Patent Publication Number: US-2023164784-A1

Title: Communication device and communication method

Description:
TECHNICAL FIELD 
     The technology (hereinafter, “the present disclosure”) disclosed in this specification relates to a communication device and a communication method that bundle a plurality of links to perform wireless communication. 
     BACKGROUND ART 
     In recent years, data traffic in wireless communication such as virtual reality (VR) and 8K video transmission has increased. In order to accommodate such traffic, improvement in throughput is required in a wireless local area network (LAN). Currently, a multi-link operation (MLO) for bundling a plurality of links to perform communication is being standardized as a technique useful for improving throughput. The multi-link operation can be roughly divided into an asynchronous transmission system in which each link performs an independent communication operation and a synchronous transmission system in which transmission timings are completely aligned between links. Since channels between links are close in the multi-link operation and leakage occurs, it may be difficult to perform transmission by one link and reception by another link. In this case, according to the synchronous transmission system in which the transmission timings are aligned in a plurality of links, simultaneous transmission and reception between the links does not occur, and the effect by the multi-link operation can be obtained. 
     When the multi-link operation by synchronous transmission is performed, it is required that all links to be used can be simultaneously transmitted, in other words, each link is simultaneously in an idle state. However, a terminal that does not support the multi-link operation, such as a legacy terminal, performs a transmission operation independently of other links by using only one link. For this reason, the time during which all the plurality of links can be transmitted by synchronous transmission in the idle state is limited, and the effect of improving the throughput by the multi-link operation cannot be expected. 
     For example, there has been proposed a communication device that, when a communication end time of a first communication system (legacy AP) is detected at one link used for a multi-link operation, suppresses transmission until the communication end time at the link, and transmits an occupation signal describing a media occupancy period ending at the communication end time at another link used for the multi-link operation to suppress transmission of the other communication systems, thereby securing a time during which all links used for the multi-link operation are idle (see Patent Document 1). 
     However, it is assumed that the communication device according to this proposal transmits a data frame by synchronous transmission after suppressing transmission until the end of communication of the first communication system by one link. For this reason, the communication device waits for transmission even if there is data desired to be transmitted by the end of communication of the first communication system. In addition, in a case where a signal indicating a media occupancy period is transmitted to suppress transmission of another communication system, the communication system that has failed in reception of the occupation signal cannot set a transmission suppression period (Network Allocation Vector: NAV) for suppressing transmission and starts transmission. Therefore, it is difficult for the communication device to secure a time during which all links used for the multi-link operation are idle. Furthermore, in order to transmit a data frame without colliding with another terminal, the communication device according to this proposal immediately transmits an occupation signal when the NAV of another communication system due to the transmission of the occupation signal expires. However, in a case where there is another communication device that similarly transmits the occupation signal at the expiration of the NAV, collision between the occupation signals occurs. 
     CITATION LIST 
     Patent Document 
     Patent Document 1: Japanese Patent Application Laid-Open No. 2006-303590 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     An object of the present disclosure is to provide a communication device and a communication method that perform a multi-link operation by synchronous transmission. 
     Solutions to Problems 
     The present disclosure has been made in view of the above problems, and a first aspect thereof is a communication device including: 
     a communication unit that performs communication by a first link and a second link; and 
     a control unit that controls a communication operation by the communication unit, in which 
     the control unit sets an occupancy period of the second link on a basis of transmission suppression information of the first link. 
     The control unit sets an occupancy period of the second link until a transmission suppression period of the first link ends, and performs control to transmit a data frame by the second link when a remaining time of the transmission suppression period of the first link is longer than a first threshold, transmit a first signal by the second link when the remaining time of the transmission suppression period of the first link is equal to or less than the first threshold and is longer than a second threshold, and transmit a second signal by the second link when the remaining time of the transmission suppression period of the first link is equal to or less than the second threshold. 
     Further, the control unit determines a transmission destination of a frame by the second link on the basis of whether or not simultaneous transmission and reception between links of a transmission source or a transmission destination of a signal for setting the transmission suppression period in the first link is possible. 
     Further, a second aspect of the present disclosure is a communication method of a communication device that performs communication by a first link and a second link, the communication method including the steps of: 
     setting a transmission suppression period of the first link on a basis of a signal received by the first link; and 
     setting the second occupancy period on a basis of the first transmission suppression information. 
     Effects of the Invention 
     According to the present disclosure, it is possible to provide a communication device and a communication method that perform a multi-link operation by synchronous transmission. 
     Note that the effects described in the present specification are merely examples, and the effects brought by the present disclosure are not limited thereto. Furthermore, the present disclosure may further provide additional effects in addition to the above effects. 
     Still other objects, features, and advantages of the present disclosure will become apparent from a more detailed description based on embodiments to be described later and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating a configuration example of a communication system  100 . 
         FIG.  2    is a diagram illustrating an example of channel selection of a first link (link1) and a second link (link2). 
         FIG.  3    is a diagram illustrating an example of channel selection of the first link (link1) and the second link (link2). 
         FIG.  4    is a diagram illustrating a configuration example of a communication device  200 . 
         FIG.  5    is a diagram illustrating an example of a communication sequence in which a multi-link operation is performed using a first link and a second link (an example of aligning times during which respective links are idle by using data frames). 
         FIG.  6    is a diagram illustrating an example of a communication sequence in which a multi-link operation is performed by using a first link and a second link (an example of aligning times during which respective links are idle by using null packets). 
         FIG.  7    is a flowchart illustrating a processing procedure for a communication device capable of performing a multi-link operation to transmit a data frame. 
