Patent Publication Number: US-2020288536-A1

Title: User device and base station apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a user device and a base station apparatus in a radio communication system. 
     BACKGROUND ART 
     In 3rd Generation Partnership Project (3GPP), a radio communication scheme (hereinafter, the radio communication scheme is referred to as an “NR”) called 5G or new radio (NR) has been discussed in order to realize a more increase in a system capacity, more acceleration of a data transmission speed, a lower delay in a radio section, and the like. In the NR, various radio technologies have been discussed in order to satisfy requirement conditions in which delay of a radio section is set to 1 ms or less while realizing a throughput of 10 Gbps or more. 
     Here, in Long Term Evolution (LTE), a user entity (UE) category is defined as information indicating a baseband capability of a UE. It is defined that a UE indicates, to all networks, an RF capability (radio capability) and a UE category (for example, see Non-Patent Document 1). The RF capability includes, for example, information indicating a band combination (band combination information) supported by a UE and information indicating the number of multiple-input and multiple-output (MIMO) layers (for example, see Non-Patent Document 2). 
     CITATION LIST 
     Non-Patent Document 
     
         
         Non-Patent Document 1: 3GPP TS 36.331 V14.3.0 (2017-06) 
         Non-Patent Document 2: 3GPP TS 36.306 V14.3.0 (2017-06) 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     In NR, in order for a network side to acquire a radio capability or a baseband capability of a user device, it is necessary to appropriately perform UE capability notification (indication) by considering a signaling overhead. In addition, it is necessary for a base station apparatus to accurately identify a capability of a user device and cause the user device to perform efficient communication. 
     The invention is made in view of the foregoing circumstances and an object of the invention is to allow a base station apparatus to accurately identify a capability of a user device and perform efficient communication in a radio communication system. 
     Means for Solving Problem 
     According to the technology of the present disclosure, there is provided a user device that performs communication with a base station apparatus, the user device including: a control unit that computes a buffer size based on a radio capability parameter of the user device; a transmission unit that transmits a capability indication including the radio capability parameter to the base station apparatus; and a reception unit that receives a signal transmitted from the base station apparatus using a buffer with the computed buffer size. 
     Effect of the Invention 
     According to the technology of the present disclosure, it is possible to allow a base station apparatus to accurately identify a capability of a user device and perform efficient communication in a radio communication system. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration example of a radio communication system according to an embodiment of the invention; 
         FIG. 2  is a diagram illustrating an example (1) of UE categories in LTE; 
         FIG. 3  is a diagram illustrating an example (2) of the UE categories in LTE; 
         FIG. 4  is a diagram illustrating an example (3) of the UE categories in LTE; 
         FIG. 5  is a sequence diagram illustrating an example of UE capability indication according to the embodiment of the invention; 
         FIG. 6  is a sequence diagram illustrating an example (1) in which a UE buffer size is changed according to the embodiment of the invention; 
         FIG. 7  is a sequence diagram illustrating an example (2) in which the UE buffer size is changed according to the embodiment of the invention; 
         FIG. 8  is a diagram illustrating an example of a functional configuration of a base station apparatus  100  according to the embodiment of the invention; 
         FIG. 9  is a diagram illustrating an example of a functional configuration of a user device  200  according to the embodiment of the invention; and 
         FIG. 10  is a diagram illustrating an example of a hardware configuration of the base station apparatus  100  and the user device  200  according to the embodiment of the invention. 
     
    
    
     MODE(S) FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments of the invention will be described with reference to the drawings. Note that embodiments to be described below are exemplary and the embodiments to which the invention is applied are not limited to the following embodiments. 
     In an operation of a radio communication system according to the embodiment, conventional technologies are appropriately used. Here, the conventional technologies are, for example, conventional LTE, but the conventional technologies are not limited to the conventional LTE. The term “LTE” used in the present specification is assumed to have a broad meaning including LTE-Advanced and a scheme subsequent to LTE-Advanced (for example, NR) unless otherwise stated. 
     In an embodiment to be described below, terms such as a synchronization signal (SS), a primary SS (PSS), a secondary SS (SSS), a physical broadcast channel (PBCH), a physical RACH (PRACH), a physical downlink control channel (PDCCH), and a physical downlink shared channel (PDSCH) used in the conventional LTE will be used for the sake of description convenience. However, the same signals, functions, and the like may be referred to other names. The above-described terms in the NR correspond to an NR-SS, an NR-PSS, an NR-SSS, an NR-PBCH, an NR-PRACH, an NR-PDCCH, an NR-PDSCH, and the like. 
