Multi-link device operating with multiple links and operation method of multi-link device

Abstract

To provide a wireless communication method using a multilink and a wireless communication terminal using the same.SOLUTION: In a wireless communication system, a multi-link device including a plurality of stations 100 each operating with a plurality of links includes a transmitting / receiving unit and a processor. The processor transmits a target wake time (TWT) element from a first station, which is one of the plurality of stations and is coupled to a first AP via a first link, and requests a TWT agreement for a second station operating with a second link and a second AP coupled to the second station.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a multi-link device that operates with multiple links and a method for operating a multi-link device. [Background technology]

[0002] Recently, as the use of mobile devices has become more widespread, wireless LAN technology that can provide them with high-speed wireless Internet services has been attracting attention. Wireless LAN technology is a technology that enables mobile devices such as smartphones, smart pads, laptop PCs, portable multimedia players, embedded devices, etc. to wirelessly connect to the Internet at home, in business, or in specific service areas based on short-distance wireless communication technology.

[0003] Since IEEE (Institute of Electronics Engineers) 802.11 supported the initial wireless LAN technology using the 2.4GHz frequency band, it has put into practical use or is currently developing various technology standards. First, IEEE 802.11b uses the 2.4GHz frequency band and supports a maximum communication speed of 11Mbps. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses the 5GHz frequency band instead of the 2.4GHz band, reducing the impact of interference compared to the significantly more congested 2.4GHz frequency band, and uses OFDM technology to increase communication speeds to a maximum of 54Mbps. However, IEEE 802.11a has the disadvantage of a shorter communication distance than IEEE 802.11b. IEEE 802.11g, like IEEE 802.11b, uses the 2.4GHz band and achieves a maximum transmission speed of 54Mbps and satisfies backward compatibility, which has attracted considerable attention, but it also has an advantage over IEEE 802.11a in communication distance.

[0004] IEEE 802.11n is a technical standard established to overcome the communication speed limitations that have been pointed out as a weakness of wireless LAN. The purpose of IEEE 802.11n is to increase the speed and reliability of the network and to extend the operating distance of the wireless network. In detail, IEEE 802.11n supports a high throughput (HT) of up to 540Mbps or more in data processing speed, and is based on MIMO (Multiple Inputs and Multiple Outputs) technology that uses multiple antennas on both the transmitting and receiving ends to minimize transmission errors and optimize data speed. This standard also uses a coding method that transmits multiple duplicate copies to increase data reliability.

[0005] As the use of wireless LANs becomes more widespread and applications using them become more diverse, the need for new wireless LAN systems to support data throughput rates (Very High Throughput, VHT) higher than those supported by IEEE 802.11n is emerging. Among them, IEEE 802.11ac supports wide bandwidth (80MHz~160MHz) at 5GHz frequency. Although the IEEE 802.11ac standard is defined only in the 5GHz band, it is expected that initial 11ac chipsets will also support operation in the 2.4GHz band for backward compatibility with existing 2.4GHz band products. Theoretically, this standard allows multi-station wireless LAN speeds of at least 1Gbps and maximum single link speeds of at least 500Mbps. This is done by extending the air interface concepts accepted by 802.11n, such as wider radio frequency bandwidth (up to 160MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high density modulation (up to 256QAM). Also, there is IEEE 802.11ad, a method of transmitting data using the 60GHz band instead of the conventional 24GHz / 5GHz. IEEE 802.11ad is a transmission standard that uses beamforming technology to provide speeds of up to 7Gbps, and is suitable for streaming large amounts of data and high bitrate videos such as uncompressed HD video. However, the 60GHz frequency band has the disadvantage that it is difficult to pass through obstacles and can only be used between devices in close proximity.

[0006] Meanwhile, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard is being developed and is in the final stages as the WLAN standard after 802.11ac and 802.11ad to provide high-efficiency and high-performance WLAN communication technology in high-density environments where APs and terminals are densely packed. In an 802.11ax-based WLAN environment, it is necessary to provide high-frequency efficient communication indoors / outdoors in the presence of high density stations and APs (Access Points), and various technologies are being developed to realize this.

[0007] In addition, new WLAN standards have begun to be developed to increase maximum transmission speeds to support new multimedia applications such as high-definition video and real-time games. IEEE 802.11be (Extremely High Throughput, EHT), the 7th generation WLAN standard, is currently being developed with the goal of supporting transmission rates of up to 30Gbps in the 2.4 / 5 / 6GHz bands through wider bandwidth, increased spatial streams, and multiple AP cooperation. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of one embodiment of the present invention is to provide a wireless communication method using multilinks and a wireless communication terminal using the same. [Means for solving the problem]

[0009] According to an embodiment of the present invention, a multi-link device including a plurality of stations each operating on a plurality of links includes a transceiver unit and a processor, the processor being one of the plurality of stations and configured to transmit a target wake time (TWT) element from a first station coupled to a first AP via a first link and to request a TWT agreement for a second station operating on a second link and a second AP coupled to the second station.

[0010] The TWT element may include a bitmap indicating information indicating the links to which the TWT agreement that the TWT element is attempting to establish applies.

[0011] A TWT request station of a TWT agreement for the second station and the second AP may be the second station, and a TWT responding station of a TWT agreement for the second station and the second AP may be the second AP.

[0012] The processor may release a TWT agreement for the second station and the second AP when it receives a TWT release frame from the second AP or when it successfully sends the TWT release frame to the second AP.

[0013] The processor may release the TWT agreement for the second station and the second AP when the second link is deactivated, even without receiving or transmitting a TWT release frame that releases the TWT agreement for the second station and the second AP.

[0014] The TWT element may request multiple TWT agreements to be established for multiple links, including the second link.

[0015] Each of the multiple TWT agreements established for the multiple links may be identified based on a link ID of each of the multiple links.

[0016] Each of the multiple TWT agreements established on the multiple links may be identified based on a link ID of each of the multiple links, a medium access control (MAC) address of the multi-link device, and a TWT Flow ID of each of the multiple TWT agreements established on the multiple links.

[0017] When the processor successfully transmits a TWT release frame or receives the TWT release frame, it can release at least one of multiple TWT agreements established for multiple links based on the link ID indicated by the TWT release frame.

[0018] The processor may release a TWT agreement for the second station and the second AP and transfer a TWT agreement for the second station and the second AP to the first station and the first AP.

[0019] When the processor inherits the TWT agreement for the second station and the second AP to the first station and the first AP, it can apply TWT parameters of the TWT agreement for the second station and the second AP to the TWT agreement for the first station and the first AP.

[0020] An operating method of a multi-link device including a plurality of stations each operating on a plurality of links according to an embodiment of the present invention includes a step of transmitting a target wake time (TWT) element from a first station, which is one of the plurality of stations and is coupled to a first AP via a first link, and requesting a TWT agreement for a second station operating on a second link and a second AP coupled to the second station.

[0021] The TWT element may include a bitmap indicating information indicating the links to which the TWT agreement that the TWT element is attempting to establish applies.

[0022] A TWT request station of a TWT agreement for the second station and the second AP may be the second station, and a TWT responding station of a TWT agreement for the second station and the second AP may be the second AP.

[0023] The operating method may further include a step of releasing a TWT agreement for the second station and the second AP when a TWT release frame is received from the second AP or when the TWT release frame is successfully transmitted to the second AP.

[0024] The operating method may further include a step of releasing a TWT agreement for the second station and the second AP when the second link is deactivated, even without receiving or transmitting a TWT release frame releasing the TWT agreement for the second station and the second AP.

[0025] The TWT element may request multiple TWT agreements to be established for multiple links, including the second link.

[0026] Each of the multiple TWT agreements established for the multiple links may be identified based on a link ID of each of the multiple links.

[0027] Each of the multiple TWT agreements established on the multiple links may be identified based on a link ID of each of the multiple links, a medium access control (MAC) address of the multi-link device, and a TWT Flow ID of each of the multiple TWT agreements established on the multiple links.

[0028] The operating method may further include a step of releasing at least one of a plurality of TWT agreements established for a plurality of links based on a link ID indicated by the TWT release frame when the TWT release frame is successfully transmitted or the TWT release frame is received. Effect of the Invention

[0029] An embodiment of the present invention provides a multi-link device that operates with multiple links, and a method for the multi-link device to perform TWT operation efficiently. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Diagram 2] FIG. 11 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing a configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram showing the configuration of an access point according to an embodiment of the present invention. [Diagram 5] 1 is a diagram illustrating a process in which a STA sets up a link with an AP. [Figure 6] FIG. 1 is a diagram illustrating a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication. [Figure 7] 1 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. [Figure 8] 1 illustrates an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and a method for indicating the same according to an embodiment of the present invention. [Figure 9] 1 illustrates a multi-link device according to an embodiment of the present invention. [Figure 10] 1 illustrates a multi-link operation in which transmissions on different links are performed simultaneously according to an embodiment of the present invention. [Figure 11] 1 illustrates a method for setting a broadcast TWT between an AP and a station according to an embodiment of the present invention. [Figure 12] 4 illustrates an example of an AP setting a quiet period according to an embodiment of the present invention. [Figure 13] A method for a station to set a TXOP taking into account a limited service period according to an embodiment of the present invention will now be described. [Figure 14] 13 illustrates a station re-performing a channel access procedure in consideration of a limited service period according to an embodiment of the present invention. [Figure 15] 13 illustrates an operation of an AP prematurely terminating a limited service period according to an embodiment of the present invention. [Figure 16] 1 shows a format of a TWT element according to an embodiment of the present invention. [Figure 17] 1 illustrates a multi-link device performing TWT agreement according to an embodiment of the present invention. [Figure 18]According to an embodiment of the present invention, a station included in a multilink device performs TWT negotiation for other stations included in the multilink device in which the station is included. [Figure 19] 13 illustrates an operation of a multi-link device according to an embodiment of the present invention for releasing a TWT agreement. [Figure 20] 13 shows the format of the Individual TWT parameter set field of the TWT element in an embodiment of the present invention. [Figure 21] 13 illustrates the format of the remaining TWT Flow Identifier subfields other than the first TWT Flow Identifier subfield in accordance with an embodiment of the present invention. [Figure 22] 13 shows the format of a Control field included in a TWT element transmitted by a multilink device according to an embodiment of the present invention. [Diagram 23] 13 shows a format of an Action field of a TWT release frame transmitted by a multi-link device according to an embodiment of the present invention. [Figure 24] 13 illustrates an MLD TWT Flow field according to an embodiment of the present invention. [Diagram 25] 13 shows the format of an MLD TWT Flow field for yet another embodiment of the present invention. [Figure 26] 13 illustrates a TWT release frame for releasing a TWT agreement established in a multilink device according to an embodiment of the present invention. [Figure 27] 13 illustrates an embodiment of the present invention in which a TWT agreement established between multilink devices is implicitly terminated. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The terms used in this specification are selected as general terms that are currently widely used as much as possible in consideration of the functions of the present invention, but this may vary depending on the intentions, customs, or the emergence of new technologies of the engineers in the relevant technical field. In addition, in certain cases, the applicant may arbitrarily select terms, and in such cases, the meanings of the terms will be described in the description of the relevant invention. Therefore, it is clear that the terms used in this specification should be interpreted not simply as terms, but based on the substantial meanings of the terms and the contents of this specification as a whole.

[0032] Throughout the specification, when a component is "connected" to another component, this includes not only when it is "directly connected" to another component, but also when it is "electrically connected" with another component in between. Furthermore, when a component "includes" a specific component, this means that it may further include the other component, not excluding the other component, unless otherwise specified to the contrary. In addition, limitations such as "greater than" or "less than" based on a specific critical value may be appropriately replaced with "more than" or "less than" depending on the embodiment.

[0033] Hereinafter, in the present invention, the terms field and subfield may be used interchangeably.

[0034] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention.

[0035] A wireless LAN system includes one or more Basic Service Sets (BSS), which are a set of devices that can successfully synchronize and communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

[0036] As shown in FIG. 1, infrastructure BSSs BSS1 and BSS2 include one or more stations STA1, STA2, STA3, STA4, and STA5, access points AP-1 and AP-2 which are stations providing a distribution service, and a distribution system DS which connects multiple access points AP-1 and AP-2.

[0037] A station (STA) is any device including a medium access control (MAC) and a physical layer interface for a wireless medium according to the IEEE 802.11 standard, and in a broad sense includes not only non-AP stations but also APs. In this specification, the term "terminal" refers to either a non-AP or an AP, or both. A station for wireless communication includes a processor and a communication unit, and further includes a user interface unit and a display unit, etc., depending on the embodiment. The processor generates frames to be transmitted through a wireless network, processes frames received through the wireless network, and performs various other processes for controlling the station. The communication unit is functionally connected to the processor and transmits and receives frames through the wireless network for the station. In the present invention, the term "terminal" is used to include a user equipment (UE).

[0038] An access point (AP) is an entity that provides a connection to a distribution system DS via a wireless medium for a station associated therewith. In an infrastructure BSS, communication between non-AP stations is generally performed via the AP, but when a direct link is set up, direct communication is possible between non-AP stations. Meanwhile, in the present invention, AP is used as a concept including a personal BSS coordination point (PCP), but in a broad sense, AP includes all concepts such as a central controller, a base station (BS), a node B, a base transceiver system (BTS), or a site controller. In the present invention, AP is also referred to as a base wireless communication terminal, but in a broad sense, the base wireless communication terminal is used as a term including an AP, a base station, an eNodeB (eNB), and a transmission point TP. In addition, the base wireless communication terminal includes various types of wireless communication terminals that allocate communication medium resources and perform scheduling in communication with a plurality of wireless communication terminals.

[0039] A plurality of infrastructure BSSs are connected to each other via a distribution system DS. In this case, a plurality of BSSs connected to each other via the distribution system is called an Extended Service Set (ESS).

[0040] 2 is a diagram showing an independent BSS, which is a wireless LAN system according to another embodiment of the present invention, in which the same or corresponding parts in the embodiment of FIG. 2 are the same as or correspond to the embodiment of FIG.

[0041] BSS3 shown in Figure 2 is an independent BSS and does not include an AP, so all stations (STA6, STA7) are not connected to an AP. An independent BSS is not allowed to connect to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) is directly connected to each other.

[0042] 3 is a block diagram showing a configuration of a station 100 according to an embodiment of the present invention. As shown in the figure, the station 100 according to the embodiment of the present invention includes a processor 110, a communication unit 120, a user interface unit 140, a display unit 150, and a memory 160.

[0043] First, the communication unit 120 transmits and receives wireless signals such as wireless LAN packets, and may be built into or externally provided in the station 100. According to an embodiment, the communication unit 120 may include at least one communication module using different frequency bands. For example, the communication unit 120 may include communication modules of different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to an embodiment, the station 100 may include a communication module using a frequency band of 7.125 GHz or more and a communication module using a frequency band of 7.125 GHz or less. Each communication module may perform wireless communication with an AP or an external station based on the wireless LAN standard of the frequency band supported by the communication module. The communication unit 120 may operate only one communication module at a time or operate multiple communication modules simultaneously according to the performance and requirements of the station 100. When the station 100 includes multiple communication modules, each communication module may be provided in an independent form, or multiple modules may be integrated into one chip. In an embodiment of the present invention, the communication unit 120 may represent a radio frequency (RF) communication module that processes RF signals.

[0044] Next, the user interface 140 includes various types of input / output means provided in the station 100. That is, the user interface unit 140 receives user input using various input means, and the processor 110 controls the station 100 based on the received user input. Also, the user interface unit 140 performs output based on a command from the processor 110 using various output means.

[0045] Then, the display unit 150 outputs an image on a display screen. The display unit 150 outputs various display objects such as a user interface based on the contents performed by the processor 110 or a control command of the processor 110. The memory 160 also stores control programs used by the station 100 and various data associated therewith. Such control programs include connection programs required for the station 100 to connect to an AP or an external station.

[0046] The processor 110 of the present invention executes various commands or programs to process data within the station 100. The processor 110 also controls each unit of the station 100 and controls transmission and reception of data between the units. According to an embodiment of the present invention, the processor 110 executes a program for connection with an AP stored in the memory 160 and receives a communication setup message transmitted by the AP. The processor 110 also reads information on the priority conditions of the station 100 included in the communication setup message and requests a connection to the AP based on the information on the priority conditions of the station 100. The processor 110 of the present invention may refer to a main control unit of the station 100, or may refer to a control unit for individually controlling some components of the station 100, for example, the communication unit 120, depending on the embodiment. That is, the processor 110 may be a modem that modulates and demodulates a wireless signal transmitted and received from the communication unit 120, or a modulator and / or demodulator. The processor 110 controls various operations of transmitting and receiving wireless signals of the station 100 according to an embodiment of the present invention. A detailed embodiment of the present invention will be described later.

