Wireless communication method using multilink and wireless communication terminal using the same

Abstract

To provide a method and a device for traffic transmission performed by a terminal in a wireless communication system.SOLUTION: A non-AP STA according to an embodiment can receive a trigger frame to trigger transmission of a PPDU from an access point (AP). The trigger frame includes information indicating at least one traffic identifier (TID) that is permitted to be transmitted during a target wake time (TWT) period. The TWT period may represent a period during which transmission of traffic for the at least one TID having a specific transmission condition is permitted and transmission of traffic that does not have the specific transmission condition is restricted. The non-AP STA then transmits a PPDU including traffic corresponding to the at least one TID to the AP within the TWT period.SELECTED DRAWING: Figure 23

Description

[Technical Field]

[0001] The present invention relates to a wireless communication method using multilinks and a wireless communication terminal using the same. [Background technology]

[0002] Recently, as the popularity of mobile devices has increased, wireless LAN technology, which can provide them with high-speed wireless Internet services, has been gaining attention. Wireless LAN technology is a technology that uses short-range wireless communication technology to enable mobile devices such as smartphones, smart pads, laptop PCs, portable multimedia players, embedded devices, etc. to connect to the Internet wirelessly at home, in business, or in specific service areas.

[0003] Since supporting early wireless LAN technology using the 2.4 GHz frequency band, IEEE (Institute of Electronics Engineers) 802.11 has since implemented or is currently developing various other technology standards. IEEE 802.11b uses the 2.4 GHz frequency band and supports a maximum communication speed of 11 Mbps. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses the 5 GHz frequency band instead of the 2.4 GHz band, reducing the impact of interference compared to the significantly more congested 2.4 GHz frequency band, and uses OFDM technology to improve communication speeds to a maximum of 54 Mbps. 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 has attracted considerable attention for its backward compatibility, but it also has an advantage over IEEE 802.11a in terms of communication distance.

[0004] IEEE 802.11n is a technical standard established to overcome the communication speed limitations that have been identified as a weakness of wireless LANs. IEEE 802.11n aims to increase network speed and reliability and extend the operating distance of wireless networks. Specifically, IEEE 802.11n supports high throughput (HT) with data processing speeds of up to 540 Mbps and is based on MIMO (Multiple Inputs and Multiple Outputs) technology, which uses multiple antennas on both the transmitter and receiver 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 WLAN adoption continues to grow and applications become more diverse, the need for new WLAN systems is emerging to support data throughput rates (Very High Throughput, VHT) higher than those supported by IEEE 802.11n. Among these, IEEE 802.11ac supports wide bandwidth (80MHz-160MHz) in the 5GHz frequency band. While the IEEE 802.11ac standard is defined only in the 5GHz band, initial 802.11ac chipsets are expected to support operation in the 2.4GHz band as well for backward compatibility with existing 2.4GHz products. Theoretically, this standard enables multi-station WLAN speeds of at least 1Gbps and maximum single-link speeds of at least 500Mbps. This is achieved by expanding the air interface concepts adopted in 802.11n, including wider radio frequency bandwidth (up to 160MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and denser modulation (up to 256QAM). Additionally, IEEE 802.11ad is a method of transmitting data using the 60GHz band instead of the conventional 24GHz / 5GHz band. IEEE 802.11ad is a transmission standard that uses beamforming technology to provide speeds of up to 7Gbps, making it suitable for streaming large amounts of data and high-bitrate video, such as uncompressed HD video. However, the 60GHz frequency band has the disadvantage of being 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 nearing completion as the successor to 802.11ac and 802.11ad in order 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, high-frequency-efficient communication must be provided both indoors and outdoors in the presence of a high density of stations and APs (Access Points), and various technologies are being developed to achieve this.

[0007] Additionally, development of a new WLAN standard has begun 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 seventh 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 multi-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.

[0009] Another object of an embodiment of the present invention is to provide a method for transmitting traffic in a restricted section.

[0010] The technical problems to be solved by the present specification are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention pertains from the following description. [Means for solving the problem]

[0011] In the wireless communication system according to the present invention, a terminal (non-AP STA) that transmits traffic includes a transceiver unit and a processor, and the processor receives a trigger frame from an AP (Access Point) that triggers transmission of a PPDU, the trigger frame including information indicating at least one TID (Traffic Identifier) ​​that is allowed to be transmitted in a TWT (Target Wake Time) period, the TWT period representing a period during which transmission of traffic for the at least one TID having specific transmission conditions is allowed and transmission of traffic that does not have the specific transmission conditions is restricted, and transmits a PPDU (Physical layer Protocol Data Unit) including traffic corresponding to the at least one TID to the AP within the TWT period.

[0012] In addition, in the present invention, the trigger frame is transmitted within the TWT interval.

[0013] In addition, in the present invention, an MPDU (MAC (Medium Access Control) protocol data unit) including traffic corresponding to TIDs other than the at least one TID is combined with the MPDU of the PPDU including the traffic corresponding to the at least one TID and transmitted in the form of an A (Aggregated)-MPDU.

[0014] In addition, in the present invention, traffic for a TID corresponding to an access category of the at least one TID is allowed to be transmitted within the TWT interval.

[0015] In addition, in the present invention, the TWT interval includes a first interval and a second interval, the first interval being an interval in which only transmission of the traffic corresponding to the at least one TID is permitted, and the second interval being an interval in which transmission of traffic corresponding to TIDs other than the at least one TID is permitted.

[0016] In addition, in the present invention, the specific transmission condition is a condition related to a traffic transmission delay.

[0017] In addition, in the present invention, a channel access procedure by Enhanced Distributed Channel Access (EDCA) for ACs other than the AC corresponding to the at least one TID is restricted within the TWT period.

[0018] Also, in the present invention, a backoff counter of the channel access procedure by the EDCA for the other AC during the TWT interval is not decreased.

[0019] In addition, in the present invention, the channel state for the channel access procedure by the EDCA for the other AC within the TWT interval is in an occupied state (busy state) until the TWT interval ends.

[0020] The present invention also provides a wireless communication method for receiving a trigger frame from an AP (Access Point) that triggers transmission of a PPDU, the trigger frame including information indicating at least one TID (Traffic Identifier) ​​that is allowed to be transmitted in a TWT (Target Wake Time) period, the TWT period representing a period during which transmission of traffic for the at least one TID having a specific transmission condition is allowed and transmission of traffic not having the specific transmission condition is restricted, and transmitting a PPDU (Physical Layer Protocol Data Unit) including traffic corresponding to the at least one TID to the AP within the TWT period. [Effects of the Invention]

[0021] An embodiment of the present invention provides a wireless communication method that efficiently uses multilinks and a wireless communication terminal that uses the same.

[0022] The effects obtained from the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those having ordinary skill in the art to which the present invention pertains from the following description. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing the configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating a configuration of an access point according to an embodiment of the present invention. [Figure 5] 1 is a diagram illustrating a process in which a STA establishes 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] 1A and 1B are diagrams illustrating examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. [Figure 8] 1A and 1B are diagrams showing examples of various EHT (Extremely High Throughput) PPDU (Physical Protocol Data Unit) formats and methods for indicating the same according to an embodiment of the present invention. [Figure 9] 1 is a diagram illustrating a multi-link device according to an embodiment of the present invention. [Figure 10] 1 illustrates a method for setting up a broadcast TWT between an AP and a station according to an embodiment of the present invention. [Figure 11]10 illustrates an AP setting a quiet interval according to an embodiment of the present invention. [Figure 12] 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 13] 10 shows a station according to an embodiment of the present invention re-performing a channel access procedure in consideration of a limited service period. [Figure 14] 10 illustrates an operation in which an AP prematurely terminates a limited service period according to an embodiment of the present invention. [Figure 15] 10 illustrates an example of a TWT element for setting a broadcast TWT SP (Target Wake Time Service Period) according to an embodiment of the present invention. [Figure 16] 10 illustrates an example of a restricted TWT traffic information field for setting a restricted TWT SP according to an embodiment of the present invention. [Figure 17] 10 shows values ​​of fields included in a Broadcast TWT Parameter Set field according to an embodiment of the present invention. [Figure 18] 10 illustrates an example of a format of a trigger frame including information about the TID of traffic that can be transmitted in a restricted TWT SP according to an embodiment of the present invention. [Figure 19] 10 illustrates an example of the format of a user information field of a trigger frame containing information about the TID of traffic that can be transmitted over a restricted TWT SP according to an embodiment of the present invention. [Figure 20] 1 illustrates an example of an Enhanced Distributed Channel Access (EDCA) operation for channel access in a restricted TWT SP according to an embodiment of the present invention. [Figure 21]10 illustrates an example of a method for transmitting traffic for TIDs for which transmission is permitted and for which transmission is restricted in a restricted TWT SP according to an embodiment of the present invention. [Figure 22] 10 illustrates an example of a method for applying different operation policies to different sections in a single-restricted TWT SP according to an embodiment of the present invention. [Figure 23] 10 is a flowchart illustrating an example of an operation of a terminal according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The terms used in this specification are generally used as widely as possible, taking into consideration the functions of the present invention. However, these may vary depending on the intentions of engineers in the relevant technical field, customs, or the emergence of new technologies. In addition, in certain cases, the applicant may have arbitrarily selected terms, and in such cases, the meanings thereof will be described in the relevant description of the invention. Therefore, it is made clear that the terms used in this specification should be interpreted not simply as names of terms, but based on the substantive meanings of the terms and the overall content of this specification.

[0025] Throughout this specification, when a component is referred to as being "coupled" to another component, this includes not only when it is "directly coupled" to another component, but also when it is "electrically coupled" with another component interposed therebetween. Furthermore, when a component "includes" a specific component, this does not mean that it excludes the other component, but that it may further include the other component, unless otherwise specified. In addition, limitations such as "greater than" or "less than" a specific threshold value may be appropriately substituted with "exceed" or "less than," respectively, depending on the embodiment. Hereinafter, in the present invention, the terms "field" and "subfield" may be used interchangeably.

[0026] FIG. 1 is a diagram showing a wireless LAN system according to an embodiment of the present invention.

[0027] A wireless LAN system includes one or more Basic Service Sets (BSSs), which are a set of devices that can synchronize and communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

[0028] 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 that are stations providing distribution services, and a distribution system DS that connects multiple access points AP-1 and AP-2.

[0029] A station (STA) is any device that includes a medium access control (MAC) and a physical layer interface for a wireless medium according to the IEEE 802.11 standard. In a broad sense, the term "station" encompasses 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 may further include a user interface and a display unit, depending on the embodiment. The processor generates frames to be transmitted over a wireless network, processes frames received over 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 over the wireless network for the station. In this specification, the term "terminal" encompasses user equipment (UE).

[0030] An access point (AP) is an entity that provides a connection to a distribution system (DS) via a wireless medium for associated stations. In an infrastructure BSS, communication between non-AP stations is generally performed via the AP. However, if a direct link is established, direct communication is also possible between non-AP stations. Meanwhile, in the present invention, the term AP is used as a concept including a personal BSS coordination point (PCP), but in a broader sense, it also includes 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, an AP is also referred to as a base wireless communication terminal, but in a broader sense, the term 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 for communication with multiple wireless communication terminals.

[0031] A plurality of infrastructure BSSs are connected to each other via a distribution system DS, and the plurality of BSSs connected via the distribution system are called an Extended Service Set (ESS).

[0032] 2 is a diagram showing an independent BSS, which is a wireless LAN system according to another embodiment of the present invention. In the embodiment of FIG. 2, the same or corresponding parts as those in the embodiment of FIG. 1 will not be described again.

[0033] BSS3 shown in Figure 2 is an independent BSS and does not include an AP, so none of the stations (STA6, STA7) are 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.

[0034] 3 is a block diagram showing the configuration of a station 100 according to an embodiment of the present invention. As shown, 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.

[0035] First, the communication unit 120 transmits and receives wireless signals such as WLAN packets and may be incorporated into or external to 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 using 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 above 7.125 GHz and a communication module using a frequency band below 7.125 GHz. Each communication module may perform wireless communication with an AP or an external station based on the WLAN standard of the frequency band supported by the communication module. The communication unit 120 may operate only one communication module at a time or multiple communication modules simultaneously, depending on the performance and requirements of the station 100. When the station 100 includes multiple communication modules, each communication module may be provided independently, or multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit 120 may represent a radio frequency (RF) communication module that processes RF signals.

[0036] 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 instructions from the processor 110 using various output means.

[0037] The display unit 150 then outputs an image on a display screen. The display unit 150 outputs various display objects, such as content generated by the processor 110 or a user interface based on a control command from the processor 110. The memory 160 also stores control programs and various data used by the station 100. The control programs include a connection program required for the station 100 to connect to an AP or an external station.

[0038] 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 the 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 about the station 100's preferences contained in the communication setup message and requests connection to the AP based on the information about the station 100's preferences. The processor 110 of the present invention may refer to a main control unit of the station 100, or, depending on the embodiment, may refer to a control unit for individually controlling some components of the station 100, such as the communication unit 120. That is, the processor 110 may be a modem that modulates and demodulates wireless signals transmitted and received by the communication unit 120, or a modulator and / or demodulator. The processor 110 controls various operations for transmitting and receiving wireless signals in the station 100 according to an embodiment of the present invention. A detailed embodiment of this will be described later.

[0039] The station 100 shown in FIG. 3 is a block diagram according to an embodiment of the present invention, and the separate blocks indicate the logically separated elements of the device. Therefore, the above-described device elements may be mounted on a single chip or multiple chips depending on the device design. For example, the processor 110 and the communication unit 120 may be integrated into a single chip or may be mounted on separate chips. Furthermore, in embodiments 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.

[0040] 4 is a block diagram showing the configuration of an AP 200 according to an embodiment of the present invention. As shown, 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, duplicated descriptions 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.

[0041] 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 multiple 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, 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP 200 may include a communication module using a frequency band above 7.125 GHz and a communication module using a frequency band below 7.125 GHz. 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 multiple communication modules simultaneously, depending on the performance and requirements of the AP 200. In the embodiment of the present invention, the communication unit 220 may represent an RF (Radio Frequency) communication module that processes RF signals.

[0042] The memory 260 stores control programs used by the AP 200 and various data associated therewith. These control programs include a connection program that manages station connections. The processor 210 also controls each unit of the AP 200 and controls data transmission and reception between the units. According to an embodiment of the present invention, the processor 210 executes a program for connecting with a station stored in the memory 260 and transmits a communication setup message to one or more stations. The communication setup message includes information about connection preferences for each station. The processor 210 also performs connection setup in response to a station connection request. According to an embodiment, the processor 210 is a modem or a modulator / demodulator that modulates and demodulates wireless signals transmitted and received by the communication unit 220. The processor 210 controls various operations for transmitting and receiving wireless signals by the AP 200 according to an embodiment of the present invention. A detailed embodiment of this will be described later.

[0043] FIG. 5 is a diagram illustrating a process in which a STA establishes a link with an AP.

[0044] 5, a link between the STA 100 and the AP 200 is established through three steps: scanning, authentication, and association. First, the scanning step is a step in which the STA 100 acquires connection information for the BSS operated by the AP 200. There are two scanning methods: 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.

[0045] The STA 100 that successfully receives wireless connection information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200, and performs the authentication step (S107b). After the authentication step is performed, the STA 100 transmits an association request (S109a), receives an association response from the AP 200, and performs the association step (S109b). In this specification, association basically means wireless association, but the present invention is not limited to this, and association in a broad sense includes both wireless association and wired association.

[0046] Meanwhile, an 802.1X-based authentication step S111 and an IP address acquisition step S113 via DHCP are additionally performed. In Fig. 5, server 300 is a server that processes 802.1X-based authentication with STA 100, and may be physically connected to AP 200 or may exist as a separate server.

[0047] FIG. 6 is a diagram showing a Carrier Sense Multiple Access (CSMA) / Collision Avoidance (CA) method used in wireless LAN communication.

[0048] A terminal performing WLAN communication performs carrier sensing to check whether a channel is occupied before transmitting data. If a wireless signal above a certain strength 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 a signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold received by a terminal is identified as 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 with strength below the CCA threshold is detected, the channel is determined to be idle.

