Patent Publication Number: US-2023164837-A1

Title: Apparatus and method for coordinated spatial reuse in wireless communication

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/347,800 filed Jun. 15, 2021, which is based on and claims priority under 35 U.S.C. § 119 to U.S. Provisional Patent Application No. 63/041,284, filed on Jun. 19, 2020, and Korean Patent Application No. 10-2021-0022026, filed on Feb. 18, 2021, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     TECHNICAL FIELD 
     Example embodiments of the inventive concept relate to wireless communication, and in particular, to an apparatus and a method for coordinated spatial reuse in wireless communication. 
     DISCUSSION OF RELATED ART 
     As an example of wireless communication, a wireless local area network (WLAN) is a technology that connects two or more apparatuses to each other using a wireless signal transmission method. WLAN technology may be based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. The 802.11 standard has evolved into 802.11b, 802.11a, 802.11g, 802.11n, 802.11ac, and 802.11ax, and may support a transmission speed of up to 1Gbyte/s based on orthogonal frequency-division multiplexing (OFDM) technology. 
     In 802.11ac, data may be simultaneously transmitted to multiple users through multi-user multi-input multi-output (MU-MIMO) technology. In 802.11ax, also referred to as high efficiency (HE), both MU-MIMO and also orthogonal frequency-division multiple access (OFDMA) technology are applied to divide and provide usable subcarriers to users, thereby implementing multiple access. Therefore, WLAN systems to which 802.11ax is applied may effectively support communication in dense areas and outdoors. 
     802.11be, which is also referred to as extremely high throughput (EHT), is intended to implement support of a 6 GHz unlicensed frequency band, utilization of a bandwidth of maximum 320 MHz per channel, introduction of hybrid automatic repeat and request (HARD), support of maximum 16×16 MIMO, or the like. Next-generation WLAN systems are expected to effectively support low latency and ultra-high-speed transmission like new radio (NR), which is a 5G technology. 
     SUMMARY 
     Embodiments of the inventive concept provide an apparatus and a method for efficiently performing spatial reuse in wireless communication. 
     According to an embodiment of the inventive concept, a wireless communication method performed by a first apparatus may include acquiring a transmit opportunity (TXOP) to transmit or receive a first physical layer protocol data unit (PPDU), identifying a second apparatus for sharing the TXOP, permitting at least one of transmission and reception of a second PPDU to the second apparatus in the shared TXOP, and transmitting the first PPDU to at least one third apparatus or receiving the first PPDU from the at least one third apparatus in the shared TXOP. 
     According to an embodiment of the inventive concept, a first apparatus for wireless communication may include a transceiver and a processing circuitry. The processing circuitry is configured to obtain a TXOP to transmit or receive a first PPDU through the transceiver, identify a second apparatus for sharing the TXOP, permit at least one of transmission and reception of a second PPDU to the second apparatus through the transceiver in the shared TXOP, and transmit the first PPDU to at least one third apparatus through the transceiver in the shared TXOP or receive the first PPDU from at least one third apparatus. 
     According to an embodiment of the inventive concept, a wireless communication method performed by a first apparatus may include acquiring a transmit opportunity (TXOP) to transmit or receive a first physical layer protocol data unit (PPDU), identifying a second apparatus for sharing the TXOP, providing a tolerable interference limit of transmission or reception of the first PPDU in the shared TXOP to the second apparatus, and transmitting the first PPDU to at least one third apparatus in the shared TXOP or receiving the first PPDU from at least one third apparatus. 
     According to an embodiment of the inventive concept, a wireless communication method performed by a third apparatus associated with a second apparatus in a TXOP shared by a first apparatus and the second apparatus may include receiving a frame from the first apparatus, determining a path loss between the first apparatus and the third apparatus based on the frame, transmitting information on the path loss to the second apparatus, and receiving a physical layer protocol data unit (PPDU) in the shared TXOP or transmitting the PPDU to the second apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present inventive concept will become more apparent by describing in detail example embodiments thereof with reference to the accompanying drawings, in which: 
         FIG.  1    is a diagram illustrating a wireless communication system according to an example embodiment of the inventive concept; 
         FIG.  2    is a block diagram illustrating a wireless communication system according to an example embodiment of the inventive concept; 
         FIGS.  3 A to  3 D  are diagrams illustrating scenarios of coordinated spatial reuse according to example embodiments of the inventive concept; 
         FIG.  4    is a message diagram illustrating a method for coordinated spatial reuse according to an example embodiment of the inventive concept; 
         FIG.  5    is a diagram illustrating an example of information provided to a shared access point by a sharing access point according to an example embodiment of the inventive concept; 
         FIG.  6    is a message diagram illustrating a method for coordinated spatial reuse according to an example embodiment of the inventive concept; 
         FIG.  7    is a diagram illustrating a wireless communication system according to an example embodiment of the inventive concept; 
         FIGS.  8 A and  8 B  are diagrams illustrating examples of a wireless communication system according to example embodiments of the inventive concept; 
         FIG.  9    is a message diagram illustrating a method for coordinated spatial reuse according to an example embodiment of the inventive concept; 
         FIG.  10    is a message diagram illustrating a method for coordinated spatial reuse according to an example embodiment of the inventive concept; 
         FIG.  11    is a message diagram illustrating a method for coordinated spatial reuse according to an example embodiment of the inventive concept; 
         FIG.  12    is a diagram illustrating a frame according to an example embodiment of the inventive concept; 
         FIG.  13    is a timing diagram illustrating transmission based on coordinated spatial reuse according to an example embodiment of the inventive concept; 
         FIG.  14    is a timing diagram illustrating transmission based on coordinated spatial reuse according to an example embodiment of the inventive concept; 
         FIGS.  15 A and  15 B  are timing diagrams illustrating transmission based on coordinated spatial reuse according to example embodiments of the inventive concept; 
         FIG.  16    is a diagram illustrating a wireless communication system according to an example embodiment of the inventive concept; and 
         FIG.  17    is a diagram illustrating examples of an apparatus for wireless communication according to an example embodiment of the inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Example embodiments of the present inventive concept will be described more fully hereinafter with reference to the accompanying drawings. Like reference numerals may refer to like elements throughout the accompanying drawings. 
     Herein, when two or more elements or values are described as being substantially the same as or about equal to each other, it is to be understood that the elements or values are identical to each other, the elements or values are equal to each other within a measurement error, or if measurably unequal, are close enough in value to be functionally equal to each other as would be understood by a person having ordinary skill in the art. For example, the term “about” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (e.g., the limitations of the measurement system). For example, “about” may mean within one or more standard deviations as understood by one of the ordinary skill in the art. Further, it is to be understood that while parameters may be described herein as having “about” a certain value, according to exemplary embodiments, the parameter may be exactly the certain value or approximately the certain value within a measurement error as would be understood by a person having ordinary skill in the art. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
       FIG.  1    is a diagram illustrating a wireless communication system  10  according to an example embodiment of the inventive concept. In some embodiments, the wireless communication system may be a wireless local area network (WLAN) system. 
     Hereinafter, in describing embodiments of the inventive concept in detail, an orthogonal frequency-division multiplexing (OFDM) or OFDMA-based wireless communication system, in particular, the IEEE 802.11, standard will be described as being implemented. However, embodiments of the inventive concept are not limited thereto, and may be applied to other communication systems such as, for example, a cellular communication system such as long term evolution (LTE), LTE-advanced (LTE-A), new radio (NR), and wireless broadband (WiBro), a global system for mobile communication (GSM), or a short-range communication system such as BLUETOOTH and near field communication (NFC), having similar technical background and channel types with slight modifications within the scope not significantly departing from the scope of embodiments of the inventive concept. 
