Low-latency wireless communication method, and wireless communication terminal using same

Abstract

A station that is not a TXOP holder is disclosed. The station comprises a transmission / reception unit and a processor. The processor receives an initial control frame for starting frame exchange, does not transmit a response frame to the initial control frame if a predetermined condition is satisfied, and transmits the response frame if the predetermined condition is not satisfied.

Description

Low-latency wireless communication method and wireless communication terminal using the same

[0001] The present invention relates to a wireless communication method supporting low-latency communication and a wireless communication terminal using the same.

[0002] With the recent proliferation of mobile devices, wireless LAN (WLAN) technology, which can provide them with fast wireless Internet service, is attracting significant attention. WLAN technology utilizes short-range wireless communication technology to enable mobile devices such as smartphones, tablets, laptops, portable multimedia players, and embedded devices to wirelessly connect to the Internet at home, in businesses, or in specific service areas.

[0003] Since supporting the initial wireless LAN technology using the 2.4 GHz frequency, IEEE (Institute of Electrical and Electronics Engineers) 802.11 has been commercializing or developing various technology standards. First, IEEE 802.11b supports a communication speed of up to 11 Mbps while using the 2.4 GHz band. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses the 5 GHz band instead of the 2.4 GHz band, thereby reducing the impact of interference compared to the considerably crowded 2.4 GHz band. It also uses OFDM (orthogonal frequency division multiplexing) technology to increase the communication speed to up to 54 Mbps. However, IEEE 802.11a has the disadvantage of a shorter communication range than IEEE 802.11b. And IEEE 802.11g, like IEEE 802.11b, uses the 2.4GHz band to achieve a communication speed of up to 54Mbps and satisfies backward compatibility, which has garnered considerable attention. It is also superior to IEEE 802.11a in terms of communication distance.

[0004] And to overcome the limitations of communication speed, which has been pointed out as a vulnerability in wireless LAN, there is IEEE 802.11n, a technical standard established. IEEE 802.11n aims to increase the speed and reliability of networks and extend the operating range of wireless networks. More specifically, IEEE 802.11n supports High Throughput (HT) with data processing speeds of up to 540 Mbps or more, and is based on MIMO (Multiple Inputs and Multiple Outputs) technology that uses multiple antennas at both the transmitter and receiver to minimize transmission errors and optimize data rates. In addition, this standard can use a coding method that transmits multiple redundant copies to increase data reliability.

[0005] As wireless LAN becomes more widespread and applications diversify, the need for new wireless LAN systems that support very high throughput (VHT) higher than the data processing speed supported by IEEE 802.11n has arisen. Among these, IEEE 802.11ac supports a wide bandwidth (80MHz to 160MHz) at the 5GHz frequency. Although the IEEE 802.11ac standard is defined only for the 5GHz band, early 11ac chipsets will also support operation in the 2.4GHz band to ensure backward compatibility with existing 2.4GHz band products. Theoretically, according to this specification, multi-station wireless LAN speeds can reach at least 1Gbps and a maximum single-link speed of at least 500Mbps. This is achieved by extending the wireless interface concepts accepted in 802.11n, such as wider radio frequency bandwidth (up to 160 MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high-density modulation (up to 256 QAM). In addition, there is IEEE 802.11ad, which transmits data using the 60 GHz band instead of the existing 2.4 GHz / 5 GHz. IEEE 802.11ad is a transmission standard that provides speeds of up to 7 Gbps using beamforming technology, making it suitable for streaming high-bitrate video such as large amounts of data or uncompressed HD video. However, the 60 GHz frequency band has a disadvantage in that it has difficulty passing through obstacles, so it can only be used between devices in short distances.

[0006] Meanwhile, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard, which follows 802.11ac and 802.11ad as a wireless LAN standard, is nearing completion to provide high-efficiency and high-performance wireless LAN communication technology in high-density environments with densely packed APs and terminals. In an 802.11ax-based wireless LAN environment, high-frequency efficient communication must be provided indoors and outdoors in the presence of high-density stations and APs (Access Points), and various technologies have been developed to achieve this.

[0007] Additionally, development of new wireless LAN standards has begun to increase maximum transmission speeds to support emerging multimedia applications such as high-definition video and real-time gaming. The 7th generation wireless LAN standard, IEEE 802.11be (Extremely High Throughput, EHT), is currently under development with the goal of supporting transmission rates of up to 30 Gbps in the 2.4 / 5 / 6 GHz bands through wider bandwidth, increased spatial streams, and multi-AP cooperation.

[0008] Recently, discussions have begun on Ultra High Reliability (UHR) wireless LAN communication technology, a successor to the 802.11be standard, to overcome reliability issues that have been identified as limitations of wireless LAN. The UHR standard is currently under development with the goal of supporting low latency and low jitter in wireless LAN traffic with a high probability (e.g., greater than 99.9999%).

[0009] An embodiment of the present invention aims to provide a wireless communication method supporting low-latency communication and a wireless communication terminal using the same.

[0010] A station that is not a TXOP holder according to one embodiment of the present invention includes a transceiver; and a processor. The processor receives an initial control frame for initiating frame exchange, and if a predefined condition is satisfied, does not transmit a response frame for the initial control frame, and if the predefined condition is not satisfied, transmits the response frame.

[0011] The above-mentioned pre-specified conditions may include cases where the restricted-target wake time (R-TWT) scheduled by the access point (AP) of the basic service set (BSS) to which the station belongs through a beacon frame and the frame exchange initiated by the initial control frame overlap.

[0012] The above R-TWT may be an R-TWT scheduled by an AP of an OBSS (overlapping BSS).

[0013] When receiving the initial control frame from the AP, the processor can transmit the response frame.

[0014] The above initial control frame can initiate the exchange of traffic corresponding to the TID allowed in transmission in the SP (service period) of the R-TWT.

[0015] The above station is a station affiliated to a multi-link device, and the predefined condition may include a case where the station operates on one of a non-simultaneous transmit and receive (NSTR) link pair, and when the station receives the initial control frame, it performs frame exchange on another link of the NSTR link pair.

[0016] The above station is a station affiliated to a multi-link device, and the predefined condition may include that the station operates in an enhanced multi-link singlie radio (EMLSR) mode, receives the initial control frame on a first link, and performs frame exchange on a second link on which the multi-link device operates.

[0017] The above station is a station affiliated to a multi-link device, and when receiving the initial control frame on a first link and attempting to transmit low-latency traffic on a second link, the predefined condition may include that the low-latency traffic is not mapped to the first link.

[0018] An operating method of a station other than a TXOP holder according to an embodiment of the present invention may include: receiving an initial control frame for initiating frame exchange; not transmitting a response frame to the initial control frame if a pre-specified condition is satisfied; and transmitting the response frame if the pre-specified condition is not satisfied.

[0019] The above-mentioned pre-specified conditions may include cases where the restricted-target wake time (R-TWT) scheduled by the access point (AP) of the basic service set (BSS) to which the station belongs through a beacon frame and the frame exchange initiated by the initial control frame overlap.

[0020] The above R-TWT may be an R-TWT scheduled by an AP of an OBSS (overlapping BSS).

[0021] If the above pre-specified condition is not satisfied, the step of transmitting the response frame may include a step of the processor transmitting the response frame when receiving the initial control frame from the AP.

[0022] The above initial control frame can initiate the exchange of traffic corresponding to the TID allowed in transmission in the SP (service period) of the R-TWT.

[0023] The above station is a station affiliated to a multi-link device, and the predefined condition may include a case where the station operates on one of a non-simultaneous transmit and receive (NSTR) link pair, and when the station receives the initial control frame, it performs frame exchange on another link of the NSTR link pair.

[0024] The above station is a station affiliated to a multi-link device, and the predefined condition may include that the station operates in an enhanced multi-link singlie radio (EMLSR) mode, receives the initial control frame on a first link, and performs frame exchange on a second link on which the multi-link device operates.

[0025] The above station is a station affiliated to a multi-link device, and when receiving the initial control frame on a first link and attempting to transmit low-latency traffic on a second link, the predefined condition may include that the low-latency traffic is not mapped to the first link.

[0026] How it works.

[0027] One embodiment of the present invention provides a wireless communication method that efficiently supports low-latency communication and a wireless communication terminal using the same.

[0028] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0029] Figure 2 illustrates a wireless LAN system according to another embodiment of the present invention.

[0030] Figure 3 shows the configuration of a station according to one embodiment of the present invention.

[0031] Figure 4 shows the configuration of an access point according to one embodiment of the present invention.

[0032] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0033] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0034] FIG. 7 shows various standard generation-specific physical layer protocol data unit (PPDU) formats according to an embodiment of the present invention.

[0035] Figure 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0036] FIG. 9 shows a transmission / TXOP protection method using an RTS frame and a CTS frame according to an embodiment of the present invention.

[0037] FIG. 10 shows a transmission / TXOP protection method using an MU-RTS frame and a CTS frame according to an embodiment of the present invention.

[0038] FIG. 11 shows that a station according to an embodiment of the present invention sets a NAV through an RTS frame / CTS frame exchange, which delays transmission of a low-latency traffic PPDU.

[0039] FIG. 12 shows an operation in which a station according to an embodiment of the present invention does not transmit a response frame to an initial control frame.

[0040] FIG. 13 illustrates an operation of a station according to an embodiment of the present invention to indicate the type of traffic to be exchanged in a frame exchange sequence initiated by an initial control frame.

[0041] FIG. 14 illustrates an operation of a non-AP station, which is a TXOP responder, transmitting a low-latency traffic PPDU through preemption according to an embodiment of the present invention.

[0042] FIG. 15 shows an operation in which an AP, which is a TXOP responder, transmits a low-latency traffic PPDU through preemption according to an embodiment of the present invention.

[0043] FIG. 16 illustrates an operation in which an AP, which is a TXOP responder, transmits low-latency traffic PPDUs to multiple stations through preemption according to an embodiment of the present invention.

[0044] FIG. 17 shows the format of a Control field of a MAC header including information about low-latency traffic according to an embodiment of the present invention.

[0045] FIG. 18 shows a station transmitting a response frame to an initial control frame based on an R-TWT SP according to an embodiment of the present invention.

[0046] FIG. 19 shows a station according to an embodiment of the present invention determining whether to transmit a response frame to an initial control frame based on a Co-RTWT SP.

[0047] The terms used in this specification have been selected from widely used and current terms, taking into account the functions of the present invention. However, these terms may vary depending on the intentions of those skilled in the art, customs, or the emergence of new technologies. Furthermore, in certain cases, the applicant may arbitrarily select terms, in which case their meanings will be described in the description of the relevant invention. Therefore, it should be noted that the terms used in this specification should be interpreted based on their substantive meaning and the overall content of this specification, rather than simply their names.

[0048] Throughout the specification, when a component is said to be "connected" to another component, this includes not only the case where the component is "directly connected," but also the case where the component is "electrically connected" with another component intervening therebetween. Furthermore, when a component is said to "include" a particular component, this does not exclude the other component, but rather allows the inclusion of other components, unless specifically stated otherwise. Furthermore, the terms "more than" or "less than" with respect to a specific threshold may be appropriately replaced with "greater than" or "less than", respectively, depending on the embodiment.

[0049] Hereinafter, in the present invention, fields and subfields may be used interchangeably.

[0050] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0051] A wireless LAN system includes one or more Basic Service Sets (BSSs), which represent a collection of devices that have successfully synchronized and can communicate with each other. BSSs can generally be categorized as infrastructure BSSs and independent BSSs (IBSSs). Figure 1 illustrates an infrastructure BSS.

[0052] As illustrated in FIG. 1, the infrastructure BSS (BSS1, BSS2) includes one or more stations (STA1, STA2, STA3, STA4, STA5), an access point (AP-1, AP-2) that provides a distribution service, and a distribution system (DS) that connects multiple access points (AP-1, AP-2).

[0053] A station (STA) is any device that includes a medium access control (MAC) and a physical layer interface for a wireless medium that complies with the IEEE 802.11 standard, and broadly includes both non-access point (AP) stations and access points (APs). In addition, the term "terminal" in this specification may refer to a non-AP STA or an AP, or both. A station for wireless communication includes a processor and a communication unit, and may further include a user interface unit and a display unit, depending on the embodiment. The processor may generate a frame to be transmitted through a wireless network or process a frame received through the wireless network, and may perform various other processes for controlling the station. In addition, the communication unit is functionally connected to the processor and transmits and receives frames through the wireless network for the station. In the present invention, a terminal may be used as a term that includes a user equipment (UE).