[0049] If the channel is determined to be idle, each terminal with data to transmit performs a backoff procedure after an Inter Frame Space (IFS), such as an Arbitration IFS (AIFS) or a PCF IFS (PIFS), depending on the status of each terminal. In some embodiments, the AIFS is used as a configuration replacing the conventional DCF IFS (DIFS). Each terminal waits while decreasing a slot time by a random number determined for the corresponding terminal during the idle interval of the channel, and a terminal that has exhausted all slot times attempts to access the corresponding channel. The period during which each terminal performs the backoff procedure is called a contention window period.

[0050] If a specific terminal successfully accesses the channel, it transmits data over 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 new random numbers assigned to each terminal are determined within a range (2*CW) twice the range of the random numbers previously assigned to the terminal (contention window, CW). Meanwhile, each terminal attempts access by performing a backoff procedure again in the next contention window period. At this time, each terminal performs the backoff procedure from the slot time remaining in the previous contention window period. In this way, terminals communicating over a wireless LAN can avoid collisions with each other on a specific channel.

[0051] Hereinafter, in the present invention, a terminal may be referred to as a non-AP STA, an AP STA, an AP, an STA, a receiving device, or a transmitting device, and the present invention is not limited thereto. Also, in the present invention, an AP STA may be referred to as an AP.

[0052] <Examples of various PPDU formats>

[0053] Figure 7 shows examples of various standard generation PPDU (PLCP Protocol Data Unit) formats. More specifically, Figure 7(a) shows an example of a legacy PPDU format based on 802.11a / g, Figure 7(b) shows an example of an HE PPDU format based on 802.11ax, and Figure 7(c) shows an example of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. Also, Figure 7(d) shows detailed field configurations of L-SIG and RL-SIG commonly used in the PPDU formats.

[0054] 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.

[0055] Referring to FIG. 7(b), the preamble of the HE PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a High Efficiency Signal A field (HE-SIG-A), a High Efficiency Signal B field (HE-SIG-B), a High Efficiency Short Training field (HE-STF), and a High Efficiency Long Training field (HE-LTF) 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 vary depending on the HE PPDU format. For example, HE-SIG-B may be used only in the HE MU PPDU format.

[0056] Referring to FIG. 7(c), the preamble of the EHT PPDU further includes a Repeated Legacy Short Training field (RL-SIG), a Universal Signal field (U-SIG), an Extremely High Throughput Signal A field (EHT-SIG-A), an Extremely High Throughput Signal B field (EHT-SIG-A), an Extremely High Throughput Short Training field (EHT-STF), and an Extremely High Throughput Long Training field (EHT-LTF) 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 referred to as an EHT preamble. The specific configuration of the non-legacy preamble may vary depending on the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some EHT PPDU formats.

[0057] The L-SIG field included in the PPDU preamble is configured with a total of 64 subcarriers using 64 FFT OFDM. Of these, 48 subcarriers, excluding guard subcarriers, DC subcarriers, and pilot subcarriers, are used for L-SIG data transmission. BPSK and Rate=1 / 2 MCS (Modulation and Coding Scheme) are applied to the L-SIG, so it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of the L-SIG.

[0058] 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 rates of 6, 9, 12, 18, 24, 36, 48, or 54 Mbps, which is a combination of a modulation scheme such as BPSK, QPSK, 16-QAM, or 64-QAM and a code rate such as 1 / 2, 2 / 3, or 3 / 4. The combined information in the L_RATE and L_LENGTH fields indicates the total length of the PPDU. In the non-legacy PPDU format, the L_RATE field is set to the minimum rate of 6 Mbps.

[0059] The L_LENGTH field is in bytes, and a total of 12 bits are allocated, allowing a maximum of 4095 to be signaled. In combination with the L_RATE field, it can indicate the length of the corresponding PPDU. In this case, legacy and non-legacy terminals can interpret the L_LENGTH field in different ways.

[0060] First, a legacy or non-legacy terminal analyzes the length of the corresponding PPDU using the L_LENGTH field as follows. When the value of the L_RATE field is set to indicate 6 Mbps, 3 bytes (i.e., 24 bits) may be transmitted during 4 us, which is the duration of one 64 FFT symbol. Therefore, by adding the 3 bytes corresponding to the SVC field and Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the transmission amount of one symbol, the number of 64 FFT reference symbols after the L-SIG is obtained. The obtained number of symbols is multiplied by 4 us, which is the duration of one symbol, and then 20 us, which is required to transmit the L-STF, L-LTF, and L-SIG, to obtain the length of the corresponding PPDU, i.e., the reception time (RXTIME). This can be expressed mathematically as shown in Equation 1 below.

[0061]

number

[0062] At this time,

number

[0063]

number

[0064] Here, TXTIME is the total transmission time constituting the PPDU, and is expressed as the following equation 3. In this case, TX represents the transmission time of X.

[0065]

number

[0066] 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.

[0067] Referring to Figure 7(e), the U-SIG (Universal SIG) field remains in the EHT PPDU and subsequent generation WLAN PPDUs, and serves to distinguish which generation of PPDU it is, including 11be. The U-SIG is two 64FFT-based OFDM symbols and can transmit a total of 52 bits of information. Of these, 43 bits excluding 9 bits of CRC / tail are roughly divided into a VI (Version Independent) field and a VD (Version Dependent) field.

[0068] The VI bit will maintain its current bit configuration, so even if a subsequent generation PPDU is defined, current 11be UEs can obtain information about the PPDU from the VI field of the PPDU. To this end, the VI field consists of the PHY version, UL / DL, BSS color, TXOP, and Reserved fields. The PHY version field is 3 bits long and serves to sequentially distinguish between 11be and subsequent generations of WLAN standards. 11be has a value of 000b. The UL / DL field identifies whether the PPDU is an uplink or downlink PPDU. The BSS color represents a BSS identifier defined in 11ax and has a value of 6 or more bits. The TXOP represents the transmit opportunity duration (Transmit Opportunity Duration) transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP containing the PPDU can be inferred without decoding the MPDU, and has a value of 7 or more bits.

[0069] The VD field, which is signaling information useful only for 11be version PPDUs, may consist of fields commonly used in any PPDU format, such as the PPDU format and BW, as well as fields defined differently for each PPDU format. The PPDU format is a separator that distinguishes between EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs. The BW field broadly signals five basic PPDU BW options: 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), as well as various remaining PPDU BWs formed by preamble puncturing. After signaling at 320 MHz, a portion of 80 MHz may be punctured. In addition, the punctured and modified channel shape may be signaled directly in the BW field, or may be signaled using both the BW field and a field that appears after the BW field (for example, 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.

[0070] The fields located after the BW field vary depending on the type and format of the PPDU. MU PPDUs and SU PPDUs may be signaled using the same PPDU format, and a field for distinguishing between MU PPDUs and SU PPDUs may be located before the EHT-SIG field, requiring additional signaling. Both SU PPDUs and MU PPDUs include an EHT-SIG field, but some fields not required for the SU PPDU may be compressed. In this case, the information of the compressed fields may be omitted or may have a reduced size compared to the size of the original fields included in the MU PPDU. For example, the SU PPDU may have a different configuration, such as the common fields of the EHT-SIG being omitted or replaced, or the user-specific fields being replaced or reduced to one.

[0071] Alternatively, the SU PPDU may further include a compression field indicating whether or not it is compressed, and some fields (such as the RA field) may be omitted depending on the value of the compression field.

[0072] When a portion 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). In the case of an 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 sent to it. 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 in the EHT-SIG field and / or the MCS, which is the modulation method. The EHT-SIG field may include information on the size and location of the RU assigned to each user.

[0073] In the case of an 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 efficiently receive the SU PPDU only by recognizing punctured RUs in between. Therefore, the AP can transmit the SU PPDU including information on punctured RUs among the RUs assigned to the STA (e.g., puncturing pattern of the RUs). That is, in the case of an 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 can signal the type of discontinuous channels appearing within the bandwidth.

[0074] The type of 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, since the SU PPDU is a PPDU transmitted only to a single UE, the STA can recognize its allocated bandwidth from the BW field included in the PPDU and can recognize punctured resources within 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 excluding specific channels of the punctured resource units. In this case, multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0075] The reason why only limited discontinuous channel types are signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing can be performed for each 20 MHz subchannel, if puncturing is performed on a BW having multiple 20 MHz subchannels, such as 80, 160, or 320 MHz, in the case of 320 MHz, the discontinuous channel type (when only the end 20 MHz is punctured and considered discontinuous) must be signaled by expressing whether or not each of the remaining 15 20 MHz subchannels excluding the primary channel is in use. Using 15 bits to signal the discontinuous channel type for single-user transmission can result in excessive signaling overhead when considering the low transmission rate of the signaling part.

[0076] This invention proposes a method for signaling the discontinuous channel type of the SU PPDU, shows 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.

[0077] In addition, one embodiment of the present invention proposes a method of varying the PPDU configuration indicated by the preamble puncturing BW value according to the PPDU format signaled in the PPDU format field. Assuming the length of the BW field is 4 bits, in the case of an EHT SU PPDU or TB PPDU, an EHT-SIG-A symbol of one symbol may be further signaled after the U-SIG, or no EHT-SIG-A may be signaled at all. Taking this into consideration, up to 11 puncturing modes must be signaled using only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, an EHT-SIG-B symbol is further signaled after the U-SIG, so up to 11 puncturing modes may be signaled in a different manner than in the SU PPDU. In the case of an EHT ER PPDU, the BW field can be set to 1 bit to signal whether the PPDU uses a 20 MHz or 10 MHz bandwidth.

[0078] Figure 7(f) shows the format-specific field configuration of the VD field when the PPDU format field of the U-SIG indicates an EHT MU PPDU. For an MU PPDU, SIG-B, a signaling field for simultaneous reception by multiple users, is required. SIG-B may be transmitted after the U-SIG without a separate SIG-A. For this purpose, the U-SIG must signal information for decoding SIG-B. These fields include the SIG-B MCS, SIG-B DCM, number of SIG-B symbols, SIG-B compression, and number of EHT-LTF symbols.

[0079] FIG. 8 illustrates various Extremely High Throughput (EHT) Physical Protocol Data Unit (PPDU) formats and exemplary methods for indicating the same according to an embodiment of the present invention.

[0080] 8, a PPDU may be configured with a preamble and a data portion, and the format of one type, EHT PPDU, may be distinguished by a U-SIG field included in the preamble. Specifically, whether the format of the PPDU is EHT PPDU may be indicated based on a PPDU format field included in the U-SIG field.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 8(d) shows an example of an EHT ER SU PPDU format used for single-user transmission with STAs in an extended range. The EHT ER SU PPDU may be used for single-user transmission with STAs in a wider range than the EHT SU PPDU described in FIG. 8(a), and the U-SIG field may be repeated on the time axis.

[0085] The EHT MU PPDU described in (c) of Figure 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 transmitted PPDU to the STA through the user specific field of the EHT-SIG-B. 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.

[0086] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information regarding the configuration of resource units (e.g., the division type of resource units) in a specific bandwidth (e.g., 20 MHz) on the frequency axis. That is, the RA field may indicate the configuration of resource units divided by the bandwidth for transmitting the HE MU PPDU so that the STA can receive the PPDU. Information about 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.

[0087] For example, among the multiple divided resource units, the user field corresponding to at least one resource unit used for data transmission may include the AID of the receiver or sender, and the user field corresponding to the remaining resource units not used for data transmission may include a previously set null STA ID.

[0088] Two or more PPDUs shown in FIG. 8 can be indicated by a value indicating the same PPDU format. That is, two or more PPDUs can be indicated as the same PPDU format by the same value. For example, an EHT SU PPDU and an EHT MU PPDU can be indicated by the same value using the U-SIG PPDU format subfield. In this case, the EHT SU PPDU and the EHT MU PPDU can be distinguished depending on the number of STAs receiving the PPDU. For example, a PPDU received by only one STA may be identified as an EHT SU PPDU, and when the number of STAs is set so that two or more STAs can receive the PPDU, it may be identified as an EHT MU PPDU. In other words, two or more PPDU formats shown in FIG. 8 can be indicated using the same subfield value.

[0089] In addition, some of the fields or some information of the fields shown in Figure 8 may be omitted, and such a case where some of the fields or some information of the fields is omitted can be defined as a compression mode or a compressed mode.

[0090] FIG. 9 is a diagram illustrating a multi-link device according to an embodiment of the present invention.

[0091] Referring to FIG. 9, the concept of a device to which one or more STAs are affiliated may be defined. As another example, according to an embodiment of the present invention, a device to which more than one STA (i.e., two or more) is affiliated may be defined. In this case, the device may be a logical concept. Therefore, such a device to which one or more STAs are affiliated may be referred to as a multi-link device (MLD), a multi-band device, or a multi-link logical entity (MLLE).

[0092] Alternatively, the above conceptual device can be called a multi-link entity (MLE). Also, an MLD may have one MAC medium access control service access point (SAP) to a logical link control (LLC), and an MLD may have one MAC data service.

[0093] A STA included in an MLD can operate on one or more links or channels. That is, a STA included in an MLD can operate on multiple different channels. For example, a STA included in an MLD can operate using channels in different frequency bands, such as 2.4 GHz, 5 GHz, and 6 GHz. This allows MLD to gain benefits in channel access and improve overall network performance. While existing WLANs operate on a single link, MLD operation can use multiple links to obtain more channel access opportunities or allow STAs to operate efficiently on multiple links taking into account channel conditions.

[0094] Also, if the STA affiliated with the MLD is an AP, the MLD to which the AP is affiliated may be an AP MLD, but if the STA affiliated with the MLD is a non-AP STA, the MLD to which the non-AP is affiliated may be a non-AP MLD.

[0095] An AP MLD (Multi-link Device) may be a device including one or more wireless access points (APs) and connected to a higher layer via one interface. That is, the AP MLD may be connected to the LLC (Logical Link Control) layer via one interface. Multiple APs included in the AP MLD may share some functions in the MAC layer. Each AP in the AP MLD may operate on a separate link. An STA MLD may be a device including one or more non-AP STAs and connected to a higher layer via one interface.

[0096] That is, the STA MLD may be connected to the LLC layer via a single interface. Multiple STAs included in the STA MLD may share some functions at the MAC layer. The STA MLD may also be called a non-AP MLD. The AP MLD and STA MLD can perform multi-link operations, communicating using multiple individual links. That is, if the AP MLD includes multiple APs, each AP can configure a separate link and transmit and receive frames using multiple links with each UE included in the STA MLD. Each link can operate in the 2.4 GHz, 5 GHz, or 6 GHz band, and each link can perform bandwidth extension. For example, if the AP MLD configures one link in the 2.4 GHz band and two links in the 5 GHz band, the 2.4 GHz band can transmit frames at a bandwidth of 40 MHz using a bandwidth extension scheme, and each link using the 5 GHz band can transmit frames at a maximum bandwidth of 320 MHz using discontinuous bandwidths.

[0097] Meanwhile, due to interference issues within the device, the AP MLD or STA MLD may prevent one terminal in the MLD from receiving while another terminal is transmitting. This operation, in which one AP or terminal in the MLD receives while another AP or terminal in the MLD is transmitting, is called STR (Simultaneous Transmit and Receive). The AP MLD is capable of STR operation for all links. Alternatively, STR operation is not possible for some links of the AP MLD. An STR-capable terminal MLD may be connected to an AP MLD, or an STR-incapable MLD may be connected to some or all links. Furthermore, terminals (e.g., IEEE 802.11a / b / g / n / ac / ax terminals) that do not belong to the MLD may also be connected to an AP included in the AP MLD.

[0098] The AP MLD and the STA MLD may perform a negotiation process for a multiple link usage operation during the scanning and connection process described in FIG. 5. For example, during the scanning process described in FIG. 5, an AP included in the AP MLD may transmit a beacon frame including an indicator indicating that a multiple link operation is available, the number of available links, and information on the number of available links. Alternatively, a terminal belonging to the STA MLD may transmit a probe request frame including an indicator indicating that a multiple link operation is available, and an AP belonging to the AP MLD may transmit a probe response frame including an indicator indicating that a multiple link operation is available. In this case, the AP may further transmit the number of available links, link information, etc. during the multiple link operation.

