Patent Publication Number: US-2021185562-A1

Title: Radio communication device, radio communication system, and radio communication method

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2019-225333, filed on Dec. 13, 2019, the disclosure of which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a radio communication device, a radio communication system, and a radio communication method. In particular, the present disclosure relates to a radio communication device, a radio communication system, and a radio communication method using a plurality of wireless lines. 
     BACKGROUND ART 
     A Link Aggregation technique may be used in order to widen the transmission bandwidth between radio communication devices. The link aggregation technique is a technique that virtually bundles a plurality of physical lines into one line and enables use of bandwidth depending on a total number of the bands of the physical lines. 
     International Patent Publication No. WO2018/116965 discloses a radio communication device that bundles a plurality of radio communication means to transmit packets. The radio communication device described in International Patent Publication No. WO2018/116965 divides a packet into a plurality of divided packets and allocates the divided packets to radio communication means having a minimum radio transmission delay. When the radio transmission delay is calculated, it is necessary to consider the number of divided packets retained in the radio communication means. The number of divided packets retained in the radio communication means can be calculated based on the number of allocated divided packets and so on. 
     SUMMARY 
     As described above, in order to properly allocate divided packets to a plurality of radio communication means, it is necessary to acquire the exact number of divided packets retained in the radio communication means. However, there has been a problem that the number of divided packets retained in the radio communication means cannot be accurately calculated, and thus the divided packets cannot be appropriately allocated. 
     An object of the present disclosure is to provide a radio communication device, a radio communication system, and a radio communication method capable of notifying a radio communication unit of retention information of divided packets retained in a radio communication unit and allocating the divided packets based on the notification. 
     An example object of the present disclosure is a radio communication device including: a plurality of radio transmission means each including a buffer for storing a transmission packet to be transmitted; division means for dividing an input packet into a plurality of transmission packets; retention information notification means for notifying about retention information of the transmission packets retained in the buffer; and allocation means for allocating the transmission packets to at least one of the plurality of radio transmission units based on the notified retention information. 
     In another example aspect of the present disclosure, a radio communication system includes: a first radio communication device that includes a plurality of radio transmission means each including a buffer for storing a transmission packet to be transmitted, division means for dividing an input packet into a plurality of transmission packets, retention information notification means for notifying about retention information of the transmission packets retained in the buffer, and allocation means for allocating the transmission packets to at least one of the plurality of radio transmission units based on the notified retention information; and a second radio communication device that includes plurality of radio reception means for receiving the transmission packets transmitted by the plurality of radio transmission units, and an assembly means for reproducing the packet from the transmission packets. 
     In another example aspect of the present disclosure, a radio communication method includes: dividing an input packet into a plurality of transmission packets; notifying about retention information of the transmission packets retained in a buffer for storing the transmission packets; and allocating the transmission packets to at least one of a plurality of radio transmission means each including a buffer based on the notified retention information. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure. 
         FIG. 1  is a block diagram showing a configuration example of a radio communication system  300  according to a first example embodiment; 
         FIG. 2  is a block diagram showing a functional configuration of a radio communication device  100  according to the first example embodiment; 
         FIG. 3  is a block diagram showing a configuration of a radio communication system  300  according to a second example embodiment; 
         FIG. 4  is a block diagram showing a configuration of a radio communication device  100  according to the second example embodiment; 
         FIG. 5  is a block diagram showing a configuration of a radio communication device  200  according to the second example embodiment; 
         FIG. 6  is an overview diagram schematically showing generation of divided packets according to the second example embodiment; 
         FIG. 7  is a diagram showing an example of a radio delay of the radio communication device  100  according to the second example embodiment; 
         FIG. 8  is a flowchart showing an operation of the radio communication device  100  according to the second example embodiment; 
         FIG. 9  is a flowchart showing an operation for managing a retention amount of a packet buffer; 
         FIG. 10  is an overview diagram showing an overview of overheads of divided packets; 
         FIG. 11  shows a change in a retention amount of a packet buffer; 
         FIG. 12  is an overview diagram showing a method for allocating the divided packets based on a radio transmission delay; 
         FIG. 13  is a block diagram showing a configuration of a radio communication device  100  including three radio transmission means; 
         FIG. 14  is a block diagram showing a configuration of a radio communication device  200  including three radio reception means; and 
         FIG. 15  is a flowchart showing a method for allocating divided packets among to three radio communication means. 
     
    
    
     EMBODIMENTS 
     First Example Embodiment 
       FIG. 1  is a block diagram showing a configuration example of a radio communication system  300  according to a first example embodiment. A radio communication system  300  includes a radio communication device  100  and a radio communication device  200 . The radio communication device  100  includes an antenna  105 A and an antenna  105 B. The radio communication device  200  includes an antenna  205 A and an antenna  205 B. The radio communication device  100  divides an input packet into a plurality of transmission packets and transmits the transmission packets from the antennas  105 A and  105 B. The radio communication device  200  receives the transmission packets from the antennas  205 A and  205 B and reproduces the packets from the transmission packets. 
       FIG. 2  is a block diagram showing a functional configuration of the radio communication device  100  according to the first example embodiment. The radio communication device  100  includes radio transmission units  120 A and  120 B, a division unit  112 , a retention information notification unit  124 , and an allocation unit  113 . 
     The radio transmission unit  120 A includes a buffer  122 A. The buffer  122 A stores the transmission packets. The radio transmission unit  120 B includes a buffer  122 B. The buffer  122 B stores the transmission packets. The radio transmission unit  120 A and the radio transmission unit  120 B transmit the transmission packets allocated by the allocation unit  113 , which will be described later, to the outside. The transmission packets allocated by the allocation unit  113  may be retained in the buffers  122 A and  122 B. 
