Patent Publication Number: US-2023141814-A1

Title: Apparatus and method for multi-link-based wireless communication

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0151663, filed on Nov. 5, 2021, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     Technical Field 
     The inventive concept relates to wireless communication, and more particularly, to an apparatus and method for multi-link-based wireless communication. 
     Discussion of Related Art 
     Wireless local area network (WLAN) is a wireless communication technology that wirelessly connects an access point (AP) to one or more wireless devices. The AP may be typically connected to the Internet and acts as a gateway to allow allowing the connected wireless device(s) to also connect to the Internet. WLAN technology may be based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, often referred to as WiFi. 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 rate of up to 1 Gbyte/s based on orthogonal frequency-division multiplexing (OFDM) technology. 
     In 802.11ac, data may be simultaneously transmitted to a plurality of users via a multi-user multi-input multi-output (MU-MIMO) scheme. In 802.11ax, referred to as high efficiency (HE), multiple access is implemented by dividing and providing available subcarriers to users by applying not only MU-MIMO but also orthogonal frequency-division multiple access (OFDMA) technology. In this manner, a WLAN system, to which 802.11ax is applied, may effectively support communication in dense regions and in localized outdoor spaces. 
     In 802.11be, referred to as extremely high throughput (EHT), support for a 6 GHz unlicensed frequency band, utilization of bandwidth of up to 320 MHz per channel, introduction of hybrid automatic repeat and request (HARQ), and support for up to 16×16 MIMO are implemented. In this manner, a next-generation WLAN system is expected to effectively support low latency and ultrahigh-speed transmission like new radio (NR), which is 5 th  generation (5G) technology. 
     Recent proposals for a next generation WiFi have introduced the concept of multi-link communication, in which a single wireless device communicating with an AP may achieve higher throughput by aggregating data transmitted/received over a plurality of links, each associated with a different frequency band such as the 2.4 GHz, 5 GHz and 6 GHz bands. However, challenges remain to achieve high data throughput, particularly in a noisy environment. 
     SUMMARY 
     Embodiments of the inventive concept provide an apparatus and method for a higher throughput in multi-link-based wireless communication. 
     According to an aspect of the inventive concept, a wireless communication method performed by a first apparatus may include obtaining back-off counts of a plurality of links, when a back-off count of a first link among the plurality of links is zero, selecting a first transmission method or a second transmission method, when the first transmission method is selected, immediately transmitting first data to a second apparatus over the first link, and when the second transmission method is selected, delaying transmission of the first data to the second apparatus until a back-off count of a second link among the plurality of links becomes zero. 
     According to an aspect of the inventive concept, a first apparatus configured to communicate with a second apparatus over a plurality of links may include a transceiver that provides functionality of stations respectively corresponding to the plurality of links, and processing circuitry configured to control the transceiver, wherein the processing circuitry may select one of a first transmission method and a second transmission method when a back-off count of a first link among the plurality of links is zero, transmit first data to the second apparatus over the first link via the transceiver when the first transmission method is selected, and delay transmission of the first data to the second apparatus until a back-off count of a second link among the plurality of links becomes zero when the second transmission is selected. 
     According to an aspect of the inventive concept, a non-transitory computer-readable medium may store instructions executable by at least one processor to perform the wireless communication method outlined above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the inventive concept will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG.  1    is a diagram of a wireless communication system according to an example embodiment; 
         FIG.  2    is a block diagram showing a wireless communication system according to an example embodiment; 
         FIG.  3    is a block diagram showing a wireless communication system according to an example embodiment; 
         FIG.  4    is a timing diagram showing an example of a multi-link operation, according to an example embodiment; 
         FIG.  5    is a timing diagram showing an example of a multi-link operation; 
         FIG.  6    is a timing diagram showing an example of a multi-link operation; 
         FIGS.  7 A and  7 B  are timing diagrams showing examples of a multi-link operation, according to example embodiments; 
         FIG.  8    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment; 
         FIG.  9    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment; 
         FIG.  10    is a diagram showing measurement types included in a measurement request, according to an example embodiment; 
         FIG.  11    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment; 
         FIG.  12    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment; 
         FIG.  13    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment; 
         FIG.  14    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment; 
         FIG.  15    is a block diagram showing a system according to an example embodiment; and 
         FIG.  16    is a diagram showing examples of an apparatus for wireless communication, according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG.  1    is a diagram showing a wireless communication system  10  according to an example embodiment. Specifically,  FIG.  1    shows a wireless local area network (WLAN) system as an example of the wireless communication system  10 . 
     In specifically describing embodiments, an orthogonal frequency-division multiplexing (OFDM) or orthogonal frequency-division multiple access (OFDMA)-based wireless communication system, in particular, the Institute of Electrical and Electronic Engineers (IEEE) 802.11 standard, is the main object, but example embodiments are applicable to other communication systems (e.g., a cellular communication system such as long-term evolution (LTE), LTE-advanced (LTE-A), new radio (NR), wireless broadband (WiBro), and global system for mobile communication (GSM), or a near-field communication system such as Bluetooth and near-field communication (NFC)) having a similar technical background and channel form with slight modifications not greatly departing from the scope of the inventive concept, which may be understood by those skilled in the art. 
     Referring to  FIG.  1   , the wireless communication system  10  may include a first access point AP-a, a second access point AP-b, a first station STA-a, a second station STA-b, a third station STA-c, and a fourth station STA-d. The first and second access points AP-a and AP-b may access a network  13  such as the Internet, an Internet protocol (IP) network, or other suitable network. The first access point AP-a may provide the first through fourth stations STA-a to STA-d with access to the network  13  within a first coverage region  11 , and the second access point AP-b may also provide the third and fourth stations STA-c and STA-d with access to the network  13  within a second coverage region  12 . The first and second access points AP-a and AP-b may communicate with at least one station among the first to fourth stations STA-a to STA-d, based on wireless fidelity (WiFi) or other WLAN access technology. 
     An access point may be referred to as a router, a gateway, and the like, and a station may be referred to as 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 mobile apparatus such as a mobile phone, a laptop computer, or a wearable apparatus, or may be a stationary apparatus such as a desktop computer or a smart TV. Herein, the station may be referred to as a first apparatus, and the access point may be referred to as a second apparatus. Examples of the access point and the station may be described below with reference to  FIG.  16   . 