[0099] The STA MLD, which has confirmed whether the AP MLD is to operate multiple links and the link information to be used during the scanning process, can perform a connection process with the AP MLD. At this time, the AP MLD and the STA MLD can start a negotiation process for the multiple link operation. At this time, the negotiation process for the multiple link operation can be performed during the connection process between an AP belonging to the AP MLD and a terminal belonging to the STA MLD. That is, a terminal (e.g., STA1) belonging to the STA MLD can send a connection request frame to an AP (e.g., AP1) belonging to the AP MLD, and can send an indicator indicating that the terminal's multiple link operation is available and a request indicator requesting the terminal to perform the multiple link operation. The AP receiving the connection request frame from the terminal can check the indicator requesting the multiple link operation, and if the AP is capable of the multiple link operation, can send a connection response frame to the terminal that allows the multiple link operation, including link information to be used for the multiple link operation and parameters used for each link. The parameters for the multi-link operation may include one or more of the bandwidth of each link to be used, a bandwidth expansion direction, a Target Beacon Transmission Time (TBTT), and whether or not to perform STR operation. After the connection process, the AP MLD and the STA MLD, which have confirmed the use of the multi-link operation by exchanging the connection request frame and the response frame, can perform a frame transmission operation on multiple links via multiple APs included in the AP MLD and multiple UEs included in the STA MLD.

[0100] 9, there may be an MLD including multiple STAs, and the multiple STAs included in the MLD may operate on multiple links. In FIG. 9, an MLD including APs AP1, AP2, and AP3 may be called an AP MLD, and an MLD including non-AP STAs non-AP STA1, non-AP STA2, and non-AP STA3 may be called a non-AP MLD. The STAs included in the MLD may operate on Link 1, Link 2, Link 3, or some of Links 1 to 3.

[0101] According to an embodiment of the present invention, a multi-link operation may include a multi-link setup operation. The multi-link setup operation may be an operation corresponding to association performed in a single-link operation. In order to exchange frames over multiple links, multi-link setup must precede the multi-link setup. The multi-link setup operation may be performed using a multi-link setup element. Here, the multi-link setup element may include capability information related to the multiple links. The capability information may include information on whether a STA included in the MLD can receive frames over one link while another STA included in the MLD can transmit frames over another link. That is, the capability information may include information on whether a STA (non-AP STA) and / or an AP (or AP STA) can simultaneously transmit / receive frames in different transmission directions through links included in the MLD. The capability information may also include information on available links or operating channels. The multi-link setup may be set up through negotiation between peer STAs, and a multi-link operation may be set up over a single link.

[0102] According to one embodiment of the present invention, a mapping relationship may exist between a TID and an MLD link. For example, when a TID and a link are mapped, the TID may be transmitted on the mapped link. The mapping between a TID and a link may be direction-based. For example, a mapping may be performed for each direction between MLD1 and MLD2. Also, a default setting may exist for the mapping between a TID and a link. For example, the mapping between a TID and a link may basically be such that all TIDs are mapped to a certain link.

[0103] FIG. 10 illustrates a method for establishing a broadcast TWT between an AP and a station according to an embodiment of the present invention.

[0104] The service period for TWT may be set as follows: The AP requests stations associated with the AP to join TWT. Stations can join broadcast TWT or negotiate with the AP for individual TWT. In this case, the AP can request stations to join 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 using a management frame, for example, a beacon frame, to convey information necessary for stations to join broadcast TWT. In this case, 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 similar to the service period of TWT.

[0105] In the embodiment of FIG. 10, the first station (STA1) requests TWT configuration from the AP. The AP and the first station (STA1) configure TWT parameters, such as the initial TBTT and listen interval. Accordingly, the AP and the first and second stations (STA1 and STA2) configure broadcast TWT. The AP uses a beacon frame to indicate a broadcast TWT service period. During the broadcast TWT service period, the AP can transmit downlink (DL) physical layer protocol data units (PPDUs) to the first and second stations (STA1 and STA2) or can trigger uplink (UL) transmissions by transmitting trigger frames 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 beacon frames. The first and second stations (STA1 and STA2) acquire TWT information from the received beacon frames. The AP sends a trigger frame to the first station (STA1) and the second station (STA2), the first station (STA1) sends a PS-Poll frame to the AP, and the second station (STA2) sends a QoS Null frame to the AP. The AP receives the PS-Poll frame and QoS Null frame sent by the first station (STA1) and the second station (STA2) and determines that the first station (STA1) and the second station (STA2) are awake. The AP sends a multi-STA Block ACK frame to the first station (STA1) and the second station (STA2). The AP sends a DL PPDU to the first station (STA1) and the second station (STA2).

[0106] In the existing TWT service period, stations that do not participate in TWT are not restricted from accessing the channel or transmitting. TWT is intended to help stations that participate in TWT enter a doze state. However, a restricted service period to prevent transmission delays of low-latency traffic must guarantee the priority transmission of low-latency traffic, and a method for protecting the restricted service period is required.

[0107] During the restricted service period, stations that do not participate in the restricted TWT may be restricted from accessing the channel. Specifically, during the restricted service period, stations that do not participate in the restricted TWT may be unable to access the channel. If 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 other words, restarting channel access during the restricted service period may mean an action of postponing transmission, such as reselecting the backoff counter and restarting channel access, and may mean attempting channel access again when the restricted service period ends, since channel access is again permitted.

[0108] Furthermore, the station's channel access may represent an EDCA backoff procedure. Completion of channel access may represent the backoff counter of the EDCA backoff procedure reaching 0. Furthermore, when the station restarts the channel access procedure, it may randomly obtain an integer within the CW used in the previous channel access and use the obtained integer as the backoff counter. That is, the station does not need to 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 restrictions may only be applied to stations that support restricted TWT. Specifically, such channel access restrictions may only be applied to non-legacy (EHT) stations that have dot11RestrictedTWTOptionImplemented set to true in the EHT Capabilities element, and may not be applied to non-legacy (EHT) stations that have dot11RestrictedTWTOptionImplemented set to false in the EHT Capabilities element. In this specification, a non-legacy station may refer to an EHT station and a station subsequent to an EHT station, and a legacy station may refer to a station prior to an EHT station, such as a non-HT station, an HT station, a VHT station, or an HE station.

[0109] Furthermore, during the restricted service period, non-legacy stations may be configured with a NAV for traffic other than low-latency traffic. Specifically, the stations may discontinue channel access procedures for transmitting traffic other than low-latency traffic so that the NAV is configured for 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, non-legacy stations may be limited to stations that support restricted TWT. In yet another specific embodiment, non-legacy stations may be limited to stations that participate in restricted TWT.

[0110] 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.

[0111] Furthermore, the limited service period may be repeated at a period specified by the AP. That is, the AP can specify the repetition period of the limited service period. This eliminates the need for the AP to transmit a TWT element in 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 the 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.

[0112] In addition, a quiet interval may be set for stations that do not support limited TWT. In conventional WLANs, the quiet interval is a period for supporting channel sensing. When the quiet interval is set, all stations suspend transmission. Using this characteristic of the quiet interval, the limited service period can be protected. This will be described with reference to FIG. 11. In this case, stations that do not support limited TWT may be limited to legacy stations.

[0113] FIG. 11 illustrates how an AP sets a quiet interval according to an embodiment of the present invention.

[0114] An AP operating a restricted TWT can transmit a quiet element and set a quiet period. Stations suspend channel access during the quiet period. However, if channel access of stations participating in the restricted TWT is also restricted, low-latency traffic transmission is impossible. Therefore, stations participating in the restricted TWT can 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 limited service period of the restricted TWT. Specifically, a station participating in the restricted TWT can regard the quiet period corresponding to the limited service period as the limited service period. An AP operating a restricted TWT does not need to set the quiet period to coincide with the limited service period. This is because the quiet period in the quiet element is set in TU (time unit, 1024 us) units and the TWT is set in 256 us units.

[0115] However, when a station accesses a channel in a quiet period other than a quiet period not set for a restricted service period, the quiet period not set for the restricted service period may be disturbed. Therefore, it is necessary to distinguish between a quiet period set for a restricted service period, i.e., a quiet period corresponding to the restricted service period. Therefore, a station participating in a restricted TWT cannot ignore a quiet period not corresponding to a restricted service period. A station cannot transmit at all in a quiet period not corresponding to a restricted service period. Specifically, a station participating in a restricted TWT cannot ignore a quiet period that does not overlap with a restricted service period. In a specific embodiment, a station participating in a restricted TWT cannot transmit at all in a quiet period that does not overlap with a restricted service period.

[0116] In addition, in the above embodiment, a station participating in a restricted TWT may regard a quiet interval corresponding to a restricted service period as being within a predetermined time period, if the start of the restricted service period and the start of the quiet interval are within a predetermined time period. As described above, an AP operating a restricted TWT may not set a quiet interval to coincide with the restricted service period.

[0117] In the embodiment of FIG. 11, an AP transmits a beacon frame to set a quiet interval and a restricted service period. In FIG. 11(a), the quiet interval is set to the same time interval as the restricted service period. Therefore, stations participating in the restricted TWT access the channel during the quiet interval. In FIG. 11(b), the quiet interval is set from a time earlier than the start of the restricted service period to a time later than the end of the restricted service period. In FIG. 11(b), channel access of stations participating in the restricted TWT is restricted during quiet intervals that do not overlap with the restricted service period. Stations participating in the restricted TWT access the channel during quiet intervals that overlap with the restricted service period.

[0118] As mentioned above, channel access may be restricted during a restricted service period. Therefore, such restrictions may also be applied in relation to TXOP setting. This will be explained with reference to FIG. 12.

[0119] FIG. 12 illustrates how a station sets a TXOP taking into account a limited service period according to an embodiment of the present invention.

[0120] A station that acquires a TXOP before the start of the restricted service period, i.e., a station that is a TXOP holder, may need to terminate the TXOP before the start of the restricted service period. This is because if the TXOP holder continues to exchange frames after the start of the restricted service period, 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, stations may be limited to stations that support restricted TWT. That is, stations that set the value of the dot11RestrictedTWTOptionImplemented field to false may not be subject to this restriction.

[0121] In a specific embodiment, if the station that is the TXOP holder is transmitting low latency traffic, the frame exchange can continue even after the limited service period begins.

[0122] A specific method for a station to terminate a TXOP before the limited service period will now be described.

[0123] A station can set its TXOP based on the limited service period. Specifically, the station can set the end point of the TXOP to a time before the start of the limited service period. In this case, the station can set the duration of the start frame that starts the frame exchange sequence to a time before the start of the limited service period. For example, if the station successfully accesses the channel 3 ms before the start of the limited service period, the station can set its TXOP to 3 ms before. The station can also end the TXOP by sending a CTS-to-Self frame. In this case, the station can send the CTS-to-Self frame at the basic transmission rate of 6 Mbps. By sending frames at the basic transmission rate, many legacy stations can receive the frames.

[0124] In yet another specific embodiment, a station can transmit a CF-End frame before the start of the limited service period. This allows the station to end the TXOP before the start of the limited service period. In this case, the station can transmit the CF-End frame at the basic transmission rate of 6 Mbps. By transmitting frames at the basic transmission rate, many legacy stations can receive the frames.

[0125] Furthermore, a station that is not a TXOP holder may, at the start of the restricted service period, release the NAV that was set before the start of the restricted service period. In this case, the station may support restricted TWT. That is, the station may be a station that has set the value of the dot11RestrictedTWTOptionImplemented field to True. A station that is not a TXOP holder but does not support restricted TWT cannot release the NAV that was set before the start of the restricted service period. However, if the station completes a 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 have been released at the start of the restricted service period. Specifically, the station may consider the basic NAV to have been released at the start of the restricted service period.

[0126] In yet another particular embodiment, stations may be restricted to those that participate in restricted TWTs.

[0127] In the embodiment of FIG. 12, the AP transmits a beacon frame including a TWT element to signal that a limited service period is being established. In the embodiment of FIG. 12(a), the station transmits an RTS frame to establish 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. 12(b), the station transmits an RTS frame to establish 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.

[0128] In conventional WLAN operation, exceptions to the TXOP rule define operations that can 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 an A-MSDU or an A-MPDU consisting of two or more MPDUs), and transmission of control frames and QoS Null frames (not included in an A-MPDU consisting of two or more MPDUs) can be transmitted beyond the TXOP limit. If such exceptions are recognized even for the limited service period, transmission of low-latency traffic may be delayed. Such exceptions to the TXOP limit cannot be applied in violation of the limited service period.

[0129] If the end of the TXOP and the start of the restricted service period are within a predetermined time difference, the station can determine that the TXOP was acquired before the start of the restricted service period. The predetermined time difference may be 100 us. In yet another specific embodiment, if the end of the TXOP is within the restricted service period, the station can determine that the TXOP was acquired before the start of the restricted service period.

[0130] As mentioned above, a station may need to complete a frame exchange before the limited service period. Therefore, a station may not be allowed to initiate a frame exchange if the completion time of the frame exchange falls within the limited service period. In this case, the station can perform fragmentation to complete the frame exchange before the start of the limited service period.

[0131] Furthermore, if low latency traffic is transmitted in a frame exchange performed by a station that is a TXOP holder, the station can continue the frame exchange even after the low latency service period has started.

[0132] A channel access procedure that takes into account the limited service period will be described with reference to FIG.

[0133] FIG. 13 shows a station according to an embodiment of the present invention re-performing a channel access procedure taking into account a limited service period.

[0134] As described above, even if a station completes channel access before the restricted service period, if the frame exchange completion point is after the start of the restricted service period, the station can restart the channel access procedure without transmitting. At this time, the station can acquire the backoff counter value again. At this time, the station can use the same CW size used in the previous channel access procedure. That is, the station does not need to double the size of the CW used in the previous channel access procedure, nor does it 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, the QSRC (QoS STA Retry Counter).

[0135] Also, if a station completes channel access within a pre-specified time from the start of the limited service period, the station may initiate the channel access procedure again without transmitting.

[0136] In the previous embodiment, a station attempting to transmit low latency traffic can start frame exchange after completing channel access even if the frame exchange completion point is after the start of the restricted service period. This exception may be allowed only if the station attempting to transmit low latency traffic is a station participating in the restricted TWT.

[0137] 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. 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).

[0138] In the embodiment of Figure 13, the AP transmits a beacon frame including a TWT element to signal that a limited service period is being established. The station's channel access backoff counter value reaches 0 before the start of the limited service period. The station determines that the frame exchange containing the traffic to be transmitted will be completed after the start of the service period. Therefore, the station obtains a backoff counter within the CW value used in the previous channel access procedure. The station then performs the channel access procedure again using the obtained backoff counter. At this time, the station does not increment the retransmission counter.

[0139] It may happen that all low-latency traffic transmission is completed before the end of the limited service period. In such a case, it may be inefficient for the low-latency service period to restrict the transmission of traffic other than low-latency traffic. Therefore, a method for early termination of the limited service period may be necessary. This will be explained using the example of FIG. 14.

[0140] FIG. 14 illustrates an operation for an AP to prematurely terminate a limited service period according to an embodiment of the present invention.

[0141] 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 do this, stations participating in the limited TWT can additionally transmit or signal low-latency traffic in the frames they transmit. Specifically, a station can signal the additional transmission of low-latency traffic by setting the value of the More data subfield in the Frame Control field of a frame. In this case, if the value of the More data subfield in the Frame Control field of a frame transmitted in the limited service period is 1, the More data subfield indicates the need for additional transmission of low-latency traffic and does not need to indicate whether additional transmission of traffic other than 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 low-latency traffic, the station can set the value of the More data subfield in the Frame Control field of a 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 More data subfield of the Frame Control field with a value of 0. Specifically, the AP can terminate the limited service early if there is no low-latency traffic to transmit in the AP's transmit buffer and the station participating in the limited TWT has a frame in the limited service period with a More data subfield of the Frame Control field with a value of 0.

[0142] The AP can terminate the limited 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 AP's MAC address or BSSID. The AP can also set the Individual / Group bit in the BSSID (TA) field of the CF-End frame to 1. In yet another specific embodiment, the AP can terminate the limited service period early by transmitting a pre-specified management frame.

[0143] A station that receives a frame pre-designated to end the restricted service period during the restricted service period 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 applied to the restricted service period. As described above, the pre-designated frame may be a CF-End frame. In this case, if the value of the TA (BSSID) field of the CF-End frame received by the station during the restricted service period is the MAC address of the AP to which the station is associated, the station can determine that the CF-End frame is the frame that ends the restricted service period.

[0144] As described above, a quiet interval for the limited service period may be set to protect the limited service period from legacy wireless communication terminals. In this case, the AP may transmit a CF-End frame to end the limited service period. When the AP transmits the CF-End frame, the quiet interval set for the legacy stations may also be canceled.

[0145] In the above-described embodiment, the CF-End frame may have a Frame Control field Type of Control Frame (Type value B3 B2==01) and a Subtype of CF-End Frame (Subtype value B7 B6 B4 B4==1110).