     The division unit  112  divides the input packet into a plurality of transmission packets. The retention information notification unit  124  notifies the retention information of transmission packets retained in the buffers  122 A and  122 B of the radio transmission unit  120 A and  120 B. The retention information of the transmission packets is, for example, the number of transmission packets, the amount of data, and so on. The retention information may be a ratio of a used area of the storage areas of the buffers  122 A and  122 B. The retention information notification unit  124  notifies the allocation unit  113  ,which will be described later, of the above information. 
     The retention information notification unit  124  may notify the retention timing information related to a timing at which the retention information of the radio transmission unit  120 A or the radio transmission unit  120 B is acquired to the allocation unit  113  described later. The retention information notification unit  124  may notify the allocation unit  113  of the retention information when the retention information exceeds a predetermined threshold. The retention information notification unit  124  may notify the allocation unit  113  of the retention information when the radio transmission speed of the radio transmission unit  120 A or the radio transmission unit  120 B decreases. 
     The allocation unit  113  allocates the transmission packets to the radio transmission unit  120 A or the radio transmission unit  120 B based on the retention information notified by a retention information notification unit  124 . For example, the allocation unit  113  calculates, based on the notified retention information, a radio transmission delay caused by passing through the radio transmission unit  120 A and a radio transmission delay caused by passing through the radio transmission unit  120 B. The allocation unit  113  allocates the transmission packets to one of the radio transmission units  120 A and  120 B having a smaller radio transmission delay. Note that the allocation unit  113  may allocate the transmission packets to both the radio transmission unit  120 A and the radio transmission unit  120 B. 
     When the retention information notification unit  124  notifies about the retention timing information related to the timing at which the retention information of the radio transmission unit  120 A is acquired, the allocation unit  113  may calculate the retention amount of the buffer  122 A based on the retention information, the number of transmission packets allocated to the radio transmission unit  120 A from the timing onward, and the quantity of transmission packets transmitted by the radio transmission unit  120 A from the timing onward. The allocation unit  113  can update the radio transmission delay of the radio transmission unit  120 A based on the retention amount of the packet buffer  122 A. 
     According to this example embodiment, the retention information notification unit  124  notifies the allocation unit  113  of the retention information of the transmission packets retained in the radio transmission unit  120 A or the radio transmission unit  120 B. This enables the radio communication device  100  according to this example embodiment to allocate the transmission packets to the radio transmission unit  120 A or the radio transmission unit  120 B based on the notified retention information. 
     Second Example Embodiment 
       FIG. 3  is a block diagram of a radio communication system  300  according to this example embodiment. The radio communication system  300  includes a radio communication device  100  and a radio communication device  200 . The radio communication device  100  performs radio communication with a radio communication device  200  via a radio transmission path  400 A. The radio transmission path  400 A is a radio transmission path between the antenna  105 A of the radio communication device  100  and an antenna  205 A of the radio communication device  200 . The radio communication device  100  performs radio communication with the radio communication device  200  via a radio transmission path  400 B. The radio transmission path  400 B is a radio transmission path between the antenna  105 B of the radio communication device  100  and the antenna  205 B of the radio communication device  200 . 
       FIG. 4  is a block diagram showing a configuration of the radio communication device  100  according to the second example embodiment. The radio communication device  100  performs radio transmission. The radio communication device  100  includes a division and allocation circuit  110 , a radio transmission circuit  120 A, and a radio transmission circuit  120 B. The division and allocation circuit  110  and the radio transmission circuit  120 A are connected by a serial interface. The division and allocation circuit  110  and the radio transmission circuit  120 B are connected by a serial interface. 
     The division and allocation circuit  110  divides an input packet into a plurality of divided packets and allocates the divided packets to the radio transmission circuit  120 A or the radio transmission circuit  120 B. The divided packet is also referred to as a transmission packet. 
     The radio transmission circuit  120 A has a higher radio transmission speed than that of the radio transmission circuit  120 B, and is a radio transmission circuit that is mainly used. The radio transmission circuit  120 A is referred to as a main radio transmission circuit, and the radio transmission circuit  120 B is referred to as a sub radio transmission circuit. The radio transmission circuit  120 A is also referred to as a radio transmission unit  120 A. The radio transmission circuit  120 B is also referred to as a radio transmission unit  120 B. 
     The division and allocation circuit  110  includes a packet reception unit  111 , a division circuit  112 , an allocation circuit  113 , packet transmission and reception units  114 A and  114 B, notification packet extraction units  115 A and  115 B, and a discard packet generation unit  116 . 
     The packet reception unit  111  receives packets. The packet is, for example, an Ethernet packet. The packet reception unit  111  transmits the received packets to the division circuit  112 . 
     The division circuit  112  is a circuit for dividing the packet. The division circuit  112  is also referred to as the division unit  112 . The division circuit  112  divides a packet into packets with a specified size and generates divided packets. The division circuit  112  provides a sequence ID to the head of the divided packet as an overhead. The division circuit  112  transmits the divided packets to the allocation circuit  113 . The operation of the division circuit  112  will be described later. 
     The allocation circuit  113  allocates the divided packets to the radio transmission circuit  120 A or the radio transmission circuit  120 B. The allocation circuit  113  is also referred to as the allocation unit  113 . The allocation circuit  113  calculates the radio transmission delay of the radio transmission circuit  120 A and the radio transmission delay of the radio transmission circuit  120 B based on the retention delay and the radio transmission delay information. The allocation unit  113  allocates the divided packets to the radio transmission circuit  120  having a smaller radio transmission delay. 