[0054] An Access Point (AP) is an entity that provides access to a distribution system (DS) via a wireless medium for stations associated with it. In an infrastructure BSS, communication between non-AP stations is in principle performed via the AP, but direct communication is also possible between non-AP stations when a direct link is established. Meanwhile, in the present invention, the AP is used as a concept including a Personal BSS Coordination Point (PCP), and in a broad sense, it can include concepts such as a centralized controller, a base station (BS), a node-B, a base transceiver system (BTS), or a site controller. In the present invention, the AP may also be referred to as a base wireless communication terminal, and the base wireless communication terminal may be used as a term including, in a broad sense, an AP, a base station, an eNodeB (eNB), and a transmission point (TP). In addition, the base wireless communication terminal may include various types of wireless communication terminals that allocate communication medium resources and perform scheduling in communication with multiple wireless communication terminals.

[0055] Multiple infrastructure BSSs can be interconnected via a distribution system (DS). Multiple BSSs connected via the distribution system are referred to as an Extended Service Set (ESS).

[0056] FIG. 2 illustrates an independent BSS, a wireless LAN system, according to another embodiment of the present invention. Parts of the embodiment of FIG. 2 that are identical or corresponding to those of the embodiment of FIG. 1 will not be redundantly described.

[0057] BSS3, illustrated in Figure 2, is an independent BSS and does not include an AP. Therefore, all stations (STA6, STA7) are not connected to an AP. An independent BSS does not allow access to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) can be directly connected to another.

[0058] FIG. 3 is a block diagram showing the configuration of a station (100) according to one embodiment of the present invention. As illustrated, the station (100) according to the embodiment of the present invention may include a processor (110), a communication unit (120), a user interface unit (140), a display unit (150), and a memory (160).

[0059] First, the communication unit (120) transmits and receives wireless signals such as wireless LAN packets, and may be built into or externally installed in the station (100). According to an embodiment, the communication unit (120) may include at least one communication module using different frequency bands. For example, the communication unit (120) may include communication modules of different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to one embodiment, the station (100) may include a communication module using a frequency band of 7.125 GHz or higher and a communication module using a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with an AP or an external station according to the wireless LAN standard of the frequency band supported by the corresponding communication module. The communication unit (120) may operate only one communication module at a time or may operate 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 in an independent form, or multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit (120) may represent an RF (Radio Frequency) communication module that processes RF (Radio Frequency) signals.

[0060] Next, the user interface unit (140) includes various types of input / output means provided in the station (100). That is, the user interface unit (140) can receive user input using various input means, and the processor (110) can control the station (100) based on the received user input. In addition, the user interface unit (140) can perform output based on a command of the processor (110) using various output means.

[0061] Next, the display unit (150) outputs an image on the display screen. The display unit (150) can output various display objects, such as content executed by the processor (110) or a user interface based on the control commands of the processor (110). In addition, the memory (160) stores a control program used in the station (100) and various data corresponding thereto. Such a control program may include a connection program required for the station (100) to connect to an AP or an external station.

[0062] The processor (110) of the present invention can execute various commands or programs and process data within the station (100). In addition, the processor (110) can control each unit of the above-described station (100) and control data transmission and reception between the units. According to an embodiment of the present invention, the processor (110) can execute a program for connection to an AP stored in the memory (160) and receive a communication setup message transmitted by the AP. In addition, the processor (110) can read information on the priority conditions of the station (100) included in the communication setup message and request connection to the AP based on the information on the priority conditions of the station (100). The processor (110) of the present invention may refer to the main control unit of the station (100), and according to an 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 or modulator and / or demodulator that modulates and / or demodulates wireless signals transmitted and received from the communication unit (120). The processor (110) controls various operations of transmitting and receiving wireless signals of the station (100) according to an embodiment of the present invention. A specific embodiment thereof will be described later.

[0063] The station (100) illustrated in FIG. 3 is a block diagram according to one embodiment of the present invention, and the blocks shown separately are logically distinguished elements of the device. Accordingly, the elements of the above-described device may be mounted as one chip or as multiple chips depending on the design of the device. For example, the processor (110) and the communication unit (120) may be implemented by being integrated into one chip or may be implemented as separate chips. In addition, in the embodiment of the present invention, some components of the station (100), such as the user interface unit (140) and the display unit (150), may be selectively provided in the station (100).

[0064] Fig. 4 is a block diagram illustrating the configuration of an AP (200) according to one embodiment of the present invention. As illustrated, the AP (200) according to the embodiment of the present invention may include a processor (210), a communication unit (220), and a memory (260). In Fig. 4, redundant descriptions of portions of the configuration of the AP (200) that are identical or corresponding to the configuration of the station (100) of Fig. 3 will be omitted.

[0065] Referring to FIG. 4, the AP (200) according to the present invention has a communication unit (220) for operating a BSS in at least one frequency band. As described above in the embodiment of FIG. 3, the communication unit (220) of the AP (200) may also include a plurality of communication modules that utilize different frequency bands. That is, the AP (200) according to the embodiment of the present invention may include two or more communication modules for different frequency bands, such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP (200) may include a communication module that utilizes a frequency band of 7.125 GHz or higher and a communication module that utilizes a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with a station according to the wireless LAN standard of the frequency band supported by the corresponding communication module. The communication unit (220) may operate only one communication module at a time or may operate multiple communication modules simultaneously, depending on the performance and requirements of the AP (200). In an embodiment of the present invention, the communication unit (220) may represent an RF communication module that processes an RF (Radio Frequency) signal.

[0066] Next, the memory (260) stores the control program used in the AP (200) and various data according to the control program. This control program may include a connection program that manages the connection of the station. In addition, the processor (210) controls each unit of the AP (200) and may control data transmission and reception between the units. According to an embodiment of the present invention, the processor (210) may execute a program for connection with a station stored in the memory (260) and transmit a communication setup message to one or more stations. At this time, the communication setup message may include information on the connection priority conditions of each station. In addition, the processor (210) performs connection setup according to a connection request from a station. According to one embodiment, the processor (210) may be a modem or a modulator and / or demodulator that modulates and demodulates a wireless signal transmitted and received from the communication unit (220). The processor (210) controls various operations of wireless signal transmission and reception of the AP (200) according to an embodiment of the present invention. Specific examples of this will be described later.

[0067] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0068] Referring to FIG. 5, the link between STA (100) and AP (200) is largely established through three stages: scanning, authentication, and association. First, the scanning stage is a stage in which STA (100) acquires access information of the BSS operated by AP (200). Methods for performing scanning include a passive scanning method in which information is acquired only by utilizing a beacon message (S101) periodically transmitted by AP (200), and an active scanning method in which STA (100) acquires access information by transmitting a probe request to AP (S103) and receiving a probe response from AP (S105).

[0069] The STA (100) that successfully receives wireless access information in the scanning step transmits an authentication request (S107a) and receives an authentication response from the AP (200) (S107b) to perform the authentication step. After the authentication step is performed, the STA (100) transmits an association request (S109a) and receives an association response from the AP (200) (S109b) to perform the association step. In this specification, association basically means wireless association, but the present invention is not limited thereto, and association in a broad sense may include both wireless association and wired association.

[0070] Meanwhile, an additional 802.1X-based authentication step (S111) and an IP address acquisition step (S113) via DHCP may be performed. In Fig. 5, the authentication server (300) is a server that processes STA (100) and 802.1X-based authentication, and may be physically connected to the AP (200) or may exist as a separate server.

[0071] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0072] A terminal performing wireless LAN communication performs carrier sensing before transmitting data to check whether the channel is busy. If a wireless signal above a certain strength is detected, the channel is determined to be busy, and the terminal delays access to the channel. This process is called clear channel assessment (CCA), and the level that determines whether the signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold received by the terminal is intended for the terminal, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected on the channel or a wireless signal with a strength lower than the CCA threshold is detected, the channel is determined to be idle.

[0073] When the channel is determined to be idle, each terminal with data to transmit performs a backoff procedure after an IFS (Inter Frame Space) time, such as AIFS (Arbitration IFS) or PIFS (PCF IFS), depending on the status of each terminal. In some embodiments, the AIFS may be used as a configuration to replace the existing DIFS (DCF IFS). Each terminal waits while decreasing the slot time by a random number determined for the terminal during the idle interval of the channel, and a terminal that has exhausted all slot times attempts to access the channel. The period during which each terminal performs the backoff procedure is called a contention window period. At this time, the random number may be referred to as a backoff counter. That is, the initial value of the backoff counter is set by an integer, which is a random number obtained by the terminal. If the terminal detects that the channel is idle during the slot time, the terminal may decrease the backoff counter by 1. Additionally, if the backoff counter reaches 0, the terminal may be permitted to perform channel access on the corresponding channel. Accordingly, transmission by the terminal may be permitted if the channel is idle during the AIFS time and the slot time of the backoff counter.

[0074] If a specific terminal successfully accesses the channel, the terminal can transmit data through the channel. However, if the terminal attempting access collides with another terminal, the collided terminals are each assigned a new random number and perform a backoff procedure again. According to one embodiment, the random number newly assigned to each terminal may be determined within a range twice (2*CW) of the random number range (contention window, CW) previously assigned to the terminal. Meanwhile, each terminal performs the backoff procedure again in the next contention window period to attempt access, and at this time, each terminal performs the backoff procedure starting from the slot time remaining in the previous contention window period. In this way, each terminal performing wireless LAN communication can avoid collisions with each other for a specific channel.

[0075] <Various PPDU format examples>

[0076] FIG. 7 shows various standard generation-specific physical layer protocol data unit (PPDU) formats according to an embodiment of the present invention.

[0077] More specifically, FIG. 7(a) illustrates an embodiment of a legacy PPDU format based on 802.11a / g, FIG. 7(b) illustrates an embodiment of a HE PPDU format based on 802.11ax, and FIG. 7(c) illustrates an embodiment of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. In addition, FIG. 7(d) illustrates a detailed field configuration of L-SIG and RL-SIG commonly used in the above PPDU formats.

[0078] Referring to FIG. 7(a), the preamble of a 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.

[0079] Referring to FIG. 7(b), the preamble of the HE PPDU additionally includes RL-SIG (Repeated Legacy Short Training field), HE-SIG-A (High Efficiency Signal A field), HE-SIG-B (High Efficiency Signal B field), HE-STF (High Efficiency Short Training field), and HE-LTF (High Efficiency Long Training field) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF may be referred to as a HE preamble. The specific configuration of the HE preamble may be modified according to the HE PPDU format. For example, HE-SIG-B may be used only in the HE MU PPDU format.

[0080] Referring to FIG. 7(c), the preamble of the EHT PPDU additionally includes, in addition to the legacy preamble, an RL-SIG (Repeated Legacy Short Training field), a U-SIG (Universal Signal field), an EHT / UHR-SIG-A (Extremely High Throughput / Ultra High Reliability Signal A field), an EHT / UHR-SIG-A (Extremely High Throughput / Ultra High Reliability Signal B field), an EHT-STF (Extremely High Throughput Short Training field), and an EHT-LTF (Extremely High Throughput Long Training field). In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF may be referred to as an EHT preamble. The specific configuration of the non-legacy preamble may be modified according to the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B can only be used in some of the EHT PPDU formats.

[0081] In this way, the PPDU used in the UHR standard may have a format similar to the PPDU format used in the EHT standard. This is because the EHT PPDU format defined in 802.11be includes a U-SIG field that multiple wireless LAN generations have agreed to use in common. At this time, the value of the PHY Version Identifier field of the U-SIG field included in the EHT PPDU may be 0, and the value of the PHY Version identifier field of the U-SIG field included in the UHR PPDU may have a non-zero value, such as 1. The EHT PPDU includes an EHT-STF (Extremely High Throughput Short Training field) field in the STF field, and an EHT-LTF (Extremely High Throughput Long Training field) field in the LTF field. The UHR PPDU includes a UHR-STF (Ultra High Reliability Short Training field) field in the STF field, and a UHR-LTF (Ultra High Reliability Long Training field) field in the LTF field.

[0082] The L-SIG field included in the PPDU preamble applies 64FFT OFDM and consists of a total of 64 subcarriers. Of these, 48 subcarriers, excluding the guard subcarrier, DC subcarrier, and pilot subcarrier, are used for L-SIG data transmission. Since L-SIG applies BPSK, Rate=1 / 2 Modulation and Coding Scheme (MCS), it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of L-SIG.

[0083] Referring to Fig. 7(d), L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field consists of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which combine modulation methods such as BPSK / QPSK / 16-QAM / 64-QAM and inefficiencies such as 1 / 2, 2 / 3, and 3 / 4. Combining the information in the L_RATE field and the L_LENGTH field can indicate the total length of the corresponding PPDU. In non-legacy PPDU formats, the L_RATE field is set to the minimum speed of 6 Mbps.

[0084] The L_LENGTH field is allocated in bytes, with a total of 12 bits, allowing for signaling up to 4095. In combination with the L_RATE field, it can indicate the length of the corresponding PPDU. At this time, legacy and non-legacy terminals may interpret the L_LENGTH field in different ways.