         FIG.  8    is a flowchart illustrating a processing procedure for a communication device capable of performing a multi-link operation to transmit a data frame. 
         FIG.  9    is a diagram illustrating an example of a communication sequence in which a multi-link operation is performed using a first link and a second link. 
         FIG.  10    is a flowchart illustrating a processing procedure for a communication device capable of performing a multi-link operation to transmit a data frame. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, the present disclosure will be described in the following order with reference to the drawings. 
     A. Overview 
     B. System Configuration 
     C. Device Configuration 
     D. Operation Example 1 
     E. Operation Example 2 
     F. Effect 
     A. Overview 
     A communication device to which the present disclosure is applied performs a multi-link operation by synchronous transmission in which transmission timings of a first link and a second link are aligned. The communication device to which the present disclosure is applied transmits data or a signal having a short signal length by the second link until the NAV ends in accordance with the length of the NAV set at the first link and the presence or absence of data to be immediately transmitted. In a case where the length of the NAV is sufficiently long, the communication device to which the present disclosure is applied can suppress transmission even in a case where another communication device cannot set the NAV by transmitting the data frame by the second link, and can secure a time during which the first link and the second link are all in the idle state. In addition, after the NAV expires, each communication device sets a preferential random waiting time, so that the communication device to which the present disclosure is applied performs preferential transmission to a communication device that does not support a multi-link operation while avoiding collision of communication between communications that perform the multi-link operation. 
     Furthermore, the communication device to which the present disclosure is applied may set a NAV longer than that until the end of communication of another communication device. In this case, the communication device to which the present disclosure is applied suppresses further attempt of transmission by another communication device after the end of communication by the other communication device, and easily acquires the transmission right for the multi-link operation by synchronous transmission. For example, when a communication device to which the present disclosure is applied secures a transmission right by a second link during a period in which a NAV is set by reception of a frame that is not addressed to the communication device itself by a first link, the communication device transmits a frame for setting a channel occupancy period (Transmission Opportunity: TXOP) until a time when the NAV of the first link ends in accordance with a length of the NAV of the first link, presence or absence of data to be transmitted, an amount of data, and a communication scheme such as a modulation and coding scheme (MCS) to be used. The frame may be a data frame, a request to send (RTS) frame, a clear to send (CTS)-to-self frame, a null data packet (NDP), or the like. Furthermore, the communication device to which the present disclosure is applied may set the TXOP of the second link to be longer than the end of the NAV of the first link so that transmission can be preferentially performed after the end of the NAV of the first link, and can perform transmission using the first link and the second link by channel confirmation for a certain period after the end of the NAV of the first link. 
     B. System Configuration 
       FIG.  1    schematically illustrates a configuration example of a communication system  100  to which the present disclosure is applied. The illustrated communication system  100  includes an access point (AP)  110  and a terminal (STA)  120 . The terminal  120  is not an access point (that is, is a non-AP). In the communication system  100 , a first link and a second link can be used, and the access point  110  and the terminal  120  are connected via the first link and the second link. 
     Both the access point  110  and the terminal  120  are communication devices (Multi-link Devices: MLDs) that perform the multi-link operation using the first link (link1) and the second link (link2), that is, an AP MLD and a non-AP MLD, respectively. Note that, hereinafter, when simply referred to as “multi-link operation”, multi-link operation by synchronous transmission is indicated unless otherwise specified. 
     In the example shown in  FIG.  1   , two access points, AP1-1 operating on a first link and AP1-2 operating on a second link, are included in the access point  110 . Also. Two terminals, a non-AP STA1-1 that operates on the first link and a non-AP STA1-2 that operates on the second link, are included in the terminal  120 . However, the number of access points and terminals included in each of the access point  110  and the terminal  120  is not limited to two, and may be three or more. That is, the number of links connecting the access point  110  and the terminal  120  is not limited to two, and they may be connected through three or more links. In addition, although only one access point and one terminal are illustrated in the communication system  100  in  FIG.  1    for simplification of the drawing, a plurality of access points and terminals may be connected. Furthermore, one communication device may include one or more access points (AP MLD) and one or more terminals (non-AP MLD). 
     An MLD management entity is an entity that manages operations in the access point  110  and the terminal  120  that are MLDs, respectively. In addition, MAC-SAP to LLC is a point (Serivice Access Point) that provides a service of a Media Access Control (MAC) layer to a Logical Link Control (LLC) layer, which is an upper layer of the MAC layer. 
     The “link” mentioned in the present specification is a wireless transmission path through which data transmission can be performed between two communication devices. The individual links are selected from among a plurality of wireless transmission paths (channels) divided, for example, in a frequency domain and independent from each other.  FIGS.  2  and  3    illustrate two examples regarding channel selection of the first link (link1) and the second link (link2) used in the communication system  100 . In each drawing, each of a band A and a band B is any one of bands such as a 2.4 GHz band, a 5 GHz band, a 6 GHz band, and a 920 GHz band. The band A and the band B may be, for example, an unlicensed band that does not require a radio station license, and are allowed to be used by database access such as a Spectrum Access System (SAS). 
     Each of the band A and the band B includes a plurality of channels. In the example illustrated in  FIGS.  2  and  3   , the band A includes six channels, and the band B includes five channels. The MLD such as the access point  110  and the terminal  120  operating in the communication system  100  selects channels to be used for the first link (link1) and the second link (link2) from the band A and the band B. In the example illustrated in  FIG.  2   , channels to be used for the first link (link1) and the second link (link2) are selected from the band A. Furthermore, in the example illustrated in  FIG.  3   , a channel to be used for the first link (link1) is selected from the band A, and a channel to be used for the second link (link2) is selected from the band B. 