     The retention delay used in the calculation of the radio transmission delay is a delay caused by the retention of divided packets in the packet buffers  122 A and  122 B, which will be described later. The radio transmission delay information used for the calculation of the radio transmission delay is a delay that does not include consideration over the retention of the retained divided packets. The radio transmission delay information includes, for example, a delay caused by a radio transmission path. The specific operation of the allocation circuit  113  will be described later. 
     The allocation circuit  113  generates discard information based on information from the notification packet extraction units  115 , which will be described later, and transmits it to the discard packet generation unit  116 . The discard information is a sequence ID of a divided packet to be discarded. The discard information is generated when the radio transmission delay is large. The case where the radio transmission delay is large is, for example, a case where the number of retained divided packets is large. 
     The packet transmission and reception unit  114 A is an interface with the radio transmission circuit  120 A. The packet transmission and reception unit  114 A transmits the divided packets to the radio transmission circuit  120 A. The packet transmission and reception unit  114 A receives a notification packet, which will be described later, from the radio transmission circuit  120 A. The packet transmission and reception unit  114 A receives a discard packet from the discard packet generation unit  116 , which will be described later, and transmits the discard packet to the radio transmission circuit  120 A. The packet transmitted and received by the packet transmission and reception unit  114 A is, for example, an Ethernet packet. The packet transmission and reception unit  114 A transmits the notification packet to the notification packet extraction unit  115 A. The packet transmission and reception unit  114 A controls a transmission order of the divided packets and the discard packets. 
     The packet transmission and reception unit  114 B is an interface with the radio transmission circuit  120 B. The packet transmission and reception unit  114 B transmits the divided packets to the radio transmission circuit  120 B. The packet transmission and reception unit  114 B receives the notification packet, which will be described later, from the radio transmission circuit  120 B. The packet transmission and reception unit  114 B receives the discard packet from the discard packet generation unit  116 , which will be described later, and transmits the discard packet to the radio transmission circuit  120 B. The packet transmitted and received by the packet transmission and reception unit  114 B is, for example, an Ethernet packet. The packet transmission and reception unit  114 B transmits the notification packet to the notification packet extraction unit  115 B. The packet transmission and reception unit  114 B controls the transmission order of the divided packets and the discard packets. 
     The notification packet extraction units  115 A and  115 B extract the notification packets from the packets received by the packet transmission and reception units  114 A and  114 B, respectively. The notification packet extraction unit  115 A transmits information included in the notification packet to the allocation circuit  113 . That is, the notification packet extraction unit  115  extracts retention timing information, retention information, and band information, which will be described later, from the notification packet, and notifies the allocation circuit  113  of them. 
     The discard packet generation unit  116  receives the discard information from the allocation circuit  113  and generates a discard packet. The discard packet generation unit  116  transmits the discard packet to the packet transmission and reception units  114 A and  114 B. 
     The radio transmission circuit  120 A includes a packet transmission and reception unit  121 A, a packet buffer  122 A, a radio transmission processing unit  123 A, a notification packet generation unit  124 A, and a discard packet extraction unit  125 A. The radio transmission circuit  120 B has the same functional configuration as that of the radio transmission circuit  120 A. 
     The packet transmission and reception unit  121 A is an interface with the division and allocation circuit  110 . The packet transmission and reception unit  121 A receives the divided packet from the division and allocation circuit  110  and transmits it to the packet buffer  122 A. The packet transmission and reception unit  121 A transmits the notification packet generated by the notification packet generation unit  124 A, which will be described later, to the division and allocation circuit  110 . The packet transmission and reception unit  121 A receives the discard packet from the division and allocation circuit  110  and transmits it to the discard packet extraction unit  125 A. The packet transmitted and received by the packet transmission and reception unit  121 A is, for example, an Ethernet packet. 
     The packet buffer  122 A receives the divided packet from the packet transmission and reception unit  121 A. The packet buffer  122 A buffers the received divided packet. 
     The radio transmission processing unit  123 A wirelessly transmits the divided packets from the antenna  105 A. The radio transmission processing unit  123 A may transmit a plurality of divided packets by multiplexing them on a radio frame. The radio transmission processing unit  123 A receives the discard information from the discard packet extraction unit  125 A, which will be described later, multiplexes the discard information as an overhead of the radio frame, and transmits the multiplexed information. The radio transmission processing unit  123 A supports the adaptive modulation method and can change the radio communication band. 
     The notification packet generation unit  124 A acquires the number of divided packets retained in the packet buffer  122 A as the retention information. The notification packet generation unit  124 A generates the notification packet by packetizing the retention information when the radio communication band of the radio transmission processing unit  123 A is changed or when the retention information of the divided packet retained in the packet buffer  122 A is changed. The notification packet generation unit  124 A may include, in the notification packet, the band information indicating a radio communication band of the radio transmission processing unit  123 A. The notification packet generation unit  124 A transmits the generated notification packet to the packet transmission and reception unit  121 A. 
     The discard packet extraction unit  125 A extracts the discard packet from the packet received by the packet transmission and reception unit  121 A. The discard packet extraction unit  125 A extracts the discard information from the discard packet and transmits the discard information to the radio transmission processing unit  123 A. 
       FIG. 5  is a block diagram showing a configuration of the radio communication device  200  according to the second example embodiment. The radio communication device  200  performs radio reception. The radio communication device  200  includes a radio reception circuit  210 A, a radio reception circuit  210 B, and an assembly unit  220 . The radio reception circuit  210 A and the assembly unit  220  are connected by a serial interface. The radio reception circuit  210 B and the assembly unit  220  are connected by a serial interface. 