     The access point may allocate at least one resource unit (RU) to at least one station. The access point may transmit data via at least one allocated RU, and at least one station may receive the data via the at least one allocated RU. In 802.11ax (hereinafter, high efficiency (HE)), the access point may allocate only a single RU to at least one station, whereas in 802.11be (hereinafter, extremely high throughput (EHT)) or next-generation IEEE 802.11 standards (hereinafter, EHT+), the access point may allocate a multi-RU (MRU) including two or more RUs to at least one station. For example, the first access point AP-a may allocate an MRU to at least one of the first through fourth stations STA-a to STA-d and may transmit data via the allocated MRU. 
     The access point and the station may communicate with each other based on a multi-link. For example, as described below with reference to  FIG.  3   , an access point and a station may transmit or receive data over two or more links. Accordingly, the access point and the station may communicate data at a higher throughput than when only a single link is used. As described below with reference to  FIGS.  5  and 6   , in the case of links causing interference each other, aligning data transmissions in the time domain may be required in a related art example, but the aligning of the data transmissions may not necessarily guarantee a high throughput. 
     In embodiments described below, the access point or the station may adaptively determine whether to transmit data over a multi-link. For example, the access point or the station may adaptively determine, based on states of links, whether to transmit data over a single link or whether to transmit data over two or more links, and may select a transmission method that provides optimal throughput. Accordingly, a higher throughput may be achieved than when only a multi-link is used, and as a result, efficiency of the wireless communication system  10  may increase. Hereinafter, example embodiments will be described primarily with reference to EHT, but it will be understood that example embodiments may also be applied to other protocols, e.g., EHT+. 
       FIG.  2    is a block diagram showing a wireless communication system  20  according to an example embodiment. Here, the block diagram of  FIG.  2    shows a first wireless communication apparatus  21  and a second wireless communication apparatus  22 , which communicate with each other in the wireless communication system  20 . Wireless communication system  20  may be an example of wireless communication system  10 , where any of the wireless communication apparatuses in  FIG.  1    may include the same or similar components of the first wireless communication apparatus  21  or the second wireless communication apparatus  22 . 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 or simply an apparatus. Each of the first wireless communication apparatus  21  and the second wireless communication apparatus  22  may be an access point (e.g., any of AP-a and AP-b) or a station (e.g., any of STA-a to STA-d) of a 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, repeated descriptions of the first wireless communication apparatus  21  and the second wireless communication apparatus  22  will be omitted. 
     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 multiple input multiple output (MIMO). Also, in some embodiments, the antenna  21 _ 2  may include a phased array for beamforming. 
     The transceiver  21 _ 4  may process a signal received from the second wireless communication apparatus  22  via the antenna  21 _ 2 , and may provide the processed signal to the processing circuitry  21 _ 6 . Also, the transceiver  21 _ 4  may process a signal provided from the processing circuitry  21 _ 6 , and may output the processed signal via the antenna  21 _ 2 . In some embodiments, the transceiver  21 _ 4  may include an analog circuitry, such as a low noise amplifier, a mixer, a filter, a power amplifier, and an oscillator. In some embodiments, the transceiver  21 _ 4  may process, based on the control by the processing circuitry  21 _ 6 , a signal received from the antenna  21 _ 2  and/or a signal received from the processing circuitry  21 _ 6 . 
     The processing circuitry  21 _ 6  may extract information transmitted by the second wireless communication apparatus  22  by processing a 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 . Also, the processing circuitry  21 _ 6  may generate a signal including information to be transmitted to the second wireless communication apparatus  22 , and provide the signal to the transceiver  21 _ 4 . For example, the processing circuitry  21 _ 6  may provide the transceiver  21 _ 4  with a signal generated by encoding and modulating data to be transmitted to the second wireless communication apparatus  22 . In some embodiments, the processing circuitry  21 _ 6  may include a programmable component such as a central processing unit (CPU) and a digital signal processor (DSP), may include a reconfigurable component such as a field programmable gate array (FPGA), and may include a component that provides a fixed function such as an intellectual property (IP) core. In some embodiments, the processing circuitry  21 _ 6  may include a memory storing data and/or a series of instructions, or may access the memory. 
     Herein, the transceiver  21 _ 4  and/or the processing circuitry  21 _ 6  performing operations may be simply referred to as the first wireless communication apparatus  21  performing the operations. Accordingly, operations performed by an access point may be performed by a transceiver and/or a processing circuitry included in the access point, and operations performed by a station may be performed by a transceiver and/or a processing circuitry included in the station. 
       FIG.  3    is a block diagram showing a wireless communication system  30  according to an example embodiment. Here, the block diagram of  FIG.  3    shows multi-link devices (MLDs) that communicate with each other based on a multi-link in the wireless communication system  30 . Wireless communication system  30  may be an example of wireless communication system  10 , where any of the additional wireless communications apparatus in  FIG.  1    may also have multi-link functionality as described below. 
     Apparatuses for wireless communication may communicate with each other over two or more links. As shown in  FIG.  3   , an AP MLD  32  may be an example of either access point AP-a or AP-b, and a non-AP MLD  34  may be an example of any of the stations STA 1  to STA 4  of  FIG.  1   . The AP MLD  32  may include first to third “logical access points” AP 1  to AP 3 , and the non-AP MLD  34  may include first to third “logical stations” STA 1  to STA 3 . Any of the logical Aps AP 1  to AP 3  may include the same communication functionality as a stand-alone AP but may have transceiver/processing resources for communicating over only one frequency band among a plurality of frequency bands, e.g., 2.4 GHz, 5 GHz or 6 GHz bands, that may be used for the multi-link communication. Similarly, any logical STA may include the same communication functionality as a stand-alone STA, but may likewise have transceiver/processing resources for communicating over only one of the frequency bands usable for the multi-link communication. Hereafter, the logical APs AP 1  to AP 3  may each be referred to simply as AP and the logical STAs STA 1  to STA 3  will be referred to simply as a station. 
     In other embodiments, the AP MLD  32  and the non-AP MLD  34  may communicate with each other over just two links (using two respective frequency bands), or over at least four links (using four respective frequency bands). In some embodiments, the transceiver  21 _ 4  included in the first wireless communication apparatus  21  of  FIG.  2    may provide the functionality for all of the first to third access points AP 1  to AP 3 , and the processing circuitry  21 _ 6  may control the first to third access points AP 1  to AP 3 . Also, in some embodiments, the transceiver  22 _ 4  included in the second wireless communication apparatus  22  of  FIG.  2    may provide the functionality for all of the first to third stations STA 1  to STA 3 , and the processing circuitry  22 _ 6  may control the first to third stations STA 1  to STA 3 . 