[0085] First, the method by which a legacy terminal or non-legacy terminal interprets the length of the PPDU using the L_LENGTH field is as follows. If the value of the L_RATE field is set to indicate 6 Mbps, 3 bytes (i.e., 24 bits) can be transmitted during 4 us, which is the duration of one symbol of 64 FFT. Therefore, by adding 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 symbols based on 64 FFT after L-SIG is obtained. Multiplying the obtained number of symbols by 4 us, which is the duration of one symbol, and then adding 20 us required for transmission of L-STF, L-LTF, and L-SIG, the length of the PPDU, i.e., the reception time (RXTIME) is obtained. This can be expressed as a formula as shown in Mathematical Expression 1 below.

[0086]

[0087] At this time, represents the smallest natural number greater than or equal to x. Since the maximum value of the L_LENGTH field is 4095, the length of the PPDU can be set to a maximum of 5.484 ms. A non-legacy terminal transmitting the PPDU must set the L_LENGTH field as in Mathematical Expression 2 below.

[0088]

[0089] Here, TXTIME is the total transmission time that constitutes the corresponding PPDU, as shown in mathematical expression 3 below. In this case, TX represents the transmission time of X.

[0090]

[0091] Referring to the above formulas, the length of the PPDU is calculated based on the rounded 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.

[0092] Referring to Fig. 7(e), the U-SIG (Universal SIG) field continues to exist in EHT / UHR PPDUs and subsequent generation wireless LAN PPDUs, and serves to distinguish which generation of PPDU it is, including EHT / UHR. In addition, the U-SIG field can serve to facilitate spatial reuse of EHT / UHR and subsequent generation wireless LANs. U-SIG is an OFDM 2 symbol based on 64FFT and can convey a total of 52 bits of information. Of these, 43 bits, excluding the 9 bits of CRC / Tail, are largely divided into the VI (Version Independent) field and the VD (Version Dependent) field.

[0093] The VI bit maintains its current bit configuration in the future so that even if a subsequent generation PPDU is defined, current EHT / UHR terminals can obtain information about the PPDU through the VI fields of the PPDU. For this purpose, the VI field consists of PHY version, UL / DL, BSS Color, TXOP, and Reserved fields. The PHY version ID field is 3 bits and sequentially distinguishes EHT / UHR and subsequent generation wireless LAN standards by version. The PHY version ID field of the EHT (11be) PPDU has a value of 000b, and the PHY version ID field of the UHR PPDU has a value other than 000b. The UL / DL field distinguishes whether the PPDU is an uplink / downlink PPDU. BSS Color means an identifier for each BSS defined in 11ax and has a value of 6 bits or more. TXOP stands for Transmit Opportunity Duration transmitted in the MAC header. By adding it to the PHY header, the length of the TXOP containing the corresponding PPDU can be inferred without having to decode the MPDU, and has a value of 7 bits or more.

[0094] The VD field of EHT is signaling information that is only useful for PPDUs of version 11be. It can be composed of fields that are commonly used in any PPDU format, such as PPDU format and BW, and fields that are defined differently for each PPDU format. The PPDU format is a delimiter that distinguishes EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs.

[0095] The BW field largely signals five basic PPDU BW options of 20, 40, 80, 160 (80+80), and 320 (160+160) MHz (a BW that can be expressed in the form of an exponential of 20*2 can be called the basic BW), and various remaining PPDU BWs configured through Preamble Puncturing. In addition, some 80 MHz can be signaled in a punctured form after being signaled at 320 MHz. In addition, the punctured and modified channel form can be signaled directly in the BW field, or by using the BW field together with 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 signaling is possible, so only a maximum of 3 puncturing modes can be signaled. If the BW field is 4 bits, a total of 16 BW signaling is possible, so the puncturing mode can signal up to 11.

[0096] The VD field of the UHR is a field that indicates signaling information that is only useful for the UHR PPDU. However, the information indicated by each field included in the VD field of the UHR PPDU may be identical to or more extended than the information indicated by the field that plays the same role as the VD field of the EHT (11be). For example, the field indicating the puncturing pattern included in the VD field of the UHR PPDU may indicate a wider variety of patterns than the field indicating the puncturing pattern included in the VD field of the EHT PPDU. Alternatively, the field indicating the puncturing pattern included in the VD field of the UHR PPDU may be interpreted in conjunction with the BW field. This allows for indicating a wider variety of puncturing patterns.

[0097]

[0098] Figure 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0099] The EHT / UHR PPDU format can be indicated by the PPDU Format field of the U-SIG field of the PPDU. Fig. 8 (a) shows an EHT / UHR SU PPDU according to an embodiment of the present invention. The EHT / UHR SU PPDU is a PPDU used for single-user transmission between an AP and a single station, and may include an EHT-SIG-A field for additional signaling after the U-SIG.

[0100] FIG. 8(b) illustrates an EHT / UHR Trigger-based PPDU according to an embodiment of the present invention. An EHT / UHR Trigger-based PPDU is an uplink PPDU used for transmission in response to a trigger frame, and may not have a separate EHT / UHR-SIG-A field after the U-SIG.

[0101] Figure 8(c) illustrates an EHT / UHR MU PPDU according to an embodiment of the present invention. An EHT / UHR MU PPDU is a PPDU used for transmission to one or more terminals. The EHT / UHR MU PPDU format may include a HE-SIG-B field after the U-SIG field.

[0102] Figure 8(d) illustrates an EHT / UHR ER SU PPDU according to an embodiment of the present invention. The EHT / UHR ER SU PPDU is used for single-user transmission to stations in an extended range. The EHT / UHR ER SU PPDU format allows the U-SIG to be repeated along the time axis.

[0103] The EHT / UHR MU PPDU described through (c) of FIG. 8 can be used by an AP to perform downlink transmission to multiple stations. At this time, the EHT / UHR MU PPDU can include scheduling information for multiple stations to simultaneously receive the PPDU. At this time, the EHT / UHR MU PPDU can convey AID information of the receiver or transmitter of the corresponding PPDU through the user specific field of EHT / UHR-SIG-B. A station that receives the EHT / UHR MU PPDU can perform a spatial reuse operation based on the AID information obtained from the preamble of the PPDU. More specifically, the resource unit allocation (RA) field of EHT / UHR-SIG-B can include information on a resource unit (RU) partitioning form in a specific bandwidth (e.g., 20 MHz) in the frequency domain. Additionally, information about the station assigned to each partitioned resource unit may be conveyed via a user-specific field of EHT / UHR-SIG-B. The user-specific field may include one or more user fields corresponding to each partitioned resource unit.

[0104] Among the multiple resource units divided, the AID of the receiver or sender may be inserted into the user field corresponding to the resource unit in which data transmission is performed. A pre-specified null STA ID may be inserted into the user field corresponding to the remaining resource units in which data transmission is not performed.

[0105] Two or more PPDUs described through FIG. 8 may be indicated by the same PPDU format. For example, the value of the U-SIG PPDU format subfield indicating an EHT / UHR SU PPDU and the value of the U-SIG PPDU format subfield indicating an EHT / UHR MU PPDU may be the same.

[0106] Some fields or some information within a field included in the PPDU format described above may be omitted. This may be referred to as compression mode or compressed mode.

[0107]

[0108] <Wi-Fi 단말의 채널 액세스 방법>

[0109] Wi-Fi terminals (APs, non-AP STAs, etc.) perform communication using unlicensed bands, so before transmitting a frame, they check whether the channel they want to transmit is in use by another device. CSMA (Carrier Sense Multiple Access) is a channel access method in which a terminal that wants to transmit a packet performs carrier sense to check whether the channel is in use by another device, and transmits only if the channel is determined to be idle. Since a terminal using CSMA can perform an action of not attempting transmission at least when it is determined that another device is using the medium (channel) (when it is determined to be busy), the transmission that was initiated first can be protected from other devices.

[0110] However, multiple terminals that recognize that the medium is occupied by another device experience a transmission collision by simultaneously attempting to transmit packets when it is confirmed that the medium occupation from the other device has ended (the medium has changed to Idle). That is, as multiple other terminals simultaneously attempt to transmit packets when a specific terminal attempts to transmit a packet, a terminal that is supposed to receive the packet transmitted by the specific terminal is unable to properly receive and decode the packet that it is supposed to receive due to interference caused by the transmissions performed by the multiple other terminals.

[0111] CSMA / CA (CSMA with collision avoidance) is a channel access mechanism that prevents multiple terminals from simultaneously attempting packet transmission when the medium has changed to Idle, as described above. Terminals accessing the medium (channel) using CSMA / CA attempt to transmit after waiting for a random amount of time when the state of the medium they observe changes to Idle. The random amount of time may be an aslottime (typically 9 microseconds) equal to a random number (random backoff counter) generated by each terminal attempting to transmit. In other words, terminals accessing the medium using CSMA / CA attempt to transmit after waiting for different random amounts of time, so they attempt to transmit at different times, unlike when CSMA alone is used. In this case, when a specific terminal that waited for the shortest random amount of time after the medium changed to Idle attempts to transmit first, other terminals can recognize that the medium has been occupied (changed to busy) by the specific terminal and abort the channel access procedure. At this time, the specific terminal may perform an operation of decreasing the backoff counter maintained by it by 1 every aslottime while the medium is maintained as Idle, and may attempt transmission when the backoff counter becomes 0, or when the aslottime has passed after the backoff counter becomes 0. At this time, the specific terminal that performed the transmission may generate a new random number (new backoff counter) after the transmission is finished, and may attempt transmission when the new random number becomes 0 again, or after it becomes 0.

[0112] The CSMA / CA and random backoff procedures briefly explained above are applied to DCF (Distributed coordination function) and EDCAF (Enhanced distributed channel access), which are the basic functions used by Wi-Fi terminals when attempting to access a channel. Since these are well-known and widely used unlicensed band channel access methods, a more detailed explanation will be omitted.

[0113]

[0114] The DCF and EDCAF utilized by the MAC of the Wi-Fi terminal evaluate the channel status by considering not only the channel status (idle / busy) confirmed by each terminal performing its own physical CS (Carrier Sense) but also the results of a virtual CS. In more detail, even if the result of the physical CS performed on the channel is idle, if the result of the virtual CS is busy, the Wi-Fi terminal considers the channel status to be busy. At this time, the Virtual CS is a channel evaluation method that determines the channel to be busy if the NAV (Network allocation vector) is not 0. The NAV may be a value maintained for future traffic that is predicted to occupy the medium. To explain in more detail, when the MAC of Wi-Fi receives an RTS / CTS frame, it can set the NAV (NAV count) based on the duration information of the received frame, for example, the value of the duration field, and maintain the NAV as a non-zero value for the expected time that the medium will be occupied after the RTS / CTS frame exchange. In other words, the value maintained as NAV decreases over time. If the NAV value of a specific MAC is 0, it can be interpreted that the future traffic recognized by the specific MAC is no longer occupying the medium. If the NAV is 0, the MAC can determine the virtual CS result as Idle. At this time, the MAC of Wi-Fi can also set the NAV based on the duration value obtained from not only the RTS / CTS frame but also other received MAC frames.

[0115] The channel assessment method (determine the state of the medium) that considers the results of the physical CS and virtual CS briefly described above is also one of the well-known Wi-Fi MAC functions, so a detailed explanation is omitted.

[0116]

[0117] <EDCA와 TXOP>

[0118] EDCA provides a mechanism to differentiate and manage traffic into four types of ACs (access categories) according to the characteristics of the traffic. At this time, the four types of ACs are AC_VO (AC Voice), AC_VI (AC Video), AC_BE (AC Best effort), and AC_BK (AC Background), and each AC can have different CW (contention window), TXOP (transmit opportunity), and AIFSN parameters. Simply put, EDCA is a mechanism that differentiates the CW, TXOP, and AIFSN parameters for the four types of ACs and controls the transmission priority of traffic transmitted using each AC. To this end, EDCA can map traffic (MSDU) that the MAC must service to one of the four ACs according to the TC (traffic category) or TS (traffic stream). At this time, the traffic mapped to one of the four ACs by EDCA is divided and managed into four queues for each AC. At this time, the four queues may be logically separated rather than physically separated.

[0119] AC_VO is an AC that can be utilized for traffic that is vulnerable to transmission delays, although the absolute volume of traffic, such as voice traffic, is not large. It has relatively small CW and AIFSN parameter values ​​to increase the probability of being serviced preferentially over traffic from other ACs. The TXOP parameter of AC_VO is limited to a relatively small value compared to the TXOP parameters of other ACs, ensuring only a shorter transmission time than other ACs.

[0120] AC_VI is an AC that is more delay-tolerant than voice traffic, but can still be utilized for traffic such as video that requires low-latency transmission and high traffic volume. AC_VI has larger CW and AIFSN parameter values ​​than AC_VO but smaller than other ACs, and its TXOP is approximately twice as long as AC_VI.