     C. Device Configuration 
       FIG.  4    illustrates a configuration example of the communication device  200  that can operate as the access point  110  and the terminal  120 . The communication device  200  is a device or an MLD that performs a multi-link operation using a first link (link1) and a second link (link2). 
     The illustrated communication device  200  includes a control unit  210 , a power supply unit  220 , a plurality of (two in the illustrated example) communication units  230 - 1  and  230 - 2 , an antenna unit  240 - 1  corresponding to the communication unit  230 - 1 , and an antenna unit  240 - 2  corresponding to the communication unit  230 - 2 . 
     The combination of the communication unit  230 - 1  and the antenna unit  240 - 1  and the combination of the communication unit  230 - 2  and the antenna unit  240 - 2  are provided for each band used by the communication device  200 . In the example illustrated in  FIG.  4   , data communication using the first link (link1) is performed by the combination of the communication unit  230 - 1  and the antenna unit  240 - 1 , and data communication using the second link (link2) is performed by the combination of the communication unit  230 - 2  and the antenna unit  240 - 2 . Therefore, in a case where the communication device  200  uses three or more bands, a combination of a communication unit and an antenna unit (not illustrated) is additionally provided. The communication unit  230 - 1  and the communication unit  230 - 2  may control and exchange information with each other. 
     Note that, since the communication unit  230 - 1  and the communication unit  230 - 2 , and the antenna unit  240 - 1  and the antenna unit  240 - 2  have the same configuration, the communication unit  230 - 1  and the communication unit  230 - 2  will be referred to as a communication unit  230 , and the antenna unit  240 - 1  and the antenna unit  240 - 2  will be referred to as an antenna unit  240  for simplification. 
     The communication unit  230  is configured by, for example, a processor such as a microprocessor and a circuit, and includes a memory unit  238 , a wireless control unit  231 , a data processing unit  232 , a modulation/demodulation unit  233 , a signal processing unit  234 , a channel estimation unit  235 , a plurality of wireless interface (IF) units  236 - 1 , . . . , and  236 -N arranged in parallel, and amplifier units  237 - 1 , . . . , and  237 -N connected in series to the wireless interface units  236 - 1 , . . . , and  236 -N (here, N is an integer of 2 or more.). Then, each antenna element constituting the antenna unit  240  corresponding to the communication unit  230  is connected to each of the amplifier units  237 - 1 , . . . , and  237 -N. 
     With the wireless interface unit  236 , the amplifier unit  237 , and the antenna unit  240  connected in series as one set, one or more sets may be a component of the communication unit  230 . In addition, the wireless interface units  236 - 1 , . . . , and  236 -N may include the functions of the corresponding amplifier units  237 - 1 , . . . , and  237 -N, respectively. 
     The memory unit  238  temporarily stores data (for example, transmission data) input from the upper layer of the communication protocol and provides the data to the data processing unit  232 . In addition, the memory unit  239  temporarily stores the data (for example, received data) delivered from the data processing unit  232  and provides the data to the upper layer of the communication protocol. That is, the memory unit  238  is used as a transmission queue or a reception queue. 
     Note that a part or the whole of the memory unit  238  may be arranged outside the communication unit  230 . Furthermore, the memory unit  238 - 1  arranged in one communication unit  230 - 1  may be shared with another communication unit  230 - 2 , or the memory unit  238  arranged outside the communication unit  230  may be shared by a plurality of communication units  230 - 1 ,  230 - 2 , . . . . 
     At the time of transmission in which data is input from an upper layer of its own communication protocol, the data processing unit  232  generates a packet for wireless transmission from the data, further performs processing such as addition of a header for media access control (MAC) or addition of an error detection code, and provides the processed data to the modulation/demodulation unit  233 . Furthermore, at the time of reception in which there is an input from the modulation/demodulation unit  233 , the data processing unit  232  performs processing such as analysis of the MAC header, detection of a packet error, and packet reordering, and provides the processed data to its own protocol upper layer. 
     The wireless control unit  231  controls delivery of information between respective units in the communication device  200 . In addition, the wireless control unit  231  performs parameter setting in the modulation/demodulation unit  233  and the signal processing unit  234 , packet scheduling in the data processing unit  232 , parameter setting of the wireless interface unit  236  and the amplifier unit  237 , and transmission power control. 
     At the time of transmission, the modulation/demodulation unit  233  performs encoding, interleaving, and modulation processing on the input data from the data processing unit  232  on the basis of the encoding system and the modulation system set by the wireless control unit  231 , generates a data symbol stream, and provides the data symbol stream to the signal processing unit  234 . Furthermore, at the time of reception, the modulation/demodulation unit  233  performs demodulation processing, deinterleaving, and decoding processing opposite to those at the time of transmission on the input symbol stream from the signal processing unit  234 , and provides data to the data processing unit  232  or the wireless control unit  231 . 
     At the time of transmission, the signal processing unit  234  performs signal processing to be used for spatial separation on the input from the modulation/demodulation unit  233  as necessary, and provides the obtained one or more transmission symbol streams to the wireless interface units  236 - 1 , . . . . Furthermore, at the time of reception, the signal processing unit  234  performs signal processing on the received symbol streams input from the respective wireless interface units  236 - 1 , . . . performs spatial decomposition of the streams as necessary, and provides the streams to the modulation/demodulation unit  233 . 