     The first to third access points AP 1  to AP 3  and the first to third stations STA 1  to STA 3  may set up first to third links L 1  to L 3 , respectively. For example, the AP MLD  32  and the non-AP MLD  34  may perform an access procedure and/or a negotiation procedure for a multi-link operation (MLO). The non-AP MLD  34  may identify a band available for communication with the AP MLD  32 , and may negotiate with the AP MLD  32  to use two or more links among links supported by the AP MLD  32  for a multi-link. A method of communication via two or more links as described above may be referred to as an MLO, and apparatuses that communicate with each other based on a multi-link may each be referred to as an MLD. Due to an MLO, the wireless communication system  30  may provide high throughput. 
       FIG.  4    is a timing diagram showing an example of an MLO, according to an example embodiment. Specifically, the timing diagram of  FIG.  4    shows an example of an MLO performed by the wireless communication system  30  of  FIG.  3   . Hereinafter,  FIG.  4    will be described with reference to  FIG.  3   . 
     The AP MLD  32  and the non-AP MLD  34  of  FIG.  3    may support simultaneous transmit and receive (STR). For example, the AP MLD  32  may transmit data to the non-AP MLD  34  over the first link L 1  and simultaneously receive data from the non-AP MLD  34  over the second link L 2 . In some embodiments, the first to third access points AP 1  to AP 3  may have different medium access control (MAC) addresses, and may respectively be in charge of the first to third links L 1  to L 3 . Accordingly, each of the first to third access points AP 1  to AP 3  may function as an independent access point. Also, the first to third stations STA 1  to STA 3  may have different MAC addresses, and each of the first to third stations STA 1  to STA 3  may function as an independent station. The AP MLD  32  and the non-AP MLD  34  may communicate with each other in a multi-band. For example, the first link L 1  may use a bandwidth (e.g., 40 MHz) in a band of 2.4 GHz, the second link L 2  may use a bandwidth (e.g., 160 MHz) in a 5 GHz band, and the third link L 3  may use a bandwidth (e.g., 160 MHz) in a 6 GHz band. 
     Referring to  FIG.  4   , at time t 41 , the first access point AP 1  may initiate transmission of first data D 1  over the first link L 1 , and the first station STA 1  may receive the first data D 1 . While the first access point AP 1  transmits the first data D 1 , at time t 42 , the second station STA 2  may initiate transmission of second data D 2  over the second link L 2 , and the second access point AP 2  may receive the second data D 2 . Although the transmission of the first data D 1  and the transmission of the second data D 2  overlap in the time domain, due to STR, the first station STA 1  and the second access point AP 2  may normally receive the first data D 1  and the second data D 2 , respectively. Also, while the first access point AP 1  transmits the first data D 1  and the second station STA 2  transmits the second data D 2 , at time t 43 , the third access point AP 3  may initiate transmission of third data D 3  over the third link L 3 , and the third station STA 3  may receive the third data D 3 . Although the transmission of the first data D 1 , the transmission of the second data D 2 , and the transmission of the third data D 3  overlap in the time domain, due to STR, the first station STA 1 , the second access point AP 2 , and the third station STA 3  may normally receive the first data D 1 , the second data D 2 , and the third data D 3 , respectively. 
       FIG.  5    is a timing diagram showing an example of an MLO, according to an example embodiment. Specifically, the timing diagram of  FIG.  5    shows an example of non-STR (NSTR) in an MLO. Hereinafter,  FIG.  5    will be described with reference to  FIG.  3   . 
     In an MLO, there may be links that do not support STR. For example, when bands of links are not sufficiently apart from each other in a frequency domain, interference between the links may occur, and accordingly, the links may not support STR. Also, when there is interference between links due to various causes (e.g., RF signal power leakage) within an MLD (e.g., a non-AP MLD), the links may not support STR. As such, links of an MLO may include links that do not support STR, that is, an NSTR link group, and in particular, two links that do not support STR due to interference in the NSTR link group may be referred to as an NSTR link pair. The NSTR link group may be mutually identified in a process of the AP MLD  32  and the non-AP MLD  34  setting up a multi-link. 
     Referring to  FIG.  5   , the first link L 1  and the second link L 2  are assumed to be an NSTR link pair. For example, the first link L 1  may use a 6 GHz band, and the second link L 2  may use a 5 GHz band. At time t 51 , the first access point AP 1  may obtain Transmit Opportunity (TXOP) and initiate transmission of the first data D 1  over the first link L 1 , and the first station STA 1  may receive the first data D 1 . TXOP is a MAC-layer feature used in the IEEE 802.11 protocol, which defines a time duration for which a station can send frames after it has won contention for a transmission medium. At time t 52 , the second station STA 2  may initiate transmission of the second data D 2  over the second link L 2 , but when the first link L 1  and the second link L 2  are an NSTR link pair, interference between the transmission of the second data D 2  and the reception of the first data D 1  may occur. Accordingly, the second access point AP 2  may not normally receive the second data D 2 , and the first station STA 1  may not normally receive the first data D 1 . To prevent such interference, while transmission over the first link L 1  is performed, transmission over the second link L 2  may be suspended. However, in some cases according to embodiments herein, transmissions of data may simultaneously occur even in the NSTR link pair, an example of which will be described below with reference to  FIG.  6   . Hereinafter, the first link L 1  and the second link L 2  of  FIG.  3    are assumed to be an NSTR link pair. 
       FIG.  6    is a timing diagram showing an example of an MLO. Here, the timing diagram of  FIG.  6    shows an example in which transmissions of data simultaneously occur in the first link L 1  and the second link L 2 , which are the NSTR link pair. 