     In addition, various functions described below may be implemented or supported by one or more computer programs, each of which is configured of a computer readable program code and executed on a computer readable medium. The terms “application” and “program” refer to one or more computer programs, software components, instruction sets, procedures, functions, objects, classes, instances, related data, or portions thereof suitable for implementation of a suitable computer readable program code. The term “computer-readable program code” includes all types of computer codes including source code, object code, and executable code. The term “computer-readable medium” means all types of media that may be accessed by a computer, such as, for example, read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or some other type of memory. “Non-transitory” computer-readable media excludes wired, wireless, optical, or other communication links that transmit transient electrical or other signals. Non-transitory computer-readable media includes media on which data may be permanently stored, and media on which data may be stored and later overwritten, such as a rewritable optical disk or erasable memory apparatus. 
     The wireless communication system  10  may expand a service area by an access point (AP). A station (STA) may communicate with the access point in a basic service set (BSS) provided by the access point, and may access a network such as the Internet or an Internet Protocol (IP) network through the access point. For example, as illustrated in  FIG.  1   , a first access point AP 1  may provide a first BSS BSS 1 , and a first station STA 1 , a third station STA 3 , a fourth station STA 4 , and a fifth station STA 5  may communicate with the first access point AP 1 . In addition, a second access point AP 2  may provide a second BSS BSS 2 , and the first station STA 1 , a second station STA 2 , the third station STA 3 , and a sixth station STAG may communicate with the second access point AP 2 . As illustrated in  FIG.  1   , the first station STA 1  and the third station STA 3  may access both the first access point AP 1  and the second access point AP 2 . In  FIG.  1   , dotted lines indicate an approximate extent of each of the first BSS BSS 1  and the second BSS BSS 2 , and may have a shape different from a circular shape illustrated in  FIG.  1   . 
     The access points and stations may communicate with each other using wireless fidelity (Wi-Fi) or any other WLAN communication technology. The access point may be referred to as, for example, a router, a gateway, and the like, and the station may be referred to as, for example, a mobile station, a subscriber station, a terminal, a mobile terminal, a wireless terminal, a user equipment, a user, and the like. The station may be a portable apparatus such as, for example, a mobile phone, a laptop computer, or a wearable apparatus, or may be a stationary apparatus such as, for example, a desktop computer or a smart TV. Examples of the access points and the stations will be described in further detail below with reference to  FIG.  17   . 
     The 802.11-based medium access control (MAC) protocol may regard the simultaneous execution of two or more signal transmissions as collision, and accordingly, the access points and the stations may use channels through competition. For example, the access point and the station may communicate with each other based on carrier sense multiple access (CSMA) and/or collision avoidance (CA), and accordingly, while the first access point AP 1  performs the transmission to the first station STA 1 , the second access point AP 2  may delay the transmission for the third station STA 3 . The collision may occur frequently in an overlapping basic service set (OBSS) environment in which a plurality of access points and a plurality of stations exist, and accordingly, the performance of the wireless communication system  10 , for example, a throughput, may be limited. 
     Spatial reuse (SR) may enable colliding transmissions to occur simultaneously. For example, while the first access point AP 1  performs the first transmission to the first station STA 1 , the second access point AP 2  may perform the second transmission to the second station STA 2  with a level of transmission power that does not interfere with reception of the first station STA 1 , instead of delaying the transmission to the second station STA 2 . Accordingly, the first transmission to the first station STA 1  and the second transmission to the second station STA 2  may be performed in parallel, and an amount of transmission in the wireless communication system  10  may increase. Herein, a transmission associated with an access point that obtains a transmit opportunity (TXOP) may be referred to as the first transmission, and a transmission associated with an access point that is provided with a shared TXOP may be referred to as the second transmission. 
     In 802.11ax, the access point or the station may identify the first transmission based on a preamble, and if the first transmission is identified, may perform the second transmission, which at least partially overlaps the first transmission, with the transmission power determined based on reception power of the preamble. However, the second transmission may not be considered in the first transmission, and thereby, the efficiency of spatial reuse may be limited. As will be described below with reference to the drawings, in spatial reuse, in addition to the second transmission considering the first transmission, the first transmission may also consider the second transmission, and thus, more efficient spatial reuse may be achieved. 
     Herein, spatial reuse in which the first transmission considers the second transmission may be referred to as coordinated spatial reuse (C-SR). In addition, the access point associated with the first transmission (that is, acquiring the TXOP) may be referred to as a sharing access point, and the BSS provided by the sharing access point may be referred to as a sharing BSS. The access point associated with the second transmission may be referred to as a shared access point, and the BSS provided by the shared access point may be referred to as a shared BSS. Unless otherwise stated, it is assumed that the first access point AP 1  is the sharing access point, and the second access point AP 2  is the shared access point. The first access point AP 1  and the second access point AP 2  may be referred to as a first apparatus and a second apparatus, respectively, and each of the stations may be referred to as a third apparatus or a fourth apparatus. A physical layer protocol data unit (PPDU) transmitted between the first access point AP 1  and at least one station included in the first BSS BSS 1  provided by the first access point AP 1  may be referred to as a first PPDU. A PPDU transmitted between the second access point AP 2  and at least one station included in the second BSS BSS 2  provided by the second access point AP 2  may be referred to as a second PPDU. 
       FIG.  2    is a block diagram illustrating a wireless communication system  20  according to an example embodiment of the inventive concept. For example, the block diagram of  FIG.  2    illustrates a first wireless communication apparatus  21  and a second wireless communication apparatus  22  communicating with each other in the wireless communication system  20 . Each of the first wireless communication apparatus  21  and the second wireless communication apparatus  22  of  FIG.  2    may be any apparatus that communicates in the wireless communication system  20 , and may be referred to as an apparatus for wireless communication. In some embodiments, each of the first wireless communication apparatus  21  and the second wireless communication apparatus  22  may be an access point or station of the WLAN system. 
     Referring to  FIG.  2   , the first wireless communication apparatus  21  may include an antenna  21 _ 2 , a transceiver  21 _ 4 , and a processing circuitry  21 _ 6 . In some embodiments, the antenna  21 _ 2 , the transceiver  21 _ 4 , and the processing circuitry  21 _ 6  may be included in one package, or may be included in different packages, respectively. The second wireless communication apparatus  22  may also include an antenna  22 _ 2 , a transceiver  22 _ 4 , and a processing circuitry  22 _ 6 . Hereinafter, redundant descriptions of the first wireless communication apparatus  21  and the second wireless communication apparatus  22  will be omitted for convenience of explanation. 
     The antenna  21 _ 2  may receive a signal from the second wireless communication apparatus  22  and provide the signal to the transceiver  21 _ 4 , and may transmit a signal provided from the transceiver  21 _ 4  to the second wireless communication apparatus  22 . In some embodiments, the antenna  21 _ 2  may include a plurality of antennas for a multiple input multiple output (MIMO). Further, in some embodiments, the antenna  21 _ 2  may include a phased array for beam forming. 
     The transceiver  21 _ 4  may process a signal received from the second wireless communication apparatus  22  through the antenna  21 _ 2  and may provide the processed signal to the processing circuitry  21 _ 6 . In addition, the transceiver  21 _ 4  may process a signal provided from the processing circuitry  21 _ 6 , and may output the processed signal through the antenna  21 _ 2 . In some embodiments, the transceiver  21 _ 4  may include an analog circuit such as, for example, a low noise amplifier, a mixer, a filter, a power amplifier, or an oscillator. In some embodiments, the transceiver  21 _ 4  may process a signal received from the antenna  21 _ 2  and/or a signal received from the processing circuitry  21 _ 6  based on the control of the processing circuitry  21 _ 6 . 