[0047] The station 100 shown in FIG. 3 is a block diagram according to an embodiment of the present invention, and the separate blocks are used to logically distinguish the elements of the device. Thus, the above-mentioned device elements may be mounted on one chip or multiple chips depending on the design of the device. For example, the processor 110 and the communication unit 120 may be integrated and embodied on one chip, or may be embodied on separate chips. In addition, in an embodiment of the present invention, some components of the station 100, such as the user interface unit 140 and the display unit 150, may be selectively provided in the station 100.

[0048] 4 is a block diagram showing a configuration of an AP 200 according to an embodiment of the present invention. As shown in the figure, the AP 200 according to the embodiment of the present invention includes a processor 210, a communication unit 220, and a memory 260. In FIG. 4, a duplicated description of parts of the configuration of the AP 200 that are the same as or correspond to the configuration of the station 100 in FIG. 3 will be omitted.

[0049] Referring to FIG. 4, the AP 200 according to the present invention includes a communication unit 220 for operating a BSS in at least one frequency band. As described above in the embodiment of FIG. 3, the communication unit 220 of the AP 200 may also include a plurality of communication modules using different frequency bands. That is, the AP 200 according to the embodiment of the present invention may include two or more communication modules using different frequency bands, for example, any of 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP 200 may include a communication module using a frequency band of 7.125 GHz or higher and a communication module using a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with a station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 220 may operate only one communication module at a time or operate multiple communication modules simultaneously according to the performance and requirements of the AP 200. In the embodiment of the present invention, the communication unit 220 may represent an RF communication module that processes RF (Radio Frequency) signals.

[0050] Next, the memory 260 stores control programs used in the AP 200 and various data associated therewith. Such control programs include a connection program for managing the connection of stations. Also, the processor 210 controls each unit of the AP 200 and controls transmission and reception of data between the units. According to an embodiment of the present invention, the processor 210 executes a program for connection with a station stored in the memory 260 and transmits a communication setting message to one or more stations. At this time, the communication setting message includes information regarding connection priority conditions of each station. Also, the processor 210 performs connection setting in response to a connection request of a station. According to an embodiment, the processor 210 is a modem or a modulation / demodulation unit that modulates and demodulates a wireless signal transmitted and received from the communication unit 220. The processor 210 controls various operations of transmitting and receiving wireless signals of the AP 200 according to an embodiment of the present invention. A detailed embodiment thereof will be described later.

[0051] FIG. 5 is a diagram illustrating a process in which a STA establishes a link with an AP.

[0052] 5, the link between the STA 100 and the AP 200 is set up through three steps: scanning, authentication, and association. First, the scanning step is a step in which the STA 100 acquires connection information of the BSS operated by the AP 200. There are two methods for performing scanning: a passive scanning method in which the STA 100 acquires information using only a beacon message S101 periodically transmitted by the AP 200, and an active scanning method in which the STA 100 transmits a probe request to the AP S103, receives a probe response from the AP S105, and acquires connection information.

[0053] The STA 100 that has successfully received wireless connection information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200 (S107b), and performs an authentication step. After the authentication step is performed, the STA 100 transmits an association request (S109a), receives an association response from the AP 200, and performs an association step (S109b). In this specification, association basically means wireless association, but the present invention is not limited thereto, and association in a broad sense includes both wireless association and wired association.

[0054] Meanwhile, an 802.1X-based authentication step S111 and an IP address acquisition step S113 via DHCP are additionally performed. In Fig. 5, the server 300 is a server that processes 802.1X-based authentication with the STA 100, and may be physically connected to the AP 200 or may exist as a separate server.

[0055] FIG. 6 is a diagram showing a Carrier Sense Multiple Access (CSMA) / Collision Avoidance (CA) method used in wireless LAN communication.

[0056] A terminal performing wireless LAN communication performs carrier sensing before transmitting data to check whether a channel is occupied or not. If a wireless signal of a certain strength or more is detected, the channel is determined to be occupied and the terminal delays access to the channel. This process is called Clear Channel Assessment (CCA), and the level that determines whether or not the signal is detected is called the CCA threshold. If a wireless signal of a strength greater than the CCA threshold is received by the terminal and the terminal is the receiver, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected from the channel or a wireless signal of a strength less than the CCA threshold is detected, the channel is determined to be idle.

[0057] If the channel is determined to be in an idle state, each terminal having data to transmit performs a backoff procedure after an IFS (Inter Frame Space) according to the status of each terminal, for example, an AIFS (Arbitration IFS) or a PIFS (PCF IFS). In some embodiments, the AIFS is used as a configuration to replace the conventional DIFS (DCF IFS). Each terminal waits while decreasing a slot time of a random number determined for the corresponding terminal during an interval of the idle state of the channel, and a terminal that has exhausted all the slot time attempts to access the corresponding channel. In this manner, a section in which each terminal performs a backoff procedure is called a contention window section. At this time, the random number can be called a backoff counter. That is, an initial value of the backoff counter is set by an integer that is a random number obtained by the terminal. If the terminal detects that the channel is idle during the slot time, the terminal can decrease the backoff counter by 1. Also, if the backoff counter reaches 0, the terminal may be allowed to perform channel access on the corresponding channel. Thus, a terminal may be allowed to transmit if the channel is idle during the AIFS time and the backoff counter slot time.

[0058] If a specific terminal succeeds in accessing the channel, the terminal transmits data through the channel. However, if the terminal attempting access collides with another terminal, the colliding terminals are assigned new random numbers and perform a backoff procedure again. According to one embodiment, the random numbers newly assigned to each terminal are determined within a range (2*CW) twice the range (contention window, CW) of the random numbers previously assigned to the terminal. Meanwhile, each terminal attempts access by performing a backoff procedure again in the next contention window period, and at this time, each terminal performs the backoff procedure from the slot time remaining in the previous contention window period. In this manner, each terminal performing wireless LAN communication can avoid collision with each other on a specific channel.

[0059] <Examples of various PPDU formats>

[0060] FIG 7 shows an example of various standard generation PPDU (PLCP Protocol Data Unit) formats. More specifically, FIG 7(a) shows an example of a legacy PPDU format based on 802.11a / g, FIG 7(b) shows an example of a HE PPDU format based on 802.11ax, and FIG 7(c) shows an example of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. Also, FIG 7(d) shows detailed field configurations of L-SIG and RL-SIG commonly used in the PPDU formats.

[0061] 7(a), the preamble of the legacy PPDU includes a legacy short training field (L-STF), a legacy long training field (L-LTF), and a legacy signal field (L-SIG). In an embodiment of the present invention, the L-STF, L-LTF, and L-SIG may be referred to as a legacy preamble.

[0062] Referring to FIG. 7(b), the preamble of the HE PPDU further includes a RL-SIG (Repeated Legacy Short Training field), a HE-SIG-A (High Efficiency Signal A field), a HE-SIG-B (High Efficiency Signal B field), a HE-STF (High Efficiency Short Training field), and a HE-LTF (High Efficiency Long Training field) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF can be referred to as an HE preamble. The specific configuration of the HE preamble may be modified according to the HE PPDU format. For example, the HE-SIG-B may be used only in the HE MU PPDU format.

[0063] Referring to FIG. 7(c), the preamble of the EHT PPDU further includes a RL-SIG (Repeated Legacy Short Training field), a U-SIG (Universal Signal field), an EHT-SIG-A (Extremely High Throughput Signal A field), an EHT-SIG-A (Extremely High Throughput Signal B field), an EHT-STF (Extremely High Throughput Short Training field), and an EHT-LTF (Extremely High Throughput Long Training field) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF can be called an EHT preamble. The specific configuration of the non-legacy preamble may be modified according to the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some formats of the EHT PPDU format.

[0064] The L-SIG field included in the preamble of the PPDU is configured with a total of 64 subcarriers by applying 64 FFT OFDM. Of these, 48 subcarriers excluding the guard subcarriers, DC subcarriers, and pilot subcarriers are used for L-SIG data transmission. Since BPSK and Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information configuration of the L-SIG.

[0065] Referring to FIG. 7(d), the L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field is composed of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which is a combination of a modulation method such as BPSK / QPSK / 16-QAM / 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The total length of the PPDU can be indicated by combining the information in the L_RATE field and the L_LENGTH field. In the non-legacy PPDU format, the L_RATE field is set to the minimum speed of 6 Mbps.

[0066] The unit of the L_LENGTH field is byte, and a total of 12 bits are allocated so that a maximum of 4095 can be signaled. The length of the corresponding PPDU can be indicated in combination with the L_RATE field. In this case, legacy and non-legacy terminals can interpret the L_LENGTH field in different ways.

[0067] First, a method in which a legacy or non-legacy terminal analyzes the length of the PPDU using the L_LENGTH field is as follows. When the L_RATE field is set to 6 Mbps, 3 bytes (i.e., 24 bits) may be transmitted at 4 us, which is one symbol duration of 64 FFT. Therefore, the number of 64 FFT reference symbols after the L-SIG is obtained by adding 3 bytes corresponding to the SVC field and the Tail field to the L_LENGTH field value and dividing it by 3 bytes, which is the transmission amount of one symbol. The length of the PPDU, i.e., the reception time (RXTIME), is obtained by multiplying the obtained number of symbols by 4 us, which is one symbol duration, and adding 20 us for the transmission of the L-STF, L-LTF, and L-SIG. This can be expressed as the following Equation 1.

[0068]

number

[0069] At this time,

[0070]

number

[0071] represents the smallest natural number greater than or equal to x. Since the maximum value of the L_LENGTH field is 4095, the length of the PPDU may be set to a maximum of 5.484 ms. A non-legacy terminal transmitting the PPDU must set the L_LENGTH field as shown in Equation 3 below.

[0072]

number

[0073] Here, TXTIME is the total transmission time constituting the PPDU, and is expressed as the following Equation 4. In this case, TX represents the transmission time of X.

[0074]

number

[0075] Referring to the above formula, the length of the PPDU is calculated based on the rounded up value of L_LENGTH / 3. Therefore, for any value of k, three different values ​​of L_LENGTH={3k+1, 3k+2, 3(k+1)} indicate the same PPDU length.

[0076] Referring to FIG. 7(e), the U-SIG (Universal SIG) field remains in the EHT PPDU and the PPDU of the succeeding generation of WLAN, and plays a role in identifying which generation of PPDU it is, including 11be. The U-SIG is two symbols of 64FFT-based OFDM and can transmit a total of 52 bits of information. Of these, 43 bits excluding the CRC / tail 9 bits are roughly divided into a VI (Version Independent) field and a VD (Version Dependent) field.

[0077] The VI bit will maintain the current bit configuration, and even if a subsequent generation PPDU is defined, a current 11be terminal can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field is composed of PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits, and serves to sequentially distinguish 11be and subsequent generation WLAN standards by version. 11be has a value of 000b. The UL / DL field distinguishes whether the corresponding PPDU is an uplink / downlink PPDU. The BSS color means a BSS-specific identifier defined in 11ax, and has a value of 6 bits or more. The TXOP means a transmit opportunity duration that was transmitted in the MAC header, but by adding it to the PHY header, the length of the TXOP containing the corresponding PPDU can be inferred without decoding the MPDU, and has a value of 7 bits or more.

[0078] The VD field may be composed of fields commonly used in any PPDU format, such as PPDU format and BW, which are signaling information useful only for PPDUs of the 11be version, and fields defined differently for each PPDU format. The PPDU format is a division factor that distinguishes EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), EHT ER (Extended Range) PPDU, etc. The BW field mainly signals five basic PPDU BW options of 20, 40, 80, 160 (80+80), and 320 (160+160) MHz (BWs that can be expressed in the form of a power of 20*2 can be called basic BWs), and various remaining PPDU BWs formed by preamble puncturing. After being signaled at 320 MHz, some 80 MHz may be signaled in a punctured form. Also, the punctured and modified channel shape may be directly signaled in the BW field, or may be signaled using both the BW field and a field that appears after the BW field (e.g., a field in the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signalings are possible, so a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signalings are possible, so a maximum of 11 puncturing modes can be signaled.

[0079] The fields located after the BW field vary depending on the type and format of the PPDU. The MU PPDU and the SU PPDU may be signaled in the same PPDU format, and a field for distinguishing the MU PPDU from the SU PPDU may be located before the EHT-SIG field, and additional signaling may be performed for this purpose. Both the SU PPDU and the MU PPDU include an EHT-SIG field, but some fields that are not necessary in the SU PPDU may be compressed. In this case, the information of the compressed field may be omitted or may have a reduced size compared to the size of the original field included in the MU PPDU. For example, in the case of the SU PPDU, the common field of the EHT-SIG may be omitted or replaced, or the user-specific field may be replaced or reduced to one, and may have a different configuration.

[0080] Alternatively, the SU PPDU may further include a compression field indicating whether or not it is compressed, and some fields (eg, the RA field, etc.) may be omitted depending on the value of the compression field.

[0081] When a part of the EHT-SIG field of the SU PPDU is compressed, the information included in the compressed field may be signaled together in an uncompressed field (e.g., a common field, etc.). In the case of the MU PPDU, since it is a PPDU format for simultaneous reception by multiple users, the EHT-SIG field must be transmitted after the U-SIG field, and the amount of information signaled may be variable. That is, since multiple MU PPDUs are transmitted to multiple STAs, each STA must recognize the location of the RU to which the MU PPDU is transmitted, the STA to which each RU is assigned, and whether the transmitted MU PPDU was transmitted to itself. Therefore, the AP must transmit the above information in the EHT-SIG field. To this end, the U-SIG field signals information for efficiently transmitting the EHT-SIG field, which may be the number of symbols of the EHT-SIG field and / or MCS, which is a modulation method. The EHT-SIG field may include the size and location information of the RU assigned to each user.

[0082] In the case of a SU PPDU, a STA may be assigned multiple RUs, and the multiple RUs may be contiguous or discontinuous. If the RUs assigned to the STA are not contiguous, the STA can receive the SU PPDU efficiently only by recognizing the RUs punctured in between. Therefore, the AP can transmit the SU PPDU including information on the punctured RUs among the RUs assigned to the STA (e.g., the puncturing pattern of the RUs, etc.). That is, in the case of a SU PPDU, a puncturing mode field including information indicating whether a puncturing mode is applied and the puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field may signal the type of discontinuous channels that appear within the bandwidth.

[0083] The form of the signaled discontinuous channel is limited, and indicates the BW and discontinuous channel information of the SU PPDU in combination with the value of the BW field. For example, in the case of a SU PPDU, since it is a PPDU transmitted only to a single UE, the STA can recognize the bandwidth allocated to itself from the BW field included in the PPDU, and can recognize the punctured resources of the allocated bandwidth from the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the UE can receive the PPDU in the remaining resource units other than the specific channel of the punctured resource unit. In this case, the multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0084] The reason why only limited discontinuous channel types are signaled is to reduce the signaling overhead of SU PPDU. Since puncturing may be performed for each 20 MHz subchannel, if puncturing is performed for a BW having multiple 20 MHz subchannels such as 80, 160, and 320 MHz, in the case of 320 MHz, the discontinuous channel type (when only the end 20 MHz is punctured and considered as discontinuous) must be signaled by expressing whether or not the remaining 15 20 MHz subchannels other than the primary channel are used. In this way, using 15 bits to signal discontinuous channel types for single user transmission may result in excessive signaling overhead when considering the low transmission speed of the signaling part.

[0085] The present invention proposes a method for signaling the discontinuous channel type of the SU PPDU, illustrates the discontinuous channel type determined by the proposed method, and proposes a method for signaling the primary 160 MHz and secondary 160 MHz puncturing types in the 320 MHz BW configuration of the SU PPDU.

[0086] In addition, in one embodiment of the present invention, a method is proposed in which the configuration of the PPDU indicated by the preamble puncturing BW value is different depending on the PPDU format signaled in the PPDU format field. Assuming that the BW field is 4 bits, in the case of EHT SU PPDU or TB PPDU, one symbol of EHT-SIG-A is further signaled after U-SIG, or EHT-SIG-A does not need to be signaled from the beginning, so that up to 11 puncturing modes must be completely signaled using only the BW field of U-SIG in consideration of this. However, in the case of EHT MU PPDU, EHT-SIG-B is further signaled after U-SIG, so up to 11 puncturing modes can be signaled in a different manner from SU PPDU. In the case of EHT ER PPDU, the BW field is set to 1 bit, and it is possible to signal whether the PPDU uses a 20 MHz or 10 MHz band. Detailed puncturing patterns for each PPDU type will be described in detail below with reference to FIG. 11 and FIG. 12.

[0087] FIG. 7(f) shows the format-specific field configuration of the VD field when the PPDU format field of the U-SIG indicates EHT MU PPDU. In the case of MU PPDU, SIG-B, which is a signaling field for simultaneous reception by multiple users, is required, and SIG-B may be transmitted after U-SIG without a separate SIG-A. For this purpose, U-SIG must signal information for decoding SIG-B. Such fields include SIG-B MCS, SIG-B DCM, Number of SIG-B Symbols, SIG-B Compression, and Number of EHT-LTF Symbols.

[0088] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and a method for indicating the same according to an embodiment of the present invention.