[0121] AC_BE is an AC that can be utilized for traffic that is robust to transmission delays, and most general traffic, excluding voice data and streaming video data, can be classified as AC_BE. AC_BE uses CW and AIFSN parameters with values ​​greater than AC_VO and AC_VI. In addition, AC_BE does not have a separate TXOP. Therefore, traffic corresponding to AC_BE cannot be utilized in the TXOP transmission sequence, which transmits a PPDU, receives an ACK in response, and then transmits a PPDU again after SIFS.

[0122] AC_BK, similar to AC_BE, is a delay-tolerant traffic, but can be utilized for lower-priority traffic than BE traffic. AC_BK utilizes the same CW parameter values ​​as AC_BE, and the AIFSN parameter values ​​are larger than those of AC_BE. In addition, traffic corresponding to AC_BK does not have a separate TXOP like AC_BE, so it cannot be utilized in the TXOP transmission sequence.

[0123] The four types of EDCA AC described above are mapped to the UP (user-priority) of 802.1D, and the EDCA AC is determined based on the UP value of the traffic received through the wire or the TID of the MSDU indicated from the upper layer. At this time, if the TID of the MSDU indicates a value between 0 and 7, the value indicated by the TID can correspond one-to-one with the UP.

[0124] In addition, the four types of EDCA AC described above have default CW (CWmin, CWmax), AIFSN, and TXOP parameters defined in the standard, and the parameter values ​​of each AC can be changed by the AP, so that different values ​​can be used for each BSS.

[0125]

[0126] Using the EDCA mechanism, Wi-Fi traffic is stored in one of four queues corresponding to four ACs, and can be transmitted to the destination device only if the AC containing the traffic wins the channel access competition with other ACs. At this time, in the channel access competition between ACs, each AC competes using its assigned access parameters (CW[AC], AIFSN[AC]), and the channel access competition operation performed by each AC is identical to DCF. At this time, if a specific AC does not have any traffic to transmit in its queue, the specific AC may not participate in the competition.

[0127] However, as described above, since the CW and AIFSN parameter values ​​utilized by each AC are different, the AC_VO with the smallest CW and AIFSN parameters is more likely to win the channel access competition with other ACs, and thus the traffic of AC_VO is more likely to be serviced with priority over the traffic of other ACs.

[0128] In addition, the EDCA mechanism stipulates internal competition rules such as when an (internal) collision occurs between ACs, the AC with a higher priority wins, and increases the CW of the other AC that caused the collision, and rules for composing a PPDU including traffic from an AC other than the AC that won the competition (primary AC), but a detailed description is omitted because it is not closely related to the proposal of the present invention.

[0129] As described above, EDCA provides the EDCA TXOP (EDCA Transmission Opportunity) function along with the function of operating differentiated ACs according to the type of traffic (frames, packets, etc.) to enhance QoS. EDCA TXOP refers to the time during which the EDCAF (EDCA Function) of a specific AC can control the medium without being disturbed by other devices during the TXOP period (duration) when it obtains a channel access opportunity, i.e., becomes a TXOP holder. At this time, the EDCA TXOP may be limited by the TXOP limit advertised by the AP. The TXOP holder must ensure that its own transmission and the transmission of the response frame responded to by its own transmission can be terminated within the TXOP limit.

[0130] A TXOP holder can transmit multiple frames (multiple PPDUs) during an EDCA TXOP period. If the transmission of each frame is performed within the acquired TXOP period, the TXOP holder can transmit multiple frames continuously without performing a separate channel access procedure, such as a backoff procedure, between transmissions of each frame. At this time, if the multiple frames are MPDUs or A-MPDUs (Aggregated MAC protocol data units) that do not request an immediate ack, the transmission of the multiple frames can be performed at an interval of a short interframe space (SIFS) or a reduced interframe space (RIFS). At this time, if there is an MPDU or A-MPDU requesting an immediate ack among the multiple frames, the TXOP holder can transmit a frame requesting an immediate ack, receive the ack, and transmit the next frame after an SIFS.

[0131] At this time, traffic (packets, frames, etc.) of other ACs other than the specific AC that is the TXOP holder may also be transmitted together within the TXOP acquired by the TXOP holder (specific AC) when certain conditions are satisfied. The transmission of traffic of other ACs other than the TXOP holder within the TXOP may be an operation due to TXOP sharing between ACs, and detailed information regarding the above-mentioned certain conditions is omitted because it is not related to the present invention.

[0132]

[0133] As described above, a TXOP holder can perform continuous frame transmission without performing a separate channel access procedure within the TXOP. This may be an operation that can be achieved when other terminals understand and protect the TXOP interval acquired by the TXOP holder. In other words, in order for the TXOP holder to acquire medium control authority for the EDCA TXOP interval, a procedure may be required to notify other terminals of the acquired TXOP interval so that they can recognize it.

[0134] To this end, a terminal (AC) that becomes a TXOP holder or initiates transmission after completing a channel access procedure may attempt to allow other terminals to recognize the TXOP section by transmitting an RTS frame. At this time, the RTS frame means a frame in which the Type subfield (the fourth bit (B3), the third bit (B2) of the Frame Control field) of the Frame Control field of the MAC frame header is set to 01b (Type = Control frame) and the Subtype subfield (the eighth bit (B7), the seventh bit (B6), the sixth bit (B5), the fifth bit (B4) of the Frame Control field) is set to 1011b. Another terminal that receives an RTS frame from a TXOP holder may set an NAV based on information related to the duration included in the RTS frame, for example, the value of the Duration field. The set NAV may be maintained as a non-zero value for a time corresponding to the TXOP of the TXOP holder. However, the terminal indicated as the destination device of the RTS frame must respond with a CTS frame instead of setting the NAV based on the information in the RTS frame. At this time, the destination device of the RTS frame transmitted to start TXOP is a TXOP responder and must transmit a CTS frame in response to the RTS (SIFS after the RTS frame is received). At this time, the Duration field of the responding CTS frame is set to a value calculated as the value indicated in the Duration field of the received RTS frame - the CTS frame transmission time - SIFS. The terminals receiving the CTS frame can set the NAV based on information related to the duration included in the CTS frame (e.g., the value of the Duration field).

[0135] Therefore, the NAV of the terminal that received the RTS frame from the TXOP holder and the terminal that received the CTS frame from the TXOP responder are set to 0 after the TXOP acquired by the TXOP holder ends. This allows the Wi-Fi MAC mechanism to protect the TXOP holder and the TXOP responder from exchanging multiple frames without interruption during the TXOP.

[0136] However, if the TXOP holder transmits an RTS frame as a non-HT duplicate PPDU over the primary 80 MHz band, but the CTS frame (non-HT duplicate PPDU) responded to by the TXOP responder is responded to only in the primary 40 MHz band, the TXOP holder may use only the bandwidth of the primary 40 MHz or less than the primary 40 MHz, for example, the primary 20 MHz, for frame exchange during the acquired TXOP. The CH_BANDWIDTH (a type of TXVECTOR parameter) of the PPDU transmitted by the TXOP holder shall be set to a value equal to or smaller than the CH_BANDWIDTH_IN-NON_HT (a type of RXVECTOR parameter) of the received CTS frame. In this case, the RTS frame may be an RTS frame that allows the CTS frame to be responded to in a BW smaller than the BW in which the RTS frame was transmitted. An RTS frame may be an RTS frame transmitted with DYN_BANDWIDTH_IN_NON_HT (a type of TXVECTOR parameter) set to Dynamic. If DYN_BANDWIDTH_IN_NON_HT is set to Static and the RTS frame is transmitted from a TXOP holder, the TXOP responder may have to respond with a CTS frame with the same BW as the BW in which the RTS frame was received.

[0137]

[0138] FIG. 9 shows a transmission / TXOP protection method using an RTS frame and a CTS frame according to an embodiment of the present invention.

[0139] Before transmitting a PPDU, the first station (STA1) transmits an RTS frame to the second station (STA2), which is the destination of the PPDU, and the second station (STA2) recognizes that the received RTS frame is an RTS frame destined for itself and responds with a CTS frame after SIFS.

[0140] STA1_Neighbor, a neighbor station of the first station (STA1), sets the NAV based on the value indicated by the Duration field of the RTS frame after receiving the RTS frame transmitted by the first station (STA1). STA2_Neighbor, a neighbor station of the second station (STA2), sets the NAV based on the information indicated by the Duration field of the CTS frame after receiving the CTS frame transmitted by the second station (STA2). STA1_Neighbor and STA2_Neighbor determine that the virtual CS is busy while the set NAV (counter) is maintained at a non-zero value after receiving the RTS / CTS frame, and perform actions such as not decreasing the backoff counter. As a result, the neighboring terminals that received the RTS / CTS frame do not attempt transmission during the period in which the NAV is maintained at a non-zero value. Therefore, the first station (STA1) and the second station (STA2) may not be disturbed by surrounding terminals while exchanging PPDU and Ack frames.

[0141] Even if the first station (STA1) and STA2_Neighbor are in a relationship where signals due to each other's transmissions are not detected (hidden), STA2_Neighbor can perform an operation that takes into account that the channel (channel, WM, Wireless medium) is in use while the first station (STA1) transmits a PPDU.

[0142]

[0143] <MU-RTS 트리거 프레임을 이용한 TXOP 보호>

[0144] 11ax (6th generation Wi-Fi, Wi-Fi6, HEW, High Efficiency WLAN) defines the MU-RTS Trigger / CTS frame exchange procedure, and adds a function that enables the AP to start TXOP and protect the TXOP frame exchange procedure using the MU-RTS trigger frame (hereinafter referred to as MU-RTS, MU-RTS frame). The MU-RTS frame is a type of trigger frame. When the MU-RTS frame is received, the station whose AID12 (the LSB 12 bits of the Association ID) is indicated in the User field included in the MU-RTS frame simultaneously responds with a CTS frame. When the AP protects the TXOP using the MU-RTS frame, since multiple stations respond with CTS frames, the TXOP can be protected from the peripheral devices of each of the multiple stations that are the destination devices of the DL MU PPDU (Down link multi-user PPDU). In addition, the MU-RTS frame can be used to protect the UL MU PPDU. In more detail, before requesting a TB (Trigger based) PPDU from multiple stations through a trigger frame, the AP can transmit an MU-RTS frame to cause multiple stations that will respond to the TB PPDU to respond with a CTS frame. At this time, the CTS frames responded to by the multiple stations induce the surrounding stations of each station to set a NAV that protects the TB PPDU and the Ack frame (Ack, Block Ack, etc.) to be transmitted after the TB PPDU, and through this, legacy stations STAs that cannot recognize (interpret, decode) the trigger frame and TB PPDU may not perform channel access during the packet exchange sequence period (or TXOP) initiated through the trigger frame.

[0145]

[0146] FIG. 10 shows a transmission / TXOP protection method using an MU-RTS frame and a CTS frame according to an embodiment of the present invention.

[0147] In the embodiment of FIG. 10, before transmitting an MU PPDU, the AP transmits an MU-RTS frame to the first station (STA1) and the second station (STA2), which are the destination devices of the MU PPDU, and the first station (STA1) and the second station (STA2) receive the MU-RTS frame and, after SIFS, each respond to the MU-RTS frame with a CTS frame.

[0148] STA1_Neighbor, a neighboring station of the first station (STA1), sets its NAV based on the information indicated by the Duration field of the CTS frame after receiving the CTS frame transmitted by the first station (STA1). STA2_Neighbor, a neighboring station of the second station (STA2), sets its NAV based on the information indicated by the Duration field of the CTS frame after receiving the CTS frame transmitted by the second station (STA2). STA1_Neighbor and STA2_Neighbor perform actions such as not decreasing the backoff counter, assuming that the Virtual CS (Virtual Carrier Sense) is busy while the NAV (counter) set after receiving the CTS frame remains at a non-zero value. Therefore, neighboring terminals that have received the CTS frame do not attempt to transmit during the period in which the NAV remains at a non-zero value. This allows the AP to transmit MU PPDUs and the first station (STA1) and the second station (STA2) to transmit Ack frames without being interrupted by surrounding terminals.

[0149] The trigger frame described above is a frame type defined in 11ax, and is a frame type in which the Type (fourth bit (B3) and third bit (B2)) and Subtype (eighth bit (B7), seventh bit (B6), sixth bit (B5), and fifth bit (B4)) subfields of the Frame Control field are set to 01b and 0010b, respectively. A trigger frame is a frame of Control Type in which the Type subfield of the Frame Control field is 01b, and the Subtype value 0010 indicates that it is a Trigger frame type. In 11ax, a trigger frame is defined so that an AP can request a response frame for multiple stations at once, and an MU-RTS frame is used so that an AP can request a CTS frame for multiple stations (non-AP STAs). Trigger Types other than the MU-RTS frame include the Basic Tigger frame requesting UL MU PPDU, the Beamforming Report Poll Tigger frame requesting Beamforming Report, the MU-BAR Tigger frame (BlockAck request), the BSRP trigger frame requesting Buffer Status Report, the GCR MU-BAR trigger frame, the Bandwidth Query Report Poll (BQRP) trigger frame, and the NDP Feedback Report Poll trigger frame. Trigger Types other than the MU-RTS frame are not related to the content of the present invention, so a detailed description thereof is omitted.

