Wireless communication methods and wireless communication terminals in high-density environments including overlapping basic service sets

Abstract

We provide wireless communication terminals that communicate wirelessly. [Solution] A wireless communication terminal that communicates wirelessly is disclosed. The wireless communication terminal includes a transmitting and receiving unit, A processor is included. The processor transmits a first PPDU (PLCP) via the transmitting / receiving unit. The signaling field of the Protocol Data Unit is received, Identify the BSS (Basic Service Set) indicated by the signaling field. Access the channel based on the information provided.

Description

Technical Field

[0001] The present invention relates to a wireless communication method and a wireless communication terminal in a high-density environment including overlapping basic service sets.

Background Art

[0002] Recently, as the popularity of mobile devices has expanded, wireless LAN (Wireless Local Area Network) technology that provides fast wireless Internet services to these devices has been in the spotlight. Wireless LAN technology is a technology that enables mobile devices such as smartphones, smart pads, laptop computers, portable multimedia players, and embedded devices to be wirelessly connected to the Internet at home, in enterprises, or in a specific service-providing area based on wireless communication technology. Since IEEE (Institute of Electrical and Electronics Engineers) 802.11 supported the initial wireless LAN technology using a frequency of 2.4 GHz, various technical standards have been put into practical use or are under development. First, IEEE 802.11b supports a communication speed of up to 11 Mbps while using a frequency in the 2.4 GHz band. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses a frequency in the 5 GHz band instead of the 2.4 GHz band, reducing the impact on interference compared to the rather congested 2.4 GHz band frequency, and improving the communication speed up to 54 Mbps using OFDM technology. However, IEEE 802.11a has the disadvantage of a shorter communication distance compared to IEEE 802.11b. And IEEE 802.11g uses a frequency in the 2.4 GHz band like IEEE 802.11b to implement a maximum communication speed of 54 Mbps and has received considerable attention because it satisfies backward compatibility, but it is also superior to IEEE 802.11a in terms of communication distance. Furthermore, IEEE 802.11n is a technical standard established to overcome the limitations in communication speed that have been pointed out as a vulnerability of wireless LANs. The purpose of IEEE 802.11n is to increase network speed and reliability and extend the operating range of wireless networks. More specifically, IEEE 802.11n supports high throughput (HT) with a data processing speed of up to 540 Mbps or more, and is based on MIMO (Multiple Inputs and Multiple Outputs) technology, which uses multiple antennas at both the transmitter and receiver ends to minimize transmission errors and optimize data speed. In addition, this standard uses a coding method that transmits multiple duplicate copies to increase data reliability. As the proliferation of wireless LANs accelerated and the applications utilizing them diversified, a demand arose for new wireless LAN systems that could support very high throughput (VHT) higher than the data processing speeds supported by IEEE 802.11n. Among these, IEEE 802.11ac supports a wide bandwidth (80MHz to 160MHz) at the 5GHz frequency. While the IEEE 802.11ac standard was defined only in the 5GHz band, early 11ac chipsets also supported operation in the 2.4GHz band for backward compatibility with older 2.4GHz band products. Theoretically, according to this standard, the speed of a multi-station wireless LAN can reach a minimum of 1Gbps, and the speed of a single link can reach a minimum of 500Mbps. This is achieved by extending the wireless interface concepts accepted in 802.11n, including wider radio frequency bandwidth (up to 160MHz), more MIMO spatial streams (up to 8), multiple user MIMO, and high-density modulation (up to 256QAM). Another method for transmitting data using the 60GHz band instead of the conventional 2.4GHz / 5GHz band is IEEE 802.11ad. IEEE 802.11ad is a transmission standard that utilizes beamforming technology to provide speeds of up to 7Gbps, making it suitable for streaming large amounts of data and high-bitrate video such as uncompressed HD video. However, the 60GHz frequency band has the disadvantage of being difficult to pass through obstacles, limiting its use to short-range devices. Meanwhile, discussions are currently underway to provide highly efficient and high-performance wireless LAN communication technologies for high-density environments as the standard for next-generation wireless LANs, starting with 801.11ac and 802.11ad. In other words, in next-generation wireless LAN environments, highly frequency-efficient communication should be provided both indoors and outdoors in the presence of high-density stations and access points (APs), and a variety of technologies are needed to realize this.

[0003] In particular, as the number of devices using wireless LANs increases, it becomes necessary to use the designated channels efficiently. Therefore, there is a need for technology that efficiently utilizes bandwidth by simultaneously transmitting data between multiple stations and access points (APs). [Overview of the project] [Problems that the invention aims to solve]

[0004] One embodiment of the present invention aims to provide a wireless communication method and a wireless communication terminal for high-density environments that include overlapping basic service sets. [Means for solving the problem]

[0005] A wireless communication terminal that communicates wirelessly according to one embodiment of the present invention includes a transceiver unit and a processor, the processor receiving a signaling field of a first PPDU (PLCP Protocol Data Unit) via the transceiver unit and accessing the channel based on information identifying the BSS (Basic Service Set) indicated by the signaling field.

[0006] If the first determination, based on information identifying the BSS, determines whether the BSS containing the first PPDU is the same as the BSS containing the wireless communication terminal, and the second determination, based on the Address field of the MAC header contained in the PPDU, differs, the processor accesses the channel based on the second determination, and the Address field of the MAC header indicates the MAC address relating to the MPDU (MAC Protocol Data Unit).

[0007] The size of the field indicating the information identifying the BSS may be smaller than the maximum value that the MAC address may have.

[0008] The processor determines the BSS containing the first PPDU based on one of the following fields in the MAC header: the transmitting STA address (TA) field, the receiving STA address (RA) field, and the BSSID field.

[0009] If the first PPDU includes a trigger frame transmitted from a BSS other than the BSS containing the wireless communication terminal, the processor measures the received signal strength of the first PPDU, and if the second PPDU is transmitted after the transmission of the trigger frame is completed, it adjusts the transmission power based on the received signal strength.

[0010] When the processor transmits the second PPDU while the uplink PPDU transmitted based on the trigger frame is being transmitted, it adjusts the transmission power based on the received signal strength.

[0011] When the processor transmits the second PPDU during the TXOP (Transmission Opportunity) indicated by the trigger frame, it adjusts the transmission power based on the received signal strength.

[0012] The signaling field of the first PPDU includes information indicating whether spatial reuse (SR) operation is permissible, and the processor adjusts the transmission power based on the information indicating whether the SR operation is permissible.

[0013] The signaling field of the first PPDU includes information regarding the transmission power of the first PPDU.

[0014] The frequency band used by the wireless communication terminal is divided into a main channel and a sub-channel, and the processor performs CCA operation in both the main channel and the sub-channel.

[0015] The processor may use a different CCA (Clear Channel Assessment) threshold in the sub-channel than the CCA threshold used in the main channel.

[0016] If no PPDU is transmitted from the main channel, the processor determines that the PPDU transmitted from the sub-channel was transmitted from a BBS other than the BSS containing the wireless communication terminal.

[0017] An operation method for a wireless communication terminal that communicates wirelessly according to one embodiment of the present invention includes the steps of receiving a signaling field of a first PPDU and accessing a channel based on information identifying the BSS indicated by the signaling field.

[0018] The step of accessing the channel includes a first determination, based on the BSS color, that determines whether the BSS containing the first PPDU is the same as the BSS containing the wireless communication terminal, and a second determination, based on the Address field of the MAC header contained in the PPDU, that determines whether the BSS containing the first PPDU is the same as the BSS containing the wireless communication terminal, and if these two determinations differ, the step of accessing the channel based on the second determination, wherein the Address field of the MAC header indicates the MAC address relating to the PPDU.

[0019] The size of the field indicating the information identifying the BSS may be smaller than the maximum value that the MAC address may have.

[0020] The step of accessing a channel based on the second determination includes determining the BSS containing the first PPDU based on one of the transmission station address field, the receiving station address field, and the BSSID field of the Address field of the MAC head.

[0021] The first PPDU includes a trigger frame transmitted from a BSS different from the BSS including the wireless communication terminal, and further includes a step of measuring the received signal strength of the first PPDU, and a step of adjusting the transmission power based on the received signal strength when transmitting a second PPDU after the transmission of the trigger frame is completed.

[0022] The step of transmitting the second PPDU includes a step of adjusting the transmission power based on the received signal strength when transmitting the second PPDU while an uplink PPDU transmitted based on the trigger frame is being transmitted.

[0023] The signaling field of the first PPDU includes information indicating whether spatial reuse operation is permitted, and the step of transmitting the second PPDU includes a step of adjusting the transmission power based on the information indicating whether the SR operation is permitted.

[0024] The signaling field of the first PPDU includes information regarding the transmission power of the first PPDU.

Advantages of the Invention

[0025] An embodiment of the present invention provides a wireless communication method and a wireless communication terminal in a high-density environment including overlapping basic service sets.

Brief Description of the Drawings

[0026] [Figure 1] FIG. is a diagram showing a wireless LAN system according to an embodiment of the present invention. [Figure 2] FIG. is a diagram showing a wireless LAN system according to another embodiment of the present invention. [Figure 3] FIG. is a block diagram showing the configuration of a station according to an embodiment of the present invention. [Figure 4] FIG. is a block diagram showing the configuration of an access point according to an embodiment of the present invention. [Figure 5]This diagram schematically illustrates the process by which a station according to one embodiment of the present invention establishes a link with an access point. [Figure 6] This figure shows a wireless communication terminal according to an embodiment of the present invention accessing a wireless medium via a competitive procedure. [Figure 7] This figure shows the PPDU format used in a wireless communication method according to an embodiment of the present invention. [Figure 8] This figure shows the A-MPDU format used in a wireless communication method according to an embodiment of the present invention. [Figure 9] This figure shows the operation of a wireless communication terminal when receiving a PPDU indicating a BSS color corresponding to a BSS that includes a wireless communication terminal according to an embodiment of the present invention. [Figure 10] This figure shows the operation of a wireless communication terminal according to an embodiment of the present invention when it receives a PPDU indicating BSS color corresponding to OBSS. [Figure 11] This diagram shows cases where inter-BSS colors collide or intra-BSS colors become confused. [Figure 12] This figure shows the operation of a wireless communication terminal according to an embodiment of the present invention when it receives a legacy PPDU corresponding to OBSS. [Figure 13] This figure shows the SR and power saving operations of a wireless communication terminal according to an embodiment of the present invention, depending on the type of PPDU and whether OBSS is enabled or disabled, when the wireless communication terminal receives a PPDU. [Figure 14] This figure shows the SR and power saving operations of a wireless communication terminal according to an embodiment of the present invention, depending on the type of PPDU and whether OBSS is enabled or disabled, when the wireless communication terminal receives a PPDU. [Figure 15] This figure shows a method for determining whether a frame received by a wireless communication terminal according to an embodiment of the present invention is an Intra-BSS frame or an Inter-BSS frame. [Figure 16]This figure shows a method by which a wireless communication terminal according to an embodiment of the present invention determines whether a received frame is an Intra-BSS frame or an Inter-BSS frame based on the frame type and the value of the MAC header field. [Figure 17] This figure shows the actions of a wireless communication terminal according to an embodiment of the present invention to correct an Inter-BSS color collision and to prevent Intra-BSS color confusion when the wireless communication terminal detects an Inter-BSS color collision. [Figure 18] This figure shows a method by which a wireless communication terminal according to one embodiment of the present invention bonds frequency bands for broadband communication. [Figure 19] This figure shows a method by which a wireless communication terminal according to one embodiment of the present invention transmits a broadband PPDU. [Figure 20] This figure shows that a wireless communication terminal according to an embodiment of the present invention transmits PPDU over a frequency band having a frequency bandwidth of 40 MHz. [Figure 21] This figure shows that a wireless communication terminal according to an embodiment of the present invention adjusts the transmission power during SR operation. [Figure 22] This figure shows that a wireless communication terminal according to an embodiment of the present invention performs SR operation considering the transmission probability of the PPDU transmitted from OBSS. [Figure 23] This figure shows the operation of a wireless communication terminal according to an embodiment of the present invention. [Modes for carrying out the invention]

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings, so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clarify the present invention, parts unrelated to the description have been omitted from the drawings, and similar parts throughout the specification are denoted by similar reference numerals.

[0028] Furthermore, when we say that a part "includes" a certain component, unless otherwise stated, this means that it includes other components rather than excluding them.

[0029] This application claims priority based on Korean Patent Applications No. 10-2015-0146203 (October 20, 2015), No. 10-2015-0150311 (October 28, 2015), No. 10-2015-0154100 (November 3, 2015), No. 10-2016-0029975 (March 12, 2016), No. 10-2016-004465 (April 11, 2016), and No. 10-2016-0062425 (May 20, 2016), and the embodiments and descriptions described in the aforementioned applications that form the basis of the priority claim are included in the detailed description of this application.

[0030] Figure 1 shows a wireless LAN system according to one embodiment of the present invention. The wireless LAN system includes one or more Basic Service Sets (BSS), where a BSS refers to a collection of devices that can successfully synchronize and communicate with each other. Generally, BSSs are classified into infrastructure BSSs and independent BSSs (IBSSs), and Figure 1 shows an infrastructure BSS.

[0031] As shown in Figure 1, the infrastructure BSSBSS1 and BSS2 include one or more stations STA1, STA2, STA3, STA4, and STA5, access points PCP / AP-1 and PCP / AP-2 which are stations that provide distribution services, and a distribution system (DS) that connects a number of access points PCP / AP-1 and PCP / AP-2.

[0032] A station (STA) is any device that includes Medium Access Control (MAC) and a Physical Layer interface to a wireless medium in accordance with the IEEE 802.11 standard, and in a broad sense includes not only non-APs but also access points (APs). In this specification, "terminal" is used to refer to a non-AP STA or AP, or to refer to both. A station for wireless communication includes a processor and a transmit / receive unit, and depending on the embodiment, may further include a user interface unit and a display unit. The processor generates frames to be transmitted over the wireless network or processes frames received over the wireless network, and also performs various other processes for controlling the station. The transmit / receive unit is functionally connected to the processor and transmits and receives frames over the wireless network for the station.

[0033] An access point (AP) is an individual device that provides connectivity to a distribution system (DS) via a wireless medium for the stations it is connected to. In an infrastructure BSS, communication between non-AP stations is generally conducted via APs, but direct communication between non-AP stations becomes possible when a direct link is established. On the other hand, in this invention, AP is used as a concept that includes PCP (Personal BSS Coordination Point), and in a broad sense, it includes all concepts such as central controllers, base stations (BS), node B, BTS (Base Transceiver System), or site controllers.

[0034] Multiple infrastructure BSSs are interconnected via a distribution system. In this case, multiple BSSs connected via the distribution system are referred to as an Extended Service Set (ESS).

[0035] Figure 2 shows an independent BSS, which is a wireless LAN system according to another embodiment of the present invention. In the embodiment of Figure 2, redundant explanations are omitted for parts that are the same as or corresponding to the embodiment of Figure 1.

[0036] As shown in Figure 2, BSS3 is an independent BSS and does not include APs, so all stations STA6 and STA7 are not connected to APs. An independent BSS is not allowed to connect to a distribution system and forms a self-contained network. In an independent BSS, each station STA6 and STA7 is directly connected to one another.

[0037] Figure 3 is a block diagram showing the configuration of station 100 according to one embodiment of the present invention.

[0038] As shown in the figure, the station 100 according to an embodiment of the present invention includes a processor 110, a transceiver 120, a user interface 140, a display unit 150, and a memory 160.

[0039] First, the transceiver unit 120 transmits and receives wireless signals such as wireless LAN packets and is either built into the station 100 or provided as an external component. According to one embodiment, the transceiver unit 120 includes at least one transceiver module that utilizes different frequency bands. For example, the transceiver unit 120 includes transceiver modules for different frequency bands such as 2.4GHz, 5GHz, and 50GHz. According to one embodiment, the station 100 includes a transceiver module that utilizes a frequency band of 6GHz or higher and a transceiver module that utilizes a frequency band of 6GHz or lower. Each transceiver module performs wireless communication with an AP or external station according to the wireless LAN standard of the frequency band supported by the transceiver module. Depending on the performance and requirements of the station 100, the transceiver unit 120 may operate only one transceiver module at a time or operate multiple transceiver modules together simultaneously. When the station 100 has multiple transceiver modules, each transceiver module may be provided in an independent form, or multiple modules may be integrated into a single chip.

[0040] Next, the user interface unit 140 is provided in the station 100 and includes various forms of input / output means. In other words, the user interface unit 140 receives user input using various input means, and the processor 110 controls the station 100 based on the received user input. The user interface unit 140 also outputs based on instructions from the processor 110 using various output means.