[0146] When a quiet interval for a restricted service period is configured, a station participating in the restricted TWT may not be allowed to transmit a CF-End frame during 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 during the quiet interval corresponding to the restricted service period. This is because when a station participating in the restricted TWT transmits a CF-End frame, the NAV set for the legacy station is canceled. 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 during the restricted service period.

[0147] In the embodiment of FIG. 14, an AP transmits a beacon frame including a TWT element and a Quiet element. Stations supporting restricted TWT determine that a restricted service period has been established, while stations not supporting restricted TWT determine that a quiet interval has been established. When the AP determines that all low-latency traffic transmissions within the restricted service period have been completed, the AP transmits a CF-End frame to prematurely terminate the restricted service period and release the quiet interval established for legacy stations. At this time, stations supporting restricted TWT determine that the channel access restrictions applied during the restricted service period have been lifted. Specifically, as described above, when the embodiment in which a NAV is set during a restricted service period is applied, stations supporting restricted TWT may determine that the NAV for the restricted service period has been released. Furthermore, stations not supporting restricted TWT that receive the CF-End frame release their NAV.

[0148] <TID restrictions with limited TWT> As described above, the TWT SP may be configured by the AP to allow transmission of traffic that meets specific conditions and restrict transmission of traffic that does not meet the specific conditions. In this case, the AP transmits information related to TIDs corresponding to traffic that meets specific conditions (e.g., information indicating TIDs corresponding to traffic that meets specific conditions), and non-AP STAs can transmit and receive traffic corresponding to the TIDs transmitted from the AP within the TWT SP. In this case, the specific conditions may be conditions related to traffic transmission delay (e.g., low-latency traffic), and transmission of traffic that does not meet the specific conditions may be restricted. Restriction of transmission may mean that transmission is not possible during the TWT SP, transmission is possible under specific constraints (e.g., transmission in combination with an MPDU of traffic corresponding to a TID that meets specific conditions, or transmission in combination with an MPDU of traffic corresponding to a TID that meets specific conditions within a specific interval set in the TWT SP), or channel access by the EDCAF of an AC corresponding to a TID not specified by the AP is restricted.

[0149] Alternatively, the configured R-TWT SP may be further comprised of multiple intervals, and in at least one specific interval, only traffic for TIDs corresponding to traffic having a specific condition may be transmitted, and in the remaining intervals except for the at least one specific interval, traffic for TIDs corresponding to traffic not having the specific condition may be allowed to be transmitted under limited conditions (or specific constraints). For example, if the R-TWT SP is comprised of a first interval and a second interval, in the first interval, only traffic for TIDs corresponding to traffic having a specific condition (e.g., low latency) may be transmitted, and in the second interval, traffic for TIDs corresponding to traffic not having the specific condition may be allowed to be transmitted under limited conditions (or specific constraints).

[0150] The information related to the TID may be transmitted in a bitmap format, with each bit indicating a specific TID, in a user information field containing information about the trigger frame or each terminal of the trigger frame.

[0151] For example, if a restricted TWT SP (hereinafter referred to as R-TWT SP) that can transmit only low-latency traffic is configured, each STA may be allowed to transmit only low-latency traffic within the R-TWT SP, and the transmission of traffic other than low-latency traffic may be restricted. In this case, the type of traffic that a STA can transmit within a specific R-TWT SP may be restricted to traffic corresponding to a TID specified by the AP. That is, during the process of setting up an R-TWT SP, the AP may set the TID of traffic that can be transmitted within the R-TWT SP and notify the STA of the set TID. In this case, a non-AP STA may transmit only traffic corresponding to a TID specified by the AP within the R-TWT SP, and the transmission of traffic corresponding to a TID not specified by the AP may be restricted.

[0152] Hereinafter, low latency traffic may refer to latency sensitive traffic, traffic whose transmission time must be within a certain time, or traffic whose transmission time has a specific condition.

[0153] The AP may use a TWT element transmitted to establish an R-TWT SP to indicate information related to TIDs that can be transmitted within the R-TWT SP. If the AP indicates a specific TID using a TWT element transmitted to establish a specific R-TWT SP, the AP and STAs may transmit only traffic corresponding to the specific TID within the specific R-TWT SP. In this case, transmission of traffic corresponding to TIDs other than the specific TID may be restricted. In this case, traffic (MPDU, MSDU, etc.) corresponding to the other TIDs may be transmitted only in the form of aggregation (e.g., A-MPDU) using a PPDU in which a frame corresponding to the specific TID is transmitted.

[0154] FIG. 15 illustrates an example of a TWT element for setting a broadcast TWT SP (Target Wake Time Service Period) according to an embodiment of the present invention.

[0155] Referring to FIG. 15, the AP can set a specific interval as an R-TWT SP to allow transmission of only traffic having the above-mentioned specific conditions, and can transmit a TWT element to transmit information of the set R-TWT SP.

[0156] Specifically, the Broadcast TWT Parameter Set field can refer to one or more parameter set fields included in the TWT Parameter Information field of the TWT element when the Negotiation Type subfield (of the Control field) of the TWT element indicates a Broadcast TWT.

[0157] Referring to (a) of FIG. 15, the Broadcast TWT Parameter Set field may include a Restricted TWT Traffic Info field. The Restricted TWT Information field indicates information about a TID considered to be low-latency traffic in the R-TWT SP set by the TWT element, which will be described in more detail in an embodiment of FIG. 16 below. As such, the Broadcast TWT Parameter Set field may or may not include the Restricted TWT Traffic Info field. Therefore, a STA (AP, non-AP STA) receiving the TWT element needs to be informed of whether the Broadcast TWT Parameter Set field includes the Restricted TWT Traffic Info field. That is, the TWT element needs to include information indicating that the set TWT SP is an R-TWT SP, which is a TWT SP for traffic with specific conditions (e.g., low-latency traffic), and / or information indicating whether it includes a traffic information field associated with the R-TWT SP.

[0158] Whether the broadcast TWT information field includes a restricted TWT traffic information field may be indicated by the broadcast TWT information field. More specifically, the broadcast TWT information field (see FIG. 15(b)) may include a restricted TWT traffic information present subfield. When the restricted TWT traffic information present subfield is set to 1, the broadcast TWT information field including the restricted TWT traffic information present subfield may include the restricted TWT traffic information field. Conversely, when the restricted TWT traffic information present subfield is set to 0, the broadcast TWT information field including the restricted TWT traffic information present subfield may not include the restricted TWT traffic information field. In this case, the restricted TWT traffic information present subfield may be included only in the broadcast TWT parameter set field transmitted to establish the R-TWT SP. That is, only the broadcast TWT parameter set field corresponding to the R-TWT may have the restricted TWT traffic information present subfield set to 1. In this case, the STA that transmits the TWT element to establish the R-TWT SP may be the AP that schedules the R-TWT SP.

[0159] FIG. 16 illustrates an example of a restricted TWT traffic information field for setting a restricted TWT SP according to an embodiment of the present invention.

[0160] Referring to FIG. 16(a), the restricted TWT traffic information field may include a traffic information control field, a restricted TWT DL TID Bitmap field, and a restricted TWT UL TID Bitmap field. The traffic information control field (see FIG. 16(b)) may include a DL (UL) TID Bitmap Valid subfield and a UL TID Bitmap Valid subfield. If the DL (UL) TID Bitmap Valid subfield is indicated as 0, the restricted TWT DL (UL) TID Bitmap subfield is reserved, which may mean that traffic corresponding to all TIDs is considered low-latency traffic. In other words, if the DL (UL) TID Bitmap Valid subfield is indicated as 0, TID-related restrictions are not applied to DL (UL) traffic transmitted within the R-TWT SP.

[0161] On the other hand, if the DL(UL)TID Bitmap Valid subfield is indicated as 1, only the TIDs corresponding to the bits indicated as 1 in the restricted TWT DL(UL)TID Bitmap subfield may be considered as low-latency traffic. More specifically, if the k-th bit of the DL(UL)TID Bitmap subfield is indicated as 1, downlink (uplink) traffic corresponding to downlink (uplink) TID k may be considered as low-latency traffic, and if the n-th bit is indicated as 0, traffic corresponding to TID n may not be considered as low-latency traffic. Therefore, traffic for TIDs corresponding to bits set to '1' in the DL(UL)TID Bitmap subfield may be recognized as traffic having specific conditions and may be transmitted within the configured R-TWT SP.

[0162] In this case, the restricted TWT DL / UL Bitmap subfield may be included in the restricted TWT traffic information field only when the DL / UL Bitmap Valid subfields of the traffic information control field are respectively indicated as 1. That is, a restricted TWT traffic information field in which the DL TID Bitmap Valid subfield is indicated as 0 may have a configuration in which the restricted TWT DL TID Bitmap subfield is not included. In the following description and embodiments of the present invention, for convenience of explanation, a TID that is indicated to be considered as low latency traffic will be referred to as a low latency TID.

[0163] For example, if the UL TID Bitmap subfield is set to 1 and the Restricted TWT UL TID Bitmap subfield is set to 00001111 in the Restricted TWT Traffic Information field corresponding to a specific R-TWT SP, the specific R-TWT SP may be an R-TWT SP that specifies only TID4 to TID7 as low-latency TIDs in the UL direction. In this case, a scheduled STA may transmit only traffic corresponding to TID4 to TID7 when transmitting UL traffic within the R-TWT SP. In this case, the transmission of traffic corresponding to the remaining TIDs (TID0 to TID3) other than TID4 to TID7 may be restricted. In this case, the restriction of transmission may mean that transmission (TXOP) cannot be initiated (acquired) by the EDCAF of the AC (Access Category, Access Class) corresponding to TID0 to TID3. Channel access restriction related to TIDs will be described in more detail in accordance with an embodiment of the present invention, which will be described later.

[0164] As described above, the broadcast TWT parameter set field transmitted to establish an R-TWT SP includes a restricted TWT traffic information present subfield, as considered in the embodiment of FIG. 15 . In this case, the restricted TWT traffic information present subfield may be indicated (included) only when the corresponding broadcast TWT parameter set field is transmitted to establish an R-TWT SP. In other words, if the broadcast TWT parameter set field is not for establishing an R-TWT SP, the broadcast TWT parameter set may not include a restricted TWT traffic information present subfield. That is, the restricted TWT traffic information present subfield shown in FIG. 15(b) may be set to reserved. In this way, the broadcast TWT parameter set field transmitted to establish a broadcast TWT SP other than an R-TWT SP and the broadcast TWT parameter set field transmitted to establish an R-TWT SP may have different formats. Therefore, a STA receiving a broadcast TWT parameter set field needs to know whether the broadcast TWT parameter set field is transmitted to establish an R-TWT SP.

[0165] Therefore, a STA that transmits a broadcast TWT parameter set field to establish an R-TWT SP can indicate whether the broadcast TWT parameter set field is for establishing an R-TWT SP using the Request Type field of the broadcast TWT parameter set field. More specifically, a STA that transmits a broadcast TWT parameter set field to establish an R-TWT SP can indicate that the broadcast TWT parameter set field has a format associated with R-TWT by setting the Broadcast TWT Recommendation field value included in the Request Type field of the broadcast TWT parameter set field to a specific value (e.g., 4).

[0166] In addition, a STA that sends a broadcast TWT parameter set field for establishing an R-TWT SP can set the value of the broadcast TWT Recommendation field to indicate information related to TID restrictions that can be transmitted within the established R-TWT SP.

[0167] The TWT element transmitted / received by an 11ax STA may include a Broadcast TWT Recommendation field. The Broadcast TWT Recommendation field is used to indicate the type of frame to be transmitted during the established Broadcast TWT SP and restrictions related to the characteristics of the Broadcast TWT SP. The way in which an 11ax STA (AP, non-AP STA) uses Broadcast TWT Recommendation field values ​​0 to 3 is as follows.

[0168] If the Broadcast TWT Recommendation field is set to a value of 0, it may be indicated / interpreted as meaning that this is a Broadcast TWT SP with no restrictions on frames to be transmitted.

[0169] If the Broadcast TWT Recommendation field is set to a value of 1 or 2, it may be indicated / interpreted as meaning that the TWT scheduled STA is a broadcast TWT SP that is recommended to request only specific types of status and feedback.

[0170] If the Broadcast TWT Recommendation field is set to a value of 3, it may be indicated / interpreted as meaning that there are no restrictions on the frames to be transmitted, but that this is a broadcast TWT SP in which the AP must transmit a TIM frame or a FILS Discovery frame containing a TIM element at the start of every TWT SP.

[0171] An R-TWT SP can be considered a type of broadcast TWT SP, and the value of the Broadcast TWT Recommendation field may indicate that it is an R-TWT SP and whether a frame transmission restriction is applied to the R-TWT SP. In this case, the frame transmission restriction may be applied to the R-TWT SP by restricting the TID of the traffic to be transmitted to a specific TID. In this case, the specific TID may be a low-latency TID.

[0172] As an example, when the value of the Broadcast TWT Recommendation field transmitted in association with a specific R-TWT SP indicates a specific value (e.g., 5), the specific R-TWT SP may be restricted to transmitting only low-latency TIDs. In this case, MPDUs of TIDs that are not low-latency TIDs may not be allowed to be aggregated and transmitted with low-latency traffic. That is, when the value of the Broadcast TWT Recommendation field is set to a specific value, channel access by the corresponding EDCAF for TIDs that are not designated as low-latency TIDs is restricted, and aggregation with low-latency traffic is also restricted, making it impossible for them to be transmitted within the R-TWT SP. That is, when the value of the Broadcast TWT Recommendation field is set to a specific value, MPDUs that do not correspond to low-latency TIDs cannot be transmitted within the R-TWT SP. This may be understood as applying restrictions on MPDU transmission (or MPDU aggregation) in addition to restrictions on EDCAFs (of ACs) that do not support low-latency TIDs. In the present invention, the R-TWT SP is named TID-restricted-TWT (TID-R-TWT) SP.

[0173] When the Broadcast TWT Recommendation field value is specified as a specific value, the Restricted TWT Traffic Information Present subfield and the DL / UL TID Bitmap Valid subfield (or at least one of the subfields) should always be set to 1. This is because transmission restrictions for traffic of non-low latency TIDs can be applied only when a low latency TID is specified.

[0174] As another example, if the value of the Broadcast TWT Recommendation field transmitted in association with a specific R-TWT SP indicates another specific value (e.g., 4), the specific R-TWT SP may be restricted so that low-latency TIDs may be transmitted first. That is, within the configured R-TWT SP, traffic having a specific condition (e.g., low latency) may be transmitted with priority over other traffic, and other traffic may be transmitted under restrictive conditions.

[0175] For example, the restrictive conditions may mean that transmission is not allowed, that it is transmitted in combination with traffic having specific conditions, or that it is transmitted only in a specific section of the R-TWT SP, either alone or in combination with traffic having specific conditions. Alternatively, traffic (frames, MPDUs, packets, etc.) that is not a low-latency TID can be transmitted in the R-TWT SP only when there is no more traffic for the low-latency TID to be transmitted. As an example, an EDCAF corresponding to a TID that is not a low-latency TID may be restricted to perform channel access only when the transmission queue of the AC corresponding to the low-latency TID is empty. As another example, a frame (MPDU) corresponding to a TID that is not a low-latency TID may be restricted to be aggregated into an A-MPDU of low-latency traffic only when the transmission queue of the AC corresponding to the low-latency TID is empty. In other words, if an MPDU for a TID that is not a low-latency TID is included in a multi-TID A-MPDU, it is only allowed when there are no more frames for the low-latency TID.

[0176] As yet another example, whether only transmission of low latency TIDs is allowed in a specific R-TWT SP or whether transmission of traffic other than low latency TIDs is also allowed in a limited manner can be implicitly indicated / determined. More specifically, whether transmission of only low latency TIDs is allowed in a specific R-TWT SP may be indicated / determined depending on whether the duration of the R-TWT SP exceeds a specific length.

[0177] In this case, if the length of an R-TWT SP is shorter than a specific value (previously agreed value), the R-TWT SP may be designated / determined as an R-TWT SP in which only frames with low latency TIDs are transmitted. Therefore, non-AP STAs that are members of an R-TWT SP whose length is shorter than a specific value (hereinafter, less than) must transmit only frames with low latency TIDs within the R-TWT SP.

[0178] On the other hand, a non-AP STA that is a member of an R-TWT SP whose length is longer than a certain value (above, exceeds) can first transmit frames with a low latency TID within that R-TWT SP, and then transmit frames with other TIDs that are not low latency TIDs.