[0150]

[0151] <Transmission delay issues that occur while the medium is occupied>

[0152] As previously explained, a TXOP holder can exchange frames without being interrupted by other stations. At this time, the network allocation vector (NAV) is set to a value greater than 0 for stations that are not TXOP holders. However, due to this NAV, stations attempting to transmit low-latency traffic are prevented from doing so. Furthermore, channel access by other stations is restricted during the time that the PPDU for frame exchange with the TXOP holder occupies the transmission medium. Consequently, the transmission of low-latency traffic may be delayed.

[0153]

[0154] <How to exchange initial control frames>

[0155] After a station successfully accesses a channel, for example, after successfully completing a backoff procedure using EDCA, the station can secure a TXOP by transmitting an initial control frame. The initial control frame may be an RTS, MU-RTS, or BSRP trigger frame. Non-AP stations may transmit an RTS frame as their initial control frame.

[0156] The RTS frame can be used for initial collision detection and NAV setup. Specifically, a station can set the NAV by exchanging RTS frames and CTS frames. If a CTS frame is not transmitted in response to an RTS frame, the station can determine that the RTS frame transmission failed due to a transmission collision.

[0157] A multi-user (MU)-RTS frame triggers the transmission of a CTS frame by one or more stations indicated by the MU-RTS frame. The one or more stations indicated by the MU-RTS frame respond with a CTS frame to the MU-RTS frame. The MU-RTS frame can be used for initial collision detection and NAV setup. The MU-RTS frame can include a padding field of variable length. A station transmitting an MU-RTS frame can allow a station transmitting a response to the MU-RTS frame time to prepare to transmit its response. For example, an AP that initiates a frame exchange with a non-AP station in enhanced multi-link single radio (EMLSR) mode can transmit an MU-RTS frame including a padding field as an initial control frame to allow the non-AP station time to prepare to receive.

[0158] The BSRP (Buffer Status Report Poll) frame triggers the transmission of a BSR (Buffer Status Report) frame by one or more stations indicated by the BSRP frame. The BSR frame indicates the buffer status of the non-AP station that transmitted the BSR frame. The AP can trigger uplink transmission by transmitting a trigger frame based on the received BSR frame.

[0159] A station that receives an initial control frame senses the channel on which it will transmit a response frame. If the channel sensed by the station is idle, the station may be forced to transmit a response frame. This ensures that the station that transmitted the initial control frame acquires a TXOP. However, this may delay the transmission of low-latency traffic. This is explained in Figure 11.

[0160] FIG. 11 shows that a station according to an embodiment of the present invention sets a NAV through an RTS frame / CTS frame exchange, which delays transmission of a low-latency traffic PPDU.

[0161] The first station (STA1) transmits an RTS frame to the second station (STA2). The second station (STA2) is performing a backoff procedure to transmit low-latency traffic, but transmits a CTS frame in response to the RTS frame. The first station (STA1) transmits a PPDU to the second station (STA2) within the TXOP secured by the RTS frame / CTS frame exchange. The second station (STA2) transmits an ACK frame to the first station (STA1). The second station (STA2) then resumes the backoff procedure to transmit low-latency traffic.

[0162] In this way, if a response to the initial control frame is forced, transmission of low-latency traffic may be delayed. To address this, if the station that received the initial control frame (i.e., the TXOP responder) attempts to transmit low-latency traffic, allowing the transmission of low-latency traffic first can ensure smooth transmission of low-latency traffic.

[0163]

[0164] <Early Transmission Method for Low-Latency Traffic>

[0165] A station intending to transmit low-latency traffic can select whether to transmit a response frame to an initial control frame based on predefined conditions. Specifically, a station intending to transmit low-latency traffic may not transmit a response frame to the initial control frame. In this case, a station that is the TXOP holder may determine that transmission of the initial control frame has failed because it does not receive the response frame. A station that determines that transmission of the initial control frame has failed may initiate the channel access procedure again. A station intending to transmit low-latency traffic may continue the channel access procedure without transmitting a response to the initial control frame. In this case, if the station successfully accesses the channel, the station may transmit a low-latency traffic PPDU. Furthermore, the station may not be permitted to transmit traffic other than low-latency traffic. Specifically, when a station transmits low-latency traffic using an A-MPDU, the station may not be permitted to include an MPDU of a TID corresponding to low-latency traffic in the A-MPDU and to include an MPDU of a TID not corresponding to low-latency traffic in the A-MPDU. Additionally, a station may transmit low-latency traffic, and may not be permitted to transmit non-low-latency traffic within the TXOP it has acquired. For convenience of explanation, a station that acquires a TXOP without responding to the initial control frame is referred to as a preemption station.

[0166] A preemption station can transmit low-latency traffic and allocate remaining TXOPs to other stations. The other stations may be the stations that transmitted the initial control frames. This allows for compensation for transmission opportunities for stations whose transmissions were delayed due to preemption. Specifically, if the preemption station is an AP, the AP can trigger uplink transmission by transmitting a trigger frame to the station that transmitted the initial control frame. Furthermore, the AP can share TXOPs by transmitting an MU-RTS TXS (TXOP sharing) frame to the station that transmitted the initial control frame. Specifically, if the preemption station is a non-AP station, the non-AP station can transfer remaining TXOPs to the AP. Furthermore, it may be mandatory for the preemption station to transfer remaining TXOPs after transmitting low-latency traffic to other stations. Specifically, it may be mandatory for the preemption station to transfer remaining TXOPs after transmitting low-latency traffic to the station that transmitted the initial control frame.

[0167] In these embodiments, the preemption station may perform preemption transmission only when a predefined condition is satisfied. The predefined condition is described below.

[0168] The predefined conditions may include that the TID of the traffic to be transmitted by the preemption station corresponds to a predefined TID. For example, TID values ​​6 and 7 may be designated as low-latency traffic. In this case, the station may not transmit a response frame to the initial control frame only if the TID value to be transmitted by the preemption station is 6 or 7.

[0169] The predefined conditions may include a case where the lifetime timer value of the traffic to be transmitted by the preemption station is less than or equal to the predefined value. If the lifetime timer value of the traffic to be transmitted by the preemption station is less than or equal to the predefined value, the preemption station may not transmit a response frame to the initial control frame. If the lifetime timer value of the traffic to be transmitted by the preemption station is greater than the predefined value, the station may be required to transmit a response frame to the initial control frame. In another specific embodiment, if the lifetime timer is expected to expire within the TXOP secured by the initial control frame, the preemption station may not transmit a response frame to the initial control frame. If the lifetime timer is not expected to expire within the TXOP secured by the initial control frame, the preemption station may not be permitted to transmit a response frame to the initial control frame. In these embodiments, if the lifetime timer expires, the station discards the MSDU.

[0170] The predefined conditions may include a case where the amount of traffic to be transmitted by the preemption station is less than or equal to a predefined value. In another specific embodiment, the predefined conditions may include a case where the length of a low-latency PPDU containing the traffic to be transmitted by the preemption station is less than or equal to a predefined length. If the length of the low-latency PPDU to be transmitted by the preemption station is less than or equal to a predefined value, the preemption station may not transmit a response frame to the initial control frame. If the length of the low-latency PPDU to be transmitted by the preemption station is greater than the predefined value, the station may be required to transmit a response frame to the initial control frame.

[0171] Predefined conditions may include that the destination device of the traffic to be transmitted by the preempting station is a TXOP holder. For example, if the station receives an initial control frame from an AP, the station may not transmit a response frame to the initial control frame if it intends to transmit low-latency traffic to the AP. If the station receives an initial control frame from an AP, the station may not be permitted to transmit a response frame to the initial control frame if it intends to transmit low-latency traffic to a station other than the AP.

[0172] These examples can prevent abuse of transmissions via preemption. Furthermore, they can minimize the damage caused by delayed transmissions due to transmissions via preemption.

[0173] FIG. 12 shows an operation in which a station according to an embodiment of the present invention does not transmit a response frame to an initial control frame.

[0174] The first station (STA1) transmits an RTS frame to the second station (STA2). At this time, the second station (STA2) does not transmit a CTS frame for the initial control frame in order to transmit low-latency traffic. The second station (STA2) may have determined that all of the previously described pre-defined conditions are satisfied. Since the first station (STA1) did not receive a CTS frame in response to the RTS frame, it performs channel access again. The second station (STA2) resumes channel access and transmits an RTS frame to the first station (STA1). The first station (STA1) transmits a CTS frame to the second station (STA2) in response to the RTS frame. The second station (STA2) transmits a low-latency PPDU to the first station (STA1) and receives an ACK frame from the first station (STA1).

[0175]

[0176] According to the embodiments described above, if the preemption station does not transmit a response to the initial control frame, a problem may arise when the TXOP holder station also attempts to transmit low-latency traffic. Specifically, even if the TXOP holder station attempts to transmit traffic with a higher priority than the traffic the preemption station is attempting to transmit, the preemption station may cause transmission delays. An embodiment that can prevent this is described below.

[0177] A station may include information about traffic to be exchanged in a frame exchange sequence initiated by the initial control frame in an initial control frame. Specifically, the station may include information about traffic to be exchanged in a frame exchange sequence in another frame included in at least one of the payload of the initial control frame, the MAC header, or the PPDU including the initial control frame. The information about traffic may be information about the type of traffic. Specifically, the information about traffic may include information about whether the traffic is low-latency traffic, the TID of the traffic, the AC of the traffic, and the priority of the traffic. Priorities may be assigned to each TID for each BSS. For example, a specific BSS may designate TID values ​​0 to 3 as the lowest priority, TID values ​​4 to 5 as the medium priority, and TID values ​​6 to 7 as the highest priority. In this case, a station that is a TXOP holder may include information indicating the priority of the traffic to be exchanged in the frame exchange sequence in the initial control frame.

[0178] A preemption station may determine whether to transmit a response frame to an initial control frame based on information about the traffic indicated by the initial control frame. Specifically, the preemption station may determine whether a predefined condition according to the embodiments described above and a condition based on information about the traffic indicated by the initial control frame are satisfied. At this time, if the predefined condition and the condition based on the information about the traffic are satisfied, the station may not transmit a response frame to the initial control frame. If either of the predefined condition and the condition based on the information about the traffic is not satisfied, the station may not be permitted to not transmit a response frame to the initial control frame. In a specific embodiment, if the initial control frame indicates that the traffic to be exchanged in the frame exchange sequence is low-latency traffic, the station may not be permitted to not transmit a response frame to the initial control frame. At this time, if the initial control frame indicates that the traffic to be exchanged in the frame exchange sequence is not low-latency traffic, the station may not transmit a response frame to the initial control frame. In another specific embodiment, if the initial control frame indicates that the priority of the traffic to be exchanged in the frame exchange sequence is equal to or higher than the priority of the traffic to be transmitted by the preemption station, the preemption station may not be permitted to not transmit a response frame to the initial control frame. In this case, if the initial control frame indicates that the priority of the traffic to be exchanged in the frame exchange sequence is lower than the priority of the traffic to be transmitted by the preemption station, the preemption station may not transmit a response frame to the initial control frame.

[0179] Additionally, a station holding a TXOP may indicate through an initial control frame whether it is permissible to not transmit a response frame to the initial control frame. In this case, if the initial control frame indicates that it is permissible to not transmit a response frame to the initial control frame, the preempting station may not transmit a response to the initial control frame.

[0180] FIG. 13 illustrates an operation of a station according to an embodiment of the present invention to indicate the type of traffic to be exchanged in a frame exchange sequence initiated by an initial control frame.

[0181] In the embodiment of FIG. 13, the first station (STA1) successfully accesses a channel for transmitting low-latency traffic. The first station (STA1) transmits an initial control frame, which indicates that low-latency traffic will be exchanged in the frame exchange sequence initiated by the initial control frame. The second station (STA2), which is preparing to transmit low-latency traffic, transmits a response frame according to the information indicated by the initial control frame.

[0182]

[0183] <Frame sequence adjustment to ensure priority transmission of low-latency traffic>

[0184] In the previously described embodiment, the station responding to the TXOP can determine whether to perform transmission via preemption. Considering that the station holding the TXOP succeeds in the channel access procedure first, fairness may be an issue. Therefore, in a specific embodiment, the station that transmitted the initial control frame can determine whether to perform transmission via preemption.