[0041] Next, the display unit 150 outputs an image to the display screen. The display unit 150 outputs various display objects, such as content or user interfaces based on control instructions from the processor 110. The memory 160 stores control programs used by the station 110 and various data associated with them. Such control programs include connection programs necessary for the station 100 to connect with APs or external stations.

[0042] The processor 110 of the present invention executes various instructions or programs and processes data within the station 100. The processor 110 also controls each unit of the station 100 and controls data transmission and reception between units. According to an embodiment of the present invention, the processor 110 executes a program for connection with the AP stored in the memory 160 and receives a communication setup message transmitted by the AP. The processor 110 also interprets information regarding the priority conditions of the station 100 contained in the communication setup message and requests a connection to the AP based on the information regarding 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, or, depending on the embodiment, may refer to a control unit for individually controlling a part of the station 100, such as the transmitting / receiving unit 120. In other words, the processor 110 is a modulation unit or demodulator that modulates the wireless signals transmitted and received from the transmitting / receiving unit 120. The processor 110 controls various operations of wireless signal transmission and reception of the station 100 according to an embodiment of the present invention. Specific embodiments of this will be described later.

[0043] The station 100 shown in Figure 3 is a block diagram according to one embodiment of the present invention, and the separately shown blocks represent logically distinguished elements of the device. Therefore, the above-mentioned elements of the device are implemented on one chip or multiple chips depending on the device design. For example, the processor 110 and the transceiver unit 120 may be integrated and implemented on a single chip, or they may be implemented on separate chips. Furthermore, 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, are selectively provided in the station 100.

[0044] Figure 4 is a block diagram showing the configuration of AP200 according to one embodiment of the present invention. As shown in the figure, AP200 according to one embodiment of the present invention includes a processor 210, a transceiver 220, and a memory 260. In Figure 4, redundant explanations are omitted for parts of the AP200 configuration that are the same as or correspond to the configuration of station 100 in Figure 3.

[0045] Referring to Figure 4, the AP200 according to the present invention includes a transceiver unit 220 for operating a BSS in at least one frequency band. As described in the embodiment of Figure 3, the transceiver unit 220 of the AP200 also includes a plurality of transceiver modules that utilize different frequency bands. In other words, the AP200 according to the embodiment of the present invention includes two or more transceiver modules from different frequency bands, for example, 2.4 GHz, 5 GHz, and 60 GHz. Preferably, the AP200 includes a transceiver module that utilizes a frequency band of 6 GHz or higher and a transceiver module that utilizes a frequency band of 6 GHz or lower. Each transceiver module communicates wirelessly with the station according to the wireless LAN standard of the frequency band supported by the transceiver module. Depending on the performance and requirements of the AP200, the transceiver unit 220 may operate only one transceiver module at a time, or it may operate a plurality of transceiver modules together simultaneously. Next, the memory 260 stores the control program used by the AP200 and various data associated with it. Such a control program includes a management program that manages the station connection. The processor 210 controls each unit of the AP200 and controls the transmission and reception of data between units. According to one embodiment of the present invention, the processor 210 executes the program for connecting with stations stored in the memory 260 and transmits a communication setting message to one or more stations. In this case, the communication setting message includes information regarding the connection priority conditions of each station. The processor 210 also performs connection settings in response to connection requests from stations. According to one embodiment, the processor 210 is a modulation or demodulation unit that modulates the wireless signals transmitted and received from the transmitting and receiving unit 220. The processor 210 controls various operations of wireless signal transmission and reception of the AP200 according to the embodiment of the present invention. Specific embodiments of this will be described later.

[0046] Figure 5 schematically illustrates the process by which the STA establishes a link with the AP.

[0047] Referring to Figure 5, the link between STA100 and AP200 is established through three main steps: scanning, authentication, and association. First, the scanning step is the step in which STA100 obtains access information for the BSS operated by AP200. There are two methods for performing scanning: passive scanning, which obtains information using only beacon messages (S101) periodically transmitted by AP200, and active scanning, in which STA10 transmits a probe request (S103) to AP, receives a probe response (S105) from AP, and obtains access information.

[0048] If STA100 successfully receives wireless access information during the scanning step, it transmits an authentication request (S107a), receives an authentication response from AP200 (S107b), and performs the authentication step. After the authentication step is performed, STA100 transmits an association request (S109a), receives an association response from AP200 (S109b), and performs the association step. In this specification, "association" basically means wireless coupling, but the present invention is not limited to this, and in a broad sense, coupling includes both wireless and wired coupling.

[0049] On the other hand, an additional 802.1X-based authentication step (S111) and an IP address acquisition step via DHCP (S113) are performed. In Figure 5, the authentication server 300 is a server that processes authentication between STA100 and the 802.1X-based system, and may be physically connected to AP200 or exist as a separate server.

[0050] With the proliferation of mobile devices and the widespread use of wireless communication, wireless communication terminals are increasingly communicating in dense environments. In particular, wireless communication terminals are increasingly communicating in environments where many BSSs overlap. When many BSSs overlap, the communication efficiency of wireless communication terminals may decrease due to interference with other wireless communication terminals. Especially when using frequency bands via competitive procedures, wireless communication terminals may not even be able to secure a transmission opportunity due to interference with other wireless communication terminals. To solve this problem, wireless communication terminals perform space reuse operations. Specifically, SR operation includes operations to approach a channel depending on whether the received frame is a frame transmitted from the BSS containing the wireless communication terminal or a frame transmitted from another BSS. In specific embodiments, the operation to approach a channel includes CCA operation and deferral operation. For example, a wireless communication terminal adjusts the CCA threshold depending on whether the frame it receives is a frame transmitted from the BSS containing the wireless communication terminal or a frame transmitted from an OBSS. Also, during SR operation, the wireless communication terminal adjusts the transmission power of the PPDU to be transmitted according to the result of the CCA operation. An example of the SR operation of a wireless communication terminal will be explained with reference to Figures 6 to 23.

[0051] For the sake of explanation, a BSS that includes wireless communication terminals will be referred to as Intra-BSS, and the basic service set that overlaps with Intra-BSS will be referred to as OBSS (Overlapped Basic Service Set). Furthermore, frames transmitted from Intra-BSS will be referred to as Intra-BSS frames, and frames transmitted from OBSS will be referred to as OBSS frames or Inter-BSS frames.

[0052] Figure 6 shows how a wireless communication terminal according to an embodiment of the present invention accesses a wireless medium via a competitive procedure.

[0053] Before transmitting data, a wireless communication terminal senses the carrier on the channel through which the data will be transmitted. If a wireless signal above a certain strength is detected, the wireless communication terminal determines that the channel is busy. If the channel is busy, the wireless communication terminal defers access to that channel. This operation is called CCA (Charge Chain Access). The criterion by which the wireless communication terminal determines whether or not a wireless signal can be detected is called the CCA threshold. Specifically, if the wireless communication terminal detects a wireless signal below the CCA threshold, the wireless communication terminal determines that the channel is idle.

[0054] If a channel is idle for a certain period of time or longer, the wireless communication terminal performs a competition procedure using a backoff window. In this case, the certain period of time is one of the IFS (InterFrame Space) defined in 802.11. For example, the certain period of time may be either AIFS (Arbitration InterFrame Space) or PIFS (PCF InterFrame Space). Specifically, the wireless communication terminal acquires an arbitrary value within the contention window as the backoff counter. In this case, if the idle time of the channel in question lasts for a period longer than the slot time, the wireless communication terminal decrements the value of the backoff counter. In this case, the slot time is 9us. The wireless communication terminal waits until the value of the backoff counter becomes 0. When the value of the backoff counter becomes 0, the wireless communication terminal accesses the channel in question. The period of time during which the terminal waits while decrementing the backoff counter is called the contention window interval.

[0055] After approaching a channel, the wireless communication terminal transmits data. If a wireless communication terminal's access to a channel conflicts with another wireless communication terminal's access to a channel, the wireless communication terminal can acquire any number of additional channels within the competition window and perform a competition procedure. In this case, the wireless communication terminal adjusts the value of the competition window to twice its previous size.

[0056] Furthermore, the channel may become in use before the backoff counter reaches zero. If the channel becomes in use before the backoff counter reaches zero, the wireless communication terminal will have the channel idle for a longer period of time, and if it remains idle for a certain duration or longer, it will perform further competition procedures according to the backoff window. In this case, the wireless communication terminal will perform the backoff procedure based on the value of the backoff counter remaining from the previous competition procedure.

[0057] Through the CCA procedure described above, wireless communication terminals can avoid collisions that occur when multiple wireless communication terminals access the same channel. However, if there are an excessive number of wireless communication terminals located in a narrow area and multiple OBSSs exist, there is a risk of persistent low-level signal interference. Therefore, performing the same CCA and deferral operations without distinguishing whether a signal is transmitted from an OBSS or a BSS can be inefficient. Thus, wireless communication terminals need to efficiently utilize wireless resources through SR operations. More specifically, wireless communication terminals need to perform CCA and deferral operations depending on whether the received frame is an Inter-BSS frame or an Intra-BSS frame. To this end, when a wireless communication terminal transmits a frame, it is necessary to signal the BSS containing the wireless communication terminal. This will be explained with reference to Figures 7 and 8.

[0058] Figure 7 shows the PPDU format used in the wireless communication method according to an embodiment of the present invention.

[0059] Figure 7(a) shows the PPDU format according to the 802.11a / 11g standard. Figure 7(b) shows the PPDU format according to the 802.11n standard. Figure 7(c) shows the PPDU format according to the 802.11ac standard. Figures 7(d) and 7(e) show the PPDU format according to one embodiment of the present invention. Figure 7(d) shows the case where the PPDU is transmitted over a frequency band with a bandwidth of 200 MHz, and Figure 7(e) shows the case where the PPDU is transmitted over a frequency band with a bandwidth of 400 MHz.

[0060] The PPDU according to an embodiment of the present invention is divided into L-STF, L-LTF, L-SIG field, RL-SIG field, HE-SIG-A field, HE-SIG-B field, HE-STF, HE-LTF, SVC field, data field, and Tail & Padding (T&P) field. The wireless communication terminal transmits the L-STF, L-LTF, L-SIG field, RL-SIG field, HE-SIG-A field, and HE-SIG-B field using OFDM based on 64FFT. The wireless communication terminal also transmits the HE-STF, HE-LTF, SVC field, data field, and Tail & Padding (T&P) field using OFDM based on 256FFT.

[0061] The L-SIG field signals information that can be decoded even by legacy wireless communication terminals that do not support embodiments of the present invention. L-STF and L-LTF are training signals used to receive the L-SIG field. Legacy wireless communication terminals perform AGC (Automatic Gain Control) and FOD (Frequency Offset Detection) based on L-STF and L-LTF. The RL-SIG field signals that the L-SIG field is a repeating form and is a PPDU according to embodiments of the present invention. The HE-SIG-A field and HE-SIG-B field signal information related to the PPDU. HE-STF and HE-LTF are training signals for receiving the data field. Wireless communication terminals estimate the channel on which the PPDU is transmitted based on HE-STF and HE-LTF and perform AGC and FOD. In addition, HE-LTF is transmitted in a variable number depending on the number of spatial streams. HE-LTF is classified into HE-LTF-short and HE-LTF-long depending on the application. HE-LTF-short is used for indoor communication and has a duration of 6.4us plus the guard interval, while HE-LTF-long is used for outdoor communication and has a duration of 12.8us plus the guard interval.

[0062] The data field indicates the data contained in the PPDU. In this case, the data may be an A-MPDU. The SVC field indicates the start of the data field. In the Tail & Padding (T&P) field, Padding indicates the padding bits if padding is required for symbol-unit transmission. In the Tail & Padding (T&P) field, Tail is present if the PPDU is protected by a convolution code.

[0063] The HE-SIG-A field contains information for decoding the PPDU. Specifically, if the PPDU contains an HE-SIG-B field, the HE-SIG-A field contains information about the length of the HE-SIG-B field and the MCS (Modulation & Coding Scheme) of the signal containing the HE-SIG-B field. The HE-SIG-A field also includes an indicator showing whether the PPDU transmission is a downlink or uplink transmission. Furthermore, the HE-SIG-A field contains information identifying the BSS to which the wireless communication terminal transmitting the PPDU belongs. In this case, the information identifying the BSS is the BSS color. Specifically, the size of the field indicating the BSS color may be smaller than the maximum value that the BSS identifier (BBSID) can have. This is because the number of symbols transmitted in the HE-SIG-A field is fixed at two, limiting the size of the field that can be used to indicate the BSS color. In this case, the BSSID is the MAC address of the access point included in the BSS.

[0064] BSS colors are set through various embodiments. Specifically, a wireless communication terminal may set a BSS color based on the MAC address of the connected access point. In a particular embodiment, a wireless communication terminal may set a BSS color using the MAC address of the access point associated with the wireless communication terminal and an arbitrary unidirectional function. In such an embodiment, the access point may omit a separate operation to signal the BSS color set on the wireless communication terminal connected to the access point. However, if the size of the field indicating the BSS color is smaller than the maximum value that the MAC address can have, different BSSs will be set to the same BSS color even if the MAC addresses of the access points are unique.

[0065] In other specific embodiments, the access point may arbitrarily set the BSS color. In this case, the access point should separately signal the set BSS color to the wireless communication terminal connected to the access point. Specifically, the access point may signal the BSS color to the wireless communication terminal connected to the access point via a separate message. The wireless communication terminal obtains the BSS color value from the PPDU transmitted by the access point. As in the embodiments described above, if the size of the field indicating the BSS color is smaller than the maximum value that the MAC address can have, different BSSs may have the same BSS color value even if the MAC addresses of the access points are unique.

[0066] If a PPDU containing the HE-SIG-B field is a downlink transmission multi-user (MU), the HE-SIG-B field signals user-specific resource allocation information. Furthermore, the HE-SIG-B field has a variable length. Specifically, the number of symbols transmitted in the HE-SIG-B field may also be variable.

[0067] As described above, the signaling field of the PPDU contains information that identifies the BSS to which the wireless communication terminal that transmitted the PPDU belongs. Therefore, the wireless communication terminal can identify the BSS to which the wireless communication terminal that transmitted the PPDU belongs via the signaling field of the PPDU. More specifically, the wireless communication terminal determines, based on the signaling field of the PPDU, whether the received PPDU was transmitted from the BSS to which the wireless communication terminal belongs or from the OBSS. For example, the wireless communication terminal determines, based on the BSS color filter in the HE-SIG-A field, whether the received PPDU was transmitted from the BSS to which the wireless communication terminal belongs or from the OBSS. The identification of the BSS to which the wireless communication terminal that transmitted the PPDU belongs via the MAC header will be explained with reference to Figure 8.

[0068] Figure 8 shows the A-MPDU format used in a wireless communication method according to an embodiment of the present invention.

[0069] An A-MPDU is a collection of multiple MPDUs. An A-MPDU can contain up to 64 MPDUs, because the bitmap of a Compressed Block ACK can represent 64 MPDUs. An A-MPDU includes a delimiter to separate multiple MPDUs and pads for padding. The delimiter includes an EOF (End-Of-Frame) field indicating whether the MPDU is the last of the multiple MPDUs contained in the A-MPDU, an MPDU Length field indicating the length of the MPDU, and CRC and signature fields used to check for errors in the MPDU.

[0070] An individual MPDU includes a frame body containing the data transmitted by the MPDU, a MAC header signaling information about the MPDU, and an FCS field used to determine if the MPDU contains an error. The frame body is in the form of an MSDU (MAC Service Data Unit) or an A-MSDU, which is a collection of multiple MSDUs. The MAC header includes multiple Address fields indicating the MAC address of the MPDU. Specifically, the MAC header includes four Address fields. These Address fields include at least one of the following: a BSSID field indicating the BSSID that identifies the BSS from which the MPDU was transmitted; a transmitting STA address (TA) field indicating the MAC address of the wireless communication terminal that transmitted the MPDU; and a receiving STA address (RA) field indicating the MAC address of the wireless communication terminal that received the MPDU. In this case, the BSSID is the MAC address of the access point. When an access point transmits or receives an MPDU, one of the Address fields indicates the MAC address of the access point. Depending on the frame type, the MAC header may also include a BSSID field. Therefore, a wireless communication terminal can determine whether the received MPDU is an Inter-BSS frame or an Intra-BSS frame based on the MAC header. More specifically, a wireless communication terminal can determine whether the received MPDU is an Inter-BSS frame or an Intra-BSS frame based on the Address field of the MAC header. For example, if either the RA field or the TA field of the received MPDU indicates the MAC address of the access point to which the wireless communication terminal is connected, the wireless communication terminal will determine that the received MPDU is an Intra-BSS frame.