     The channel estimation unit  235  calculates complex channel gain information of the propagation path from the preamble portion and the training signal portion of the input signals from the wireless interface units  236 - 1 , . . . . The calculated complex channel gain information is used for demodulation processing in the modulation/demodulation unit  233  and spatial processing in the signal processing unit  234  via the wireless control unit  231 . 
     At the time of transmission, the wireless interface unit  236  converts an input from the signal processing unit  234  into an analog signal, performs filtering, up-conversion to a carrier frequency, and phase control, and transmits the resultant signal to the corresponding amplifier unit  237  or antenna unit  240 . Furthermore, at the time of reception, the wireless interface unit  236  performs processing such as down-conversion, filtering, and conversion into a digital signal opposite to that at the time of transmission on the input from the corresponding amplifier unit  237  or antenna unit  240 , and provides data to the signal processing unit  234  and the channel estimation unit  235 . 
     At the time of transmission, the amplifier unit  237  amplifies the analog signal input from the wireless interface unit  236  to predetermined power and transmits the amplified analog signal to the corresponding antenna element in the antenna unit  240 . Furthermore, at the time of reception, the amplifier unit  237  amplifies the signal input from the corresponding antenna element in the antenna unit  240  with low noise to predetermined power, and outputs the amplified signal to the wireless interface unit  236 . 
     Note that at least one of the function at the time of transmission or the function at the time of reception of the amplifier unit  237  may be included in the wireless interface unit  236 . Furthermore, at least one of the function at the time of transmission or the function at the time of reception of the amplifier unit  237  may be a component other than the communication unit  230 . 
     One set of the wireless interface unit  236  and the amplifier unit  237  constitutes one radio frequency (RF) branch. It is assumed that transmission and reception of one band can be performed by one RF branch. In the device configuration example illustrated in  FIG.  4   , the communication unit  230  includes N RF branches. 
     The control unit  210  is configured by, for example, a processor such as a microprocessor and a circuit, and controls the wireless control unit  231  and the power supply unit  220 . Furthermore, the control unit  210  may perform at least a part of the above-described operation of the wireless control unit  231  instead of the wireless control unit  231 . In particular, in the present embodiment, the control unit  210  and the wireless control unit  231  control the operation of each unit in order to realize the operation according to each embodiment described later. 
     The power supply unit  220  is configured by a battery power supply or a fixed power supply, and supplies driving power to the communication device  200 . 
     Note that the control unit  210  and the communication unit  230  can be collectively configured by one or a plurality of large scale integration (LSI). 
     Furthermore, while the communication device  200  is on standby, the communication unit  230  may transition to a standby state or a sleep state (alternatively, a state in which at least a part of the functions is stopped) to achieve low power consumption. In the device configuration example illustrated in  FIG.  4   , the communication unit  230  includes N RF branches, but may be configured to be able to transition to a standby state or a sleep state for each RF branch. 
     D. Operation Example 1 
     In this section, a first operation example of a communication device (MLD) that performs a multi-link operation using a first link and a second link will be described. Specifically, an operation in which the communication device (MLD) sets the TXOP of the second link on the basis of the NAV information of the first link, sets both the first link and the second link to the idle state, and facilitates a multi-link operation by synchronous transmission will be described. 
       FIG.  5    illustrates a communication sequence example illustrating this operation. However,  FIG.  5    assumes a communication system in which the first link (link1) and the second link (link2) can be used and three terminals (STA MLD1, STA MLD2, STA MLD3) operate under control of one access point (AP MLD1). The AP MLD1 includes an AP1-1 operating on the first link and an AP1-2 operating on the second link. In addition, the STA MLD1 includes an STAT-1 operating on the first link and an STAT-2 operating on the second link, the STA MLD2 includes an STA2-1 operating on the first link and an STA2-2 operating on the second link, and the STA MLD3 includes an STA3-1 operating on the first link and an STA3-2 operating on the second link. 
     Note that the horizontal axis in  FIG.  5    is a time axis, and indicates a communication operation of the access point and each terminal for each time on the first link and the second link. A square block drawn by a solid line indicates a transmission frame, a solid arrow in the vertical direction indicates frame transmission to a destination, and a dotted arrow in the vertical direction indicates arrival of a frame addressed to other than the destination. In addition, a parallelogram block drawn by a solid line indicates a backoff operation, and a square block drawn by a dotted line indicates a period in which the NAV is set. 
     First, the AP1-1 of the AP MLD1 expires the backoff of waiting for a random waiting time, acquires a period (for example, TXOP) of occupying a channel at the first link (link1) at time T1, and transmits a data frame (Data) to the STA MLD3-1. 
     When receiving a data frame that is not addressed to the STA 1-1 and the STA2-1 from the AP1-1, the STAT-1 and the STA2-1 set a transmission suppression period (NAV) until time T3 at which returning of a reception acknowledgement (ACK) from the STA3-1 to the AP3-1 is completed on the basis of the time described in the Duration/ID field of the header of the data frame, and perform transmission suppression of the frame at the first link (link1). The time information used to set the transmission suppression period may be a length field or a TXOP DURATION of Extreme High Throughput (EHT)-SIG (SIGNAL). 
     Thereafter, the STA1-2 expires the backoff at the second link (link2) at time T2. The STA1-2 may attempt to acquire the transmission right after the STA1-1 receives the data frame not addressed to the STA1-1 itself, but in the example illustrated in  FIG.  5   , the STA1-2 starts backoff before the STA1-1 receives the data frame not addressed to the STA1-1 itself. The STA1-2 sets TXOP at the second link (link2) in accordance with the time until the end of the NAV of the STA1-1, the presence or absence of data to be transmitted before the end of the NAV of the STA1-1, the amount of data, and the modulation and coding scheme (MCS) to be used. 