       FIG. 1  is a diagram illustrating a configuration example of a radio communication system according to the embodiment of the invention. The radio communication system according to the embodiment of the invention includes a base station apparatus (base station device)  100  and a user device  200 , as illustrated in  FIG. 1 . In  FIG. 1 , one base station apparatus  100  and one user device  200  are illustrated, but this is exemplary and the plurality of base station apparatus and the plurality of user devices may be used. 
     The base station apparatus  100  is a communication device that provides one or more cells and performs radio communication with the user device  200 . As illustrated in  FIG. 1 , the base station apparatus  100  transmits broadcast information, control information, or data to the user device  200 . The broadcast information is transmitted through an NR-PBCH and an NR-PDSCH, the control information is transmitted through an NR-PDCCH and an NR-PDSCH, and data is transmitted through an NR-PDSCH. Both the base station apparatus  100  and the user device  200  can transmit and receive a signal by performing beamforming. 
     The user device  200  is a communication device that has a radio communication function, such as a smartphone, a mobile phone, a tablet, a wearable terminal, or a communication module for machine-to-machine (M2M) and is wirelessly connected to the base station apparatus  100  to use various communication services provided by the radio communication system. As illustrated in  FIG. 1 , the user device  200  transmits a capability indication by an uplink to the base station apparatus  100 . The uplink transmission is performed through, for example, an NR-physical uplink control channel (PUCCH) or an NR-physical uplink shared channel (PUSCH). Control information is transmitted through the NR-PUCCH and data and control information are transmitted through the NR-PUSCH. 
     In the embodiment, a duplex scheme may be a time division duplex (TDD) scheme, may be a frequency division duplex (FDD) scheme, or may be another scheme (for example, a flexible duplex scheme or the like). 
     In the following description, transmission of a signal using a transmission beam may be transmission of a signal multiplied by a precoding vector (precoded by a precoding vector). Similarly, reception of a signal using a reception beam may be reception of a signal multiplied by a signal received with a predetermined weight vector. In addition, transmission of a signal using a transmission beam may be expressed by transmitting a signal using a specific antenna port. Similarly, reception of a signal using a reception beam may be expressed by receiving a signal using a specific antenna port. The antenna port refers to a logical antenna port or a physical antenna port defined in compliance with the 3GPP standard. It should be noted that methods of forming a transmission beam and a reception beam are not limited to the foregoing methods. For example, a method of changing an angle of each antenna in the base station apparatus  100  and the user device  200  including a plurality of antennas may be used, a method of combining a method of using a precoding vector and a method of changing an angle of an antenna may be used, another antenna panel may be changed and used, a method of combining methods used in accordance with a plurality of antenna panels, or other methods may be used. In addition, for example, a plurality of different transmission beams may be used at a high-frequency band. Using a plurality of transmission beams is referred to as a multi-beam operation and using one transmission beam is referred to as a single beam operation. 
     Embodiment 
     Hereinafter, one or more embodiments will be described. 
       FIG. 2  is a diagram illustrating an example (1) of a UE category in LTE. As illustrated in  FIG. 2 , as parameters defined for each UE category in a downlink physical layer, the maximum number of transmission and reception bits per transmission time interval (TTI), the maximum software buffer size, and the maximum number of MIMO layers are defined. As illustrated in  FIG. 2 , for example, in Category 6, the maximum number of transmission and reception bits per TTI is 301504, the maximum number of transmission and reception bits per TTI corresponding to one transport block is 149776 in the case of 4 layers 64 quadrature amplitude modulation (QAM) and is 75376 in the case of 2 layers 64 QAM, the maximum software buffer size is 3654144, and the maximum number of MIMO layers is 2 or 4. In addition, for example, in Category 12, the maximum number of transmission and reception bits per TTI is 603008, the maximum number of transmission and reception bits per TTI corresponding to one transport block is 149776 in the case of 4 layers 64 QAM, is 195816 in the case of 4 layers 256 QAM, is 75376 in the case of 2 layers 64 QAM, and is 97896 in the case of 2 layers 256 QAM, the maximum software buffer size is 7308288, and the maximum number of MIMO layers is 2 or 4. The other UE categories are defined in the same way. 
       FIG. 3  is a diagram illustrating an example (2) of the UE categories in LTE. In  FIG. 3 , as parameters defined for each UE category in an uplink physical layer, the maximum number of transmission and reception bits per TTI and whether to support 64 QAM are defined. As illustrated in  FIG. 3 , for example, in Category 3, the maximum number of transmission and reception bits per TTI is 51024, the maximum number of transmission and reception bits per TTI corresponding to one transport block is 51024, and 64 QAM is not supported. In addition, for example, in Category 8, the maximum number of transmission and reception bits per TTI is 1497760, the maximum number of transmission and reception bits per TTI corresponding to one transport block is 149776, and 64 QAM is supported. The other UE categories are defined in the same way. 