[0071] A wireless communication terminal performs SR (Sensorship) operations based on whether the MPDU in question is an Inter-BSS frame or an Intra-BSS frame. It also performs Power Save operations based on whether the MPDU in question is an Inter-BSS frame or an Intra-BSS frame. For a wireless communication terminal to determine whether a received MPDU is an Inter-BSS frame based on the MAC header, it must receive the entire MPDU and decode it up to the FCS field. Therefore, if a wireless communication terminal receives a PPDU containing only one MPDU, it may be difficult to perform SR and Power Save operations based on the MAC header. If a wireless communication terminal receives a PPDU containing an A-MPDU, it determines based on the MAC header whether the first MPDU in the A-MPDU is an Inter-BSS frame. If the first MPDU in the A-MPDU is an Inter-BSS frame, it performs SR and Power Save operations during the transmission duration of the remaining MPDUs.

[0072] Furthermore, when a wireless communication terminal determines whether a received MPDU is an Intra-BSS frame or an Inter-BSS frame, the determination based on the BSS color indicated by the PPDU's signaling field may differ from the determination based on the Address field in the MAC header. In this case, the wireless communication terminal determines whether the MPDU is an Intra-BSS frame or an Inter-BSS frame based on the Address field in the MAC header. Specifically, even if the BSS color indicated by the PPDU's signaling field is the same as the BSS color of the BSS containing the wireless communication terminal, if the value of the Address field in the MAC header, which corresponds to the access point's MAC address, is not the MAC address of the access point to which the wireless communication terminal is connected, the wireless communication terminal will determine the received MPDU to be an Inter-BSS frame. Also, even if the BSS color indicated by the PPDU's signaling field is different from the BSS color of the BSS containing the wireless communication terminal, if the value of the Address field in the MAC header, which corresponds to the access point's MAC address, is the MAC address of the access point to which the wireless communication terminal is connected, the wireless communication terminal will determine the received MPDU to be an Intra-BSS frame.

[0073] When a wireless communication terminal receives a wireless signal, it processes the received signal by separating it into a physical layer and a MAC layer. The interface between the physical layer and the MAC layer is called a primitive. The physical layer of the wireless communication terminal is controlled by a PLME (PHY Sublayer Management Entity), and the MAC layer is controlled by an MLME (MAC Sublayer Management Entity). The operation of the wireless communication terminal receiving PPDUs transmitted from a BSS (Broadcasting Station) and an OBSS (Observation Station) via primitives is explained with reference to Figures 9 to 11.

[0074] Figure 9 shows the operation of a wireless communication terminal when receiving a PPDU indicating a BSS color, which corresponds to a BSS containing a wireless communication terminal according to an embodiment of the present invention.

[0075] When a wireless communication terminal receives a PPDU preamble, it measures the received signal strength indicator (RSSI) and begins receiving the PPDU. The start of signal reception is reported by the PHY-CCA.indication(BUSY, Channel-list) primitive in the MAC hierarchy from the physical hierarchy of the wireless communication terminal. In this case, the Channel-list parameter is used to indicate the channel that the CCA has determined to be in use if the wireless communication terminal is using a frequency band with a bandwidth greater than 200 MHz.

[0076] When a PHY-CCA.indicator is received from the physical layer, the wireless communication terminal receives a symbol that transmits the L-LTF of the PPDU and receives the L-SIG field. The wireless communication terminal decodes the L-SIG field to determine the length of the PPDU. If the parity value of the L-SIG field is invalid, the wireless communication terminal receives the PHYRXEND.indication(FormatViolation) primitive from the physical layer.

[0077] If the parity value of the L-SIG field is valid, and the CRC and other fields of the HE-SIG-A field are also valid, the wireless communication terminal determines whether the BSS color indicated by the HE-SIG-A field is the same as the BSS color of the BSS containing the wireless communication terminal. As shown in the embodiment in Figure 9, if the BSS color indicated by the HE-SIG-A field is the same as the BSS color of the BSS containing the wireless communication terminal, the physical hierarchy of the wireless communication terminal maintains the PHY-CCA.indication primitive in a busy state for the duration of the L_LENGTH field contained in the L-SIG field.

[0078] The wireless communication terminal receives the HE-SIG-A field, followed by the HE-SIG-B field and the HE training signal. The HE training signal consists of HE-STF and HE-LTF. Depending on the PPDU transmission mode, the HE-SIG-B field may not be present. Specifically, if the PPDU is in Downlink (DL) Single User (SU) mode, the HE-SIG-B field may not be present.

[0079] The MAC layer of a wireless communication terminal determines that PPDU reception has started when it receives the PHY-RXSTART.indication(RXVECTOR) primitive from the physical layer. In this case, the PHY-RXSTART.indication(RXVECTOR) primitive contains the received signal strength value. However, PPDUs are filtered out from the physical layer depending on various conditions. In this case, the MAC layer of the wireless communication terminal receives the PHY-RXEND.indication(Filtered) primitive from the physical layer. Also, if the received signal disappears before the PSDU reception ends, the MAC layer of the wireless communication terminal receives the PHY-RXEND.indication(CarrierLost) primitive from the physical layer. In such cases, the MAC layer of the wireless communication terminal receives the PHY-CCA.indication(IDLE) primitive from the physical layer after the PSDU has finished receiving.

[0080] When a PPDU is successfully received, the physical layer of the wireless communication terminal combines and decodes the received PSDU bits octet by octet. The MAC layer of the wireless communication terminal receives the decoded PSDU from the physical layer via the PHY-DATA.indication(DATA) primitive. The wireless communication terminal also determines whether it needs to receive the corresponding MPDU based on the Address field of the MAC header.

[0081] If the wireless communication terminal does not need to receive the MPDU, it will stop receiving the PPDU. This is because, at least one of the following conditions must be met: the receiving address in the MPDU's Address field is different from the wireless communication terminal's MAC address, or the MPDU is not a broadcast frame. Specifically, the wireless communication terminal's MAC layer transmits the MAC-RXEND.request primitive to the physical layer and stops receiving the PPDU.

[0082] If the relevant MPDU needs to be received, the radio communication terminal continues to receive the PPDU. After the physical layer of the radio communication terminal finishes receiving the last bit, padding, and tail of the PSDU, it transmits the PHY-RXEND.indication(NoError) primitive to the MAC layer. Next, the physical layer of the radio communication terminal enters the RX IDLE state.

[0083] Figure 10 shows the operation of a wireless communication terminal according to an embodiment of the present invention when it receives a PPDU indicating the BSS color corresponding to OBSS.

[0084] As described above, the wireless communication terminal performs SR operation when receiving an Inter-BSS frame. Specifically, the wireless communication terminal adjusts the CCA threshold depending on whether the frame it receives is an Intra-BSS frame or an Inter-BSS frame. Therefore, the wireless communication terminal may adjust the CCA threshold based on the BSS color indicated by the HE-SIG-A field. Specifically, the wireless communication terminal decodes the HE-SIG-A field as explained via Figure 9. If the BSS color indicated by the HE-SIG-A field is different from the BSS color of the BSS containing the wireless communication terminal, the wireless communication terminal applies the OBSS PD CCA threshold, which is the CCA threshold used to detect the preamble of the PPDU transmitted from the OBSS (Preamble Detection, PD), and performs CCA. As shown in the embodiment in Figure 10, if the strength of the received signal is less than the OBSS PD CCA threshold, the wireless communication terminal determines that the channel is idle. In this case, the physical layer of the wireless communication terminal transmits the PHY-CCA.indication(OBSS,IDLE) primitive to the MAC layer. Therefore, the MAC layer of the wireless communication terminal can receive the PHY-CCA.indication(OBSS,IDLE) primitive from the physical layer. The wireless communication terminal applies the PD CCA threshold, which is the CCA threshold used for the PPDU PD transmitted from the BSS containing the wireless communication terminal, from the point when the transmission of the PPDU transmitted from the OBSS ends, and performs CCA. In this case, the OBSS PD CCA threshold may be greater than the PD CCA threshold.

[0085] As illustrated in the embodiment shown in Figure 10, if another wireless communication terminal included in the same BSS misinterprets the BSS color indicated by the PPDU's signaling field as the BSS color corresponding to the OBSS for any reason, the wireless communication terminal will not be able to receive the PPDU transmitted by the other wireless communication terminal included in the same BSS. Furthermore, if a wireless communication terminal incorrectly determines the BSS color corresponding to the BSS in which it is included, the wireless communication terminal will not be able to receive the PPDU transmitted by the other wireless communication terminal included in the same BSS. For the sake of explanation, this phenomenon in which a wireless communication terminal is unable to receive PPDUs transmitted by other wireless communication terminals included in the same BSS due to BSS color confusion will be referred to as intra-BSS color confusion.

[0086] As mentioned above, because the size of the field indicating the BSS color is limited, different BSSs may be set to the same BSS color. In this case, when a wireless communication terminal included in another BSS transmits a PPDU, the wireless communication terminal applies the PD CCA threshold instead of the OBSS PD CCA threshold. For the sake of explanation, the case in which different BSSs correspond to the same BSS color is called an inter-BSS color collision. Specific examples of intra-BSS color confusion and inter-BSS color collision will be explained with reference to Figure 11.

[0087] Figure 11 shows the cases where inter-BSS colors collide or intra-BSS colors become confused.

[0088] In the embodiment shown in Figure 11(a), the first access point (HE A), the second access point (HE B), and the third access point (HE C) are located in the same space. In this case, the second access point (HE B) and the third access point (HE C) may coincidentally select the same BSS color. In this case, the BSS operated by the second access point (HE B) and the BSS operated by the third access point (HE C) will correspond to the same BSS color, resulting in an inter-BSS color collision.

[0089] In Figure 11(b), the second access point (HE B) changes the BSS color to avoid an Inter-BSS color collision. The second access point (HE B) signals the BSS color change to the wireless communication terminals included in the BSS operated by the second access point (HE B). In this case, if any one of the wireless communication terminals included in the BSS operated by the second access point (HE B) fails to recognize the BSS color change, an Inter-BSS color confusion will occur.

[0090] To prevent Intra-BSS color confusion and Inter-BSS color collisions, wireless communication terminals determine whether a received MPDU is an Intra-BSS frame or an Inter-BSS frame not only based on the BSS color indicated by the PPDU's signaling field, but also based on the Address field in the MAC header. Specifically, when determining whether the MPDU contained in a received PPDU is an Intra-BSS frame or an Inter-BSS frame, if the determination based on the BSS color indicated by the HE-SIG-A field differs from the determination based on the Address field in the MAC header, the wireless communication terminal can determine whether the MPDU is an Intra-BSS frame or an Inter-BSS frame based on the Address field in the MAC header. This is because the MAC address of a wireless communication terminal is fixed and unique for each individual wireless communication terminal, so there is little risk of overlap or confusion with the BSS color. Therefore, wireless communication terminals can determine whether Intra-BSS color confusion and Inter-BSS color collisions have occurred based on the MAC header.

[0091] More specifically, the wireless communication terminal determines whether intra-BSS color confusion and inter-BSS color collisions have occurred based on the Address field of the MAC header. In a specific embodiment, even if intra-BSS color confusion occurs, if the strength of the received signal is greater than the OBSS PD CCA threshold, the wireless communication terminal waits without attempting transmission on the channel in question. In this case, the wireless communication terminal decodes the MAC header contained in the PPDU and checks the Address field. The wireless communication terminal determines whether intra-BSS color confusion has occurred based on the Address field. Alternatively, if the strength of the received signal is less than the OBSS PD CCA threshold, the wireless communication terminal may decode the MAC header before attempting transmission after decoding the signaling field of the PPDU, rather than immediately attempting transmission. This allows the wireless communication terminal to decode the MAC header, check the Address field, and determine whether intra-BSS color confusion has occurred based on the Address field.

[0092] Furthermore, in a specific embodiment, when a wireless communication terminal determines whether it needs to receive the relevant MPDU based on the Address field of the MAC header, it determines whether intra-BSS color confusion and inter-BSS color collision have occurred based on the Address field of the MAC header.

[0093] Figure 12 shows the operation of a wireless communication terminal according to an embodiment of the present invention when it receives a legacy PPDU corresponding to OBSS.

[0094] When a wireless communication terminal receives a legacy PPDU, it performs an SR operation based on the Address field of the MAC header. This is because the signaling field of the legacy PPDU does not contain the BSS color. The operation of the wireless communication terminal to receive the L-SIG field of the PPDU is the same as the PPDU reception operation described in Figures 9 to 10.

[0095] In detail, when a wireless communication terminal receives a PPDU preamble, it measures the strength of the received signal and begins receiving the PPDU. The start of signal reception is reported from the physical layer of the wireless communication terminal to the MAC layer by the PHY-CCA.indication(BUSY, Channel-list) primitive. In this case, the Channel-list parameter is used to indicate the channel that the CCA has determined to be in use if the wireless communication terminal is using a frequency band with a bandwidth greater than 200 MHz.

[0096] When the PHY-CCA.indication is received from the physical layer, the radio communication terminal receives a symbol that transmits the L-LTF of the PPDU and receives the L-SIG field. The radio communication terminal decodes the L-SIG field to determine the length of the PPDU. If the parity value of the L-SIG field is invalid, the radio communication terminal receives the PHYRXEND.indication(FormatViolation) primitive from the physical layer.

[0097] If the parity value of the L-SIG field is valid, the wireless communication terminal receives the signaling field after the L-SIG field.

[0098] If the legacy PPDU is an 802.11n standard VHT PPDU, the radio communication terminal will receive the VHT-SIG-A field if the parity value of the L-SIG field is valid. Unlike the HE-SIG-A field, the VHT-SIG-A field does not contain BSS color.

[0099] After receiving the VHT-SIG-A field, the wireless communication terminal receives VHT training signals, such as VHT-STF and VHT-LTF, and the VHT-SIG-B field. In specific embodiments, the VHT-SIG-B field may be omitted.

[0100] When the MAC layer of a wireless communication terminal receives the PHY-RXSTART.indication(RXVECTOR) primitive from the physical layer, the MAC layer determines that PPDU reception has begun. However, the physical layer of the wireless communication terminal filters out the received PPDU depending on various conditions. If the physical layer of the wireless communication terminal filters out the PSDU, the MAC layer of the wireless communication terminal receives the PHY-RXEND.indication(Filtered) primitive from the physical layer. Also, if the received signal disappears before the PSDU reception ends, the MAC layer of the wireless communication terminal receives the PHY-RXEND.indication(CarreirLost) primitive from the physical layer. In this case, the MAC layer of the wireless communication terminal receives the PHY-CCA.indication(IDLE) primitive from the physical layer after the PSDU has finished.

[0101] When a wireless communication terminal successfully receives a PPDU, the terminal's physical layer combines and decodes the received PSDU bits octet by octet. The terminal's MAC layer receives the decoded PSDU from the physical layer via the PHY-DATA.indication(DATA) primitive. If the PPDU contains an A-MPDU, the terminal can determine whether the MPDU is an Intra-BSS frame or an Inter-BSS frame based on the Address field in the MAC header. More specifically, if the PPDU contains an A-MPDU, the terminal checks the FCS field of the first MPDU among the multiple MPDUs contained in the A-MPDU. If the FCS field is valid, the terminal can determine whether the MPDU is an Intra-BSS frame or an Inter-BSS frame based on the Address field in the MAC header. The terminal also determines whether it needs to receive the MPDU based on the Address field in the MAC header.

[0102] If a wireless communication terminal does not need to receive the MPDU, it will stop receiving the PPDU. If a wireless communication terminal does not need to receive the MPDU, it is at least one of the following: the MPDU is an Inter-BSS frame, the receiving address in the Address field of the MPDU's MAC header is different from the wireless communication terminal's MAC address, or the MPDU is an Inter-BSS frame but not a broadcast frame, as shown in the embodiment in Figure 12. Specifically, the MAC layer of the wireless communication terminal transmits the MAC-RXEND.request primitive to the physical layer and stops receiving the PPDU.

[0103] As shown in the example in Figure 12, if the MPDU in question is an Inter-BSS frame, the wireless communication terminal applies the OBSS PD CCA threshold to perform SR operation. More specifically, the wireless communication terminal applies the OBSS PD CCA threshold to perform CCA. As shown in the example in Figure 12, if the strength of the received signal is less than the OBSS PD CCA threshold, the wireless communication terminal determines that the channel is idle. In this case, the physical layer of the wireless communication terminal transmits the PHY-CCA.indication(OBSS,IDLE) primitive to the MAC layer, and the MAC layer of the wireless communication terminal receives the PHY-CCA.indication(OBSS,IDLE) primitive. Furthermore, the wireless communication terminal applies the PD CCA threshold to perform CCA from the point when the transmission of the PPDU transmitted from OBSS ends.