[0089] 8, a PPDU may be composed of a preamble and a data portion, and the format of an EHT PPDU, which is one type, may be distinguished by a U-SIG field included in the preamble. Specifically, whether the format of the PPDU is an EHT PPDU may be indicated based on a PPDU format field included in the U-SIG field.

[0090] 8(a) shows an example of an EHT SU PPDU format for a single STA. The EHT SU PPDU is a PPDU used for single user (SU) transmission between an AP and a single STA, and an EHT-SIG-A field for additional signaling may be located after the U-SIG field.

[0091] 8(b) shows an example of an EHT trigger-based PPDU format, which is an EHT PPDU transmitted based on a trigger frame. The EHT trigger-based PPDU is an EHT PPDU transmitted based on a trigger frame, and is an uplink PPDU used for responding to the trigger frame. Unlike the EHT SU PPDU, the EHT PPDU does not have an EHT-SIG-A field after the U-SIG field.

[0092] 8(c) shows an example of an EHT MU PPDU format, which is an EHT PPDU for multiple users. The EHT MU PPDU is a PPDU used to transmit a PPDU to one or more STAs. In the EHT MU PPDU format, an HE-SIG-B field may be located after the U-SIG field.

[0093] Fig. 8(d) shows an example of an EHT ER SU PPDU format used for single-user transmission with an STA in an extended range. The EHT ER SU PPDU may be used for single-user transmission with a STA in a wider range than the EHT SU PPDU described in Fig. 8(a), and the U-SIG field may be repeatedly positioned on the time axis.

[0094] The EHT MU PPDU described in (c) of FIG. 8 can be used by the AP for downlink transmission to multiple STAs. In this case, the EHT MU PPDU can include scheduling information so that multiple STAs can simultaneously receive the PPDU transmitted from the AP. The EHT MU PPDU can convey AID information of the receiver and / or sender of the PPDU transmitted through the user specific field of the EHT-SIG-B to the STA. Therefore, multiple terminals receiving the EHT MU PPDU can perform spatial reuse based on the AID information of the user specific field included in the preamble of the received PPDU.

[0095] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information regarding a resource unit configuration (e.g., a resource unit division form) in a specific bandwidth (e.g., 20 MHz, etc.) on the frequency axis. That is, the RA field may indicate a resource unit configuration divided by a bandwidth for transmitting the HE MU PPDU so that the STA receives the PPDU. Information on the STA allocated (or designated) to each divided resource unit may be included in a user specific field of the EHT-SIG-B and transmitted to the STA. That is, the user specific field may include one or more user fields corresponding to each divided resource unit.

[0096] For example, a user field corresponding to at least one resource unit used for data transmission among the multiple divided resource units may include the AID of a receiver or sender, and a user field corresponding to the remaining resource units not used for data transmission may include a null STA ID that has already been set.

[0097] For ease of explanation, the term frame or MAC frame may be used interchangeably with MPDU in this specification.

[0098] When one wireless communication device communicates using multiple links, the communication efficiency of the wireless communication device can be improved. In this case, the link is a physical path, and may be configured as one wireless medium that can be used to transmit MSDU (MAC service data unit). For example, when the frequency band of any one link is being used by another wireless communication device, the wireless communication device can continue to communicate using another link. In this way, the wireless communication device can effectively use multiple channels. Also, when the wireless communication device simultaneously communicates using multiple links, the overall throughput can be increased. However, the existing wireless LAN is specified on the premise that one wireless communication device uses one link. For this reason, a wireless LAN operation method for using multiple links is required. A wireless communication method of a wireless communication device using multiple links will be described with reference to Figs. 9 to 26. First, a specific form of a wireless communication device using multiple links will be described with reference to Fig. 9.

[0099] FIG. 9 shows a multi-link device according to an embodiment of the present invention.

[0100] For the wireless communication method using the above-mentioned multiple links, a multi-link device (MLD) may be defined. The multi-link device may represent a device having one or more affiliated stations. According to a specific embodiment, the multi-link device may represent a device having two or more affiliated stations. Also, the multi-link device may exchange a multi-link element. The multi-link element includes information on one or more stations or one or more links. The multi-link element may include a multi-link setup element, which will be described later. In this case, the multi-link device may be a logical entity. Specifically, the multi-link device may have multiple affiliated stations. The multi-link device may be called a multi-link logical entity (MLLE) or a multi-link entity (MLE). The multi-link device may have one MAC service access point (SAP) up to a logical link control (LLC). Also, the MLD may have one MAC data service.

[0101] The stations included in the multilink device can operate on multiple links. Also, the stations included in the multilink device can operate on multiple channels. Specifically, the stations included in the multilink device can operate on different links or different channels. For example, the stations included in the multilink device can operate on different channels of 2.4 GHz, 5 GHz, and 6 GHz.

[0102] The operation of the multilink device may be referred to as multilink operation, MLD operation, or multi-band operation. If a station associated with the multilink device is an AP, the multilink device may be referred to as AP MLD. If a station associated with the multilink device is a non-AP station, the multilink device may be referred to as non-AP MLD.

[0103] FIG. 9 shows the operation of communication between non-AP MLD and AP-MLD. Specifically, non-AP MLD and AP-MLD each communicate using three links. AP MLD includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). Non-AP MLD includes a first non-AP STA (non-AP STA1), a second non-AP STA (non-AP STA2), and a third non-AP STA (non-AP STA3). The first AP (AP1) and the first non-AP STA (non-AP STA1) communicate through a first link (Link1). Also, the second AP (AP2) and the second non-AP STA (non-AP STA2) communicate through a second link (Link2). Also, the third AP (AP3) and the third non-AP STA (non-AP STA3) communicate through a third link (Link3).

[0104] The multi-link operation may include a multi-link setup operation. The multi-link setup corresponds to the association operation of the single-link operation described above, and must be preceded for frame exchange in the multi-link. The multi-link device may obtain information required for the multi-link setup from the multi-link setup element. Specifically, the multi-link setup element may include capability information related to the multi-link. In this case, the capability information may include information indicating whether one of the multiple devices included in the multi-link device can transmit and the other devices can receive at the same time. In addition, the capability information may include information regarding links available to each station included in the MLD. In addition, the capability information may include information regarding channels available to each station included in the MLD.

[0105] The multilink setting may be set by negotiation between peer stations. Specifically, the multilink setting may be set by communication between stations without communication with the AP. The multilink setting may be set through any one of the links. For example, even if the first link to the third link are set through the multilink, the multilink setting may be set through the first link.

[0106] Also, a mapping between a traffic identifier (TID) and a link may be set. Specifically, a frame corresponding to a specific TID value may be exchanged only through a link designated in advance. The mapping between a TID and a link may be set on a directional-based basis. For example, when a plurality of links are set between a first multilink device and a second multilink device, the first multilink device may be set to transmit a frame of a first TID to a plurality of first links, and the second multilink device may be set to transmit a frame of a second TID to the first link. Also, a default setting may exist for the mapping between a TID and a link. Specifically, when there is no additional setting in the multilink setting, the multilink device may exchange frames corresponding to a TID in each link according to a default setting. In this case, the default setting may be that all TIDs are exchanged in any one link.

[0107] The TID will be specifically described. The TID is an ID for classifying traffic and data to support QoS (quality of service). The TID may be used and assigned in a layer higher than the MAC layer. The TID may indicate a traffic category (TC) or a traffic stream (TS). The TID may be classified into 16 types. For example, the TID may be designated as one of 0 to 15. The TID value to be used may be designated differently depending on an access policy, a channel access, or a medium access method. For example, when EDCA (enhanced distributed channel access) or HCAF (hybrid coordination function contention based channel access) is used, the TID value may be assigned in the range of 0 to 7. When EDCA is used, the TID may indicate a user priority (UP). In this case, the UP may be designated by the TC or the TS. The UP may be assigned in a layer higher than the MAC. Also, when HCCA (HCF controlled channel access) or SPCA is used, the TID may be assigned a value in the range of 8 to 15. When HCCA or SPCA is used, the TID may indicate a TSID. Also, when HEMM or SEMM is used, the TID may be assigned a value in the range of 8 to 15. When HEMM or SEMM is used, the TID may indicate a TSID.

[0108] UP and AC (access category) may be mapped. AC may be a label for providing QoS in EDCA. AC may be a label for indicating an EDCA parameter set. EDCA parameters or EDCA parameter sets are parameters used in channel contention in EDCA. QoS stations can guarantee QoS using AC. AC may include AC_BK, AC_BE, AC_VI, and AC_VO. AC_BK, AC_BE, AC_VI, and AC_VO may indicate background, best effort, video, and voice, respectively. AC_BK, AC_BE, AC_VI, and AC_VO may be classified into lower ACs. For example, AC_VI may be subdivided into AC_VI primary and AC_VI alternate. AC_VO may be subdivided into AC_VO primary and AC_VO alternate. UP or TID may be mapped to AC. For example, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI, AC_VI, AC_VO, and AC_VO, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may be mapped to AC_BK, AC_BK, AC_BE, AC_BE, AC_VI alternate, AC_VI primary, AC_VO primary, and AC_VO alternate, respectively. Also, 1, 2, 0, 3, 4, 5, 6, and 7 in UP or TID may have a higher priority in that order. That is, 1 may have a lower priority, and 7 may have a higher priority. Therefore, the priority may be higher in the order of AC_BK, AC_BE, AC_VI, and AC_VO. Also, AC_BK, AC_BE, AC_VI, and AC_VO may correspond to ACI (AC index) 0, 1, 2, and 3, respectively. Due to the characteristics of such a TID, the mapping between a TID and a link may represent the mapping between an AC and a link.Additionally, the mapping between links and ACs can represent the mapping between TIDs and links.

[0109] As described above, a TID may be mapped to each of a plurality of links. The mapping may be a designation of a link through which traffic corresponding to a particular TID or AC may be exchanged. Also, a TID or AC that may be transmitted for each transmission direction within a link may be designated. As described above, there may be a default setting for mapping between a TID and a link. Specifically, if there is no additional setting in the multilink setting, the multilink device may exchange frames corresponding to the TID on each link according to the default setting. In this case, the default setting may be that all TIDs are exchanged on any one link. At any given time, any TID or AC may be mapped to at least one link. Management frames and control frames may be transmitted on all links.

[0110] When a link is mapped to a TID or AC, only data frames corresponding to the TID or AC mapped to the link may be transmitted on the link. Therefore, when a link is mapped to a TID or AC, frames not corresponding to the TID or AC not mapped to the link may not be transmitted on the link. When a link is mapped to a TID or AC, an ACK may also be transmitted based on the link to which the TID or AC is mapped. For example, a Block ACK agreement may be determined based on the mapping between the TID and the link. In yet another specific embodiment, the mapping between the TID and the link may be determined based on the Block ACK agreement. Specifically, a Block ACK agreement may be set for a TID mapped to a specific link.

[0111] The above-mentioned TID-to-link mapping may ensure QoS. Specifically, a high priority AC or TID may be mapped to a link where a relatively small number of stations are in operation or where channel conditions are good. The above-mentioned TID-to-link mapping may also allow stations to stay in a power saving state for a longer period of time.

[0112] FIG. 10 illustrates simultaneous transmission of different links in a multi-link operation according to an embodiment of the present invention.

[0113] Depending on the implementation of the multilink device, simultaneous operation in the multilink may not be supported. For example, the multilink device may support simultaneous transmission in multiple links, simultaneous reception in multiple links, or transmission in one link and reception in another link. Reception or transmission in one link may affect reception or transmission in another link. Specifically, transmission in one link may act as interference in another link. Interference from one link of a multilink device acting on another link may be called internal leakage. The smaller the frequency interval between the links, the larger the internal leakage may be. If the internal leakage is not too large, transmission can be performed in another link when transmission is performed in one link. If the internal leakage is large, transmission cannot be performed in another link when transmission is performed in one link. In this way, the simultaneous operation of the multilink device in multiple links may be called STR (simultaneous transmit and receive, simultaneous transmission and reception). For example, a multilink device may transmit on multiple links simultaneously, transmit on one link while simultaneously receiving on another link, or receive on multiple links simultaneously, all of which may be referred to as STR.

[0114] As mentioned above, the multilink device can support STR or can support it in a limited manner. Specifically, the multilink device can support STR only under certain conditions. For example, if the multilink device operates with a single radio, the multilink device may not be able to perform STR. Also, if the multilink device operates with a single antenna, the multilink device may not be able to perform STR. Also, if an internal leak is detected to be equal to or greater than a pre-specified magnitude, the multilink device may not be able to perform STR.

[0115] A station can exchange information on the STR capability of the station with other stations. Specifically, a station can exchange information on the presence or absence of a restriction on the capability of the station to simultaneously transmit on multiple links or simultaneously receive on multiple links with other stations. Specifically, the information on the presence or absence of a restriction on the capability of transmitting or receiving on multiple links can indicate whether the station transmits on multiple links simultaneously, receives on multiple links simultaneously, or transmits and receives simultaneously. In addition, the information on the presence or absence of a restriction on the capability of transmitting or receiving on multiple links may be information indicated in stages. Specifically, the information on the presence or absence of a restriction on the capability of transmitting or receiving on multiple links may be information indicating a stage indicating the magnitude of the internal leakage. In a specific embodiment, the information indicating a stage indicating the magnitude of the internal leakage may be information indicating a stage indicating the magnitude of interference generated by the internal leakage. In yet another specific embodiment, the information indicating a stage indicating a frequency interval between links that may affect the internal leakage may be information indicating a stage indicating the magnitude of the internal leakage. In addition, the information indicating a stage indicating the magnitude of the internal leakage may be information indicating a relationship between the frequency interval between the links and the magnitude of the internal leakage in stages.

[0116] In FIG. 10, a first station (STA1) and a second station (STA2) are affiliated to one non-AP multilink device. Also, a first AP (AP1) and a second AP (AP2) may be affiliated to one non-AP multilink device. A first link (link1) is established between the first AP (AP1) and the first station (STA1), and a second link (link2) is established between the second AP (AP2) and the second station (STA2). In FIG. 10, the non-AP multilink device may perform STR in a limited manner. When the second station (STA2) transmits through the second link (Link2), the first station (STA1)'s reception through the first link (Link1) may be interrupted by the transmission through the second link (Link2). For example, in the following case, the first station (STA1)'s reception through the first link (Link1) may be interrupted by the transmission through the second link (Link2). The second station (STA2) transmits the first data (Data1) via the second link (Link2), and the first AP (AP1) transmits a response (Ack for Data1) to the first station (STA1). The second station (STA2) transmits the second data (Data2) via the second link (Link2). At this time, the transmission time of the second data (Data2) and the transmission time of the response (Ack for Data1) to the first data (Data1) may overlap. At this time, the transmission to the second station (STA2) via the second link (Link2) may cause interference to the first link (Link1). As a result, the first station (STA1) may not be able to receive the response (Ack for Data1) to the first data (Data1).

[0117] The operation of the multilink device performing channel access will now be described. The multilink operation not specifically described can follow the channel access procedure described in FIG.

[0118] The multilink device may perform channel access independently from a plurality of links. In this case, the channel access may be a back-off based channel access. When the multilink device performs channel access independently from a plurality of links and the back-off counters reach 0 in the plurality of links, the multilink device may start transmission simultaneously from the plurality of links. In a specific embodiment, when any one of the back-off counters of the links of the multilink reaches 0 and a pre-specified condition is satisfied, the multilink device may perform channel access not only for the link whose back-off counter reaches 0 but also for other links whose back-off counters have not reached 0. Specifically, when any one of the back-off counters of the links of the multilink reaches 0, the multilink device may perform energy sensing in other links whose back-off counters have not reached 0. In this case, when energy equal to or greater than a pre-specified magnitude is not detected, the multilink device may perform channel access not only for the link whose back-off counter reaches 0 but also for the link whose energy sensing has been performed. In this way, the multilink device may start transmission simultaneously from the plurality of links. The threshold value used for energy sensing may be smaller than the threshold value used when determining whether to decrease the back-off counter. In addition, when determining whether to decrease the back-off counter, the multilink device can sense any type of signal, not just a WLAN signal. In addition, in the above-mentioned energy sensing, the multilink device can sense any type of signal, not just a WLAN signal. Internal leakage may not be detected as a WLAN signal. In such a case, the multilink device can sense a signal detected due to internal leakage by energy sensing. In addition, as described above, the threshold value used for energy sensing may be smaller than the threshold value used when determining whether to decrease the back-off counter. Therefore, even when transmission is being performed on one link, the multilink device can decrease the back-off counter on the other link.

[0119] Depending on the degree of interference between links used by the multilink apparatus, the multilink apparatus may determine whether stations operating on each link can operate independently. In this case, the degree of interference between links may be the magnitude of interference sensed by other stations of the multilink apparatus when any one station of the multilink apparatus transmits on any one link. When the transmission of a first station of the multilink apparatus on the first link causes interference of a predetermined magnitude or more to a second station of the multilink apparatus operating on the second link, the operation of the second station may be restricted. Specifically, the reception or channel access of the second station may be restricted. When interference occurs, the second station may fail to decode a signal received due to the interference. Also, when interference occurs, the second station may determine that the channel is in use when the second station accesses the channel using backoff.