     The radio reception circuit  210 A communicates with the radio transmission circuit  120 A of the radio communication device  100 . The radio reception circuit  210 A includes a radio reception unit  211 A, a packet transmission and reception unit  212 A, and a discard packet generation unit  213 A. 
     The radio reception unit  211 A receives the radio frame and extracts the divided packet from the radio frame. The radio reception unit  211 A transmits the divided packet to the packet transmission and reception unit  212 A. The radio reception unit  211 A extracts the discard information from the overhead of the radio frame. The radio reception unit  211 A transmits the discard information to the discard packet generation unit  213 A. 
     The packet transmission and reception unit  212 A arbitrates the divided packets and the discard packets received from the discard packet generation unit  213 A, which will be described later, and transmits the packets to the assembly unit  220 . The packet to be transmitted is, for example, an Ethernet packet. The packet transmission and reception unit  212 A is an interface with a packet transmission and reception unit  221 A. 
     The discard packet generation unit  213 A receives the discard information from the radio reception unit  211 A. The discard packet generation unit  213 A generates the discard packet by packetizing the discard information. The discard packet generation unit  213 A transmits the discard packet to the packet transmission and reception unit  212 A. The radio reception circuit  210 B has the same functional configuration as that of the radio reception circuit  210 A. 
     The assembly unit  220  assembles the divided packets. The assembly unit  220  includes packet transmission and reception units  221 A and  221 B, discard packet extraction units  222 A and  222 B, an assembly circuit  223 , and a packet transmission unit  224 . 
     The packet transmission and reception units  221 A and  221 B receive the divided packets and the discard packets from radio reception circuits  210 A and  210 B, respectively. The received packet is, for example, an Ethernet packet. The packet transmission and reception units  221 A and  221 B are interfaces with the packet transmission and reception units  212 A and  212 B, respectively. The packet transmission and reception units  221 A and  221 B transmit the divided packets to the assembly circuit  223 . The packet transmission and reception units  221 A and  221 B transmit the discard packets to the discard packet extraction units  222 A and  222 B, respectively. The discarded packet extraction units  222 A and  222 B extract the discard information from the discard packets transmitted from the packet transmission and reception units  221 A and  221 B, respectively, and notify the assembly circuit  223  of the discard information. 
     The assembly circuit  223  receives the divided packets from the packet transmission and reception units  212 A and  212 B for the radio reception circuits  210 A and  210 B, respectively, and assembles them in the order of the sequence ID described in the overhead of the divided packets. The assembly circuit  223  transmits the assembled packet to the packet transmission unit  224 . The assembly circuit  223  receives the discard information from the discard packet generation units  213 A and  213 B for the radio reception circuits  210 A and  210 B, respectively, and discard the divided packets based on the discard information. The packet transmission unit  224  transmits packets. The packet to be transmitted is, for example, an Ethernet packet. 
     Next, an overview diagram of the generation of the divided packets will be described.  FIG. 6  is an overview diagram showing an overview of the generation of the divided packet. After the packet reception unit  111  receives packet from a packet interface, the division circuit  112  divides the received packet into packets with a specified fixed length and transmits the divided packets to the allocation circuit  113 . The packet received by the packet reception unit  111  is provided with an FCS (Frame Check Sequence) at the end. 
     When the packet is divided, the division circuit  112  adds last divided bit information and a sequence ID to the head of the divided data as an overhead. The last divided bit information indicates whether or not the packet is the last divided packet. The details of the overhead will be described later. The divided data provided with the overhead is referred to as a divided packet.  FIG. 6  shows an example in which a packet is divided into four packets. The overheads of the divided packets are defined as OVH 1 , OVH 2 , OVH 3 , and OVH 4 , respectively. 
     Next, the allocation of the divided packets performed by the allocation circuit  113  will be described in detail. The allocation circuit  113  transmits the divided packets to one of the radio transmission processing units  123 A and  123 B having the smallest radio transmission delay. Here, the allocation circuit  113  manages the retention amounts of the packet buffers  122 A and  122 B for the radio transmission processing units  123 A and  123 B, respectively, and calculates the radio transmission delay based on the retention amounts. The packet transmission and reception units  114 A and  114 B provided for the radio transmission circuits  120 A and  120 B transmit the divided packets to the radio transmission circuits  120 A and  120 B, respectively, via the packet interface. 
     The condition of the allocation performed by the allocation circuit  113  will be described. As mentioned above, the radio transmission circuit  120 A is defined as Main, and the radio transmission circuit  120 B is defined as Sub. When the Formula (1) is true, the allocation circuit  113  allocates the divided packets to the radio transmission circuit  120 B. 
       [ A]+[B]&gt;[C]+[D]   Formula (1):
     [A] Radio transmission delay when the next divided packet is transmitted by the radio transmission circuit  120 A   [B] Radio transmission delay when all divided packets retained in the packet buffer  122 A are wirelessly transmitted   [C] Radio transmission delay when the next divided packet is transmitted by the radio transmission circuit  120 B   [D] Radio transmission delay when all divided packets retained in the packet buffer  122 B are wirelessly transmitted   

     Here, [A] and [C] are values that do not include consideration over the retention amount of the packet buffers  122 A and  122 B. [A] and [C] can be calculated from the radio transmission delay information and the band information. The radio transmission delay information is a value unique to the radio transmission circuits  120 A and  120 B. The band information is, for example, extracted by the notification packet extraction units  115 A and  115 B. Hereinafter, a case where the allocation circuit  113  holds the radio transmission delay information as a fixed value will be described. The allocation circuit  113  may appropriately acquire the radio transmission delay information from the radio transmission circuits  120 A and  120 B. 