[0185] When a preemption station receives an initial control frame, the preemption station may transmit a response frame indicating information about traffic to be transmitted via preemption as a response to the initial control frame. The information about the traffic to be transmitted via preemption may be information about the type of traffic. Specifically, the information about the traffic may include information about whether the traffic is low-latency traffic, information about the TID of the traffic, information about the AC of the traffic, and information about the priority of the traffic. In another specific embodiment, the information about the traffic may be information indicating whether the preemption station transmits traffic before the traffic to be exchanged by the TXOP holder via preemption. Specifically, the station may include information about traffic to be exchanged in the frame exchange sequence in at least one of the payload of the initial control frame, the MAC header, or a frame included in the PPDU including the initial control frame. A station that is a TXOP holder may receive the response frame and adjust the frame exchange sequence based on the information about the traffic indicated by the response frame. At this time, the station that is a TXOP holder may trigger transmission of the station that transmitted the response frame.

[0186] The format of the response frame to the initial control frame may be a predefined format according to the initial control frame. For example, a CTS frame may be specified as a response to an RTS frame or an MU-RTS frame. When the AP receives the initial control frame, the AP may indicate whether to perform transmission via preemption by the type of frame transmitted to the station that transmitted the response frame. If the AP intends to perform transmission via preemption, the AP may transmit a CTS-to-Self frame in which the receiver address of the CTS frame is the address of the AP as a response frame. A station that receives the CTS-to-Self frame may determine that the AP intends to perform frame exchange first within the TXOP acquired by the station. In addition, if the AP intends to perform transmission via preemption to a station other than the station that transmitted the initial control frame, the AP may transmit an MU-RTS frame or an RTS frame as a response frame to the initial control frame. For example, an AP may receive an RTS frame from a first station and the AP may attempt to transmit low-latency traffic to a second station. In response to the RTS frame, the AP may transmit an RTS frame indicating the second station as the recipient. In response to the RTS frame, the AP may receive an RTS frame from a first station and the AP may attempt to transmit low-latency traffic to the first and second stations. In response to the RTS frame, the AP may transmit an MU-RTS frame indicating the first and second stations. In this case, the User Info field of the MU-RTS frame may indicate the first and second stations.

[0187] Additionally, an AP, which is a TXOP holder, can receive a response frame from a non-AP station, which is a TXOP responder, and allocate an RU (resource unit) or TXOP to the non-AP station based on information about the traffic indicated by the response frame. Specifically, the AP can transmit a basic trigger frame or an MU-RTS TXS trigger frame to the non-AP station based on information about the traffic indicated by the response frame.

[0188] Additionally, a non-AP station that is a TXOP holder may receive a response frame from an AP that is a TXOP responder, and allow the AP's transmission based on information about the traffic indicated by the response frame. At this time, the non-AP station may implicitly accept the AP's transmission. Specifically, the AP may transmit a response frame indicating that the AP will perform transmission before the non-AP station's traffic transmission. At this time, the non-AP station may not transmit a UL PPDU within the SIFS interval of the response frame, and the AP may transmit a low-latency traffic PPDU within the SIFS interval of the response frame. At this time, the intended recipient of the low-latency traffic PPDU may be a non-AP station, not a non-AP station that is a TXOP holder.

[0189] In another specific embodiment, a station that is a TXOP holder may receive a response frame to an initial control frame and, based on information indicated in the response frame, allocate a reverse direction grant (RDG) to a station that is a TXOP responder. At this time, the station that is a TXOP responder may transmit low-latency traffic as an RD responder.

[0190] In the embodiments described above, whether transmission via preemption is permitted is determined by the AP regardless of whether the TXOP holder is an AP. This may be because the AP can exchange frames with multiple non-AP stations, but non-AP stations can only exchange frames with the AP. Furthermore, while the AP can allocate RUs and trigger transmissions by transmitting a trigger frame to a non-AP station, it may be difficult for a non-AP station to actively trigger transmissions from the AP outside of the RDG.

[0191] When transmitting low-latency traffic, a preempting station can use the More Data subfield of the MAC header to indicate whether there is additional low-latency traffic to transmit. At this time, the More Data subfield of the MAC header indicates whether low-latency traffic is queued and is not used for operations related to power save mode. If the More Data subfield of the frame transmitted by a station that is a TXOP responder indicates the presence of low-latency traffic, the station that is a TXOP holder can allocate resources to enable the station that is a TXOP responder to perform additional transmission. Specifically, the station that is a TXOP holder can allocate a TXOP to the station that is a TXOP responder or allocate an RU or an RDG by transmitting a trigger frame.

[0192] FIG. 14 illustrates an operation of a non-AP station, which is a TXOP responder, transmitting a low-latency traffic PPDU through preemption according to an embodiment of the present invention.

[0193] In the embodiment of FIG. 14, the AP transmits an RTS frame after completing a channel access procedure before a non-AP station. The non-AP station transmits a CTS frame to the AP in response to the RTS frame. At this time, the non-AP station includes information regarding low-latency traffic to be transmitted via preemption in the RTS frame. The AP determines that the non-AP station intends to transmit low-latency traffic via preemption based on the received CTS frame. The AP transmits a BSRP (buffer status report poll) frame to the non-AP station to determine the buffer status of the non-AP station. The non-AP station transmits a BSR frame to the AP in response to the BSRP frame. The AP transmits a trigger frame to the non-AP station based on the received BSR frame. The non-AP station transmits a TB PPDU including low-latency traffic via an RU allocated by the trigger frame.

[0194] FIG. 15 shows an operation in which an AP, which is a TXOP responder, transmits a low-latency traffic PPDU through preemption according to an embodiment of the present invention.

[0195] In the embodiment of FIG. 15, a non-AP station transmits an RTS frame after completing a channel access procedure before the AP. The AP transmits a CTS-to-self frame as a response frame to the RTS frame, indicating that the AP will transmit low-latency traffic before the non-AP station transmits traffic through frame exchange. The non-AP station receives the CTS-to-self frame and waits for the AP to transmit based on the CTS-to-self frame. The AP transmits a low-latency traffic PPDU at a SIFS interval with the CTS-to-self frame. After completing the transmission of the low-latency traffic PPDU, the AP transmits a TXS frame to allocate the remaining TXOP to the non-AP station. The non-AP station transmits a CTS frame in response to the TXS frame and transmits a UL PPDU to the AP.

[0196] FIG. 16 illustrates an operation in which an AP, which is a TXOP responder, transmits low-latency traffic PPDUs to multiple stations through preemption according to an embodiment of the present invention.

[0197] In the embodiment of FIG. 16, the first non-AP station (Non-AP STA1) completes a channel access procedure before the AP and then transmits an RTS frame. The AP transmits an MU-RTS frame as a response frame to the RTS frame, thereby indicating that the AP should transmit low-latency traffic to the second non-AP station (Non-AP STA2) before the first non-AP station (Non-AP STA1) transmits traffic through frame exchange. At this time, the MU-RTS frame indicates the first non-AP station (Non-AP STA1) and the second non-AP station (Non-AP STA2) through the User Info field. The first non-AP station (Non-AP STA1) and the second non-AP station (Non-AP STA2) transmit a CTS frame to the AP. The AP transmits a low-latency traffic PPDU at an SIFS interval from the CTS frame. After completing the transmission of the low-latency traffic PPDU, the AP transmits a TXS frame to allocate the remaining TXOP to the first non-AP station (Non-AP STA1). The first non-AP station (Non-AP STA1) transmits a CTS frame in response to the TXS frame and transmits a UL PPDU to the AP.

[0198] FIG. 17 shows the format of a Control field of a MAC header including information about low-latency traffic according to an embodiment of the present invention.

[0199] In the embodiments described above, the TXOP holder may include information indicating the traffic to be exchanged in the frame exchange sequence initiated by the initial control frame via the initial control frame. Furthermore, the preemption station may include information regarding low-latency traffic in the response frame to the initial control frame. Such traffic information may be included in the Control field of the frame.

[0200] As shown in (a) of FIG. 17, the Frame Control field may include at least one of a Protocol Version subfield, a Type subfield, a Subtype subfield, a To DS subfield, a From DS subfield, a More Fragments subfield, a Retry subfield, a Power Management subfield, a More Data subfield, a Protected Frame subfield, and a +HTC subfield. The values ​​of the To DS subfield, the From DS subfield, the More Fragments subfield, and the Retry subfield of the Frame Control field included in the control frame are always set to 0. At least one of the To DS subfield, the From DS subfield, the More Fragments subfield, or the Retry subfield of the Frame Control field included in the control frame may indicate information about the traffic described above. In this case, the information about the traffic may indicate that the station transmitting the control frame intends to transmit low-latency traffic. For example, if the value of any one of the To DS subfield, From DS subfield, More Fragments subfield, and Retry subfield of the Frame Control field is a predefined value, the information about the traffic may indicate that the station transmitting the control frame intends to transmit low-latency traffic. The predefined value may be 1.

[0201] In addition, information about traffic may indicate information related to the TID of traffic to be transmitted by the station transmitting the control frame. At this time, three fields, i.e., three bits, among the To DS subfield, the From DS subfield, the More Fragments subfield, and the Retry subfield may indicate any one of the values ​​0 to 7 of the TID, and one field, i.e., one bit, may indicate that the remaining three fields indicate information related to the TID. Fig. 17 (b) shows such an embodiment. When there are multiple TIDs included in the low-latency traffic, the value of the TID indicated by the three fields may indicate one of the TIDs included in the low-latency traffic. For example, the value of the TID indicated by the three fields may be the TID having the highest index among the plurality of TIDs. In another specific embodiment, the value of the TID indicated by the three fields may be the TID having the highest priority among the plurality of TIDs.

[0202] Additionally, information about traffic can indicate information related to the priority of traffic to be transmitted by a station transmitting a control frame. At this time, the To DS subfield, the From DS subfield, the More Fragments subfield, and the Retry subfield can indicate whether the traffic is low-latency traffic and the priority of the traffic. Two or three fields, i.e., two or three bits, among the To DS subfield, the From DS subfield, the More Fragments subfield, and the Retry subfield can indicate the priority of the traffic, and one field, i.e., one bit, can indicate whether the traffic is low-latency traffic. FIG. 17(c) shows such an embodiment.

[0203] Additionally, an AP that is a TXOP responder can indicate that it will transmit via preemption by using any one of the bits in the To DS subfield, From DS subfield, More Fragments subfield, and Retry subfield. These bits can be referred to as Preemption Indication bits. If the value of the Preemption Indication bit is a predefined value, a non-AP station can determine that the AP will transmit via preemption. The predefined value can be 1.

[0204]

[0205] <Frame exchange sequence adjustment using 1-bit indication>

[0206] When multiple stations indicate to transmit low-latency traffic, the frame exchange order performed within the TXOP acquired by the station that transmitted the initial control frame can be adjusted. This allows transmission of low-latency traffic to be performed with priority. The frame exchange order can be adjusted through at least one of TXOP sharing, a trigger frame, and a reverse direction (RD) protocol. A station that has received the initial control frame can act as a TXOP holder by transmitting a pre-designated frame instead of a response frame to the initial control frame. In this case, the pre-designated frame can be a CTS-to-self frame.

[0207] TXOP sharing is when a TXOP holder allocates a portion of the TXOP acquired by the TXOP holder to another station. At this time, a TXOP responder, which is a station allocated a TXOP, can perform transmission within the shared TXOP. Specifically, the TXOP holder can transmit an MU-RTS TXS frame. If the User Info field of the MU-RTS TXS frame indicates a station, the station that receives the MU-RTS TXS frame can be determined to be a shared responder. The TXOP is shared with the shared responder during the time indicated by the User Info field indicating the shared responder, e.g., the Allocation Duration subfield of the User Info field. The shared responder can operate as a TXOP holder within the shared TXOP.

[0208] In the RD protocol, a station that is a TXOP holder (RD initiator) grants an RDG (RD Grant) to a TXOP responder, and a station that is a TXOP responder can transmit a PPDU using the RDG. At this time, a station that is a TOXP holder can grant an RDG to the TXOP responder by transmitting an MPDU with the RDG subfield set to 1 to the TXOP responder.

[0209] If the TXOP responder does not intend to transmit low-latency traffic, the TXOP holder may not adjust the frame exchange order. In this case, the TXOP responder may transmit a response frame to the initial control frame to the TXOP holder, indicating that it does not intend to transmit low-latency traffic.

[0210] If both the TXOP holder and the TXOP responder intend to transmit low-latency traffic, the TXOP holder may transmit the low-latency traffic of the TXOP holder in priority. After the TXOP holder transmits the low-latency traffic of the TXOP holder, the TXOP holder may trigger the transmission of the low-latency traffic of the TXOP responder. Specifically, the TXOP holder may share the remaining TXOP with the TXOP responder, grant the TXOP responder an RDG, or transmit a trigger frame to the TXOP responder. Through this, the TXOP holder may allow the TXOP responder to transmit low-latency traffic. At this time, the TXOP holder may transmit an initial control frame indicating that it intends to transmit low-latency traffic. In addition, the TXOP responder may transmit a response frame to the initial control frame indicating that it intends to transmit low-latency traffic.