     In some embodiments, a back-off count may be a count in a back-off procedure in which a plurality of stations, e.g., single link stations or logical stations such as STA 1  and STA 2  within a multi-link device, contend to gain access to a link. For example, each contending station may initiate a random back-off count prior to a transmission attempt to gain access to the link. When the back-off count reaches zero, the transmission attempt may be made. Referring to  FIG.  6   , while a channel of the first link L 1  is not in a busy state (where “busy state” may refer to the link being in use by the AP with another station) a back-off count of the first station STA 1  corresponding to the first link L 1  may decrease, and while a channel of the second link L 2  is not in a busy state, a back-off count of the second station STA 2  corresponding to the second link L 2  may decrease. At time t 61 , the channel of the first link L 1  may enter the busy state due to other transmissions, and the back-off count of the first station STA 1  may stop decreasing. Similarly, at time t 62 , the channel of the second link L 2  may enter the busy state due to other transmissions, and the back-off count of the second station STA 2  may stop decreasing. 
     At time t 63 , the busy state in the channel of the first link L 1  may be released, and accordingly, the back-off count of the first station STA 1  may gradually decrease from  4 . Similarly, at time t 64 , the busy state in the channel of the second link L 2  may be released, and accordingly, the back-off count of the second station STA 2  may gradually decrease from  3 . 
     At time t 65 , the back-off count of the first station STA 1  may become zero, and accordingly, the first station STA 1  may enter a state in which communication may be performed over the first link L 1 . However, as described above with reference to  FIG.  5   , when transmission is initiated over the first link L 1  and then reception is performed over the second link L 2 , interference may occur. Accordingly, the first station STA 1  may delay transmission until the back-off count of link L 2  is zero, despite obtaining a channel access opportunity, so that a failure does not occur in clear channel assessment (CCA) for identifying whether the channel of the second link L 2  is in a busy state. 
     At time t 66 , the back-off count of the second station STA 2  may become zero, and accordingly, the second station STA 2  may enter a state in which communication may be performed over the second link L 2 . Accordingly, the first station STA 1  and the second station STA 2  may simultaneously initiate transmission. For example, as shown in  FIG.  6   , at the time t 66 , the first station STA 1  and the second station STA 2  may simultaneously transmit a first request to send (RTS) frame RTS 1  and a second RTS frame RTS 2  to the first access point AP 1  and the second access point AP 2 , respectively. Accordingly, the first link L 1  may be reserved for the first station STA 1 , and the second link L 2  may be reserved for the second station STA 2 . As such, an operation of simultaneously performing transmission over two links of the NSTR link pair by delaying transmission over one link may be referred to as a start time sync protocol data unit (PPDU) (physical layer protocol data unit or physical layer convergence procedure (PLCP) protocol data unit). 
     After the transmission of the first RTS frame RTS 1  and the second RTS frame RTS 2  is completed, a short inter-frame space (SIFS) elapses, and then at time t 67 , the first access point AP 1  may transmit a first clear to send (CTS) frame CTS 1  in response to the first RTS frame RTS 1 , and the second access point AP 2  may transmit a second CTS frame CTS 2  in response to the second RTS frame RTS 2 . Afterwards, at time t 68 , the first station STA 1  may transmit a first aggregated-MAC protocol data unit (A-MPDU) A-MDPU 1  to the first access point AP 1 , and the second station STA 2  may transmit a second A-MPDU A-MPDU 2  to the second access point AP 2 . As a result, data (i.e., A-MPDU 1  and A-MPDU 2 ) may be simultaneously transmitted over the first link L 1  and the second link L 2 . However, a start time sync PPDU that aligns transmissions over the first link L 1  and the second link L 2  in the time domain may not always provide optimal performance (e.g., throughput), examples of which will be described below with reference to  FIGS.  7 A and  7 B . 
       FIGS.  7 A and  7 B  are timing diagrams showing examples of an MLO, according to example embodiments. Specifically, the timing diagrams of  FIGS.  7 A and  7 B  respectively show examples that may occur in a start time sync PPDU. Hereinafter, repeated descriptions of  FIG.  6    in descriptions of  FIGS.  7 A and  7 B  will be omitted. 
     Referring to  FIG.  7 A , a channel of the first link L 1  may be in a busy state from time t 71  to time t 73 , and a channel of the second link L 2  may be in a busy state from time t 72  to time t 74 . The busy state of the channel in the first link L 1  may be released at the time t 73 , and accordingly, a back-off count of the first station STA 1  may gradually decrease. Similarly, the busy state of the channel in the second link L 2  may be released at the time t 74 , and accordingly, a back-off count of the second station STA 2  may gradually decrease. 
     At time t 75 , the back-off count of the first station STA 1  has reached zero, but the back-off count of the second station STA 2  is not yet zero, and thus transmission over the first link L 1  may be delayed based on the start time sync PPDU. At time t 76 , before the back-off count of the second station STA 2  becomes zero, the channel of the first link L 1  may enter a busy state. Accordingly, although the back-off count of the second station STA 2  has reached zero at time t 77 , transmissions over the first link L 1  and the second link L 2  may not be simultaneously performed, and the first station STA 1  may lose an obtained channel access opportunity. However, unlike the case of  FIG.  7 A , in embodiments described below, the first station STA 1  may initiate transmission at a time point at which the back-off count of the first station STA 1  reaches zero, that is, at the time t 75 . This may result in higher throughput and a technique that always utilizing the start time sync PPDU. 
     Referring to  FIG.  7 B , a channel of the first link L 1  may be in a busy state from time t 81  to time t 83 , and a channel of the second link L 2  may be in a busy state from time t 82  to time t 84 . The busy state of the channel in the first link L 1  may be released at the time t 83 , and accordingly, a back-off count of the first station STA 1  may gradually decrease. Similarly, the busy state of the channel in the second link L 2  may be released at the time t 84 , and accordingly, a back-off count of the second station STA 2  may gradually decrease. 
     At time t 85 , the back-off count of the first station STA 1  has reached zero, but the back-off count of the second station STA 2  is not yet zero, and thus transmission over the first link L 1  may be delayed based on the start time sync PPDU. At time t 86 , before the back-off count of the second station STA 2  becomes zero, the channel of the second link L 2  may enter a busy state. Accordingly, a period during which the first station STA 1  delays transmission may be extended, and accordingly, transmissions over the first link L 1  and the second link L 2  may not be simultaneously performed. Also, when the channel of the first link L 1  enters the busy state in the extended period as described above with reference to  FIG.  7 A , the first station STA 1  may lose an obtained channel access opportunity. Unlike in  FIG.  7 B , the first station STA 1  initiating transmission at a time point at which the back-off count of the first station STA 1  reaches zero, that is, at the time t 85 , may be more efficient than the start time sync PPDU. 