[0120] In addition, when the transmission of the first station of the multilink device through the first link generates interference of less than a pre-specified magnitude in the second station of the multilink device operating through the second link, the first station and the second station can operate independently. Specifically, when the transmission of the first station of the multilink device through the first link generates interference of less than a pre-specified magnitude in the second station of the multilink device operating through the second link, the first station and the second station can perform channel access independently. In addition, when the transmission of the first station of the multilink device through the first link generates interference of less than a pre-specified magnitude in the second station of the multilink device operating through the second link, the first station and the second station can perform transmission or reception independently. When interference of less than a pre-specified magnitude occurs, the second station can successfully decode the received signal even in the presence of interference. In addition, when interference of less than a pre-specified magnitude occurs, the second station can determine that the channel is idle when the second station accesses the channel using backoff.

[0121] The degree of interference occurring between stations of a multilink device may vary depending on the interval between the frequency bands of the links on which the stations operate as well as the hardware characteristics of the multilink device. For example, the internal interference occurring in a multilink device including a high RF (radio frequency) device may be smaller than the internal interference occurring in a multilink device including a low RF device. Therefore, the degree of interference occurring between stations of a multilink device may be determined based on the characteristics of the multilink device.

[0122] FIG. 10 shows that the magnitude of interference generated varies depending on the interval between the frequency bands of the links and the characteristics of the multilink device. In the embodiment of FIG. 10, the first multilink device (MLD#1) includes a first station (STA1)-1 operating on the first link (Link1) and a second station (STA1)-2 operating on the second link (Link2). The second multilink device (MLD#2) includes a first station (STA2)-1 operating on the first link (Link1) and a second station (STA2)-2 operating on the second link (Link2). The frequency interval between the first link (Link1) and the second link (Link2) in which the first multilink device (MLD#1) operates is the same as the frequency interval between the first link (Link1) and the second link (Link2) in which the second multilink device (MLD#2) operates. However, the magnitude of interference generated varies depending on the difference between the characteristics of the first multilink device (MLD#1) and the characteristics of the second multilink device (MLD#2). Specifically, the magnitude of interference generated in the second multilink device (MLD#2) may be greater than the magnitude of interference generated in the first multilink device (MLD#1). Considering that the magnitude of interference generated may differ depending on the characteristics of the multilink devices and that the presence or absence of STR support may differ depending on the multilink devices, information regarding whether STR is supported or not needs to be exchanged.

[0123] The multilink device may signal whether or not a station included in the multilink device supports STR. Specifically, the AP multilink device and the non-AP multilink device may exchange whether or not an AP included in the AP multilink device supports STR and whether or not an STA included in the non-AP multilink device supports STR. In this embodiment, an element indicating whether or not an STR is supported may be used. The element indicating whether or not an STR is supported may be called an STR support element. The STR support element may indicate whether or not an STR is supported by a station of the multilink device that transmits the STR support element by one bit. Specifically, the STR support element may indicate whether or not an STR is supported by each station included in the multilink device that transmits the STR support element by one bit. In this case, if the station supports STR, the bit value may be 1, and if the station does not support STR, the bit value may be 0. If the multilink device that transmitted the STR support element includes a first station (STA1), a second station (STA2), and a third station (STA3), and the first station (STA1) and the third station (STA3) support STR, and the second station (STA2) does not support STR, the STR support element is 101 1b It is assumed that stations operating in different frequency bands support STR, and the STR support element may omit signaling regarding the presence or absence of STR support between stations operating in different frequency bands. For example, a first station (STA1) operates in a first link of 2.4 GHz, and a second station (STA2) and a third station (STA3) operate in a second link of 5 GHz and a third link of 5 GHz, respectively. In this case, the STR support element may indicate with one bit that STR is supported between the second station (STA2) and the third station (STA3). Also, the STR support element may include only one bit when there are two stations to which the STR support element signals.

[0124] In a specific embodiment, the relationship between a link located at 2.4 GHz and a link located at 5 GHz or 6 GHz among the links of the multi-link device may always be determined as an STR, and therefore, signaling regarding the presence or absence of an STR between the link located at 2.4 GHz and the link located at 5 GHz or 6 GHz may be omitted.

[0125] In the above-mentioned embodiment, the operation of the station of the multilink device may be replaced by the operation of the multilink device. Also, in the above-mentioned embodiment, the operation of the AP may be replaced by the operation of the non-AP station, and the operation of the non-AP station may be replaced by the operation of the AP. Thus, the operation of the AP of the non-STR multilink device may be replaced by the operation of the non-AP station of the non-STR multilink device, and the operation of the non-AP station of the STR multilink device may be replaced by the operation of the AP of the STR multilink device. Also, the operation of the non-AP station of the non-STR multilink device may be replaced by the operation of the AP of the non-STR multilink device, and the operation of the AP of the STR multilink device may be replaced by the operation of the non-AP station of the STR multilink device.

[0126] Scheduling for low-latency traffic transmission will be described with reference to Figs. 11 to 15. In conventional wireless LAN communication, channel access parameters are set for each AC using enhanced distributed channel access (EDCA), and traffic is supported to be processed according to priority for each AC using the set channel access parameters. However, since the existing EDCA provides channel access with high priority in a probabilistic manner, it is insufficient in supporting the transmission of low-latency traffic. To compensate for this, a time period in which low-latency traffic can be preferentially transmitted can be set. For convenience of explanation, the time period in which low-latency traffic is preferentially transmitted is called a limited service period. Most services requiring low-latency traffic transmission, such as VR / AR, require periodic traffic transmission, and therefore the limited service period has a large effect of reducing the transmission delay of low-latency traffic.

[0127] The limited service period may be a time period in which the transmission of low latency traffic and the transmission of a response to the low latency traffic are preferentially permitted. Specifically, the limited service period may be a time period in which only the transmission of low latency traffic and the transmission of a response to the low latency traffic are permitted. In yet another specific embodiment, the limited service period may be a time period in which the transmission of low latency traffic and the transmission of a response to the low latency traffic are performed, and the transmission of traffic other than the low latency traffic is permitted after the transmission of the low latency traffic and the transmission of the response to the low latency traffic are completed.

[0128] First, a method for setting a restricted service period will be described. The restricted service period may be set by the TWT of an existing WLAN. The TWT sets a service period through negotiation between an AP and a station, and supports the AP and the station to transmit and receive during the service period and enter a low power mode during periods other than the service period. This will be described in detail with reference to FIG. 11. For ease of explanation, the operation of the AP and the station based on the restricted service period, in which the restricted service period is set by the TWT, is called a restricted TWT.

[0129] FIG. 11 illustrates a method for setting up a broadcast TWT between an AP and a station according to an embodiment of the present invention.

[0130] The service period in TWT may be set as follows: The AP requests stations associated with the AP to join the TWT. The stations can join the broadcast TWT or negotiate with the AP about individual TWT. At this time, the AP can request stations to join the TWT by setting the value of the TWT Required subfield of the HE Operation element to 1. The AP can also transmit the broadcast TWT element in a management frame, for example a beacon frame, to convey information required for stations to join the broadcast TWT. At this time, the AP can signal that it supports broadcast TWT by setting dot11TWTOptionActivated to true and the Broadcast TWT Support field of the HE Capabilities element to 1. The AP can set the limited service period to be similar to the service period of the TWT.

[0131] In the embodiment of FIG. 11, the first station (STA1) requests the AP to set the TWT. The AP and the first station (STA1) set TWT parameters, such as an initial TBTT and a listen interval. As a result, the AP and the first and second stations (STA1 and STA2) are set to broadcast TWT. The AP indicates a broadcast TWT service period using a beacon frame. During the broadcast TWT service period, the AP can transmit a downlink (DL) physical layer protocol data unit (PPDU) to the first and second stations (STA1 and STA2) or can trigger an uplink (UL) transmission by transmitting a trigger frame to the first and second stations (STA1 and STA2). During the broadcast TWT service period, the first and second stations (STA1 and STA2) wake up to receive a beacon frame. The first and second stations (STA1 and STA2) obtain information about the TWT from the received beacon frame. The AP transmits a trigger frame to the first station (STA1) and the second station (STA2), the first station (STA1) transmits a PS-Poll frame to the AP, and the second station (STA2) transmits a QoS Null frame to the AP. The AP receives the PS-Poll frame and the QoS Null frame transmitted by the first station (STA1) and the second station (STA2), and determines that the first station (STA1) and the second station (STA2) are in an awake state. The AP transmits a multi-STA Block ACK frame to the first station (STA1) and the second station (STA2). The AP transmits a DL PPDU to the first station (STA1) and the second station (STA2).

[0132] In the service period of the existing TWT, stations that do not participate in the TWT are not restricted from accessing the channel or transmitting because the TWT is intended to help stations participating in the TWT enter a doze state. However, the restricted service period to prevent transmission delays of low-latency traffic must guarantee the preferential transmission of low-latency traffic, and therefore a method for protecting the restricted service period is required.

[0133] During the restricted service period, a station that does not participate in the restricted TWT may be restricted from accessing the channel. Specifically, during the restricted service period, a station that does not participate in the restricted TWT may not be able to access the channel. When a station that does not participate in the restricted TWT completes channel access during the restricted service period, the station may restart the channel access procedure without transmitting. In this case, the station may restart the channel access procedure when the restricted service period ends. In addition, the channel access of the station may represent an EDCA backoff procedure. Completion of the channel access may represent a backoff counter of the EDCA backoff procedure reaching 0. In addition, when the station restarts the channel access procedure, the station may randomly obtain an integer within the CW used in the previous channel access and use the obtained integer for the backoff counter. That is, the station may not double the size of the CW used in the previous channel access. In this case, the CW may be maintained for each AC. Such channel access restriction may be applied only to stations that support the restricted TWT. Specifically, such channel access restriction is applied only to non-legacy (EHT) stations in which dot11RestrictedTWTOptionImplemented in the EHT Capabilities element is set to true, and may not be applied to non-legacy (EHT) stations in which dot11RestrictedTWTOptionImplemented in the EHT Capabilities element is set to false. In this specification, non-legacy stations may refer to EHT stations and stations after EHT stations. Also, legacy stations are stations before EHT stations, and may refer to non-HT stations, HT stations, VHT stations, and HE stations.

[0134] Also, during the restricted service period, a NAV may be set for a non-legacy station for traffic other than low-latency traffic. Specifically, as a NAV is set for traffic other than low-latency traffic, the station may discontinue channel access procedures for transmission of traffic other than low-latency traffic. In such an embodiment, the NAV may be a NAV independent of the conventional NAV (basic NAV, Intra-BSS NAV). In this case, the non-legacy station may be limited to stations that support the restricted TWT. In yet another specific embodiment, the non-legacy station may be limited to stations that participate in the restricted TWT.

[0135] The limited service period may be included within the broadcast TWT service period. In yet another specific embodiment, the limited service period may not be included within the broadcast TWT service period.

[0136] Also, the limited service period may be repeated at a period specified by the AP. That is, the AP may specify a period for repeating the limited service period. This eliminates the need for the AP to transmit a TWT element of a beacon frame every time to set the limited service period. In this case, the period of the service period may be set according to the characteristics of a low-latency service in which low-latency traffic is used. For example, the period of the low-latency service period in which low-latency traffic is generated every 50 ms may be 50 ms.

[0137] In addition, a quiet interval may be set for stations that do not support the restricted TWT. In a conventional WLAN, the quiet interval is a period for supporting channel sensing. When the quiet interval is set, all stations stop transmission. Using the characteristics of the quiet interval, the restricted service period can be protected. This will be described with reference to FIG. 12. In this case, stations that do not support the restricted TWT may be limited to legacy stations.

[0138] FIG. 12 illustrates how an AP sets a quiet period according to an embodiment of the present invention.

[0139] An AP operating a restricted TWT may transmit a quiet element and set a quiet period. In the quiet period, the station suspends channel access. However, if the channel access of a station participating in the restricted TWT is also restricted, low latency traffic cannot be transmitted. Therefore, a station participating in the restricted TWT may ignore the quiet period corresponding to the restricted service period. In this case, the quiet period corresponding to the restricted service period represents a quiet period set to protect the restricted service period of the restricted TWT. Specifically, a station participating in the restricted TWT may regard the quiet period corresponding to the restricted service period as the restricted service period. An AP operating a restricted TWT may not set the quiet period to coincide with the restricted service period. This is because the quiet period is set in TU (time unit, 1024 us) units in the quiet element and the TWT is set in 256 us units.

[0140] However, when a channel access is performed in a quiet interval other than the quiet interval not set for the restricted service period, the quiet interval not set for the restricted service period may be disturbed. For this reason, it is necessary to distinguish the quiet interval set for the restricted service period, i.e., the quiet interval corresponding to the restricted service period. Therefore, a station participating in the restricted TWT may not be able to ignore the quiet interval not corresponding to the restricted service period. In the quiet interval not corresponding to the restricted service period, the station cannot perform all transmissions. Specifically, a station participating in the restricted TWT may not be able to ignore the quiet interval that does not overlap with the restricted service period. In a specific embodiment, a station participating in the restricted TWT may not be able to perform all transmissions in the quiet interval that does not overlap with the restricted service period.

[0141] In addition, in the above embodiment, a station participating in a restricted TWT may consider a quiet period corresponding to a restricted service period if the start time of the restricted service period and the start time of the quiet period are within a pre-specified time, and the start time of the service period and the start time of the quiet period are within a pre-specified time, because, as described above, an AP operating a restricted TWT does not need to set a quiet period to coincide with the restricted service period.

[0142] In the embodiment of FIG. 12, the AP transmits a beacon frame to set a quiet period and a restricted service period. In FIG. 12(a), the quiet period is set to the same time period as the restricted service period. Therefore, a station participating in the restricted TWT in the quiet period performs channel access. In FIG. 12(b), the quiet period is set from a time earlier than the start time of the restricted service period to a time later than the end time of the restricted service period. In FIG. 12(b), channel access of a station participating in the restricted TWT in a quiet period that does not overlap with the restricted service period is restricted. A station participating in the restricted TWT in a quiet period that overlaps with the restricted service period performs channel access.

[0143] As mentioned above, channel access may be restricted during restricted service periods, and such restrictions may also be applied in relation to TXOP settings, as illustrated in FIG.

[0144] FIG. 13 illustrates a method for a station to set a TXOP taking into account a limited service period according to an embodiment of the present invention.

[0145] A station that has obtained a TXOP before the restricted service period begins, i.e., a station that is a TXOP holder, may need to terminate the TXOP before the restricted service period begins. This is because if the TXOP holder continues to exchange frames even after the restricted service period begins, it may interfere with the transmission of low-latency traffic. In this case, the station may be a non-legacy station. In yet another specific embodiment, the station may be limited to stations that support restricted TWT. That is, such restrictions may not be applied to stations for which the value of the dot11RestrictedTWTOptionImplemented field is set to false.

[0146] In an illustrative embodiment, if a station that is a TXOP holder is transmitting low latency traffic, it may continue exchanging frames after the limited service period has begun.

[0147] A specific method for a station to terminate a TXOP before a limited service period will now be described.

[0148] The station can set TXOP based on the limited service period. Specifically, the station can set the end point of TXOP to be before the start of the limited service period. At this time, the station can set the duration of the start frame that starts the frame exchange sequence to be before the start of the limited service period. For example, if the station succeeds in channel access 3m before the start of the limited service period, the station can set TXOP to be 3ms before. Also, the station may end TXO by transmitting a CTS-to-Self frame. At this time, the station can transmit the CTS-to-Self frame at the basic transmission rate of 6Mbps. This is because many legacy stations can receive frames when the station transmits frames at the basic transmission rate.

[0149] In yet another specific embodiment, the station can transmit a CF-End frame before the start of the limited service period, so that the station can end the TXOP before the start of the limited service period. In this case, the station can transmit the CF-End frame at a basic transmission rate of 6 Mbps, because many legacy stations can receive the frames when the station transmits the frames at the basic transmission rate.

[0150] Also, a station that is not a TXOP holder may cancel the NAV set before the start of the restricted service period at the start of the restricted service period. In this case, the station may be a station that supports restricted TWT. That is, the station may be a station that sets the value of the dot11RestrictedTWTOptionImplemented field to True. A station that is not a TXOP holder but does not support restricted TWT cannot cancel the NAV set before the start of the restricted service period at the start of the restricted service period. However, when the station completes frame exchange and the remaining duration of the TXOP is less than twice the sum of the time required to transmit the CF-End frame and the SIFS, the station may not transmit the CF-End frame. In this case, the station may consider the TXOP to be released at the start of the restricted service period. Specifically, the station may consider the basic NAV to be released at the start of the restricted service period.

[0151] In yet another illustrative embodiment, stations may be limited to those that participate in a restricted TWT.

