Patent Publication Number: US-2023164663-A1

Title: Multi-link device and method of switching operation mode of multi-link device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a Wi-Fi network, and in particular, to a multi-link device and a method of switching an operation mode of a multi-link device. 
     2. Description of the Prior Art 
     IEEE 802.11be standard specifies communication protocols of wireless access technologies for the next generation of Wi-Fi 7, supporting multi-link multi-radio (MLMR), 320 MHz bandwidth, 4096-quadrature amplitude modulation (QAM), and 16 spatial streams, thereby achieving high speed rate, high throughput, and low latency. 
     SUMMARY OF THE INVENTION 
     According to an embodiment of the invention, a method of switching an operation mode of a first multi-link device (MLD) comprising the first multi-link device establishing a plurality of links to a second multi-link device, and the first multi-link device determining, according to a channel condition, whether to receive a plurality of streams via the plurality of links or via one of the plurality of links. 
     According to another embodiment of the invention, a first multi-link device comprising a plurality of radio circuits and a processor coupled to the plurality of radio circuits. The plurality of radio circuits are used to establish a plurality of links to a second multi-link device. The processor is used to determine whether to receive a plurality of streams via the plurality of links or via one of the plurality of links. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of a multi-link communication system according to an embodiment of the present invention. 
         FIG.  2    is a schematic diagram of a transmission sequence of the simultaneous transmit and receive mode. 
         FIG.  3    is a schematic diagram of a transmission sequence of the non-simultaneous transmit and receive mode. 
         FIG.  4    is a schematic diagram of a transmission sequence of the enhanced mode of the multi-link multi-radio circuit. 
         FIG.  5    is a block diagram of the non-AP MLD in  FIG.  1   . 
         FIG.  6    is a flowchart of the method of switching the operation mode of the non-AP MLD in  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    is a schematic diagram of a multi-link communication system  1  according to an embodiment of the invention. The multi-link communication system  1  includes an AP multi-link device (AP MLD)  10  and a non-AP multi-link device (non-AP MLD)  12 . The multi-link communication system  1  is compatible with IEEE 802.11 protocol, for example, the IEEE 802.11be protocol. 
     The AP MLD  10  includes access points (AP)  101  and  102 , and the non-AP MLD  12  includes stations (STA)  121  and  122 . The APs  101  and  102 , and the STAs  121  and  122  may be logical devices, and may be implemented by hardware, software, firmware, or a combination thereof. The AP MLD  10  and the non-AP MLD  12  may establish links  141  and  142  therebetween. For example, the AP  101  may communicate with the STA  121  via the link  141 , and the AP  102  may communicate with the STA  122  via the link  142 . The non-AP MLD  12  may include 2 sets of full function radio circuits and support an enhanced multi-link multi-radio (EMLMR) mode, and may switch an operation mode according to the channel condition. For example, the operation modes may be switched to a baseline mode or an enhanced mode. The baseline mode may also be referred to as a multi-link multi-radio (MLMR) mode, and the enhanced mode may also be referred to as an enhanced multi-link multi-radio (EMLMR) mode. The two radio circuits of the non-AP MLD  12  may be respectively used for data transmissions at two identical or different frequency bands. For example, the  2  frequency bands may include 2.4 GHz and 5 GHz channels. In another example, the  2  frequency bands may include 5 GHz and 6 GHz channels. When the EMLMR mode is enabled, the non-AP MLD  12  may communicate with the AP MLD  10  using the enhanced mode. When the EMLMR mode is disabled, the non-AP MLD  12  may communicate with the AP MLD  10  using the baseline mode. In the baseline mode, the non-AP MLD  12  may simultaneously use 2 sets of radio circuits to perform transmissions with the AP MLD  10  via both the link  141  and the link  142 , N spatial streams (Nss=N) may be transmitted over the link  141 , and N spatial streams (Nss=N) may be transmitted over the link  142 , N being greater than or equal to 1. In the enhanced mode, the non-AP MLD  12  may use 1 set of the radio circuit to perform transmissions with the AP MLD  10  via one of the link  141  and the link  142 , 2N spatial streams (Nss=2N) may be transmitted over one of the link  141  and the link  142 , increasing the throughput by adjusting the number of spatial streams (Nss=2N) on the link. In the baseline mode, the non-AP MLD  12  may operate in a simultaneous transmit and receive (STR) mode or a non-simultaneous transmit and receive (NSTR) mode. In the enhanced mode, the non-AP MLD  12  may operate in the EMLMR mode. When the non-AP device  12  includes only a single set of full function radio circuit, also referred to as a multi-link single radio circuit, it is not possible to perform transmissions between the non-AP device  12  and the AP MLD  10  using N spatial streams on both the link  141  and the link  142 . However, the non-AP device  12  can still operate in the EMLSR mode to perform transmissions with the AP MLD  10  using 2N spatial streams on one of the link  141  and the link  142 . Since the multi-link single radio circuit may only perform transmissions in the EMLSR mode, there is no need to switch the operation mode of the multi-link single radio circuit.  FIGS.  2  to  4    show schematic diagrams of transmission sequences of the STR mode, the NSTR mode and the enhanced mode of the multi-link multi-mode radio circuit, respectively, and explanation therefor will be detailed in the subsequent paragraphs. 
