Wireless communication method for supporting power saving operation and wireless communication terminal using same

Abstract

According to the present invention, an access point (AP) multi-link device that wirelessly communicates with a non-AP station multi-link device and comprises a plurality of APs, comprises: a transmission and reception unit; and a processor. The processor operates a first AP, which is any one of the plurality of APs, in a scheduled power saving mode. In the scheduled power saving mode, the first AP can maintain an awake state in a predetermined awake period, and enter a doze state in a period other than the awake period.

Description

Wireless communication method supporting power saving operation and wireless communication terminal using the same

[0001] The present invention relates to a wireless communication method supporting power saving operation 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, the Institute of Electrical and Electronics Engineers (IEEE) 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 object of one embodiment of the present invention is to provide a wireless communication method supporting power saving operation and a wireless communication terminal using the same.

[0010] According to one embodiment of the present invention, an AP multi-link device that wirelessly communicates with a non-AP (access point) station multi-link device and includes a plurality of APs, the AP multi-link device including a transceiver; and a processor. The processor operates a first AP, which is one of the plurality of APs, in a scheduled power saving mode. In the scheduled power saving mode, the first AP maintains an awake state during a pre-designated awake time period, and can enter a dull state during a time period other than the awake time period.

[0011] The first AP can maintain an awake state at the target beacon transmission time (TBTT) of the basic service set (BSS) operated by the first AP.

[0012] The above first AP may perform the frame exchange in a time period other than the awake time period if the frame exchange started in the awake time period does not end in the awake time period.

[0013] The processor may transmit a management frame including a first element including information regarding the awake time interval to the non-AP station multi-link device.

[0014] The first element may include information about an interval of the awake time period and information about a duration of the awake time period.

[0015] The above first AP can operate in dynamic power saving mode during the awake time period.

[0016] In the above dynamic power saving mode, the first AP can switch back and forth between the listening mode and the enhanced mode. The first AP can only support reception of initiation control frames transmitted by a pre-designated transmission method in the listening mode, and can support reception other than reception of initiation control frames transmitted by the pre-designated transmission method in the enhanced mode.

[0017] The first AP may receive the initiation control frame in the listening mode and immediately switch to the enhanced mode if a pre-specified condition is satisfied.

[0018] The above pre-specified conditions may be such that low-latency traffic exchange is scheduled to be performed in a frame exchange sequence initiated by the above initiation control frame.

[0019] According to an embodiment of the present invention, a non-AP station multi-link device that wirelessly communicates with an AP (access point) multi-link device and includes a plurality of non-AP stations includes a transceiver; and a processor. The processor performs frame exchange with the first AP when the first AP, which is one of the APs of the AP multi-link device, operates in a scheduled power saving mode and the first AP operates in an awake time period. In the scheduled power saving mode, the first AP maintains an awake state during a pre-designated awake time period and can enter a dull state during a time period other than the awake time period.

[0020] The first AP can maintain an awake state at the target beacon transmission time (TBTT) of the basic service set (BSS) operated by the first AP.

[0021] The above processor may perform the frame exchange in a time period other than the awake time period if the frame exchange started in the awake time period does not end in the awake time period.

[0022] The processor may receive a management frame from the AP multi-link device, the management frame including a first element including information regarding the awake time interval.

[0023] The first element may include information about an interval of the awake time period and information about a duration of the awake time period.

[0024] The first AP operates in a dynamic power saving mode during the awake time period, and in the dynamic power saving mode, the first AP can switch back and forth between a listening mode and an enhanced mode. When the first AP operates in the listening mode, the processor can transmit an initiation control frame to the first AP using a pre-designated transmission method.

[0025] The processor may receive a response frame from the first AP in response to the initiation control frame, wherein the response frame may instruct the first AP to receive the initiation control frame and immediately switch from the listening mode to the enhanced mode.

[0026] The first AP may immediately switch from the listening mode to the enhanced mode upon receiving the initiation control frame and satisfying a predefined condition. The predefined condition may be that low-latency traffic exchange is scheduled to be performed in the frame exchange sequence initiated by the initiation control frame.

[0027] According to an embodiment of the present invention, a method of operating an AP multi-link device that wirelessly communicates with a non-AP (access point) station multi-link device and includes a plurality of APs includes the step of operating a first AP among the plurality of APs in a scheduled power saving mode. In the scheduled power saving mode, the first AP maintains an awake state during a pre-designated awake time period, and can enter a dull state during a time period other than the awake time period.

[0028] The first AP can maintain an awake state at the target beacon transmission time (TBTT) of the basic service set (BSS) operated by the first AP.

[0029] The step of operating the first AP in the scheduled power saving mode may include a step of performing the frame exchange in a time period other than the awake time period, if the frame exchange started in the awake time period does not end in the awake time period.

[0030] One embodiment of the present invention provides a wireless communication method for efficiently supporting relay communication and a wireless communication terminal using the same.

[0031] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0032] Figure 2 illustrates a wireless LAN system according to another embodiment of the present invention.

[0033] Figure 3 shows the configuration of a station according to one embodiment of the present invention.

[0034] Figure 4 shows the configuration of an access point according to one embodiment of the present invention.

[0035] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0036] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0037] FIG. 7 shows various standard generation-specific physical layer protocol data unit (PPDU) formats according to an embodiment of the present invention.

[0038] Figure 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0039] FIG. 9 shows a transmission / TXOP protection method using an RTS frame and a CTS frame according to an embodiment of the present invention.

[0040] 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.

[0041] Figure 11 shows the link setup of AP MLD and non-AP MLD according to an embodiment of the present invention.

[0042] FIG. 12 shows the operation of an AP and a non-AP station in a scheduled power saving mode of the AP according to an embodiment of the present invention.

[0043] FIG. 13 shows the operation of an AP operating in dynamic power saving mode according to an embodiment of the present invention.

[0044] FIG. 14 shows the operation of an AP and a non-AP station when the AP operates in dynamic power saving mode according to an embodiment of the present invention.

[0045] FIG. 15 illustrates the operation of an AP and a non-AP station when the AP operates using both scheduled power saving mode and dynamic power saving mode according to one embodiment of the present invention.

[0046] FIG. 16 shows an AP according to an embodiment of the present invention performing scheduled power saving operations divided into enhanced mode and listening mode.

[0047] FIG. 17 shows the format of an element including information notifying activation of a power saving mode according to an embodiment of the present invention.

[0048] 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.

[0049] 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.

[0050] Hereinafter, in the present invention, fields and subfields may be used interchangeably.

[0051] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0052] 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.

[0053] 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) which is a station providing a distribution service, and a distribution system (DS) which connects multiple access points (AP-1, AP-2).

[0054] 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).

[0055] 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.

[0056] 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).

[0057] 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.

[0058] 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 one another.

[0059] 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).

[0060] 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 the 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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).

[0065] 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.

[0066] 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.

[0067] 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.

[0068] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0069] 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).

[0070] 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.

[0071] 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.

[0072] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] <Various PPDU format examples>

[0077] FIG. 7 shows various standard generation-specific physical layer protocol data unit (PPDU) formats according to an embodiment of the present invention.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087]

[0088] 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.

[0089]

[0090] 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.

[0091]

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098]

[0099] Figure 8 shows an EHT / UHR PPDU format according to an embodiment of the present invention.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108]

[0109] <Wi-Fi 단말의 채널 액세스 방법>

[0110] 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.

[0111] 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.

[0112] 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.

[0113] The CSMA / CA and random backoff procedures briefly explained above are applied to DCF (Distributed coordination function) and EDCAF (Enhanced distributed channel access function), which are basic functions used by Wi-Fi terminals when attempting channel access. Since these are well-known and widely used unlicensed band channel access methods, a more detailed explanation will be omitted.

[0114]

[0115] 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.

[0116] 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.

[0117]

[0118] <EDCA와 TXOP>

[0119] EDCA provides a mechanism to differentiate and manage traffic into four types of ACs (access categories) according to the characteristics of the traffic. 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.

[0120] 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.

[0121] AC_VI is an AC that is more delay-tolerant than voice traffic, but can still be used for low-latency transmission and high-volume traffic such as video. AC_VI has larger CW and AIFSN parameter values ​​than AC_VO but smaller than other ACs. However, its TXOP is about twice as long as AC_VI.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126]

[0127] 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 contention with other ACs. At this time, in the channel access contention between ACs, each AC competes using its assigned access parameters (CW[AC], AIFSN[AC]), and the channel access contention 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 contention.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133]

[0134] 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.

[0135] 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).

[0136] 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.

[0137] 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.

[0138]

[0139] FIG. 9 shows a transmission / TXOP protection method using an RTS frame and a CTS frame according to an embodiment of the present invention.

[0140] 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.

[0141] 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.

[0142] 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.

[0143]

[0144] <MU-RTS 트리거 프레임을 이용한 TXOP 보호>

[0145] 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.

[0146]

[0147] 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.

[0148] 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.

[0149]

[0150] 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 operations 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.

[0151] 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.

[0152]

[0153] <MLD(Multi-Link Device)>

[0154] Wi-Fi 7 (802.11be, Extremely High Throughput (EHT)) introduced the Multi-Link Device (MLD). An MLD is an entity that associates multiple stations. An AP MLD includes multiple APs, and a non-AP MLD includes multiple non-AP stations.