     As described below, when a back-off count of a link reaches zero, an MLD may determine whether to perform a transmission method (herein, which may be referred to as a “first transmission method” or “first transmission”) over at least one link for which a back-off count is zero, or whether to delay the first transmission method until a back-off count of the additional link reaches zero and perform a transmission (herein, which may be referred to as a “second transmission method” or “second transmission”) over a plurality of links together with an additional link. The MLD may select a transmission method that provides optimal performance (e.g., throughput) among the first and second transmission methods, and accordingly, an efficiency of an MLO may be increased. Hereinafter, a non-AP MLD will be mainly described, but it will be understood that example embodiments may also be applied to an AP MLD. 
       FIG.  8    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment. As shown in  FIG.  8   , the multi-link-based wireless communication method may include a plurality of operations S 100  to S 600 . In some embodiments, the method of  FIG.  8    may be performed by the non-AP MLD  34  of  FIG.  3   . Hereinafter,  FIG.  8    will be described with reference to  FIG.  3   , and the first link L 1  and the second link L 2  of  FIG.  3    are assumed to be an NSTR link pair. It is noted here that in the flowchart of  FIG.  8   , as well as in the other flowcharts herein ( FIGS.  9  and  11 - 14   ), the order of the illustrated operations may be changed as desired in other embodiments, and/or some of the operations may be performed in parallel. 
     Referring to  FIG.  8   , in operation S 100 , information about links may be collected. For example, the non-AP MLD  34  may collect information about the first link L 1  and the second link L 2 , which are the NSTR link pair, and select an appropriate transmission method based on the collected information. An example of operation S 100  will be described below with reference to  FIG.  9   . 
     In operation S 200 , back-off counts may be obtained. For example, the non-AP MLD  34  (e.g., a processing circuitry included in the non-AP MLD  34 ) may obtain a back-off count from the first station STA 1  corresponding to the first link L 1 , and may obtain a back-off count from the second station STA 2  corresponding to the second link L 2 . 
     In operation S 300 , a back-off count that has reached zero may be detected. For example, as shown in  FIG.  8   , when a back-off count STA_BC_i corresponding to an i th  link among N links included in an NSTR link group reaches zero (STA_BC_i=0), operation S 400  may be performed subsequently (N is an integer greater than 1, 1≤i≤N). On the other hand, when a back-off count that has reached zero is not detected, operation S 100  and operation S 200  may be performed again. 
     When the back-off count STA_BC_i corresponding to the i th  link reaches zero, a transmission may be selected in operation S 400 . For example, when the back-off count of the first station STA 1  reaches zero, the non-AP MLD  34  may select one of a transmission over the first link L 1 , that is, a first transmission method (“first transmission”), and a transmission over both the first link L 1  and the second link L 2 , that is, a second transmission method (“second transmission”). As shown in  FIG.  8   , when the first transmission method is selected, operation S 500  may be performed subsequently, whereas, when the second transmission method is selected, operation S 600  may be performed subsequently. The non-AP MLD  34  may select one of the first transmission method and the second transmission method based on the information collected in operation S 100 , and an example of operation S 400  will be described below with reference to  FIG.  11   . 
     When the first transmission is selected, i th  data may be immediately transmitted over the i th  link in operation S 500 . For example, the non-AP MLD  34  may control the first station STA 1  to transmit first data over the first link L 1  without any intentional delay, i.e., irrespective of a back-off count associated with the second link L 2 . On the other hand, when the second transmission is selected, transmission of the i th  data may be delayed in operation S 600 . For example, the non-AP MLD  34  may delay transmitting the first data over the first link L 1  until the back-off count of the second station STA 2  becomes zero. When the second transmission is selected and the back-off count of the second station STA 2  reaches zero, the non-AP MLD  34  may control the first station STA 1  and the second station STA 2  to simultaneously transmit first data and second data over the first link L 1  and the second link L 2 , respectively. 
       FIG.  9    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment. Specifically, the flowchart of  FIG.  9    shows an example of operation S 100  of  FIG.  8   . As described above with reference to  FIG.  8   , information about links included in an NSTR link group may be collected in operation S 100 ′ of  FIG.  9   . As shown in  FIG.  9   , operation S 100 ′ may include operation S 120  and operation S 140 , and operation S 120  may include operation S 122  and operation S 124 . In some embodiments, unlike in  FIG.  9   , operation S 100  of  FIG.  8    may include only one of operation S 120  and operation S 140  of  FIG.  9   . Hereinafter,  FIG.  9    will be described with reference to  FIG.  3   . 
     “First information” may be collected based on a request and a response in operation S 120 . To this end, a request for the first information may be transmitted in operation S 122 , and a response including the first information may be received in operation S 124 . For example, the non-AP MLD  34  may transmit, to the AP MLD  32 , a request for first information corresponding to each of links. The wireless communication system  30  may provide frames for requesting for a variety of information and responding between wireless communication apparatuses, and elements included in each of the frames. For example, as described below with reference to  FIG.  10   , the non-AP MLD  34  may transmit a spectrum measurement request frame to the AP MLD  32 , as one example of the first information. 
     The AP MLD  32  may transmit, to the non-AP MLD  34 , a response including the first information in response to the request from the non-AP MLD  34 . For example, the AP MLD  32  may transmit a measurement report frame to the non-AP MLD  34 . Also, in some embodiments, the AP MLD  32  may transmit a request for first information to the non-AP MLD  34 , and the non-AP MLD  34  may transmit a response including the first information to the AP MLD  32 . As such, the first information indicating states of links may be explicitly collected and may be used as a basis for selecting an optimal transmission. However, the first information is not limited to the examples described above, and may include any information about a link, which may be collected via a request and a response, in which the information is sufficient to make at least part of the determination regarding which transmission method to use. 
     Additionally, “second information” may be extracted from frames observed over links in operation S 140 . For example, the non-AP MLD  34  may extract second information by monitoring links. Frames observed over a link, for example, a frame received from the AP MLD  32  to the non-AP MLD  34  over a link, a frame transmitted by the AP MLD  32  or another non-AP MLD or a station over a link, and the like, may include information about the link, and accordingly, the non-AP MLD  34  may extract the second information from the frames observed over the links. For example, the non-AP MLD  34  may extract a basic service set (BSS) load element from a probe response frame or beacon frame, which is transmitted by the AP MLD  32 , and identify utilization in the time domain and in a frequency domain of a corresponding link, based on the BSS load element. As such, the second information indicating states of links may be implicitly collected and may be used as a basis for selecting an optimal transmission. However, the second information is not limited to the examples described above, and may include any information about a link, which may be extracted from an observed frame. 