       FIG.  2    shows a schematic diagram of a transmission sequence of the STR mode of the baseline mode of the multi-link multi-mode radio circuit. When channel spacing between channels used by the two radio circuits of the non-AP MLD  12  is sufficient, e.g., the two radio circuits use 2.4G and 5G channels, respectively, the transmissions on the link  141  and the link  142  will not interfere with each other, and therefore, the non-AP MLD  12  may adopt the STR mode to perform transmissions with the AP MLD  10 . In the STR mode, the non-AP MLD  12  uses 2 sets of radio circuits to perform transmissions via the link  141  and the link  142 , and the channel access of the link  141  and the link  142  are independent of each other. The uplink transmissions and downlink transmissions on the link  141  and the link  142  do not need to be synchronized. For example, in  FIG.  2   , an uplink transmission  200  and a downlink transmission  202  are performed on the link  141 , while a downlink transmission  220  is performed on the link  142 . 
       FIG.  3    shows a schematic diagram of a transmission sequence of the NSTR mode of the baseline mode of the multi-link multi-mode radio circuit. When channel spacing between channels used by the two radio circuits of the non-AP MLD  12  is insufficient, e.g., the two radio circuits use 5G and 6G channels, respectively, the transmissions on the link  141  and the link  142  may interfere with each other, and therefore, the non-AP MLD  12  may adopt the NSTR mode to perform transmissions with the AP MLD  10 . In the NSTR mode, the non-AP MLD  12  uses 2 sets of radio circuits to perform transmissions via the link  141  and the link  142 . If data packets are transmitted over one of the link  141  and the link  142 , there will be no packet transmitted over the other one of the link  141  and the link  142 . As a consequence, uplink transmissions or downlink transmissions will be transmitted over the link  141  and the link  142  simultaneously. In addition, in order to avoid in-device coexistence interference between the link  141  and the link  142 , the uplink transmissions and downlink transmissions on the link  141  and the link  142  must be synchronized, and must comply with the physical protocol data unit (PPDU) end time alignment, the start time sync PPDU medium access, and the medium access recovery in the physical layer protocol as specified by the IEEE 802.11be, resulting in a lower throughput in the NSTR mode than that in the STR mode. For example, in  FIG.  3   , a downlink transmission  300  on the link  141  and a downlink transmission  320  on the link  142  may be synchronized; an uplink transmission  302  on the link  141  and an uplink transmission  322  on forward link  142  may be synchronized. 
       FIG.  4    shows a schematic diagram of a transmission sequence of the enhanced mode of the multi-link multi-mode radio circuit. In the enhanced mode, each data transmission may be performed over one of the link  141  and the link  142 . For example, in  FIG.  4   , the non-multi-link AP device  12  listens to messages ( 400  and  420 ) on the link  141  and  142 , detects a multi-user request to send (MU-RTS) frame  402  from the link  141 , and is ready to receive data from the link  141 . When ready, the non-AP MLD  12  transmits a clear to send (CTS) frame  404  over the link  141 , and performs a receive radio link switch (Rx chain switch)  424  to switch a radio chain of the link  142  to the link  141 . In response to the CTS  404 , the AP MLD  10  transmits an aggregated media access control protocol data unit (AMPDU) frame  406  on the link  141  using 2N spatial streams. After receiving the AMPDU frame  406 , the non-AP MLD  12  transmits a block acknowledgment (BA) frame  408  over the link  141 , performs a receive wireless link switch  410  to switch the radio chain of the link  142  back to the link  142 , and then the non-AP MLD  12  listens to the messages on the link  141  and the link  142  once again ( 412  and  426 ). The enhanced mode enables the non-AP MLD  12  to use all the available spatial streams (Nss=2N) for transmissions over one of the link  141  and the link  142 , thereby increasing the overall throughput. 
       FIG.  5    is a block diagram of the non-AP MLD  12 . The non-AP MLD  12  includes a processor  52 , radio circuits  541  and  542 , and a timer  56 . The processor  52  is coupled to the radio circuit  541 , the radio circuit  542 , and the timer  56 . 
     The radio circuits  541  and  542  may include respective antennas, transceivers, and other radio frequency components. The radio circuit  541  may establish the link  141  with the AP MLD  10 , and the radio circuit  542  may establish the link  142  with the AP MLD  10 . The processor  52  may determine whether to receive a plurality of streams via one of the link  141  and the link  142  or via the link  141  and the link  142  according to the channel condition. When the channel condition is busy, the probability of the link  141  and the link  142  transmitting simultaneously will decrease, and thus, the processor  52  determines to switch to the enhanced mode to receive a plurality of spatial streams via one of the link  141  and the link  142 . When the channel condition is idle, the probability of the link  141  and the link  142  transmitting simultaneously will increase, and thus, the processor  52  determines to switch to the baseline mode to receive the plurality of streams via the link  141  and the link  142 . 
     In some embodiments, the processor  52  may generate a channel busy ratio (CBR) of the non-AP MLD  12  according to a channel busy time T b  and a data transmission time T tx  during a measurement time T m , so as to estimate the channel condition. The channel busy ratio CBR of the non-AP MLD  12  may be expressed by Equation (1): 
       CBR=( T   b   +T   tx )/ T   m   Equation (1)
 