[0155] Multiple stations of an MLD operate on different links, respectively. For example, a first station of a first MLD operates on a link in a 2.4 GHz band, a second station of the first MLD operates on a link in a 5 GHz band, and a third station of the first MLD operates on a link in a 6 GHz band. An AP MLD and a non-AP MLD can exchange frames through multiple links. An AP MLD can perform a multi-link setup to exchange frames with a non-AP MLD through multiple links. An AP MLD and a non-AP MLD can perform a multi-link setup on one of the links to establish multiple links between the AP MLD and the non-AP MLD. A frame exchanged for the multi-link setup can include a Multi-Link element. The Multi-Link element can include capability information of a station included in the MLD transmitting the Multi-Link element, for example, a Per-STA profile. In addition, the AP MLD and the non-AP MLD can negotiate the types of traffic that can be exchanged on the multiple established links, such as TID-to-Link Mapping (TTLM). If an agreement is reached on the types of traffic that can be exchanged on each link, the AP MLD and the non-AP MLD exchange traffic according to the agreement. Specifically, the AP MLD and the non-AP MLD can transmit traffic corresponding to the TID defined for each link in the agreement on each link. At this time, the designated traffic may vary depending on the transmission direction of each link, whether it is uplink transmission or downlink transmission. For example, the AP MLD can map TID 0 to TID 3 to downlink transmission on the first link. Additionally, the AP can map TID 4 to TID 7 to downlink transmission on the second link.At this time, the AP MLD can transmit a frame including traffic corresponding to TID 0 to TID 3 on the first link, and transmit a frame including traffic corresponding to TID 4 to TID 7 on the second link.

[0156] Figure 11 shows the link setup of AP MLD and non-AP MLD according to an embodiment of the present invention.

[0157] In the embodiment of FIG. 11, the AP MLD includes a first AP (AP1), a second AP (AP2), and a third AP (AP3). The non-AP MLD includes a first station (STA1), a second station (STA2), and a third station (STA3). The first AP (AP1), the second AP (AP2), and the third AP (AP3) each operate on a first link (Link1), a second link (Link2), and a third link (Link3), respectively. The first station (STA1), the second station (STA2), and the third station (STA3) each operate on a first link (Link1), a second link (Link2), and a third link (Link3), respectively. In the embodiments described above, the operating channels of the APs operating on each link do not overlap each other. The AP MLD and the non-AP MLD can increase throughput and improve QoS performance by establishing multiple links.

[0158]

[0159] <AP 및 AP MLD의 전력 소모 문제>

[0160] In AP MLD, APs can operate on up to 15 links. Each AP on each link performs the same role as a previous individual AP. Therefore, AP MLD can consume more power than a single AP. Conventionally, power-saving operations were defined for non-AP stations, as these stations can operate on battery power. Power-saving operations can conserve power by suspending some hardware operations of the station or by activating some operations only at specific times. Power-saving operations can include Spatial Modulation (SM) Power Save or Target Wake Time (TWT). Power-saving operations can also include operations that reduce power consumption during receive standby, such as enhanced multi-link single radio (EMLSR). In EMLSR mode, a multi-link device can only support receiving PPDUs transmitted in a predefined format, transmission bandwidth, and data rate on the EMLSR link. The predefined format can be a non-HT PPDU. Additionally, the predefined data rate may be 6 Mbps. Additionally, the predefined bandwidth may be 20 MHz.

[0161] APs are typically wall-powered. Therefore, existing wireless LAN standards have not introduced separate power-saving measures for APs. Some APs have reduced power consumption by modifying their capabilities. For example, APs can reduce power consumption by reducing the bandwidth of the operating channel they operate or the number of spatial streams they support. AP Multi-Layer Distributed Link (MLD) can also reduce power consumption by reducing the number of links it operates. However, these measures have significant limitations in terms of power-saving effects and may not be easily configurable. Therefore, measures to reduce AP power consumption are necessary. The embodiments described below can be applied not only to APs included in AP MLD but also to APs not included in AP MLD. Furthermore, they can be applied not only to non-AP stations included in non-AP MLD but also to non-AP stations not included in non-AP MLD.

[0162]

[0163] <AP를 위한 스케줄드 절전 모드(scheduled power save mode for AP)>

[0164] In scheduled power-saving mode, the AP transitions between its activity states based on predefined time intervals. Specifically, the AP can transition from an awake state to a doze state, or from a doze state to an awake state, based on predefined time intervals. In scheduled power-saving mode, the AP can perform an activity state transition similar to that of a non-AP station using the target wake time (TWT).

[0165] We first describe the power-saving behavior of non-AP stations using TWT. APs and non-AP stations can establish individual TWT agreements. In the TWT agreement, an agreement on a TWT service period (SP) can be established between the AP and non-AP stations. Once a TWT SP is established, non-AP stations remain awake during the TWT SP. During periods outside of the TWT SP, non-AP stations can enter a doze state. An AP can establish a broadcast TWT SP applicable to stations belonging to the BSS operated by the AP. The AP can establish the broadcast TWT SP by transmitting a beacon frame containing a TWT element. Non-AP stations belonging to the BSS operated by the AP remain awake during the period corresponding to the broadcast TWT SP. At this time, non-AP stations can enter a doze state during periods outside of the broadcast TWT SP.

[0166] In scheduled power save mode, an AP can transmit a frame containing information indicating a time period during which the AP should remain in an awake state. For convenience of explanation, the element containing information indicating a time period during which the AP should remain in an awake state is referred to as a scheduled power save information element. The time period during which the AP should remain in an awake state is referred to as an awake time period. Specifically, the AP can transmit the scheduled power save information element using a management frame. In this case, the management frame can include at least one of a beacon frame, a probe request frame, a probe response frame, an association request frame, an association response frame, and a power save announcement frame. In these embodiments, the AP can indicate an interval between awake time periods and a duration of the awake time periods.

[0167] In addition, the time period during which the awake state should be maintained can be indicated based on the value of the Timestamp field included in the beacon frame. If the value of the Timestamp field of the beacon frame is x and the beacon frame indicates that the duration of the awake time period is y us, the non-AP station can determine that the AP will maintain the awake state for the time period from x until the TSF timer of the non-AP STA reaches x+y. In addition, if the value of the Timestamp field of the beacon frame is x and the beacon frame indicates that the interval of the awake time period is z us, the non-AP station can determine that the AP has transitioned to the awake state when the TSF timer of the non-AP STA reaches x+z.

[0168] An AP may be required to remain in an awake state for all target beacon transmission times (TBTTs) of the BSS operated by the AP. Specifically, the AP may transition to an awake state at all TBTTs of the BSS operated by the AP. In a specific embodiment, all TBTTs of the BSS operated by the AP may be configured to fall within the AP's awake time period.

[0169] When the AP operates in power save mode, the AP may disassociate or reject connections from legacy non-AP stations that do not support the AP's power save operation. This prevents malfunctions of the legacy non-AP stations. At this time, the AP may not transmit beacon frames and probe response frames. This prevents the legacy non-AP stations from discovering the AP. In another specific embodiment, the AP may transmit beacon frames and probe response frames using a PPDU format that the legacy non-AP stations do not support. At this time, the PPDU format may be a UHR PPDU format. This embodiment allows information to be transmitted through beacon frames and probe frames while preventing legacy stations from discovering the AP.

[0170] A non-AP station may attempt frame exchange during the awake time period of the AP, and may not attempt frame exchange during time periods other than the awake time period. Attempting frame exchange may include the non-AP station performing a channel access procedure for transmitting a UL PPDU, or the non-AP station waiting to receive a DL PPDU. In the present specification, waiting or expecting reception may include the non-AP station maintaining an awake state at a time when reception is expected. In addition, waiting or expecting reception may include the non-AP station waking up from a doze state before the time when reception is expected. In addition, not attempting frame exchange may include the non-AP station maintaining a doze state. The non-AP station may maintain a doze state while an AP associated with the non-AP station maintains a doze state.

[0171] Additionally, if a predefined condition is satisfied, the AP and non-AP stations can exchange frames in a time period other than the awake time period. The predefined condition may include a case where a frame exchange that started in the awake time period of the AP does not end within the awake time period. Specifically, the AP and non-AP stations can continue to exchange frames in a time period other than the awake time period until the TXOP of the frame exchange performed within the awake time period of the AP ends. In this case, even if the time point at which the AP enters the doze state is delayed, the time point of the next awake time period may not be delayed. Specifically, even if the interval between the time points at which the AP enters the doze state varies, the interval between the start times of the awake time periods may be maintained constant.

[0172] When an AP transitions from a busy state to an awake state, the AP may apply a medium sync delay. Specifically, when the AP transitions from a busy state to an awake state, the AP may set the NAV timer to a value smaller than the NAVSyncDelay value. This is similar to setting the NAV timer to the NAVSyncDelay value to ensure fairness when a non-AP station transitions from a busy state to an awake state, but this is an embodiment that takes into account the characteristics of an AP operating a BSS.