[0152] In the embodiment of FIG. 13, the AP transmits a beacon frame including a TWT element to signal that a limited service period is set. In the embodiment of FIG. 13(a), the station transmits an RTS frame to set a TXOP. At this time, the station sets the value of the Duration field of the RTS frame to "before the limited service period". The station exchanges frames with the AP and completes the frame exchange before the start of the limited service period. At this time, the station finally transmits a CTS-to-Self frame. In the embodiment of FIG. 13(b), the station transmits an RTS frame to set a TXOP. At this time, the station sets the value of the duration field of the RTS frame without considering the limited service period. The station exchanges frames with the AP and completes the frame exchange before the start of the limited service period. At this time, the station finally transmits a CF-end frame to release the TXOP.

[0153] In conventional WLAN operation, an exception to the TXOP rule defines an operation that may be transmitted beyond the TXOP limit. For example, retransmission of a single MPDU, transmission of a single MSDU under a Block ack agreement (not included in A-MSDU and A-MPDU consisting of two or more MPDUs), and transmission of a control frame and a QoS Null frame (not included in A-MPDU consisting of two or more MPDUs) may be transmitted beyond the TXOP limit. If such an exception is recognized even for a limited service period, the transmission of low latency traffic may be delayed. Such an exception to the TXOP limit must not be applied in violation of the limited service period.

[0154] If the end time of the TXOP and the start time of the restricted service period are within a pre-specified time difference, the station can determine that the TXOP is a TXOP obtained before the start of the restricted service period. The pre-specified time may be 100 us. In yet another specific embodiment, if the end time of the TXOP is within the restricted service period, the station can determine that the TXOP is a TXOP obtained before the start of the restricted service period.

[0155] As mentioned above, a station may need to complete a frame exchange before the restricted service period. Thus, a station may not be allowed to start a frame exchange if the completion time of the frame exchange is within the restricted service period. In this case, the station may perform fragmentation to complete the frame exchange before the start of the restricted service period.

[0156] Also, if low latency traffic is transmitted in a frame exchange performed by a station that is a TXOP holder, the station may continue the frame exchange even after the low latency service period begins.

[0157] A channel access procedure taking into account limited service periods is illustrated in FIG.

[0158] FIG. 14 illustrates a station according to an embodiment of the present invention re-performing a channel access procedure taking into account a limited service period.

[0159] As described above, even if the station completes channel access before the restricted service period, if the frame exchange completion time is after the start of the restricted service period, the station can start the channel access procedure again without transmitting. At this time, the station can acquire the back-off counter value again. At this time, the station can use the size of the CW used in the previous channel access procedure as it is. That is, the station does not need to double the size of the CW used in the previous channel access procedure, and does not need to initialize it to the minimum value that the CW can have. In addition, the station does not need to increase the number of retries, for example, QSRC (QoS STA Retry Counter).

[0160] Also, if the station completes channel access within a pre-specified time from the start of the restricted service period, the station may initiate the channel access procedure again without transmitting.

[0161] In the above embodiment, a station that wishes to transmit low latency traffic may start frame exchange after completing channel access even if the frame exchange completion time is after the start of the restricted service period. Such an exception may be allowed only if the station that wishes to transmit low latency traffic is a station participating in the restricted TWT.

[0162] Also, as described above, the station can operate as if the NAV is set for the AC of traffic other than the low-latency traffic, and therefore the station can determine that the CCA result for the transmission of the AC of traffic other than the low-latency traffic is not idle (BUSY).

[0163] In the embodiment of FIG. 14, the AP transmits a beacon frame including a TWT element to signal that a limited service period is to be set. The station's channel access back-off counter value reaches 0 before the start of the limited service period. The station determines that the frame exchange including the traffic to be transmitted will be completed after the start of the service period. Therefore, the station obtains a back-off counter within the CW value used in the previous channel access procedure. The station performs the channel access procedure again using the obtained back-off counter. At this time, the station does not increment the retransmission counter.

[0164] It may happen that all low-latency traffic transmission is completed before the limited service period is completed. In such a case, it may be inefficient for the low-latency service period to restrict the transmission of traffic other than the low-latency traffic. Therefore, a method for early termination of the limited service period may be required. This will be described using the example of FIG. 15.

[0165] FIG. 15 illustrates an operation of an AP prematurely terminating a limited service period according to an embodiment of the present invention.

[0166] In order for the AP to terminate the limited service period early, it must be able to determine that all low-latency traffic transmissions of stations participating in the limited TWT have been completed. To this end, stations participating in the limited TWT can signal whether or not they will transmit further low-latency traffic in the frames they transmit. Specifically, the station can signal further transmission of low-latency traffic by setting the value of the More data subfield of the Frame Control field of the frame. In this case, if the value of the More data subfield of the Frame Control field of the frame transmitted in the limited service period is 1, the More data subfield indicates that further transmission of low-latency traffic is required, and does not need to indicate whether further transmission of traffic other than the low-latency traffic is required. For example, if a station participating in the limited TWT does not store low-latency traffic in its transmit buffer and only stores traffic other than the low-latency traffic, the station can set the value of the More data subfield of the Frame Control field of the frame transmitted by the station in the limited service period to 0. The AP can terminate the limited service period early based on whether the station participating in the limited TWT has a frame in the limited service period with a value of 0 in the More data subfield of the Frame Control field. Specifically, the AP can terminate the limited service early if the AP's transmit buffer has no low latency traffic to transmit and the station participating in the limited TWT has a frame in the limited service period with a value of 0 in the More data subfield of the Frame Control field.

[0167] The AP can terminate the restricted service period early by transmitting a pre-specified control frame. In this case, the control frame may be a CF-End frame. In this case, the AP can set the BSSID (TA) field of the CF-End frame to the MAC address or BSSID of the AP. Also, the AP can set the Individual / Group bit of the BSSID (TA) field of the CF-End frame to 1. In yet another specific embodiment, the AP can terminate the restricted service period early by transmitting a pre-specified management frame.

[0168] When a station receives a frame that is pre-designated to end the restricted service period within the restricted service period, the station can determine that the restricted service period has ended. At this time, the station that receives the pre-designated frame can resume channel access without the restrictions that apply to the restricted service period. As described above, the pre-designated frame may be a CF-End frame. At this time, if the value of the TA (BSSID) field of the CF-End frame that the station receives during the restricted service period is the MAC address of the AP to which the station is associated, the station can determine that it is a CF-End frame that ends the restricted service period.

[0169] As described above, in order to protect the limited service period from the legacy wireless communication terminal, a quiet period for the limited service period may be set. In this case, the AP can transmit a CF-End frame to end the limited service period. When the AP transmits the CF-End frame, the quiet period set for the legacy station can also be cancelled.

[0170] In the above-described embodiment, the CF-End frame may have a Frame Control field with a Type of a control frame (Type value B3 B2==01) and a Subtype of a CF-End frame (Subtype value B7 B6 B4 B4==1110).

[0171] When a quiet period for a restricted service period is set, a station participating in the restricted TWT may not be allowed to transmit a CF-End frame within the restricted service period. In a specific embodiment, a station participating in the restricted TWT may not be allowed to transmit a CF-End frame in a quiet period corresponding to the restricted service period. This is because the NAV set for the legacy station is released when a station participating in the restricted TWT transmits a CF-End frame. However, as described above, if the CF-End frame is used to terminate the restricted service period early, the AP may transmit a CF-End frame within the restricted service period.

[0172] In the embodiment of FIG. 15, the AP transmits a beacon frame including a TWT element and a Quiet element. A station supporting the restricted TWT determines that a restricted service period has been set, and a station not supporting the restricted TWT determines that a quiet period has been set. When the AP determines that the transmission of all low latency traffic has been completed within the restricted service period, the AP transmits a CF-End frame to terminate the restricted service period early and release the quiet period set for the legacy station. At this time, a station supporting the restricted TWT determines that the channel access restriction applied during the restricted service period has been removed. Specifically, as described above, when the embodiment in which the NAV is set during the restricted service period is applied, a station supporting the restricted TWT can determine that the NAV for the restricted service period has been released. Also, a station not supporting the restricted TWT that receives the CF-End frame releases the NAV.

[0173] As described above, each station included in the multilink device can perform association with other stations. Therefore, each station included in the multilink device can operate an individual TWT service period. That is, an individual TWT service period may be operated in each of a plurality of links on which the multilink device operates. In order for an individual TWT service period to be operated in this manner, an individual TWT agreement may be required. To this end, a station in the multilink device can transmit a TWT request frame, and a station receiving the TWT request frame can transmit a TWT response frame. The TWT request frame may be a TWT setup frame with a Command field value of 0 to 2. Also, the TWT response frame may be a TWT setup frame with a Command field value of 3 to 7. A specific TWT agreement method may be the same as that defined in IEEE 802.11ax.

[0174] A station can save power by TWT operation. Therefore, in order to improve power saving efficiency, a multilink device can set a TWT service period for a plurality of links on which the multilink device operates. For example, a multilink device including a first station and a second station can set a TWT service period for a first link on which the first station operates and a second link on which the second station operates, and can synchronize the operation states (awake state, doze state) of the first station and the second station. At this time, the first station can transmit a TWT request frame to a first AP to which the first station is coupled, and the second station can transmit a TWT request frame to a second AP to which the second station is coupled. At this time, the TWT parameter values ​​indicated by the TWT request frame transmitted by the first station and the TWT request frame transmitted by the second station may be the same. Therefore, transmitting TWT request frames individually on a plurality of links may reduce transmission efficiency. In a specific embodiment of the present invention, a TWT request frame transmitted on one link can perform TWT agreement for a plurality of links. This will be described with reference to FIG. 16.

[0175] FIG. 16 shows a format of a TWT element according to an embodiment of the present invention.

[0176] A TWT request frame for TWT agreement performed on multiple links may be transmitted on a first link. At this time, the TWT request frame may include TWT parameters for TWT operations performed on multiple links. Also, a TWT request frame for TWT agreement performed on a second link may be transmitted on a first link. At this time, the TWT request frame may include TWT parameters for TWT operations performed on the second link. For example, when a multilink device includes a first station operating on a first link and a second station operating on a second link, the first station can establish a TWT agreement for the second station. At this time, when the first station is coupled to a first AP and the second station is coupled to a second AP, and the first AP and the second AP are included in one multilink device, the first station can establish a TWT agreement with the first AP. This is because the stations included in the multilink device can share some functions or some information of the MAC layer. A new format of a TWT element may be required for the above-mentioned TWT agreement operation.

[0177] Specifically, the TWT element may include information about a link on which the TWT agreement is performed. In this case, the information about the link may be information about an ID of a link operated by the AP. In a specific embodiment, the TWT element may indicate multiple links on which the TWT agreement is performed. For example, the information about the link may be a bitmap. In this case, each bit of the bitmap may indicate whether the TWT element is performed on each of the multiple links. A station may transmit such a TWT element to perform TWT agreement on multiple links.

[0178] The aforementioned bitmap can be called a Link ID (identifier) ​​bitmap. The size of the Link ID bitmap can be two octets. For example, if the value of the Link ID bitmap is 1110 0000 0000 0000 2bIn this case, the Link ID bitmap may indicate TWT negotiation for a first link corresponding to the first bit, a second link corresponding to the second bit, and a third link corresponding to the third bit. In such an embodiment, a link element may be transmitted that includes information about TWT parameters for only links other than the link for which the link element is transmitted. Also, in such an embodiment, an element for one link may be transmitted for TWT negotiation to occur on multiple links.

[0179] Also, the TWT element may include a TWT flow ID indicating an identifier applied to the TWT agreement. When the TWT element is for performing a TWT agreement on multiple links, the TWT flow ID included in the TWT element may be a value that is not used in the TWT agreement of all links on which the TWT element may perform the TWT agreement. In still another specific embodiment, when the TWT element is for performing a TWT agreement on multiple links, the TWT element may include a field for indicating multiple TWT flow IDs. For example, when the TWT element is for performing a TWT agreement on multiple links, the TWT element may include multiple subfields indicating each of multiple TWT flow IDs. In this case, the multiple subfields may correspond to each of multiple links on which the TWT element may perform the TWT agreement. In these embodiments, a TWT flow ID that is not used by the link corresponding to each subfield may be used. Also, when the TWT element is to change the TWT agreement of the link corresponding to the subfield, a TWT flow ID that was previously used by the link corresponding to the subfield may be used in the subfield. This is because there is already a TWT agreement using the TWT flow ID. Therefore, when a station attempts to perform a new TWT agreement, the station may be restricted to use a TWT flow ID for the TWT agreement that does not correspond to a TWT flow ID of an existing TWT agreement, and when a station attempts to change an existing TWT agreement, the station may use a TWT flow ID for the TWT agreement that corresponds to the TWT agreement to be changed.

[0180] 16(a) shows the format of a TWT element according to an embodiment of the present invention. The TWT element may include an Element ID field, a Length field, a Control field, and a TWT Parameter Information field. In this case, the Element ID field indicates that the element in which the Element ID field is included is a TWT element. The value of the Element ID field may be 216.

[0181] FIG. 16(b) shows a specific format of the control field of the TWT element. The Control field includes an NDP Paging Indicator field, a Responder PM Mode field, a Negotiation Type field, a TWT Information Frame Disabled field, a Wake Duration Unit field, a Link ID Bitmap Present field, and a Reserved field. FIG. 16(b) further includes a Link ID Bitmap Present field compared to the TWT element defined in IEEE 802.11ax. In this case, the Link ID Bitmap Present field indicates whether the TWT element includes the above-mentioned Link ID bitmap. Specifically, when the value of the Link ID Bitmap Present field is 1, the TWT element includes a Link ID bitmap, and when the value of the Link ID Bitmap Present field is 0, the TWT element does not need to include a Link ID bitmap. A station that receives a TWT element can determine whether the TWT element includes a Link ID bitmap according to the value of the Link ID Bitmap Present field.

[0182] FIG. 16(c) shows the format of an Individual TWT Parameter Set field included in a TWT element. The Individual TWT Parameter Set field included in a TWT element may include a Request Type field, a Target Wake Time field, a TWT Group Assignment field, a Nominal Minimum TWT Wake Duration field, a TWT Wake Interval Mantissa field, a TWT Channel field, an NDP Paging field, and a Link ID Bitmap field. FIG. 16(b) further includes a Link ID Bitmap field in addition to the Individual TWT Parameter Set field defined in IEEE 802.11ax. When the TWT element includes a Link ID Bitmap field, the TWT element may indicate that a TWT request is requested for a link indicated by the Link ID Bitmap field. When a TWT request frame includes a TWT element and the TWT element includes a Link ID Bitmap field, a station receiving the TWT request frame may determine that the TWT request frame is requesting a TWT agreement for a link indicated by the Link ID Bitmap field.

[0183] 16(d) illustrates a Request Type field of a TWT element according to an embodiment of the present invention. The Request Type field of the TWT element may include a TWT Request field, a TWT Setup Command field, a Trigger field, an Implicit field, a Flow Type field, a TWT Flow Identifier field, a TWT Wake Interval Expnent field, and a TWT Protection field. The TWT Flow Identifier field indicates a TWT Flow ID for identifying a TWT agreement performed by a TWT request frame including a TWT element. In this case, the TWT Flow ID may be set according to the above-described embodiment.

[0184] FIG. 17 illustrates a multi-link device according to an embodiment of the present invention performing TWT agreement.

[0185] The AP multilink device includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). The non-AP multilink device includes a first station (STA1), a second station (STA2), and a third station (STA3). The first AP (AP1), the second AP (AP2), and the third AP (AP3) operate on a first link (Link1), a second link (Link2), and a third link (Link3), respectively. The first station (STA1), the second station (STA2), and the third station (STA3) operate on a first link (Link1), a second link (Link2), and a third link (Link3), respectively. The non-AP multilink device can transmit a TWT request frame to perform TWT agreement on the first link (Link1) to the third link (Link3). In this case, the TWT request frame may include one TWT element. Specifically, when a non-AP multilink device intends to operate a TWT service period in which the same TWT parameters are used, the TWT request frame may include one TWT element.

[0186] Specifically, the TWT element can indicate the start and end points of a TWT service period. The TWT element can also include a Link ID bitmap as described with reference to Fig. 16. Specifically, the TWT element can indicate a first link (Link1), a second link (Link2), and a third link (Link3) in a Link ID Bitmap subfield.

[0187] Since the Link ID Bitmap subfield of the TWT element of the received TWT request frame indicates the first link (Link 1), the second link (Link 2), and the third link (Link 3), the AP multilink device can determine that the TWT parameters signaled by the TWT request frame relate to the TWT service periods of the first link (Link 1), the second link (Link 2), and the third link (Link 3).

[0188] The AP multilink device can transmit a TWT response frame to the non-AP multilink device to accept the TWT setup. At this time, a TWT agreement is established for each of the first link (Link1) to the third link (Link3). At this time, the TWT agreement for each link can indicate a TWT agreement between the first station (STA1) and the first AP (AP1), a TWT agreement between the second station (STA2) and the second AP (AP2), and a TWT agreement between the third station (STA3) and the third AP (AP3).