       FIG. 4  is a diagram illustrating an example (3) of the UE categories in LTE. In  FIG. 4 , a total layer  2  buffer size and a buffer size in the case of support for split bearers are defined for each UE category. As illustrated in  FIG. 4 , for example, in Category 1, the total layer  2  buffer size is 150000 and the buffer size in the case of support for split bearers is 230000. In addition, for example, in Category 10, the total layer  2  buffer size is 5200000 and the buffer size in the case of support for split bearers is 7600000. The other UE categories are defined in the same way. 
       FIG. 5  is a sequence diagram illustrating an example of UE capability indication according to the embodiment of the invention. In step S 11  illustrated in  FIG. 5 , the user device  200  transmits a radio capability indication of the UE to the base station apparatus  100 . The base station apparatus  100  appropriately sets radio parameters, scheduling, and the like based on the received radio capability indication of the UE and performs normal communication (S 12 ). 
     Here, in NR, the indication of the UE category can be omitted on the assumption that the user device  200  supports a radio capability, that is, a baseband capability in accordance with an RF capability, that is, a BB capability. 
     However, when the radio capability exceeds the baseband capability of the user device  200 , the user device  200  indicates, to the base station apparatus  100 , the UE categories under the condition that dual connectivity (DC) is not used. The fact that the radio capability exceeds the baseband capability means that, for example, a maximum throughput is higher mathematically. 
     In the DC, cooperation of UE capabilities is necessary between network nodes, that is, master nodes or secondary nodes. Therefore, when the radio capability exceeds the baseband capability of the user device  200 , indication of the UE categories is not supported. 
     The foregoing indication of the UE categories is omitted, and thus the user device  200  does not explicitly indicate, to the base station apparatus  100 , values of the software buffer size or the total layer  2  buffer size conventionally specified (defined) in association with UE categories. Therefore, a problem occurs in that a network node side including the base station apparatus  100  cannot perform rate matching or scheduling by considering the availability of a buffer of the user device  200 . 
     Accordingly, the software buffer size or the total layer  2  buffer size of the user device  200  is defined as follows. 
     The user device  200  computes a buffer size to be prepared. 
     The base station apparatus  100  implicitly or explicitly computes a buffer size prepared by the user device  200  based on the radio capability of the UE acquired by the base station apparatus  100  by radio capability indication of the UE illustrated in step S 11  of  FIG. 5 . 
     For example, the software buffer size of the user device  200  is computed as follows: 
       Software buffer size=The number of receivable bits×The number of hybrid automatic repeat-request (ARQ) (HARQ) processes×The number of component carriers (CCs)×The number of MIMO layers
 
     Here, “the number of receivable bits” may be an instantaneous value per unit time, may be a value based on TDD config, or may be a value in which UL simultaneous transmission capability is considered. TDD config is, for example, a disposition configuration in a time domain of a symbol used in an uplink or a downlink of a radio frame. 
     In addition, for “the number of HARQ processes,” a software buffer size may be computed from an HARQ round-trip time (RTT). When the user device  200  supports a plurality of HARQ processes or RTTs, the software buffer size may be computed based on a minimum value, a maximum value, or an average value of the plurality of HARQ processes or RTTs. 
     In addition, “the number of CCs” may be the maximum number in band combination supported by the user device  200 . 
     The number of MIMO layers may be the maximum number in the band combination supported by the user device  200 . 
     The network, that is, the base station apparatus  100  may explicitly indicate, to the user device  200 , some or all of the foregoing parameters by broadcast information or individual signaling. In addition, for example, some or all of the parameters may be implicitly indicated based on a release version which is supported by gNB which is the base station apparatus  100  in NR. 
     For example, the total layer  2  buffer size of the user device  200  is computed as follows: 
       Total layer 2 buffer size=The number of receivable bits×RTT+The number of transmittable bits×RTT
 
     Here, “the number of receivable bits” may be an instantaneous value per unit time, may be a value based on TDD config, or may be a value in which UL simultaneous transmission capability is considered, as in the computation of the software buffer size. 
     The RTT may be a value to which a radio link control (RLC) RTT, a scheduling delay, and a delay in a network, that is, a delay in an X2 interface or the like are added. 