     The processing circuitry  21 _ 6  may extract information transmitted by the second wireless communication apparatus  22  by processing the signal received from the transceiver  21 _ 4 . For example, the processing circuitry  21 _ 6  may extract information by demodulating and/or decoding a signal received from the transceiver  21 _ 4 . In addition, a signal including information to be transmitted to the second wireless communication apparatus  22  may be generated and provided to the transceiver  21 _ 4 . For example, the processing circuitry  21 _ 6  may provide a signal generated by encoding and/or modulating data to be transmitted to the second wireless communication apparatus  22 , to the transceiver  21 _ 4 . In some embodiments, the processing circuitry  21 _ 6  may include a programmable component such as, for example, a central processing unit (CPU) or a digital signal processor (DSP), a reconfigurable component such as, for example, a field programmable gate array (FPGA), or a component providing a fixed function such as, for example, an intellectual property (IP) core. In some embodiments, the processing circuitry  21 _ 6  may include a memory that stores data and/or a series of instructions, or accesses the memory. Herein, performing operations by the transceiver  21 _ 4  and/or the processing circuitry  21 _ 6  may be referred to as performing the operations by the first wireless communication apparatus  21 . Accordingly, operations performed by the access point may be performed by the transceiver and/or the processing circuitry included in the access point, and operations performed by the station may be performed by the transceiver and/or the processing circuitry included in the station. 
       FIGS.  3 A to  3 D  are diagrams illustrating scenarios of coordinated spatial reuse according to example embodiments of the inventive concept. For example,  FIGS.  3 A to  3 D  illustrate wireless communication systems  30   a ,  30   b ,  30   c , and  30   d  each including the first access point AP 1 , the second access point AP 2 , the first station STA 1 , the second station STA 2 , and the third station STA 3 . Hereinafter, transmission of the PPDU including data by the access point to the station may be referred to as a downlink (DL) transmission, and transmission of the PPDU including data by the station to the access point may be referred to as an uplink (UL) transmission. In describing  FIGS.  3 A to  3 D , for convenience of explanation, a further description of elements and technical aspects previously described may be omitted. 
     Referring to  FIG.  3 A , a first downlink transmission DL 1  of a first BSS BSS 1  and a second downlink transmission DL 2  of a second BSS BSS 2  may occur. For example, the first access point AP 1  may obtain the TXOP to transmit the first PPDU to the first station STA 1 . The first access point AP 1  may transmit the first PPDU to the first station STA 1  in the shared TXOP, and the second access point AP 2  may transmit the second PPDU to the second station STA 2  in the shared TXOP. As illustrated by the dotted arrow in  FIG.  3 A , the second downlink transmission DL 2  may act as interference for the first station STA 1  to process the first downlink transmission DL 1 . As transmission power of the second downlink transmission DL 2  increases, a signal-to-interference ratio (SIR) at the first station STA 1  may decrease, and accordingly, the second access point AP 2  may perform the second downlink transmission DL 2  in consideration of an appropriate signal-to-interference ratio of the first station STA 1 . Herein, the example of  FIG.  3 A  may be referred to as a DL/DL scenario or a DL/DL case of the coordinated spatial reuse. 
     In some embodiments, different from that illustrated in  FIG.  3 A , the first access point AP 1  may provide the downlink transmission to a multi-user (MU), that is, a plurality of stations. In addition, in some embodiments, the second access point AP 2  may also provide the downlink transmission to the plurality of stations. Herein, it is noted that the DL/DL scenario or the DL/DL case of coordinated spatial reuse may cover the above-described multi-user downlink transmission as well as the single user (SU) downlink transmission illustrated in  FIG.  3 A . 
     Referring to  FIG.  3 B , a first uplink transmission UL 1  of the first BSS BSS 1  and a second downlink transmission DL 2  of the second BSS BSS 2  may occur. For example, the first access point AP 1  may obtain the TXOP to receive the first PPDU from the first station STA 1 . The first station STA 1  may transmit the first PPDU to the first access point AP 1  in the shared TXOP, and the second access point AP 2  may transmit the second PPDU to the second station STA 2  in the shared TXOP. As illustrated by a dotted arrow in  FIG.  3 B , the second downlink transmission DL 2  may act as interference for the first access point AP 1  to process the first uplink transmission UL 1 . As transmission power of the second downlink transmission DL 2  increases, the signal-to-interference ratio at the first access point AP 1  may decrease, and accordingly, the second access point AP 2  may perform the second downlink transmission DL 2  in consideration of an appropriate signal-to-interference ratio of the first access point AP 1 . Herein, the example of  FIG.  3 B  may be referred to as a UL/DL scenario or a UL/DL case of the coordinated spatial reuse. 
     In some embodiments, unlike  FIG.  3 B , multiple users, that is, the plurality of stations, may provide uplink transmissions to the first access point AP 1 . Further, in some embodiments, the second access point AP 2  may provide downlink transmissions to the plurality of stations. Herein, it is noted that the UL/DL scenario or the UL/DL case of coordinated spatial reuse may cover both the single-user uplink transmission and the single-user downlink transmission illustrated in  FIG.  3 B , as well as the multi-user uplink transmission and/or the multi-user downlink transmission. 
     Referring to  FIG.  3 C , the first downlink transmission DL 1  of the first BSS BSS 1  and the second uplink transmissions UL 21  and UL 22  of the second BSS BSS 2  may occur. For example, the first access point AP 1  may obtain the TXOP to transmit the first PPDU. The first access point AP 1  may transmit the first PPDU to the first station STA 1  in the shared TXOP, and the second station STA 2  and the third station STA 3  may transmit the second PPDUs to the second access point AP 2  in the shared TXOP. As illustrated by dotted arrows in  FIG.  3 C , the second uplink transmissions UL 21  and UL 22  may act as interference for processing the first downlink transmission DL 1 . As transmission power of the second uplink transmissions UL 21  and UL 22  increases, the signal-to-interference ratio at the first station STA 1  may decrease, and accordingly, the second station STA 2  and the third station STA 3  may perform the second uplink transmissions UL 21  and UL 22  in consideration of an appropriate signal-to-interference ratio of the first station STA 1 . Herein, the example of  FIG.  3 C  may be referred to as the DL/UL scenario or the DL/UL case of the coordinated spatial reuse. 
     In some embodiments, unlike  FIG.  3 C , the first access point AP 1  may provide the downlink transmission to the multi-user (MU), that is, the plurality of stations. Further, in some embodiments, the single user, that is, one station, may provide the uplink transmission to the second access point AP 2 . Herein, it is noted that the DL/UL scenario or the DL/UL case of coordinated spatial reuse may cover single-user downlink transmission and the multi-user uplink transmission illustrated in  FIG.  3 C , as well as the multi-user downlink transmission and/or the single-user uplink transmission. 
     Referring to  FIG.  3 D , the first uplink transmission UL 1  of the first BSS BSS 1  and the second uplink transmissions UL 21  and UL 22  of the second BSS BSS 2  may occur. For example, the first access point AP 1  may obtain the TXOP to receive the first PPDU. The first station STA 1  may transmit the first PPDU to the first access point AP 1  in the shared TXOP, and the second station STA 2  and the third station STA 3  may transmit the second PPDUs to the second access point AP 2  in the shared TXOP. As illustrated by dotted arrows in  FIG.  3 D , the second uplink transmissions UL 21  and UL 22  may act as interference in processing the first uplink transmission UL 1 . As transmission power of the second uplink transmissions UL 21  and UL 22  increases, the signal-to-interference ratio at the first access point AP 1  may decrease, and accordingly, the second station STA 2  and the third station STA 3  may perform second uplink transmissions UL 21  and UL 22  in consideration of an appropriate signal-to-interference ratio of the first access point AP 1 . Herein, the example of  FIG.  3 D  may be referred to as the UL/UL scenario or the UL/UL case of the coordinated spatial reuse. 