     where T m  is the measurement time; 
     T b  is the channel busy time; and 
     T tx  is the data transmission time of the non-AP MLD  12 . 
     The channel busy time T b  may be obtained via a physical carrier sense mechanism or a virtual carrier sense mechanism. In the physical carrier detection mechanism, the non-AP MLD  12  may detect whether the channel power exceeds a threshold of clear channel assessment (CCA), e.g., the threshold of CCA may be −82 dBm. If the channel power exceeds the threshold, the processor  52  may determine that the channel is busy and compute the channel busy time T b . In the virtual carrier detection mechanism, the non-AP MLD  12  may monitor for a network allocation vector (NAV) in an RTS message. When NAV is not 0, the processor  52  may determine that the channel is busy and compute the channel busy time T b . When CBR approaches 1, the channel may be busy or congested. 
     In other embodiments, the AP MLD  10  may periodically broadcast a beacon frame containing a network load reports, and the processor  52  of the non-AP MLD  12  may generate a channel busy ratio CBR_OBSS of an overlapping basic service set (OBSS) according to the network load report of the multi-link communication system  1 . Since the other APs near the multi-link communication system  1  may perform data transmission at the same time, the AP MLD  10  may collect the traffic of other nearby APs to generate the network load report. The network load report may be a Qload report, and the format of the Qload report is shown in Table 1: 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 Element 
                 Length 
                 Potential 
                 Allocated 
                 Allocated 
                 EDCA 
                 HCCA 
                 HCCA 
                 Overlap 
                 Sharing 
                 Optional 
               