     In addition, as in the computation of the software buffer size, the network, that is, the base station apparatus  100  may explicitly indicate, to the user device  200 , some or all of the foregoing parameters by broadcast information or individual signaling. In addition, for example, some or all of the parameters may be implicitly indicated based on a release version which is supported by gNB which is the base station apparatus  100  in NR. 
       FIG. 6  is a sequence diagram illustrating an example (1) in which a UE buffer size is changed according to the embodiment of the invention. A conventional software buffer or total layer  2  buffer is prepared independently from another buffer of the user device  200 . On the other hand, for example, with an increase in a peak rate in the NR, it is necessary to mount a buffer with a large size, and thus a problem occurs in that cost of the user device  200  increases. Accordingly, a region prepared for the software buffer or the total layer  2  buffer is assumed to be shared with a functional unit inside another user device  200 , for example, a functional unit other than a radio functional unit. 
     Therefore, it is also necessary to recognize a buffer-occupied situation (buffer availability) inside the user device  200  on the network side. Accordingly, there is consideration of performing control or signaling in which the user device  200  indicates, to the network, a buffer sharing capability inside the device and the size of the buffer. 
     For example, when a change in a size or the like occurs in a buffer which can be used for radio, the user device  200  indicates, to the network side, that is, the base station apparatus  100 , the change. As illustrated in  FIG. 6 , in step S 22  after RRC connection reconfiguration of step S 21 , the indication including information indicating a change in the buffer may be transmitted from the user device  200  to the base station apparatus  100  through UE assistance information. Based on the indicated change in the buffer, the base station apparatus  100  adjusts the radio parameters, the scheduling, or the like and performs normal communication (S 23 ). 
     For example, when the change occurs in the buffer which can be used for radio and the user device  200  indicates, to the network side, that is, the base station apparatus  100 , the change, the user device  200  may implicitly indicate to the base station apparatus  100  by using information included in UECapabilityInformation which is a response at the time of reception (S 24 ) of UECapabilityEnquiry from the base station apparatus  100  (S 25 ). That is, in step S 24 , the user device  200  can indicate the change in the buffer in step S 25  only when the network, that is, the base station apparatus  100  makes a request. The information included in UECapabilityInformation may be, for example, band combination or may be other radio parameter. Based on the indicated change in the buffer, the base station apparatus  100  adjusts the radio parameters, the scheduling, or the like and performs normal communication (S 26 ). 
       FIG. 7  is a sequence diagram illustrating an example (2) in which the UE buffer size is changed according to the embodiment of the invention. Indication for explicitly or implicitly specifying a buffer size of the UE is performed as in  FIG. 5 or 6 . 
     In step S 31 , the user device  200  transmits an explicit or implicit indication related to the change in the buffer size of the UE to the base station apparatus  100 . Subsequently, in step S 32 , the base station apparatus  100  may reject the indication related to the change in the buffer size of the UE. Due to the rejection, the user device  200  prepares a radio buffer before the change in the buffer size. Accordingly, normal communication is performed without changing the buffer size of the user device  200  (S 33 ). 
     In step S 34 , the base station apparatus  100  may transmit an indication for explicitly or implicitly specifying the buffer size of the UE. The user device  200  prepares the specified buffer size based on the indication for explicitly or implicitly designating the buffer size of the UE and performs normal communication (S 35 ). 
     In addition, to avoid changing the buffer size of the UE frequently, the base station apparatus  100  may specify a frequency for the change in the buffer size in the user device  200 . For example, the base station apparatus  100  may specify the frequency for the change in the buffer size in the user device  200  by explicitly indicating, to the user device  200 , the frequency itself such as one time per minute. 
     In addition, for example, a “suppression timer” for suppressing the change in the buffer size may be introduced. The user device  200  activates the suppression timer at the time of the change in the buffer size and the indication related to the change in the buffer size. During a timer operation, the change in the buffer size and the indication related to the change in the buffer size may not be performed. When the timer expires, the change in the buffer size and the indication related to the change in the buffer size can be performed. The suppression timer may be activated or reactivated at the time of transmission of UE capability information. 