     In some embodiments, unlike  FIG.  3 D , the multi-user, that is, the plurality of stations, may provide the uplink transmissions to the first access point AP 1 . Further, in some embodiments, the single user, that is, one station, may provide the uplink transmission to the second access point AP 2 . Herein, it is noted that the UL/UL scenario or the UL/UL case of the coordinated spatial reuse may cover the single-user uplink transmission and the multi-user uplink transmission illustrated in  FIG.  3 D , as well as the multi-user uplink transmission and/or the single-user uplink transmission. Examples of a method for coordinated spatial reuse corresponding to the scenarios described above with reference to  FIGS.  3 A to  3 D  will be described further below. 
       FIG.  4    is a message diagram showing a method for the coordinated spatial reuse according to an example embodiment of the inventive concept. As illustrated in  FIG.  4   , the method for the coordinated spatial reuse may include a plurality of operations (S 41  to S 45 ). As described above with reference to  FIG.  1   , the first access point AP 1  of  FIG.  4    may be the sharing access point, and the second access point AP 2  may be the shared access point. In  FIG.  4   , the first station STA 1  may be associated with the first access point AP 1  in the first BSS BSS 1  provided by the first access point AP 1 , and the second station STA 2  may be associated with the second access point AP 2  in the second BSS BSS 2  provided by the second access point AP 2 . 
     Referring to  FIG.  4   , in operation S 41 , the first access point AP 1  may obtain the TXOP. For example, the first access point AP 1  may obtain the TXOP to transmit the first PPDU to the first station STA 1  or receive the first PPDU from the first station STA 1 . As described above with reference to  FIG.  1   , the first access point AP 1  may obtain the TXOP through competition with at least one station or another access point. For spatial reuse, the TXOP obtained by the first access point AP 1  may be shared with the second access point AP 2 . 
     In operation S 42 , the first access point AP 1  may share the TXOP with the second access point AP 2 . For example, the first access point AP 1  may permit at least one of transmission and reception of a second PPDU to the second access point AP 2  in the shared TXOP. The first access point AP 1  may permit the uplink transmission and/or the downlink transmission in the second BSS so as not to interfere with transmission or reception of the first PPDU in the first BSS BSS 1 . In some embodiments, the first access point AP 1  may transmit a signal (for example, AF or PPDU 0  in  FIG.  13   ) including information indicating permission of the uplink transmission and/or the downlink transmission to the second access point AP 2 . An example of information indicating the permission of the uplink transmission and/or the downlink transmission will be described later with reference to  FIG.  5   . 
     As will be described later with reference to  FIGS.  8 A and  8 B , estimating the interference caused by the second transmission by the first access point AP 1  may be more difficult in a case in which the uplink transmission occurs in the second BSS BSS 2  than in a case in which downlink transmission occurs in the second BSS BSS 2 . Accordingly, the first access point AP 1  may permit at least one of the uplink transmission and the downlink transmission to the second access point AP 2  so as not to interfere with transmission or reception of the first PPDU. In some embodiments, in a case in which a path loss between the first access point AP 1  and the first station STA 1  is higher than a predefined threshold value, the first access point AP 1  may permit only the downlink transmission to the second access point AP 2 . In some embodiments, the coordinated spatial reuse may define only the downlink transmission in the shared BSS (that is, the second BSS BSS 2 ), and accordingly, operation S 42  and operation S 43  to be described later may be omitted, and the second access point AP 2  may only perform the downlink transmission, that is, the transmission of the second PPDU in the shared TXOP. 
     In operation S 43 , the second access point AP 2  may identify at least one of permitted uplink transmission and downlink transmission. For example, the second access point AP 2  may extract information permitting the uplink transmission and/or the downlink transmission from a signal received from the first access point AP 1  in operation S 42 . In some embodiments, in a case in which the uplink transmission is permitted, the second access point AP 2  may transmit a trigger frame to the second station STA 2  to receive the second PPDU PPDU 2 . 
     The first PPDU PPDU 1  may be transmitted between the first access point AP 1  and the first station STA 1  in operation S 44 , and the second PPDU PPDU 2  may be transmitted between the second access point AP 2  and the second station STA 2  in operation S 45 . For example, in operation S 44 , the first access point AP 1  may transmit the first PPDU PPDU 1  to the first station STA 1  in the shared TXOP, or the first station STA 1  may transmit the first PPDU PPDU 1  to the first access point AP 1  in the shared TXOP. In addition, when the uplink transmission is identified in operation S 43 , the second station STA 2  may transmit the second PPDU PPDU 2  to the second access point AP 2 , and when downlink transmission is identified in operation S 43 , the second access point AP 2  may transmit the second PPDU PPDU 2  to the second station STA 2 . 
       FIG.  5    is a diagram illustrating an example of information provided to a shared access point by a sharing access point according to an example embodiment of the inventive concept. For example,  FIG.  5    illustrates a table including values provided by the first access point AP 1  to permit at least one of the uplink transmission and the downlink transmission to the second access point AP 2  in operation S 42  of  FIG.  4   . Hereinafter,  FIG.  5    will be described with reference to  FIG.  4   . 
     In some embodiments, permission of at least one of the uplink transmission and the downlink transmission may be expressed as a value of 2-bit. For example, as illustrated in  FIG.  5   , a most significant bit (MSB) of 2-bits may indicate whether the downlink transmission is permitted, and a least significant bit (LSB) of 2-bits may indicate whether the uplink transmission is permitted. Accordingly, “01” may correspond to permission of uplink transmission, “10” may correspond to permission of downlink transmission, and “11” may correspond to permission of both uplink transmission and downlink transmission. In some embodiments, as described below with reference to  FIG.  13   , the 2-bit value of  FIG.  5    may correspond to a field included in an announcement frame (for example, AF of  FIG.  13   ) transmitted from the first access point AP 1  to the second access point AP 2 . In some embodiments, to represent the three combinations described above, the 2-bit value having different values as illustrated in  FIG.  5    may be used. 
       FIG.  6    is a message diagram showing a method for the coordinated spatial reuse according to an example embodiment of the inventive concept. For example, the message diagram of  FIG.  6    illustrates operations performed in each of the DL/DL scenario and the UL/DL scenario of the coordinated spatial reuse, as described above with reference to  FIGS.  3 A and  3 B . As illustrated in  FIG.  6   , the method for the coordinated spatial reuse may include a plurality of operations (S 60  to S 69 ). In  FIG.  6   , the first station STA 1  may be included in the first BSS BSS 1  provided by the first access point AP 1 , and the second station STA 2  may be included in the second BSS BSS 2  provided by the second access point AP 2 . In addition, before operations S 60  and S 65  are respectively performed in  FIG.  6   , it is assumed that the first access point AP 1  has obtained the TXOP. 
     Referring to  FIG.  6   , in operation S 60 , the first access point AP 1  may determine a transmit power limit (TPL) in the shared TXOP. The transmit power limit may correspond to maximum transmit power allowed when the second access point AP 2  transmits the second PPDU to the second station STA 2  in the shared TXOP. For example, the first access point AP 1  may obtain the TXOP to transmit the first PPDU to the first station STA 1 , and may determine the transmit power limit based on at least one path loss associated with the first station STA 1 . An example of the operation of determining the transmit power limit in the DL/DL scenario and the UL/DL scenario of the coordinated spatial reuse will be described in further detail with reference to  FIG.  7   . 
     In operation S 61 , the first access point AP 1  may provide the transmit power limit to the second access point AP 2 . For example, the first access point AP 1  may transmit a signal including the transmit power limit determined in operation S 60  to the second access point AP 2 . In some embodiments, as described below with reference to  FIG.  13   , the transmit power limit may be included in the announcement frame. 
     In operation S 62 , the second access point AP 2  may identify the transmit power limit. For example, the second access point AP 2  may extract the transmit power limit from the signal received from the first access point AP 1  in operation S 61 . In some embodiments, the transmit power limit may have the same format as that of a transmit power field included in a transmit power control (TPC) report, and the second access point AP 2  may identify the transmit power limit corresponding to a value of the transmit power limit. 