               
                 identifier 
                   
                 traffic 
                 traffic 
                 traffic 
                 factor 
                 peak 
                 factor 
                   
                 policy 
                 sub-elements 
               
               
                   
                   
                 self 
                 self 
                 shared 
               
               
                   
               
            
           
         
       
     
     Where Element identifier represents the number of the Qload report; 
     Length represents the length of the Qload report; 
     Potential traffic self represents the longest medium time allocated by the AP MLD  10  during a predetermined period of time, e.g., 7 days; 
     Allocated traffic self represents the current medium time allocated by the AP MLD  10 , including an average and a standard deviation; 
     Allocated traffic shared represents the medium time allocated to all APs (including the AP MLD  10 ) near the AP MLD  10 , including an average μ s  and a standard deviation σ s ; 
     Enhanced distributed channel access (EDCA) factor represents the medium time using the EDCA mechanism; 
     Hybrid coordinated channel access (HCCA) peak indicates the peak medium time using the HCCA mechanism; 
     HCCA factor represents the medium time using the HCCA mechanism; 
     Overlap represents the number of APs using the same channel; 
     Sharing strategy represents a channel sharing strategy adopted by the AP; and 
     Optional sub-components represent other information. 
     In some embodiments, the non-AP MLD  12  may generate a long-term channel busy ratio CBR_OBSS1 according to the EDCA factor and the HCCA factor in the Qload report, and is expressed by Equation (2): 
       CBR_OBSS1=(EDCA factor+HCCA factor)/64  Equation (2)
 
     64 in Equation (2) represents the decimal point precision of EDCA factor and HCCA factor. 
     In other embodiments, the non-AP MLD  12  may generate a short-term channel busy ratio CBR_OBSS2 according to the allocated traffic shared in the Qload report, and is expressed by Equation (3): 
       CBR_OBSS2=μ s +2σ s   Equation (3)
 