       FIG. 7  is a diagram showing an example of the radio transmission delay information. The allocation circuit  113  may store data related to the radio transmission delay shown in  FIG. 7  in a tabular form. The radio transmission delay is determined by the baud rate and modulation method. The baud rate is a value indicating the number of times digital data can be modulated per second. The radio transmission circuits  120 A and  120 B notify the allocation circuit  113  of the baud rate and the modulation method used ,as the band information. The allocation circuit  113  can acquire the radio transmission delay based on the notification. 
     The allocation unit  113  calculates [B] and [D] based on the retention timing information, the retention information, and band information received from the notification packet extraction unit  115 . The calculation method will be described later. 
       FIG. 8  is a flowchart showing the operation of the allocation circuit  113 . The allocation circuit  113  first determines whether or not the divided packets have been received from the division circuit  112  (Step S 101 ). When the divided packets are received (Yes in Step S 101 ), the allocation unit  113  starts allocation processing (Step S 102 ). Next, the allocation unit  113  acquires the retention amount of the packet buffer  122 A of the radio transmission circuit  120 A as the retention information (Step S 103 ). Next, the allocation unit  113  acquires the retention amount of the packet buffer  122 B of the radio transmission circuit  120 B as the retention information (Step S 104 ). Next, the allocation unit  113  determines whether the Formula (1) is true or false (Step S 105 ). If Formula (1) is false (Yes in Step S 105 ), the allocation unit  113  allocates the divided packet to the radio transmission circuit  120 A (Step S 106 ). If the Formula (1) is true (No in Step S 105 ), the allocation unit  113  allocates the divided packets to the radio transmission circuit  120 B (Step S 107 ). 
       FIG. 9  is a flowchart showing an operation performed when the allocation unit  113  manages the retention amounts of the packet buffers  122 A and  122 B. Hereinafter, the process shown in  FIG. 9  is referred to as a retention amount management process. The retention amount management process is operated for each of the radio transmission circuits  120 A and  120 B and manages the retention amounts of the packet buffers  122 A and  122 B. 
     The allocation unit  113  subtracts the data amount corresponding to the band information from the retention amount (Step S 201 ). Step S 201  is for handling a decrease in the retention amount caused by transmission of the divided packets from the packet buffer  122 . The data amount corresponding to the band information represents the number of divided packets transmitted from the radio transmission processing unit  123  by the radio transmission delay determined according to the band information. Step S 201  may be performed at constant intervals. 
     Next, the allocation unit  113  determines whether or not the notification packet has been received from the notification packets extraction unit  115  (Step S 202 ). When the notification packets are received (Yes in Step S 202 ), the allocation unit  113  updates the retention information (Step S 203 ), and when the notification packets include the band information, the allocation unit  113  may also update the band information. After the retention amount is updated, the retention amount management process returns to the process of subtracting the retention amount (Step S 201 ). 
     Next, the allocation circuit  113  determines whether or not the divided packets are allocated to the radio transmission circuits  120 A or  120 B (Step S 204 ). If the divided packets are not allocated (No in Step S 204 ), the allocation circuit  113  returns to the process of subtracting the retention amount according to the band information (Step S 201 ). When the divided packets are allocated (Yes in Step S 204 ), the allocation unit  113  adds the data amount of the allocated divided packets to the retention information (Step S 205 ). After that, the allocation unit  113  returns to the process of subtracting the retention information according to the band information (Step S 201 ). 
     Next, the operation of the allocation circuit  113  related to the generation of the discard packets will be described. 
     When the divided packets are allocated, the allocation circuit  113  holds the radio transmission delay at that time. Due to a decrease in the radio communication band and retention of the packet buffer, the radio transmission delay may increase, and the time at which the divided packets arrive at the assembly circuit  223  may exceed a specified threshold. In such a case, the discard packet generation unit  116  generates the discard information. The discard information is, for example, a sequence ID of a divided packet to be discarded. 
     The discard information is, for example, a combination of the sequence ID of the first divided packet and the sequence ID of the last divided packet with respect to the packet associated with the delayed divided packet. For example, when a packet is divided into three, the sequence ID of the first divided packet and the sequence ID of the third divided packet are used as the discard information. The discard packet generation unit  116  packetizes the discard information. The discard packet may be in any form as long as it can be distinguished from the divided packet. The allocation circuit  113  may transmit the discard packet to one of the radio transmission circuits  120 A and  120 B having the smallest radio transmission delay information specific to the radio transmission circuit. 
     The packet transmission and reception units  114 A and  114 B arbitrate the divided packets and the discard packets and transmit them to the packet transmission and reception units  121 A and  121 B of the radio transmission circuits  120 A and  120 B, respectively. The packet transmission and reception units  114 A and  114 B receive the notification packets transmitted from the packet transmission and reception units  121 A and  121 B and transmit them to the notification packet extraction units  115 A and  115 B, respectively. The notification packet extraction units  115 A and  115 B extract the retention timing information, the retention information, and band information from the notification packet, and notify the allocation circuit  113  of them. 
     Next, the operation of the radio transmission circuits  120 A and  120 B will be described. The packet transmission and reception units  121 A and  121 B receive the divided packets and the discard packets. The packet transmission and reception units  121 A and  121 B transmit the divided packets to the packet buffers  122 A and  122 B, respectively. The packet transmission and reception units  121 A and  121 B transmit the discard packets to the discard packet extraction units  125 A and  125 B. 