     In the example illustrated in  FIG.  5   , since there is data to be transmitted before the end of the NAV of the STA1-1, the STA1-2 sets TXOP by time T3 corresponding to the NAV end time of the STA1-1, and transmits a data frame (Data) to the AP1-2 at time T2 when the backoff expires. 
     Here, in a case where the time until the time T3 at which the NAV of the STA1-1 ends is longer than the first threshold, the STA1-2 sets TXOP by the NAV end time T3 of the STA1-1 and transmits the data frame as illustrated in  FIG.  5   . The first threshold here is a time length determined according to the amount of data of the data frame to be transmitted by the STAT-2 and the MCS to be used. 
     Furthermore, in a case where the time until the NAV end time T3 of the STAT-1 is shorter than the first threshold and longer than the second threshold, the STA1-2 sets TXOP until the NAV end time T3 of the STAT-1, and transmits a signal having a short signal length instead of the data frame. Here, the signal having a short signal length is an RTS frame or a CTS-to-self frame. Furthermore, the second threshold is a time length determined according to the frame length of the RTS frame or the CTS-to-self frame transmitted by the STAT-2 and the MCS to be used. 
     Furthermore, in a case where the time until the NAV end time T3 of the STAT-1 is shorter than the second threshold, the STAT-2 sets TXOP by the NAV end time T3 of the STAT-1 and transmits null packets instead of the data frame.  FIG.  6    illustrates, as a modification of the communication sequence illustrated in  FIG.  5   , a communication sequence example in which the STAT-2 aligns the time during which the first link and the second link are idle using null packets. The null packet may be, for example, a Very High Throughput (VHT) NDP or a High Efficiency (HE) NDP. Furthermore, the packet may be a packet including only a legacy preamble such as L-STF (Legacy Short Training Field) or L-LTF (Long Training Field), or a packet including only a legacy preamble and subjected to padding until the NAV end time. In a case where the time until the NAV end time T3 of the STAT-1 is shorter than the time related to the transmission of the null packet, the STAT-2 may set the NAV until the NAV end time T3 of the STAT-1 without transmitting the null packet. 
     The communication sequence example will be described with reference to  FIG.  5    again. The STA2-2 and the STA3-2, when receiving a data frame that is not addressed to the STA2-2 and STA3-2 from the STAT-2, set a transmission suppression period (NAV) on the basis of the time described in the Duration/ID field of the header of the data frame, and perform frame transmission suppression at the second link (link2) until time T3. 
     In this way, the STA MLD1 can align the time during which the first link and the second link are idle at time T3. The STAT-1 and the STAT-2 may start backoff at time T3 by setting the same random waiting time. Then, when the backoff expires at time T4, the STAT-1 and the STAT-2 transmit data frames (Data) using the first link and the second link, respectively, and can realize a multi-link operation by synchronous transmission (the same applies to the communication sequence illustrated in  FIG.  6   ). 
     In the communication sequence illustrated in  FIG.  5   , when transmitting a data frame at time T2, the STAT-2 may determine the destination of the data frame to be transmitted by link2 by using information as to whether a transmission source (Transmitter Address) and a transmission destination (Receiver Address) of a frame for which a NAV is set support simultaneous transmission and reception between links. In the communication sequence example illustrated in  FIG.  5   , in a case where the AP MLD1 does not support simultaneous transmission and reception between links, when the STA1-2 transmits a data frame to the AP1-2, the AP MLD1 fails to receive data by the AP1-2 due to interlink interference from data transmission at the AP1-1. Furthermore, in a case where the STA1-1 sets NAV by a data frame transmitted from another STA (for example, STA3-1) to the AP (for example, AP1-1), even if the STA1-2 transmits data to the AP1-2, AP1-2 fails to receive the data due to interference caused by ACK transmission from the AP1-1 to the STA3-1. Therefore, the STA1-2 transmits a data frame to another STA instead of the AP1-2 that does not support simultaneous reception, or performs only transmission of a CTS-to-self frame. 
     In short, when a communication device (MLD) that performs a multi-link operation using the first link and the second link acquires a transmission right by the other link during a period in which the NAV is set by one link, the communication device transmits a data frame, a signal having a short signal length, or a null packet by the other link according to a time until the NAV end time, thereby aligning a time during which the first link and the second link are idle and realizing the multi-link operation by synchronous transmission. 
     An EHT STA that satisfies all of the following conditions (1) to (3) continues to acquire, at one link for which an AP MLD or a non-AP MLD has acquired the transmission right (or has become a TXOP holder), the transmission right for one link until the same time as the time when NAV set by the AP MLD or non-AP MLD for another link ends. 
     (1) A multi-link support subfield of an EHT Capability Information field is set to 1, and a multi-link simultaneously transmit and receive support subfield of the EHT Capability Information field is set to 0. 
     (2) At a link that is not the link having become the TXOP holder, the NAV is set on the basis of the length field, the Duration/ID field, and the TXOP_DURATION of the EHT-SIG of a frame in which the address of the RA field does not match its own MAC address. 
     (3) The frame is held in a queue corresponding to an access category (AC) that has become a TXOP holder on the basis of Enhanced Distributed Channel Access (EDCA) that transmits the frame on the basis of the priority. 