[0211] If the TXOP holder does not intend to transmit low-latency traffic and the TXOP responder intends to transmit low-latency traffic, the TXOP holder can adjust the frame exchange order so that the TXOP responder's low-latency traffic is transmitted first. Specifically, the TXOP holder can allow the TXOP responder to transmit low-latency traffic before transmitting the TXOP holder's traffic. To do this, the TXOP holder can share the remaining TXOP with the TXOP responder, grant the TXOP responder an RDG, or transmit a trigger frame to the TXOP responder.

[0212] In the embodiments described above, the TXOP holder may indicate its intent to transmit low-latency traffic using one bit of the initial control frame. Additionally, the TXOP responder may indicate its intent to transmit low-latency traffic using one bit of the response frame to the initial control frame.

[0213]

[0214] <Frame Exchange Order Adjustment Based on Urgency Assessment of Low-Latency Traffic>

[0215] When both TXOP holders and TXOP responders wish to transmit low-latency traffic, the transmission order must be determined based on the urgency of the low-latency traffic to ensure fairness and low-latency transmission. Examples for this are described below.

[0216] Two stations performing frame exchange may exchange information regarding the urgency of low-latency traffic, and the frame exchange order may be determined based on the exchanged urgency. At this time, the information regarding the urgency may include at least one of information regarding the priority, information regarding the transmission requirement, or the remaining time until the transmission restriction of the low-latency traffic expires. In a specific embodiment, the TXOP holder may determine the frame exchange order by comparing the urgency of the low-latency traffic indicated by the TXOP responder with the urgency of the low-latency traffic of the TXOP holder. At this time, the TXOP holder may not transmit information indicating the urgency of the low-latency traffic of the TXOP holder to the TXOP responder. In the embodiments described above, the TXOP holder or the TXOP responder may indicate the urgency of the low-latency traffic using the Control field of the control frame. In another specific embodiment, a new format frame indicating the urgency of the low-latency traffic may be designated.

[0217] A TXOP responder can transmit a response frame to an initial control frame, which indicates the urgency of low-latency traffic that the TXOP responder intends to transmit. The TXOP holder can compare the urgency of the low-latency traffic indicated in the response frame received from the TXOP responder with the urgency of the low-latency traffic of the TXOP holder. The TXOP holder can determine the frame exchange order based on the comparison result. If the urgency of the low-latency traffic of the TXOP responder is higher than the urgency of the low-latency traffic of the TXOP holder, the TXOP holder can induce the TXOP responder to perform transmission first. Specifically, at least one of RDG assignment, TXOP sharing, or trigger frame transmission described above can be performed.

[0218]

[0219] <Adjusting the frame exchange order for multi-link operation>

[0220] A multi-link device includes one or more stations, each of which operates on a different link. For example, an AP multi-link device may include up to 15 APs. Each AP of the AP multi-link device operates on a different link and can perform the same functions as an independent AP. Each AP of the AP multi-link device operates its own BSS and can associate with a non-AP station. Legacy non-AP stations recognize each AP of the AP multi-link device as an independent AP and can operate in conjunction with each AP. A non-AP multi-link device may include up to 15 non-AP stations. Each non-AP station of the non-AP multi-link device can be associated with each AP of the AP multi-link device. When a non-AP multi-link device and an AP multi-link device are connected on multiple links, the AP multi-link device and the non-AP multi-link device are set up for multi-linking. The AP multi-link device and the non-AP multi-link device can exchange frames on multiple links.

[0221] Enhanced multi-link single-radio (EMLSR) mode is a mode that reduces the performance requirements of non-AP multi-link devices operating on multiple links. EMLSR mode can be applied to each link. Non-AP stations of non-AP multi-link devices operating on links where EMLSR mode is applied perform the operations defined for EMLSR mode. On links where EMLSR mode is applied, non-AP multi-link devices support data frame exchange for only one non-AP station at a time. If data frame exchange is performed on any one of the multiple EMLSR links, data frame exchange is not supported on the remaining links of the multiple EMLSR links. In this way, a multi-link device in EMLSR mode supports operation on multiple links using a single radio.

[0222] A non-AP station operating on a link with EMLSR mode applied may perform channel access or only support reception of an initial control frame in a pre-specified format. The pre-specified format may include at least one of an MU-RTS trigger frame or a BSRP trigger frame transmitted at the basic data rate using a non-HT (duplicated) PPDU with a bandwidth of 20 MHz. The non-AP station receives the initial control frame and supports frame exchange other than the initial control frame on the link on which the initial control frame was received. For example, the non-AP station may receive the initial control frame and then receive an EHT PPDU with a bandwidth of 80 MHz on the link, or may receive the trigger frame and transmit a TB PPDU. The initial control frame may include a padding field. This allows the non-AP station to secure time required to transition to a state supporting frame exchange other than reception of control frames in a pre-specified format.

[0223] When an AP multi-link device attempts to initiate a frame exchange sequence on one of the EMLSR links of a non-AP multi-link device, the AP multi-link device transmits an initial control frame in a predefined format to the non-AP multi-link device. As described above, the initial control frame may include a padding field. The non-AP multi-link device receives the initial control frame in the predefined format on one of the EMLSR links and switches to a state that supports frame exchange other than the initial exception frame in the predefined format on that link. At this time, the non-AP multi-link device does not support channel access and initial control frame reception on the remaining EMLSR links except for that link.

[0224] When a non-AP multi-link device receives an initial control frame on the first link of an EMLSR link, the non-AP multi-link device may not be able to transmit low-latency traffic on the second link of the EMLSR link even if it attempts to do so. This may result in a delay in transmission of low-latency traffic on the second link.

[0225] Additionally, in-device interference that occurs when a station transmits on the first link of a non-simulatneous transmit and receive (NSTR) link pair makes channel access and reception impossible on the second link of the NSTR link pair. Similar to the EMLSR link, a multi-link device that receives an initial control frame on the first link of the NSTR link pair may not be able to transmit low-latency traffic on the second link of the NSTR link pair. As a result, transmission of low-latency traffic may be delayed.

[0226] In this way, when one station of the multi-link device receives the initial control frame, transmission of low-latency traffic that other stations of the multi-link device are trying to transmit may be delayed.

[0227] It may be permissible for a multi-link device not to transmit a response to an initial control frame. Specifically, if a first station of a multi-link device intends to transmit low-latency traffic, it may be permissible for a second station of the multi-link device not to transmit a response to an initial control frame received by the second station. If the first link and the second link satisfy a pre-specified condition, it may be permissible for the second station not to transmit a response to the initial control frame received by the second station. In a specific embodiment, a non-AP multi-link device that receives an initial control frame in a pre-specified format on a first EMLSR link and intends to transmit low-latency traffic on a second EMLSR link may not transmit a response to the initial control frame on the first EMLSR link. Accordingly, the non-AP multi-link device may not switch to a mode in which frames other than frames in a pre-specified format are exchanged on the first EMLSR link. Additionally, these embodiments may be limited to the case where the intended recipient of the initial control frame or the non-AP station that triggers the transmission is only a station of a non-AP multi-link device operating on the first EMLSR link. For example, these embodiments may be limited to the case where the User Info field of the MU-RTS trigger frame or the BSRP trigger frame indicates only a station of a non-AP multi-link device operating on the first EMLSR link.

[0228] In a specific embodiment, a non-AP multi-link device that receives an initial control frame in a pre-specified format on a first link of an NSTR link pair and intends to transmit low-latency traffic on a second EMLSR link of the NSTR link pair may not transmit a response to the initial control frame on the first link. Such embodiments may be limited to a case where the intended recipient of the initial control frame or the non-AP station that triggers the transmission is only a station of the non-AP multi-link device operating on the first link. For example, such embodiments may be limited to a case where the User Info field of the MU-RTS trigger frame or the BSRP trigger frame indicates only a station of the non-AP multi-link device operating on the first link.

[0229] When the conditions for TID-to-link mapping are satisfied, if a first station of a multi-link device intends to transmit low-latency traffic, it may be allowed for a second station of the multi-link device not to transmit a response to an initial control frame received by the second station. Specifically, the embodiments described above may be applied only when the TID of the low-latency traffic is not mapped to a link on which the initial control frame is transmitted. In a specific embodiment, if a first station of a multi-link device transmits low-latency traffic and the TID of the low-latency traffic is not mapped to a second link, it may be allowed for a second station of the multi-link device not to transmit a response to the initial control frame received by the second station. If the TID of the low-latency traffic is mapped to the second link, the second station may transmit a response to the initial control frame and transmit the low-latency traffic through the second link. Specifically, the embodiments regarding frame exchange order adjustment described above may be applied.

[0230] Mapping a specific TID to a specific link indicates that an MSDU with that specific TID can be transmitted through the specific link. The TID-to-link mapping of a non-AP multi-link device can be changed by TID-to-Link mapping negotiation performed by the AP multi-link device and the non-AP multi-link device or by advertised TID-to-Link mapping indicated by the AP multi-link device. If the non-AP multi-link device does not perform TID-to-Link mapping negotiation with the AP multi-link device and does not receive advertised TID-to-Link mapping information from the AP multi-link device, the non-AP multi-link device has a default TID-to-Link mapping state. The advertised TID-to-Link mapping information can be indicated through the TID-To-Link mapping element of the beacon frame. The default TID-to-Link mapping state is a state in which all TIDs (TID0 to TID7) are mapped to all setup links.

[0231]

[0232] <Frame Exchange Order Management for Legacy Stations>

[0233] Even if a station transmits a response frame to an initial control frame indicating that it intends to transmit low-latency traffic, as in the embodiments described above, to a legacy station, the legacy station cannot determine that it intends to transmit low-latency traffic based on the response frame. Therefore, the frame exchange order cannot be adjusted, and the transmission of low-latency traffic may be delayed. A station that has received an initial control frame from a legacy station may be permitted not to transmit a response to the initial control frame. In this case, the station may be an AP. This allows the AP to prevent the legacy station from starting a TXOP. However, if a response frame to the initial control frame is not transmitted, the legacy station loses the opportunity to acquire a TXOP and may be disadvantaged in subsequent channel access procedures. Specifically, the legacy station must recognize the transmission failure, adjust the CW (contention window), and perform the channel access procedure again. This behavior of a station not transmitting a response frame to an initial control frame received from a legacy station can compromise fairness with the legacy station. Therefore, it may be permissible for a station not to transmit a response frame to an initial control frame received from a legacy station when a predefined condition is satisfied.

[0234] The predefined conditions may include conditions related to the R-TWT SP. Specifically, if the TXOP of the initial control frame transmitted by the legacy station overlaps with the R-TWT SP, the station may not transmit a response frame for the initial control frame. Furthermore, if the station receives the initial control frame transmitted by the legacy station within the R-TWT SP, the station may not transmit a response frame for the initial control frame. Furthermore, if the station receives the initial control frame transmitted by the legacy station within the R-TWT SP of an overlapping BSS (OBSS), the station may not transmit a response frame for the initial control frame. Furthermore, if the TXOP of the initial control frame transmitted by the legacy station overlaps with the R-TWT SP of the OBSS, the station may not transmit a response frame for the initial control frame. Furthermore, in this embodiment, a legacy station may refer to a station that does not support R-TWT operation.

[0235] In the embodiments described above, the station can determine the time interval of the TXOP initiated by the initial control frame using the value indicated by the Duration / ID field of the initial control frame. The embodiments regarding the OBSS R-TWT SP will be described in detail in the description of the embodiments regarding Co-RTWT (coordinate R-TWT) later.

[0236] R-TWT SP is a TWT SP with enhanced protection mechanisms for transmitting latency-sensitive traffic. R-TWT is a type of broadcast TWT. When R-TWT SP is operated in a BSS, member stations of the R-TWT SP can only transmit frames corresponding to the TID indicated by the AP within the R-TWT SP. In addition, non-AP stations can terminate the TXOP they acquired before the R-TWT SP starts.

[0237] In the embodiments described above, it was assumed that TXOP is initiated with an initial control frame exchange. However, TXOP may be initiated without an initial control frame exchange. For example, a station may transmit a data frame immediately after a successful channel access procedure. Therefore, in such a case, the embodiments described above that assume an initial control frame exchange may not be applicable. An AP may set operating parameters for a station of a BSS operated by the AP so that TXOP is initiated with the transmission of an RTS frame. At this time, the AP may set a value of the TXOP Duration RTS Threshold subfield of the HE Operation Parameters field so that TXOP is initiated from the transmission of an RTS frame. For example, the AP may set the value of the TXOP Duration RTS Threshold subfield to 1. A value of 1 in the TXOP Duration RTS Threshold subfield indicates 32 us.