[0104] If the wireless communication terminal needs to receive the MPDU, it continues to receive the PPDU. The wireless communication terminal needs to receive the MPDU if, at least one of the following conditions is met: the receiving address in the Address field of the MPDU's MAC header is the same as the wireless communication terminal's MAC address, or the MPDU is an Intra-BSS frame but is also a broadcast frame. In this case, the MAC layer of the wireless communication terminal does not propagate the MAC-RXEND.request primitive to the physical layer. After the physical layer of the wireless communication terminal has finished receiving the last bit, padding, and tail of the PSDU, it propagates the PHY-RXEND.indication(NoError) primitive to the MAC layer. After propagating the PHY-RXEND.indication(NoError) primitive, the physical layer of the wireless communication terminal transitions to the RX IDLE state.

[0105] Figures 13 to 14 show the SR and power saving operations of a wireless communication terminal according to an embodiment of the present invention, depending on the type of PPDU and the presence or absence of OBSS when the wireless communication terminal receives a PPDU.

[0106] Figure 13(a) shows the operation of the SR and power saving functions of a wireless communication terminal when a wireless communication terminal according to an embodiment of the present invention receives a legacy PPDU.

[0107] When a wireless communication terminal receives a legacy PPDU, it performs SR and power-saving operations based on the MAC header. This is because the signaling field of a legacy PPDU does not contain information indicating the BSS from which the PPDU was transmitted. Specifically, when a wireless communication terminal receives a legacy PPDU, it performs SR and power-saving operations based on the Address field of the MAC header. In a specific embodiment, the wireless communication terminal performs SR and power-saving operations based on the Address field of the MAC header of the first MPDU contained in A-MPDU.

[0108] If the first MPDU contained in A-MPDU is an Intra-BSS frame, the wireless communication terminal will not perform SR operation. Also, if the first MPDU contained in A-MPDU is an Intra-BSS frame, the wireless communication terminal will perform power-saving operation depending on whether or not MPDU reception is required. Specifically, if the first MPDU contained in A-MPDU is an Intra-BSS frame and the wireless communication terminal does not need to receive the first MPDU contained in A-MPDU, the wireless communication terminal will switch to power-saving mode. Specifically, if the wireless communication terminal does not need to receive the first MPDU contained in the relevant A-MPDU, it is at least one of the following: the receiving address in the Address field of the MAC header of the first MPDU contained in A-MPDU is not the MAC address of the wireless communication terminal, or the first MPDU contained in A-MPDU is not a broadcast frame.

[0109] If the first MPDU contained in A-MPDU is an Inter-BSS frame, the wireless communication terminal performs SR operation. Specifically, after the first MPDU contained in A-MPDU, the wireless communication terminal applies the OBSS PD CCA threshold and performs CCA. If the first MPDU contained in A-MPDU is an Inter-BSS frame, the wireless communication terminal is not permitted to transition to power save mode.

[0110] Figures 13(b) to 13(d) show the operation of SR and power saving of a wireless communication terminal when a wireless communication terminal according to an embodiment of the present invention receives a non-legacy PPDU. When a wireless communication terminal receives a non-legacy PPDU, the wireless communication terminal determines whether the MPDU contained in the PPDU is an Intra-BSS frame or an Inter-BSS frame based on the BSS color indicated by the HE-SIG-A field of the PPDU. In this case, as described above, if the determination based on the BSS color indicated by the HE-SIG-A field and the determination based on the Address field of the MAC header differ, the wireless communication terminal can determine whether the MPDU contained in the PPDU is an Intra-BBS frame or an Inter-BSS frame according to the Address field of the MAC header.

[0111] Figure 13(b) shows the operation of the SR and power save functions of a wireless communication terminal when a wireless communication terminal according to an embodiment of the present invention receives an uplink transmission / downlink transmission SU PPDU.

[0112] The wireless communication terminal first determines whether the MPDU contained in the PPDU is an Intra-BSS frame or an Inter-BSS frame based on the BSS color indicated by the HE-SIG-A field. If the BSS color indicated by the HE-SIG-A field is the same as the BSS color of the BSS containing the wireless communication terminal, the wireless communication terminal determines that the MPDU contained in the PPDU is an Intra-BSS frame. If the BSS color indicated by the HE-SIG-A field is different from the BSS color of the BSS containing the wireless communication terminal, the wireless communication terminal determines that the MPDU contained in the PPDU is an Inter-BSS frame. In this case, the wireless communication terminal initiates SR operation according to the determination made based on the BSS color indicated by the HE-SIG-A field regarding whether the MPDU contained in the PPDU is an Intra-BSS frame or an Inter-BSS frame. The wireless communication terminal also initiates power saving operation according to the determination made based on the BSS color indicated by the HE-SIG-A field regarding whether the MPDU contained in the PPDU is an Intra-BSS frame or an Inter-BSS frame.

[0113] However, the wireless communication terminal further determines whether the MPDU is an Intra-BSS frame or an Inter-BSS frame based on the Address field in the MPDU's MAC header. The wireless communication terminal modifies its SR operation according to the determination made based on the Address field in the MAC header regarding whether the MPDU contained within is an Intra-BSS frame or an Inter-BSS frame. The wireless communication terminal also modifies its power-saving operation according to the determination made based on the Address field in the MAC header regarding whether the MPDU is an Intra-BSS frame or an Inter-BSS frame. If it is determined to be an Intra-BSS frame, the wireless communication terminal determines whether the receiving address in the Address field of the MPDU's MAC header is the same as the wireless communication terminal's MAC address. If the receiving address in the Address field of the MPDU's MAC header is the same as the wireless communication terminal's MAC address, the wireless communication terminal receives the MPDU. If the receiving address in the Address field of the MPDU's MAC header is different from the wireless communication terminal's MAC address, the wireless communication terminal enters power-saving mode. Specifically, the wireless communication terminal enters power-saving mode and maintains it until the PPDU transmission is completed. In this case, the wireless communication terminal determines whether the PPDU transmission has ended based on the L_LENGTH field of the L-SIG field. If the wireless communication terminal determines that the MPDU is an Inter-BSS frame, the wireless communication terminal performs SR operation. The wireless communication terminal performs CCA by applying the OBSS PD CCA threshold. If the strength of the received signal is less than the OBSS PD CCA threshold, the wireless communication terminal determines that the channel is idle. If the wireless communication terminal determines that the MPDU is an Inter-BSS frame, the wireless communication terminal's power saving operation is not permitted.

[0114] Figure 13(c) shows the SR operation and power saving operation of a wireless communication terminal when a wireless communication terminal according to an embodiment of the present invention receives a UL MU PPDU.

[0115] Since UL MU PPDUs are transmitted via MU-MIMO or OFDMA, it is inefficient for other wireless communication terminals, other than the access point receiving the UL MU PPDU, to receive the PSDU contained within it. Therefore, wireless communication terminals receiving UL MU PPDUs perform SR operations based on the BSS color indicated by the HE-SIG-A field, without considering the Address field in the MAC header. Similarly, wireless communication terminals receiving UL MU PPDUs perform power-saving operations based on the BSS color indicated by the HE-SIG-A field, without considering the Address field in the MAC header.

[0116] If the BSS color indicated by the HE-SIG-A field is the same as the BSS color of the BSS containing the wireless communication terminal, the wireless communication terminal will not perform SR operation. Also, if the BSS color indicated by the HE-SIG-A field is the same as the BSS color of the BSS containing the wireless communication terminal, the wireless communication terminal will perform power-saving operation. Specifically, if the BSS color indicated by the HE-SIG-A field is the same as the BSS color of the BSS containing the wireless communication terminal, and the wireless communication terminal is not an access point that is a receiver of UL MU PPDU, the wireless communication terminal will switch to power-saving mode and maintain power-saving mode until the PPDU transmission is terminated. In this case, the wireless communication terminal will determine whether or not to terminate the PPDU transmission based on the L_LENGTH field of the L-SIG field.

[0117] If the BSS color indicated by the HE-SIG-A field differs from the BSS color of the BSS containing the wireless communication terminal, the wireless communication terminal performs SR operation. Specifically, the wireless communication terminal applies the OBSS PD CCA threshold to perform CCA. If the BSS color indicated by the HE-SIG-A field differs from the BSS color of the BSS containing the wireless communication terminal, the wireless communication terminal is not permitted to enter power-saving mode.

[0118] Figure 13(d) shows the SR operation and power saving operation of the wireless communication terminal when a wireless communication terminal according to an embodiment of the present invention receives a DL MU PPDU.

[0119] The recipient (user) field in the HE-SIG-B field of a DL MU PPDU contains the Partial Association ID (Partial AID) of the wireless communication terminal receiving the PPDU. Therefore, the wireless communication terminal can determine whether an Intra-BSS color confusion or Inter-BSS color collision has occurred based on the Partial AID in the recipient field of the HE-SIG-B field. Specifically, the wireless communication terminal determines whether the PPDU is an Intra-BSS frame or an Inter-BSS frame based on the BSS color indicated in the HE-SIG-A field, and then determines that the PPDU is an Intra-BSS frame if the recipient field of the HE-SIG-B field indicates the wireless communication terminal's Partial AID. Furthermore, if the BSS color indicated in the HE-SIG-A field is the same as the BSS color included in the wireless communication terminal, and the recipient field of the HE-SIG-B field does not indicate the wireless communication terminal's Partial AID, the wireless communication terminal will enter power-saving mode. However, the presence or absence of intra-BSS color confusion or inter-BSS color collision can only be determined if the receiver field of the HE-SIG-B field indicates the Partial AID of the wireless communication terminal. Therefore, the presence or absence of intra-BSS color confusion or inter-BSS color collision can only be determined to a limited extent via the HE-SIG-B field. Thus, even when a wireless communication terminal determines the presence or absence of intra-BSS color confusion or inter-BSS color collision based on the Partial AID of the receiver field, the wireless communication terminal can further determine the presence or absence of intra-BSS color confusion or inter-BSS color collision based on the Address field of the MAC header.

[0120] If the wireless communication terminal is an access point, it can determine whether an intra-BSS color confusion or inter-BSS color collision has occurred through a wider range of methods than if the wireless communication terminal were not an access point. Specifically, an access point determines that an inter-BSS color collision has occurred if it receives a DL SU / MU PPDU that shows the same BSS color as the BSS containing the access point.

[0121] Furthermore, if an access point receives an UL SU / MU PPDU that displays the same BSS color as the BSS containing the access point, and the value of the recipient address field in the Address field of the MAC header is an address other than the access point's MAC address, as in the embodiment described above, the access point determines that an Inter-BSS color collision has occurred. Also, if an access point receives an UL SU / MU PPDU that displays the same BSS color as the BSS color without transmitting a trigger frame, the access point determines that an Inter-BSS color collision has occurred. In this case, the trigger frame is a MAC frame that guides the transmission of the wireless communication terminal. Specifically, the trigger frame contains information about the resources that the access point has allocated to the wireless communication terminal. In a specific embodiment, the trigger frame contains information about the frequency band that the access point has allocated to the wireless communication terminal.

[0122] The wireless communication terminal includes the signaling field of the PPDU described above and determines whether the received PPDU is a UL PPDU or a DL PPDU based on an indicator that shows whether the transmission of the PPDU is a downlink transmission or an uplink transmission.

[0123] Figure 14(a) shows the SR operation and power saving operation of a wireless communication terminal according to an embodiment of the present invention, depending on whether or not an Inter-BSS color collision or Intra-BSS color mixing occurs when the wireless communication terminal receives a DL / UL SU PPDU.

[0124] When a wireless communication terminal receives a legacy PPDU, it performs an SR operation based on the Address field in the MAC header. Furthermore, since legacy PPDUs do not contain BSS color, inter-BSS color collisions do not occur.

[0125] When a wireless communication terminal receives a non-legacy PPDU, it performs a signal readiness operation based on the BSS color indicated by the PPDU's signaling field. As described above, the wireless communication terminal determines whether an Inter-BSS color collision has occurred based on the Address field in the MAC header and modifies its SR operation accordingly. Specifically, if the BSS color value indicated by the PPDU's signaling field is the same as the BSS color of the BSS containing the wireless communication terminal, and the determination based on the Address field in the MAC header indicates that the MPDU is an Inter-BSS frame, the terminal performs a CCA (Control Check) by applying the OBSS PD CCA threshold after receiving the first MPDU contained in the PPDU. In this case, if the strength of the received signal is less than the OBSS PD CCA threshold, the wireless communication terminal determines that the channel is idle. Therefore, if the channel remains idle for a certain period of time or longer, the wireless communication terminal accesses the channel. However, if the PPDU contains only one MPDU and the wireless communication terminal determines that an Inter-BSS color collision has occurred based on the MAC header, the wireless communication terminal does not perform an SR operation. This is because, at the time the MAC header of the MPDU is decoded, there is a high probability that no additional MPDUs remain to be received. This also includes cases where the PPDU contains only one MPDU, and cases where the A-MPDU contains only one MPDU.

[0126] Furthermore, if the BSS color value indicated by the PPDU's signaling field differs from the BSS color of the BSS containing the wireless communication terminal, and the MPDU is determined to be an Intra-BSS frame based on the MAC header's Address field, the SR operation is terminated. If the received signal strength is lower than the OBSS PD CCA threshold and the wireless communication terminal accesses the channel, the wireless communication terminal terminates transmission on that channel.

[0127] Furthermore, if the PPDU is transmitted from a BSS containing the wireless communication terminal, and the wireless communication terminal does not need to receive the MPDU contained in the PPDU, the wireless communication terminal will perform a power-saving operation. Specifically, the wireless communication terminal will enter power-saving mode after receiving the first MPDU contained in the PPDU. However, if the PPDU contains only one MPDU, the wireless communication terminal does not need to perform a power-saving operation. Also, if the PPDU is transmitted from a single OBSS, the power-saving operation of the wireless communication terminal is not permitted.

[0128] Figure 14(b) shows the SR operation and power saving operation of a wireless communication terminal according to an embodiment of the present invention, depending on whether or not an Inter-BSS color collision or Intra-BSS color mixing occurs when the wireless communication terminal receives a DL / UL MU PPDU.

[0129] When a wireless communication terminal receives a non-legacy MU DL PPDU, it performs a power-saving operation based on the address in the receiver field of the HE-SIG-B field. Specifically, if the BSS color indicated by the PPDU signaling field of the DL MU PPDU is the same as the BSS color of the BSS containing the wireless communication terminal, and the receiver field of the HE-SIG-B field of the DL MU PPDU does not contain the wireless communication terminal's Partial AID address, the wireless communication terminal will enter power-saving mode. If the wireless communication terminal receives a non-legacy MU PPDU and the wireless communication terminal is not the receiver, the wireless communication terminal cannot receive the PSDU contained in the MU PPDU. Therefore, if the wireless communication terminal receives a non-legacy DL MU PPDU and the wireless communication terminal is not the receiver, the wireless communication terminal cannot determine whether an Inter-BSS color collision has occurred.

[0130] Since UL MU PPDUs are transmitted via MU-MIMO or OFDMA, it is inefficient for wireless communication terminals other than the access point receiving the UL MU PPDU to receive the PSDU contained within it. Therefore, wireless communication terminals receiving UL MU PPDUs perform SR and power-saving operations based on the BSS color indicated by the PPDU's signaling field, without considering the Address field in the MAC header. Specifically, if the BSS color indicated by the PPDU's signaling field is the same as the BSS color of the BSS containing the wireless communication terminal, and the wireless communication terminal is not the access point receiving the UL MU PPDU, the wireless communication terminal enters power-saving mode and maintains this mode until the PPDU transmission is terminated. In this case, the wireless communication terminal determines whether the PPDU transmission has ended based on the L_LENGTH field of the L-SIG field.

[0131] As mentioned above, when a wireless communication terminal receives a legacy PPDU transmitted via MU-MIMO, it is inefficient for the wireless communication terminal to receive the PSDU contained within the PPDU. Therefore, when a wireless communication terminal receives a legacy PPDU transmitted via MU-MIMO, the wireless communication terminal does not perform SR operation. Also, when a wireless communication terminal receives a legacy PPDU transmitted via MU-MIMO, the wireless communication terminal does not perform power saving operation.

[0132] The operation of other wireless communication terminals is the same as when receiving DL / UL SU PPDU as described above.

[0133] Figures 6 to 14 illustrate how a wireless communication terminal according to an embodiment of the present invention performs SR operation and power saving operation. The wireless communication terminal according to an embodiment of the present invention can determine whether a received frame is an Intra-BSS frame or an Inter-BSS frame for SR operation and power saving operation, and the method for making this determination has been explained. Figures 15 to 16 illustrate a specific embodiment of the method by which a wireless communication terminal determines whether a received frame is an Intra-BSS frame or an Inter-BSS frame.