       FIGS.  7  and  8    illustrate a processing procedure for a communication device (MLD) capable of performing a multi-link operation using a first link and a second link to transmit a data frame in the form of a flowchart.  FIGS.  7  and  8    illustrate a processing procedure in which the communication device (MLD) acquires the transmission right (TXOP) at the second link (link2) during the period in which the NAV is set at the first link (link1), and aligns the time during which the first link and the second link are idle. 
     When the backoff ends at the link2 (step S 702 ) during the period in which the NAV is set at the link1 (step S 701 ), the MLD checks whether the time until the NAV of the link1 ends is longer than a first threshold (step S 703 ). The first threshold is a time length determined according to the amount of data of the data frame to be transmitted by the MLD and the MCS to be used. 
     In a case where the time until the NAV of the link1 ends is equal to or less than the first threshold (No in step S 703 ), the MLD further checks whether the time until the NAV of the link1 ends is longer than a second threshold (step S 704 ). The second threshold is a time length determined according to the amount of data of a signal having a short signal length such as an RTS frame or a CTS-to-self frame and the MCS to be used. 
     In a case where the time until the NAV of the link1 ends is equal to or less than the second threshold (No in step S 704 ), the MLD acquires the transmission right (TXOP) at the link2 and transmits the null packet (NDP) by the link2 until the time when the NAV set at the link1 ends (step S 705 ). 
     In a case where the time until the NAV of the link1 ends is longer than the first threshold (Yes in step S 703 ), the MLD subsequently checks whether there is data to be transmitted before the NAV of the link1 ends (step 
     In a case where there is data to be transmitted before the NAV of the link1 ends (Yes in step S 706 ), the MLD further checks whether a transmission source and a transmission destination of the frame that is the source in which the NAV is set at the link1 are access points (AP MLD) of a connection destination (step S 708 ). 
     In a case where the transmission source and the transmission destination of the frame that is the source in which the NAV is set at the link1 are the access points (AP MLD) of the connection destination (Yes in step S 708 ), the MLD further checks whether the AP MLD of the connection destination can perform simultaneous transmission and reception by the link1 and the link2 (step S 710 ). 
     In a case where there is no data to be transmitted before the NAV of the link1 ends (No in step S 706 ), if the time until the NAV of the link1 ends is equal to or less than the first threshold but is longer than the second threshold (Yes in step S 704 ), and if the AP MLD of the connection destination cannot perform simultaneous transmission and reception by the link1 and link2 (No in step S 710 ), the MLD acquires the transmission right (TXOP) at the link2 and transmits the first signal by the link2 until the time when the NAV set at the link1 ends (step S 707 ). The first signal is a signal having a short signal length, such as an RTS frame or a CTS-to-self frame. 
     Further, in a case where the transmission source and transmission destination of the frame that is the source in which the NAV is set at the link1 are not AP MLD of the connection destination (Yes in step S 708 ), or in a case where the AP MLD of the connection destination can simultaneously transmit and receive the frame by the link1 and the link2 (Yes in step S 710 ), the MLD acquires the transmission right (TXOP) at the link2 and transmits the data frame by the link2 until the time when the NAV set at the link1 ends (step S 709 ). 
     According to the above processing procedure, when the NAV set by the MLD at the link1 ends, both the link1 and the link2 become idle, and thus the MLD can perform the multi-link operation by synchronous transmission using the link1 and the link2. 
     For example, the STA MLD1 in the communication sequence illustrated in  FIGS.  5  and  6    operates according to the processing procedure illustrated in  FIGS.  7  and  8   . 
     E. Operation Example 2 
     Next, a second operation example of the communication device (MLD) that performs a multi-link operation using the first link and the second link will be described. Also in the second operation example, the communication device (MLD) sets the TXOP of the second link on the basis of NAV information of the first link, sets both the first link and the second link to the idle state, and facilitates the multi-link operation by synchronous transmission. 
       FIG.  9    illustrates a communication sequence example illustrating this operation. Also,  FIG.  9    assumes a communication system in which the first link (link1) and the second link (link2) can be used and three terminals (STA MLD1, STA MLD2, STA MLD3) operate under the control of one access point (AP MLD1). The AP MLD1 includes an AP1-1 operating on the first link and an AP1-2 operating on the second link. In addition, the STA MLD1 includes an STAT-1 operating on the first link and an STAT-2 operating on the second link, the STA MLD2 includes an STA2-1 operating on the first link and an STA2-2 operating on the second link, and the STA MLD3 includes an STA3-1 operating on the first link and an STA3-2 operating on the second link. 
     In addition, a horizontal axis in  FIG.  9    is a time axis, and indicates a communication operation for each time on the first link and the second link of the access point and each terminal. Note that a square block drawn by a solid line indicates a transmission frame, a solid arrow in the vertical direction indicates frame transmission to a destination, and a dotted arrow in the vertical direction indicates arrival of a frame to other than the destination. A parallelogram block drawn by a solid line indicates a backoff operation, and a square block drawn by a dotted line indicates a period in which the NAV is set. 
     First, the AP1-1 of the AP MLD1 expires the backoff of waiting for a random waiting time, acquires a period (for example, TXOP) of occupying a channel at the first link (link1) at time T1, and transmits a data frame (Data) to the STA MLD3-1. 
     When receiving a data frame that is not addressed to the STA 1-1 and the STA2-1 from the AP1-1, the STAT-1 and the STA2-1 set a transmission suppression period (NAV) until time T3 at which returning of a reception acknowledgement (ACK) from the STA3-1 to the AP3-1 is completed on the basis of the time described in the Duration/ID field of the header of the data frame, and perform transmission suppression of the frame at the first link (link1). The time information used to set the transmission suppression period may be a length field or a TXOP DURATION of Extreme High Throughput (EHT)-SIG (SIGNAL). 