     Where μ s  is the average of the medium time in the allocated traffic shared field; and 
     σ s  is the standard deviation of the medium time in the allocated traffic shared field. 
     When the long-term channel busy ratio CBR_OBSS1 or the short-term channel busy ratio CBR_OBSS2 approaches 1, the channel may be busy or congested. The processor  52  may determine the channel condition according to the channel busy ratio CBR of the non-AP MLD  12 , the long-term channel busy ratio CBR_OBSS1, and/or the short-term channel busy ratio CBR_OBSS2. Since the short-term channel busy ratio CBR_OBSS2 reflects the recently allocated medium time of the overlapping basic service set, the short-term channel busy ratio CBR_OBSS2 is more accurate than the long-term channel busy ratio CBR_OBSS1. 
     In some embodiments, the non-AP MLD  12  may set the timer  56  to periodically check the channel condition, so as to determine whether to switch the operation mode. In some embodiments, if the non-AP MLD  12  is going to enter the NSTR mode, since the throughput of the NSTR mode is low, the processor  52  determines to switch to the enhanced mode to receive 2N spatial streams via one of the link  141  and the link  142 , thereby enhancing the throughput. 
     In this manner, the non-AP MLD  12  may switch the operation mode according to the channel condition, increasing the overall throughput by exploiting flexibility of the multi-link and multi-radio circuit. 
       FIG.  6    is a flowchart of the method  600  of switching the operation mode of the non-AP MLD  12 . The method  600  includes Steps S 602  to S 624 . Steps S 602  to S 608  are used to switch to the enhanced mode for data transmission upon determining the NSTR mode is used for transmission, and Steps S 610  to S 618  are used to determine whether to use the baseline mode or the enhanced mode according to the channel condition. Steps S 620  to S 624  are used to periodically determine the channel condition. Any reasonable step change or adjustment is within the scope of the disclosure. Steps S 602  to S 624  are detailed as follows: 
     Step S 602 : The processor  52  sets up a multi-link operation (MLO); 
     Step S 604 : The processor  52  determines whether to perform a non-simultaneous transmit and receive operation? If so, go to Step S 606 ; if not, go to Step S 610 ; 
     Step S 606 : The processor  52  sets the EMLMR mode to 1; 
     Step S 608 : The processor  52  determines whether to switch channels? If so, go to Step S 602 ; if not, go to Step S 606 ; 
     Step S 610 : The processor  52  determines whether the network load report is received? If so, go to Step S 612 ; if not, go to Step S 614 ; 
     Step S 612 : The processor  52  determines whether the channel busy ratio CBR_OBSS exceeds a predetermined value α? If so, go to Step S 616 ; if not, go to Step S 618 ; 
     Step S 614 : The processor  52  determines whether the channel busy ratio CBR_OBSS exceeds a predetermined value β? If so, go to Step S 616 ; if not, go to Step S 618 ; 
     Step S 616 : The processor  52  sets the EMLMR mode to 1; go to Step S 620 ; 
     Step S 618 : The processor  52  sets the EMLMR mode to 0; 
     Step S 620 : The processor  52  resets the timer  56 ; 
     Step S 622 : The processor  52  determines whether to switch channels? If so, go to Step S 602 ; if not, go to Step S 624 ; 
     Step S 624 : The processor  52  determines whether the timer  56  has expired? If so, go to Step S 610 ; if not, go to Step S 622 . 
     In Step S 602 , the non-AP MLD  12  configures a multi-link operation setting, and the processor  52  sets the EMLMR mode to 0 to switch the non-AP MLD  12  to the baseline mode. In Step S 604 , the processor  52  sets the operation mode of the non-AP MLD  12  to the STR mode or the NSTR mode according to the channel spacing between the link  141  and the link  142 . For example, when the channel spacing between the link  141  and the link  142  is less than 1 GHz, the processor  52  sets the operation mode of the non-AP MLD  12  to the NSTR mode. When the channel spacing between the link  141  and the link  142  exceeds 1 GHz, the processor  52  sets the operation mode of the non-AP MLD  12  to the STR mode. In Step S 606 , if the operation mode is the NSTR mode, the processor  52  sets the EMLMR mode to 1 to switch the non-AP MLD  12  to the enhanced mode, so as to receive 2N spatial streams via one of the link  141  and the link  142 , thereby enhancing the throughput. In Step S 608 , if one of the radio circuit  541  and the radio circuit  542  detects that the beacon contains channel switch announcement (CSA) information, the processor  52  determines that the channel is going to be switched. Since a channel switch is going to occur, return to Step S 602  to reset the operation mode of the non-AP MLD  12 . If no CSA information is detected, return to Step S 606  and continue to use the enhanced mode to receive 2N spatial streams from one of the link  141  and the link  142 . 