     The packet buffers  122 A and  122 B transmit the divided packets according to radio bands of the radio transmission processing units  123 A and  123 B, respectively. The packet buffers  122 A and  122 B notify the notification packet generation units  124 A and  124 B, respectively, of the retention information about the retention of the divided packet. 
     The discard packet extraction units  125 A and  125 B extract the discard information from the discard packet and transmit it to the radio transmission processing units  123 A and  123 B, respectively. The radio transmission processing units  123 A and  123 B multiplex the divided packets on a radio frame and perform radio transmission. The discard information is wirelessly transmitted as the overhead of the radio frame. The radio transmission processing units  123 A and  123 B support the adaptive modulation method, and may notify the notification packet generation units  124 A and  124 B, respectively, of the band information for each modulation method. 
     The notification packet generation units  124 A and  124 B acquire the retention information from the packet buffers  122 A and  122 B, respectively. The notification packet generation units  124 A and  124 B acquire the band information from the radio transmission processing units  123 A and  123 B, respectively. The notification packet generation units  124 A and  124 B generate the notification packets at a predetermined timing. The predetermined timing is when the retention information exceeds a threshold specifically set or when the band information is changed. The notification packet is composed of the retention timing information related to the timing when an event occurs, the retention information, and the band information. The notification packet may in any form as long as it can be distinguished from the divided packet. The retention timing information includes, for example, the number of clocks at which an event occurs, time information, and the like. The allocation circuit  113  can accurately calculate the retention amount of the divided packets of the packet buffers  122 A and  122 B using the retention timing information. 
     Next, the operation of the radio reception circuits  210 A and  210 B will be described. First, the radio reception units  211 A and  211 B receive the divided packets from the radio frame. Next, the radio reception units  211 A and  211 B transmit the divided packets to the packet transmission and reception units  212 A and  212 B, respectively. The radio reception units  211 A and  211 B extract the discard information from the overhead of the radio frames and transmit it to the discard packet generation units  213 A and  213 B, respectively. Next, the packet transmission and reception units  212 A and  212 B arbitrate the divided packets and the discard packets received from the discard packet generation units  213 A and  213 B and transmit them to the packet transmission and reception units  221 A and  221 B, respectively, of the assembly unit  220 . The discard packet generation units  213 A and  213 B packetize the discard information and transmit it to packet transmission and reception units  212 A and  212 B, respectively. 
     Next, the operation of the assembly unit  220  will be described. 
     The packet transmission and reception units  221 A and  221 B receive the divided packets and the discard packets, transmit the divided packets to the assembly circuit  223 , and transmit the discard packets to the discard packet extraction units  222 A and  222 B, respectively. 
     The assembly circuit  223  refers to the overheads included at the head of the divided packets and assembles the divided packets in the order of the sequence ID. The assembly circuit  223  transmits the assembled packets to the packet transmission unit  224 . The assembly circuit  223  waits for the assembling when the final divided packet is not assembled. That is, the assembly circuit  223  stores the divided packets in the memory inside the assembly circuit  223 . The packet transmission unit  224  transmits the packets from the packet interface to the outside. The discard packet extraction units  222 A and  222 B extract the discard information from the discard packets and notify the assembly circuit of the discard information. The assembly circuit  223  receives the discard information and discards, from the memory, all the divided packets having the sequence ID in the range designated as the discard information. 
     Next, the overhead provided to the divided packet will be described.  FIG. 10  is an overview diagram showing an overview of the overhead provided to the divided packet. The division circuit  112  receives packets in the order of the packet  1 , the packet  2 , and packet  3 . Then, the division circuit  112  divides the packet  1  into four, divides the packet  2  into two, and does not divide the packet  3 . OVH  1  to  7  are added to the respective divided packets as the overheads. The overhead is a combination of the last divided bit information and the sequence ID. The last divided bit information is information indicating that the divided packet is the last divided packet. For example, the last bit information of the last divided packet is “1”, and the last bit information of the other divided packets is “0”. The last divided bit information of OVH 4 , OVH 6 , and OVH 7  is “1”. The sequence ID is information indicating the order of the divided packets and is incremented for each divided packet. For example, the sequence ID of the first divided packet may be “0”, and the incremented sequence ID may be used as the sequence ID of the next divided packet. 
     The data size of the sequence ID may be any size. In the following description, the data size of the sequence ID shall be two bytes. The value for incrementing the sequence ID may be any value. In the following description, the value for incrementing the sequence ID shall be +1. When the packet is divided into four, if the initial value of the sequence ID is 0x00, the sequences ID are 0x00 to 0x03. After that, the sequence ID is incremented by +1, and 0x00 comes after 0xff. The final bit information and the sequence ID enable the assembly circuit  223  to uniquely assemble the divided packets. 
     Next, a method in which the allocation circuit  113  calculates the radio transmission delay from the retention timing information, the retention information, and the band information will be described. First, when an event affecting the radio transmission delay occurs, the notification packet generation unit  124 A or the notification packet generation unit  124 B notifies the allocation circuit  113  of the retention timing information, the retention information, and the band information. The events affecting the radio transmission delay are that retention of packets at a threshold or more occurs in the packet buffers  122 A and  122 B, or that the radio transmission band of the radio transmission circuits  120 A and  120 B is lowered. As the retention timing information, time synchronization information and the number of clocks may be used. 
     First, a case where the time synchronization information is used as the retention timing information will be described. First, a protocol such as PTP (Precision Time Protocol)/IEEE 1588 is used to perform time synchronization using the allocation circuit  113  as Master and the radio transmission circuits  120 A and  120 B as Slave. The time synchronization information is used as the retention timing information. 