[0179] In this case, a non-AP STA that is a member of an R-TWT SP whose length is longer than a specific value (e.g., 1 TU) must transmit only frames of the low latency TID until the elapsed time of the R-TWT SP reaches the specific value, and when the elapsed time of the R-TWT SP exceeds the specific value, it can transmit frames of other TIDs that are not the low latency TID in the remaining R-TWT SP interval.

[0180] That is, the operation method of the R-TWT SP can be determined / instructed / changed depending on the length of the R-TWT SP. In this way, when different operation methods are applied to each time interval within a single R-TWT SP (i.e., there is an interval in which only frame transmission of a low latency TID is permitted and an interval in which frame transmission of other TIDs other than the low latency TID is permitted), the Broadcast TWT Recommendation field of the TWT element transmitted when the R-TWT SP is established may be set to a specific value.

[0181] For example, if a specific R-TWT SP is established with the Broadcast TWT Recommendation field set to a specific value and another R-TWT SP is established with the Broadcast TWT Recommendation field set to a different value, only the specific R-TWT SP established with the specific value may be an R-TWT SP whose operation policy is changed during the R-TWT SP interval. For example, if the Broadcast TWT Recommendation field of the TWT element transmitted when establishing the R-TWT SP is set to a specific value (e.g., 5), different operation methods may be applied to the R-TWT SP established by the TWT element for each time interval. In this case, if the Broadcast TWT Recommendation field of the TWT element transmitted when establishing the R-TWT SP is set to a different value (e.g., 4), the same operation method is applied to the R-TWT SP established by the TWT element for all time intervals corresponding to the R-TWT SP. In this case, the operation method refers to an operation method (channel access and frame transmission method) related to whether only frame transmission of a low-delay TID is permitted or whether frame transmission of other TIDs is permitted with restrictions.

[0182] In addition, frame transmission of other TIDs may be permitted while only frame transmission of a low latency TID is permitted within a single R-TWT SP. In other words, the operation method of the R-TWT SP may be changed according to a previously agreed-upon method during R-TWT SP operation. In this case, the AP may perform signaling for changing the operation method during the R-TWT SP period. Alternatively, the operation method of the R-TWT SP may be changed according to a previously agreed-upon rule. A method for changing the transmission rule related to a low latency TID within an R-TWT SP according to a previously agreed-upon method during operation will be described in more detail in accordance with an embodiment of the present invention, which will be described later, and therefore will not be described in detail here. Frame transmission rules for a situation in which the operation method is changed within a single R-TWT SP (including both cases where the operation method is changed according to the R-TWT SP configuration method and cases where the operation method is changed during R-TWT SP operation according to a previously agreed-upon method) are described in accordance with an embodiment of FIG. 22.

[0183] Alternatively, the Broadcast TWT Recommendation field may use only one value indicating R-TWT, and the presence or absence of TID restriction may be indicated in each trigger frame.

[0184] As an example, an R-TWT SP may be established with a Broadcast TWT Recommendation field value of 4, and the trigger frame transmitted to the R-TWT SP may indicate whether or not TID restriction is enabled. In this case, the trigger frame may include a 1-bit subfield indicating whether or not TID restriction is enabled. If the 1 bit indicating whether or not TID restriction is enabled is set to 1, the TB PPDU transmitted in the trigger frame may be limited to include only MPDUs for the low latency TID, as with the TB PPDU transmitted in the TID-R-TWT described above. On the other hand, if the 1 bit indicating whether or not TID restriction is enabled is set to 0, the TB PPDU transmitted in the trigger frame may include MPDUs for TIDs other than the low latency TID, for example, by combining.

[0185] The low-latency TID-related transmission restrictions applied within the R-TWT SP may take precedence over the (multi-TID) A-MPDU aggregation rule. That is, while the A-MPDU aggregation rule allows MPDUs corresponding to ACs with a higher priority than the AC of a specific EDCAF that is the TXOP holder to be aggregated into an A-MPDU, A-MPDUs transmitted within the R-TWT SP cannot be aggregated into an A-MPDU unless they are low-latency TID traffic MPDUs, even if they correspond to ACs with a higher priority than the EDCAF AC. Similarly, while MPDUs corresponding to ACs with a higher priority than the Preferred AC indicated in the trigger frame can be included in the TB PPDU in the form of a multi-TID A-MPDU, MPDUs corresponding to TIDs other than the low-latency TID cannot be included in the multi-TID A-MPDU transmitted within the R-TWT SP.

[0186] If there are no more MPDUs corresponding to the low-latency TID, the Scheduled STA must inform the Scheduling AP that there is no more low-latency traffic to send by setting the More Data subfield of the frame contained in the last PPDU it transmits to 1.

[0187] FIG. 17 illustrates field values ​​included in a Broadcast TWT Parameter Set field according to an embodiment of the present invention.

[0188] The Broadcast Parameter Set Information field transmitted to establish the R-TWT SP may indicate information related to the R-TWT SP using the Broadcast TWT Recommendation subfield value of the Request Type field.

[0189] Referring to FIG. 17, if the value of the Broadcast TWT Recommendation subfield is set to 4, it may be understood that the corresponding Broadcast TWT SP is indicated / interpreted as an R-TWT SP. Also, if the value of the Broadcast TWT Recommendation subfield is set to 5, it may be determined that the corresponding Broadcast TWT SP is indicated / interpreted as an R-TWT SP. However, two Broadcast TWT Recommendation subfield values ​​indicating an R-TWT SP may be R-TWT SPs having different restrictions on frames transmitted in the R-TWT SP. In this case, the restrictions on frames transmitted in the R-TWT SP may be restrictions related to the TID of the MPDU to be transmitted. More specifically, the two R-TWT SPs indicated by the two different values ​​may be R-TWT SPs that apply different rules to the TID of a transmittable MPDU.

[0190] For example, an R-TWT SP whose Broadcast TWT Recommendation field is set to a value of 4 may be an R-TWT SP that is proposed to transmit low-latency traffic and is restrictedly permitted to transmit MPDUs corresponding to TIDs other than low-latency TIDs. In this case, traffic other than low-latency traffic may be transmitted only when low-latency traffic is being transmitted or when there is no low-latency traffic to transmit.

[0191] As an example, a TID-R-TWT SP with a Broadcast TWT Recommendation field value of 5 is an R-TWT SP that is only allowed to transmit low-latency traffic, and other traffic that is not low-latency traffic must not be transmitted.

[0192] Therefore, when the value of the Broadcast TWT Recommendation field received from the Scheduling AP is indicated as 4, the Scheduled STA can recognize that the Broadcast TWT corresponding to the Broadcast TWT Recommendation field is the R-TWT. In this case, the Scheduled STA can preferentially transmit MPDUs with a low-latency TID within the R-TWT, and, subject to limitations, can also transmit MPDUs with other TIDs that are not low-latency TIDs.

[0193] Also, when the value of the Broadcast TWT Recommendation field received from the Scheduling AP is indicated as 5, the Scheduled STA can recognize that the Broadcast TWT corresponding to the Broadcast TWT Recommendation field is a TID-R-TWT having TID restrictions. In this case, the Scheduled STA may need to transmit only MPDUs with a low-latency TID within the TID-R-TWT.

[0194] <Settings of R-TWT SP> When a Non-AP STA attempts to request the settings of the TWT SP, it can send a request message to the AP STA to request the settings of the TWT SP. At this time, the request message may be sent including information indicating the type (or kind) of the TWT SP for which the settings are requested. For example, when the Non-AP STA requests the settings of the R-TWT SP, the Non-AP STA can set a specific bit value requesting the setting of the R-TWT SP to "1" and send it in the message requesting the settings of the TWT SP. Thereafter, after setting the TWT SP in response to the request of the Non-AP STA, the AP STA can include information related to the set TWT SP in a beacon frame or a management frame and send it.

[0195] Specifically, a Non-AP STA can request the AP to schedule an R-TWT SP by transmitting a TWT Request frame to the AP. At this time, the Non-AP STA can set the DL (UL) TID Bitmap Valid bit to 1 in the TWT element (contained in the TWT Request frame) transmitted to request the AP for an R-TWT SP. This may be interpreted as the Non-AP STA requesting to schedule an R-TWT SP that considers the TIDs indicated using a restricted TWT DL (UL) TID Bitmap as low-latency TIDs. In this case, when the DL (UL) TID Bitmap Valid bit contained in the TWT element of the received TWT Request frame is set to 1, the AP may need to respond with a TWT Response frame with a restricted TWT DL (UL) TID Bitmap subfield set to the same as the restricted TWT DL (UL) TID Bitmap subfield contained in the TWT Request frame. In other words, when receiving a request to schedule an R-TWT SP from a Scheduled STA, the Scheduling AP may need to schedule an R-TWT SP that considers the TID indicated by the STA as a low-latency TID.

[0196] <Operation of R-TWT SP> According to an embodiment of the present invention described above, the broadcast TWT parameter set field transmitted to establish an R-TWT SP may have a configuration including a restricted TWT traffic information field. The restricted TWT traffic information field indicates information regarding TIDs to be considered as low-latency traffic in the established R-TWT SP, and the Scheduled STA and / or Scheduling AP of the R-TWT SP perform traffic transmission based on the TID information indicated in the R-TWT SP establishment process. That is, a specific established R-TWT SP is an SP that always considers the same TID as a low-latency TID even when the SP is repeated.

[0197] However, the traffic that each STA should treat as low-latency may be determined regardless of the TID. For example, application program traffic processed by a specific STA may have characteristics that require it to be treated as low-latency even though it is not video (AC_VI) or voice (AC_VO) data, while application program traffic processed by another STA may not need to be treated as low-latency even though it is video or voice data. In this way, the traffic that should be treated as low-latency is determined according to the needs of each STA and may not be collectively classified based on information related to the traffic type, such as the TID. Therefore, each Scheduled STA may need to perform operations that consider different TIDs as low-latency TIDs.

[0198] Furthermore, even within a single R-TWT SP, there may be cases where preferential processing is desired for a specific time interval, as necessary. For example, within a single R-TWT SP where TIDs 4 to 7 are considered to be low-latency TIDs, the Scheduling AP may plan to transmit a total of four trigger frames. In this case, the AP may intend to receive only the MPDU corresponding to TID 7 using the TB PPDU in response to the first trigger frame, and may prefer to receive the MPDU corresponding to TID 6 in response to the second trigger frame, and the MPDUs for TIDs 5 and 4 in response to the third and fourth trigger frames, respectively. In this case, the Scheduling AP needs to transmit a trigger frame and indicate information regarding the TIDs of the MPDUs it wishes to receive in response to the trigger frame.

[0199] Therefore, an AP that has configured an R-TWT SP can transmit a trigger frame containing information indicating the TIDs of traffic that are permitted to be transmitted in the configured R-TWT SP. The information indicating the TIDs of traffic that are permitted to be transmitted in the R-TWT SP can be included in a bitmap format, and each bit in the bitmap can indicate whether the corresponding TID is a TID for traffic that is permitted to be transmitted in the R-TWT SP. For example, if a bit in the bitmap is set to "0," transmission of the corresponding TID within the configured R-TWT SP may be restricted, and if set to "1," transmission of the corresponding TID within the configured R-TWT SP may be permitted.

[0200] Alternatively, information for indicating the TID of traffic permitted to be transmitted in the configured R-TWT SP may be included in a user information field, which is information about each terminal in the trigger frame. In this case, the user information field may include information about only one TID, and the TIDs in each user information field may be different from each other.

[0201] Specifically, the Scheduling AP may use a trigger frame transmitted within an R-TWT SP to indicate information regarding a TID to be considered as a low-latency TID in a TB PPDU responded to the trigger frame. A scheduled STA that is assigned an RU by a specific trigger frame and responds with a TB PPDU, and a scheduled STA that responds with a TB PPDU using an RA-RU, must respond with a TB PPDU by considering the TID indicated in the specific trigger frame as a low-latency TID. In this case, responding with a TB PPDU by considering the low-latency TID may mean limiting the TID of an MPDU included in a multi-TID A-MPDU transmitted in a TB PPDU to a low-latency TID.

[0202] Information about the low latency TID may be indicated only when the trigger frame is transmitted within the R-TWT SP. The subfield (bit) indicating the low latency TID in the trigger frame transmitted within the R-TWT SP may be a reserved subfield or a subfield for other uses in the trigger frame transmitted outside the R-TWT SP.

[0203] When the scheduling AP indicates information about a low latency TID using a trigger frame, it may need to indicate a TID from only TIDs that the R-TWT SP that transmits the trigger frame considers as low latency TIDs. That is, if the R-TWT SP considers TID4 to TID7 as low latency TIDs, the scheduling AP may need to indicate a TID from only TID4 to TID7 when indicating a low latency TID for the TB PPDU.

[0204] When information regarding a low-latency TID is indicated in a trigger frame, a scheduled STA may need to operate based on the low-latency TID information indicated in the trigger frame when responding with a TB PPDU to the trigger frame. In other words, a scheduled STA may need to respond with a TB PPDU based on TID information indicated as a low-latency TID in the trigger frame, which is not a TID indicated as a low-latency TID in the R-TWT SP. In other words, when a specific TID indicated as a low-latency TID in the R-TWT SP is not indicated as a low-latency TID in the trigger frame, an MPDU for the specific TID may be restricted from being transmitted (responded) by a TB PPDU. At this time, the TB PPDU response method taking into account a low-latency TID has been described in the above-described embodiment of the present invention, and therefore a detailed description thereof will be omitted.

[0205] However, the low latency TID indicated by the trigger frame may be applied only when a TB PPDU is in response to the trigger frame.

[0206] FIG. 18 illustrates an example of a format of a trigger frame including information about the TID of traffic that can be transmitted in a restricted TWT SP according to an embodiment of the present invention.

[0207] The trigger frame transmitted by the Scheduling AP in the R-TWT SP may include a TID indicator in the Common Info field. More specifically, a TID Bitmap may be included. Each bit of the TID Bitmap corresponds to a different TID, and if a specific bit is indicated as 1, the TID corresponding to the specific bit may be indicated / interpreted as a low-latency TID.

[0208] 18, the Common Info field of the trigger frame may include a Low Latency TID Bitmap subfield. The Low Latency TID Bitmap subfield is composed of 8 bits, and each of the 8 bits may be analyzed in one-to-one correspondence with TID0 to TID7.

[0209] When the Scheduling AP transmits a trigger frame within the R-TWT SP, it may attempt to receive a response from the responding STA (Scheduled STA) with a TB PPDU containing only an MPDU for a specific low-latency TID. In this case, the Scheduling AP may indicate the specific low-latency TID using a low-latency TID bitmap. In this case, the Scheduling AP sets the bit (in the low-latency TID bitmap) corresponding to the specific low-latency TID to 1.

[0210] When a scheduled STA receives a trigger frame within an R-TWT SP, it may need to respond with a TB PPDU that includes only MPDUs for the low-latency TIDs indicated in the trigger frame. In this case, the scheduled STA may need to configure a (multi-TID) A-MPDU to be included in the TB PPDU, considering that the TIDs indicated in the low-latency TID bitmap are low-latency TIDs.

[0211] According to one embodiment of the present invention, the Scheduling AP may use a trigger frame transmitted within an R-TWT SP to indicate to each Scheduled STA information regarding a TID to be considered as a low-latency TID in a TB PPDU to be responded to the trigger frame. A Scheduled STA that is assigned an RU in the trigger frame and responds with a TB PPDU must respond with the TB PPDU by considering the TID indicated in the user information field (information related to its own AID is indicated by the AID12 subfield) included in the trigger frame as a low-latency TID. In this case, responding with a TB PPDU by considering the low-latency TID may mean limiting the TIDs of MPDUs included in the multi-TID A-MPDU transmitted in the TB PPDU to the low-latency TID. Alternatively, responding with a TB PPDU by considering the low-latency TID may mean responding only with MPDUs corresponding to TIDs indicated as low-latency TIDs by the TB PPDU.

[0212] When indicating a low-latency TID using the user information field in this way, the Scheduling AP can indicate different TIDs as low-latency TIDs to each Scheduled STA. Therefore, even when each Scheduled STA receives the same trigger frame within a specific R-TWT SP, it can operate while recognizing different TIDs as low-latency TIDs.