       FIG.  10    is a diagram showing measurement types included in a measurement request, according to an example embodiment. As described above with reference to  FIG.  9   , the first information used as a basis for selecting an optimal transmission may be collected based on a request and a response. A table presented in  FIG.  10    is merely an example of the first information, and it is noted that the first information corresponding to any information collectable via a request and a response is not limited to  FIG.  10   . Hereinafter,  FIG.  10    will be described with reference to  FIG.  3   . 
     The non-AP MLD  34  may transmit a measurement request frame to the AP MLD  32 . As shown in  FIG.  10   , various measurements may be requested via measurement request frames. In some embodiments, the non-AP MLD  34  may transmit, to the AP MLD  32 , a measurement request corresponding to one of measurement types shown in  FIG.  10   . The AP MLD  32  may transmit, to the non-AP MLD  34 , a measurement report frame including a value corresponding to a measurement type, in response to the measurement request. 
       FIG.  11    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment. Here, the flowchart of  FIG.  11    shows an example of operation S 400  of  FIG.  8    involving selecting a transmission method. As described above with reference to  FIG.  8   , an optimal transmission method may be selected from the first and second transmission methods. As shown in  FIG.  11   , operation S 400 ′ may include a plurality of operations S 420 , S 440 , and S 460 . Operation S 400 ′ may be performed by the non-AP MLD  34  (or a processing circuitry included in the non-AP MLD  34 ) of  FIG.  3   . Hereinafter,  FIG.  11    will be described with reference to  FIG.  3   , and the first link L 1  and the second link L 2  are assumed to be an NSTR link pair. 
     A first expected throughput of the first link L 1  may be calculated in operation S 420 , and a second expected throughput of the second link L 2  may be calculated in operation S 440 . To this end, an expected throughput may be calculated based on at least one of a bandwidth and a signal-to-noise ratio (SNR). For example, a first expected throughput T 1  and a second expected throughput T 2  may be calculated as in [Equation 1] below. 
         T   1   =f ( BW   1   ,SNR   1 , . . . ) 
         T   2   =f ( BW   2   ,SNR   2 , . . . )  [Equation 1]
 
     In [Equation 1], BW 1  is a bandwidth of the first link L 1 , SNR 1  is an SNR of the first link L 1 , BW 2  is a bandwidth of the second link L 2 , and SNR 2  is an SNR of the second link L 2 . Thus, an expected throughput may be defined as a function f of parameters including a bandwidth and an SNR. 
     In operation S 460 , the first transmission method or the second transmission method may be determined. For example, an optimal transmission method may be selected from the first and second transmission methods, based on the first and second expected throughputs in operations S 420  and S 440 , respectively. Based on the first expected throughput and the second expected throughput, a gain using the first transmission method (“first gain”) and a gain using the second transmission method (“second gain”) may be derived, and a transmission method that provides a higher gain may be selected. Herein, the term “gain”, as used in association with at least one link, may be understood as a collective (multi-link) throughput using the at least one link. “Gain” may also be understood in a relative sense as a gain in throughput of a multi-link communication as compared to a single link operation. An example of operation S 460  will be described below with reference to  FIG.  12   . 
       FIG.  12    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment. The flowchart of  FIG.  12    shows an example of operation S 460  of  FIG.  11   . As described above with reference to  FIG.  11   , the first or second transmission methods may be determined in operation S 460 ′ of  FIG.  12   . As described in  FIG.  12   , operation S 460 ′ may include a plurality of operations S 461 , S 463 , S 465 , S 467 , and S 469 . In some embodiments, operation S 460 ′ may be performed by the non-AP MLD  34  (or a processing circuitry included in the non-AP MLD  34 ) of  FIG.  3   . Hereinafter,  FIG.  12    will be described with reference to  FIG.  3   , and the first link L 1  and the second link L 2  are assumed to be an NSTR link pair. 
     Referring to  FIG.  12   , a first gain using the first transmission may be calculated in operation S 461 . For example, the non-AP MLD  34  may determine the first gain as the first expected throughput of the first link L 1 , which has been calculated in operation S 420  of  FIG.  11   . That is, the first gain may correspond to a throughput expected when the first transmission method is performed. 
     In operation S 463 , a second gain using the second transmission method may be calculated. The second gain may correspond to a throughput expected when transmission is performed over the first link L 1  and the second link L 2 , and may be calculated based on the first expected throughput of the first link L 1  and the second expected throughput of the second link L 2 . An example of operation S 463  will be described below with reference to  FIG.  13   . 
     In operation S 465 , the first gain and the second gain may be compared. As described above, the first gain may correspond to a throughput expected when the first transmission is performed, and the second gain may correspond to a throughput expected when the second transmission is performed. Accordingly, as shown in  FIG.  12   , when the first gain equals or exceeds the second gain, the first transmission method may be determined in operation S 467 , whereas, when the first gain is less than the second gain, the second transmission method may be determined in operation S 469 . When the first transmission method is used, transmission of data may be initiated earlier than when the second transmission method is used. 
       FIG.  13    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment. Specifically, the flowchart of  FIG.  13    shows an example of operation S 463  of  FIG.  12   . As described above with reference to  FIG.  12   , the second gain of the second transmission may be calculated in operation S 463 ′ of  FIG.  13   . As shown in  FIG.  13   , operation S 463 ′ may include a plurality of operations S 463 _ 2 , S 463 _ 4 , and S 463 _ 6 . In some embodiments, operation S 463 ′ may be performed by the non-AP MLD  34  (or a processing circuitry included in the non-AP MLD  34 ) of  FIG.  3   . Hereinafter,  FIG.  13    will be described with reference to  FIG.  3   , and the first link L 1  and the second link L 2  are assumed to be an NSTR link pair. 