[0189] FIG. 18 illustrates a station included in a multilink device performing TWT negotiation for another station included in the multilink device in which the station is included, according to an embodiment of the present invention.

[0190] As described above, a TWT request frame for TWT agreement in the second link may be transmitted in the first link. To this end, a first station operating in the first link may transmit a TWT request frame in the first link. In this case, a TWT element of the TWT request frame may include a TWT Link ID bitmap, and the TWT Link ID bitmap may indicate the second link. A first AP operating in the first link may determine that the TWT request frame is transmitted for TWT agreement in the second link based on the TWT Link ID bitmap.

[0191] In the embodiment of FIG. 18, the AP multi-link device includes a first AP (AP1) and a second AP (AP2). The non-AP multi-link device includes a first station (STA1) and a second station (STA2). The first AP (AP1) and the second AP (AP2) operate on a first link (Link1) and a second link (Link2), respectively. The first station (STA1) and the second station (STA2) operate on a first link (Link1) and a second link (Link2), respectively. The first station (STA1) transmits a TWT request frame for TWT agreement on the second link (Link2) on the first link (Link1). The first AP (AP1) transmits a TWT response frame to the first station (STA1) to accept the TWT agreement on the second link (Link2). Thus, a TWT agreement is established between the second station (STA2) and the second AP (AP2).

[0192] In this case, the station that transmits the TWT request frame is different from the station to which the TWT agreement applies. Also, as mentioned above, the station that transmits the TWT request frame is one station, but the TWT agreement may apply to multiple stations. Therefore, the station that may cancel the TWT agreement may become an issue.

[0193] In the existing TWT operation, a 3-bit TWT Flow ID and the MAC addresses of two stations that have made the TWT agreement may be used to identify the TWT agreement. Specifically, the TWT agreement can be identified by the MAC address of the TWT request station, the MAC address of the TWT response station, and the TWT Flow ID. As described above, the TWT agreement set by the multilink device may be difficult to identify because the station that made the TWT agreement and the station to which the TWT agreement applies may be different. For example, in the embodiments of FIG. 17 and FIG. 18, the TWT request station is the first station, and the TWT response station is the first AP. However, in the embodiment of FIG. 17, the TWT agreement is applied to the first station and the first AP, the second station and the second AP, and the third station and the third AP. In the embodiment of FIG. 18, the TWT agreement is applied to the second station and the second AP. In addition, in the embodiment of Fig. 17, one TWT Flow ID may be applied to the first station and the first AP, the second station and the second AP, and the third station and the third AP in the same manner. Therefore, the TWT agreement cannot be identified. In order to solve this problem, the following embodiment can be applied.

[0194] A station that may cancel the TWT agreement may be a station to which the TWT agreement applies. To this end, the TWT request station may not be a station that has transmitted a TWT request frame, but a station that operates on a link to which the TWT agreement applies. Specifically, the TWT request station may be a station that operates on a link to which the TWT agreement applies among the stations of the multilink device that have transmitted a TWT request frame. Also, the TWT response station may be a station that operates on a link to which the TWT agreement applies, but not a station that has transmitted a TWT response frame. Specifically, the TWT response station may be a station that operates on a link to which the TWT agreement applies among the stations of the multilink device that have transmitted a TWT response frame.

[0195] In addition, the following embodiment may be applied as a method for identifying the TWT agreement.

[0196] In a specific embodiment, the TWT agreement may be identified based on the ID of the link. Specifically, the TWT agreement may be identified based on the TWT Flow ID, the MAC address of the TWT request station, the MAC address of the TWT response station, and the ID of the link to which the TWT agreement is applied. In the embodiment of FIG. 17, the first TWT agreement, which is the TWT agreement established between the first station and the first AP, may be identified by the TWT Flow ID, the MAC address of the first station, the MAC address of the first AP, and the ID of the first link. The second TWT agreement, which is the TWT agreement established between the second station and the second AP, may be identified by the TWT Flow ID, the MAC address of the first station, the MAC address of the first AP, and the ID of the second link. The third TWT agreement, which is the TWT agreement established between the third station and the third AP, may be identified by the TWT Flow ID, the MAC address of the first station, the MAC address of the first AP, and the ID of the third link. According to a specific embodiment, the TWT Flow ID may be set for each link.

[0197] Also, the TWT agreement may be regarded as being made for each multilink device. Therefore, in order to identify the TWT agreement, the MAC address of the TWT requesting multilink device may be used instead of the MAC address of the TWT requesting station, and the MAC address of the TWT responding multilink device may be used instead of the MAC address of the TWT responding station. In the embodiment of FIG. 17, the first TWT agreement, which is the TWT agreement established between the first station and the first AP, may be identified by the TWT Flow ID, the MAC address of the non-AP multilink device, the MAC address of the AP multilink device, and the ID of the first link. The second TWT agreement, which is the TWT agreement established between the second station and the second AP, may be identified by the TWT Flow ID, the MAC address of the non-AP multilink device, the MAC address of the AP multilink device, and the ID of the second link. The third TWT agreement, which is the TWT agreement established between the third station and the third AP, may be identified by the TWT Flow ID, the MAC address of the non-AP multilink device, the MAC address of the AP multilink device, and the ID of the third link. According to a specific embodiment, the TWT Flow ID may be set for each link. According to a specific embodiment, the TWT Flow ID may be set for each link.

[0198] Also, the TWT request station may be a station that operates on a link to which the TWT agreement is applied, not a station that has transmitted a TWT request frame. Specifically, the TWT request station may be a station that operates on a link to which the TWT agreement is applied, among the stations of the multi-link device that have transmitted the TWT request frame. Also, the TWT response station may be a station that operates on a link to which the TWT agreement is applied, not a station that has transmitted a TWT response frame. Specifically, the TWT response station may be a station that operates on a link to which the TWT agreement is applied, among the stations of the multi-link device that have transmitted the TWT response frame. In the embodiment of FIG. 17, the first TWT agreement, which is a TWT agreement established between the first station and the first AP, may be identified by a TWT Flow ID, a MAC address of the first station, and a MAC address of the first AP. The second TWT agreement, which is a TWT agreement established between the second station and the second AP, may be identified by a TWT Flow ID, a MAC address of the second station, and a MAC address of the second AP. A third TWT agreement, which is a TWT agreement established between the third station and the third AP, may be identified by a TWT Flow ID, a MAC address of the third station, and a MAC address of the third AP. According to a specific embodiment, the TWT Flow ID may be set for each link.

[0199] Also, the TWT agreement may be identified based on the link through which the TWT request frame is transmitted. Specifically, the TWT agreement may be identified based on the TWT Flow ID, the MAC address of the TWT request station, the MAC address of the TWT response station, and the ID of the link through which the TWT request frame is transmitted. In the embodiment of FIG. 17, the first TWT agreement, which is the TWT agreement established between the first station and the first AP, may be identified by the TWT Flow ID, the MAC address of the first station, the MAC address of the first AP, and the ID of the first link. The second TWT agreement, which is the TWT agreement established between the second station and the second AP, may be identified by the TWT Flow ID, the MAC address of the first station, the MAC address of the first AP, and the ID of the first link. The third TWT agreement, which is the TWT agreement established between the third station and the third AP, may be identified by the TWT Flow ID, the MAC address of the first station, the MAC address of the first AP, and the ID of the first link. According to a specific embodiment, the TWT Flow ID may be set for each link.

[0200] The method for the multilink device to set up a TWT agreement has been described above. A method for the multilink device to tear down a TWT agreement will be described with reference to FIG.

[0201] FIG. 19 illustrates an operation of a multilink device according to an embodiment of the present invention for releasing a TWT agreement.

[0202] In an embodiment of the present invention, a multi-link device can cancel a TWT agreement applied to multiple links in one link. In a conventional WLAN, a station transmits a TWT release frame to cancel a TWT agreement. At this time, the TWT release frame can be transmitted by a TWT request station or a TWT response station. The TWT release frame includes a TWT Flow Identifier field indicating a TWT Flow ID. At this time, the TWT Flow Identifier field may be a 3-bit field. When a station to which a TWT agreement is applied receives a TWT release frame, the station can release the TWT agreement corresponding to the TWT Flow ID indicated by the TWT release frame. When the TWT release frame is successfully transmitted, the station that transmitted the TWT release frame can release the TWT agreement corresponding to the TWT Flow ID indicated by the TWT release frame. Therefore, the station that releases the TWT agreement and the TWT agreement to be released may be identified based on the MAC address of the sender of the TWT release frame, the MAC address of the receiver of the TWT release frame, and the TWT Flow ID.

[0203] However, as described above, when a TWT agreement is established among stations in a multi-link device, the station that transmitted the TWT request frame may be different from the station to which the TWT agreement applies. Also, as described above, the station that transmitted the TWT request frame may be one station, but the TWT agreement may apply to multiple stations. Therefore, a method for canceling a TWT agreement that can be applied in such cases is required.

[0204] The TWT release frame may include information about a link identifier. In this case, a station of the multilink device may release at least one of the multiple TWT agreements based on a link identifier, for example, a link ID, indicated by the TWT release frame. Specifically, when a station of the multilink device operates in a first link and the station releases a TWT agreement made in a second link, the station may transmit a TWT release frame including information about a link identifier in the first link. In these embodiments, the link identifier may be an identifier of a link to which the TWT agreement to be released applies. For example, the TWT release frame may include a TWT Flow Identifier field indicating a TWT Flow ID and a Link ID field indicating an identifier of a link to which the TWT agreement to be released applies. Also, the TWT release frame may include one Link ID field. Also, the TWT release frame may include multiple Link ID fields. For this reason, the format of a TWT release frame transmitted by a station included in the multilink device may be different from the format of a TWT release frame transmitted by a station not included in the multilink device. In yet another specific embodiment, the format of a TWT release frame transmitted by a station included in the multilink device may be the same as the format of a TWT release frame transmitted by a station not included in the multilink device.

[0205] When the first multilink device transmits a TWT release frame to the second multilink device through the first link and the second multilink device successfully receives the TWT release frame, the first multilink device and the second multilink device can release the TWT agreement corresponding to the TWT Flow ID indicated by the TWT release frame among the TWT agreements established between the first multilink device and the second multilink device. At this time, the first multilink device and the second multilink device can release the TWT agreement corresponding to the information related to the link indicated by the TWT release frame among the TWT agreements established between the first multilink device and the second multilink device. Specifically, the first multilink device and the second multilink device can release the TWT agreement corresponding to the TWT Flow ID indicated by the TWT release frame and the information related to the link indicated by the TWT release frame among the TWT agreements established between the first multilink device and the second multilink device.

[0206] In yet another specific embodiment, when the first multilink device transmits a TWT release frame to the second multilink device through the first link and the second multilink device successfully receives the TWT release frame, the first multilink device and the second multilink device can release the TWT agreement corresponding to the MAC address of the station that transmitted the TWT release frame and the MAC address of the station that received the TWT release frame among the TWT agreements established between the first multilink device and the second multilink device. In yet another specific embodiment, when the first multilink device transmits a TWT release frame to the second multilink device through the first link and the second multilink device successfully receives the TWT release frame, the first multilink device and the second multilink device can release the TWT agreement corresponding to the MAC address of the station that made the TWT agreement and the MAC address of the station that made the TWT agreement among the TWT agreements established between the first multilink device and the second multilink device. In yet another specific embodiment, the station that received the TWT release frame and the station that sent the TWT release frame can release the TWT agreement corresponding to the TWT Flow ID indicated by the TWT release frame within the link on which the stations are operating.

[0207] In addition, when a TWT agreement is set for multiple links by one TWT element, the TWT agreement set for the multiple links may be cancelled by one TWT cancellation frame. In this case, the TWT parameters of the TWT agreements set for the multiple links may be the same. In addition, the TWT Flow IDs of the TWT agreements set for the multiple links may be the same. For example, when a TWT agreement is established for the first link to the third link at one time between the first multilink device and the second multilink device by, for example, one TWT element, the first multilink device or the second multilink device can transmit a TWT cancellation frame for any one of the first link to the third link to cancel the TWT agreement established for the first link to the third link.

[0208] The AP multilink device includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). The non-AP multilink device includes a first station (non-AP STA1), a second station (non-AP STA2), and a third station (non-AP STA3). The first AP (AP1), the second AP (AP2), and the third AP (AP3) operate on a first link (Link1), a second link (Link2), and a third link (Link3), respectively. The first station (non-AP STA1), the second station (non-AP STA2), and the third station (non-AP STA3) operate on a first link (Link1), a second link (Link2), and a third link (Link3), respectively. A first station (non-AP STA1) is associated with a first AP (AP1), a second station (non-AP STA2) is associated with a second AP (AP2), and a third station (non-AP STA3) is associated with a third AP (AP3). A TWT agreement is established between the first station (non-AP STA1) and the first AP (AP1), and the TWT Flow ID of the TWT agreement is x. A TWT agreement is established between the second station (non-AP STA2) and the second AP (AP2), and the TWT Flow ID of the TWT agreement is y. A TWT agreement is established between the third station (non-AP STA3) and the third AP (AP3), and the TWT Flow ID of the TWT agreement is z.

[0209] At this time, the non-AP multilink device transmits a TWT release frame to release the TWT agreement between the first station (non-AP STA1) and the first AP (AP1) and the TWT agreement between the third station (non-AP STA3) and the third AP (AP3). At this time, the TWT release frame indicates x corresponding to the TWT Flow ID of the TWT agreement between the first station (non-AP STA1) and the first AP (AP1) and z corresponding to the TWT Flow ID of the TWT agreement between the third station (non-AP STA3) and the third AP (AP3).

[0210] The AP multilink device sends an ACK for the TWT cancellation frame to the non-AP multilink device. The AP multilink device then cancels the TWT agreement between the first station (non-AP STA1) and the first AP (AP1), and the TWT agreement between the third station (non-AP STA3) and the third AP (AP3). The non-AP multilink device receives an ACK for the TWT cancellation frame. The non-AP multilink device then cancels the TWT agreement between the first station (non-AP STA1) and the first AP (AP1), and the TWT agreement between the third station (non-AP STA3) and the third AP (AP3).

[0211] The TWT elements for setting and releasing the TWT agreement according to the above embodiment will be described with reference to FIG.

[0212] FIG. 20 shows the format of the Individual TWT parameter set field of the TWT element according to an embodiment of the present invention.

[0213] The Request Type field of the Individual TWT parameter set field of the TWT element includes a TWT Request subfield, which is a 1-bit field, a TWT Setup Command subfield, which is a 3-bit field, a Trigger subfield, which is a 1-bit field, an Implicit subfield, which is a 1-bit field, a 1-bit Flow Type subfield, a TWT Flow Identifier subfield, which is a 3-bit field, a TWT Wake Interval Exponent subfield, which is a 5-bit field, and a TWT Protection subfield, which is a 1-bit field.

[0214] If the value of the TWT Request subfield is 1, the station transmitting the TWT element may be a TWT requesting station or a TWT scheduled station, and if the value of the TWT Request subfield is 0, the station transmitting the TWT element may be a TWT responding station or a TWT scheduling AP.

[0215] The TWT Setup Command subfield may indicate the type of TWT command. The value of the TWT Setup Command subfield may be set to 0 to 7. When the value of the TWT Setup Command subfield is 0 to 7, the TWT Setup Command subfield may indicate that the TWT element including the TWT Setup Command subfield is a Request TWT, a Suggest TWT, a Demand TWT, a TWT Grouping, an Accept TWT, an Alternate TWT, a Dictate TWT, or a Reject TWT. This may be the same as the setting of the conventionally used TWT Setup Command subfield.

[0216] When the value of the Trigger subfield is 1, the Trigger subfield may indicate that one or more trigger frames are to be transmitted during the TWT service period when a TWT agreement is established by the TWT element.

[0217] The Implicit subfield indicates whether the TWT element requests implicit TWT. If the value of the Implicit subfield is 1, the Implicit subfield may indicate that the TWT element requests implicit TWT. If the value of the Implicit subfield is 0, the Implicit subfield may indicate that the TWT element requests explicit TWT.

[0218] The Flow Type subfield indicates an interaction method between a TWT request station and a TWT response station during a TWT service period. The value of the Flow Type subfield may be set to the same value as the Flow Type subfield defined in the conventional WLAN standard.

[0219] The TWT Flow Identifier subfield indicates an ID value for distinguishing the TWT agreement. In the conventional WLAN standard, the TWT element includes only one TWT Flow Identifier subfield. However, as described above, when a TWT agreement is set for multiple links by one TWT element, the TWT element may include multiple TWT Flow Identifier subfields. In this case, each of the multiple TWT Flow Identifier subfields may indicate the TWT Flow ID of the TWT agreement set for each of the multiple links.

[0220] The TWT wake interval subfield indicates the average interval between TWT service periods configured by the TWT element. In this case, the average interval is an expected value. The value of the TWT wake interval subfield may be set to the same value as defined in the conventional WLAN standard.

[0221] If the value of the TWT protection subfield is 1, the TWT protection subfield indicates that the TWT request station requests the TWT responder station to support protection for the TWT service period. In this case, the method of protecting the TWT service period may be the same as that defined in the conventional WLAN standard.