     In operation S 63 , the first access point AP 1  may transmit the first PPDU to the first station STA 1  in the shared TXOP, and in operation S 64  the second access point AP 2  may transmit the second PPDU to the second station STA 2  in the shared TXOP. The second access point AP 2  may transmit the second PPDU with a transmit power about equal to or less than the transmit power limit identified in operation S 62 , and accordingly, interference caused by the transmission of the second PPDU may be reduced or eliminated. The first station STA 1  may successfully receive the first PPDU. 
     In operation S 65 , the first access point AP 1  may determine the transmit power limit in the shared TXOP. For example, the first access point AP 1  may obtain the TXOP to receive the first PPDU from the first station STA 1 , and may determine the transmit power limit based on at least one path loss associated with the first access point AP 1 . An example of the operation of determining the transmit power limit will be described later with reference to  FIG.  7   . 
     In operation S 66 , the first access point AP 1  may provide the transmit power limit to the second access point AP 2 . In operation S 67 , the second access point AP 2  may identify the transmit power limit. 
     In operation S 68 , the first station STA 1  may transmit the first PPDU to the first access point AP 1  in the shared TXOP, and in operation S 69 , the second access point AP 2  may transmit the second PPDU to the second station STA 2  in the shared TXOP. The second access point AP 2  may transmit the second PPDU with transmit power about equal to or less than the transmit power limit identified in operation S 67 , and accordingly, interference caused by the transmission of the second PPDU may be reduced or eliminated. The first access point AP 1  may successfully receive the first PPDU. 
       FIG.  7    is a diagram illustrating a wireless communication system  70  according to an example embodiment of the inventive concept. For example, the diagram of  FIG.  7    illustrates examples of the path loss considered in the coordinated spatial reuse in a case in which the downlink transmission occurs in the shared BSS. As illustrated in  FIG.  7   , a first path loss PL 1  between the first access point AP 1  and the first station STA 1 , a second path loss PL 2  between the second access point AP 2  and the second station STA 2 , and a third path loss PL 3  between the first access point AP 1  and the second access point AP 2  may be considered. In addition, the first access point AP 1  may provide the first BSS BSS 1 , the second access point AP 2  may provide the second BSS BSS 2 , and the first station STA 1  may be included in the first BSS BSS 1 . 
     In the DL/DL scenario (for example, in operation S 60  of  FIG.  6   ), the transmit power limit may be determined based on the first path loss PL 1  and the second path loss PL 2 . For example, the first path loss PL 1  may correspond to the loss of the signal transmitted by the first access point AP 1 , and the second path loss PL 2  may correspond to the loss of the signal transmitted by the second access point AP 2 . As the first path loss PL 1  is low and the second path loss PL 2  is high, it may be advantageous for the first station STA 1  to successfully receive the first PPDU from the first access point AP 1 . Accordingly, the first access point AP 1  may determine the transmit power limit based on the transmission power of the first access point AP 1 , the first path loss PL 1 , and the second path loss PL 2 . For example, the transmit power limit TPL Ap2  in the DL/DL scenario may satisfy the following Equation 1 when the transmission power of the first access point AP 1  is P AP1 , and the minimum signal-to-interference ratio for the first station STA 1  to successfully receive the first PPDU is SIR sTA1 . 
         TPL   AP2   ≤P   AP1 −( PL   1   −PL   2 )− SIR   sTA1   [Equation 1]
 
     In the UL/DL scenario (for example, in operation S 65  of  FIG.  6   ), the transmit power limit may be determined based on the first path loss PL 1  and the third path loss PL 3 . For example, the first path loss PL 1  may correspond to the loss of the signal transmitted by the first access point AP 1 , and the third path loss PL 3  may correspond to the loss of the signal transmitted by the second access point AP 2 . As the first path loss PL 1  is low and the third path loss PL 3  is high, it may be advantageous for the first access point AP 1  to successfully receive the first PPDU from the first station STA 1 . Accordingly, the first access point AP 1  may determine the transmit power limit based on the transmission power of the first station STA 1 , the first path loss PL 1 , and the third path loss PL 3 . For example, in the UL/DL scenario, the transmit power limit TPL Ap2  may satisfy the following Equation 2 when the transmission power of the first station STA 1  is P AP1  and the minimum signal-to-interference ratio for the first access point AP 1  to successfully receive the first PPDU is SIR Ap1 . 
         TPL   AP2   ≤P   STA1 −( PL   1   −PL   3 )− SIR   Ap1   [Equation 2]
 
     In some embodiments, the first station STA 1  may calculate the first path loss PL 1  based on the frame output from the first access point AP 1 , and calculate the second path loss PL 2  based on the frame output from the second access point AP 2 . The first station STA 1  may report the first path loss PL 1  and the second path loss PL 2  to the first access point AP 1 . In addition, the first access point AP 1  (or the second access point AP 2 ) may calculate the third path loss PL 3  based on the frame output from the second access point AP 2  (or the first access point AP 1 ). Accordingly, the shared access point, that is, the first access point AP 1 , may obtain information on the first path loss PL 1 , the second path loss PL 2 , and the third path loss PL 3 . An example of an operation of calculating the path loss based on the received frame will be described later with reference to  FIG.  12   . 
       FIGS.  8 A and  8 B  are diagrams illustrating examples of a wireless communication system according to example embodiments of the inventive concept. For example, the diagram of  FIG.  8 A  illustrates examples of the path loss considered in the DL/UL scenario of the coordinated spatial reuse in the wireless communication system  80   a , and the diagram of  FIG.  8 B  illustrates examples of the path loss considered in the UL/UL scenario of the coordinated spatial reuse in the wireless communication system  80   b . As illustrated in  FIGS.  8 A and  8 B , the first station STA 1  may be included in the first BSS BSS 1  provided by the first access point AP 1 , and the second station STA 2  and the third station STA 3  may be included in the second BSS BSS 2  provided by the second access point AP 2 . 
     Referring to  FIG.  8 A , in the DL/UL scenario, a first path loss PL 11a  between the first access point AP 1  and the first station STA 1 , a second path loss PL 12a  between the second station STA 2  and the first station STA 1 , and a third path loss PL 13a  between the third station STA 3  and the first station STA 1  may be considered. As the first path loss PL 11a  is low and the second path loss PL 12a  and the third path loss PL 13a  are high, it may be advantageous for the first access point AP 1  to successfully receive the first PPDU from the first station STA 1 . The first station STA 1  may calculate the first path loss PL 11a  based on the frame received from the first access point AP 1 , while obtaining of information on the second path loss PL 12a  and the third path loss PL 13a  may not be easy due to the second station STA 2  and the third station STA 3  that do not output frames. 
     Referring to  FIG.  8 B , in the UL/UL scenario, a first path loss PL 11b  between the first access point AP 1  and the first station STA 1 , a second path loss PL 12b  between the first access point AP 1  and the second station STA 2 , and a third path loss PL 13b  between the first access point AP 1  and the third station STA 3  may be considered. As the first path loss PL 11b  is low and the second path loss PL 12b  and the third path loss PL 13b  are high, it may be advantageous for the first access point AP 1  to successfully receive the first PPDU from the first station STA 1 . The first access point AP 1  may receive information on the first path loss PL 11b  from the first station STA 1 . In addition, as will be described later with reference to  FIG.  11   , the second access point AP 2  may receive information on the second path loss PL 12b  and the third path loss PL 13b  from the second station STA 2  and the third station STA 3 . 
