defined by the appended claims.

[0126] Industrial availability This invention can be applied to devices and recording media in wireless local area network systems.

Claims

1. A method for use as a station operator (STA) in a wireless local area network system, the method comprising: Receive information about the time the frame was sent from the first access point (AP); Receive a scan response message generated based on information about the time the frame was sent; Frames are received from the second AP based on the scan response message; The channel is measured based on frames received from the second AP; as well as Send a measurement report message to the first AP. The information regarding the time of frame transmission includes the time when the frame was transmitted by at least one AP, including the second AP.

2. The method according to claim 1, further comprising: Switch the operation link to the link operated by the second AP in order to receive frames from the second AP; as well as Switch the operation link to the link operated by the first AP to send the measurement report message.

3. The method according to claim 2, further comprising: Before switching the operation link to the link operated by the second AP, a scan start message is sent to the first AP; as well as After switching the operation link to the link operated by the first AP, a scan completion message is sent to the first AP.

4. The method of claim 1, further comprising: A scan request message is sent, which includes scheduling information for measuring the channel of the second AP. Among them, scheduling information is generated based on information about the time of frame transmission; The scan response message is sent based on the scan request message and includes information related to the approval, modification, or rejection of scheduling information.

5. The method according to claim 4, wherein, A scan request message is sent based on whether the scan conditions are met. The scanning conditions include cases where the Received Signal Strength Indication (RSSI) or Signal-to-Noise Ratio (SNR) of the frame sent by the first AP is equal to or lower than a predefined threshold.

6. The method according to claim 4, wherein, The scan response message includes information related to changes or rejections of scheduling information, and the scan response message includes scheduling information generated by the first AP.

7. The method according to claim 4, wherein, The scheduling information includes information about the time of frame transmission, the link ID of at least one AP, the BSSID of at least one AP, or at least one operating frequency of at least one AP.

8. The method according to claim 1, wherein, The scan response message is generated based on the collaboration between the first AP and at least one other AP.

9. The method according to claim 1, wherein, The measurement report message includes at least one of the signal strength, SNR, or link congestion of the second AP measured by the STA.

10. The method according to claim 1, wherein, The frame includes at least one of a beacon frame, an NDP frame, or a probe frame.

11. A method for operating a first access point (AP) in a wireless local area network, the method comprising: Obtain information about the time the frame was sent; Send information about the time the frame was sent to the station (STA); Send a scan response message generated based on information about the time the frame was sent; as well as Receive measurement report message from STA. The information regarding the time of frame transmission includes information about the time when the frame was transmitted by at least one AP. The measurement report message includes channel measurement results for a second AP, which is one of at least one AP.

12. The method of claim 11, further comprising receiving a scan request message, in, The scan request message includes scheduling information for the STA to perform channel measurements, and the scheduling information is generated based on information about the time of frame transmission.

13. The method according to claim 12, wherein, A scan response message is sent based on a scan request message, and the scan response message includes information related to the approval, modification, or rejection of scheduling information.

14. The method according to claim 11, wherein, The scan response message is obtained based on cooperation with at least one AP.

15. The method according to claim 11, wherein, The measurement report message includes channel measurement results for the second AP, and includes at least one of the second AP's signal strength, SNR, or link congestion.

16. The method of claim 12, further comprising: Based on scheduling information, prohibited periods are set, during which communication with STA is not performed.

17. A station (STA) in a wireless local area network system, the STA comprising: transceiver; and The processor, which is connected to the transceiver, The processor is configured as follows: Receive information about the time the frame was sent from the first access point (AP); Receive a scan response message generated based on information about the time the frame was sent; Frames are received from the second AP based on the scan response message; The channel is measured based on frames received from the second AP; and Send a measurement report message to the first AP. The information regarding the time of frame transmission includes the time when the frame was transmitted by at least one AP, including the second AP.

18. A first access point (AP) in a wireless local area network, the first AP comprising: transceiver; and The processor, which is connected to the transceiver, The processor is configured as follows: Obtain information about the time the frame was sent; Send information about the time the frame was sent to the station (STA); Send a scan response message generated based on information about the time of the transmitted frame; and Receive measurement report message from STA. The information regarding the time of frame transmission includes information about the time when the frame was transmitted by at least one AP. The measurement report message includes channel measurement results for a second AP, which is one of at least one AP.

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