[0222] The Target Wake Time field, TWT Group Assignment field, Nominal Minimum TWT Wake Duration field, TWT Wake Interval Mantissa field, TWT Channel field, and NDP Paging field of the Individual TWT Parameter Set field may be set to the same as defined in conventional WLAN standards.

[0223] The Individual TWT Parameter Set field may include a Link ID Bitmap subfield as in the embodiment described with reference to FIG 16. If the Link ID Bitmap subfield indicates multiple links, the TWT element may request TWT agreement for multiple links. In this case, if TWT agreement is established for multiple links, TWT service periods having the same TWT parameters may be applied to the multiple links.

[0224] In addition, even if a TWT agreement is set for multiple links by one TWT element, the multiple TWT agreements set for the multiple links may have different TWT Flow IDs. This is because the TWT agreement is applied to different links and different stations and APs even if it is set at once. The TWT element may include multiple TWT Flow Identifier fields. Specifically, the TWT element may include multiple TWT Flow Identifier fields corresponding to the multiple links to which the TWT agreement is applied. In this case, the number of TWT Flow Identifier fields included in the TWT element may be the same as the number of links indicated by the Link ID Bitmap subfield. For example, if the Link ID Bitmap subfield indicates two links, the TWT element including the Link ID Bitmap subfield may include two TWT Flow Identifier fields. The first TWT Flow Identifier subfield among the multiple TWT Flow Identifier fields included in the TWT element may be the TWT Flow ID included in the Request Type field. The remaining subfields other than the first TWT Flow Identifier subfield may be included in another field of the TWT element, such as the Additional TWT Flow ID field in FIG. 20. Also, the first TWT Flow Identifier subfield may indicate the TWT Flow ID of the TWT agreement established on the link through which the TWT request frame is transmitted. The remaining TWT Flow Identifier subfields other than the first TWT Flow Identifier subfield may indicate the TWT Flow ID of the TWT agreement established on the remaining links through which the TWT agreement is established, other than the link through which the TWT request frame is transmitted. As described above, the remaining links through which the TWT agreement is established, other than the link through which the TWT request frame is transmitted, may be indicated by the Link ID Bitmap subfield.Furthermore, the remaining TWT Flow Identifier subfields other than the first TWT Flow Identifier subfield may be mapped to links in the order of the size of the Link ID values. Among the remaining TWT Flow Identifier subfields other than the first TWT Flow Identifier subfield, the first subfield may be mapped to the link having the smallest link ID value among the remaining links other than the link through which the TWT request frame is transmitted, the second subfield may be mapped to the link having the second smallest link ID value among the remaining links other than the link through which the TWT request frame is transmitted, and the third subfield may be mapped to the link having the third smallest link ID value among the remaining links other than the link through which the TWT request frame is transmitted.

[0225] If the TWT element requests only one TWT agreement, the TWT element may not include the remaining TWT Flow Identifier subfields other than the first TWT Flow Identifier subfield. If the TWT element requests only one TWT agreement on a link other than the link on which the TWT request frame is transmitted, the TWT element may not include the remaining TWT Flow Identifier subfields other than the first TWT Flow Identifier subfield. In this case, the first TWT Flow Identifier subfield may indicate the TWT Flow ID corresponding to the TWT agreement requested by the TWT request frame.

[0226] FIG. 21 illustrates a format of the remaining TWT Flow Identifier subfields other than the first TWT Flow Identifier subfield according to an embodiment of the present invention.

[0227] As described above, the size of the Additional TWT Flow ID field may be determined by the number of links indicated by the Link ID bitmap of the TWT element. In a conventional WLAN, the maximum number of TWT agreements that a station can establish is eight. Therefore, in a conventional WLAN, the TWT Flow Identifier subfield is a 3-bit field. When the maximum number of TWT agreements that a multi-link device can establish is eight, the TWT Flow Identifier subfield may be a 3-bit field. Also, the Additional TWT Flow ID field may include one or more subfields having a 3-bit size. When a TWT element requests n TWT agreements, the Additional TWT Flow ID field may include n-1 3-bit subfields. In this case, as described above, the first TWT Flow Identifier subfield may be the TWT Flow ID included in the Request Type field. In yet another specific embodiment, when a TWT element requests n TWT agreements, the Additional TWT Flow ID field may include n 3-bit subfields. Also, the Additional TWT Flow ID field may include a reserved field so that the TWT Parameter Set field has a length in octets. Such an embodiment is shown in FIG.

[0228] In the per-octet format of Figure 21 (a), the Additional TWT Flow ID field includes two TWT Flow ID subfields in one octet. Specifically, when a TWT element requests three TWT agreements, the Additional TWT Flow ID field may include two TWT Flow ID subfields in one octet.

[0229] Also, when the Additional TWT Flow ID field indicates an odd number of TWT Flow IDs, the last octet included in the Additional TWT Flow ID field may indicate one TWT Flow ID, and the remaining 5 bits may be set as a reserved field. Such an embodiment is shown in Figure 22(b).

[0230] In the above embodiment, the size of the TWT Flow ID subfield is 3 bits. However, the above embodiment may also be applied to a case where the size of the TWT Flow ID subfield is 4 bits.

[0231] As mentioned above, one TWT element can request TWT agreement on multiple links. Therefore, it is necessary to transmit additional information required for this. This will be explained with reference to Figure 22.

[0232] FIG. 22 shows the format of a Control field included in a TWT element transmitted by a multilink device according to an embodiment of the present invention.

[0233] The additional information required when one TWT element requests TWT agreement on multiple links may include a Link ID Bitmap, which is information indicating the links on which the TWT agreement is performed, and an Additional TWT Flow Identifier field, which is the TWT Flow ID corresponding to the TWT agreement. However, when a station of a multi-link device transmits a TWT request frame to a station to which the station is coupled, the TWT element included in the TWT request frame may not include such additional information. The TWT element may include a field indicating whether to include a Link ID Bitmap field and an Additional TWT Flow Identifier field. A station receiving the TWT element can determine the format of the TWT element based on the field indicating whether to include a Link ID Bitmap field and an Additional TWT Flow Identifier field.

[0234] If the TWT element sent by the TWT requesting station includes a Link ID Bitmap subfield, the TWT requesting station can set the value of the Link ID Bitmap Present subfield in the Control field of the TWT element to 1. If the value of the Link ID Bitmap Present subfield in the Control field of the TWT element is 1, the TWT responding station that receives the TWT element can determine that the TWT element includes a Link ID Bitmap subfield and is intended to establish a TWT agreement on multiple links or on a link different from the link on which the TWT request frame including the TWT element was sent.

[0235] If the TWT element sent by the TWT requesting station includes an Additional TWT Flow ID subfield, the TWT requesting station can set the value of the Additional TWT Flow ID Present subfield in the Control field of the TWT element to 1. If the value of the Additional TWT Flow ID Present subfield in the Control field of the TWT element is 1, the TWT responding station receiving the TWT element can determine that the TWT element includes an Additional TWT Flow ID subfield and is for establishing TWT agreement across multiple links.

[0236] In another specific embodiment, the Additional TWT Flow ID Present subfield may be omitted. In this case, the TWT responding station receiving the TWT element can determine whether the TWT element includes the Additional TWT Flow ID subfield based on the Link ID Bitmap subfield. Also, the TWT responding station receiving the TWT element can determine the size of the Additional TWT Flow ID subfield included in the TWT element based on the Link ID Bitmap subfield.

[0237] As described above, the multilink device can transmit a TWT release frame on a first link to release a TWT agreement that applies to a second link, and the multilink device can transmit a TWT release frame on one link to release a TWT agreement that applies to multiple links.

[0238] Similarly, the TWT release frame may include additional information in the TWT release frame in the conventional wireless LAN. This will be described with reference to FIG.

[0239] FIG. 23 shows a format of the Action field of a TWT release frame transmitted by a multilink device according to an embodiment of the present invention.

[0240] The TWT release frame transmitted by the multilink device may be defined as a new action frame. For convenience of explanation, the TWT release frame transmitted by the multilink device is called an MLD TWT release frame. The MLD TWT release frame may be specified as Unprotected S1G in the category of the Action field. A value not used in the conventional WLAN among the values ​​of the Action field of Unprotected S1G may be assigned to the MLD TWT release frame. For example, as in the embodiment of FIG. 23(a), 12 may be assigned to the MLD TWT release frame. In this case, when the station is going to transmit the MLD TWT release frame, the station can set the category value to 22 in the action frame and the value of the Unprotected S1G Action field to 12.

[0241] In addition, the Action field of the MLD TWT Release frame may include a field indicating the TWT agreement that the TWT Release frame intends to release. This field may be called the MLD TWT Flow field. The MLD TWT Flow field may indicate the link ID of the link corresponding to the TWT agreement that the TWT Release frame intends to release, and the TWT Flow ID corresponding to the TWT agreement that the TWT Release frame intends to release. Figure 23(b) shows an example of the Action field included in the TWT Release frame.

[0242] The MLD TWT Flow field may be indicated by the Action field of other categories as well as the Unprotected S1G category. For example, the MLD TWT release frame may be transmitted in the Protected Action frame format of the S1G category. In this case, the Action field of the S1G category action frame may include the MLD TWT Flow field.

[0243] The TWT release frame may be used in a format different from the action frame described in this embodiment, and a frame other than the action frame may be used as the TWT release frame. A specific format of the MLD TWT Flow field will be described with reference to FIG.

[0244] FIG. 24 shows an MLD TWT Flow field according to an embodiment of the present invention.

[0245] The MLD TWT Flow field may include a field having a variable length. Specifically, the MLD TWT Flow field may include a variable-length field indicating a TWT Flow ID corresponding to a TWT agreement to be released by the MLD TWT release frame. In a specific embodiment, the MLD TWT Flow field may include an MLD TWT Flow Control field having a fixed length and an MLD TWT Flow IDs field having a variable length. The MLD TWT Flow Control field may be a one-octet field. Also, the MLD TWT Flow Control field may indicate information for parsing the MLD TWT Flow IDs field. Specifically, the MLD TWT Control field may indicate information regarding the size of the MLD TWT Flow IDs field. The MLD TWT Flow IDs field may indicate a TWT Flow ID corresponding to a TWT agreement to be released. Also, the MLD TWT Flow IDs field may be omitted depending on the setting of the MLD TWT Flow Control field. The MLD TWT Flow field according to such an embodiment is shown in FIG. 24(a).

[0246] The MLD TWT Flow Control field may include a field indicating the length of the MLD TWT Flow IDs field. In this case, this field may be referred to as a Length of MLD Flow IDs field. The Length of MLD Flow IDs field may indicate the length of the MLD TWT Flow IDs field in units of 1 octet. In this case, if the length of the MLD TWT Flow IDs field is 5 octets, the value of the Length of MLD Flow IDs field may be set to 5 or 4. An MLD TWT Flow field according to such an embodiment is shown in FIG. 24(b).

[0247] In addition, the TWT Flow Control field may include a subfield indicating that all TWT agreements established between the multilink device transmitting the MLD TWT release frame and the multilink device receiving the MLD TWT release frame are to be released. Such a subfield is called a Teardown All TWT of All Link field. When the multilink device is to release all TWT agreements established with the recipient of the MLD TWT release frame, the multilink device may set the value of the Teardown All TWT of All Link subfield of the MLD TWT release frame to 1. When the MLD TWT release frame with the Teardown All TWT of All Link subfield set to 1 is successfully received, all TWT agreements established between the multilink device transmitting the MLD TWT release frame and the multilink device receiving the MLD TWT release frame are released. When the Teardown All TWT of All Link subfield is 1, the Length of MLD Flow IDs field may be set to a reserved field. Therefore, the MLD TWT Flow field does not need to include MLD TWT Flow IDs when the Teardown All TWT of All Link subfield is set to 1. A TWT Flow Control field according to such an embodiment is shown in FIG.

[0248] The MLD TWT Flow IDs field may include a 3-bit TWT Identifier subfield, a 4-bit Link ID field, and a 1-bit Teardown All TWT subfield, repeated for each octet. In this case, the consecutive TWT Identifier subfield and Link ID field can identify the TWT agreement to be released by the MLD TWT release frame. An MLD TWT Flow IDs field according to such an embodiment is shown in FIG. 24(c).

[0249] In addition, the Teardown All TWT subfield may indicate that all TWT agreements related to the link corresponding to the Teardown All TWT subfield are released. In this case, the link corresponding to the Teardown All TWT subfield is the link corresponding to the Link Id field included in the same octet as the Teardown All TWT subfield. In addition, when the value of the Teardown All TWT subfield is 1, the TWT Identifier subfield may be set as a reserved field. An MLD TWT Flow IDs field according to such an embodiment is shown in FIG. 24(e).

[0250] In yet another specific embodiment, the Teardown All TWT subfield may indicate that all TWT agreements corresponding to the TWT Flow ID corresponding to the Teardown All TWT subfield are released. In this case, the link corresponding to the Teardown All TWT subfield is the TWT Flow ID corresponding to the TWT Flow Identifier subfield included in the same octet as the Teardown All TWT subfield. Also, when the value of the Teardown All TWT subfield is 1, the Link ID subfield may be set as a reserved field. An MLD TWT Flow IDs field according to this embodiment is shown in FIG. 24(f).

[0251] In yet another specific embodiment, the MLD TWT Flow IDs field may include a plurality of TWT Identifier subfields in succession, a plurality of Link ID fields in succession, and a Teardown All TWT subfield in succession. In such an embodiment, the TWT Identifier subfields and the Link ID fields in the same order may identify the TWT agreement to be released by the MLD TWT Release frame. For example, a combination of a first TWT Identifier subfield and a first Link ID field may identify the TWT agreement to be released by the MLD TWT Release frame, and a combination of a second TWT Identifier subfield and a second Link ID field may identify the TWT agreement to be released by the MLD TWT Release frame. At least one of the number of TWT Flow Identifier subfields, the number of Link ID subfields, and the number of Teardown All TWT subfields included in the MLD TWT Flow IDs field may be proportional to the size of the MLD TWT Flow IDs field. Also, the Teardown All TWT subfields and the Link ID fields may correspond sequentially. For example, the first Teardown All TWT subfield may correspond to the first Link ID field, and the second Teardown All TWT subfield may correspond to the second Link ID field. Also, the Teardown All TWT subfields and the TWT Flow Identifier subfields may correspond sequentially. For example, the first Teardown All TWT subfield may correspond to the first TWT Flow Identifier subfield, and the second Teardown All TWT subfield may correspond to the second TWT Flow Identifier subfield.

[0252] In yet another specific embodiment, the MLD TWT release frame may include a Link ID bitmap for indicating multiple links. This may be the same as the format of the Link ID Bitmap field included in the TWT element described above. In addition, the MLD TWT release frame may include a bitmap to signal information for releasing multiple TWT agreements. This will be described with reference to FIG. 25.

[0253] FIG. 25 shows a format of an MLD TWT Flow field according to yet another embodiment of the present invention.

[0254] As described above, the MLD TWT release frame may have a variable length. In this case, the MLD TWT release frame may include a fixed-length MLD TWT Flow Control field and an MLD TWT Bitmap field. That is, the MLD TWT release frame may include an MLD TWT Bitmap field instead of the MLD TWT Flow IDs field mentioned in the embodiment described in FIG. 24. In this case, the length of the MLD TWT Flow Control field may be 1 octet. Also, in the MLD TWT release frame, the MLD TWT Bitmap field may be omitted depending on the value of the MLD TWT Flow Control field. The format of the MLD TWT Flow field according to such an embodiment is shown in FIG. 25(a).

[0255] The MLD TWT Control field may include a subfield indicating information related to the size of the MLD TWT Bitmap field. Such a subfield is called a Length of Bitmap subfield. The Length of Bitmap field may indicate the size of the MLD TWT Bitmap field in units of 3 octets. For example, if the size of the MLD TWT Bitmap field is 9 octets, the value of the Length of Bitmap field may be set to 3 or 2. The Length of Bitmap subfield may be a 3-bit field. In this case, the number of length types that the MLD TWT Bitmap field can have may be limited to 8 or less. This is because the number of TWT Flow IDs is 8 or less. The format of the MLD TWT Control field according to such an embodiment is shown in FIG. 25(b).

[0256] As described in FIG. 24, the MLD TWT Flow Control field may include a subfield indicating that all TWT agreements established between the multilink device transmitting the MLD TWT release frame and the multilink device receiving the MLD TWT release frame are to be released. Such a subfield is called a Teardown All TWT of All Link field. When the multilink device is to release all TWT agreements established with the recipient of the MLD TWT release frame, the multilink device may set the value of the Teardown All TWT of All Link subfield of the MLD TWT release frame to 1. When the MLD TWT release frame with the Teardown All TWT of All Link subfield set to 1 is successfully received, all TWT agreements established between the multilink device transmitting the MLD TWT release frame and the multilink device receiving the MLD TWT release frame are released. When the Teardown All TWT of All Link subfield is 1, the Length of TWT Bitmap field may be set as a reserved field. Therefore, the MLD TWT Flow field does not need to include the TWT Bitmap field when the Teardown All TWT of All Link subfield is set to 1. A TWT Flow Control field according to such an embodiment is shown in FIG.