[0173] In these embodiments, even before the NAV timer expires, the AP may perform transmission if a predefined condition is satisfied. For example, even before the NAV timer expires, the AP may be permitted to transmit a control frame of a predefined form. In this case, the predefined control frame may be an MU-RTS trigger frame. Furthermore, even before the NAV timer expires, the AP may transmit a beacon frame according to the TBTT.

[0174] In the above-described embodiments, the NAV timer was used as an example, but the timer may be a timer for channel access restriction other than the NAV timer. During a time period in which the value of the timer is not 0, the AP may perform a channel access procedure using a value lower than the CCA threshold used when the value of the timer is 0. In addition, during a time period in which the value of the timer is not 0, if the AP succeeds in the channel access procedure, the AP may only transmit control frames in a pre-specified format.

[0175] FIG. 12 shows the operation of an AP and a non-AP station in a scheduled power saving mode of the AP according to an embodiment of the present invention.

[0176] In the embodiment of FIG. 12, the AP transmits a beacon frame to signal information about the scheduled power saving mode. Specifically, the beacon frame indicates an awake time period of the scheduled power saving mode. The beacon frame can directly indicate the awake time period. In another specific embodiment, the beacon frame can indicate a time period during which the AP can enter a doze state. A non-AP station can obtain information about the awake time period from the beacon frame. The non-AP station can exchange frames with the AP based on the information about the awake time period. The non-AP station can receive a DL PPDU and transmit a UL PPDU within the awake time period of the AP. In addition, the non-AP station can enter the doze state during a time period other than the awake time period of the AP. The awake time period is repeatedly set, and the interval between the awake time periods can be indicated by the beacon frame.

[0177]

[0178] <AP를 위한 다이나믹 절전 모드(dynamic PS mode for AP)>

[0179] In AP dynamic power saving mode, the AP switches between the first and second states according to a predefined procedure. Specifically, in AP dynamic power saving mode, the AP maintains the first state and transitions to the second state when a predefined condition is met. The operation of the AP dynamic power saving mode can be applied with the characteristics of the enhanced multi-link single radio (EMLSR) mode of non-AP multi-link devices.

[0180] First, the operation of a non-AP multi-link device in EMLSR mode according to an embodiment of the present invention will be described.

[0181] 1. To operate in EMLSR mode, a non-AP multi-link device transmits an EML Operating Mode Notification frame to the AP multi-link device. At this time, the non-AP MLD can apply EMLSR mode to some of the links on which the non-AP stations of the non-AP MLD operate.

[0182] The EML Operating Mode Notification frame contains an EML Control field. The EML Control field contains an EMLSR Mode bit, and a non-AP multi-link device that wishes to switch to EMLSR mode transmits an EML Operating Mode Notification frame with the EMLSR Mode bit set to 1 to the AP MLD.

[0183] The EML Control field may contain an EMLSR / EMLMR Link Bitmap subfield. The EMLSR / EMLMR Link Bitmap subfield is an EMLSR Link Bitmap subfield when the EMLSR Mode bit is set to 1. The EMLSR Link Bitmap subfield contains 16 bits corresponding to each link of the AP multi-link device, and a non-AP multi-link device transmits an EMLSR Link Bitmap subfield with the bit corresponding to the link for which it wants to operate in EMLSR mode set to 1 to the AP multi-link device.

[0184] 2. When an AP multi-link device wants to transmit a DL PPDU on a link where a non-AP multi-link device has applied the EMLSR mode, the AP multi-link device transmits an initiation control frame using a PPDU in a pre-specified format.

[0185] The initiation control frame is transmitted as a non-HT PPDU or a non-HT duplicated PPDU. Furthermore, the initiation control frame is transmitted at a data rate of 6 Mb / s, 12 MB / s, or 24 Mb / s.

[0186] The initiation control frame includes a Padding field. The length of the Padding field is determined based on information indicated by the non-AP multi-link device. The Padding may be used to secure the time required for the non-AP station to transition from listening mode to frame switching mode (a mode that supports MIMO and / or EHT PPDU formats).

[0187] The frame type of the initiation control frame is a MU-RTS (Multi-User RTS) trigger frame or a BSRP (Buffer Status Report Poll) trigger frame.

[0188] 3. A non-AP multi-link device that receives an initiation control frame in a link in EMLSR mode from an AP multi-link device transmits a response frame according to the frame type of the received initiation control frame.

[0189] Non-AP stations in a non-AP multi-link device operating on a link in EMLSR mode remain in listening mode until a start control frame is received. In listening mode, non-AP stations only support receiving start control frames transmitted via PPDUs in a predefined format. In listening mode, non-AP stations can utilize only one RF chain.

[0190] A non-AP station of a non-AP multi-link device operating on a link in EMLSR mode supports frame exchange using multiple receiving chains after transmitting a response frame to an initiation control frame. At this time, the frame exchange may use a PPDU in a format other than the format used for the initiation control frame, such as an EHT PPDU, HE PPDU, or UHR PPDU. For convenience of explanation below, a frame exchange initiated by an initiation control frame is referred to as an initiated frame exchange, and a frame exchange sequence initiated by the initiation control frame is referred to as an initiated frame exchange sequence.

[0191] 4. When the AP multi-link device receives a response frame to an initiation control frame from a non-AP station in EMLSR mode, the AP multi-link device performs an initiation frame exchange with the non-AP station without any restrictions according to the listening mode.

[0192] 5. A non-AP station operating on a link in EMLSR mode switches back to listening mode after the frame exchange initiated with the AP is terminated.

[0193] A non-AP station considers an initiated frame exchange sequence to be complete when no more PPDUs are received from the AP or when the received PPDUs are not intended for transmission to a non-AP station.

[0194]

[0195] In EMLSR mode, non-AP stations support only a relatively lower set of capabilities when performing frame exchange compared to when not performing frame exchange. In listening mode, non-AP stations only support reception of pre-defined data rates, pre-defined frame types, and pre-defined PPDU formats. This allows non-AP stations to perform power-saving operations and prevents a sharp increase in power consumption as the number of links supported by the non-AP station increases. Similarly, APs can transition to a mode in which they only support a subset of pre-defined capabilities when not performing frame exchange. For convenience of explanation, this mode in which the AP can enter a doze state is referred to as dynamic AP power-saving mode.

[0196] When an AP is about to transition to dynamic AP power save mode, the AP may indicate that the dynamic AP will transition to power save mode. In addition, the AP may indicate information regarding a start control frame to be received in the listening mode of the dynamic AP power save mode. At this time, the information regarding the start control frame may include information regarding the length of a padding field to be included in the start control frame. The information regarding the length of the padding field may be a minimum value of the length of the padding field. For convenience of explanation, an element including information indicating transition to power save mode or information regarding a start control frame to be received by the AP in the listening mode is referred to as a dynamic power save information element. The AP may transmit a management frame including the dynamic power save information element. The management frame may include at least one of a beacon frame, a probe response frame, an association response frame, or a power save announcement frame. In a time period other than the awake time period of the AP, a non-AP station may transmit a start control frame to the AP using a pre-designated transmission method. At this time, the non-AP station can transmit a PPDU of a pre-specified format including a pre-specified initiation control frame at a pre-specified data rate. The pre-specified type of initiation control frame can be an MU-RTS trigger frame or a BAR trigger frame. In addition, the pre-specified data rate can include at least one of 6 Mb / s, 12 Mb / s, or 24 Mb / s. In addition, the PPDU of the pre-specified format can be a non-HT PPDU or a non-HT duplicated PPDU. In the embodiment described above, if the pre-specified type of initiation control frame is a BAR trigger frame, it can be a BAR trigger frame of a pre-specified format.

[0197] Specifically, the initiation control frame may include information regarding the capabilities supported in the initiated frame exchange sequence. Specifically, the information regarding the capabilities may include at least one of information regarding the bandwidth used for the initiated frame exchange, the number of spatial streams, N_SS, or information regarding the priority of traffic to be transmitted in the initiated frame exchange sequence. In this case, the information regarding the priority of the traffic may include the TID of the traffic to be exchanged in the initiated frame exchange sequence or whether the traffic to be exchanged in the initiated frame exchange sequence is low latency traffic. In this case, the low latency traffic may be traffic that is pre-designated as low latency traffic among a plurality of traffic types. If the initiation control frame is a BAR trigger frame, the BAR Control field of the BAR trigger frame may include information regarding the priority of the traffic to be exchanged in the initiated frame exchange sequence. In another specific embodiment, the BAR Information field of the BlockAckReq frame may include information regarding the priority of the traffic to be exchanged in the initiated frame exchange sequence. At this time, the format of the BAR Information field may be the format used when the BAR trigger frame is used as an initiation control frame. In addition, when the BAR trigger frame is transmitted as an initiation control frame, the BAR trigger frame may be transmitted without BlockACK negotiation. This is because when the BAR trigger frame is transmitted as an initiation control frame, the purpose is not to induce BlockACK transmission.