     As in the above-described embodiment, the base station apparatus  100  or the user device  200  can compute and identify a necessary buffer size in accordance with the radio capability parameter of the UE. Accordingly, the base station apparatus  100  can identify the buffer size of the user device  200  and adjust the rate matching and the scheduling based on the buffer size without having the UE categories indicated by the user device  200 . In addition, the base station apparatus  100  can also specify the buffer size by explicitly or implicitly indicating, to the user device  200 , the necessary buffer size. In addition, based on the radio capability parameters of the UE, the base station apparatus  100  or the user device  200  implicitly computes the buffer size. Thus, because it is not necessary to indicate the buffer size, it is possible to reduce signaling. In addition, because the user device  200  does not explicitly indicate the value of the software buffer size or the total layer  2  buffer size conventionally specified (defined) based on the UE categories, it is difficult for the network side, that is, the base station apparatus  100 , to perform rate matching or scheduling in accordance with availability of a buffer of the user device  200 . However, since the base station apparatus  100  can compute and identify a necessary buffer size based on the radio capability parameter of the UE according to the above-described embodiment, the network side, that is, the base station apparatus  100 , can perform rate matching or scheduling in accordance with availability of a buffer of the user device  200 . 
     That is, in the radio communication system, the base station apparatus can accurately identify the capability of the user device and perform efficient communication. 
     (Device Configurations) 
     Next, functional configurations of the base station apparatus  100  and the user device  200  performing the above-described processing and operations will be described. The base station apparatus  100  and the user device  200  each have at least functions of realizing the embodiment. Here, the base station apparatus  100  and the user device  200  may each have only some of the functions in the embodiment. 
       FIG. 8  is a diagram illustrating an example of a functional configuration of the base station apparatus  100 . As illustrated in  FIG. 8 , the base station apparatus  100  includes a transmission unit  110 , a reception unit  120 , a setting information management unit  130 , and a buffer management unit  140 . The functional configuration illustrated in  FIG. 8  is merely exemplary. Any functional division and any name of the functional unit can be used as long as the operations according to the embodiment of the invention can be performed. 
     The transmission unit  110  has a function of generating a signal to be transmitted to the user device  200  and wirelessly transmitting the signal. The reception unit  120  has a function of receiving various signals transmitted from the user device  200  and acquiring information regarding, for example, higher layers from the received signals. In addition, the transmission unit  110  has a function of transmitting the NR-PSS, the NR-SSS, the NR-PBCH, the NR-PDCCH, the NR-PDSCH, or the like to the user device  200 . In addition, the transmission unit  110  transmits the broadcast information, the control information, or the data to the user device  200 . 
     The setting information management unit  130  stores preset setting information and various kinds of setting information to be transmitted to the user device  200 . Examples of content of the setting information include broadcast information and control information. 
     The buffer management unit  140  specifies various buffer sizes of the user device  200  and performs scheduling in accordance with the buffer sizes, as described in the embodiment. 
       FIG. 9  is a diagram illustrating an example of a functional configuration of the user device  200 . As illustrated in  FIG. 9 , the user device  200  includes a transmission unit  210 , a reception unit  220 , a setting information management unit  230 , and a buffer control unit  240 . The functional configuration illustrated in  FIG. 9  is merely exemplary. Any functional division and any name of the functional unit can be used as long as the operations according to the embodiment of the invention can be performed. 
     The transmission unit  210  creates a transmission signal from transmission data and wirelessly transmits the transmission signal. The reception unit  220  wirelessly receives various signals and acquires signals of the higher layers from the received signals of the physical layer. The reception unit  220  has a function of receiving the NR-PSS, the NR-SSS, the NR-PBCH, the NR-PDCCH, the NR-PDSCH, or the like transmitted from the base station apparatus  100 . The transmission unit  210  transmits an uplink signal to the base station apparatus  100  and the reception unit  120  receives the broadcast information, the control information, the data, or the like from the base station apparatus  100 . The setting information management unit  230  stores various kinds of setting information received from the base station apparatus  100  by the reception unit  220 . The setting information management unit  230  also stores preset setting information. Examples of content of the setting information include the information regarding the various buffer sizes of the user device  200 . 
     The buffer control unit  240  autonomously determines various buffer sizes in the user device  200  or controls the buffer sizes in response to a request from the base station apparatus  100 , as described in the embodiment. It should be noted that a functional unit related to reception of a control signal or the like in the buffer control unit  240  may be included in the reception unit  220 . 
     (Hardware Configuration) 
     The diagrams of the functional configurations ( FIGS. 8 and 9 ) used to describe the embodiment of the above-described invention illustrate blocks of functional units. The functional blocks (configuration units) are realized by any combination of hardware and/or software. In addition, realization means of each functional block is not particularly limited. That is, each functional block may be realized by one device in which a plurality of elements are joined physically and/or logically or may be realized by a plurality of devices in which two or more devices that are separated physically and/or logically are connected directly and/or indirectly (for example, a wired and/or wireless manner). 