     The allocation circuit  113  acquires time information t 2  of the allocation circuit  113  about a time when the notification packet is received. The allocation circuit  113  acquires time information t 1  about a time when an event occurs from the retention timing information included in the notification packet. The allocation circuit  113  can calculate an “amount of data corresponding to the number of divided packets allocated to the radio transmission processing units  123 A and  123 B after the occurrence of the event” (a) based on the difference between the time information t 1  and the time information t 2 . The allocation circuit  113  calculates an “amount of data transmitted from the packet buffers  122 A and  122 B to the radio transmission processing units  123 A and  123 B after the occurrence of the event” (b) from the band information based on the difference between the time information t 1  and the time information t 2 . 
     When the allocation circuit  113  receives the notification packets, the retention amounts of the packet buffers  122 A and  122 B become “retention information +(a)-(b)”. Thus, the allocation circuit  113  can calculate the radio transmission delay when the divided packets are allocated to the radio transmission circuits  120 A and  120 B. 
       FIG. 11  is an overview diagram showing an example of a change in the retention amount of the packet buffer  122 A in the radio transmission circuit  120 A. The retention amount is obtained by adding “(a)-(b)” to the retention information. The time t 1  indicates the timing of the occurrence of the event affecting the radio transmission delay. The time t 2  indicates the timing at which the allocation circuit  113  has received the notification packets.  FIG. 11  shows a case where the allocation circuit  113  stops allocating divided packets to the radio transmission circuit  120 A at the time t 2 . The retention amount increases from the time t 1  to the time t 2 . The retention amount decreases from the time t 2 , because the allocation of the divided packets is stopped at the time t 2 . 
       FIG. 12  is an overview diagram showing an overview of the radio transmission delay in the radio transmission circuits  120 A and  120 B. The radio transmission delay of the radio transmission circuit  120 A is indicated by a solid line. The radio transmission delay of the radio transmission circuit  120 B is indicated by a dotted line. From the time t 1  to time t 2 , the retention amount increases, and the radio transmission delay increases. At the time t 2 , since the radio transmission delay of the radio transmission circuit  120 A is smaller than the radio transmission delay of the radio transmission circuit  120 B, the Formula (1) is false. Thus, the allocation circuit  113  allocates the divided packets to the radio transmission circuit  120 A. 
     By the above-described operation, the retention amount of the packet buffer  122 A increases, and the radio transmission delay of the radio transmission circuit  120 A increases. Since the condition of the Formula (1) becomes true at A 1 , the allocation circuit  113  allocates the divided packets to the radio transmission circuit  120 B. Thus, from the time of A 1  onward, the retention amount of the packet buffer  122 B increases, and the radio transmission delay of the radio transmission circuit  120 B increases. After that, as the retention amount of the packet buffer  122 B decreases, the radio transmission delay of the radio transmission circuit  120 B starts to decrease. 
     At A 2 , the condition of the Formula (1) becomes true again, and the allocation circuit  113  allocates the divided packets to the radio transmission circuit  120 B. By repeating the above operations, the divided packets can be transmitted with the minimum latency. 
     Next, a case where the number of clocks is used as the retention timing information will be described. In such a case, it is necessary to measure in advance the “number of clocks until the heads of the divided packets reach the packet buffers  122 A and  122 B from the allocation circuit  113  (c)” and the “number of clocks until the notification packets arrive from the radio transmission circuits  120 A and  120 B to the allocation circuit  113  (d)”. The notification packet generation units  124 A and  124 B notify the allocation circuit  113  of the “number of clocks required for writing the divided packets written in the packet buffers  122 A and  122 B (e)”, respectively, as the retention timing information. The allocation circuit  113  calculates (c)+(d)+(e). By using the number of divided packets (a) allocated between the calculated number of clocks and the amount of data (b) transmitted from the packet buffer between the calculated number of clocks, the allocation circuit  113  can calculate the radio transmission delay in the same manner as when the time synchronization information is used. 
     In the above example, the case where the division and allocation circuit  110  and the radio transmission circuits  120 A and  120 B are connected by a serial interface has been described, but this example embodiment is not limited to a serial interface. 
     Hereinafter, the effect of this example embodiment will be described. 
     In a radio communication system, a Link Aggregation technique is used in order to widen the transmission bandwidth between radio communication devices. The link aggregation technique is a technique that virtually bundles a plurality of physical lines into one line and enables use of bandwidth depending on a total number of the bands of the physical lines. MRL (Multi Radio-Linc) has been proposed as one of the link aggregation methods to efficiently use the radio band of Multiband. The MRL divides a packet, allocates the divided packets to a plurality of radio communication devices, and transmits them. A radio communication device using an MRL is described in International Patent Publication No. WO2018/116965. 
     When a serial interface, such as an Ethernet interface, is connected between a circuit for dividing, allocating, or assembling packets and a radio transmission circuit, the radio transmission circuit needs to have a packet buffer. When the radio transmission speed is lowered by the adaptive modulation method, the retention of the divided packets occurs in the packet buffer. When a related technique is used, the allocation circuit cannot calculate an accurate retention amount of the packet buffer of the radio transmission circuit. This leads to a problem that the allocation circuit cannot perform the allocation according to the radio transmission delay, and the radio transmission latency becomes long. 
     Since the order of the divided packets is not allowed to be changed, the assembly circuit must perform assembling in the order the divided packets are input to the division circuit. Therefore, when the latency of the packets becomes long, the assembly circuit has to wait for the arrival of the packets. Therefore, a packet whose latency has not became long needs to be stored in a memory in the assembly circuit as an assembly waiting state. Thus, when the fluctuation in the amount of the radio transmission delay is large, there is a problem that a large amount of memory resources must be implemented. 