     Referring to  FIG.  13   , a first probability of losing channel access of the first link L 1  may be calculated in operation S 463 _ 2 . As described above with reference to  FIG.  7 A , the first station STA 1  for which the back-off count has reached zero may stand by for the back-off count of the second station STA 2  to reach zero for the start time sync PPDU. Accordingly, when the non-AP MLD  34  stands by for the back-off count of the second station STA 2  to reach zero, the non-AP MLD  34  may calculate the first probability of losing channel access of the first link L 1 . In some embodiments, the non-AP MLD  34  may calculate the first probability based on, for example, a state of the first link L 1 , such as the number of other stations related to the first link L 1  and a traffic amount related to the first link L 1 , and/or a current back-off count of the second station STA 2 . Accordingly, the first probability may increase as the number of other stations related to the first link L 1  is large, a traffic amount related to the first link L 1  is large, and a current back-off count of the second station STA 2  increases. 
     In operation S 463 _ 4 , a second probability that another device obtains channel access of the second link L 2  may be calculated. As described above with reference to  FIG.  7 B , while the second station STA 2  stands by for the back-off count of the second station STA 2  to reach zero, the second station STA 2  may lose channel access of the second link L 2 . Accordingly, the non-AP MLD  34  may calculate the second probability of losing the channel access of the second link L 2  before the back-off count of the second link L 2  reaches zero. In some embodiments, the non-AP MLD  34  may calculate the second probability based on, for example, a state of the second link L 2 , such as the number of other stations related to the second link L 2  and a traffic amount related to the second link L 2 , and/or a current back-off count of the second station STA 2 . Accordingly, the second probability may increase as the number of other stations related to the second link L 2  is large, a traffic amount related to the second link L 2  is large, and a current back-off count of the second station STA 2  increases. 
     In operation S 463 _ 6 , the second gain may be calculated. In some embodiments, the second gain may be calculated based on the first expected throughput and the second expected throughput, which are respectively calculated in operation S 420  and operation S 440 , the first probability calculated in operation S 463 _ 2 , and the second probability calculated in operation S 463 _ 4 . For example, a second gain G 2  may be calculated as in [Equation 2] below. 
         G   2   =p   1   ×f   2 ( BW   2   ,SNR   2 , . . . )+(1− p   1 )(1− p   2 )× f   1 ( BW   1   ,SNR   1 , . . . )+(1− p   1 ) p   2   ×{f   1 ( BW   1   ,SNR   1 , . . . )+ f   2 ( BW   2   ,SNR   2 , . . . )}  [Equation 2]
 
     In [Equation 2], p 1  is a first probability, p 2  is a second probability, f 1 (BW 1 , SNR 1 , . . . ) is a first expected throughput, and f 2 (BW 2 , SNR 2 , . . . ) is a second expected throughput. Also, in [Equation 2], (1−p 1 ) may indicate a probability of not losing channel access of the first link L 1 , and (1−p 2 ) may indicate a probability that the second station STA 2  obtains channel access, that is, a probability that a back-off count reaches zero without interruption. Accordingly, the second gain G 2  may correspond to a throughput expected when the second transmission is performed. 
       FIG.  14    is a flowchart showing a multi-link-based wireless communication method according to an example embodiment. Specifically,  FIG.  14    shows a wireless communication method performed when an NSTR link group includes N links in a multi-link (N is an integer greater than 2). As shown in  FIG.  14   , the multi-link-based wireless communication method may include a plurality of operations S 10  to S 90 . In some embodiments, the method of  FIG.  14    may be performed by the non-AP MLD  34  of  FIG.  3   . Hereinafter,  FIG.  14    will be described with reference to  FIG.  3   , and it is assumed that the first to third links L 1  to L 3  of  FIG.  3    are included in the NSTR link group. 
     Referring to  FIG.  14   , in operation S 10 , the number of links for which a back-off count is zero may be identified. For example, a variable m may be set to the number of links for which a back-off count reaches zero until before operation S 30  is performed (m is an integer of 0 or more). 
     In operation S 20 , information about links may be collected. For example, the non-AP MLD  34  may explicitly collect first information and/or implicitly collect second information, as information about the first to third links L 1  to L 3 . The collected information may be used as a basis for selecting an optimal transmission. 
     In operation S 30 , back-off counts may be obtained. For example, the non-AP MLD  34  (for example, a processing circuitry included in the non-AP MLD  34 ) may obtain back-off counts from the first to third stations STA 1  to STA 3  respectively corresponding to the first to third links L 1  to L 3 . 
     In operation S 40 , k back-off counts that have reached zero may be detected (k is an integer greater than 0). One back-off count may reach zero, or two or more back-off counts may simultaneously reach zero. As shown in  FIG.  14   , when a back-off count that has reached zero is not detected, operation S 10  and operation S 20  may be performed again, whereas, when k back-off counts that have reached zero are detected, operation S 40  may be performed subsequently. 
     In operation S 50 , links for which a back-off count has reached zero may be accumulated. As shown in  FIG.  14   , k may be added to the variable m, and accordingly, the variable m may correspond to the number of links for which a current back-off count has reached zero. 
     In operation S 60 , whether back-off counts have reached zero in all links of the NSTR link group may be determined. For example, as shown in  FIG.  14   , the variable m may be compared to N, and when the variable m is the same as N, that is, when back-off counts have reached zero in all links of the NSTR link group, operation S 70  may be performed subsequently. On the other hand, when the variable m is not the same as N, that is, when a back-off count has not reached zero in at least one link included in the NSTR link group, operation S 80  may be performed subsequently. 
     When the variable m is not the same as N, a transmission may be selected in operation S 80 . For example, when the back-off count of the first station STA 1  reaches zero, the non-AP MLD  34  may select one of a transmission over the first link L 1 , that is, a first transmission, and a transmission over the first link L 1  and the second link L 2  or over the first link L 1  and the third link L 3 , that is, a second transmission. Also, when the back-off counts of the first station STA 1  and the second station STA 2  are both zero, the non-AP MLD  34  may select one of a transmission over the first link L 1  and the second link L 2 , that is, a first transmission, and a transmission over all of the first to third links L 1  to L 3 , that is, a second transmission. 
     In some embodiments, the non-AP MLD  34  may consider only a link having the lowest back-off count among links for which a back-off count has not reached zero. For example, in a case where the back-off count of the first link L 1  has reached zero, when the back-off count of the second station STA 2  is less than the back-off count of the third station STA 3 , the non-AP MLD  34  may consider only a transmission over the first link L 1  and the second link L 2  among possible second transmissions. As shown in  FIG.  14   , when the first transmission is selected, operation S 70  may be performed subsequently, whereas, when the second transmission is selected, operation S 90  may be performed subsequently. 