[0213] The information about the low latency TID indicated in the user information field may have a form that directly indicates the ID of a TID that is not a TID bitmap. In other words, the number of low latency TIDs indicated in the user information field may be limited to one. This may be a signaling method that takes into consideration the limited amount of bits available for indicating a low latency TID in the user information field. However, when a specific TID is indicated as a low latency TID in the user information field, a TID with a higher priority than the specific TID may be automatically determined (analyzed) as a low latency TID. In other words, when a specific TID is indicated as a low latency TID in the user information field, not only the specific TID but also TIDs with a higher priority than the specific TID may be indicated as low latency TIDs.

[0214] Similar to the low latency TID indication using the Common Info field of the trigger frame described above, the low latency TID indicated in the user information field may also be valid only when a TB PPDU is responded to for the trigger frame containing the user information field.

[0215] FIG. 19 illustrates an example of a format of a user information field of a trigger frame containing information about the TID of traffic that can be transmitted in a restricted TWT SP according to an embodiment of the present invention.

[0216] Referring to Figure 19, the user information field of a trigger frame transmitted within an R-TWT SP may include an indicator for a low latency TID. In one embodiment of Figure 19, the indicator for a low latency TID is considered to be a low latency TID subfield. The low latency TID subfield may be a subfield included in the Trigger Dependent user information subfield of the user information field. In this case, the bit indicating the low latency TID subfield may be a subfield indicated by the bit indicating the Preferred AC subfield in the user information field of a trigger frame transmitted outside the R-TWT SP.

[0217] The low latency TID subfield indicates information about a TID that a scheduled STA that is assigned an RU in the user information field and responds with a TB PPDU should consider as a low latency TID.

[0218] The operations that a STA performing frame exchange within the R-TWT SP performs in consideration of low latency TID can be summarized as follows: 1) and 2).

[0219] 1) Works with the TXOPs you have acquired A STA that acquires a TXOP within an R-TWT SP prioritizes the transmission of frames corresponding to low-latency TIDs. When a STA transmits a multi-TID A-MPDU, only frames corresponding to low-latency TIDs may be aggregated into the multi-TID A-MPDU. In this case, restrictions related to the TXOP limit of the primary AC do not apply when frames corresponding to low-latency TIDs are aggregated into the multi-TID A-MPDU. More specifically, even if the TXOP limit of the primary AC is 0, frames of low-latency TIDs corresponding to ACs other than the primary AC may be included (aggregated) in the multi-TID A-MPDU. Furthermore, frames of low-latency TIDs corresponding to ACs with a lower priority than the primary AC may also be included in the multi-TID A-MPDU. In other words, when frames of low-latency TIDs are included in the multi-TID A-MPDU, restrictions related to the priority of the AC do not apply.

[0220] If a STA has no more frames corresponding to the low latency TID, i.e., if there are no frames corresponding to the low latency TID in the transmission queue (EDCAF), the STA can transmit other frames that do not have the low latency TID in the TXOP it has acquired, which may be aggregated with the frames of the low latency TID.

[0221] That is, a single PPDU can contain frames of a low latency TID and frames of other TIDs that are not low latency TIDs. In this case, the frames of the low latency TID included in the single PPDU are positioned before the frames of the other TIDs included together.

[0222] In addition, the STA may transmit a PPDU including only frames of other TIDs other than the low latency TID within the R-TWT SP. The condition for the STA to transmit a PPDU including only frames of other TIDs may be that there are no more frames of the low latency TID. In this case, frames of other TIDs other than the low latency TID may be aggregated according to the conventional Wi-Fi multi-TID A-MPDU configuration rule. More specifically, among frames of other TIDs other than the low latency TID, frames corresponding to ACs with a higher priority than the Primary AC may be aggregated. That is, frames of other TIDs that can be transmitted when there are no frames of the low latency TID may be limited to frames corresponding to ACs with a higher priority than the Primary AC. In this case, frames corresponding to the same AC as the low latency TID may be included (aggregated) in the PPDU transmitted within the R-TWT SP.

[0223] 2) Transmission of TB PPDU in response to trigger frame A STA that receives a trigger frame within an R-TWT SP and responds with a TB PPDU can determine the frames to include in the TB PPDU taking into account the low-latency TID. More specifically, a STA that responds with a TB PPDU within an R-TWT SP must include only frames of TIDs designated as low-latency TIDs in the TB PPDU. In this case, a STA that responds with frames of low-latency TIDs to a TB PPDU can respond with a multi-TID A-MPDU in which frames of low-latency TIDs are aggregated. In this case, a multi-TID A-MPDU included in a TB PPDU can include frames of low-latency TIDs regardless of the Preferred AC subfield value designated by the Trigger frame. In other words, a STA that responds with a TB PPDU within an R-TWT SP can respond with a multi-TID A-MPDU including a low-latency TID as a TB PPDU regardless of the Preferred AC information designated by the Trigger frame.

[0224] However, if there are no more frames with the low latency TID, the STA that responds with the TB PPDU can include frames with other TIDs that are not low latency TIDs in the TB PPDU. In this case, the STA that responds with frames with other TIDs that are not low latency TIDs in the TB PPDU must transmit the multi-TID A-MPDU in the TB PPDU according to the following rules. - First include the MPDUs corresponding to the low latency TID of the R-TWT SP. - Then, it first includes the MPDU corresponding to the Preferred AC. - Then, it first contains MPDUs of ACs with higher priority than the Preferred AC. - Contains remaining MPDUs

[0225] Additionally, after first including MPDUs corresponding to the low-latency TID, it is possible for MPDUs of other TIDs of the AC corresponding to the low-latency TID to be included in the TB PPDU. For example, when only one of two TIDs corresponding to a specific AC is indicated as the low-latency TID, the MPDU corresponding to the low-latency TID may first be included in the A-MPDU, and the MPDU corresponding to the remaining one TID may be included next. At this time, MPDUs of other ACs (of TIDs) not corresponding to the low-latency TID are included after the MPDU corresponding to the remaining one TID.

[0226] <Channel access management method in R-TWT SP> As considered in the previous embodiments of the present invention, the R-TWT SP may be instructed by the broadcast TWT parameter set field at the time of R-TWT SP establishment with information regarding the TID to be considered as the low-latency TID, and may be restricted such that only MPDUs of the low-latency TID are transmitted within the R-TWT SP.

[0227] Conventional Wi-Fi allows a Scheduled STA of a broadcast TWT SP to perform its own channel access (not channel access using a trigger frame) using EDCA or the like within the broadcast TWT SP to start transmission. Considering this, in the R-TWT SP that can be considered as a type of broadcast TWT, the Scheduled STA may also be allowed to perform its own channel access using EDCA or the like.

[0228] In this case, the R-TWT SP with restricted MPDU transmission of other TIDs that are not the low-latency TID may be understood as a channel access section with TID restriction that has not been considered in conventional Wi-Fi. Therefore, the Scheduled STA performing channel access within the R-TWT SP performs channel access considering the TID restriction.

[0229] According to one embodiment of the present invention, a scheduled STA accessing a channel within an R-TWT SP performs conventional EDCA operations but can only attempt to acquire a TXOP using an EDCAF corresponding to a low-latency TID in the UL direction. More specifically, when a scheduled STA of an R-TWT SP attempts to access a channel by itself to acquire a TXOP, it may need to contention for channel access only using the EDCAF of the AC corresponding to the low-latency TID. For example, when a specific R-TWT SP is established, the low-latency TIDs of the R-TWT SP may be designated as TID4 to TID7, and TID4 to TID7 may be TIDs corresponding to AC_VI and AC_VO. In this case, when a scheduled STA of the specific R-TWT SP attempts to access a channel using EDCA within the R-TWT SP, it may need to acquire a TXOP only using the EDCAF of AC_VI and AC_VO.

[0230] Meanwhile, EDCAFs of other ACs that do not correspond to the AC designated as a low-latency TID in the R-TWT SP may not participate in contention for TXOP acquisition within the R-TWT SP. That is, the other EDCAFs may be considered to be in an inactive state. When a specific EDCAF does not participate in contention for TXOP acquisition (i.e., in an inactive state), it may perform at least one of the following operations. In this case, the EDCAF's non-participation in contention for TXOP acquisition, which will be described later, may be performed in a TID-R-TWT SP to which a transmission restriction for the TID is applied. In this case, the TID-R-TWT SP may be identified based on at least one of whether the DL / UL TID Bitmap Valid subfield has a value of 1 or whether the Broadcast TWT Recommendation field has a specific value.

[0231] 1) First, in the case of a channel connection procedure using EDCA for an AC that does not correspond to an AC of a TID that is allowed to transmit within an R-TWT SP, the channel state determined by carrier sensing (CS) of the channel is always determined to be occupied within the R-TWT SP, and the backoff counter does not need to be decreased.

[0232] That is, an EDCAF that is not participating in contention for TXOP acquisition within an R-TWT SP can consider the medium to be virtually busy within the R-TWT SP. That is, an EDCAF that is not participating in contention does not need to decrement its backoff counter during the R-TWT SP. In this case, an EDCAF that is not participating in contention for TXOP acquisition within an R-TWT SP can suspend its backoff operation without evaluating the medium status within the R-TWT SP.

[0233] 2) Second, in the channel access procedure by EDCA of an AC that does not correspond to the AC of the TID that is allowed to transmit within the R-TWT SP, the backoff counter can maintain the value of 0 even if it reaches 0.

[0234] That is, an EDCAF that does not participate in the contention for TXOP acquisition within an R-TWT SP can consider the transmission queue of the corresponding AC within the R-TWT SP to be empty, i.e., even if the backoff counter reaches 0 during an R-TWT SP, the EDCAF that does not participate in the contention can maintain the backoff counter at 0 without attempting transmission.

[0235] 3) Third, in the channel access procedure by EDCA for an AC that does not correspond to the AC of the TID allowed for transmission within the R-TWT SP, if the backoff counter reaches 0, a new backoff counter can be selected again and the backoff procedure can be restarted.

[0236] That is, an EDCAF that is not participating in contention for TXOP acquisition within an R-TWT SP may need to invoke a new backoff procedure if the backoff counter within the R-TWT SP reaches 0. That is, an EDCAF that is not participating in contention may initiate a new backoff procedure without attempting transmission once the backoff procedure is completed during the R-TWT SP.

[0237] Here, the above-mentioned operations 1), 2), and 3) are performed by an EDCAF corresponding to each AC. However, for convenience of explanation, in the present invention, an entity performing channel access and backoff procedures may be described as an STA (e.g., a Scheduled STA). That is, it may be expressed that an STA does not transmit an MPDU corresponding to a specific TID, which may mean that, among the EDCAFs of the EDCA operation performed by the STA, the EDCAF of the AC corresponding to the specific TID does not participate in contention for acquiring a TXOP. Here, the TXOP may mean both a transmission opportunity in which a frame exchange sequence can be performed more than once and a channel access opportunity in which a single frame can be transmitted (and a response frame can be received).

[0238] Meanwhile, since each AC in EDCA corresponds to two TIDs, only one of the two TIDs corresponding to a specific AC may be a low-latency TID, and the other TID may not be a low-latency TID. In this case, the specific AC can be considered to be an AC corresponding to the low-latency TID. That is, even though the specific TID is not considered a low-latency TID in the R-TWT SP (is not designated as a low-latency TID by the Scheduling AP), the EDCAF of the corresponding AC can still participate in contention for TXOP acquisition.

[0239] Alternatively, if only one of two TIDs corresponding to a specific AC is a low-latency TID and the other TID is not a low-latency TID, the specific AC may be considered not to be an AC corresponding to the low-latency TID. In this case, the EDCAF corresponding to the specific AC may not participate in contention for TXOP acquisition, and an MPDU for the low-latency TID of the two TIDs corresponding to the specific AC may be transmitted in a TXOP acquired by another EDCAF. In this case, the method for the EDCAF corresponding to the specific AC not to participate in contention for TXOP acquisition may be the same as or similar to the method for the EDCAF of an AC not corresponding to the low-latency TID not to perform channel access, as described above.

[0240] When a Scheduled STA of an R-TWT SP participates in TXOP acquisition contending only with an EDCAF corresponding to a specific TID (e.g., a low-latency TID) according to method 1) and does not participate in TXOP acquisition contending with other EDCAFs, the other EDCAFs may cancel backoff regardless of the medium state (IDLE or BUSY) confirmed by the PHY CS. This may be similar to the operation of considering the medium to be busy only for some of the EDCAFs of the Scheduled STA. Therefore, the Scheduled STA may perform the operation described in 1) above by setting a Network Allocation Vector (NAV) for EDCAFs that do not correspond to the low-latency TID so that the NAV becomes a non-zero value during the R-TWT SP. In this case, the NAV may be a per-EDCAF NAV that is applied to each EDCAF, unlike the NAV used in conventional Wi-Fi. In this case, the per-EDCAF NAV may be a kind of timer applied to each EDCAF. An EDCAF having a non-zero per-EDCAF NAV may need to operate without decrementing its backoff counter, similar to when the medium is virtually busy. In this case, the per-EDCAF NAV may be maintained at a non-zero value only within the R-TWT SP. That is, the per-EDCAF NAV is set at the start of the R-TWT SP as a value taking into account the duration of the R-TWT SP, and the per-EDCAF value may be continuously decreased during the R-TWT SP. However, if the R-TWT SP ends earlier than the scheduled duration, the per-EDCAF NAV may be initialized (i.e., set to 0) upon the end of the R-TWT SP. Conversely, if the R-TWT SP is extended beyond the scheduled duration, the per-EDCAF NAV may also be reset taking into account the extended duration of the R-TWT SP.Alternatively, the R-TWT Scheduled STA may set the per-EDCAF NAV of EDCAFs that do not support low-latency TIDs to a non-zero value when the R-TWT SP starts, and initialize all per-EDCAFs to 0 when the R-TWT SP ends. Alternatively, the R-TWT SP-NAV, which is commonly applied to EDCAFs that do not support low-latency TIDs, may be used instead of the per-EDCAF NAV. When the R-TWT SP-NAV has a non-zero value, the remaining EDCAFs, except for the EDCAFs that correspond to TIDs considered as low-latency TIDs in the R-TWT SP, may not participate in contention for TXOP acquisition.

[0241] The term "commonly applied to EDCAFs not corresponding to the low latency TID" may mean that the timer is commonly applied to all EDCAFs (AC_VO, AC_VI, AC_BE, AC_BK) but ignored by the EDCAF corresponding to the low latency TID. That is, the timer (R-TWT SP-NAV) maintained at a non-zero value during the R-TWT SP may be commonly applied to all EDCAFs and ignored by the EDCAF corresponding to the low latency TID. That is, the EDCAF corresponding to the low latency TID may decrease the backoff counter or start transmission for TXOP acquisition even when the timer is non-zero.

[0242] The R-TWT SP-NAV may be managed in the same / similar manner as the per-EDCAF NAV described above, and therefore a detailed description thereof will be omitted.

[0243] To perform operation 1), the Scheduled STA may set the per-EDCAF NAV of a specific EDCAF when a specific R-TWT SP begins, taking into account the duration of the specific R-TWT SP. In this case, the per-EDCAF NAV may be used in a carrier sense (Virtual CS) mechanism together with a conventional NAV commonly used by EDCAFs. That is, even if the per-EDCAF NAV is 0, if the NAV is a non-zero value, each EDCAF may need to determine the result of the Virtual CS as busy. On the other hand, even if the NAV is 0, if the per-EDCAF NAV of a specific EDCAF is a non-zero value, the specific EDCAF does not need to decrement its backoff counter, as if the result of the Virtual CS was busy.

[0244] When a Scheduled STA of an R-TWT SP participates in contention for TXOP acquisition only with an EDCAF corresponding to a specific TID (e.g., a low-latency TID) in the method b), other EDCAFs may need to invoke a backoff procedure again when the R-TWT SP ends. More specifically, an EDCAF whose backoff counter was kept at 0 during the R-TWT SP by the above operation 2) may need to invoke a new backoff procedure when the R-TWT SP ends. In this case, the operation of invoking the backoff procedure again may mean regenerating the backoff counter.

[0245] The reason why the EDCAF must invoke the backoff procedure at the end of the R-TWT SP is as follows.