     In addition, for example, both the base station apparatus  100  and the user device  200  according to an embodiment of the invention function as computers that perform the processing according to the embodiment of the invention.  FIG. 10  is a diagram illustrating an example of a hardware configuration of a radio communication device which is the base station apparatus  100  or the user device  200  according to the embodiment of the invention. Each of the base station apparatus  100  and the user device  200  described above may be configured as a computer device that physically includes a processor  1001 , a storage device  1002 , an auxiliary storage device  1003 , a communication device  1004 , an input device  1005 , an output device  1006 , a bus  1007 , and the like. 
     It should be noted that, in the following description, a term “device” can be substituted with a circuit, a device, a unit, or the like. The hardware configuration of the base station apparatus  100  and the user device  200  may be configured to include one device or a plurality of devices among devices denoted by reference numerals  1001  to  1006  illustrated in the drawing or may be configured not to include some of the devices. 
     Each function in the base station apparatus  100  and the user device  200  is realized by reading predetermined software (a program) on hardware such as the processor  1001 , the storage device  1002 , and the like so that the processor  1001  performs an operation and controlling communication of the communication device  1004  and reading and/or writing data in the storage device  1002  and the auxiliary storage device  1003 . 
     The processor  1001  controls, for example, the entire computer by operating an operating system. The processor  1001  may be configured as a central processing unit (CPU) that includes an interface with a peripheral device, a control device, an operation device, a register, and the like. 
     In addition, the processor  1001  reads a program (a program code), a software module, or data from the auxiliary storage device  1003  and/or the communication device  1004  to the storage device  1002  and performs various kinds of processing in accordance with the program, the software module, or the data. As the program, a program causing a computer to execute at least some of the operations described in the above-described embodiment is used. For example, the transmission unit  110 , the reception unit  120 , the setting information management unit  130 , and the buffer management unit  140  of the base station apparatus  100  illustrated in  FIG. 8  may be stored in the storage device  1002  and may be realized by a control program operated by the processor  1001 . In addition, for example, the transmission unit  210 , the reception unit  220 , the setting information management unit  230 , and the buffer control unit  240  of the user device  200  illustrated in  FIG. 9  may be stored in the storage device  1002  and may be realized by a control program operated by the processor  1001 . The above-described various kinds of processing performed by one processor  1001  have been described, but may be performed simultaneously or in sequence by two or more processors  1001 . The processor  1001  may be mounted on one or more chips. It should be noted that the program may be transmitted from a network via an electric communication line. 
     The storage device  1002  is a computer-readable recording medium and may be configured as at least one of, for example, a read-only memory (ROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a random access memory (RAM), and the like. The storage device  1002  may be called a register, a cache, a main memory (a main memory device), or the like. The storage device  1002  can store a program (a program code), a software module, or the like which can be executed to perform processing according to an embodiment of the invention. 
     The auxiliary storage device  1003  is a computer-readable recording medium and may be configured as at least one of, for example, an optical disc such as a compact disc ROM (CD-ROM), a hard disk drive, a flexible disc, a magneto-optical disc (for example, a compact disc, a digital versatile disc, a Blu-ray (registered trademark) disc), a smart card, a flash memory (for example, a card, a stick, a key drive), a floppy (registered trademark) disk, a magnetic strip, and the like. The auxiliary storage device  1003  may be called an auxiliary storage device. The above-described storage medium may be, for example, a database including the storage device  1002  and/or the auxiliary storage device  1003  or an appropriate medium other than a server. 
     The communication device  1004  is hardware (a transceiving device) that performs communication between computers via a wired and/or wireless network and is also referred to as, for example, a network device, a network controller, a network card, a communication module, or the like. For example, the transmission unit  110  and the reception unit  120  of the base station apparatus  100  may be realized in the communication device  1004 . The transmission unit  210  and the reception unit  220  of the user device  200  may be realized in the communication device  1004 . 
     The input device  1005  is an input device (for example, a keyboard, a mouse, a microphone, a switch, a button, a sensor, or the like) that receives an input from the outside. The output device  1006  is an output device (for example, a display, a speaker, an LED lamp, or the like) that performs an output to the outside. It should be noted that the input device  1005  and the output device  1006  may be an integrated configuration (for example, a touch panel). 
     In addition, the devices such as the processor  1001  and the storage device  1002  are connected via the bus  1007  to communicate information. The bus  1007  may be configured as a single bus or may be configured as different buses between the devices. 
     In addition, the base station apparatus  100  and the user device  200  may each include hardware such as a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a programmable logic device (PLD), and a field programmable gate array (FPGA) or some or all of the functional blocks may be realized by the hardware. For example, the processor  1001  may be mounted as at least one of the hardware. 