     In this example embodiment, the retention timing information, the retention information, and the band information are notified to the allocation circuit by the radio transmission circuit. The allocation circuit obtains the radio transmission delay in the retention state from the retention information and the packet amount transmitted to the allocation circuit from the timing indicated in the retention timing information onward. 
     According to this example embodiment, the retention information of the packet buffer of the radio transmission circuit can be accurately transmitted from the radio transmission circuit to the allocation circuit. This enables the allocation circuit to allocate the divided packets to the radio transmission circuit having the smallest radio transmission delay. In this manner, the radio communication device according to this example embodiment can perform radio transmission with the shortest latency. 
     Further, according to this example embodiment, the allocation circuit transmits a discard notification to the assembly circuit for the divided packet in which the radio transmission delay has increased to a greater extent than that at the time of allocation. The assembly circuit can discard the divided packet in the assembly waiting state. Thus, according to this example embodiment, it is possible to improve an amount of memory resource consumption and shortage of memory resources in the assembly circuit, thereby reducing the quantity of memory resources to be implemented. 
     Note that the present disclosure is not limited to the above-described example embodiment, and may be modified as appropriate without departing from the spirit of the disclosure. 
     In the above-described example, although the radio communication device  100  has two radio communication means, the same operation can be performed even when three or more radio communication means are included.  FIG. 13  is a block diagram of a radio communication device  100  including three radio communication means. The configuration of the radio communication device  100  is the same as that shown in  FIG. 4  except that a radio transmission circuit  120 C, a packet transmission and reception unit  114 C, and a notification packet extraction unit  115 C are further included. The radio transmission circuit  120 C has the same functional configuration as that of the radio transmission circuits  120 A and  120 B, and transmits the divided packets using an antenna  105 C. The radio transmission circuit  120 A is also referred to as Main, the radio transmission circuit  120 B is also referred to as Sub 1 , and the radio transmission circuit  120 C is also referred to as Sub 2 . 
       FIG. 14  is a block diagram of a radio communication device  200  including three radio communication means. The operation is the same as that shown in FIG. 
       5  except for a radio reception circuit  210 C, a packet transmission and reception unit  221 C, and a discard packet extraction unit  222 C. The radio reception circuit  210 C has the same functional configuration as that of the radio reception circuits  210 A and  210 B, and uses an antenna  205 C to receive the divided packets. 
       FIG. 15  is a flowchart showing an operation of the allocation circuit  113  when the divided packets are allocated to the three radio communication means. In such a case, the divided packets are allocated according to whether the following Formulas (2), (3), and (4) are true or false. 
       [ A]+[B]&gt;[C 1]+[ D 1].   Formula (2):
 
       [ A]+[B]&gt;[C 2]+[ D 2].   Formula (3):
 
       [ C 1]+[ D 1]&gt;[ C 2]+[ D 2].   Formula (4):
     [A] Radio transmission delay when the next divided packet is wirelessly transmitted by Main (radio transmission circuit  120 A)   [B] Radio transmission delay when all divided packets retained in the packet buffer  122 A of the main are wirelessly transmitted   [C 1 ] Radio transmission delay when the next divided packet is wirelessly transmitted by Sub 1  (radio transmission circuit  120 B)   [D 1 ] Radio transmission delay when all divided packets retained in the packet buffer  122 B of Sub 1  are wirelessly transmitted   [C 2 ] Radio transmission delay when the next divided packet is wirelessly transmitted by Sub 2  (radio transmission circuit  120 C)   [D 2 ] Radio transmission delay when all the divided packets retained in the packet buffer  122 C of the Sub 2  are transmitted wirelessly   

     Steps S 301  to S 304  of  FIG. 15  are the same as Steps S 101  to S 104  of  FIG. 8 , respectively. In Step S 305 , the allocation circuit  113  acquires the number of divided packets retained in the packet buffer  122 C of the radio transmission circuit  120 C. 
     In Step S 306 , it is determined whether the Formula (2) is true or false. If the Formula (2) is false (Yes in Step S 306 ), the allocation unit  113  determines whether the Formula (3) is true or false (Step S 307 ). If Formula (2) is true (No in Step S 306 ), the allocation unit  113  proceeds to Step S 309 . 
     If the Formula (3) is false (Yes in Step S 307 ), the allocation unit  113  allocates the divided packets to the radio transmission circuit  120 A. If the Formula (3) is true (No in Step S 307 ), the process proceeds to Step S 309 . 
     In Step S 309 , if the Formula (4) is false (Yes in Step S 309 ), the allocation unit  113  allocates the divided packet to the radio transmission circuit  120 B (Step S 310 ). In Step S 309 , if the Formula (4) is true (No in Step S 309 ), the allocation unit  113  allocates the divided packets to the radio transmission circuit  120 C (Step S 311 ). 
     A case where four or more radio communication means are included will be described. When four or more radio communication means are included, an index is provided to Sub radio communication means. In the above example, 1 and 2 are indices for Sub 1  and Sub 2 , respectively. When four or more radio communication means are added, a comparison expression with the radio communication means of the Main corresponding to the Formula (2) and a comparison expression with the radio communication means of the small index (Sub) are added to the Formulas (2) to (4). By using the added Formulas and Formulas (2) to (4), the allocation circuit  113  can perform allocation appropriately. 
     According to the present disclosure, it is possible to provide a radio communication device, a radio communication system, and a radio communication method capable of notifying a radio communication unit of retention information of divided packets retained in a radio communication unit and allocating the divided packets based on the notification. 
     While the disclosure has been particularly shown and described with reference to example embodiments thereof, the disclosure is not limited to these example embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the claims.