[0246] If some EDCAFs do not participate in the contention for TXOP acquisition according to method 2), the some EDCAFs may maintain a backoff counter value of 0 when the R-TWT SP ends. This may be because some EDCAFs considered the transmission queue of their associated AC to be empty and attempted transmission even though the backoff counter was 0, or did not regenerate the backoff counter. In this case, when the R-TWT SP ends, the some EDCAFs (whose backoff counters were maintained at 0) may immediately attempt transmission, as if a frame to be transmitted had been generated in the transmission queue of the AC. That is, two or more EDCAFs may simultaneously attempt transmission when the R-TWT SP ends, and this may also be the case for EDCAFs of other STAs. In this way, multiple EDCAFs may attempt to transmit (acquire TXOP) simultaneously at the end of the R-TWT SP, resulting in a high probability of collisions. To prevent collisions, EDCAFs whose backoff counters were maintained at 0 by operation 2) above may need to generate new backoff counters (invoke a backoff procedure) at the end of the R-TWT SP. In this case, each EDCAF invoking a new backoff procedure at the end of the R-TWT SP invokes the new backoff procedure while maintaining the existing values ​​of the Contention Window (CW[AC]) and QoS STA Retry Counter (QSRC[AC]) of the corresponding AC.

[0247] When a scheduled STA of an R-TWT SP participates in contention for TXOP acquisition only with an EDCAF corresponding to a specific TID (e.g., a low-latency TID) according to method 3), other EDCAFs may need to invoke a new backoff procedure once the backoff procedure in the R-TWT SP is completed. In other words, an EDCAF that does not support a low-latency TID may need to invoke a new backoff procedure without starting transmission for TXOP acquisition when its backoff counter reaches 0 (at the current slot boundary or the next slot boundary). This may be understood as an operation of repeating the backoff procedure of an EDCAF corresponding to another TID in order not to transmit MPDUs for other TIDs that are not considered low-latency TIDs to a specific R-TWT SP. In this case, the EDCAF invoking a new backoff procedure may need to invoke the new backoff procedure without changing the existing CW[AC] and QSRC[AC] of the corresponding AC.

[0248] Meanwhile, the method of not transmitting an EDCAF that does not correspond to a low-latency TID during an R-TWT SP by the above-described operations 1), 2), and 3) may be applied only when queued frames (such as MSDU, A-MSDU, and MMPDU) exist in the transmit (hereinafter, TX) queue of the EDCAF that corresponds to the low-latency TID. That is, even in an R-TWT SP, if the TX queue of the EDCAF that corresponds to the low-latency TID is empty, the inactive state of the EDCAF that does not correspond to the low-latency TID may be canceled (i.e., activated). In this case, if only traffic corresponding to a TID other than the low-latency TID exists in the TX queue of the EDCAF that corresponds to the low-latency TID, the TX queue of the EDCAF that corresponds to the low-latency TID may be considered empty. That is, the TX queue of the EDCAF that corresponds to the low-latency TID being empty may mean one of the following: 1. There are no frames in the TX queue; or 2. There are no frames corresponding to the low-latency TID in the TX queue.

[0249] Alternatively, the method of not transmitting EDCAFs that do not support low-latency TIDs during an R-TWT SP by performing the operations 1), 2), and 3) may be applied until another instruction is received from the AP. More specifically, the AP may perform signaling to release the TXOP acquisition enforcement restriction associated with the low-latency TID during the R-TWT SP. This signaling may be signaling issued when the AP determines that a member STA of the R-TWT SP no longer has traffic corresponding to the low-latency TID. That is, the AP performs signaling to release the TXOP acquisition enforcement restriction associated with the low-latency TID when the AP determines that a member STA of the R-TWT SP no longer has traffic corresponding to the low-latency TID during the R-TWT SP. Upon receiving this signaling, non-AP STAs that are members of the R-TWT SP can change the EDCAFs that do not support low-latency TIDs to an active state (a state in which TXOP acquisition enforcement is possible). In an embodiment described later, the condition for releasing the channel access restriction applied to an EDCAF that does not support a low-latency TID is mainly considered to be when the transmit queue of the EDCAF corresponding to the low-latency TID is changed to empty, but the condition can also be changed to when the AP sends signaling to release the TXOP acquisition enforcement restriction associated with the low-latency TID. That is, in an embodiment described later, the operation performed based on whether the transmit queue of the EDCAF corresponding to the low-latency TID is empty may be appropriately understood as an operation performed based on whether signaling to release the TXOP acquisition enforcement restriction associated with the low-latency TID is received from the AP.

[0250] To explain the above 1) in more detail, the timer applied to an EDCAF that does not support the low latency TID may be applied only when there is a queued frame in the TX queue of the EDCAF that supports the low latency TID. In other words, if the TX queue of the EDCAF that supports the low latency TID is empty, the EDCAF that does not support the low latency TID may also be allowed to decrease the backoff counter or start transmission to acquire a TXOP.

[0251] To explain the above 2) in more detail, the operation of considering the TX queue of an EDCAF that does not support a low latency TID as empty may be applied only when there are queued frames in the TX queue of the EDCAF that supports the low latency TID. In other words, if the TX queue of the EDCAF that supports the low latency TID is empty, the TX queue of the EDCAF that does not support the low latency TID does not need to be considered as empty.

[0252] To explain the above 3) in more detail, the operation of re-invoking the backoff procedure of the EDCAF that does not support the low latency TID may be applied only when there is a queued frame in the TX queue of the EDCAF that supports the low latency TID. In other words, if the TX queue of the EDCAF that supports the low latency TID is empty, the EDCAF that does not support the low latency TID can start transmission to acquire a TXOP when the backoff counter becomes 0 without invoking a new backoff procedure.

[0253] Furthermore, the above-described operations 1), 2), and 3) may be applied to all EDCAFs of STAs that are not members of the R-TWT SP. That is, STAs that are not members of the R-TWT SP do not need to attempt channel access during the R-TWT SP by managing the channel access procedures of all EDCAFs in the same manner as the management method of EDCAFs that do not support low-latency TIDs considered in the above-described operations 1), 2), and 3).

[0254] To explain the operation of a STA that is not a member of an R-TWT SP in more detail in relation to 1), a STA that is not a member of an R-TWT SP can manage the backoff procedure of each EDCAF using a timer that is commonly applied to all EDCAFs. In this case, the timer is maintained at a non-zero value during the R-TWT SP, and while the timer is non-zero, each EDCAF considers the channel state to be busy and freezes the backoff procedure. In this way, a STA that is not a member of an R-TWT SP does not need to attempt channel access (TXOP acquisition) during the R-TWT SP.

[0255] To explain the operation of a STA that is not a member of an R-TWT SP in more detail in relation to 2), a STA that is not a member of an R-TWT SP can consider the TX queues of all EDCAFs as empty. In this case, the time period during which a STA that is not a member of an R-TWT SP considers the TX queues as empty may be the R-TWT SP of which it is not a member. In this case, a STA that is not a member of an R-TWT SP can invoke a new backoff procedure for each EDCAF whose backoff counter is 0 when an R-TWT SP of which it is not a member ends. In this way, a STA that is not a member of an R-TWT SP does not need to attempt channel access (TXOP acquisition) during the R-TWT SP.

[0256] To explain in detail the operation of a STA that is not a member of an R-TWT SP in relation to 3), a STA that is not a member of an R-TWT SP can invoke a new backoff procedure when the backoff procedure of each EDCAF is completed. In this case, the condition for a STA that is not a member of an R-TWT SP to newly invoke the backoff procedure of each EDCAF may be that the point at which the backoff procedure of each EDCAF is completed corresponds to an R-TWT SP of which it is not a member. In this way, a STA that is not a member of an R-TWT SP does not need to attempt channel access (TXOP acquisition) during an R-TWT SP.

[0257] That is, all EDCAFs of STAs that are not members of the R-TWT SP may be deactivated during the R-TWT SP (no attempt to acquire a TXOP) by methods such as 1), 2), and 3) described above. This may be understood as the STAs that are not members of the R-TWT SP considering all EDCAFs as EDCAFs that do not support low-latency TIDs, regardless of the type of TID specified / promised as a low-latency TID in the R-TWT SP. In this case, the method by which STAs that are not members of the R-TWT SP manage each EDCAF is the same / similar to the above-described method of managing EDCAFs that do not support low-latency TIDs, and detailed description thereof will be omitted.

[0258] FIG. 20 illustrates an example of an Enhanced Distributed Channel Access (EDCA) operation for channel access in a restricted TWT SP according to an embodiment of the present invention.

[0259] Referring to FIG. 20 , after the Beacon frame transmitted by the AP, an R-TWT SP begins, which considers TID4 to TID7 as low-latency TIDs. The R-TWT SP considers TID4 to TID7 as low-latency TIDs, and is an R-TWT SP in which transmission of MPDUs corresponding to TIDs other than the low-latency TIDs is restricted. A non-AP STA, which is a scheduled STA of the R-TWT SP, can stop contending for TXOP acquisition from EDCAFs other than the EDCAF corresponding to the low-latency TID in order to not transmit MPDUs other than the low-latency TIDs within the R-TWT SP. That is, a scheduled STA of the R-TWT SP attempts channel access only through the EDCAF of the AC corresponding to the low-latency TID within the R-TWT SP period. In this case, the operation shown in one embodiment of FIG. 20 is a method of not participating in contention for TXOP acquisition using the above-described method 1).

[0260] As shown in FIG. 20, a non-AP STA can decrement only the backoff counter of the EDCAF corresponding to the low-latency TID within the R-TWT SP. More precisely, among the EDCAFs of the non-AP STA, only the EDCAF corresponding to the low-latency TID can decrement the backoff counter at the slot boundary. In other words, among the EDCAFs of the non-AP STA, the EDCAFs of AC_BK and AC_BE corresponding to TID0 to TID3 may need to perform an operation (decision) to maintain the backoff counter without decrementing it at each slot boundary within the R-TWT SP, regardless of whether the slot is idle or busy.

[0261] A non-AP STA that is a scheduled STA of an R-TWT SP can stop contending for TXOP acquisition from EDCAFs other than the EDCAF corresponding to the low latency TID in order to not transmit other MPDUs that are not low latency TIDs within the R-TWT SP. That is, a scheduled STA of an R-TWT SP attempts channel access only through the EDCAF of an AC corresponding to the low latency TID within the R-TWT SP. In this case, the operation shown in one embodiment of FIG. 20 is a method of not participating in contending for TXOP acquisition using the above-mentioned method 1).

[0262] A non-AP STA can decrement only the backoff counter of the EDCAF corresponding to the low-latency TID within the R-TWT SP. More precisely, among the EDCAFs of the non-AP STA, only the EDCAF corresponding to the low-latency TID can decrement the backoff counter at the slot boundary. In other words, among the EDCAFs of the non-AP STA, the EDCAFs of AC_BK and AC_BE corresponding to TID0 to TID3 may need to perform an operation (decision) at each slot boundary within the R-TWT SP to maintain the backoff counter without decrementing it, regardless of whether the slot is idle or busy.

[0263] Also, although not shown in Figure 20, non-AP STAs that are not members of the R-TWT SP keep all EDCAFs in an inactive state during the R-TWT SP, i.e., non-AP STAs that are not members of the R-TWT SP do not attempt to acquire a TXOP during the R-TWT SP by not decrementing the backoff counter of each EDCAF, by considering the transmission queues of all EDCAFs as empty, or by invoking a new backoff procedure when the backoff procedure of each EDCAF is completed.

[0264] FIG. 21 illustrates an example of a method for transmitting traffic for TIDs for which transmission is permitted and for which transmission is restricted in a restricted TWT SP according to an embodiment of the present invention.

[0265] 21, after the Beacon frame transmitted by the AP, an R-TWT SP begins in which TID4 to TID7 are considered as low-latency TIDs. That is, within the R-TWT SP, AC_VI and AC_VO are EDCAFs corresponding to low-latency TIDs, while AC_BE and AC_BK are EDCAFs not corresponding to low-latency TIDs. Therefore, among the EDCAFs of non-AP STAs that are Scheduled STAs of the R-TWT SP, AC_VO and AC_VI, which are EDCAFs corresponding to low-latency TIDs, are in an active state, while AC_BE and AC_BK are in an inactive state.

[0266] A non-AP STA, which is a scheduled STA of the R-TWT SP, acquires a TXOP using AC_VO, a low-latency EDCAF, and transmits frames with TID6 and TID7 corresponding to AC_VO and frames with TID4 and TID5 corresponding to AC_VI in PPDU#1.

[0267] After transmitting PPDU#1, the non-AP STA has no more queued frames in its AC_VI and AC_VO transmission queues.

[0268] In this case, since the transmission queues of all EDCAFs corresponding to the TIDs designated / promised as low latency TIDs in the R-TWT SP become empty, the remaining EDCAFs that do not correspond to low latency TIDs, i.e., AC_BK and AC_BE, are converted to the active state.

[0269] The non-AP STA acquires a TXOP through AC_BE (i.e., AC_BE becomes the TXOP holder) and transmits a frame (MSDU, A-MSDU, etc.) corresponding to TID0 or TID3 through PPDU#2.

[0270] Also, although not shown in FIG. 21, non-AP STAs that are not members of the R-TWT SP maintain all EDCAs in an inactive state within the R-TWT SP. That is, non-AP STAs that are not members of the R-TWT SP do not reduce the backoff counter of each EDCA within the R-TWT SP, consider the transmission queues of all EDCAs as empty, or attempt to acquire a TXOP by calling a new backoff procedure when the backoff procedure of each EDCA is completed.

[0271] <Channel Access Management Method Considering TID-to-Link Mapping> TID-to-Link mapping means a mechanism that enables determination of which TID is to be transmitted / received over which link between two MLDs that have established a multi-link setup. TID-to-Link mapping may be determined separately for the DL and UL directions. When TID-to-Link mapping negotiation is performed between an AP MLD and a STA MLD, the AP MLD and the STA MLD may need to determine the transmission link considering the TID of the frame they are transmitting. As an example, the AP MLD and the (non-AP) STA MLD may perform a multi-link setup over two links and negotiate to map TID0 to TID3 to Link1 and TID4 to TID7 to Link2 for the DL direction. In this case, when the AP MLD transmits DL traffic to the STA MLD, traffic (such as MSDU, MPDU, etc.) corresponding to TID0 to TID3 must be transmitted only over Link1, and traffic corresponding to TID4 to TID8 must be transmitted only over Link2.

[0272] Similarly, non-AP STA MLD may also need to transmit UL traffic taking into account TID-to-Link mapping negotiation in the UL direction. For example, AP MLD and (non-AP) STA MLD may perform multilink setup with two links and negotiate to map TID0 to TID3 to Link1 and TID4 to TID7 to Link2 in the UL direction. In this case, when non-AP STA MLD transmits UL traffic to AP MLD, it must transmit traffic (MSDU, MPDU, etc.) corresponding to TID0 to TID3 only on Link1, and traffic corresponding to TID4 to TID8 only on Link2.

[0273] In this way, when two MLDs that have performed multi-link setup negotiate a TID-to-link mapping (a mapping other than the default TID-to-link mapping mode), both MLDs may need to transmit traffic of a specific TID only on a specific link in consideration of the TID-to-link mapping. That is, they should not attempt to transmit traffic for the specific TID on a link where the specific TID is not mapped in the transmission direction.

[0274] Therefore, when a non-AP STA MLD transmits traffic of a specific TID to an AP MLD, it should not attempt to transmit traffic corresponding to the specific TID on a link to which the specific TID is not mapped. In this case, the non-AP STA MLD does not need to perform channel access through the EDCAF corresponding to the specific TID for a non-AP STA operating on a link to which the specific TID is not mapped in the UL direction. In other words, when a specific TID is not mapped in the UL direction to a specific link, the non-AP MLD does not need to participate in contention for TXOP acquisition with some of the EDCAFs of STAs operating on the specific link.

[0275] If a specific link of a non-AP STA MLD is in the disabled state (no TID is mapped), the STA of the non-AP STA MLD operating on the specific link shall not perform channel access by any EDCAF. That is, it may be understood that all EDCAFs of the STA of the non-AP STA MLD operating on a Disabled link (no TID is mapped) are in an inactive state. At this time, the EDCAF deactivated by the TID-to-Link mapping state may have a state similar to the EDCAF deactivated within the R-TWT SP (see FIG. 20). That is, the EDCAF deactivated by the TID-to-Link mapping state does not need to participate in the contention for TXOP acquisition using the operations 1), 2), and 3) described above. However, the EDCAF deactivated by the TID-to-Link mapping state does not perform operations considering the duration of the R-TWT SP and can continue to maintain the inactive state until the TID-to-Link mapping is changed.