[0134] Figure 15 shows a method for determining whether a frame received by a wireless communication terminal according to an embodiment of the present invention is an Intra-BSS frame or an Inter-BSS frame.

[0135] As described above, wireless communication terminals determine whether a received frame is an Intra-BSS frame or an Inter-BSS frame based on the BSS color indicated by the PPDU's signaling field or the Address field in the MAC header. However, since the size of the field indicating the BSS color is limited, different BSSs may have the same BSS color, as mentioned above. Also, the MAC address value of a wireless communication terminal is unique. Therefore, when determining whether a received frame is an Intra-BSS frame or an Inter-BSS frame based on the BSS color, the wireless communication terminal cannot accurately determine whether the received frame is an Intra-BSS frame or an Inter-BSS frame. Thus, if the determination of whether a received frame is an Intra-BSS frame or an Inter-BSS frame based on the BSS color differs from the determination of whether a received frame is an Intra-BSS frame or an Inter-BSS frame based on the Address field in the MAC header, the wireless communication terminal can determine whether the received frame is an Intra-BSS frame or an Inter-BSS frame based on the Address field in the MAC header. In more detail, if the BSS color indicated by the signaling field of the PPDU containing the received frame is the same as the BSS color of the BSS containing the wireless communication terminal, but the Address field of the MAC header of the received frame indicates that it is an Inter-BSS frame, the wireless communication terminal will ultimately determine that the received frame is an Inter-BSS frame. In another specific embodiment, if the BSS color indicated by the signaling field of the PPDU containing the received frame is different from the BSS color of the BSS containing the wireless communication terminal, but the Address field of the MAC header of the received frame indicates that it is an Intra-BSS frame, the wireless communication terminal will ultimately determine that the received frame is an Intra-BSS frame.

[0136] If any one of the Address fields in the MAC header of a frame received by a wireless communication terminal indicates the BSSID of the BSS containing the wireless communication terminal, the wireless communication terminal determines that the received frame is an Intra-BSS frame. Conversely, if none of the Address fields in the MAC header of a frame received by a wireless communication terminal indicate the BSSID of the BSS containing the wireless communication terminal, the wireless communication terminal determines that the received frame is an Inter-BSS frame. However, depending on the type of MAC frame, the wireless communication terminal may not be able to determine whether the received frame is an Intra-BSS frame or an Inter-BSS frame based solely on the Address field. This is because the information indicated by the Address field in the MAC header can vary depending on the frame type and the settings of the To DS field and From DS field. Therefore, the wireless communication terminal can determine whether the received frame is an Intra-BSS frame or an Inter-BSS frame based on the type of MAC frame and the MAC Address field. This will be explained in detail with reference to Figure 16.

[0137] Figure 16 shows a method by which a wireless communication terminal according to an embodiment of the present invention determines whether a received frame is an Intra-BSS frame or an Inter-BSS frame based on the frame type and the value of the MAC header field.

[0138] A wireless communication terminal determines whether a frame is a data frame based on the value of the Type field in the Frame Control field of the MAC header. If it is a data frame, the information indicated in the Address field may differ depending on the To DS field and the From DS field. Therefore, if the Type field of the Frame Control field in the MAC header indicates that it is a data frame, the wireless communication terminal can determine whether the received frame is an Intra-BSS frame or an Inter-BSS frame based on the values ​​of the To DS field, From DS field, and Address field.

[0139] More specifically, if the frame received by the wireless communication terminal is a data frame and the values ​​of the To DS field and From DS field are all 0, the Address 3 field will indicate the BSSID. Therefore, if the frame received by the wireless communication terminal is a data frame and the values ​​of the To DS field and From DS field are all 0, the wireless communication terminal will determine the received frame to be an Intra-BSS frame if the value of the Address 3 field is the BSSID of the BSS that includes the wireless communication terminal. Also, if the frame received by the wireless communication terminal is a data frame and the values ​​of the To DS field and From DS field are all 0, the wireless communication terminal will determine the received frame to be an Inter-BSS frame if the value of the Address 3 field is not the BSSID of the BSS that includes the wireless communication terminal.

[0140] Furthermore, if the frame received by the wireless communication terminal is a data frame, and the value of the To DS field is 0 and the value of the From DS field is 1, the Address 2 field indicates the BSSID. Therefore, if the frame received by the wireless communication terminal is a data frame, and the value of the To DS field is 0 and the value of the From DS field is 1, the wireless communication terminal will determine the received frame to be an Intra-BSS frame if the value of the Address 2 field is the BSSID of the BSS that the wireless communication terminal includes. Also, if the frame received by the wireless communication terminal is a data frame, and the value of the To DS field is 0 and the value of the From DS field is all 1, the wireless communication terminal will determine the received frame to be an Inter-BSS frame if the value of the Address 2 field is not the BSSID of the BSS that the wireless communication terminal includes. Furthermore, if the value of the To DS field is 0 and the value of the From DS field is 1, and the MSDU included in the MPDU is a basic A-MSDU, the Address 3 field indicates the BSSID. Therefore, if the frame received by the wireless communication terminal is a data frame, with a value of 0 in the To DS field and a value of 1 in the From DS field, and the MSDU contained in the MPDU is a basic A-MSDU, the wireless communication terminal will determine the received frame to be an Intra-BSS frame if the value of the Address 3 field is the BSSID of the BSS containing the wireless communication terminal. Also, if the frame received by the wireless communication terminal is a data frame, with a value of 0 in the To DS field and a value of 1 in the From DS field, and the MSDU contained in the MPDU is a basic A-MSDU, the wireless communication terminal will determine the received frame to be an Inter-BSS frame if the value of the Address 3 field is not the BSSID of the BSS containing the wireless communication terminal.

[0141] Furthermore, if the frame received by the wireless communication terminal is a data frame, and the value of the To DS field is 1 and the value of the From DS field is 0, the Address 1 field indicates the BSSID. Therefore, if the frame received by the wireless communication terminal is a data frame, and the value of the To DS field is 1 and the value of the From DS field is 0, the wireless communication terminal will determine the received frame to be an Intra-BSS frame if the value of the Address 1 field is the BSSID of the BSS that the wireless communication terminal includes. Also, if the frame received by the wireless communication terminal is a data frame, and the value of the To DS field is 1 and the values ​​of the From DS field are all 0, the wireless communication terminal will determine the received frame to be an Inter-BSS frame if the value of the Address 1 field is not the BSSID of the BSS that the wireless communication terminal includes. Furthermore, if the value of the To DS field is 1 and the value of the From DS field is 0, and the MSDU included in the MPDU is a basic A-MSDU, the Address 3 field indicates the BSSID. Therefore, if the frame received by the wireless communication terminal is a data frame, with a value of 1 in the To DS field and a value of 0 in the From DS field, and the MSDU contained in the MPDU is a basic A-MSDU, the wireless communication terminal will determine the received frame to be an Intra-BSS frame if the value of the Address 3 field is the BSSID of the BSS to which the wireless communication terminal is contained. Also, if the frame received by the wireless communication terminal is a data frame, with a value of 1 in the To DS field and a value of 0 in the From DS field, and the MSDU contained in the MPDU is a basic A-MSDU, the wireless communication terminal will determine the received frame to be an Inter-BSS frame if the value of the Address 3 field is not the BSSID of the BSS to which the wireless communication terminal is contained. Furthermore, if the frame received by the wireless communication terminal is a data frame, with a value of 1 in the To DS field and a value of 1 in the From DS field, and the MSDU contained in the frame is a BASIC A-MSDU, then the Address 3 and Address 4 fields will indicate the BSSID.If a wireless communication terminal receives a data frame, with a value of 1 in the To DS field and a value of 1 in the From DS field, and the MSDU contained in the frame is BASIC A-MSDU, the wireless communication terminal will determine the received frame to be an Intra-BSS frame if the value of either the Address 3 field or the Address 4 field matches the BSSID of the BSS containing the wireless communication terminal. Alternatively, if a wireless communication terminal receives a data frame, with a value of 1 in the To DS field and a value of 1 in the From DS field, and the MSDU contained in the frame is BASIC A-MSDU, the wireless communication terminal will determine the received frame to be an Inter-BSS frame if the values ​​of both the Address 3 field and the Address 4 field do not match the BSSID of the BSS containing the wireless communication terminal.

[0142] If the received frame is a management frame, the Address 1 field is the RA field and the Address 2 field is the TA field. Also, if the received frame is a management frame, the Address 3 field is the BSSID field. Therefore, if the frame received by the wireless communication terminal is a management frame, the wireless communication terminal will determine that the received frame is an Intra-BSS frame if any one of the values ​​in the Address 1, Address 2, and Address 3 fields is the BSSID of the BSS that includes the wireless communication terminal. Furthermore, if the frame received by the wireless communication terminal is a management frame, the wireless communication terminal will determine that the received frame is an Intra-BSS frame unless all of the values ​​in the Address 1, Address 2, and Address 3 fields are the BSSID of the BSS that includes the wireless communication terminal.

[0143] Furthermore, if the BSS containing the wireless communication terminal has a BSSID included in a Multiple BSSID set, the wireless communication terminal will consider the BSSID included in the Multiple BSSID set as the BSSID of the BSS containing the wireless communication terminal when determining whether a received frame is an Intra-BSS frame or an Inter-BSS frame (regard). Specifically, if the value of the Address field described above is the BSSID of the BSS containing the wireless communication terminal, this includes the case where the value of the Address field is one of the multiple BSSIDs included in the Multiple BSSID set if the BSS containing the wireless communication terminal has a BSSID included in a Multiple BSSID set.

[0144] Furthermore, if the value of the Address field is the BSSID of the BSS containing the wireless communication terminal, setting the Individual / Group bit in the Address field to 0 includes the case where it is the same as the BSSID of the BSS containing the wireless communication terminal. Also, if the value of the Address field is the BSSID of the BSS containing the wireless communication terminal, it includes the case where the value of the Address field is the bandwidth signaling variant of the BSSID of the BSS containing the wireless communication terminal.

[0145] Furthermore, if the value of the FCS field in the MPDU is valid, the wireless communication terminal will determine whether the received frame is an Intra-BSS frame or an Inter-BSS frame based on the MAC header or the Address field of the MAC header.

[0146] Figure 17 shows the actions of a wireless communication terminal according to an embodiment of the present invention to correct an Inter-BSS color collision and to prevent Intra-BSS color confusion when the wireless communication terminal detects an Inter-BSS color collision.

[0147] If a wireless communication terminal that is not an access point detects an Inter-BSS color collision, the wireless communication terminal transmits a frame to the access point requesting a BSS color change.

[0148] Furthermore, when an access point changes the BSS color, the access point transmits a frame indicating the BSS color change. In this case, a wireless communication terminal that receives the frame indicating the BSS color change does not need to perform SR operations based on the BSS color indicated by the PPDU's signaling field for a certain period of time. Also, a wireless communication terminal that receives the frame indicating the BSS color change does not need to perform power saving operations based on the BSS color indicated by the PPDU's signaling field for a certain period of time. In this case, the frame indicating the BSS color change includes information indicating a certain period of time. In a specific embodiment, if a wireless communication terminal whose BSS color is 1 receives a frame indicating that the BSS color will change to 2, the wireless communication terminal will operate as follows: The wireless communication terminal will not perform SR operations related to the PPDU showing BSS color 2 for a certain period of time from the time it receives the frame indicating the BSS color change. Also, the wireless communication terminal will not perform power saving operations related to the PPDU showing BSS color 2 for a certain period of time from the time it receives the frame indicating the BSS color change.

[0149] Furthermore, the frame indicating a BSS color change includes a counter that indicates the BSS color change history. Specifically, the counter value toggles between 0 and 1. In other specific embodiments, the counter value increases in a wrap-around manner within a certain range. A wireless communication terminal that receives a frame indicating a BSS color change determines that the BSS color has changed if the counter value changes.

[0150] In other specific embodiments, the frame that changes the BSS color includes a counter indicating when the BSS color is applied. Specifically, the access point periodically transmits frames indicating the change in BSS color over a certain period of time. During this time, the wireless communication terminal decrements the counter value each time it transmits a frame indicating the change in BSS color. When the wireless communication terminal receives a frame indicating the change in BSS color, it applies the changed BSS color if the counter value is 0.

[0151] The wireless communication terminal prevents the occurrence of Intra-BSS color confusion through this operation. A specific example in which this operation is applied will be explained with reference to Figures 17(a) and 17(b).

[0152] The embodiment shown in Figure 17(a) represents a case where a station detects an Inter-BSS color collision. In this case, the station transmits a frame requesting a BSS color change to the access point. The access point receives the frame requesting a BSS color change and transmits an ACK frame to the station for the frame requesting a BSS color change. The access point changes the BSS color and transmits a frame indicating the BSS color change. In this case, the counter value of the frame indicating the BSS color change is 1. The counter value indicates the BSS color change history. Furthermore, a wireless communication terminal that receives the frame indicating a BSS color change will not perform SR operation or power saving operation for a certain period of time from the time it receives the frame indicating the BSS color change.

[0153] The embodiment shown in Figure 17(b) represents a case where an access point detects an Inter-BSS color collision. In this case, the access point transmits a frame indicating a BSS color change. Specifically, the access point periodically transmits frames indicating a BSS color change for a certain period of time. During this time, the access point decrements a counter value contained in the frame indicating the BSS color change to indicate when the BSS color should be applied. When a wireless communication terminal receives a frame indicating a BSS color change with a counter value of 0, it applies the changed BSS color.

[0154] Figure 18 shows a method by which a wireless communication terminal according to one embodiment of the present invention combines frequency bands for broadband communication.

[0155] In OFDMA transmission, unless a sub-frequency band is used, the wireless communication terminal uses one of the following frequency bands with a bandwidth of 20 MHz, 40 MHz, 80 MHz, and 160 MHz. Specifically, the wireless communication terminal uses a primary channel with a bandwidth of 20 MHz and a secondary channel adjacent to the primary channel with a bandwidth of 20 MHz. In this case, the primary channel is specified for each access point. The combined frequency band is referred to as the primary 40 MHz channel. The wireless communication terminal also uses a primary 40 MHz channel and a secondary channel adjacent to the primary 40 MHz channel with a bandwidth of 40 MHz. In this case, the combined frequency band is referred to as the primary 80 MHz channel. The wireless communication terminal also uses a primary 80 MHz channel and a secondary channel adjacent to the primary 80 MHz channel with a bandwidth of 80 MHz. Furthermore, the wireless communication terminal uses a primary 80 MHz channel and a secondary channel that is not adjacent to the primary 80 MHz channel with a bandwidth of 80 MHz. For convenience of explanation, in this specification, a frequency band with a bandwidth greater than 20 MHz is referred to as broadband. When wireless communication terminals perform broadband communication, the bandwidth of the frequency band requiring CCA also widens. Therefore, when wireless communication terminals approach a channel via competitive procedures, an efficient CCA method for broadband communication is required. The method by which wireless communication terminals perform CCA for broadband communication will be explained with reference to Figures 19 to 20.

[0156] Figure 19 shows a method by which a wireless communication terminal according to one embodiment of the present invention transmits broadband PPDU.

[0157] The wireless communication terminal performs a competition procedure on the main channel, which has a channel-specific frequency bandwidth. During this procedure, the wireless communication terminal transmits the PPDU by combining it with a previously idle subchannel during a certain preceding time period determined via the competition procedure on the main channel. Specifically, the subchannel is the frequency bandwidth adjacent to the main channel. The specified time period is PIFS. Furthermore, the channel-specific frequency bandwidth represents the minimum frequency bandwidth that the wireless communication terminal can use in OFDMA transmission, unless the wireless communication terminal is using a sub-frequency band. The channel-specific frequency bandwidth may be 20 MHz, as described above.

[0158] In the competition procedure, the specific operation of the wireless communication terminal is the same as in the embodiment described with reference to Figure 6. Specifically, if a channel is idle for a certain period of time or longer, the wireless communication terminal performs a competition procedure using a backoff window. In this case, the certain period of time is one of the IFS defined in 802.11. For example, the certain period of time may be either AIFS or PIFS. Specifically, the wireless communication terminal acquires an arbitrary value within the competition window as the backoff counter. If the idle time of the channel in question lasts for a period longer than the slot time, the wireless communication terminal decrements the value of the backoff counter. In this case, the slot time is 9us. The wireless communication terminal waits until the backoff value becomes 0. When the value of the backoff counter becomes 0, the wireless communication terminal accesses the channel in question.

[0159] The channel may become in use before the backoff counter reaches zero. In such cases, the wireless communication terminal will perform further competition procedures according to the backoff window if the channel remains idle for a certain period of time or longer. At this time, the wireless communication terminal will perform the backoff procedure based on the value of the backoff counter remaining from the previous competition procedure.