[0198] In addition, a BAR trigger frame, which is an initiation control frame, may indicate in the BAR Control field of the BAR trigger frame that it is an initiation control frame. The value of the BAR Control field of the initiation control frame may be different from the value of the BAR Control field of the BAR trigger frame for triggering BlockACK transmission. If the BAR trigger frame is an initiation control frame, the value of a pre-designated bit of the BAR Control field of the BAR trigger frame may be set to 1. At this time, if the BAR trigger frame is not an initiation control frame, the value of the pre-designated bit of the BAR Control field of the BAR trigger frame is set to 0. In addition, if the BAR trigger frame is an initiation control frame, all bits other than the pre-designated bits of the BAR Control field of the BAR trigger frame may be set to 0. In another specific embodiment, if the BAR trigger frame is an initiation control frame, the value of the BAR Type subfield of the BAR Control field may be set to a pre-designated value. At this time, the pre-designated value may be a value designated as a reserved value in a previous standard technology. Specifically, the pre-specified value may be one of 0, 4, 5, 7 to 9, or one of 11 to 15. In addition, if the BAR trigger frame is an initiation control frame, the values ​​of all subfields other than the BAR Type subfield in the BAR Control field may be set to 0. In addition, the BAR trigger frame, which is an initiation control frame, may not include a BAR Information field. In addition, the BAR trigger frame, which is an initiation control frame, may include a padding field after the BAR Control field. In this case, the length of the padding field may be determined based on information received from the AP. In addition, the padding field may be included after the first FCS field.A BAR trigger frame may include a 2-octet Frame Control field, a 2-octet Duration field, a 6-octet RA field, a 6-octet TA field, a 2-octet BAR Control field, a 4-octet FCS1 field, a padding field, and a 4-octet FCS2 field. The value of the FCS1 field is used for the CRC (cyclic redundancy check) of the Frame Control field, the Duration field, the RA field, the TA field, and the BAR Control field. In addition, the value of the FCS2 field is used for the CRC of the Frame Control field, the Duration field, the RA field, the TA field, the BAR Control field, the FCS1 field, and the padding field. The AP can perform a CRC using the value of the FCS1 field and then change the operation mode without decoding the padding field following the FCS1 field. This allows time for the operation mode change through the padding field.

[0199] If the initiation control frame is an MU-RTS trigger frame, the User Info field of the MU-RTS trigger frame may include information about functions supported in the initiated frame exchange sequence. In this case, the value of the AID12 subfield of the subfield of the User Info field including information about functions supported in the initiated frame exchange sequence may have a predefined value. The predefined value may be 2007 or 2006.

[0200] In dynamic power saving mode, an AP can operate in two modes. The two modes may include a listening mode in which it waits for the reception of a start control frame transmitted according to a pre-defined transmission method, and an enhanced mode in which it can perform frame exchange after receiving a start control frame. In the listening mode of the dynamic power saving mode, if the AP receives a start control frame, the AP can transmit a response frame to the start control frame and switch to the enhanced mode. Specifically, the AP can switch to the enhanced mode when it decodes the first FCS field included in the start control frame. In addition, the AP can complete the switch to the enhanced mode before the short inter-frame space (SIFS) elapses from the time it finishes transmitting the response frame. In this case, the specific completion time of the switch to the enhanced mode may not be specified. This ensures the freedom of the AP's implementation. In the enhanced mode, the AP can perform frame exchange. In the dynamic power saving mode, the AP maintains the enhanced mode when it is not in the listening mode. If a delay occurs between mode transitions, the AP can only support operations in the previous mode. For example, if a delay occurs when switching from Listening mode to Enhanced mode, the AP can only support functions in Listening mode. If a delay occurs when switching from Enhanced mode to Listening mode, the AP can only support functions in Enhanced mode.

[0201] FIG. 13 shows the operation of an AP operating in dynamic power saving mode according to an embodiment of the present invention.

[0202] In the embodiment of FIG. 13, the AP transmits a beacon frame indicating that the AP operates in dynamic power saving mode. At this time, the beacon frame may indicate a minimum value of the length of a padding field that must be included in the initiation control frame.

[0203] A non-AP station receives a beacon frame and transmits an initiation control frame when the AP is in listening mode. At this time, the length of the padding field included in the initiation control frame (ICF) may be equal to or greater than the minimum length of the padding field indicated by the AP. The padding field allows the AP time to switch operation modes. In addition, the initiation control frame (ICF) is transmitted using a single spatial stream through a non-HT PPDU with an MCS of 16-QAM or lower.

[0204] Upon receiving the Initiation Control Frame (ICF), the AP switches from listening mode to enhanced mode and transmits a response frame (ICR) to the Initiation Control Frame (ICF). Non-AP stations receiving the response frame (ICR) transmit a UL PPDU to the AP. The transmission restrictions applicable to the Initiation Control Frame (ICF) transmission do not apply to the transmission of the UL PPDU.

[0205] The AP receives the UL PPDU transmitted by the non-AP station. The AP transmits a BlockAck frame to the non-AP station. After the frame exchange is completed, the AP switches to the listening mode. As in the embodiment of FIG. 13, after the AP switches from the listening mode to the enhanced mode without receiving the initiation control frame, the AP may transmit a BSRP trigger frame to the non-AP station. At this time, the non-AP station may receive the BSRP (buffer status report poll) trigger frame and transmit a BSR (buffer status report) to the AP. The AP may receive the BSR and transmit a DL PPDU to the non-AP station. The non-AP station may receive the DL PPDU and transmit a BlockAck frame. The AP that receives the BlockAck frame may transmit a Basic trigger frame to trigger uplink transmission of the non-AP station. The non-AP station that receives the Basic trigger frame may transmit a TB PPDU to the AP based on the Basic trigger frame.

[0206]

[0207] Comparison of Scheduled Sleep Mode and Dynamic Sleep Mode

[0208] When an AP operates in scheduled power saving mode, the BSS it operates may periodically experience service interruptions. If the AP enters a busy state, frame exchange between the AP and non-AP stations may be blocked. This can delay the processing of low-latency traffic and reduce the maximum throughput supported by the BSS. However, the power saving effect of the AP can be enhanced by maximizing the time period during scheduled power saving mode during which the AP can enter busy state.

[0209] When an AP operates in dynamic power saving mode, listening mode can prevent the BSS it operates from completely shutting down. Listening mode can also reduce the AP's power consumption. However, operating in listening mode may not provide as significant a power saving effect as operating in normal mode.

[0210] Additionally, when an AP operates in dynamic power saving mode, power saving effects may be reduced if the AP frequently receives initiation control frames. For example, if the AP is associated with an excessive number of non-AP stations, the AP may continuously receive initiation control frames from non-AP stations. In this case, the AP may have difficulty maintaining listening mode. An embodiment for improving this situation is described below.

[0211]

[0212] Enhanced Dynamic Power Saving Mode

[0213] Even if an AP operating in dynamic power saving mode receives an initiation control frame in listening mode, the AP may optionally switch to enhanced mode. Specifically, even if the AP receives an initiation control frame in listening mode, the AP may maintain the listening mode if a predefined condition is satisfied. In a specific embodiment, a non-AP station may indicate information about an initiated frame exchange. At this time, the AP may determine whether to maintain the listening mode based on the information about the initiated frame exchange indicated by the initiation frame. If the AP determines to maintain the listening mode, then in enhanced mode, the AP may induce uplink transmission by transmitting a triggering frame to a non-AP station that has refused to switch to enhanced mode. This allows the non-AP station to transmit a pending buffered unit (BU) stored in the queue. At this time, the triggering frame may include at least one of a basic trigger frame, a frame with the RDG / More PPDU subfield set to 1, or a frame including a TRS Control subfield. In the following description, a frame that induces uplink transmission of non-AP transmission is referred to as a triggering frame.

[0214] Additionally, the AP can transition from listening mode to enhanced mode without receiving a triggering control frame. Specifically, the AP can transition from listening mode to enhanced mode without receiving a triggering control frame at a predetermined time. Furthermore, the AP can transition from listening mode to enhanced mode without receiving a triggering control frame at its discretion. The AP can instruct non-AP stations about the timing at which the AP intends to transition to enhanced mode. Furthermore, non-AP stations that have transmitted a triggering control frame but have not yet exchanged frames can expect to receive a triggering frame from the AP after the AP transitions to enhanced mode.

[0215] If the AP receives a pre-specified number of initiation control frames without entering the enhanced mode, the AP may transition to the enhanced mode. The pre-specified number may be 5. For example, the AP may not transition to the enhanced mode even after receiving 4 initiation control frames. In this case, if the AP receives the initiation control frame, the AP may transition to the enhanced mode. In this embodiment, the AP not transitioning to the enhanced mode may include the AP not transitioning to the enhanced mode according to a decision based on a pre-specified condition even after receiving the initiation control frame, as described above. If the AP transitions to the enhanced mode, the AP may transmit a triggering frame to induce transmission of a non-AP station that transmitted the initiation control frame a pre-specified number of times. These embodiments may maximize the time that the AP maintains the listening mode.

[0216] In addition, if the initiation control frame received by the AP indicates that low-latency traffic exchange will be performed, the AP may switch to enhanced mode based on the initiation control frame. Specifically, if the initiation control frame received by the AP indicates that low-latency traffic exchange will be performed, the AP may not be permitted to not switch to enhanced mode after receiving the initiation control frame. In this case, the AP may switch to enhanced mode immediately after receiving the initiation control frame. In addition, if the initiation control frame received by the AP does not indicate that low-latency traffic exchange will be performed, the AP may be permitted not to switch to enhanced mode immediately after receiving the initiation control frame.