[0276] Another difference is that the EDCAF deactivated in relation to the R-TWT SP is activated when the R-TWT SP ends, while the EDCAF deactivated by the TID-to-Link mapping state may be activated when the TID-to-Link mapping is changed to the default mode, or when the TID-to-Link mapping negotiation for mapping the TID corresponding to the inactive EDCAF to the link (for the UL direction) is performed.

[0277] <Step-by-step operation method of R-TWT SP> According to an embodiment of the present invention described above, the AP can set two types of R-TWT SPs. One of the two types of R-TWT SPs may be a more strict SP that allows only the transmission of low-latency TIDs, and the other may be a flexible SP that allows the transmission of other TIDs when there are no low-latency TIDs.

[0278] The reason why two types of R-TWT SPs are considered in the present invention is to enable selection between a method of strengthening priority for low-latency TIDs and a more efficient use of the time interval corresponding to the R-TWT SP. The characteristics of the two types of R-TWT SPs are as follows.

[0279] 1) When only traffic of a low latency TID can be transmitted within an R-TWT SP, only a portion of the time interval in the R-TWT SP may be utilized for the service of the low latency TID, and the remaining time interval may be wasted.

[0280] 2) When traffic transmission of other TIDs is allowed within the R-TWT SP, transmission of other STAs with low latency TIDs may be delayed while traffic of other TIDs is being served.

[0281] Therefore, APs and non-APs may wish to operate R-TWT SPs in different ways depending on their purposes, and as considered in the present invention, they can selectively operate / join as members of one of two types of R-TWT SPs.

[0282] However, if the availability of traffic for TIDs other than the low latency TID is determined on an R-TWT SP basis, a time period may be continuously wasted for a particular R-TWT SP, and the processing of low latency TID traffic for other R-TWT SPs may be delayed.

[0283] To solve this problem, according to one embodiment of the present invention, it is possible to divide the intervals of a single R-TWT SP and operate them according to different policies. More specifically, only traffic of a low latency TID may be transmitted in a portion of the time interval of a single R-TWT SP, and traffic of other TIDs other than the low latency TID may be transmitted in the remaining interval. However, since the remaining interval is also a time interval within the R-TWT SP, traffic transmission of the low latency TID is still prioritized, and traffic transmission of other TIDs is only permitted when there is no traffic of the low latency TID.

[0284] In this case, the time intervals to which different operation policies are applied may be determined by a partial ratio and a remaining ratio of the R-TWT SP duration. For example, the R-TWT SP corresponding to the first half of the R-TWT SP duration may be an interval in which only low latency TID transmission is permitted, and the R-TWT SP corresponding to the remaining half may be an interval in which other TID transmission is permitted. In this case, information related to the time intervals to which different policies are applied for the R-TWT SP duration may be information that the AP indicates in the TWT element when indicating the R-TWT SP. In this case, if the AP does not indicate information related to the time intervals to which different policies are applied for the R-TWT SP duration, the already-committed time interval (ratio) of the R-TWT SP may be determined as the time interval in which only low latency TID transmission is permitted. In other words, the time interval of the R-TWT SP corresponding to the already-committed ratio between the AP and the non-AP STA may be determined as the time interval in which only low latency TID transmission is permitted. In this case, the remaining time interval may be a time interval during which traffic of a TID other than the low latency TID can be transmitted when there is no low latency TID. In this case, the non-AP STA must transmit only traffic corresponding to the low latency TID during the time interval during which only the low latency TID can be transmitted among the R-TWT SPs, and can transmit traffic of other TIDs other than the low latency TID during the remaining time interval.

[0285] Alternatively, the rule for changing the operation policy (method) within the R-TWT SP (a method for transmitting only frames with a low latency TID, while restrictively allowing transmission of frames with other TIDs other than the low latency TID) may be determined based on whether a specific time has elapsed since the start of the R-TWT SP. More specifically, after the start of the R-TWT SP, only transmission of frames with a low latency TID may be allowed until the already-committed time has elapsed, and after the already-committed time has elapsed, transmission of frames with other TIDs other than the low latency TID may be allowed. For example, the time interval corresponding to the first TU of the R-TWT SP may be an interval in which only frames with a low latency TID may be transmitted, and the remaining time interval may be an interval in which transmission of frames with other TIDs other than the low latency TID is allowed.

[0286] As another method, the rule for changing the operation policy (method) within the R-TWT SP may be determined based on whether the R-TWT SP overlaps with a specific other time interval. More specifically, the time interval of the R-TWT SP that overlaps with a quiet interval (duration) set for protecting the R-TWT SP may be a period in which only frames with a low latency TID are allowed to be transmitted. In this case, the remaining R-TWT SP periods that do not overlap with the quiet interval may be a period in which frames with TIDs other than the low latency TID are allowed to be transmitted. In this case, the time interval that is also set to specify the period in which the operation method of the R-TWT SP is changed may be a time interval other than the quiet interval. In this case, the other time interval may be a time interval that is set to start at the same time as the start time of the R-TWT SP. In this case, the other time interval may be set by the AP to specify the time point at which the operation method of the R-TWT SP is changed.

[0287] Alternatively, the operation method within the R-TWT SP may be changed by an explicit instruction from the AP. More specifically, the AP may perform signaling to change the operation method during the R-TWT SP. In this case, the signaling may be performed in a specific frame that has already been agreed upon, or in the A-Control (indicated in the HT Control field of the MAC header) or the More Data subfield (a bit included in the Frame Control field of the MAC header). In this case, the signaling may be performed in a frame (group addressed, broadcast) that is not an individually addressed frame.

[0288] For example, the AP may transmit a previously committed frame (e.g., a CF-END frame) during the R-TWT SP interval to allow frame transmission of a TID other than the low latency TID. If a non-AP STA receives a previously committed frame from the AP during the R-TWT SP interval in which only frames of a low latency TID can be transmitted, the non-AP STA may recognize that the operation method for the remaining R-TWT SP interval has been changed to one that allows frame transmission of a TID other than the low latency TID.

[0289] As another example, an AP can set the More Data subfield of a non-individually addressed frame (group addressed frame) to 0 to allow transmission of frames with TIDs other than the low-latency TID during the R-TWT SP period. In other words, the More Data subfield transmitted by the AP during the R-TWT SP period does not indicate whether the AP has group addressed bufferable units (BUs), but may be used to indicate a change in the R-TWT SP operation method. A non-AP STA that confirms that the More Data subfield of a group addressed frame received from the AP during an R-TWT SP period in which only frames with low-latency TIDs can be transmitted has been set to a specific value (e.g., 0) can recognize that the operation method for the remaining R-TWT SP period has been changed to allow transmission of frames with TIDs other than the low-latency TID. In this case, a method for distinguishing whether a frame received from the AP is a group addressed frame may be determined by whether the receiver addressed (RA) in the MAC header of the received frame includes a group address. In this way, when the More Data subfield is used to indicate the operation method of the R-TWT SP, the value indicated in the More Data subfield may be changed while an R-TWT SP that allows frame transmission of other TIDs other than the low latency TID is in progress, thereby changing the R-TWT SP to one that only allows frame transmission of low latency TIDs. That is, when the More Data subfield value of the group addressed frame transmitted by the AP is a specific value, only frame transmission of low latency TIDs is allowed in the R-TWT SP, and when the More Data subfield value is another value, frame transmission of other TIDs other than the low latency TID may be allowed in the R-TWT SP.

[0290] FIG. 22 illustrates an example of a method in which different operation policies are applied to different sections in a single-restricted TWT SP according to an embodiment of the present invention.

[0291] Referring to FIG. 22, after the Beacon frame transmitted by the AP, the R-TWT SP begins, which considers TID4 to TID7 as low-latency TIDs.

[0292] Among the time intervals corresponding to the R-TWT SP, the previous time interval (the Low latency TID only interval in FIG. 22) is an interval in which only transmission of the low latency TID is permitted, and the remaining time interval (the Low latency TID first interval in FIG. 22) is an interval in which transmission of traffic of other TIDs is permitted when there is no more traffic corresponding to the low latency TID.

[0293] Therefore, when a non-AP STA that is a member of an R-TWT SP transmits Multi-TID A-MPDU#1 in the previous time interval of the R-TWT SP, it transmits only MPDUs with TID4 to TID7, which are low-latency TIDs of the R-TWT SP.

[0294] Since there are no more frames of TID4 to TID7 in Multi-TID A-MPDU#2, which the Non-AP STA transmits after the end of the previous time interval, the Non-AP STA aggregates and transmits TID0 to TID3 MPDUs.

[0295] FIG. 23 is a flowchart illustrating an example of the operation of a terminal according to an embodiment of the present invention.

[0296] Referring to Figure 23, when an AP STA sets an interval in which only specific frames can be transmitted, a non-AP STA receives information related to the TID for traffic that can be transmitted in the set interval from the AP STA, and can transmit traffic corresponding to the TID in the set interval based on the received information.

[0297] Specifically, the non-AP STA receives a trigger frame from the AP-STA to trigger the transmission of a PPDU (S23010). At this time, the trigger frame includes information indicating at least one TID (Traffic Identifier) ​​that is permitted to be transmitted in a TWT period, and the TWT period may refer to a period in which transmission of traffic for the at least one TID having a specific transmission condition is permitted and transmission of traffic that does not have the specific transmission condition is restricted.

[0298] Specifically, as described with reference to FIGS. 15 to 22, the AP may configure the R-TWT SP so that transmission of traffic that satisfies certain conditions is permitted and transmission of traffic that does not satisfy the certain conditions is restricted. In this case, whether or not the certain conditions are satisfied is determined by the AP transmitting information related to the TID corresponding to the traffic (e.g., information indicating the TID corresponding to the traffic that satisfies the certain conditions), and the non-AP STA can transmit and receive traffic corresponding to the TID transmitted from the AP within the TWT SP. In this case, the certain conditions may be conditions related to the transmission delay of the traffic (e.g., low-latency traffic), and transmission of traffic that does not satisfy the certain conditions may be restricted. Restriction of transmission may mean that transmission is not possible within the R-TWT SP, transmission is possible under certain constraints (e.g., combined with an MPDU of traffic corresponding to a TID that satisfies certain conditions and transmitted, or combined with an MPDU of traffic corresponding to a TID that satisfies certain conditions and transmitted within a certain interval set in the TWT SP), or channel access using the EDCAF of an AC corresponding to a TID not specified by the AP is restricted.

[0299] Alternatively, the configured R-TWT SP may be reconfigured with multiple intervals, and in at least one specific interval, only traffic for TIDs corresponding to traffic having a specific condition may be transmitted, and in the remaining intervals except for the at least one specific interval, traffic for TIDs corresponding to traffic not having the specific condition may be allowed to be transmitted under limited conditions (or specific constraints). For example, if the R-TWT SP is configured with a first interval and a second interval, in the first interval, only traffic for TIDs corresponding to traffic having a specific condition (e.g., low latency) may be transmitted, and in the second interval, traffic for TIDs corresponding to traffic not having the specific condition may be allowed to be transmitted under limited conditions (or specific constraints).

[0300] Information related to the TID may be transmitted in a bitmap format, with each bit indicating a specific TID, in a trigger frame or in a user information field containing information about each terminal in the trigger frame.

[0301] For example, when a restricted TWT SP (hereinafter referred to as R-TWT SP) that can transmit only low-latency traffic is configured, each STA may be allowed to transmit only low-latency traffic within the R-TWT SP, and the transmission of traffic other than low-latency traffic may be restricted. In this case, the type of traffic that a STA can transmit within a specific R-TWT SP may be restricted to traffic corresponding to a TID specified by the AP. That is, during the process of setting up an R-TWT SP, the AP may set the TID of traffic that can be transmitted within the R-TWT SP and notify the STA of the set TID. In this case, a non-AP STA may transmit only traffic corresponding to a TID specified by the AP within the R-TWT SP, and the transmission of traffic corresponding to a TID not specified by the AP may be restricted.

[0302] Thereafter, the non-AP STA can transmit a PPDU (Physical Layer Protocol Data Unit) including traffic corresponding to at least one TID to the AP within the TWT period (S23020).

[0303] In this case, the trigger frame may be transmitted within the TWT interval.

[0304] The above description of the present invention is for illustrative purposes only, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. Therefore, the above-described embodiments should be understood as illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed form, and similarly, each component described as a distributed type may be implemented in a combined form.

[0305] The scope of the present invention is indicated by the claims set forth below rather than by the above detailed description, and all modifications and variations that fall within the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims

1. A wireless communication terminal of a wireless communication system, a transceiver; and a processor; The processor: Receive a trigger frame from an AP (Access Point) that triggers the transmission of a PPDU; The trigger frame includes information indicating at least one TID (Traffic Identifier) ​​that is allowed to be transmitted during a TWT (Target Wake Time) period; The TWT interval represents an interval in which transmission of traffic for the at least one TID having a specific transmission condition is permitted and transmission of traffic not having the specific transmission condition is restricted; A wireless communication terminal transmits a physical layer protocol data unit (PPDU) including traffic corresponding to the at least one TID to the AP during the TWT interval.

2. The wireless communication terminal according to claim 1 , wherein the trigger frame is transmitted within the TWT interval.

3. 2. The wireless communication terminal of claim 1, wherein an MPDU (MAC (Medium Access Control) protocol data unit) including traffic corresponding to TIDs other than the at least one TID is combined with an MPDU of the PPDU including the traffic corresponding to the at least one TID and transmitted in the form of an A (Aggregated)-MPDU.

4. The wireless communication terminal according to claim 1, wherein traffic for a TID corresponding to an access category of the at least one TID is allowed to be transmitted within the TWT interval.

5. The TWT section includes a first section and a second section, the first section is a section in which only transmission of the traffic corresponding to the at least one TID is permitted; The wireless communication terminal according to claim 1 , wherein the second interval is an interval in which transmission of traffic corresponding to a TID other than the at least one TID is permitted.

6. The wireless communication terminal according to claim 1 , wherein the specific transmission condition is a condition related to a traffic transmission delay.

7. The wireless communication terminal according to claim 1, wherein, in the TWT interval, a channel access procedure by Enhanced Distributed Channel Access (EDCA) for ACs other than the AC corresponding to the at least one TID is restricted.

8. The wireless communication terminal according to claim 7, wherein a back-off counter of the channel access procedure by the EDCA for the other AC is not decreased during the TWT interval.

9. The wireless communication terminal according to claim 7, wherein a channel state for the channel access procedure by the EDCA for the other AC during the TWT interval is in a busy state until the TWT interval ends.

10. 1. A method of traffic transmission performed by a terminal in a wireless communication system, the method comprising: Receive a trigger frame from an AP (Access Point) that triggers the transmission of a PPDU; The trigger frame includes information indicating at least one TID (Traffic Identifier) ​​that is allowed to be transmitted during a TWT (Target Wake Time) period; The TWT interval represents an interval in which transmission of traffic for the at least one TID having a specific transmission condition is permitted and transmission of traffic not having the specific transmission condition is restricted; A wireless communication method for transmitting a physical layer protocol data unit (PPDU) including traffic corresponding to the at least one TID to the AP within the TWT interval.

11. The wireless communication method according to claim 10 , wherein the trigger frame is transmitted within the TWT interval.

12. 11. The wireless communication method of claim 10, wherein an MPDU (MAC (Medium Access Control) protocol data unit) including traffic corresponding to TIDs other than the at least one TID is combined with an MPDU of the PPDU including the traffic corresponding to the at least one TID and transmitted in the form of an A (Aggregated)-MPDU.

13. The wireless communication method of claim 10, wherein traffic for a TID corresponding to an access category of the at least one TID is allowed to be transmitted within the TWT interval.

14. The TWT section includes a first section and a second section, the first section is a section in which only transmission of the traffic corresponding to the at least one TID is permitted; The wireless communication method according to claim 10 , wherein the second time period is a time period during which transmission of traffic corresponding to TIDs other than the at least one TID is permitted.

15. The wireless communication method according to claim 10 , wherein the specific transmission condition is a condition related to a transmission delay of traffic.

16. The wireless communication method according to claim 10, wherein, in the TWT interval, a channel access procedure by Enhanced Distributed Channel Access (EDCA) for ACs other than the AC corresponding to the at least one TID is restricted.

17. The wireless communication method of claim 16, wherein a backoff counter of the channel access procedure by the EDCA for the other AC is not decreased within the TWT interval.

18. The wireless communication method of claim 16, wherein a channel state for the channel access procedure by the EDCA for the other AC during the TWT interval is in a busy state until the TWT interval ends.

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