[0160] In the embodiment shown in Figure 19(a), the wireless communication terminal performs the competition procedure on the Primary 20MHz Channel. From the moment the backoff counter value becomes 0, both the secondary 20MHz Channel and the secondary 40MHz Channel have remained idle during the previous PIFS. Therefore, the wireless communication terminal transmits the PPDU via a frequency band with an 80MHz bandwidth when the backoff counter value becomes 0.

[0161] In the embodiment shown in Figure 19(b), the wireless communication terminal performs the competition procedure on the main 20MHz channel. From the point when the backoff counter value became 0, the secondary 20MHz channel remained idle during the previous PIFS. However, from the point when the backoff counter value became 0, the secondary 40MHz channel did not remain idle during the previous PIFS. Therefore, the wireless communication terminal transmits the PPDU over a frequency band with a bandwidth of 40MHz. In the embodiments shown in Figures 19(a) and 19(b), the wireless communication terminal should dynamically allocate the PPDU according to the available frequency bandwidth. A case where it is difficult for the wireless communication terminal to dynamically allocate the PPDU according to the bandwidth of the available frequency band will be explained via Figure 19(c).

[0162] If transmission is not possible within the frequency band selected by the wireless communication terminal during transmission preparation, the wireless communication terminal will wait without transmitting, even if the main channel is idle for a period longer than the backoff window indicated by the backoff counter value. In this case, the wireless communication terminal will wait until it can transmit the PPDU from the frequency band selected by the wireless communication terminal during transmission preparation.

[0163] In the embodiment shown in Figure 19(c), the wireless communication terminal performs the competition procedure on the main 20MHz channel. From the point when the backoff counter value becomes 0, the sub 20MHz channel was idle during the previous PIFS, but the sub 40MHz channel did not remain idle. Therefore, the wireless communication terminal waits until transmission becomes possible in a frequency band with an 80MHz bandwidth.

[0164] Figure 20 shows that a wireless communication terminal according to an embodiment of the present invention transmits PPDU over a frequency band having a frequency bandwidth of 40 MHz.

[0165] As described above, before initiating the backoff procedure, the wireless communication terminal performs a CCA operation to determine if the channel is idle. Furthermore, during the backoff procedure, the wireless communication terminal performs a CCA operation during the slot time to determine if the channel is idle. In this case, the wireless communication terminal performs the CCA operation based on at least one of the following: preamble detection and energy detection (ED). Additionally, the wireless communication terminal performs the CCA operation based on repeat detection (RD).

[0166] PD (Predictive Determination) is a method by which a wireless communication terminal detects a repeating signal pattern transmitted from the L-STF (Laser-Splitting Frame), which is the leading part of the PPDU (Public Power Unit), and detects the strength of the signal used for PPDU transmission. Energy Detection (ED) is a method by which a wireless communication terminal detects the energy strength of an arbitrary radio signal. RD (Radio Dynamics) is a method by which a wireless communication terminal detects a repeating pattern from the signal used for PPDU transmission and detects the strength of the signal used for PPDU transmission. The threshold used by a wireless communication terminal when performing CCA (Control Cancellation) based on PD from the main channel is called the first PD CCA threshold. The threshold used by a wireless communication terminal when performing CCA based on ED from the main channel is called the first ED CCA threshold. The threshold used by a wireless communication terminal when performing CCA based on RD from the main channel is called the first RD CCA threshold. The first RD CCA threshold may be the same as the first PD CCA threshold. When a PPDU received by a wireless communication terminal is transmitted from OBSS (Observation Basis Station), the wireless communication terminal applies the OBSS first PD CCA threshold to the PPDU transmitted from OBSS and performs a CCA operation. In this context, the OBSS 1st PD CCA threshold refers to the threshold for performing CCA based on PD on the main channel. The wireless communication terminal determines whether the received PPDU is a PPDU transmitted from OBSS based on at least one of the BSS color indicated by the PPDU's signaling field and the Address field of the MAC header. More specifically, the wireless communication terminal determines whether the received PPDU is a PPDU transmitted from OBSS according to the embodiment described in Figures 6 to 16.

[0167] In a specific embodiment, the OBSS 1st PD CCA threshold may be the same as or greater than the 1st PD CCA threshold, and less than or the same as the 1st ED CCA threshold. Furthermore, the wireless communication terminal adjusts the value of OBSS 1st PD based on the transmission power (TXPWR) used when the wireless communication terminal transmits PPDU data. For example, the wireless communication terminal adjusts the value of OBSS 1st PD based on the transmission power used when the wireless communication terminal transmits PPDU data, within the range of 1st PD (-82 dBm) ≤ OBSS 1st PD ≤ 1st ED (-62 dBm).

[0168] As described above, when a wireless communication terminal transmits a PPDU, it transmits the fields for legacy wireless communication terminals and non-legacy signaling fields via OFDM based on 64FFT. Specifically, the fields for legacy wireless communication terminals are the L-STF, L-LTF, and L-SIG fields. The non-legacy signaling fields are the RL-SIG field, HE-SIG-A field, and HE-SIG-B field. When a wireless communication terminal transmits a PPDU via OFDM based on 64FFT, the signal transmitted in the PPDU consists of data with a duration of 3.2us and a cyclic prefix (CP) with a duration of 0.4us or 0.8us, repeated. Therefore, the wireless communication terminal receives approximately 6-7 symbols via CCA during PIFS (25us) to measure the signal strength.

[0169] A wireless communication terminal transmits the data and part of the preamble contained in the PPDU using OFDM based on 256FFT. When a wireless communication terminal transmits a PPDU using OFDM based on 256FFT, the signal transmitting the PPDU consists of data with a duration of 12.8us and repeating cyclic prefixes with a duration of one of 0.8us, 1.6us, or 3.2us. Therefore, the wireless communication terminal measures the signal strength by receiving a maximum of 1-2 symbols via CCA during the PIFS (25us). Thus, when a wireless communication terminal receives a signal that transmits a PPDU using OFDM with both 64FFT and 256FFT, it is difficult for the wireless communication terminal to determine whether the signal received during the PIFS is the signal transmitting the PPDU. Therefore, if the wireless communication terminal fails to determine whether the received signal is the signal transmitting the PPDU, the wireless communication terminal performs CCA based on ED. Furthermore, when a wireless communication terminal receives a signal that transmits a PPDU via OFDM using both 64FFT and 256FFT, the wireless communication terminal determines whether the received signal is a signal that transmits a PPDU based not only on the PD but also on the RD.

[0170] In the embodiment shown in Figure 20(a), the wireless communication terminal performs a competition procedure based on the backoff counter on the main channel. At this time, the wireless communication terminal performs a CCA based on the PD and ED. The wireless communication terminal also performs a CCA on the sub-channel based on the PD, ED, and RD, and determines whether it was idle during the previous PIFS from the point when the backoff counter becomes 0.

[0171] Furthermore, if the subchannel is idle for a certain period of time from the transmission time determined via the competition procedure on the main channel, the wireless communication terminal will combine the main channel and the subchannel to transmit the PPDU, but this certain period may be longer than the PIFS. As mentioned above, when the PPDU is transmitted via OFDM based on 256FFT, it is difficult for the wireless communication terminal to determine whether the radio signal is a PPDU during the PIFS. In this case, the certain period may be shorter than or equal to the AIFS. If the wireless communication terminal obtains 0 as the backoff counter in the competition procedure on the main channel, the wireless communication terminal determines whether the main channel is idle during the AIFS time. Therefore, when the wireless communication terminal determines whether the subchannel is idle for a time interval longer than the AIFS, the idle time interval required to transmit the PPDU from the subchannel may be longer than the idle time interval required to transmit the PPDU from the main channel.

[0172] In other specific embodiments, the fixed time may be equal to or shorter than the sum of the time indicated by AIFS and the time indicated by the backoff counter. Through this, the wireless communication terminal can improve the accuracy of detecting PPDUs transmitted via the subchannel. However, the accuracy of detecting PPDUs transmitted via the subchannel may be variable depending on the backoff counter value. In the embodiment of Figure 20(b), the wireless communication terminal performs the competition procedure on the main channel as described in the embodiment of Figure 20(a). In the competition procedure on the main channel, the wireless communication terminal determines whether the subchannel remained idle during the xIFS time prior to the point when the backoff counter was 0. In this case, xIFS indicates a frame interval greater than PIFS.

[0173] In other specific embodiments, when a wireless communication terminal determines whether a subchannel was idle for a certain period of time prior to the transmission time determined via the competition procedure of the main channel, the length of that period can be adjusted by the modulation method of the received signal. In this case, the modulation method is either OFDM transmission using 64FFT or OFDM transmission using 256FFT. Specifically, when the signal received from the subchannel is transmitted via OFDM based on 64FFT, the wireless communication terminal determines whether the subchannel was idle for a first time interval prior to the transmission time determined via the competition procedure of the main channel. Also, when the signal received from the subchannel is transmitted via OFDM based on 256FFT, the wireless communication terminal determines whether the subchannel was idle for a second time interval prior to the transmission time determined via the competition procedure of the main channel. In this case, the first time interval may be shorter than the second time interval. In a specific embodiment, the first time interval is PIFS, and the second time interval may be longer than the time indicated by PIFS and shorter than the sum of the time indicated by AIFS and the time indicated by the backoff counter.

[0174] If the sum of the time indicated by AIFS and the time indicated by the backoff counter obtained from the main channel competition procedure is greater than the minimum time required to detect a signal transmitted via OFDM based on 256FFT, and the radio communication terminal receives a signal transmitted via OFDM based on 256FFT from the subchannel, the time the radio communication terminal can determine whether the subchannel has remained idle is xIFS, which is longer than PIFS. If the sum of the time indicated by AIFS and the time indicated by the backoff counter obtained from the main channel competition procedure is greater than the minimum time required to detect a signal transmitted via OFDM based on 256FFT, and the radio communication terminal receives a signal transmitted via OFDM based on 64FFT from the subchannel, the time the radio communication terminal can determine whether the subchannel has remained idle is either PIFS or xIFS.

[0175] If the sum of the time indicated by AIFS and the time indicated by the backoff counter obtained from the main channel's competition procedure is shorter than the minimum time required to detect a signal transmitted via OFDM based on 256FFT, it can be determined whether the subchannel was idle between the transmission time determined via the main channel's competition procedure and PIFS. In this case, if the wireless communication terminal detects a signal transmitted via OFDM from the subchannel based on 256FFT, it determines whether the subchannel was idle during PIFS based on ED. Also, if the wireless communication terminal detects a signal transmitted via OFDM from the subchannel based on 64FFT, it determines whether the subchannel was idle during PIFS based on PD, RD, and ED. This is because the probability of failing to detect OFDM symbols is high when the wireless communication terminal attempts to detect OFDM symbols transmitted from the subchannel based on 256FFT in a relatively short time.

[0176] In the embodiments shown in Figure 20(c) and Figure 20(d), when the signal received by the wireless communication terminal is transmitted via OFDM based on 64FFT, the wireless communication terminal determines whether the subchannel was idle during the PIFS prior to the time when transmission was decided in the competitive procedure of the main channel. Furthermore, when the signal received by the wireless communication terminal is transmitted via OFDM based on 256FFT, the wireless communication terminal determines whether the subchannel was idle during the xIFS prior to the time when transmission was decided in the competitive procedure of the main channel. In this case, xIFS represents a time greater than PIFS.

[0177] Wireless communication terminals apply different PD CCA thresholds depending on whether the signal received from the subchannel is transmitted via OFDM based on 64FFT or 256FFT. For convenience of explanation, the threshold used by wireless communication terminals when performing CCA based on PD from the subchannel is referred to as the second PD CCA threshold. More specifically, wireless communication terminals apply a larger second PD CCA threshold to radio signals transmitted via OFDM based on 256FFT than to radio signals transmitted via OFDM based on 64FFT. Even if the signal received by the wireless communication terminal from the subchannel is an OBSS PPDU, the wireless communication terminal applies different PD CCA thresholds depending on whether the received OBSS PPDU is transmitted via OFDM based on 64FFT or 256FFT. In this case, the threshold applied to the CCA operation performed based on PD for the OBSS PPDU transmitted from the subchannel is referred to as the OBSS second PD CCA threshold. Furthermore, the threshold applied when OBSS PPDU is transmitted via OFDM on a subchannel based on 64FFT is called the OBSS second legacy PD CCA threshold, and the threshold applied when OBSS PPDU is transmitted via OFDM on a subchannel based on 256FFT is called the OBSS second non-legacy PD CCA threshold. Additionally, the CCA operation performed on an ED from a subchannel is called the second ED CCA threshold. More specifically, the OBSS second PD CCA threshold may be greater than or equal to the second PD CCA threshold, and less than or equal to the second ED CCA threshold. The wireless communication terminal adjusts the OBSS second PD CCA threshold based on the transmission power used when transmitting the PPDU. The second RD CCA threshold, which is the threshold used when the wireless communication terminal performs CCA on an RD from a subchannel, may be the same as the second PD CCA threshold. Due to these operations, the wireless communication terminal needs to determine whether an OBSS PPDU is being received from a subchannel.

[0178] The wireless communication terminal determines whether the signal received from the sub-channel is an OBSS PPDU based on its judgment regarding the signal received from the main channel. Specifically, when the wireless communication terminal receives a PPDU from the main channel, it applies the judgment regarding the PPDU received from the main channel. Specifically, if the PPDU received by the wireless communication terminal from the main channel is a PPDU transmitted from OBSS, the wireless communication terminal applies the OBSS 1st PD CCA threshold to the main channel and performs a CCA operation, and applies the OBSS 2nd PD CCA threshold to the sub-channel and performs a CCA operation. In this case, the OBSS 1st PD CCA threshold and the OBSS 2nd PD CCA threshold may be the same. In the embodiment shown in Figure 20(c), the wireless communication terminal determines that the PPDU received from the main channel is a PPDU transmitted from OBSS. As a result, the wireless communication terminal applies the OBSS 1st PD CCA threshold to the main channel and performs a CCA operation. The wireless communication terminal also applies the OBSS 2nd PD CCA threshold to the sub-channel and performs a CCA operation.

[0179] Furthermore, if a wireless communication terminal does not detect a PPDU from the main channel, it may determine that a PPDU detected from the sub-channel is a PPDU transmitted from OBSS. This is because wireless communication terminals included in the same BSS extend the frequency band by including the main channel, as explained through Figure 18. In the embodiment shown in Figure 20(d), the wireless communication terminal cannot detect the reception of a PPDU from the main channel. Therefore, the wireless communication terminal determines that the PPDU received from the sub-channel is an OBSS PPDU. The wireless communication terminal applies the OBSS second PD CCA threshold to the sub-channel and performs CCA operation.

[0180] Furthermore, the OBSS second PD CCA threshold may be greater than or equal to the second PD CCA threshold, and may be less than or equal to the second ED CCA threshold. The wireless communication terminal adjusts the OBSS second PD CCA threshold based on the transmission power of the PPDU transmitted by the wireless communication terminal.

[0181] In detail, the wireless communication terminal adjusts the OBSS second legacy PD CCA threshold within the range of second legacy PD CCA threshold (-72dBm) ≤ OBSS second legacy PD CCA threshold ≤ second ED CCA (-62dBm) threshold, based on the transmission power of the PPDU transmitted by the wireless communication terminal. When a symbol based on 64FFT OFDM is detected, it is unclear whether the PPDU contained in the symbol is a legacy PPDU or a non-legacy PPDU. Therefore, in order to maintain fairness with legacy wireless communication terminals, the wireless communication terminal uses a value greater than -72dBm, which is the CCA threshold applied by legacy wireless communication terminals when performing subchannel CCA, as the threshold for the second legacy PD CCA.

[0182] In another specific embodiment, if a wireless communication terminal detects a signal transmitted via OFDM based on 256FFT from a subchannel, the wireless communication terminal adjusts the OBSS second non-legacy PD CCA threshold within the range of second non-legacy PD CCA threshold (-82dBm) ≤ OBSS second non-legacy PD CCA threshold ≤ second ED CCA threshold (-62dBm) based on the transmission power of the PPDU transmitted by the wireless communication terminal. This is because, since it is clear that the detected symbol based on 256FFT ODFM is a non-legacy PPDU, there is no need to consider equity issues with legacy wireless communication terminals.