[0257] The TWT Bitmap field may include a 1-octet TWT Flow ID Bitmap subfield and a 2-octet Link ID Bitmap subfield, repeated every 3 octets. A TWT Bitmap field according to such an embodiment is shown in FIG. 25(d). The TWT Flow ID Bitmap subfield may indicate a TWT Flow ID corresponding to a TWT agreement that the TWT release frame intends to release. When the MLD TWT release frame releases a TWT agreement with a TWT Flow ID of 1 to 3, the TWT Flow ID Bitmap subfield may be set to 1110 0000. 2b In this case, the TWT Flow ID values ​​1 to 8 are mapped to the first to eighth bits of the TWT Flow ID Bitmap subfield. In addition, the Link ID Bitmap subfield can indicate the link ID of the link corresponding to the TWT agreement that the TWT release frame intends to release. When the MLD TWT release frame releases the TWT agreement set for the link whose Link ID is 1 to 3, the Link ID Bitmap subfield can be set to 1110 0000. 2b In this case, each of the Link ID values ​​1 to 8 is mapped to the first bit to the eighth bit of the Link ID Bitmap subfield. Also, as described above, the TWT Flow ID may be indicated by 3 bits. Therefore, the TWT Flow ID Bitmap can indicate one TWT Flow ID value in a 3-bit size field. In this case, 5 bits of the TWT Flow ID Bitmap subfield may be a reserved field. A TWT Bitmap field according to such an embodiment is shown in FIG. 25(e).

[0258] In yet another specific embodiment, the TWT Bitmap field may include a series of TWT Flow ID Bitmap subfields and a series of Link ID Bitmap subfields, and at least one of the lengths of the TWT Flow ID Bitmap subfields and the Link ID Bitmap subfields included in the TWT Bitmap field may be proportional to the size of the TWT Bitmap field.

[0259] The TWT agreement to be released by the TWT release frame corresponds to the TWT Flow ID indicated by the TWT Flow ID Bitmap subfield and the Link ID indicated by the Link ID Bitmap subfield.

[0260] The above-mentioned MLD TWT release frame is not a TWT release frame used in conventional wireless LANs, but is a newly defined frame for releasing a TWT agreement established between multi-link devices. A method for releasing a TWT agreement established between multi-link devices using a conventional TWT release frame will be described. Specifically, the following methods will be described: 1) a method for releasing all TWT agreements established on a link where a TWT release frame is transmitted, 2) a method for releasing all TWT agreements established on a specific link, 3) a method for releasing a TWT agreement corresponding to a specific TWT Flow ID on all links, and 4) a method for releasing all TWT agreements set on all links.

[0261] FIG. 26 shows a TWT release frame for releasing a TWT agreement established in a multilink device according to an embodiment of the present invention.

[0262] A conventional TWT release frame includes a TWT Flow field having a length of one octet. In this case, the first bit to the third bit (B0-B2) of the TWT Flow field is a TWT Flow Identifier subfield indicating a TWT Flow ID. The fourth bit to the fifth bit (B3-B4) of the TWT Flow field is a reserved subfield. The sixth bit to the seventh bit (B5-B6) of the TWT Flow field is a Negotiation Type subfield indicating a negotiation type. In this case, the sixth bit to the eighth bit (B7) of the TWT Flow field may be set as a Teardown All TWT subfield. The Teardown All TWT subfield may indicate that all TWT agreements established between the station transmitting the TWT release frame and the station receiving the TWT release frame are to be released. The format of the above-mentioned TWT Flow field may be a case where the value of the Negotiation Type subfield is 0 or 1. If the value of the Teardown All TWT subfield is 1, the TWT Flow Identifier subfield may be set as a reserved field and the value of the TWT Flow Identifier subfield may be set to 0.

[0263] First, a method of releasing all TWT agreements established on a link on which a TWT release frame is transmitted will be described. In order to signal the release of all TWT agreements established on a link on which a TWT release frame is transmitted, the value of the Teardown all TWT subfield (B7) of the TWT release frame may be set to 1, and the value of the Teardown Type subfield (B4) may be set to 0. In this case, the first bit to the fourth bit (B0-B3) of the TWT Flow field may be set as a reserved field. The format of the TWT Flow field according to this embodiment is shown in FIG. 26(a). When the value of the Teardown all TWT subfield of the TWT Flow field is 1 and the value of the Teardown Type subfield is 0, the multilink device that transmitted the TWT release frame including the TWT Flow field and the multilink device that received the TWT release frame can release all TWT agreements established on the link on which the TWT release frame is transmitted, among all TWTs established between the two multilink devices.

[0264] A method of releasing all TWT agreements established on a specific link will be described. In order to signal the release of all TWT agreements established on a specific link, the value of the Teardown all TWT subfield (B7) of the TWT Release frame may be set to 0, and the value of the Teardown Type subfield (B4) may be set to 1. In this case, the first bit to the fourth bit (B0-B3) of the TWT Flow field may be set as a Link ID field indicating the link corresponding to the TWT agreement to be released by the TWT Release frame. The format of the TWT Flow field according to this embodiment is shown in FIG. 26(b). When the value of the Teardown all TWT subfield of the TWT Flow field is 0 and the value of the Teardown Type subfield is 1, the multilink device that transmitted the TWT Release frame including the TWT Flow field and the multilink device that received the TWT Release frame can release all TWT agreements established on the link indicated by the Link ID field.

[0265] A method of releasing a TWT agreement corresponding to a specific TWT Flow ID in all links will be described. In order to signal the release of a TWT agreement corresponding to a specific TWT Flow ID in all links, the value of the Teardown all TWT subfield (B7) of the TWT Release frame may be set to 0, the value of the Teardown Type subfield (B4) may be set to 0, and the value of the All Link subfield (B3) may be set to 1. The format of the TWT Flow field according to such an embodiment is shown in FIG. 26(c). When the value of the Teardown all TWT subfield of the TWT Release frame is 0, the value of the Teardown Type subfield is 0, and the value of the All Link subfield is 1, the multilink device that transmitted the TWT Release frame including the TWT Flow field and the multilink device that received the TWT Release frame can release all TWT agreements corresponding to the TWT Flow IDs indicated by the TWT Flow Identifier field among the TWT agreements established with both multilink devices.

[0266] A method of releasing all TWT agreements established on all links will be described. In order to signal the release of all TWT agreements established on all links, the value of the Teardown all TWT subfield (B7) of the TWT release frame may be set to 1, and the value of the Teardown Type subfield (B4) may be set to 1. In this case, the TWT Flow field (B0-B3) may be set as a reserved field. The format of the TWT Flow field according to this embodiment is shown in FIG. 26(d). When the value of the Teardown all TWT subfield of the TWT release frame is 1, and the value of the Teardown Type subfield is 1, the multilink device that transmitted the TWT release frame including the TWT Flow field and the multilink device that received the TWT release frame can release the TWT agreements established with both multilink devices.

[0267] In the above embodiment, the TWT agreement is cancelled by the TWT cancellation frame. However, the TWT agreement may be cancelled even if the TWT cancellation frame is not transmitted or received. This is called implicit cancellation. This will be described with reference to FIG. 27.

[0268] FIG. 27 illustrates that a TWT agreement established between multilink devices according to an embodiment of the present invention is implicitly terminated.

[0269] When an association between an AP and a non-AP station is released, a TWT agreement established between the AP and the non-AP station may be implicitly released. Also, when a link through which the AP and the non-AP station are associated is disabled, a TWT agreement established between the AP and the non-AP station may be implicitly released. In this case, the link being deactivated may include the disappearance of a TID mapped to the link. In the following description, for convenience of explanation, a case in which an association between an AP and a non-AP station is released will be described, but this may also be applied to a case in which a link through which the AP and the non-AP station are associated is disabled.

[0270] As described above, a TWT agreement may be established for multiple links by one TWT element. In this case, the TWT Flow IDs of the TWT agreements established for the multiple links may be the same. In addition, the requesting station of the TWT agreements established for the multiple links may be the same, and the responding station of the TWT agreements established for the multiple links may be the same. For this reason, it may be difficult to distinguish the TWT agreements established for the multiple links from each other, and the TWT agreements may have to be simultaneously terminated when the TWT agreement is terminated. In addition, in the conventional WLAN standard, when the AP and the non-AP station are decoupled, the AP and the non-AP station implicitly terminate the TWT agreement established between the AP and the non-AP station. At this time, information regarding the TWT agreement established between the AP and the non-AP station is deleted.

[0271] A single TWT element establishes TWT agreements on multiple links, the TWT Flow IDs of the TWT agreements established on multiple links are the same, and when the TWT request station and the TWT response station are decoupled, all the multiple TWT agreements may be implicitly terminated.

[0272] In yet another specific embodiment, when a first station included in a multilink device is deassociated with a second station associated with the first station, a TWT agreement in which the first station is a TWT responding station or the first station is a TWT requesting station may be implicitly terminated. In this case, the first station operates in the first link. The terminated TWT agreement may be inherited by a station operating in a link other than the first link among the links in which the multilink device including the first station operates. In this case, signaling including a link ID may be performed to inherit the TWT agreement. Also, the signaling for inheriting the TWT agreement may be transmitted in a management frame. Also, such inheritance of the TWT agreement may be applied even when any one station is not associated with a station associated with the station. When inheritance of the TWT agreement is performed, the TWT agreement established before the inheritance may be terminated. In the above embodiment, TWT agreement inheritance may indicate that the TWT parameters applied to the previously established TWT agreement are applied to the new TWT agreement.

[0273] In the embodiment of FIG. 27, the non-AP multi-link device (non-AP MLD) includes a first station (STA1), a second station (STA2), and a third station (STA3). The first station (STA1), the second station (STA2), and the third station (STA3) each operate on a first link (Link1), a second link (Link2), and a third link (Link3). The AP multi-link device (AP MLD) includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). The first AP (AP1), the second AP (AP2), and the third AP (AP3) each operate on a first link (Link1), a second link (Link2), and a third link (Link3). The first station (STA1) and the first AP (AP1) are associated and establish TWT agreements (TWT1, TWT2, TWT3) on the first link (Link1), the second link (Link2), and the third link (Link3). The requesting station and the responding station of the TWT agreements (TWT1, TWT2, TWT3) on the first link (Link1), the second link (Link2), and the third link (Link3) are the first station (STA1) and the first AP (AP1). The non-AP multilink device (non-AP MLD) and the AP multilink device (AP MLD) perform a reassociation procedure, and the first station (STA1) and the first AP (AP1) may be deassociated. All TWT agreements in which the first station (STA1) and the first AP (AP1) are the TWT responding station or the TWT requesting station may be implicitly terminated. Therefore, the TWT agreements (TWT1, TWT2, TWT3) on the first link (Link1), the second link (Link2), and the third link (Link3) are all cancelled.

[0274] By reassociating, the first station (STA1) can be associated with the fourth AP (AP4), which is a different AP from the first AP (AP1) in the AP multilink device (AP MLD), and operate on another link. At this time, the TWT agreement between the first station (STA1) and the first AP (AP1) may be inherited by the first station (STA1) and the fourth AP (AP4). In this way, the TWT agreement may be set on the new link by TWT agreement inheritance, regardless of the link on which the initial TWT setting was performed.

[0275] Although the present invention has been described above with reference to wireless LAN communication, the present invention is not limited thereto and can be equally applied to other communication systems such as cellular communication, etc. Also, although the method, apparatus and system of the present invention have been described in relation to a specific embodiment, some or all of the components and operations of the present invention can be embodied by a computer system having a general-purpose hardware architecture.

[0276] The features, structures, effects, etc. described in the above embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to only one embodiment. The features, structures, effects, etc. exemplified in each embodiment can be combined or modified in other embodiments by a person having ordinary skill in the art to which the embodiment belongs. Therefore, the contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

[0277] The above description focuses on the embodiments, but these are merely illustrative and do not limit the present invention. Those skilled in the art will understand that various modifications and applications not exemplified above are possible without departing from the essential characteristics of the present embodiment. For example, each component specifically illustrated in the embodiments can be modified. Furthermore, differences related to such modifications and applications should be interpreted as being included in the scope of the present invention as defined in the appended claims. [Explanation of symbols]

[0278] 100 Stations 110 Processor 120 Communications Department 140 User Interface Section 150 display units 160 Memory 200 AP 210 Processor 220 Communications Department 260 Memory 300 Servers S101 Beacon Message S103 probe request S105 probe response S107a Authentication request S107b Authentication response S109a Association request S109b Association response S111 Authentication step S113 IP address acquisition step

Claims

1. 1. A multi-link device including a plurality of stations each operating on a plurality of links, A transceiver unit; and A processor is included. The processor, A multi-link device that transmits a target wake time (TWT) element from a first station, which is one of a plurality of stations and is coupled to a first AP via a first link, and requests a TWT agreement for a second station operating on a second link and a second AP coupled to the second station.

2. 2. The multi-link device according to claim 1, wherein the TWT element includes a bitmap indicating information indicating a link to which the TWT agreement that the TWT element is attempting to establish applies.

3. a TWT requesting station of a TWT agreement for the second station and the second AP is the second station; 2. The multi-link apparatus of claim 1, wherein a TWT responding station of a TWT agreement for the second station and the second AP is the second AP.

4. The processor, The multi-link device of claim 3 , further comprising: a TWT agreement for the second station and the second AP is cancelled when a TWT cancel frame is received from the second AP or when the TWT cancel frame is successfully transmitted to the second AP.

5. The processor, The multilink device of claim 1, further comprising: a TWT agreement for the second station and the second AP that is terminated when the second link is deactivated, even without receiving or transmitting a TWT termination frame that terminates the TWT agreement for the second station and the second AP.

6. 2. The multi-link device of claim 1, wherein the TWT element requests multiple TWT agreements to be established on multiple links including the second link.

7. 7. The multi-link device of claim 6, wherein each of a plurality of TWT agreements established for the plurality of links is identified based on a link ID of each of the plurality of links.

8. 8. The multi-link device according to claim 7, wherein each of the plurality of TWT agreements established on the plurality of links is identified based on a link ID of each of the plurality of links, a medium access control (MAC) address of the multi-link device, and a TWT Flow ID of each of the plurality of TWT agreements established on the plurality of links.

9. The processor, The multi-link device of claim 7, wherein when a TWT release frame is successfully transmitted or when the TWT release frame is received, at least one of a plurality of TWT agreements established on a plurality of links is released based on a link ID indicated by the TWT release frame.

10. The processor, Releasing a TWT agreement for the second station and the second AP; 2. The multilink apparatus of claim 1, wherein the TWT agreement for the second station and the second AP is inherited by the first station and the first AP.

11. The processor, The multilink device of claim 10, wherein when the TWT agreement for the second station and the second AP is transferred to the first station and the first AP, a TWT parameter of the TWT agreement for the second station and the second AP is applied to the TWT agreement for the first station and the first AP.

12. 1. A method of operating a multilink device including a plurality of stations each operating on a plurality of links, comprising: An operating method including the steps of transmitting a target wake time (TWT) element from a first station, which is one of a plurality of stations and is coupled to a first AP via a first link, and requesting a TWT agreement for a second station operating on a second link and a second AP coupled to the second station.

13. The method of claim 12 , wherein the TWT element includes a bitmap indicating information indicating links to which the TWT agreement that the TWT element is attempting to establish applies.

14. a TWT requesting station of a TWT agreement for the second station and the second AP is the second station; The method of claim 12 , wherein a TWT responding station of a TWT agreement for the second station and the second AP is the second AP.

15. The method of operation includes: The method of claim 14, further comprising the step of canceling a TWT agreement for the second station and the second AP when a TWT cancel frame is received from the second AP or when the TWT cancel frame is successfully transmitted to the second AP.

16. The method of operation includes: The operating method of claim 12, further comprising the step of releasing the TWT agreement for the second station and the second AP even without receiving or transmitting a TWT release frame releasing the TWT agreement for the second station and the second AP when the second link is deactivated.

17. 13. The method of claim 12, wherein the TWT element requests multiple TWT agreements to be established on multiple links including the second link.

18. 20. The method of claim 17, wherein each of a plurality of TWT agreements established for the plurality of links is identified based on a link ID of each of the plurality of links.

19. 20. The method of claim 18, wherein each of the plurality of TWT agreements established on the plurality of links is identified based on a link ID of each of the plurality of links, a medium access control (MAC) address of the multi-link device, and a TWT Flow ID of each of the plurality of TWT agreements established on the plurality of links.

20. The method of operation includes: The method of claim 18, further comprising the step of canceling at least one of a plurality of TWT agreements established on a plurality of links based on a link ID indicated by the TWT cancel frame when the TWT cancel frame is successfully transmitted or the TWT cancel frame is received.

Images