     If in Step S 604 , the processor  52  sets the operation mode of the non-AP MLD  12  to the non-NSTR mode (i.e., STR mode), the processor  52  further determines whether a network load report is received (Step S 610 ). If so, the processor  52  generates the channel busy ratio CBR_OBSS of the overlapping service set according to the network load report, and estimates the channel condition according to the channel busy ratio CBR_OBSS (Step S 612 ). The channel busy rate CBR_OBSS may be the long-term channel busy rate CBR_OBSS1 or the short-term channel busy rate CBR_OBSS2. In some embodiments, the processor  52  generates the short-term channel busy ratio CBR_OBSS2 according to the allocated traffic shared in the Qload report to serve as the channel busy ratio CBR_OBSS of the overlapping basic service set, thereby increasing the accuracy of the channel busy ratio. In some embodiments, the processor  52  may generate the long-term channel busy ratio CBR_OBSS1 to serve as the channel busy ratio CBR_OBSS of the overlapping basic service set. If the channel busy ratio CBR_OBSS exceeds a predetermined value α, the channel condition is busy; and if the channel busy ratio CBR_OBSS is less than the predetermined value α, the channel condition is idle. The predetermined value α may be between 0 and 1, for example, the predetermined value a may be between 0.4 and 0.5. 
     If in Step S 610 , the processor  52  determines that the network load report is not received, a channel busy ratio CBR of the non-AP MLD  12  may be generated. If the channel busy ratio CBR exceeds a predetermined value β, the channel condition is busy; and if the channel busy ratio CBR is less than the predetermined value β, the channel condition is idle. The predetermined value β may range between 0 and 1, for example, the predetermined value β may be between 0.4 and 0.5. The predetermined value α and the predetermined value β may be equal or different. 
     If in the Step S 612  or Step S 614 , the processor  52  determines that the channel condition is busy, then the EMLMR mode is set to 1 to switch the non-AP MLD  12  to the enhanced mode, so as to receive 2N spatial streams via one of the link  141  and the link  142 , thereby enhancing the throughput (Step S 616 ). If in the Step S 612  or Step S 614 , the processor  52  determines that the channel condition is idle, then the EMLMR mode is set to 0 to switch the non-AP MLD  12  to the baseline mode, so as to receive N spatial streams via the link  141  and the link  142 , respectively (Step S 618 ). 
     In Step S 620 , the processor  52  resets the timer  56  to a predetermined time. The predetermined time may be longer than dot11QLoadReportIntervalDTIM as specified in IEEE 802.11be standard. In Step S 622 , if the radio circuit  541  or the radio circuit  542  detects that the beacon contains CSA information, the processor  52  determines that the channel is going to be switched. Since a channel switch is going to occur, return to Step S 602  to reset the operation mode of the non-AP MLD  12 . If no CSA information is detected, proceed to Step S 624  to determine whether the timer  56  has expired. If the timer  56  has not expired, the processor  52  continues to determine whether to switch the channel (Step S 622 ). If the timer  56  has expired, the processor  52  sets the operation mode according to the channel condition (S 610  to S 618 ). 
     In Steps S 602 , S 606 , S 616 , and S 618 , upon the switch of the operation mode of the non-AP MLD  12 , e.g., the EMLMR mode changes from 1 to 0, or from 0 to 1, the radio circuit  541  and/or the radio circuit  542  sends an enhanced multi-link (EML) operation mode notification frame with the EMLMR mode setting to the AP MLD  10  via the link  141  and/or the link  142 , notifying the AP MLD  10  to change the transmission mode thereof. 
     While in the embodiments of  FIGS.  1  to  6    the non-AP MLD  12  only include two sets of radio circuits and only two links are established, the non-AP MLD  12  may further include more sets of radio circuits and establish more links. Those skilled in the art may modify the non-AP MLD  12  according to the principle of the invention for the non-AP MLD  12  to receive the stream via one of the plurality of links or receive the streams via the plurality of links according to the channel condition. Further, while in the embodiment of the invention when the non-AP MLD  12  operates in the baseline mode, the link  141  and the link  142  may respectively perform transmissions of N spatial streams, in some embodiments, the number of the spatial streams on the link  141  and the link  142  may be unequal. For example, in the baseline mode, N1 spatial streams may be transmitted over the link  141 , N2 spatial streams may be transmitted over the link  142 . In the enhanced mode, one of link  141  and the link  142  may transmit (N1+N2) spatial streams. Furthermore, while the downlink transmission has been used to explain the operations in the embodiment of the invention, those skilled in the art may apply the present invention to uplink transmission according to a similar principle of the present invention. 
     The non-AP MLD  12  switches between the baseline mode and the enhanced mode according to the channel conditions, increasing the overall throughput by exploiting flexibility of the multi-link and multi-radio circuit. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.