     Thereafter, the STAT-2 expires the backoff at the second link (link2) at time T2. The STAT-2 may start the backoff before the STAT-1 receives the data frame not addressed to the STAT-1 itself, but in the example illustrated in FIG. 9, the STAT-2 attempts to acquire the transmission right after the STAT-1 receives the data frame not addressed to the STAT-1 itself. The STAT-2 sets, at link2, a TXOP longer than time T3 at which the NAV of the STAT-1 ends, and transmits the first data frame until the NAV end time of the link1 . In the example illustrated in  FIG.  9   , a period until time T5 at which reception of the ACK from the transmission destination for the data frame transmitted second by the STAT-2 is completed is set as TXOP at link2. 
     When the STA2-2 and the STA3-2 receive a data frame that is not addressed to themselves and is first transmitted by the STA1-2, the STA2-2 and the STA3-2 set a transmission suppression period (NAV) on the basis of the time described in the Duration/ID field of the header of the data frame, and perform frame transmission suppression at the second link (link2) until time T5. 
     The STA1-2 may adjust the data length and transmit the data frame so that transmission of the first data frame after acquiring the TXOP at time T2 or reception of the ACK for the data frame from the transmission destination ends at end time T3 of the NAV set at the link1. In a case where the transmission of the first data frame or the reception of the ACK for the data frame from the transmission destination cannot be completed by the end time T3 of the NAV set at the link1 the STA1-2 may transmit a null packet in which the time until the completion of the transmission of the next data frame is described in the Duration/ID field. 
     Then, after the NAV set at the link1 by the STA1-1 ends at the time T3, the STA1-1 and the STA1-2 confirm whether the link1 and the link2 are idle for a first time, respectively. 
     The first time here is, for example, a Short Interframe Space (SIFS), a Point coordination function IFS (PIFS), or a SIFS+Random ( )×SlotTime. Random ( ) is an integer uniformly and randomly determined from a certain range. The first time may be a time common between the link1 and the link2, or may be set to a different time according to a transmission situation or the like at each link. Assuming that in addition to the STA MLD 1 , there is a terminal that sets a NAV at the link1 by a data frame transmitted by the AP1-1 to the STA3-1 and intends to perform a multi-link operation using the link1 and the link2 after the NAV ends, the first time may be set as a random waiting time in order to avoid a collision between terminals. In the example illustrated in  FIG.  9   , the PIFS is used in the first time at both link1 and link2. 
     In this way, the STA MLD1 can align the time during which the first link and the second link are idle at time 
     T3. Then, at time T4 at which the first time has elapsed from time T3, the STAT-1 and the STAT-2 transmit data frames (Data) using link1 and link2, respectively, and can realize the multi-link operation by synchronous transmission. In the example illustrated in  FIG.  9   , the STAT-1 and the STAT-2 transmit data frames to the AP1-1 and the AP1-2 using link1 and link2, respectively. Then, after completing the reception of the data frames, the AP1-1 and the AP1-2 return the ACK using link1 and link2, respectively. 
       FIG.  10    illustrates a processing procedure for a communication device (MLD) capable of performing a multi-link operation using the first link and the second link to transmit a data frame in the form of a flowchart. 
     When the backoff ends at the link2 (step  1002 ) during the period in which the NAV is set at the link1 (step S 1001 ), the MLD checks whether the time until the NAV of the link1 ends is longer than the first threshold (step S 1003 ). The first threshold is a time length determined according to the amount of data of the data frame to be transmitted by the MLD and the MCS to be used. 
     In a case where the time until the NAV of the link1 ends is longer than the first threshold (Yes in step S 1003 ), the MLD sets TXOP at link2, and transmits the data frame by the link2 until the NAV end time of the link1 (step S 1004 ). The first threshold is a time length determined according to the amount of data of the data frame transmitted first by the MLD and the MCS to be used. In addition, in  51004 , the MLD sets the TXOP of the link2 to be longer than the NAV end of the link1. 
     Furthermore, in a case where the time until the NAV of the link1 ends is equal to or less than the first threshold (No in step S 1003 ), the MLD further checks whether the time until the NAV of the link1 ends is longer than a second threshold (step S 1005 ). The second threshold is a time length determined according to the amount of data of a signal having a short signal length such as an RTS frame or a CTS-to-self frame and the MCS to be used. 
     In a case where the time until the NAV of the link1 ends is longer than the second threshold (Yes in step S 1005 ), the MLD sets TXOP at link2, and transmits a first signal by the link2 until the NAV end time of the link1 (step S 1006 ). The first signal is a signal having a short signal length, such as an RTS frame or a CTS-to-self frame. In addition, in S 1006 , the MLD sets the TXOP of the link2 to be longer than the NAV end of the link1. 
     Furthermore, in a case where the time until the NAV of the link1 ends is equal to or less than the second threshold (No in step S 1005 ), the MLD sets the TXOP at link2 and transmits the null packet (NDP) by the link2 until the NAV end time of the link1 (step S 1007 ). In S 1007 , the MLD sets the TXOP of the link2 to be longer than the NAV end of the link1. 
     Thereafter, the MLD waits until the NAV set at the link1 ends (No in step S 1008 ). Then, the MLD waits until the NAV set at the link1 ends (Yes in step S 1008 ), and when the transmission in step S 1004 , S 1006 , or S 1007  ends at the link2 (step S 1009 ), the MLD checks whether the link1 is idle for a first time (step S 1010 ). 