[0217] Additionally, the initiation control frame may include information related to the capability requested by the non-AP station in the initiated frame exchange sequence. The AP may determine whether to switch to enhanced mode based on the capability requested by the non-AP station indicated by the initiation control frame in the initiated frame exchange sequence. Specifically, the AP may perform a frame exchange sequence that supports the capability requested in the initiated exchange sequence. In this case, the AP may use only the capability requested by the initiation control frame in the initiated frame exchange sequence even if the capability supported by the AP exceeds the capability requested in the exchange sequence indicated by the initiation control frame. For example, even if the AP supports a bandwidth of 320 MHz, if the initiation control frame requests an 80 MHz bandwidth, the AP may perform the frame exchange sequence with an 80 MHz bandwidth in the initiated frame exchange sequence. Even if the AP supports three or more spatial streams, if the initiation control frame requests two spatial streams, the AP may perform the frame exchange sequence using two spatial streams in the initiated frame exchange sequence.

[0218] The information contained in the initiation control frame and how the AP determines whether to switch to enhanced mode are described in the following embodiments.

[0219]

[0220] The operation of AP and non-AP stations in dynamic power saving mode based on the embodiments described above is described.

[0221] 1. The AP can use management frames to indicate that the AP is operating in power-saving mode.

[0222] A management frame may include at least one of a beacon frame, a probe response frame, an association response frame, or a frame containing information related to a power save operation, such as a power save announcement frame.

[0223] The AP may include an element containing information related to power-saving operations in the management frame. The element may be the dynamic power save information element described above. Additionally, the element may be the scheduled power save information element described above.

[0224] An AP belonging to an AP multi-link device can transmit information related to the power saving mode of other APs belonging to the AP multi-link device to which the AP belongs. Specifically, an AP can transmit information related to the power saving mode of other APs belonging to the AP multi-link device to which the AP belongs using the Per-STA Profile subelement of the AP. A non-AP multi-link device that has performed multi-link setup with an AP multi-link device can determine information related to the power saving operation of the AP based on the Per-STA Profile subelement corresponding to the AP associated with each non-AP multi-link device.

[0225] If the power saving mode indicated by the management frame is a dynamic power saving mode, this describes information related to the power saving mode indicated by the management frame.

[0226] As previously explained, information related to the power-saving mode indicated by the management frame may include information regarding the length of the padding field of the initiation control frame. A non-AP station may determine the padding length of the initiation control frame based on the information regarding the length of the padding field of the initiation control frame.

[0227] Additionally, information related to the power saving mode indicated by the management frame may include a policy for the AP to operate the dynamic power saving mode.

[0228] At this time, the policy may include whether to immediately switch to enhanced mode. In this specification, switching to enhanced mode within a predetermined time after receiving an initiation control frame is expressed as an immediate switch. Specifically, the initiation control frame may indicate a delayed switch. At this time, the AP may immediately switch to enhanced mode only if a predetermined condition is met, and may not immediately switch to enhanced mode if the predetermined condition is not met. The predetermined condition may include that low-latency traffic is scheduled to be exchanged in the initiation frame exchange sequence.

[0229] Additionally, the predefined conditions may include a case where the AP maintains the listening mode continuously for a period of time longer than a predefined time. The predefined time may be indicated via a management frame. If the AP does not switch to enhanced mode even after receiving the initiation control frame, the non-AP station that transmitted the initiation control frame may wait to receive a triggering frame from the AP within a predefined time from the time the initiation control frame was transmitted. At this time, the non-AP station may remain in an awake state to receive the triggering frame.

[0230] Additionally, the predefined condition may include that a predefined time has elapsed since the first initiation control frame is received after switching to listening mode. The AP may switch to enhanced mode after a predefined time since the first initiation control frame is received after switching to listening mode. The predefined time may be indicated via a management frame. If the AP does not switch to enhanced mode even after receiving the initiation control frame, the non-AP station that transmitted the initiation control frame may wait to receive a triggering frame from the AP within a predefined time since transmitting the initiation control frame. At this time, the non-AP station may remain in an awake state to receive the triggering frame.

[0231] The predefined conditions may include the passage of a time indicated by the AP's response frame to the initiation control frame. The AP may include information indicating the time to enter enhanced mode in the response frame to the initiation control frame. The non-AP station may wait to receive a triggering frame within a predefined error interval from the time to enter enhanced mode indicated by the response frame to the control frame. At this time, the non-AP station may remain in an awake state to receive the triggering frame.

[0232] Additionally, the initiation control frame can indicate an immediate transition. In this case, the AP can receive the initiation control frame and enter enhanced mode without any additional conditions. Therefore, if the initiation control frame indicates an immediate transition, the AP can switch to enhanced mode whenever it receives the initiation control frame.

[0233]

[0234] 2. When the AP operates in dynamic power saving mode, a non-AP station that wishes to transmit a UL PPDU to the AP can initiate a frame exchange sequence by transmitting an initiation control frame to the AP.

[0235] As previously explained, the length of the padding field of the initiation control frame can be determined based on the length information indicated by the AP.

[0236] If a non-AP station does not intend to attempt low-latency traffic exchange in the initiated frame exchange sequence, the non-AP station may not include a padding field in the initiation control frame. This is because if the non-AP station does not attempt low-latency traffic exchange in the initiated frame exchange sequence, the AP may not immediately switch to enhanced mode.

[0237] If a non-AP station does not intend to exchange low-latency traffic in the initiated frame exchange sequence, the non-AP station may not be permitted to transmit an initiation control frame to an AP in listening mode. In this case, the non-AP station may request frame exchange for traffic other than low-latency traffic only when the AP is in enhanced mode. If a non-AP station intends to exchange low-latency traffic in the initiated frame exchange sequence, the non-AP station may be permitted to transmit an initiation control frame to an AP in listening mode.

[0238] A non-AP station can indicate whether it intends to attempt low-latency traffic exchange in the initiated frame exchange sequence as described above. For convenience of explanation, the traffic to be exchanged in the initiated frame exchange sequence is referred to as the exchange target traffic. If a specific bit in the initiation control frame has a pre-designated value, the initiation control frame can indicate that the exchange target traffic is low-latency traffic. In this case, the pre-designated value may be 1. The pre-designated bit may be a bit included in the Frame control field of the MAC header of the initiation control frame. In addition, the pre-designated bit may be a reserved bit included in the Frame control field, such as a To DS field, a From DS field, a More Fragment field, or a Retry field. In another specific embodiment, the initiation control frame may indicate information related to the TID of the exchange target traffic. The information related to the TID may be a TID or an AC. In addition, a non-AP station that does not support UL MU OFDMA can always indicate the exchange target traffic as low-latency traffic. This can ensure fair transmission opportunities with other stations.

[0239] A non-AP station may include information regarding the buffer status in an initiation control frame. The initiation control frame may indicate the queue size of the TID of the traffic to be exchanged. Specifically, a non-AP station may include a BSR transmitted in response to a BSRP in the initiation control frame. The information regarding the buffer status may be included in the frame body of the initiation control frame. In another specific embodiment, the information regarding the buffer status may be included in the MAC header. The information regarding the buffer status may be included in the BSR Control field of the A-Control field.

[0240] A non-AP station can use an initiation control frame to indicate the end point of a TXOP of an initiated frame exchange sequence. Specifically, the value of the Duration / ID field of the initiation control frame can be set according to the end point of the TXOP of the initiated frame exchange sequence. The AP can determine whether to switch to enhanced mode based on the end point of the TXOP of the frame exchange sequence indicated by the initiation control frame. If the duration of the TXOP of the frame exchange sequence indicated by the initiation control frame is greater than a predetermined time, the AP may not switch to enhanced mode.

[0241] 3. The AP receives the initiation control frame and transmits a response frame to the initiation control frame. The interval between the initiation control frame and the response frame can be SIFS or PIFS. The response frame can indicate whether the AP will immediately enter enhanced mode or remain in listening mode.

[0242] An AP can decide whether to switch to enhanced mode based on information indicated by the initiation control frame. The information indicated by the initiation control frame may include whether the traffic to be exchanged is low-latency traffic. If the traffic to be exchanged is low-latency traffic, the AP can switch to enhanced mode. The method by which the initiation control frame indicates whether the traffic to be exchanged is low-latency traffic may follow the previously described embodiments. The information indicated by the initiation control frame may include the queue size of a non-AP station. If the queue size indicated by the initiation control frame exceeds a predefined value, the AP can switch to enhanced mode.

[0243] The AP transmits a response frame indicating whether to immediately enter the enhanced mode. In a specific embodiment, the format of the response frame may be determined by the AP. The format of the response frame may indicate whether the AP immediately switches to the enhanced mode. For example, if the AP immediately switches to the enhanced mode, the AP may transmit a first type of response frame. If the AP does not immediately switch to the enhanced mode, the AP may transmit a second type of response frame. If the response frame received by the non-AP station is of the first type, the non-AP station may determine that the AP immediately switches to the enhanced mode. If the response frame received by the non-AP station is of the second type, the non-AP station may determine that the AP does not immediately switch to the enhanced mode. In another specific embodiment, a pre-designated bit included in the response frame may indicate whether the AP immediately switches to the enhanced mode. Specifically, if the value of the pre-specified bit is a pre-specified value, the response frame may instruct the AP to immediately switch to enhanced mode. Additionally, if the response frame indicates that the AP should immediately switch to enhanced mode, the non-AP station may set the value of the Duration / ID field of the MAC header of the response frame to the value of the Duration / ID field of the initiation control frame - SIFS - the length of the response frame.