       FIG.  9    is a message diagram showing a method for the coordinated spatial reuse according to an example embodiment of the inventive concept. For example, the message diagram of  FIG.  9    illustrates an operation performed in the DL/UL scenario of the coordinated spatial reuse described above with reference to  FIGS.  3 C and  8 A . As illustrated in  FIG.  9   , the method for the coordinated spatial reuse may include a plurality of operations (S 91  to S 96 ). In  FIG.  9   , the first station STA 1  may be included in the first BSS BSS 1  provided by the first access point AP 1 , and the second station STA 2  may be included in the second BSS BSS 2  provided by the second access point AP 2 . 
     As described above with reference to  FIG.  8 A , it may not be easy to obtain some of the path losses in the DL/UL scenario of the coordinated spatial reuse. Accordingly, in order to reduce or minimize interference with the transmission of the sharing BSS (that is, the first BSS BSS 1 ), the shared access point (that is, the second access point AP 2 ) may conservatively determine the transmit power limit by itself and limit the transmission power of the uplink transmission based on the determined transmit power limit. As described below, in some embodiments, the shared access point may determine the transmit power limit based on the reception power measured from the transmission occurring in the sharing BSS. 
     Referring to  FIG.  9   , in operation S 91 , the first station STA 1  may transmit the PPDU to the first access point AP 1 , and in operation S 92 , the second access point AP 2  may receive the PPDU from the first station STA 1 . That is, the signal output by the first station STA 1  to transmit the PPDU may reach the first access point AP 1  as well as the second access point AP 2 , and accordingly, the second access point AP 2  may receive the PPDU from the first station STA 1 . 
     In operation S 93 , the second access point AP 2  may measure the reception power of the PPDU. For example, the second access point AP 2  may measure the reception power based on a preamble of the PPDU received in operation S 92 . The second access point AP 2  may estimate a low path loss between the second access point AP 2  and the first station STA 1  when the measured reception power is high, while the second access point AP 2  may estimate a high path loss between the second access point AP 2  and the first station STA 1  when the measured reception power is low. Accordingly, in some embodiments, when the measured reception power exceeds the threshold value, the second access point AP 2  may give up the uplink transmission in the shared TXOP. 
     In operation S 94 , the second access point AP 2  may limit the transmission power to the second station STA 2 . For example, before operation S 94  is performed, TXOP may be shared by the first access point AP 1 , and if the reception power measured in operation S 93  is less than the threshold value, the second access point AP 2  may determine the transmit power limit based on the measured reception power, the minimum signal-to-interference ratio to successfully receive the second PPDU, and the path loss between the second access point AP 2  and the second station STA 2 . The second access point AP 2  may limit the transmission power of the second station STA 2  by transmitting a signal including the determined transmit power limit to the second station STA 2 . 
     In operation S 95 , the first station STA 1  may transmit the first PPDU to the first access point AP 1  in the shared TXOP, and in operation S 96 , the second station STA 2  may transmit the second PPDU to the second access point AP 2  in the shared TXOP. The second station STA 2  may transmit the second PPDU with a transmission power about equal to or less than the transmit power limit provided from the second access point AP 2  in operation S 94 , and the first access point AP 1  may successfully receive the first PPDU. 
       FIG.  10    is a message diagram showing a method for the coordinated spatial reuse according to an example embodiment of the inventive concept. For example, the message diagram of  FIG.  10    illustrates an operation performed in the UL/UL scenario of the coordinated spatial reuse described above with reference to  FIGS.  3 D and  8 B . As illustrated in  FIG.  10   , the method for the coordinated spatial reuse may include a plurality of operations (S 101  to S 106 ). In  FIG.  10   , the first station STA 1  may be included in the first BSS BSS 1  provided by the first access point AP 1 , and the second station STA 2  may be included in the second BSS BSS 2  provided by the second access point AP 2 . In the following description,  FIG.  10    will be described with reference to  FIG.  8 B . 
     In operation S 101 , the first access point AP 1  may determine a tolerable interference limit (TIL). The tolerable interference limit may correspond to the maximum interference allowed for the first access point AP 1  to successfully receive the first PPDU. For example, the first access point AP 1  may obtain the TXOP to receive the first PPDU from the first station STA 1 , and determine the tolerable interference limit based on at least one path loss associated with the first access point AP 1 . In some embodiments, the first access point AP 1  may determine the tolerable interference limit based on the transmission power of the first station STA 1 , the first path loss PL 11b  of  FIG.  8 B , and the minimum signal-to-interference ratio to successfully receive the first PPDU. For example, the signal-to-interference ratio SIR UL/UL  of the first access point AP 1  of  FIG.  8 B  may be calculated as illustrated in Equation 3 below. 
         SIR   UL/UL =( P   STA1   −PL   11b )( P   STA2   −PL   12b )( P   STA3   −PL   13b )  [Equation 3]
 
     In Equation 3, P STA1 , P STA2 , and P STA3  represent transmission powers of the first station STA 1 , the second station STA 2 , and the third station STA 3 , respectively. On the right side of Equation 3, the first term may correspond to the reception power of the signal received by the first access point AP 1  from the first station STA 1 , the second term may correspond to the reception power of the signal received by the first access point AP 1  from the second station STA 2 , and the third term may correspond to the reception power of the signal received by the first access point AP 1  from the third station STA 3 . Accordingly, the second term and the third term from the right side of Equation 3 may correspond to interference acting on the reception of the first PPDU. When the minimum signal-to-interference ratio for the first access point AP 1  to successfully receive the first PPDU is SIR Ap1 , SIR UL/UL  in Equation 3 may be greater than or about equal to SIR Ap1 , and accordingly, a tolerable interference limit I AP1   max  that satisfies SIR Ap1  may satisfy the following Equation 4 (SIR UL/UL =SIR Ap1 ). 
         I   AP1   max ( P   STA2   −PL   12b )+( P   STA3   −PL   13b )=( P   STA1   −PL   11b )− SIR   Ap1   [Equation 4]
 
     In operation S 102 , the first access point AP 1  may provide the tolerable interference limit to the second access point AP 2 . For example, the first access point AP 1  may transmit a signal including the tolerable interference limit determined in operation S 101  to the second access point AP 2 . In some embodiments, as described below with reference to  FIG.  13   , a tolerable interference limit may be included in the announcement frame. 
     In operation S 103 , the second access point AP 2  may identify the tolerable interference limit. For example, the second access point AP 2  may extract the tolerable interference limit from a signal received from the first access point AP 1  in operation S 102 . 
     In operation S 104 , the second access point AP 2  may limit the transmission power of the second station STA 2 . In some embodiments, the second access point AP 2  may determine the transmit power of the second station STA 2  based on the tolerable interference limit identified in operation S 103  and at least one path loss associated with the first access point AP 1 . For example, the transmit power limit P UL   max  of the uplink transmission may satisfy Equation 5 below based on the tolerable interference limit I AP1   max  of Equation 4. 
     
       
      
       P 
       UL 
       max 
       ≤PL 
       12b 
       +PL 
       13b 
       +I 
       AP1 
       max  
      
     
     The second access point AP 2  may distribute transmission powers to stations (for example, STA 2  and STA 3  of  FIG.  8 B ) in the multi-user (MU) environment based on Equation 5, and as illustrated in  FIG.  10   , in the single user environment, the transmit power limit P UL   max  of Equation 5 may be provided to the second station STA 2 . 
     In operation S 105 , the first station STA 1  may transmit the first PPDU to the first access point AP 1  in the shared TXOP, and in operation S 106 , the second station STA 2  may transmit the second PPDU to the second access point AP 2  in the shared TXOP. The second station STA 2  may transmit the second PPDU with a transmit power about equal to or less than the transmit power limit provided from the second access point AP 2  in operation S 104 , and the first access point AP 1  may successfully receive the first PPDU. 