     In a case where it is confirmed that the link1 is idle for the first time (Yes in step S 1010 ), the MLD starts data transmission by the link1 and the link2 and performs the multi-link operation (step S 1011 ). As a result, it is possible to increase the probability that the multi-link operation can be performed using the link1 and the link2. 
     In addition, in a case where it is not confirmed that the link1 is idle for the first time (No in step S 1010 ), the MLD starts data transmission only by the link2 (step S 1012 ), and does not perform the multi-link operation. 
     F. Effect 
     Effects brought by the present disclosure will be summarized. 
     (1) By setting the TXOP of another link on the basis of the NAV information set at one link, the communication device (MLD) can align the time when each link is idle, and thus, it is easy to perform a multi-link operation by synchronous transmission. 
     (2) The communication device (MLD) determines a transmission destination of data according to capability of simultaneous transmission and reception between links of surrounding terminals. For example, when a transmission right is acquired by another terminal before the end of the NAV set at one link, the communication device (MLD) determines a terminal that supports simultaneous transmission and reception as a data transmission destination. As a result, it is possible to avoid data reception failure due to inter-link interference in a terminal that does not support simultaneous transmission and reception. 
     (3) After the NAV set at one link ends, the communication device (MLD) performs channel confirmation for a certain period of time, and then simultaneously starts data transmission at each link. As a result, it is possible to increase the probability that the multi-link operation using each link can be performed. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiments without departing from the gist of the present disclosure. 
     For example, by applying the present disclosure to a wireless LAN system conforming to the IEEE 802.11 standard, a communication device (MLD) that implements a multi-link function can easily perform a multi-link operation by synchronous transmission, and can achieve a high throughput. 
     In short, the present disclosure has been described in the form of exemplification, and the contents described in the present specification should not be interpreted in a limited manner. In order to determine the gist of the present disclosure, the claims should be taken into consideration. 
     Note that the present disclosure can also have the following configurations. 
     (1) A communication device including: 
     a communication unit that performs communication by a first link and a second link; 
     a control unit that controls a communication operation by the communication unit, in which 
     the control unit sets an occupancy period of the second link on the basis of transmission suppression information of the first link. 
     (2) The communication device according to (1), in which 
     the control unit controls a transmission operation at a second link on the basis of a remaining time of a transmission suppression period of the first link. 
     (3) The communication device according to (1) or (2), in which 
     when the remaining time of the transmission suppression period of the first link is longer than a first threshold, the control unit performs control to set an occupancy period of the second link until the transmission suppression period of the first link ends and transmit a data frame by the second link. 
     (4) The communication device according to (3), in which 
     the first threshold is a value determined on the basis of an amount of data to be transmitted by the second link. 
     (5) The communication device according to (3) or (4), in which 
     when the remaining time of the transmission suppression period of the first link is equal to or less than the first threshold and is longer than a second threshold, the control unit performs control to set an occupancy period of the second link until the transmission suppression period of the first link ends and transmit a first signal by the second link. 
     (6) The communication device according to (5), in which 
     the second threshold is a value determined on the basis of a signal length of the first signal. 
     (7) The communication device according to (5) or (6), in which 
     the first signal is an RTS frame or a CTS-to-self frame. 
     (8) The communication device according to any one of (5) to (7), in which 
     when the remaining time of the transmission suppression period of the first link is equal to or less than the second threshold, the control unit performs control to set an occupancy period of the second link until the transmission suppression period of the first link ends and transmit a second signal by the second link. 
     (9) The communication device according to (8), in which 
     the second signal is a null packet. 
     (10) The communication device according to any one of (1) to (9), in which 
     the control unit determines a transmission destination of a frame by the second link on the basis of whether or not simultaneous transmission and reception between links of a transmission source or a transmission destination of a signal for setting a transmission suppression period at the first link is possible. 
     (11) The communication device according to (1) or (2), in which 
     the control unit sets the second occupancy period longer than the transmission suppression period of the first link. 
     (12) The communication device according to (11), in which 
     when the remaining time of the transmission suppression period of the first link is longer than a first threshold, the control unit performs control to transmit a data frame by the second link until the transmission suppression period of the first link ends. 
     (13) The communication device according to (12), in which 
     when the remaining time of the transmission suppression period of the first link is equal to or less than the first threshold and is longer than a second threshold, the control unit performs control to transmit a first signal by the second link until the transmission suppression period of the first link ends. 
     (14) The communication device according to (13), in which 
     when the remaining time of the transmission suppression period of the first link is equal to or less than the second threshold, the control unit performs control to transmit a second signal by the second link until the transmission suppression period of the first link ends. 
     (15) The communication device according to any one of (11) to (14), in which 
     the control unit checks whether or not transmission can be performed by the first link for a first time when the transmission suppression period of the first link ends, and performs control to transmit a data frame by using the first link and the second link when it is determined that transmission can be performed. 
     (16) A communication method of a communication device that performs communication by a first link and a second link, the communication method including the steps of: 
     setting a transmission suppression period of the first link on the basis of a signal received by the first link; and 
     setting the second occupancy period on the basis of the first transmission suppression information. 
     REFERENCE SIGNS LIST 
       100  Communication system 
       110  Access point 
       120  Terminal 
       200  Communication device 
       210  Control unit 
       220  Power supply unit 
       230  Communication unit 
       231  Wireless control unit 
       232  Data processing unit 
       233  Modulation/demodulation unit 
       234  Signal processing unit 
       235  Channel estimation unit 
       236  Wireless interface unit 
       237  Amplifier unit 
       238  Memory unit 
       240  Antenna unit