     Conclusion of Embodiment 
     As described above, according to an embodiment of the invention, there is provided a user device that performs communication with a base station apparatus. The user device includes: a control unit that computes a buffer size based on a radio capability parameter of the user device; a transmission unit that transmits a capability indication including the radio capability parameter to the base station apparatus; and a reception unit that receives a signal transmitted from the base station apparatus using a buffer with the computed buffer size. 
     In the foregoing configuration, the base station apparatus  100  or the user device  200  can compute and identify a necessary buffer size in accordance with a radio capability parameter of the UE. In the radio communication system, the base station apparatus can accurately identify the capability of the user device and perform efficient communication. 
     The radio parameters may include some or all of the number of bits which the user device is able to receive per predetermined time, the number of HARQ processes, the number of component carriers, and the number of MIMO layers. In the foregoing configuration, the base station apparatus  100  or the user device  200  implicitly computes the buffer size based on the radio capability parameter of the UE. Thus, because it is not necessary to indicate the buffer size, the signaling can be reduced. 
     The number of bits which the user device is able to receive per predetermined time may be computed based on a configuration of a radio frame related to time division duplex or synchronous transmission capabilities of an uplink and a downlink. The number of HARQ processes may be computed based on a round trip time of HARQ. The number of component carriers and the number of MIMO layers may be maximum numbers in a band combination supported by the user device. In the foregoing configuration, the base station apparatus  100  or the user device  200  implicitly computes the buffer size based on the radio capability parameter of the UE. Thus, because it is not necessary to indicate the buffer size, the signaling can be reduced. 
     When a radio capability exceeds a baseband capability of the user device and the user device communicates with the base station apparatus using dual connectivity, the control unit may compute the buffer size based on the radio capability parameter of the user device. In the foregoing configuration, since synchronization of the UE capability with the base station apparatus  100  performing DC is not necessary, the signaling can be reduced. 
     When the reception unit receives a request for the capability indication from the base station apparatus, a change in the buffer size may be explicitly transmitted to the base station apparatus. Alternatively, when the reception unit receives an indication for explicitly specifying the buffer size from the base station apparatus, a signal transmitted from the base station apparatus may be received using a buffer with the specified buffer size. In the foregoing configuration, since the buffer size can be updated at a timing specified by the base station apparatus  100  and the buffer size specified by the base station apparatus  100  can be applied to the user device  200 , the base station apparatus  100  can easily manage the buffer size of the user device  200 . 
     In addition, according to the embodiment of the invention, there is provided a base station apparatus that performs communication with a user device. The base station apparatus includes: a reception unit that receives a capability indication including a radio capability parameter of the user device from the user device; a management unit that computes a buffer size based on the radio capability parameter; and a transmission unit that generates a signal to be transmitted to the user device based on the computed buffer size. 
     In the foregoing configuration, the base station apparatus  100  or the user device  200  can compute and identify a necessary buffer size in accordance with a radio capability parameter of the UE. In the radio communication system, the base station apparatus can accurately identify the capability of the user device and perform efficient communication. 
     Supplements of Embodiment 
     The embodiments of the invention have been described above, but the disclosed invention is not limited to the embodiments and various modified examples, corrected examples, substituted examples, displaced examples, and the like can be understood by those skilled in the art. The description has been made using the specific numerical value examples in order to promote the understanding of the invention, but theses numerical values are merely exemplary and any appropriate values may be used unless otherwise stated. The division of the items in the foregoing description is not essential for the invention, the factors described in two or more items may be combined and used as necessary and the factors described in certain items may be applied to the factors described in the other items (unless inconsistent). The boundaries of the functional units or the processing units in the functional block diagrams not necessarily correspond to boundaries of physical components. The operation of a plurality of functional units may be performed physically by one component or the operation of one functional unit may be performed physically by a plurality of components. The procedure of the processing described in the embodiments may be switched unless the processing procedure is inconsistent. To facilitate the description of processing, the base station apparatus  100  and the user device  200  have been described with reference to the functional block diagrams, but these devices may be realized by hardware, software, or a combination thereof. Software operated by the processor included in the base station apparatus  100  according to the embodiment of the invention and software operated by the processor included in the user device  200  according to the embodiment of the invention may each be stored in a random access memory (RAM), a flash memory, a read-only memory (ROM), an EPROM, an EEPROM, a register, a hard disk (HDD), a removable disc, a CD-ROM, a database, or any appropriate storage medium other than a server. 