[0244] If the AP does not immediately switch to enhanced mode, the response frame may indicate information regarding the point in time when the AP switches to enhanced mode. At this time, the information regarding the point in time when switching to enhanced mode may include information related to the point in time when transmitting a triggering frame that triggers transmission of a non-AP station. The information regarding the point in time when the AP switches to enhanced mode may be indicated using a timing synchronization function (TSF) value. The AP may switch to enhanced mode before the point in time when switching to enhanced mode indicated by the response frame, and transmit a triggering frame to the non-AP station that triggers transmission of the non-AP station.

[0245] The response frame may indicate a maximum delay time, which is the maximum time required to switch to enhanced mode. The non-AP station may wait for reception of the triggering frame from the enhanced mode switching time indicated by the response frame to the time plus the maximum delay time indicated by the response frame. At this time, the operation of the non-AP station waiting for reception of the triggering frame may be the same as the embodiments described above. In addition, in a specific embodiment, if the response frame does not indicate a maximum delay time, the non-AP station may regard the beacon interval as the maximum delay time. At this time, the default value of the maximum delay time may be the beacon interval.

[0246] An AP may not explicitly signal the timing associated with an enhanced mode transition. Specifically, the AP may not signal the timing associated with an enhanced mode transition using an initiation control frame or a separate element. The AP may transmit a triggering frame to a non-AP station that transmitted an initiation control frame after the next TBTT after the AP receives the initiation control frame. The non-AP station that transmitted the initiation control frame to the AP may wait for reception of the triggering frame from the next TBTT after the AP receives the initiation control frame. In this case, the operation of the non-AP station waiting for reception of the triggering frame may be the same as in the embodiments described above.

[0247] If the value of the Duration / ID field in the MAC header of the response frame is 0, the response frame may indicate that the AP does not immediately switch to enhanced mode.

[0248] A non-AP station that receives a start control frame and does not immediately switch to enhanced mode can store information about the non-AP station that transmitted the start control frame.

[0249] In another specific embodiment, if the AP receives the initiation control frame and does not immediately switch to the enhanced mode, the AP may not transmit a response frame. In this case, the AP's failure to transmit a response frame may implicitly indicate that the AP does not immediately switch to the enhanced mode. A non-AP station that does not receive a response frame to the initiation control frame may determine that the AP does not immediately switch to the enhanced mode. As in the embodiment described above, the AP may transmit a triggering frame to the non-AP station that transmitted the initiation control frame after the next TBTT after receiving the initiation control frame. The non-AP station that transmitted the initiation control frame to the AP may wait to receive the triggering frame from the next TBTT after the AP receives the initiation control frame. In another specific embodiment, the AP may be required to transmit a triggering frame to the non-AP station that transmitted the initiation control frame within a predetermined time from the time the AP receives the initiation control frame, triggering the transmission of the non-AP station. At this time, the non-AP station may wait for the reception of a triggering frame within a predetermined time period from the time the AP receives the initiation control frame. In the embodiments described above, the operation of the non-AP station waiting for the reception of a triggering frame may be the same as in the embodiments described above.

[0250] If a non-AP station determines that the AP will immediately switch to enhanced mode, the non-AP station may perform frame exchange with the AP. At this time, the non-AP station transmits a PPDU containing a response frame and a UL PPDU at SIFS intervals. In addition, the non-AP station may be required to perform frame exchange according to information regarding traffic to be exchanged. Specifically, the non-AP station may not be permitted to transmit a frame containing traffic that does not correspond to the information indicated as the traffic to be exchanged in the initiated frame exchange sequence. For example, if the non-AP station indicates that the traffic to be exchanged is low-latency traffic, the non-AP station may not be permitted to transmit a frame containing traffic other than low-latency traffic in the initiated frame exchange sequence.

[0251] If a non-AP station determines that the AP will not immediately switch to enhanced mode, the non-AP station may not exchange frames with the AP. At this time, the non-AP station may reset its TXNAV to 0. At this time, the non-AP station may transmit a CF-End frame.

[0252] If the non-AP station determines that the AP will not immediately switch to enhanced mode, the non-AP station may wait to receive a triggering frame that the AP will transmit in enhanced mode. At this time, the non-AP station may determine when the AP will transmit the triggering frame based on the information indicated in the response frame. The non-AP station may remain in the awake state at the time the AP transmits the triggering frame. As described above, the non-AP station may wake up from the doze state before the time the AP transmits the triggering frame. In addition, the non-AP station may wait to receive a triggering frame until the time when the AP switches to enhanced mode plus the maximum transition time described above. At this time, the AP may transmit a triggering frame to the non-AP station until the start point plus the maximum delay time from the time when it switches to enhanced mode. In addition, if the non-AP station does not receive a triggering frame from the AP until the maximum switching time described above plus the time at which the AP switches to the enhanced mode, the non-AP station may transmit an initiation control frame indicating that the traffic to be exchanged is low-latency traffic. At this time, the non-AP station may indicate that the traffic to be exchanged is low-latency traffic even if the traffic to be exchanged is not low-latency traffic. In another specific embodiment, if the non-AP station does not receive a triggering frame from the AP until the maximum switching time described above plus the time at which the AP switches to the enhanced mode, the non-AP station may maintain a listening mode until it receives a triggering frame. At this time, the listening mode may be a state that supports only reception of control frames transmitted by a pre-designated transmission method. The pre-designated transmission method may be transmission in a non-HT (duplicated) PPDU format in a 20 MHz bandwidth.Additionally, the data rate of the pre-specified transmission method may be any one of 6 Mb / s, 12 Mb / s, or 24 Mb / s.

[0253] As previously explained, the AP may not explicitly signal the timing associated with the enhanced mode transition. In this case, a non-AP station that has transmitted an initiation control frame to the AP may wait for the reception of a triggering frame starting from the next TBTT after the AP receives the initiation control frame.

[0254] 6. If the AP does not immediately switch to the enhanced mode after receiving the initiation control frame, the AP may transmit a triggering frame to trigger transmission of the non-AP station that transmitted the initiation control frame when it first switches to the enhanced mode after receiving the initiation control frame. As described above, the non-AP station that receives the initiation control frame and does not immediately switch to the enhanced mode may store information of the non-AP station that transmitted the initiation control frame. At this time, multiple initiation control frames may be received from multiple non-AP stations. In addition, the triggering frame may include a User Info field corresponding to each of the multiple non-AP stations that transmitted the initiation control frame. In addition, when the AP switches to the enhanced mode, the triggering frame may be transmitted to all non-AP stations that transmitted the initiation control frame after the previous enhanced mode. However, if the AP shares a TXOP with the non-AP station that transmitted the initiation control frame, the AP may not transmit a triggering frame to the non-AP station with which it shared the TXOP. At this time, TXOP sharing may include the AP allowing a non-AP station to transmit UL PPDUs within the AP's TXOP using a reverse direction protocol. TXOP sharing may also include the AP sending a MU-RTS TXS (TXOP sharing) trigger frame to share a TXOP with a non-AP station.

[0255]

[0256] When any one of the APs belonging to the AP multi-link device is scheduled to operate in power-saving mode, all other APs belonging to the AP multi-link device may be required to transmit a management frame indicating that any one of the APs is operating in power-saving mode. At this time, the AP may use a Per-STA profile included in the Multi-Link element to indicate that other APs belonging to the AP multi-link device including the AP are operating in power-saving mode. When the AP multi-link device includes a first AP and a second AP, the first AP may transmit a Multi-link element including information about the power-saving mode in the Per STA profile corresponding to the second AP. The information about the power-saving mode may include information indicating that the second AP is operating in power-saving mode or information about the time when the second AP operates in power-saving mode. A non-AP station belonging to a non-AP multi-link device may obtain information about the power-saving mode of an AP operating on a link other than the link on which the non-AP station is operating from the Multi-link element. In the embodiments described above, a non-AP station may use a reduce neighbor report (RNR) element instead of a Multi-Link element. At this time, the non-AP station may use the TBTT Information field of the RNR element. Specifically, the non-AP station may set a pre-designated subfield of the TBTT Information field of an AP operating in power-saving mode to a pre-designated value, and may set the value of the AP TBTT Offset subfield to 255. At this time, the pre-designated subfield is referred to as a PS Mode Link Indication subfield. In addition, the value of the Neighbor AP TBTT Offset subfield is set to 255 because the AP may not transmit a beacon frame in power-saving mode.An AP may not transmit beacon frames to prevent association of legacy non-AP stations in power-saving mode.

[0257]

[0258] FIG. 14 shows the operation of an AP and a non-AP station when the AP operates in dynamic power saving mode according to an embodiment of the present invention.

[0259] The AP transmits a beacon frame. The beacon frame indicates that the AP is operating in dynamic power saving mode. The beacon frame may also indicate information related to the minimum padding length of the Initiation Control Frame (ICF).