       FIG.  11    is a message diagram showing a method for the coordinated spatial reuse according to an example embodiment of the inventive concept.  FIG.  12    is a diagram illustrating a frame according to an example embodiment of the inventive concept. For example, the message diagram of  FIG.  11    illustrates a method of acquiring path losses used in the UL/UL scenario of the coordinated spatial reuse, and the frame  120  of  FIG.  12    may be used in the method of  FIG.  11   . In  FIG.  11   , the second station STA 2  may be included in the second BSS BSS 2  provided by the second access point AP 2 . In the following description,  FIGS.  11  and  12    will be described with reference to  FIG.  8 B . 
     Referring to  FIG.  11   , the method for the coordinated spatial reuse may include a plurality of operations S 111  to S 113 . In operation S 111 , the first access point AP 1  may transmit the frame  120 , and the second access point AP 2  and the second station STA 2  may respectively receive the frame  120 . For example, each of the access points including the first access point AP 1  and the second access point AP 2  may periodically or aperiodically output the frame  120 , and other access points or stations may receive the frame  120 . 
     Referring to  FIG.  12   , the frame  120  may include a plurality of fields, and each of the plurality of fields may include information. For example, as illustrated in  FIG.  12   , the frame  120  may include a first field  121  including information on coordinated spatial reuse capability and a second field  122  including information on the transmission power of the frame  120 . For example, the second access point AP 2  and the second station STA 2  may extract the first field  121  from the frame  120  received from the first access point AP 1 , and identify whether the first access point AP 1  supports the coordinated spatial reuse based on the value of the first field  121 . In addition, the second access point AP 2  and the second station STA 2  may extract the second field  122  from the frame  120 , and identify the transmission power used by the first access point AP 1  for the transmission power including the frame  120  based on the value of the second field  122 . In some embodiments, the second field  122  may have the same format as that of the transmit power field included in the TPC report. The frame  120  of  FIG.  12    may be an arbitrary frame including the first field  121  and the second field  122 , for example, a beacon frame or a trigger frame. 
     Referring back to  FIG.  11   , in operation S 112 , the second station STA 2  may determine a path loss (that is, PL 1 n of  FIG.  8 B ) between the first access point AP 1  and the second station STA 2 . For example, the second station STA 2  may measure the reception power of the frame S 111  and calculate the path loss as a difference between the measured reception power and the transmit power information included in the frame  120 . In a similar manner, the path losses described above with reference to the drawings may be calculated at the access point and/or station based on the frame. 
     In operation S 113 , the second station STA 2  may report the path loss. For example, the second station STA 2  may transmit a signal including information on the path loss determined in operation S 112  to the second access point AP 2 . The second station STA 2  may report the path loss with the first access point AP 1  providing the first BSS BSS 1  and the second access point AP 2  providing the second BSS BSS 2  included therein. Accordingly, as described above with reference to  FIG.  10   , the second access point AP 2  may determine the transmit power limit of the second station STA 2  in the UL/UL scenario of the coordinated spatial reuse. 
       FIG.  13    is a timing diagram illustrating transmission based on the coordinated spatial reuse according to an example embodiment of the inventive concept. For example, the timing diagram of  FIG.  13    illustrates an example of transmissions and announcement frames (AF) occurring in the DL/DL scenario of the coordinated spatial reuse. In  FIG.  13   , the first station STA 1  may be included in the first BSS BSS 1  provided by the first access point AP 1 , and the second station STA 2  may be included in the second BSS BSS 2  provided by the second access point AP 2 . 
     Referring to  FIG.  13   , at time t 1   l , the first access point AP 1  may transmit a PPDU (PPDU 0 ) including an announcement frame AF to the second access point AP 2  to share the TXOP. The announcement frame AF may include information necessary to share the TXOP. As illustrated in the upper part of  FIG.  13   , the announcement frame AF may include a plurality of fields, and each of the plurality of fields may include information. For example, as illustrated in  FIG.  13   , the announcement frame AF may include first to sixth fields  131  to  136 . 
     The first field  131  may include identification information of the shared access point (that is, the second access point AP 2 ). The second field  132  may include information on a bandwidth of the shared TXOP. The third field  133  may include information on a period in which the PPDU transmission is performed in the shared TXOP. As described above with reference to  FIG.  4   , the fourth field  134  may include information (for example, MSB and LSB of  FIG.  5   ) indicating the type of transmission permitted to the shared access point. The fifth field  135  may include the transmit power limit (TPL) as described above with reference to  FIG.  6   . The sixth field  136  may include the tolerable interference limit (TIL) as described above with reference to  FIG.  10   . In some embodiments, at least one of the first to sixth fields  131  to  136  illustrated in  FIG.  13    may be omitted in the announcement frame AF. The shared access point may control or perform the transmission of the shared BSS based on information included in the announcement frame AF. 
     In some embodiments, the announcement frame AF may include a plurality of fields for a plurality of shared access points. For example, as will be described later with reference to  FIG.  16   , the first access point AP 1  may share the TXOP with the plurality of shared access points including the second access point AP 2 , and transmit the announcement frame AF including information to be provided to the plurality of shared access points. Accordingly, the announcement frame AF may include a plurality of fields respectively corresponding to a plurality of shared access points. For example, the announcement frame AF may include a plurality of first fields, a plurality of second fields, a plurality of third fields, a plurality of fourth fields, a plurality of fifth fields, and a plurality of sixth fields respectively corresponding to the plurality of shared access points. In addition, in some embodiments, the announcement frame AF may include a field indicating information common to the plurality of shared access points. For example, the announcement frame AF may include the second field  132  and the third field  133  common to the plurality of shared access points. Fields included in the announcement frame AF may be variously combined for the plurality of shared access points, and the configuration of the announcement frame AF is not limited to the foregoing. 
     At time t 12 , the first access point AP 1  may transmit the first PPDU PPDU 1  to the first station STA 1  in the shared TXOP, and the second access point AP 2  may transmit the second PPDU PPDU 2  to the second station STA 2  in the shared TXOP. As described above with reference to  FIG.  6   , the second access point AP 2  may transmit the second PPDU PPDU 2  with limited transmission power. Accordingly, the first station STA 1  and the second station STA 2  may successfully receive the first PPDU PPDU 1  and the second PPDU PPDU 2  in the shared TXOP, respectively, and at time t 13 , a first acknowledgment response BA 1  and a second acknowledgment response BA 2  may be transmitted to the first access point AP 1  and the second access point AP 2 , respectively. 
       FIG.  14    is a timing diagram illustrating transmission based on the coordinated spatial reuse according to an example embodiment of the inventive concept. For example, the timing diagram of  FIG.  14    illustrates the transmission occurring in the UL/DL scenario of the coordinated spatial reuse. In  FIG.  14   , first stations STA 11  and STA 12  may be included in the first BSS BSS 1  provided by the first access point AP 1 , and the second station STA 2  may be included in the second BSS BSS 2  provided by the second access point AP 2 . 
     Referring to  FIG.  14   , at time t 21 , the first access point AP 1  may transmit the PPDU PPDU 0  including the announcement frame AF to the second access point AP 2 . For example, the first access point AP 1  may obtain the TXOP to receive the first PPDUs PPDU 11  and PPDU 12 , and may transmit the announcement frame AF to the second access point AP 2  to share the obtained TXOP. 
     At time t 22 , the first access point AP 1  may transmit the PPDU PPDU 10  including the trigger frame TF to the first stations STA 11  and STA 12 , and the second access point AP 2  may transmit the second PPDU PPDU 2  to the second station STA 2 . At time t 23 , the first stations STA 11  and STA 12  may transmit the first PPDUs PPDU 11  and PPDU 12  to the first access point AP 1  in response to the trigger frame TF. 