[0183] Furthermore, the wireless communication terminal adjusts the OBSS 2nd Legacy PD CCA threshold and the OBSS 2nd Non-Legacy PD CCA threshold based on the OBSS 1st PD CCA threshold. Specifically, the wireless communication terminal applies the OBSS 1st PD CCA threshold to the OBSS 2nd Legacy PD CCA threshold and the OBSS 2nd Non-Legacy PD CCA threshold. Also, if the OBSS 1st PD CCA threshold is greater than the OBSS 2nd Legacy PD CCA threshold, the wireless communication terminal applies the OBSS 1st PD CCA threshold to the OBSS 2nd Legacy PD CCA threshold. In this case, if the OBSS 1st PD CCA threshold is less than or equal to the OBSS 2nd Legacy PD CCA threshold, it is not necessary to apply the OBSS 1st PD CCA threshold to the OBSS 2nd Legacy PD CCA threshold.

[0184] Figure 21 shows that a wireless communication terminal according to an embodiment of the present invention adjusts the transmission power during SR operation.

[0185] As described above, wireless communication terminals set the OBSS PD CCA threshold based on the transmission power of the PPDU they transmit. Specifically, if the transmission power of the transmitted PPDU is low, the wireless communication terminal increases the OBSS PD CCA threshold. Conversely, if the transmission power of the transmitted PPDU is high, the wireless communication terminal decreases the OBSS PD CCA threshold. This is because transmitting the PPDU with low transmission power reduces the impact of the wireless communication terminal on OBSS, while transmitting the PPDU with high transmission power increases the impact of the wireless communication terminal on OBSS. If the wireless communication terminal adjusts the transmission power of the PPDU not only at the CCA threshold but also during SR operation, it can reduce the impact of the wireless communication terminal's SR operation on transmission from OBSS or increase the efficiency of the SR operation.

[0186] Therefore, while an OBSS PPDU is being transmitted, the wireless communication terminal may transmit the PPDU with transmission power that is not adjusted for SR operation, or with transmission power adjusted for SR operation. In this case, the power that is not adjusted for SR operation is a predetermined transmission power. In other specific embodiments, the power that is not adjusted for SR operation is the maximum transmission power that the wireless communication terminal can output. The predetermined transmission power is specified by the access point. Specifically, when the wireless communication terminal detects the reception of an OBSS PPDU and applies the OBSS PD CCA threshold, the wireless communication terminal adjusts the transmission power based on the OBSS PD CCA threshold and transmits the PPDU. If the wireless communication terminal cannot detect the reception of an OBSS PPDU, the wireless communication terminal transmits the PPDU with transmission power corresponding to the PD CCA threshold. Specifically, if the wireless communication terminal cannot detect the reception of an OBSS PPDU, the wireless communication terminal transmits the PPDU without adjusting the transmission power corresponding to the PD CCA threshold. This is because the PD CCA threshold is not a relatively high CCA threshold like the OBSS PC CCA threshold.

[0187] In Figure 21(a), (a)-1 shows the case where the wireless communication terminal could not receive the PPDU. In this case, the wireless communication terminal applies the first PD CCA threshold PD1 and performs a CCA operation. The wireless communication terminal also transmits the PPDU with unadjusted transmission power for SR operation. Figure 21(a)-2 shows the case where the wireless communication terminal receives a PPDU from the main channel and detects that it was transmitted from OBSS. After the wireless communication terminal detects the PPDU transmitted from OBSS from the main channel, it applies the OBSS first PD CCA threshold PD1 and performs a CCA. The wireless communication terminal determines that the main channel is idle and performs a competition procedure based on backoff. When the transmission of the PPDU is decided by the competition procedure, the wireless communication terminal transmits the PPDU with the transmission power determined based on the OBSS first PD CCA threshold PD1.

[0188] Figure 21(b) shows the network topology when non-legacy access points HE A, HE B, HE C, non-legacy stations A-1, A-2, B-1, C-1, and legacy station Leg coexist. Figure 21(c) shows the PPDU format containing information about SR operation. The operation of wireless communication terminals to adjust transmission power is explained in detail through Figures 21(b) to 21(c).

[0189] A wireless communication terminal that is not an access point should apply a transmission power that allows the access point of the BSS containing the wireless communication terminal to stably receive the PPDU. To this end, the wireless communication terminal that is not an access point adjusts the transmission power according to the following embodiment. Specifically, the wireless communication terminal that is not an access point estimates the channel attenuation of the channel through which the PPDU is transmitted from the access point. Based on the estimated channel attenuation, the wireless communication terminal determines the transmission power of the PPDU to be transmitted. In this case, the wireless communication terminal estimates the channel attenuation by measuring the received signal strength of the PPDU periodically transmitted by the access point at an explicit transmission power. Specifically, the explicit transmission power is the common transmission power known in the BSS through which the PPDU in question is transmitted. The explicit transmission power represents the transmission power that a wireless communication terminal receiving the PPDU can know without separate signaling when the access point transmits the PPDU.

[0190] In other concrete embodiments, the PPDU transmitted by the access point includes information about the transmission power at which the access point transmitted the PPDU. In this case, a wireless communication terminal that is not an access point obtains information about the transmission power at which the access point transmitted the PPDU from the PPDU transmitted by the access point. The wireless communication terminal that is not an access point estimates channel attenuation based on the transmission power information and the received signal strength. Therefore, the wireless communication terminal that is not an access point adjusts the transmission power of the PPDU it transmits based on the received signal strength of the PPDU transmitted by the access point. Furthermore, the wireless communication terminal that is not an access point adjusts the transmission power of the PPDU it transmits based on the received signal strength and transmission power of the PPDU transmitted by the access point.

[0191] The PPDU transmitted by the access point includes SR application information indicating whether the PPDU has undergone power adjustment. If the SR application information indicates that the PPDU has not undergone power adjustment, the SR application information indicates that the PPDU was transmitted at an explicit power level. Furthermore, wireless communication terminals that are not access points adjust the transmission power of the PPDU they transmit based on the SR application information. The specific operation of wireless communication terminals regarding SR application information is explained with reference to Figure 21(c).

[0192] An access point should adjust its transmission power so that the wireless communication terminal furthest from the access point in the BSS containing the access point, or the wireless communication terminal transmitting the PPDU with the lowest received signal strength, can reliably receive the PPDU transmitted by the access point. To this end, the access point adjusts its transmission power according to the following embodiment. Specifically, the access point estimates the channel attenuation of the channel through which the PPDU is transmitted from a wireless communication terminal that is not an access point. Based on the estimated channel attenuation, the access point adjusts the transmission power of the PPDU it transmits. In this process, the access point estimates the channel attenuation by measuring the received signal strength of the PPDU periodically transmitted by the wireless communication terminal that is not an access point at explicit transmission power. Specifically, explicit transmission power is the common transmission power known in the BSS through which the PPDU in question is transmitted. Explicit transmission power represents the transmission power that the access point receiving the PPDU can know without separate signaling when the wireless communication terminal that is not an access point transmits the PPDU.

[0193] In other concrete embodiments, a PPDU transmitted by a wireless communication terminal that is not an access point includes information about the transmission power used to transmit the PPDU by that wireless communication terminal. In this case, the access point obtains information about the transmission power used to transmit the PPDU from the PPDU transmitted by the wireless communication terminal that is not an access point. Based on the information about the transmission power used to transmit the PPDU by the wireless communication terminal that is not an access point and the received signal strength, the access point estimates the channel attenuation of the channel through which the PPDU is transmitted from the wireless communication terminal that is not an access point. Therefore, the access point adjusts the transmission power of the PPDU it transmits based on the information about the transmission power and the received signal strength.

[0194] The PPDU transmitted by the access point includes SR application information indicating whether the PPDU has undergone power regulation. If the SR application information indicates that the PPDU has not undergone power regulation, the SR application information indicates that the PPDU was transmitted at an explicit power level. Furthermore, wireless communication terminals that are not access points adjust the transmission power of the PPDU they transmit based on the SR application information. The specific operation of wireless communication terminals regarding SR application information is explained via Figure 21(c).

[0195] The wireless communication terminal measures the received signal strength of the PPDU containing the broadcast frame received from the access point and transmits the received signal strength of the PPDU containing the broadcast frame to the access point. In this case, the broadcast frame is a beacon frame. The access point adjusts the transmission power of the PPDU it transmits based on the received signal strength of the PPDU transmitted by the wireless communication terminal that is not an access point. More specifically, the access point adjusts the transmission power of the PPDU it transmits based on the received signal strength of the PPDU containing the broadcast frame transmitted by the wireless communication terminal that is not an access point.

[0196] As described above, the PPDU signaling field includes SR application information indicating whether SR operation was applied. More specifically, the PPDU signaling field includes a TXPWR Control Indicator (TCI) field indicating whether the PPDU was transmitted based on transmission power adjustment. In a specific embodiment, the TXPWR Control Indicator field is a 1-bit field indicating whether the PPDU was transmitted based on transmission power adjustment or not.

[0197] The wireless communication terminal performs SR operation based on the SR application information contained in the PPDU transmitted from OBSS. Specifically, if the SR application information contained in the PPDU transmitted from OBSS indicates that SR operation has been applied, the wireless communication terminal adjusts the OBSS PD CCA threshold based on the SR application information. For example, if the SR application information contained in the PPDU transmitted from OBSS indicates that SR operation has been applied, the wireless communication terminal adjusts the OBSS PD CCA threshold based on the transmission power used to transmit the PPDU transmitted from OBSS. In other specific embodiments, if the SR application information contained in the PPDU transmitted from OBSS indicates that SR operation has been applied, the wireless communication terminal does not need to transmit the PPDU while receiving the OBSS PPDU, regardless of the CCA result. When SR operation is applied to the PPDU transmitted from OBSS, it is transmitted while ignoring a certain degree of signal interference. Therefore, if the wireless communication terminal performs additional SR operation, the probability that the wireless communication terminal receiving the OBSS PPDU will not be able to receive it increases due to the increase in signal interference.

[0198] In the embodiment shown in Figure 21(b), non-legacy station A-2 performs SR operation while non-legacy station B-1, which is included in another BSS, transmits a PPDU. At this time, non-legacy station A-2 and non-legacy station C-1, which is included in the other BSS, receive the PPDU transmitted by non-legacy station A-2 and acquire the SR application information contained in the PPDU. If the SR application information indicates that SR operation is applied, non-legacy station C-1 adjusts the OBSS PD CCA threshold based on the transmission power of the PPDU transmitted from OBSS. Furthermore, non-legacy station C-1 does not need to transmit a PPDU while receiving the PPDU transmitted by non-legacy station A-2, regardless of the CCA result.

[0199] When a wireless communication terminal transmits a PPDU via SR operation, and another wireless communication terminal that receives the PPDU transmits a PPDU in response, if the applicability of SR operation is not considered, the PPDU transmission may interfere with the PPDU transmission transmitted from the OBSS. In the embodiment shown in Figure 21(b), while non-legacy station B-1 is transmitting, non-legacy access point HE A AP performs SR operation. At this time, non-legacy access point HE A AP adjusts its transmission power and transmits a PPDU including a trigger frame. Non-legacy stations A-1 and A-2, which are included in the same BSS as non-legacy access point HE A AP, transmit UL MU PPDUs based on the trigger frame. At this time, if non-legacy stations A-1 and A-2 do not adjust their transmission power to an appropriate level, the PPDU transmissions of non-legacy stations A-1 and A-2 may interfere with the PPDU transmission of non-legacy station B-1. Therefore, a wireless communication terminal that should receive PPDU transmissions from non-legacy station B-1 may not be able to receive the PPDU transmitted by non-legacy station B-1. Thus, a wireless communication terminal that transmits a response frame to a given frame operates according to the following embodiment.

[0200] When a wireless communication terminal transmits an UL MU PPDU based on a trigger frame, the wireless communication terminal adjusts its transmission power so that the access point can receive the UL MU PPDU, and then transmits the UL MU PPDU. Specifically, the transmission power of the UL MU PPDU is adjusted by the embodiment described above in which a wireless communication terminal that is not an access point adjusts its transmission power. In addition, a wireless communication terminal that is not an access point adjusts the transmission power of the UL MU PPDU based on the frequency bandwidth of the frequency band to which the wireless communication terminal is assigned. Specifically, if the first frequency bandwidth is larger than the second frequency bandwidth, the wireless communication terminal uses less transmission power when transmitting the UL MU PPDU via the second frequency bandwidth than when transmitting it via the first frequency bandwidth. This is because if the frequency bandwidth through which the wireless communication terminal transmits the PPDU is smaller, the wireless communication terminal can transmit over a longer distance with the same transmission power. For example, if a wireless communication terminal has a transmission power of X that allows it to transmit a PPDU to an access point via a frequency band with a bandwidth of 20 MHz, then when the wireless communication terminal transmits the PPDU to the access point via a frequency band with a bandwidth of 10 MHz using the same transmission power X, the strength of the received signal of the PPDU received by the access point will be unnecessarily high. Therefore, when a wireless communication terminal transmits a PPDU to an access point via a 10 MHz frequency band, it can transmit the PPDU to the access point with even less transmission power than when transmitting the PPDU via a frequency band with a bandwidth of 20 MHz.

[0201] A PPDU containing a trigger frame includes the SR application information described above. Furthermore, when a wireless communication terminal transmits a PPDU after the transmission of the PPDU containing the trigger frame transmitted from OBSS is complete, it adjusts the transmission power based on the PPDU containing the trigger frame transmitted from OBSS. Specifically, when a wireless communication terminal transmits a PPDU while a UL MU PPDU is being transmitted based on a trigger frame transmitted from OBSS, the wireless communication terminal adjusts the transmission power of the PPDU based on the PPDU containing the trigger frame transmitted from OBSS. Also, when a wireless communication terminal transmits a PPDU within a TXOP indicated by a trigger frame transmitted from OBSS, the wireless communication terminal adjusts the transmission power of the PPDU based on the PPDU containing the trigger frame transmitted from OBSS. In this case, the wireless communication terminal adjusts the transmission power based on the trigger frame transmitted from OBSS and transmits the PPDU, even if it does not apply the OBSS PD CCA threshold to perform CCA operation. In other specific embodiments, the wireless communication terminal applies the OBSS PD CCA threshold to perform CCA operation and adjusts the transmission power based on the trigger frame to transmit the PPDU. Furthermore, a wireless communication terminal adjusting the transmission power based on a PPDU containing a trigger frame is equivalent to adjusting the transmission power based on the received signal strength of the PPDU containing the trigger frame.

[0202] Figure 22 shows that a wireless communication terminal according to an embodiment of the present invention performs SR operation considering the transmission probability of the PPDU transmitted from OBSS.

[0203] The wireless communication terminals perform SR operations based on PPDU exchange between the wireless communication terminals OBSS TX and OT, which initiate the data transmission sequence from the OBSS, and the wireless communication terminals OBSS RX and OR, which participate in the data transmission sequence. In this case, the wireless communication terminals are divided into wireless communication terminals MYBSS TX and MT, which initiate the data transmission sequence from the BSS containing the wireless communication terminals, and wireless communication terminals MYBSS RX and MR, which participate in the data transmission sequence. The specific relationships between MR, MT, OT, and OR are the same as the network topology shown in Figure 22(a).

[0204] If the received signal strength of the PPDU transmitted by OT and the PPDU transmitted by OR are all below the OBSS PD CCA threshold, the MT transmits the PPDU based on the SR operation. Specifically, if the received signal strength of the PPDU transmitted by OT and the PPDU transmitted by OR are all below the OBSS PD CCA threshold, the MT performs CCA based on the OBSS PD CCA threshold and transmits the PPDU. In this case, the MT maintains the data transmission MY_DATA between the MT and MR for a longer period than the time of data transmission from OBSS and the end of ACK frame transmission for data transmission. This is because the MT cannot determine the distance between MR and OT, or between MR and OR, and therefore cannot determine the influence of the PPDU transmitted from MR on the reception of the OBSS PPDU. Specifically, the MT transmits data as shown by the dotted lines in the embodiments of Figures 22(b), 22(c), and 22(d).

[0205] In other specific embodiments, the MT transmits the PPDU based on SR operation if the received signal strength of the PPDU transmitted by the OR is below the OBSS PD CCA threshold. Specifically, if the received signal strength of the PPDU transmitted by the OR is below the OBSS PD CCA threshold, the MT performs CCA based on the OBSS PD CCA threshold and transmits the PPDU. In this case, the MT maintains the data transmission MY_DATA between the MT and MR to be shorter than the time of data transmission from OBSS and the time of completion of ACK frame transmission for data transmission. Also, after data transmission in OBSS is completed, the MR transmits an ACK frame to the MT. Specifically, the MT transmits data as shown by the solid lines in the embodiments of Figures 22(b), 22(c), and 22(d). This is because the MT cannot determine the distance between the MT and OT, the distance between the MR and OT, or the distance between the MR and OR, and therefore cannot determine the effect of the PPDU transmitted from the MT or MR on the reception of the OBSS PPDU.