     When back-off counts reach zero in all links of the NSTR link group or the first transmission is selected, data may be simultaneously transmitted over m links in operation S 70 . That is, without standing by for a back-off count to reach zero in an additional link, data may be transmitted over m links for which a current back-off count is zero. 
     When the second transmission is selected, transmission of data may be delayed in operation S 90 . For example, the non-AP MLD  34  may delay transmission of data until channel access is obtained in a link corresponding to a back-off count that has not yet reached zero. In one example, when the second transmission is selected, the back-off count of the first link and the back-off count of the third link are zero, and the back-off count of the second link has not reached zero, the transmission of the first data, the transmission of the second data, and the transmission of the third data may be delayed until the back-off count of the second link is zero. In some embodiments, as described above with reference to  FIG.  8   , when a back-off count of a remaining link in the NSTR link pair reaches zero, data transmission may be performed over both links of the NSTR link pair, whereas, when the second transmission is selected while a back-off count does not reach zero in two or more links, the method of  FIG.  14    may be repeatedly performed. That is, subsequent to operation S 90 , operation S 10  may be performed. 
       FIG.  15    is a block diagram showing a system  150  according to an example embodiment. In some embodiments, the system  150  of  FIG.  15    may be implemented as at least one chip, and the system  150  implemented as one chip may be referred to as a system-on-chip. As shown in  FIG.  15   , the system  150  may include an application processor  151 , a memory  152 , an input/output (I/O) interface  153 , a hardware (HW) accelerator  154 , and a communication interface  155 , and the application processor  151 , the memory  152 , the I/O interface  153 , the HW accelerator  154 , and the communication interface  155  may communicate with each other via a bus  156 . 
     The application processor  151  may control the system  150 . For example, the application processor  151  may include at least one core, and each of the at least one core may execute a series of instructions stored in the memory  152 . In some embodiments, the application processor  151  may execute an operating system (OS), and may execute applications on the OS. The application processor  151  may control other components of the system  150 . For example, the application processor  151  may instruct the HW accelerator  154  to perform an operation by providing data to the HW accelerator  154 , and may obtain a result of the operation performed by the HW accelerator  154 . Also, the application processor  151  may instruct transmission by providing the communication interface  155  with data to be transmitted to the outside, and may obtain data received from the outside via the communication interface  155 . 
     The memory  152  may be accessed by other components via the bus  156 . The memory  152  may have any structure capable of storing data, and may include, for example, a volatile memory such as static RAM (SRAM) and dynamic RAM (DRAM), and/or a non-volatile memory such as flash memory and resistive RAM (RRAM). The memory  152  may store instructions executed by the application processor  151 , and may store data read or written by other components. 
     The I/O interface  153  may provide an interface for input to the system  150  and output from the system  150 . For example, the I/O interface  153  may communicate with an I/O device included in a product together with the system  150 , and may receive a user input or provide an output to a user via the I/O device. Also, the I/O interface  153  may communicate with peripherals included in a product together with the system  150 , and may enable the application processor  151  to control the peripherals. 
     The HW accelerator  154  may be hardware designed to perform a function at a high speed. For example, the HW accelerator  154  may be designed to perform encoding and decoding of data at a high speed. Also, the HW accelerator  154  may be designed to perform neural processing at a high speed. The HW accelerator  154  may process data stored in the memory  152 , and may store the processed data in the memory  152 . 
     The communication interface  155  may provide a communication channel to an object external to the system  150 . For example, the communication interface  155  may provide a wired communication channel and/or a wireless communication channel. In some embodiments, the communication interface  155  may perform at least one operation included in the multi-link-based wireless communication method described above with reference to the  FIGS.  1 - 14   . For example, as shown in  FIG.  15   , the communication interface  155  may include at least one processor  155 _ 1 , and the at least one processor  155 _ 1  may execute instructions to perform at least one operation included in the multi-link-based wireless communication method described above with reference to  FIGS.  1 - 14   . In some embodiments, the at least one processor  155 _ 1  may execute instructions stored in the memory  152  or a memory included in the communication interface  155 . In some embodiments, the memory  152  or the memory included in the communication interface  155  may store information about links collected, and may be accessed by the at least one processor  155 _ 1 . 
       FIG.  16    is a diagram showing examples of an apparatus for wireless communication, according to an example embodiment. Specifically,  FIG.  16    shows an Internet of Things (IoT) network system including a home gadget  161 , home appliances  162 , an entertainment device  163 , and an access point (AP)  165 . 
     In some embodiments, in apparatuses for wireless communication of  FIG.  16   , as described above with reference to  FIGS.  1 - 15   , an MLO may be supported. For instance, the AP  165  may be an example of the AP MLD  32  of  FIG.  3   , and any one of the home gadget  161 , home appliances  162 , and entertainment device  163  may be an example of the non-AP MLD  34  of  FIG.  3   . Accordingly, apparatuses for wireless communication may explicitly and/or implicitly collect information about links, and may select an optimal transmission based on the collected information. Accordingly, throughput may increase, and an efficiency of an WLAN system may increase. 
     Various functions described hereinabove may be implemented or supported by artificial intelligence technology or one or more computer programs, and each of the programs includes computer-readable program code and is implemented in a computer-readable medium. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or portions thereof adapted for implementing appropriate computer-readable program code. The term “computer-readable program code” includes any type of computer code including source code, object code, and executable code. The term “computer-readable medium” includes any type of medium that may be accessed by a computer, such as read-only memory (ROM), random-access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. “Non-transitory” computer-readable media exclude wired, wireless, optical, or other communication links that transmit transitory electrical or other signals. The non-transitory computer-readable media include media where data may be permanently stored and media where data may be stored and later overwritten, such as rewritable optical discs or erasable memory devices. 
     In various embodiments described hereinabove, a hardware approach is described as an example. However, various embodiments include technology using both hardware and software, and thus various embodiments do not exclude a software-based approach. 
     Also, terms that refer to control information, terms that refer to entries, terms that refer to network entities, terms that refer to messages, and terms that refer to components of apparatuses, which are described above, are examples for convenience of description. Other terms having equal technical meanings may be substituted. 
     While the inventive concept has been particularly shown and described with reference to embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the following claims.