[0260] A non-AP station can request the initiation of a frame exchange sequence by transmitting an Initiation Control Frame (ICF) when the AP is in listening mode. The Initiation Control Frame (ICF) indicates information about the traffic to be exchanged. In the embodiment of FIG. 14, the Initiation Control Frame includes an LL Traffic bit. If the value of the LL Traffic bit is 1, it indicates that the traffic to be exchanged is low-latency traffic. Additionally, if the value of the LL Traffic bit is 0, it indicates that the traffic to be exchanged is not low-latency traffic.

[0261] The AP receives an initiation control frame (ICF) and transmits a response frame (ICR). The response frame (ICR) can indicate whether the AP will immediately transition to enhanced mode. In the embodiment of FIG. 14, the initiation control frame includes a Mode Transition bit. If the value of the Mode Transition bit is 1, the response frame (ICR) indicates that the AP will immediately transition to enhanced mode. Additionally, if the value of the Mode Transition bit is 0, the response frame (ICR) indicates that the AP will not immediately transition to enhanced mode.

[0262] In the embodiment of FIG. 14, the first non-AP station (non-AP STA1) and the second non-AP station (non-AP STA2), which have received a response frame (ICR) indicating that the AP will not immediately switch to the enhanced mode, do not start transmitting UL PPDUs after receiving the response frame (ICR). In addition, the third non-AP station (non-AP STA3), which has received a response frame indicating that the AP will immediately switch to the enhanced mode, transmits a PPDU including the response frame (ICR) and a UL PPDU at an SIFS interval. Thereafter, the AP transmits a trigger frame to the first non-AP station (non-AP STA1) and the second non-AP station (non-AP STA2). The first non-AP station (non-AP STA1) and the second non-AP station (non-AP STA2) receive the trigger frame and perform a signal transmission. After completing the AP frame exchange, they switch to the listening mode.

[0263]

[0264] <Combination of Scheduled Sleep Mode and Dynamic Sleep Mode>

[0265] The previously described scheduled power saving mode and dynamic power saving mode can be used independently. An AP according to an embodiment of the present invention can use the scheduled power saving mode and dynamic power saving mode together to enhance power saving effects. Specifically, the AP can operate in dynamic power saving mode during the awake time period of the scheduled power saving mode. Specifically, the AP can maintain a listening mode during the awake time period of the scheduled power saving mode, receive an initiation control frame, and switch to enhanced mode. In addition, the AP can maintain a doze state during a time period other than the awake time period. In this case, the previously described embodiments regarding the scheduled power saving mode and the embodiments regarding the dynamic power saving mode can be applied. For example, when the AP is in the doze state, a non-AP station may not be permitted to transmit to the AP. When the AP operates during the awake time period, a non-AP station may only be permitted to transmit an initiation transmission frame to the AP using a pre-designated transmission method. An AP may operate in a state including a listening mode during an awake time period and an enhanced mode during an awake time period. When the AP receives a start control frame during the awake time period, the AP may initiate a frame exchange sequence with a non-AP station that transmitted the start control frame before the end of the awake time period. At this time, the non-AP station may expect to receive a triggering frame from the AP that triggers transmission of the non-AP station before the end of the awake time period in which the start control frame was transmitted. At this time, the AP may not separately signal information regarding the transition point to the enhanced mode or the transmission point of the triggering frame. Specifically, the AP may not separately signal information regarding the transition point to the enhanced mode or the transmission point of the triggering frame using a response frame.

[0266]

[0267] FIG. 15 illustrates the operation of an AP and a non-AP station when the AP operates using both scheduled power saving mode and dynamic power saving mode according to one embodiment of the present invention.

[0268] An AP operating in scheduled power saving mode maintains a listening mode during the awake time period. A non-AP station transmits an initiation control frame (ICF) to the AP during the awake time period. When the AP receives the initiation control frame (ICF), the AP switches to enhanced mode and transmits a response frame (ICR) to the non-AP station. The non-AP station receiving the response frame (ICR) transmits a UL PPDU to the AP.

[0269] An AP can enter a doze state outside of the awake time period. At this time, non-AP stations do not attempt to exchange frames with the AP. Furthermore, non-AP stations can enter a doze state while the AP remains in the doze state. The AP can operate in enhanced mode during the awake time period without receiving a start control frame. At this time, the AP can transmit DL PPDUs to non-AP stations and trigger frames to induce transmission by the non-AP stations.

[0270]

[0271] In another specific embodiment, the scheduled power saving mode may be divided into the enhanced mode and listening mode described in the dynamic power saving mode. In this case, the AP may switch between the listening mode and the enhanced mode according to a predetermined schedule. This embodiment may minimize the time period during which the AP does not exchange frames. Furthermore, the operations of the AP and non-AP in the enhanced mode and listening mode may be subject to the embodiments described above regarding the dynamic power saving mode.

[0272] FIG. 16 shows an AP according to an embodiment of the present invention performing scheduled power saving operations divided into enhanced mode and listening mode.

[0273] The AP maintains the enhanced mode during the scheduled service interval and the time interval during which it maintains the enhanced mode. The AP maintains the listening mode during the time interval outside the scheduled service interval. When a non-AP station attempts to exchange frames during the time interval outside the scheduled service interval, the non-AP station transmits an initiation control frame (ICF) to the AP. In the embodiment of FIG. 16, the initiation control frame indicates that the traffic to be exchanged is not low-latency traffic. At this time, the AP does not switch to the enhanced mode based on the initiation control frame. The AP transmits an initiation control frame (ICF) to the non-AP station indicating that it will not immediately switch to the enhanced mode. Thereafter, in the enhanced mode, the AP transmits a BSRP trigger frame to the non-AP station that transmitted the initiation control frame, and the non-AP station transmits a BSR to the AP. The AP, upon receiving the BSR, transmits a trigger frame (TF) to the non-AP station.

[0274] When the scheduled service interval ends, the AP switches to listening mode. The non-AP station transmits an initiation control frame (ICF) to the AP, indicating that the traffic to be exchanged is low-latency traffic. The AP switches to enhanced mode based on the initiation control frame. The AP also transmits a response frame (ICR) to the non-AP station, indicating an immediate transition to enhanced mode. The non-AP station receiving the response frame (ICR) transmits a UL PPDU to the AP.

[0275] <AP의 동작 모드 변경 방법>

[0276] In the listening mode of the scheduled power saving mode, the AP can receive an initiation control frame and switch to the enhanced mode based on the initiation control frame. At this time, the operation of signaling information about the transition decision, timing, and transition can follow the embodiments of the dynamic power saving mode described above. The non-AP station can receive a response frame to the initiation control frame from the AP and transmit a UL PPDU with a SIFS interval and a PPDU containing the initiation control frame.

[0277] Additionally, when the AP operates a target wake time (TWT) service period (SP) of the BSS, the AP can maintain an enhanced mode during the TWT SP. At this time, the TWT may be an R-TWT for transmitting low-latency traffic. A non-AP station can determine that the AP will maintain an enhanced mode during the R-TWT SP. At this time, the non-AP station can attempt to exchange frames with the AP without transmitting an initiation control frame during the R-TWT SP.

[0278] An AP can enter listening mode without separate signaling outside of its pre-scheduled service interval. An AP can enter listening mode when the frame exchange sequence it is performing ends. Specifically, an AP can enter listening mode when a TXOP holder or a TXOP responder terminates.

[0279]

[0280] <AP의 절전 모드 활성화 방법 및 제한>

[0281] When an AP operates in power-saving mode, non-AP stations may experience frequent transmission failures if they cannot accurately determine the AP's operation. Furthermore, non-AP stations may prefer to associate with APs that do not use power-saving mode. Considering this, a method is needed to indicate that an AP is operating in power-saving mode.

[0282] Before an AP operates in power-saving mode, the AP needs to signal for a sufficient period of time that the AP will operate in power-saving mode. The AP can indicate whether to switch to power-saving mode using a management frame. The management frame can be any one of a beacon frame, a probe response frame, or a power-saving announcement frame described above. In addition, the AP can continue to transmit management frames containing information notifying the transition to power-saving mode for a sufficient period of time for non-AP stations belonging to the BSS operated by the AP to receive at least one management frame, such as a beacon. Specifically, the AP can continue to transmit management frames containing information notifying the transition to power-saving mode during the beacon reception interval of non-AP stations belonging to the BSS operated by the AP.

[0283] Additionally, the AP may include a counter in the management frame indicating the point in time for transitioning to power-saving mode. Specifically, an element including information for notifying the activation of the power-saving mode may include a counter. For convenience of explanation, the element including information for notifying the activation of the power-saving mode is referred to as a power-saving announcement element. At this time, the counter may indicate that the AP will transition to power-saving mode after the number of TBTTs remaining until the power-saving mode activation point has elapsed. For example, if the value of the counter of the power-saving announcement element is 1, this may indicate that the AP will activate power-saving mode from the next TBTT. If the value of the counter of the power-saving announcement element is 0, this may indicate that the AP will activate power-saving mode before the next TBTT after the management frame including the element is transmitted. The power-saving announcement element may indicate the type of power-saving mode. At this time, the type of power-saving mode may indicate at least one of the various power-saving modes described above. Additionally, the power-saving announcement element may include information regarding the point in time for the power-saving mode to be activated. Additionally, the power save announcement element may include scheduling information for the detailed operation mode of the power saving mode being activated.