[0206] If the OT transmits a PPDU containing an RTS frame, and the OR transmits a PPDU containing a CTS frame based on the RTS frame, then all of the above embodiments can be applied.

[0207] When an OT transmits a PPDU containing a trigger frame, and multiple ORs transmit UL MU PPDUs based on the trigger frame, the MT does not receive the PPDU containing the trigger frame transmitted by the OT, but receives the UL MU PPDU transmitted by the ORs based on the trigger frame. In this case, the MT transmits the PPDU based on SR operation, regardless of the received signal strength of the UL MU PPDU measured by the MT. More specifically, the reason the MT transmits the PPDU based on SR operation, regardless of the received signal strength of the UL MU PPDU, is that the OT and MT are too far apart to receive the PPDU containing the trigger frame transmitted by the OT. In this case, the MT maintains the data transmission MY_DATA between the MT and MR shorter than the data transmission from OBSS and the end of the ACK frame transmission for the data transmission. Also, the MR transmits an ACK frame to the MT after the data transmission in OBSS has ended. This is because the MT cannot determine the distance between the MT and the ORs, making it difficult to determine the impact of the MT's PPDU transmission on the ORs when the OT's PPDU containing the ACK frame is received.

[0208] When an OT transmits a PPDU containing a MU-RTS frame, and then transmits a PPDU containing multiple OR SCTS (Simultaneous CTS) based on the MU-RTS frame, the received signal strength of the PPDU containing the SCTS frame, as measured by the wireless communication terminal, is the sum of the received signal strengths of the PPDUs transmitted by the multiple ORs. Therefore, the MT scales the received signal strength of the PPDU containing the SCTS frame and performs SR operation based on the scaled received signal strength. More specifically, the MT scales the received signal strength of the PPDU containing the SCTS frame and adjusts the OBSS PD CCA threshold based on the scaled received signal strength. In this case, the MT scales the received signal strength based on the number of receiving wireless communication terminals indicated by the MU-RTS frame. In other specific embodiments, the received signal strength is scaled based on a predetermined value.

[0209] The wireless communication terminal receives a PPDU transmitted from OBSS and performs an SR operation by applying the OBSS PD CCA threshold to the PPDU, or it receives one of the PPDUs transmitted from OBSS and performs an SR operation by applying the OBSS PD CCA threshold when receiving the next PPDU transmitted from OBSS. Specifically, when the wireless communication terminal receives a PPDU containing a control frame, the wireless communication terminal performs an SR operation as in the following embodiment. If the wireless communication terminal receives a PPDU from OBSS that contains only a control frame, the wireless communication terminal does not perform an SR operation on the PPDU and stores only the received signal strength of the PPDU. In this case, if the wireless communication terminal receives a PPDU from OBSS that contains only a control frame after receiving a PPDU from OBSS that contains only a data frame, the wireless communication terminal performs an SR operation based on the previously stored received signal strength. If the wireless communication terminal receives a PPDU from OBSS that contains both a control MPDU and a data MPDU, or a management MPDU, the wireless communication terminal performs an SR operation when receiving the PPDU if the duration of the PPDU is longer than a certain length. In this case, the wireless communication terminal determines the duration of the PPDU based on the L_LENGTH field of the L-SIG field.

[0210] Furthermore, when a wireless communication terminal receives a PPDU containing a data frame, the wireless communication terminal performs an SR operation as in the following embodiment. Specifically, if the wireless communication terminal receives a PPDU containing one or more data MPDUs, and the duration of the PPDU is less than or equal to a certain length, the wireless communication terminal does not perform an SR operation on the PPDU, but instead stores only the received signal strength of the PPDU. Also, if the wireless communication terminal receives a PPDU containing a control frame after receiving a PPDU containing a data frame, the wireless communication terminal does not perform an SR operation on the PPDU, but instead stores only the received signal strength of the PPDU. In this case, the control frame is an ACK frame. This is because the transmission of a data frame by a wireless communication terminal included in the OBSS and the receipt of a control frame such as an ACK frame may be an operation to inform the surrounding BSS of the received signal strength at the beginning of the transmission sequence.

[0211] Furthermore, the PPDU includes information indicating that SR operation is not permitted. A PPDU containing a control frame transmitted before data frame transmission includes information indicating that SR operation is not permitted. In addition, the wireless communication terminal performs SR operation based on the information indicating that SR operation is not permitted contained in the PPDU transmitted from OBSS. Specifically, a wireless communication terminal that receives a PPDU containing information indicating that SR operation is not permitted will not perform SR operation on the PPDU and will only store the received signal strength. Furthermore, the SR application information described above indicates that SR operation is not permitted.

[0212] Figure 23 shows the operation of a wireless communication terminal according to an embodiment of the present invention.

[0213] S2301 is the wireless communication terminal that receives the signaling field of the PPDU. Specifically, after detecting the transmission of the PPDU, the wireless communication terminal starts receiving the PPDU and receives the signaling field of the PPDU. The wireless communication terminal receives the signaling field of the PPDU according to the embodiment described in Figures 9, 10, 12, and 13.

[0214] S2303 is the wireless communication terminal's determination of the information identifying the BSS indicated by the PPDU's signaling field. In this case, the PPDU's signaling field is the HE-SIG-A field described above. The information identifying the BSS is the BSS color described above.

[0215] The wireless communication terminal performs SR operation S2305 based on information identifying the BSS. Specifically, the wireless communication terminal accesses the channel based on information identifying the BSS. In a specific embodiment, the wireless communication terminal determines whether the PPDU in question was transmitted from the BSS containing the wireless communication terminal based on the BSS color. The wireless communication terminal also determines whether the PPDU in question was transmitted from the BSS containing the wireless communication terminal based on the Address field of the MAC header contained in the PPDU. Specifically, the wireless communication terminal determines whether the PPDU in question was transmitted from the BSS containing the wireless communication terminal based on one of the transmission station address field, receiving station address field, and BSSID field of the Address field in the MAC header. If the BSS containing the wireless communication terminal has a BSSID included in a multiplexed BSSID set, when the wireless communication terminal determines whether a received frame is an Intra-BSS frame or an Inter-BSS frame, it considers the BSSID included in the multiplexed BSSID set to be the BSSID of the BSS containing the wireless communication terminal. Furthermore, when a wireless communication terminal determines whether a received frame is an Intra-BSS frame or an Inter-BSS frame, it sets the Individual / Group bit in the Address field of the MAC header to 0 and compares the value of the Address field with the BSSID of the BSS containing the wireless communication terminal.

[0216] If a first determination, based on the information identifying the BSS indicated by the PPDU's signaling field, determines whether the BSS containing the PPDU is the same as the BSS containing the wireless communication terminal, and a second determination, based on the Address field of the MAC header contained in the PPDU, differs, then the determination of whether the BSS containing the PPDU is the same as the BSS containing the wireless communication terminal is made based on the second determination. The wireless communication terminal determines whether the PPDU in question is a PPDU transmitted from the BSS containing the wireless communication terminal, according to the embodiments described in Figures 7 to 8 and Figures 15 to 16.

[0217] A wireless communication terminal performs an SR operation depending on whether the PPDU received by the wireless communication terminal is a PPDU transmitted from the BSS containing the wireless communication terminal or a PPDU transmitted from the OBSS. More specifically, the SR operation includes accessing the channel depending on whether the received PPDU is a PPDU transmitted from the BSS containing the wireless communication terminal or a PPDU transmitted from another BSS. In a specific embodiment, the channel access operation includes a CCA operation and a deferral operation. For example, the wireless communication terminal adjusts the CCA threshold depending on whether the PPDU received by the wireless communication terminal is a PPDU transmitted from the BSS containing the wireless communication terminal or a PPUD transmitted from the OBSS. In this case, the wireless communication terminal performs the CCA operation based on at least one of PD, ED, and RD. The CCA threshold may also be at least one of the PD CCA threshold, EC CCA threshold, and RD CCA threshold.

[0218] Furthermore, when a wireless communication terminal uses a frequency band divided into a main channel and a sub-channel, the wireless communication terminal performs CCA operation on both the main channel and the sub-channel. Specifically, the wireless communication terminal may use a different CCA threshold for the sub-channel than the CCA threshold used for the main channel. In this case, the CCA threshold may be a PD CCA threshold. Also, if no PPDU is transmitted from the main channel, the wireless communication terminal determines that the PPDU transmitted from the sub-channel was transmitted from a BBS other than the BSS containing the wireless communication terminal. Specifically, when a wireless communication terminal uses a frequency band divided into a main channel and a sub-channel, the wireless communication terminal operates according to the embodiment described with reference to Figures 18 to 20.

[0219] Furthermore, during SR operation, the wireless communication terminal adjusts the transmission power of the PPDU. The wireless communication terminal adjusts the transmission power based on whether it is an access point or not. The wireless communication terminal also adjusts the transmission power of the PPDU it transmits based on the type of frame contained in the PPDU transmitted from the OBSS. Specifically, the wireless communication terminal adjusts the transmission power of the PPDU it transmits depending on whether the frame contained in the PPDU is a control frame or a data frame. Furthermore, the wireless communication terminal adjusts the transmission power of the PPDU it transmits depending on whether the frame contained in the PPDU is a trigger frame or an SCTS frame. In a specific embodiment, if the PPDU received by the wireless communication terminal contains a trigger frame transmitted from the OBSS, the wireless communication terminal measures the received signal strength of the PPDU. At this time, after the transmission of the trigger frame is completed, the wireless communication terminal adjusts the transmission power based on the received signal strength and transmits the PPDU. Specifically, the wireless communication terminal adjusts the transmission power based on the received signal strength while the uplink PPDU transmitted based on the trigger frame is being transmitted and transmits the PPDU. In a specific embodiment, the wireless communication terminal adjusts the transmission power based on the received signal strength during the TXOP indicated by the trigger frame and transmits the PPDU.

[0220] Furthermore, the PPDU's signaling field includes information indicating whether space reuse operation is permissible, and adjusts the PPDU's transmission power based on information indicating whether SR operation is permissible. Specifically, the wireless communication terminal adjusts the PPDU's transmission power if the information indicating whether SR operation is permissible indicates that SR operation is permissible. Specifically, if the information indicating whether SR operation is permissible indicates that SR operation is not permissible, the wireless communication terminal does not have to perform SR operation for the PPDU in question. In this case, the wireless communication terminal saves only the received signal strength of the PPDU in question. The PPDU's signaling field also includes information regarding the PPDU's transmission power. The information regarding transmission power may be the TCI field described above. The information regarding transmission power may also be information indicating the transmission power applied to the transmission of the PPDU. Specifically, the wireless communication terminal adjusts the transmission power according to the embodiment described with reference to Figures 21 to 22.

[0221] Furthermore, the wireless communication terminal performs a power-saving operation depending on whether the PPDU received by the wireless communication terminal is a PPDU transmitted from the BSS containing the wireless communication terminal or a PPDU transmitted from the OBSS. For details, the wireless communication terminal performs the power-saving operation as described in the embodiment shown in Figures 9 to 14.

[0222] The features, structures, and effects described in the examples above are included in at least one embodiment of the present invention, but are not necessarily limited to just one embodiment. Furthermore, the features, structures, and effects exemplified in each embodiment may be combined or modified and implemented in other embodiments by a person with ordinary skill in the art to which the embodiment belongs. Therefore, such combinations and modifications should be interpreted as being within the scope of the present invention.

[0223] While the description so far has focused on embodiments, these are merely examples and do not limit the present invention. Anyone with ordinary skill in the art to which the present invention belongs should understand that various modifications and applications not exemplified above are possible without departing from the essential characteristics of these embodiments. For example, each component specifically shown in the embodiments may be modified and implemented. Such differences in modifications and applications should be interpreted as falling within the scope of the present invention as defined in the attached claims.

Claims

1. In wireless communication terminals that communicate wirelessly, Transmitter / receiver unit, Includes a processor, The aforementioned processor, The signaling field of the first PPDU (PLCP Protocol Data Unit) is received via the aforementioned transmitting / receiving unit. The channel is accessed based on information identifying the BSS (Basic Service Set) indicated by the aforementioned signaling field. Wireless communication terminal.

2. The aforementioned processor, If a first determination, based on information identifying the BSS, determines whether the BSS containing the first PPDU is the same as the BSS containing the wireless communication terminal, and a second determination, based on the Address field of the MAC header contained in the PPDU, determines whether the BSS containing the first PPDU is the same as the BSS containing the wireless communication terminal, differs, the channel is accessed based on the second determination. The wireless communication terminal according to claim 1, wherein the Address field of the MAC header indicates a MAC address relating to an MPDU (MAC Protocol Data Unit).

3. The wireless communication terminal according to claim 2, wherein the size of the field indicating information identifying the BSS is smaller than the maximum value that the MAC address may have.

4. The aforementioned processor, The wireless communication terminal according to claim 2, wherein the BSS containing the first PPDU is determined based on one of the transmission station address (transmitting STA address, TA) field, receiving station address (receiving STA address, RA) field, and BSSID field of the MAC header's Address field.

5. The aforementioned processor, If the first PPDU includes a trigger frame transmitted from a BSS other than the BSS containing the wireless communication terminal, the received signal strength of the first PPDU is measured. The wireless communication terminal according to claim 1, wherein when transmitting a second PPDU after the transmission of the trigger frame is completed, the transmission power is adjusted based on the received signal strength.

6. The aforementioned processor, The wireless communication terminal according to claim 5, wherein when transmitting the second PPDU while the uplink PPDU transmitted based on the trigger frame is being transmitted, the transmission power is adjusted based on the received signal strength.

7. The aforementioned processor, The wireless communication terminal according to claim 5, wherein when transmitting the second PPDU during a TXOP (Transmission Opportunity) indicated by the trigger frame, the transmission power is adjusted based on the received signal strength.

8. The signaling field of the first PPDU includes information indicating whether or not a Spatial Reuse (SR) operation is permissible. The aforementioned processor, The wireless communication terminal according to claim 5, which adjusts the transmission power based on information indicating whether the SR operation is permissible or not.

9. The wireless communication terminal according to claim 5, wherein the signaling field of the first PPDU includes information relating to the transmission power of the first PPDU.

10. The frequency band used by the aforementioned wireless communication terminal is divided into a main channel and a sub-channel. The aforementioned processor, The wireless communication terminal according to claim 1, wherein CCA operation is performed in the main channel and the sub-channel, respectively.

11. The aforementioned processor, The wireless communication terminal according to claim 10, wherein a different CCA threshold from the CCA (Clear Channel Assessment) threshold used in the main channel is used in the sub-channel.

12. The aforementioned processor, The wireless communication terminal according to claim 10, wherein if no PPDU is transmitted from the main channel, it is determined that the PPDU transmitted from the sub-channel was transmitted from a BBS other than the BSS containing the wireless communication terminal.

13. In the operation method of wireless communication terminals that communicate wirelessly, The steps include receiving the signaling field of the first PPDU, The step of accessing a channel based on information identifying the BSS indicated by the signaling field, How it works.

14. The step of accessing the channel is: The steps include: a first determination, based on the BSS color, to determine whether the BSS containing the first PPDU is the same as the BSS containing the wireless communication terminal; and a second determination, based on the Address field of the MAC header contained in the PPDU, to determine whether the BSS containing the first PPDU is the same as the BSS containing the wireless communication terminal, if these two determinations differ, accessing the channel based on the second determination; The operation method according to claim 13, wherein the Address field of the MAC header indicates the MAC address relating to the MPDU.

15. The operating method according to claim 14, wherein the size of the field indicating information identifying the BSS is smaller than the maximum value that the MAC address may have.

16. The step of accessing the channel based on the second decision described above is: The operation method according to claim 14, further comprising the step of determining the BSS containing the first PPDU based on one of the transmission station address field, the receiving station address field, and the BSSID field of the Address field of the MAC header.

17. The first PPDU includes a trigger frame transmitted from another BSS different from the BSS containing the wireless communication terminal. The steps include measuring the received signal strength of the first PPDU, When the second PPDU is transmitted after the transmission of the trigger frame is completed, the received signal The operating method according to claim 13, further comprising the step of adjusting the transmission power based on the signal strength.

18. The step of transmitting the second PPDU is: The operating method according to claim 17, comprising the step of adjusting the transmission power based on the received signal strength when transmitting the second PPDU while the uplink PPDU transmitted based on the trigger frame is being transmitted.

19. The signaling field of the first PPDU includes information indicating whether or not a Spatial Reuse (SR) operation is permissible. The step of transmitting the second PPDU is: The operating method according to claim 17, further comprising the step of adjusting the transmission power based on information indicating whether the SR operation is permissible or not.

20. The operating method according to claim 17, wherein the signaling field of the first PPDU includes information relating to the transmission power of the first PPDU.

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