     In addition, the indication of the information may be performed in accordance with another method without being limited to the mode/embodiment described in the present specification. For example, the indication of the information may be performed with physical layer signaling (for example, downlink control information (DCI) or uplink control information (UCI)), higher layer signaling (for example, radio resource control (RRC) signaling, a medium access control (MAC) signaling), broadcast information (master information block (MIB) or system information block (SIB)), and other signal or a combination thereof. In addition, the RRC signaling may be called an RRC message and may be, for example, RRC connection setup message, an RRC connection reconfiguration message, or the like. 
     Each mode/embodiment described in the present specification may be applied to a system using long term evolution (LTE), LTE-Advanced (LTE-A), SUPER 3G, IMT-Advanced, 4G, 5G, future radio access (FRA), W-CDMA (registered trademark), GSM (registered trademark), CDMA 2000, Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Ultra-Wide Band (UWB), Bluetooth (registered trademark), or another appropriate system and/or a next-generation system extended based thereon. 
     A sequence of the processing procedure, the sequence, the flowchart, and the like of each mode/embodiment described in the present specification may be switched unless inconsistent. For example, the methods described in the present specification suggest elements of various steps in the exemplary sequences and the invention is not limited to the suggested specific sequences. 
     A specific operation performed by the base station apparatus  100  in the present specification is also performed by an upper node thereof depending on a case. In a network formed of one network node or a plurality of network nodes including the base station apparatus  100 , it is apparent that various operations performed to communicate with the user device  200  can be performed by the base station apparatus  100  and/or another network node (for example, MME, S-GW, or the like is considered, but the invention is not limited thereto) other than the base station apparatus  100 . A case in which the number of other network nodes other than the base station apparatus  100  is one has been exemplified above, but a plurality of other network nodes (for example, MME and S-GW) may be combined. 
     Each mode/embodiment described in the present specification may be used singly, may be used in combination, or may be switched in association with execution. 
     The user device  200  is also called a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communication device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or another appropriate term by those skilled in the art. 
     The base station apparatus  100  is also called a NodeB (NB), an enhanced NodeB (eNB), a gNB, a base station, or another appropriate term by those skilled in the art. 
     The term “determining” used in the present specification includes diverse operations in some cases. The “determining” can also include the fact that, for example, judging, calculating, computing, processing, deriving, investigating, looking up (for example, looking up in a table, a database, or another data structure), or ascertaining is considered to be “determining.” In addition, the “determining” can also include the fact that receiving (for example, receiving information), transmitting (for example, transmitting information), input, output, or accessing (for example, accessing data in a memory) is considered to be “determining.” In addition, the “determining” can include the fact that resolving, selecting, choosing, establishing, or comparing is regarded as “determining.” That is, the “determining” can include the fact that any operation is considered to be “determined.” 
     The description “based on” used in the present specification does not mean “based on only” unless otherwise stated. In other words, the description “based on” means both “based on only” and “based on at least.” 
     The terms “include,” “including,” and modifications thereof are intended to be comprehensive similarly to the term “comprising” as long as the terms are used in the present specification or the claims. Further, the term “or” used in the present specification or the claims is intended not to be exclusive OR. 
     In the entire present disclosure, for example, when the articles such as a, an, and the in English are added in translation, the articles can include a plurality of articles unless clearly stated in the contexts. 
     It should be noted that, in the embodiments of the invention, the buffer control unit  240  is an example of a control unit. The buffer management unit  140  is an example of a management unit. 
     The invention has been described in detail above, but it is apparent to those skilled in the art that the invention is not limited to the embodiments described in the present specification. The invention can be embodied in correction and modification aspects without departing from the gist and the scope of the invention described in the claims. Accordingly, the description of the present specification has been made for exemplary description and does not have any limited meaning to the invention. 
     This international patent application is based on and claims priority to Japanese Patent Application No. 2017-187260, filed on Sep. 27, 2017, and the entire content of Patent Application No. 2017-187260 is incorporated herein by reference. 
     EXPLANATIONS OF LETTERS OR NUMERALS 
     
         
           100  BASE STATION APPARATUS 
           200  USER DEVICE 
           110  TRANSMISSION UNIT 
           120  RECEPTION UNIT 
           130  SETTING INFORMATION MANAGEMENT UNIT 
           140  BUFFER MANAGEMENT UNIT 
           200  USER DEVICE 
           210  TRANSMISSION UNIT 
           220  RECEPTION UNIT 
           230  SETTING INFORMATION MANAGEMENT UNIT 
           240  BUFFER CONTROL UNIT 
           1001  PROCESSOR 
           1002  STORAGE DEVICE 
           1003  AUXILIARY STORAGE DEVICE 
           1004  COMMUNICATION DEVICE 
           1005  INPUT DEVICE 
           1006  OUTPUT DEVICE