[0238]

[0239] <R-TWT SP를 고려한 초기 제어 프레임에 대한 응답>

[0240] The embodiments described above can facilitate low-latency traffic transmission by a TXOP holder or TXOP responder in a TXOP initiated with an initial control frame. However, it is difficult to facilitate low-latency traffic transmission by stations that are not TXOP holders or TXOP responders. An embodiment of adjusting the frame exchange order using the R-TWT SP is needed.

[0241] First, the R-TWT SP is described. The AP can transmit a TWT element to indicate information necessary for scheduling the R-TWT. At this time, the AP can specify a TID that is allowed to be transmitted in the R-TWT SP. The information regarding the R-TWT scheduling can include at least one of a target wake time, which is the starting point of the R-TWT SP, a TWT wake duration, which is the maintenance time of the R-TWT SP, a TWT wake interval, which is the repetition period of the R-TWT SP, or restricted TWT traffic information, which is the TID of traffic that is allowed to be transmitted in the R-TWT SP.

[0242] To prevent stations that do not support R-TWT SP from accessing the channel, the AP can set a quiet interval that starts at the same time as the R-TWT SP. This quiet interval is referred to as an overlapping quiet interval. The duration of the overlapping quiet interval is 1 TU (time unit, 1024 us). Legacy stations with a quiet interval set terminate TXOP before the start of the overlapping quiet interval and do not transmit during the overlapping quiet interval.

[0243] The TXOP holder can adjust the TXOP termination time based on the start time of the R-TWT SP announced by the AP. Specifically, the TXOP holder can terminate the TXOP before the start of the R-TWT SP. In addition, the AP, which is the TXOP holder, may not terminate the TXOP if it plans to transmit the TID allowed to be transmitted in the R-TWT SP during the remaining TXOP.

[0244] If a non-AP station determines that the frame exchange sequence to be initiated by the non-AP station will not end before the start of the R-TWT SP, the non-AP station does not transmit a PPDU. At this time, the non-AP station that does not transmit a PPDU generates a new backoff counter.

[0245] When an AP or a non-AP station receives an initial control frame from a non-AP station or a peer non-AP station receives an initial control frame from a non-AP station, if the frame exchange sequence initiated by the initial control frame overlaps with the R-TWT SP, the AP or the non-AP station may not transmit a response frame to the initial control frame. When a non-AP station receives an initial control frame from an AP, the AP may transmit a response frame to the initial control frame even if the frame exchange sequence initiated by the initial control frame overlaps with the R-TWT SP. At this time, the AP may schedule the frame exchange sequence initiated by the initial control frame in consideration of the R-TWT SP. Specifically, the AP may schedule the frame exchange procedure initiated by the initial control frame to end before the start of the R-TWT SP. In addition, the AP may schedule the TID of the traffic to be exchanged in the frame exchange procedure initiated by the initial control frame to be a TID that is allowed to be transmitted within the R-TWT SP. A non-AP station that receives an initial control frame can determine the end point of the frame exchange sequence initiated by the initial control frame based on the value of the Duration / ID field of the initial control frame.

[0246]

[0247] FIG. 18 shows a station transmitting a response frame to an initial control frame based on an R-TWT SP according to an embodiment of the present invention.

[0248] In the embodiment of FIG. 18, the AP transmits a beacon frame scheduling R-TWT. The R-TWT SP scheduled by the AP starts at t0. The non-AP station (non-AP STA) succeeds in the channel access procedure, but determines that the frame exchange sequence to be started will not end before the scheduled R-TWT SP. Therefore, the non-AP station (non-AP STA) gives up transmission and performs a new channel access procedure. Specifically, the non-AP STA generates a new backoff counter. The legacy non-AP STA that does not support the R-TWT SP is not aware of the scheduling of the R-TWT SP. The legacy non-AP STA succeeds in the channel access procedure and transmits an initial control frame (ICF). The AP determines that the end point of the frame exchange initiated by the initial control frame (ICF) is after the start of the R-TWT SP. The AP can determine that the end point of the frame exchange initiated by the Initial Control Frame (ICF) is after the R-TWT SP based on the value of the Duration / ID field of the Initial Control Frame (ICF). Therefore, the AP does not transmit a response frame (ICR) to the Initial Control Frame (ICF).

[0249]

[0250] <Co-RTWT SP를 고려한 초기 제어 프레임에 대한 응답>

[0251] Co-RTWT can be established through negotiation between APs operating adjacent BSSs. Co-RTWT is a multi-AP coordinated operation to enhance the effectiveness of R-TWT through cooperation between APs. A station can transmit a response frame to an initial control frame based on Co-RTWT. First, a method for establishing Co-RTWT will be described. A first AP transmits a coordination request including information about an R-TWT scheduled by the first AP to a second AP. At this time, the information about the R-TWT may include at least one of information about the start time of the R-TWT SP, the duration of the R-TWT SP, and the interval of the R-TWT SP. The second AP can accept or reject the cooperation request. If the second AP accepts the cooperation request, the second AP terminates the TXOP before the start of the R-TWT SP of the first AP. In addition, if the second AP accepts the cooperation request, the second AP does not initiate frame exchange that is not expected to end before the start of the R-TWT SP of the first AP. Specifically, it may not perform transmission even if the value of the backoff counter becomes 0. At this time, the second AP performs a new channel access procedure. Specifically, the second AP generates a new backoff counter. In addition, the second AP transmits information about the R-TWT SP of the first AP through a beacon frame. Specifically, if a non-AP station supporting R-TWT belongs to the BSS operated by the second AP, the second AP transmits information about the R-TWT SP of the first AP through a beacon frame. A non-AP station belonging to the BSS operated by the second AP cannot distinguish between the R-TWT of the first AP and the R-TWT scheduled by the second AP.Therefore, non-AP stations belonging to the BSS operated by the second AP can treat the R-TWT SP of the first AP in the same way as the R-TWT SP scheduled by the second AP. For convenience of explanation, the R-TWT of the second AP is referred to as co-RTWT.

[0252] If the second AP receives an initial control frame and the frame exchange initiated by the initial control frame overlaps with co-RTWT, the second AP may not transmit a response frame to the initial control frame. In this case, the second AP may determine the duration and end time of the frame exchange initiated by the initial control frame based on the Duration / ID field of the initial control frame. If any of the following cases applies, the second AP may determine that the frame exchange initiated by the initial control frame overlaps with co-RTWT.

[0253] 1) If the start point of the frame exchange starting with the initial control frame is earlier than the start point of the co-RTWT SP, and the end point of the frame exchange is after the start point of the co-RTWT SP.

[0254] 2) If the start point of the frame exchange starting from the initial control frame is within the co-RTWT SP and the end point of the frame exchange is within the co-RTWT SP.

[0255] 3) If the start point of the frame exchange starting with the initial control frame is within the co-RTWT SP and the end point of the frame exchange is after the co-RTWT SP.

[0256] In a specific embodiment, the second AP may not transmit a response frame to the initial control frame only if any of the three cases described above applies. This is because not transmitting a response frame to the initial control frame may degrade the performance of the entire BSS and harm fairness.

[0257] FIG. 19 shows a station according to an embodiment of the present invention determining whether to transmit a response frame to an initial control frame based on a Co-RTWT SP.

[0258] In the embodiment of FIG. 19, the AP receives a multi-AP cooperation request frame (MAPC Req.) from an AP of an OBSS (OBSS AP). At this time, the multi-AP cooperation request frame (MAPC Req.) includes information about an R-TWT SP (Co-RTWT SP) scheduled by the AP of the OBSS (OBSS AP). The AP transmits a multi-AP cooperation response frame (MAPC Resp.) to the AP of the OBSS (OBSS AP). At this time, the multi-AP cooperation response frame (MAPC Resp.) acknowledges protection of the R-TWT SP (Co-RTWT SP) scheduled by the AP of the OBSS (OBSS AP). The AP transmits a beacon frame including information about the R-TWT SP (Co-RTWT SP). The AP receives an initial control frame (ICF) from a non-AP station (non-AP STA). It is determined that the frame exchange initiated by the Initial Control Frame (ICF) overlaps with the R-TWT SP (Co-RTWT SP), and a response frame (ICR) to the Initial Control Frame (ICF) is not transmitted. This allows the frame exchange performed in the R-TWT SP (Co-RTWT SP) to be protected even in the BSS operated by the first AP.

[0259]

[0260] While the present invention has been described using wireless LAN communication as an example, it is not limited thereto and can be equally applied to other communication systems, such as cellular communication. Furthermore, while the methods, devices, and systems of the present invention have been described with reference to specific embodiments, some or all of the components and operations of the present invention can be implemented using a computer system with a general-purpose hardware architecture.

[0261] The features, structures, effects, etc. described in the embodiments above are included in at least one embodiment of the present invention, and are not necessarily limited to just one embodiment. Furthermore, the features, structures, effects, etc. exemplified in each embodiment can be combined or modified in other embodiments by those skilled in the art to which the embodiments pertain. Therefore, the contents related to such combinations and modifications should be construed as being included within the scope of the present invention.

[0262] Although the above has been described focusing on embodiments, these are merely examples and do not limit the present invention. Those skilled in the art to which the present invention pertains will appreciate that various modifications and applications not exemplified above are possible without departing from the essential characteristics of the present embodiment. For example, each component specifically shown in the embodiments can be modified and implemented. In addition, differences related to such modifications and applications should be interpreted as being included within the scope of the present invention defined in the appended claims.

Claims

1. At a station that is not a TXOP holder, Transmitter and receiver; and Contains a processor, The above processor Receive an initial control frame that initiates frame exchange, If a pre-specified condition is satisfied, a response frame to the initial control frame is not transmitted, If the pre-specified conditions are not satisfied, the response frame is transmitted. Station.

2. In paragraph 1, The above pre-specified conditions include cases where the R-TWT (restricted-target wake time) scheduled by the AP (access point) of the BSS (basic service set) to which the station belongs through a beacon frame and the frame exchange initiated by the initial control frame overlap. Station.

3. In paragraph 2, The above R-TWT is an R-TWT scheduled by the AP of the OBSS (overlapping BSS). Station.

4. In paragraph 2, When the initial control frame is received from the AP, the processor transmits the response frame. Station.

5. In paragraph 4, The above initial control frame initiates the exchange of traffic corresponding to the TID allowed in transmission in the SP (service period) of the R-TWT. Station.

6. In paragraph 1, The above station is a station affiliated to a multi-link device, The above predefined conditions include cases where the station operates on one of the NSTR (non-simultaneous transmit and receive) link pairs, and the station performs frame exchange on another link of the NSTR link pair when receiving the initial control frame. Station.

7. In paragraph 1, The above station is a station affiliated to a multi-link device, The above pre-specified conditions include that the station operates in enhanced multi-link single radio (EMLSR) mode, receives the initial control frame on the first link, and performs frame exchange on the second link on which the multi-link device operates. Station.

8. In paragraph 1, The above station is a station affiliated to a multi-link device, and when receiving the initial control frame on the first link and trying to transmit low-latency traffic on the second link, the pre-specified condition includes that the low-latency traffic is not mapped to the first link. Station.

9. In the operation method of a station other than a TXOP holder, A step of receiving an initial control frame to initiate frame exchange; A step of not transmitting a response frame to the initial control frame if a pre-specified condition is satisfied; and Including a step of transmitting the response frame if the pre-specified condition is not satisfied. How it works.

10. In paragraph 9, The above pre-specified conditions include cases where the R-TWT (restricted-target wake time) scheduled by the AP (access point) of the BSS (basic service set) to which the station belongs through a beacon frame and the frame exchange initiated by the initial control frame overlap. How it works.

11. In paragraph 10, The above R-TWT is an R-TWT scheduled by the AP of the OBSS (overlapping BSS). How it works.

12. In paragraph 10, If the pre-specified condition is not satisfied, the step of transmitting the response frame is When receiving the initial control frame from the AP, the processor includes a step of transmitting the response frame. How it works.

13. In paragraph 12, The above initial control frame initiates the exchange of traffic corresponding to the TID allowed in transmission in the SP (service period) of the R-TWT. How it works.

14. In paragraph 9, The above station is a station affiliated to a multi-link device, The above predefined conditions include cases where the station operates on one of the NSTR (non-simultaneous transmit and receive) link pairs, and the station performs frame exchange on another link of the NSTR link pair when receiving the initial control frame. How it works.

15. In paragraph 9, The above station is a station affiliated to a multi-link device, The above pre-specified conditions include that the station operates in enhanced multi-link single radio (EMLSR) mode, receives the initial control frame on the first link, and performs frame exchange on the second link on which the multi-link device operates. How it works.

16. In paragraph 9, The above station is a station affiliated to a multi-link device, and when receiving the initial control frame on the first link and trying to transmit low-latency traffic on the second link, the pre-specified condition includes that the low-latency traffic is not mapped to the first link. How it works.

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