     The first access point AP 1  may generate the announcement frame AF based on the UL/DL scenario of the coordinated spatial reuse, but as illustrated in  FIG.  14   , transmission of the PPDU PPDU 10  including the trigger frame TF in the shared TXOP and transmission of the second PPDU PPDU 2  may overlap. To eliminate the overlap, in a case in which the second access point AP 2  delays the transmission of the second PPDU PPDU 2  to time t 23 , the transmissions of the first PPDUs PPDU 11  and PPDU 12  and the second PPDU PPDU 2  are successful, but the completion of the transmissions in the shared TXOP may be delayed. Referring to  FIGS.  15 A and  15 B , a method for successfully performing the transmissions without delaying the completion of the transmissions in the UL/DL scenario of the coordinated spatial reuse will be described later. 
       FIGS.  15 A and  15 B  are timing diagrams illustrating transmission based on the coordinated spatial reuse according to example embodiments of the inventive concept. For example, each of the timing diagrams of  FIGS.  15 A and  15 B  represents the transmissions occurring in the UL/DL scenario of the coordinated spatial reuse. In  FIGS.  15 A and  15 B , the first stations STA 11  and STA 12  may be included in the first BSS BSS 1  provided by the first access point AP 1 , and the second station STA 2  may be included in the second BSS BSS 2  provided by the second access point AP 2 . In the description of  FIGS.  15 A and  15 B , a further description of elements and technical aspects previously described may be omitted for convenience of explanation. 
     Referring to  FIG.  15 A , at time t 31 , the first access point AP 1  may transmit the PPDU 0  including the announcement frame AF to the second access point AP 2  and the first stations STA 11  and STA 12 . The announcement frame AF may include a trigger information field  151 . For example, the announcement frame AF may include at least one subfield of at least a part of a common information field and a user information field included in the trigger frame TF of  FIG.  14   . Accordingly, transmission of a separate PPDU including the trigger frame may be omitted, and as a result, the transmissions may be successfully completed early in the UL/DL scenario of the coordinated spatial reuse. 
     At time t 32 , the first stations STA 11  and STA 12  may transmit the first PPDUs PPDU 11  and PPDU 12  to the first access point AP 1  in the shared TXOP, and the second access point AP 2  may transmit the second PPDU PPDU 2  to the second station STA 2  in the shared TXOP. For example, the first stations STA 11  and STA 12  may obtain information for the uplink transmission based on a value of the trigger information field  151  of the announcement frame AF, and may transmit the first PPDUs PPDU 11  and PPDU 12  to the first access point AP 1  based on the obtained information. The transmissions of the first PPDUs PPDU 11  and PPDU 12 , and the second PPDU 2  may be successfully completed, and accordingly, at time t 33 , the first access point AP 1  may transmit the first acknowledgment response BA 1  to the first stations STA 11  and STA 12 , and the second access point AP 2  may transmit the second acknowledgment response BA 2  to the second station STA 2 . 
     Referring to  FIG.  15 B , at time t 41 , the first access point AP 1  may transmit the PPDU PPDU 0  including the announcement frame AF and the trigger frame TF to first stations STA 11  and STA 12  and the second access point AP 2 . For example, the announcement frame AF and the trigger frame TF may be aggregated in the PPDU PPDU 0 . In some embodiments, the PPDU PPDU 0  including the aggregated announcement frame AF and the trigger frame TF may have a format of an aggregated MAC protocol data unit (A-MPDU). Accordingly, transmission of a separate PPDU including the trigger frame may be omitted, and as a result, the transmissions may be successfully completed early in the UL/DL scenario of the coordinated spatial reuse. 
     At time t 42 , the first stations STA 11  and STA 12  may transmit the first PPDUs PPDU 11  and PPDU 12  to the first access point AP 1  in the shared TXOP, and the second access point AP 2  may transmit the second PPDU PPDU 2  to the second station STA 2  in the shared TXOP. Then, at time t 43 , the first access point AP 1  may transmit the first acknowledgment response BA 1  to the first stations STA 11  and STA 12 , and the second access point AP 2  may transmit the second acknowledgment response BA 2  to the second station STA 2 . 
       FIG.  16    is a diagram illustrating a wireless communication system  160  according to an example embodiment of the inventive concept. As illustrated in  FIG.  16   , the wireless communication system  160  may include first to fifth access points AP 11  to AP 15 . 
     In some embodiments, the sharing access point may share the TXOP with a plurality of shared access points. For example, in a case in which the first access point AP 11  obtains the TXOP to transmit the PPDU, the first access point AP 11  transmits the announcement frame, thereby sharing the TXOP with the second to fifth access points AP 12  to AP 15  among neighboring access points. In some embodiments, the first access point AP 11  may permit the uplink transmission and/or the downlink transmission to each of the second to fifth access points AP 12  to AP 15 . In some embodiments, the first access point AP 11  may provide the transmit power limit and/or the tolerable interference limit to each of the second to fifth access points AP 12  to AP 15 . Accordingly, various scenarios of the coordinated spatial reuse may be implemented, and as a result, the efficiency of the wireless communication system  160  may be highly increased. 
     In some embodiments, the sharing access point may allocate radio resources used for the transmissions of the plurality of shared access points. For example, in a case in which the first access point AP 11  obtains the TXOP to transmit the PPDU, the first access point AP 11  may allocate an upper band of the bandwidth to the second access point AP 12 , and allocate a lower band of the bandwidth to the third access point AP 13  and the fourth access point AP 14 . To this end, the first access point AP 11  may transmit the announcement frame including resource allocation information, that is, band allocation information, and each of the second to fifth access points AP 12  to AP 15  may identify the band based on the band allocation information included in the band frame, and may transmit the PPDU to at least one station in the identified band. 
       FIG.  17    is a diagram showing examples of an apparatus for wireless communication according to an example embodiment of the inventive concept. For example,  FIG.  17    illustrates an Internet of Things (IoT) network system including home gadgets  171 , home appliances  172 , entertainment apparatuses  173 , and an access point  175 . 
     In some embodiments, in the apparatus for wireless communication of  FIG.  17   , the method for the coordinated spatial reuse described above with reference to the drawings may be performed. For example, the access point  175  (that is, the sharing access point) that obtains the TXOP may share the TXOP with a neighboring access point (that is, a shared access point), transmit the PPDU to the home gadgets  171 , the home appliances  172 , and/or the entertainment apparatuses  173  in the shared TXOP, or may receive the PPDU from the home gadgets  171 , the home appliances  172 , and/or the entertainment apparatuses  173 . In some embodiments, home gadgets  171 , home appliances  172  and/or the entertainment apparatuses  173  may report at least one path loss to the access point  175 . As described above with reference to the drawings, various scenarios of the coordinated spatial reuse may be supported, and accordingly, the home gadgets  171 , the home appliances  172  and/or the entertainment apparatuses  173  may successfully transmit or receive the PPDU. At the same time, in embodiments, the peripheral access points and stations do not delay the transmission of the PPDU, and as a result, the efficiency of the IoT network system may be increased. 
     As is traditional in the field of the present inventive concept, example embodiments are described, and illustrated in the drawings, in terms of functional blocks, units and/or modules. Those skilled in the art will appreciate that these blocks, units and/or modules are physically implemented by electronic (or optical) circuits such as logic circuits, discrete components, microprocessors, hard-wired circuits, memory elements, wiring connections, etc., which may be formed using semiconductor-based fabrication techniques or other manufacturing technologies. In the case of the blocks, units and/or modules being implemented by microprocessors or similar, they may be programmed using software (e.g., microcode) to perform various functions discussed herein and may optionally be driven by firmware and/or software. Alternatively, each block, unit and/or module may be implemented by dedicated hardware, or as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. 
     As will be appreciated by one skilled in the art, aspects of the present inventive concept may be embodied as a system, method or computer program product. Accordingly, aspects of the present inventive concept may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module,” “unit” or “system.” Furthermore, aspects of the present inventive concept may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a tangible, non-transitory computer-readable medium. 
     While the present inventive concept has been particularly shown and described with reference to the example thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present inventive concept as defined by the following claims.