[0284] An AP that wishes to activate power-save mode can transmit a BTM (BSS transition management) request frame to signal to non-AP stations associated with the AP that the association will be terminated. The BTM request frame may include information about a BSS to which the non-AP station can move. Non-AP stations that support operation in the AP's power-save mode may ignore the BTM request frame. In addition, the BTM request frame may include information indicating that the frame is for power-save mode activation. In this case, if a non-AP station that supports operation in the AP's power-save mode receives a BTM request frame including information indicating that the frame is for power-save mode activation, the non-AP station may ignore the received BTM request frame. This allows only non-AP stations that do not support operation in the AP's power-save mode to disassociate from the BSS and associate with a new BSS.

[0285] An AP multi-link device including an AP for which a power-saving mode is to be activated can change the TID-to-Link mapping. Specifically, the AP multi-link device can re-configure the TID-to-Link mapping so that no TID is mapped only to a link on which the AP for which the power-saving mode is to be activated operates. This is to prevent transmission delays for traffic with some TIDs due to the operation of the AP in the power-saving mode. In a specific embodiment, the AP multi-link device can transmit a TID-to-Link mapping element that sets all TIDs to be mapped to all links. At this time, the AP multi-link device can transmit the TID-to-Link Mapping element using a management frame, for example, a beacon frame or a probe response frame. The time point of changing the TID-to-Link mapping can be the same as or earlier than the time point of activating the power-saving mode. The value of the mapping switch time field of the TID-to-Link mapping element for changing the TID-to-Link mapping can be set to the same as or earlier than the time point of activating the power-saving mode.

[0286] Additionally, when the TID-to-Link mapping set by the AP multi-link device that enables the power saving mode is applied to the non-AP station multi-link device, the non-AP station multi-link device may discard the TID-to-Link mapping previously negotiated with the AP multi-link device. After the TID-to-Link mapping set by the AP multi-link device that enables the power saving mode is applied to the non-AP station multi-link device, the non-AP station multi-link device may negotiate with the AP multi-link device to apply a new TID-to-Link mapping.

[0287]

[0288] FIG. 17 shows the format of an element including information notifying activation of a power saving mode according to an embodiment of the present invention.

[0289] An AP multi-link device can transmit the power save announcement element described above. An AP that is to activate the power save mode can transmit the power save announcement element. An AP belonging to an AP multi-link device other than the AP that is to activate the power save mode can transmit the power save announcement element. The power save announcement element can include an Element ID field, a Length field, a Power Save Mode field, and a Mode Switch Count field. The Element ID field indicates the ID of the element. In addition, the Length field indicates the length of the element. The Power Save Mode field can have a length of 1 octet. Each bit of the Power Save Mode field can correspond to each of multiple power save modes. In this case, if the value of the bit is a predetermined value, the Power Save Mode field can indicate that the AP corresponding to the element operates in the power save mode corresponding to the bit. For example, the first bit of the Power Save Mode field may correspond to a scheduled power saving mode, the second bit may correspond to a dynamic power saving mode, and the third to eighth bits may be reserved bits. In another specific embodiment, the Power Save Mode field may indicate an index indicating a type of power saving mode that the AP corresponding to the element will perform. For example, a value of 0 in the Power Save Mode field may correspond to a scheduled power saving mode, 1 may correspond to a dynamic power saving mode, and 2 may correspond to a combination of the scheduled power saving mode and the dynamic power saving mode.

[0290] Additionally, if the Power Save Mode field indicates the use of a scheduled power saving mode, the power save announcement element may include a field indicating information about an awake time period of the scheduled power saving mode. The information about the awake time period may be the same as in the embodiments described above.

[0291] The Mode Switch Count field represents a counter that indicates when to switch to the power-saving mode described above.

[0292]

[0293] <Management of Multiple BSS>

[0294] When any one AP belonging to a multiple BSSID set or a co-hosted BSSID set operates in power saving mode, all APs belonging to the multiple BSSID set or the co-hosted BSSID set that includes the any one AP may also operate in power saving mode. In this case, information regarding power saving mode signaled by any one AP may be applied to all APs belonging to the multiple BSSID set or the co-hosted BSSID set that includes the any one AP. Specifically, an element including information regarding power saving mode transmitted by any one AP may be inherited by all APs belonging to the multiple BSSID set or the co-hosted BSSID set that includes the any one AP. This is because hardware functions included in the multiple BSSID set or the co-hosted BSSID set are shared, and the operation of any one AP is likely to affect other APs. In addition, this can enhance power saving effect.

[0295]

[0296] 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.

[0297] 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.

[0298] 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. In an AP multi-link device that wirelessly communicates with a non-AP (access point) station multi-link device, and includes multiple APs, Transmitter and receiver; and Contains a processor, The above processor Operating the first AP, which is one of the above plurality of APs, in scheduled power saving mode, In the above scheduled power saving mode, the first AP maintains an awake state during a pre-designated awake time period and can enter a duz state during a time period other than the awake time period. AP multi-link device.

2. In paragraph 1, The above first AP maintains an awake state at the target beacon transmission time (TBTT) of the BSS (basic service set) operated by the above first AP. AP multi-link device.

3. In paragraph 1, The above first AP If the frame exchange started in the above awake time interval does not end in the above awake time interval, the frame exchange is performed in a time interval other than the above awake time interval. AP multi-link device.

4. In paragraph 1, The above processor Transmitting a management frame including a first element including information about the awake time interval to the non-AP station multi-link device AP multi-link device.

5. In paragraph 4, The above first element is Information about the interval of the above awake time period and information about the duration of the above awake time period. AP multi-link device.

6. In paragraph 1, The above first AP Operating in dynamic power saving mode during the above awake time period AP multi-link device.

7. In paragraph 6, In the above dynamic power saving mode, the first AP switches between listening mode and enhanced mode, The above first AP supports only reception of initiation control frames transmitted by a pre-specified transmission method in the listening mode, and supports reception other than reception of initiation control frames transmitted by the pre-specified transmission method in the enhanced mode. AP multi-link device.

8. In paragraph 7, The first AP receives the initiation control frame in the listening mode and, if a pre-specified condition is satisfied, immediately switches to the enhanced mode. AP multi-link device.

9. In paragraph 8, The above pre-specified conditions are such that the exchange of low-latency traffic is scheduled to be performed in the frame exchange sequence initiated by the above initiation control frame. AP multi-link device.

10. In a non-AP station multi-link device that communicates wirelessly with an AP (access point) multi-link device and includes multiple non-AP stations, Transmitter and receiver; and Contains a processor, The above processor When the first AP, which is one of the APs of the above AP multi-link device, operates in scheduled power saving mode, the first AP performs frame exchange with the first AP when the first AP operates in an awake time period, In the above scheduled power saving mode, the first AP maintains an awake state during a pre-designated awake time period and can enter a duz state during a time period other than the awake time period. Non-AP station multi-link device.

11. In paragraph 10, The above first AP maintains an awake state at the target beacon transmission time (TBTT) of the BSS (basic service set) operated by the above first AP. Non-AP station multi-link device.

12. In paragraph 10, The above processor If the frame exchange started in the above awake time interval does not end in the above awake time interval, the frame exchange is performed in a time interval other than the above awake time interval. Non-AP station multi-link device.

13. In paragraph 10, The above processor Receiving a management frame including a first element including information about the awake time interval from the AP multi-link device Non-AP station multi-link device.

14. In paragraph 13, The above first element is Information about the interval of the above awake time period and information about the duration of the above awake time period. Non-AP station multi-link device.

15. In paragraph 10, The above first AP It operates in dynamic power saving mode during the above awake time period, In the above dynamic power saving mode, the first AP switches between listening mode and enhanced mode, The above processor When the first AP operates in listening mode, an initiation control frame is transmitted to the first AP using a transmission method designated in advance. Non-AP station multi-link device.

16. In paragraph 15, The above processor Receive a response frame in response to the initiation control frame from the first AP, The above response frame indicates that the first AP receives the initiation control frame and immediately switches from the listening mode to the enhanced mode. Non-AP station multi-link device.

17. In paragraph 16, The first AP receives the initiation control frame and immediately switches from the listening mode to the enhanced mode when a pre-specified condition is satisfied, The above pre-specified conditions are such that the exchange of low-latency traffic is scheduled to be performed in the frame exchange sequence initiated by the above initiation control frame. Non-AP station multi-link device.

18. In a method for operating an AP multi-link device that wirelessly communicates with a non-AP (access point) station multi-link device and includes multiple APs, A step of operating a first AP, which is one of the plurality of APs, in a scheduled power saving mode, In the above scheduled power saving mode, the first AP maintains an awake state during a pre-designated awake time period and can enter a duz state during a time period other than the awake time period. How it works.

19. In paragraph 18, The above first AP maintains an awake state at the target beacon transmission time (TBTT) of the BSS (basic service set) operated by the above first AP. How it works.

20. In paragraph 18, The step of operating the above first AP in the scheduled power saving mode is If the frame exchange started in the awake time interval does not end in the awake time interval, a step of performing the frame exchange in a time interval other than the awake time interval is included. How it works.

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