Patent Publication Number: US-2022217700-A1

Title: Communication apparatus, communication method, and program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 10/709,588, filed Jun. 4, 2020, which is based on PCT filing PCT/JP2018/040819, filed Nov. 2, 2018, which claims priority to JP 2017-239548, filed Dec. 14, 2017, the entire contents of each are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a communication. apparatus, a communication method, and a program. 
     BACKGROUND 
     Wireless access schemes and wireless networks of cellular mobile communication (hereinafter also referred to as Long Term Evolution (LTE), LTE-Advanced (LTE-A), LTE-Advanced Pro (LTE-A Pro), New Radio (NR), New Radio Access Technology (NRAT), Evolved Universal Terrestrial Radio Access (EUTRA), or Further EUTRA (FEUTRA)) are under review in 3rd Generation Partnership Project (3GPP). Further, in the following description, LTE includes LTE-A, LTE-A Pro, and EUTRA, and NR includes NRAT and FEUTRA. In LTE and NR, a base station device (base station) is also referred to as an evolved Node (eNodeB), a terminal apparatus (a mobile station, a mobile station device, or a terminal) is also referred to as a user equipment (UE). LTE and NR are cellular communication systems in which a plurality of areas covered by a base station device is arranged in a cell form. A single base station device may manage a plurality of cells. 
     In a fifth-generation (5G) mobile communication system following LTE/LTE-A, technology using a directional beam for communication between a base station and a terminal apparatus is being studied. The use of such technology allows communication between a base station and a terminal apparatus to achieve spatial multiplexing in addition to time and frequency multiplexing. In one example, Patent Document 1 discloses an example of a technique using a directional beam for communication between a base station and a terminal apparatus. 
     Further, as the technology for delivering content such as text, music, still images, and moving images to each terminal apparatus using the above-described wireless network, a technology called multimedia broadcast and multicast service (MBMS) is studied. The use of the MBMS technology makes it possible to efficiently deliver the above-mentioned various types of content that are broadcast as a program to a plurality of terminal apparatuses via the wireless network. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2017-157908 A 
     SUMMARY 
     Technical Problem 
     On the other hand, in the fifth-generation (5G) mobile communication system, data is transmitted to each terminal apparatus while scanning a beam having directivity (also referred to hereinafter as a “directional beam”), and so the technique of delivering content to each terminal apparatus within the communication range is different from the communication using a non-directional beam. Thus, even in a situation where a directional beam is used for communication, the technology such as MBMS capable of efficiently delivering content provided as a so-called Program (broadcasting program) to each terminal apparatus is desirable to be applicable more suitably. 
     Thus, the present disclosure provides technology enabling the delivery of content to a terminal apparatus using a directional beam to be achieved more suitably. 
     Solution to Problem 
     According to the present disclosure, a communication apparatus is provided that includes: a communication unit that performs wireless communication; and a control unit that controls in such a way as to deliver content subjected to multicast from an upper node to a terminal apparatus using at least a part pf a plurality of directional bases allocated to the terminal apparatus from the directional beams used for the wireless communication. 
     Moreover, according to the present disclosure, a communication apparatus is provided that includes: a communication unit that performs wireless communication; and a control unit that controls in such a way to receive content subjected to multicast from an upper node to a base station and delivered from the base station using at least a part of directional beams allocated from a plurality of directional beams. 
     Moreover, according to the present disclosure, a communication method executed by a computer, the method is provided that includes: performing wireless communication; and controlling in such a way as to deliver content subjected to multicast from an upper node to a terminal apparatus using at least a part of a plurality of directional beams allocated to the terminal apparatus from the directional beams used for the wireless communication. 
     Moreover, according to the present disclosure, a communication method executed by a computer is provided that includes: performing wireless communication; and controlling in such a way to receive content subjected to multicast from an upper node to a base station and delivered from the base station using at least a part of directional beams allocated from a plurality of directional beams. 
     Moreover, according to the present disclosure, a program causing a computer to execute: performing wireless communication; and controlling in such a way as to deliver content subjected to multicast from an upper node to a terminal apparatus using at least a part of a plurality of directional beams allocated to the terminal apparatus from the directional beams used for the wireless communication. 
     Moreover, according to the present disclosure, a program is provided that causes a computer to execute: performing wireless communication; and controlling in such a way to receive content subjected to multicast from an upper node to a base station and delivered from the base station using at least a part of directional beams allocated from a plurality of directional beams. 
     Advantageous Effects of Invention 
     According to the present disclosure as described above, the technology is provided that enables the delivery of content to the terminal apparatus using the directional beam more suitably. 
     Note that the effects described above are not necessarily limitative. With or in the place of the above effects, there may be achieved any one of the effects described in this specification or other effects that may be grasped from this specification. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrated to describe an example of a schematic configuration of a system according to an embodiment of the present disclosure. 
         FIG. 2  is a block diagram illustrating an example of a configuration of a base station according to the present embodiment. 
         FIG. 3  is a block diagram illustrating an example of a configuration of a terminal apparatus according to the present embodiment. 
         FIG. 4  is a diagram illustrated to describe an overview of MBMS network architecture. 
         FIG. 5  is a diagram illustrated to describe an example of a procedure for performing “counting”. 
         FIG. 6  is a diagram illustrating an example of a protocol stack of an M1 interface between an MBMS gateway and a base station. 
         FIG. 7  is a sequence diagram illustrating an example of an MBMS session start procedure in LTE. 
         FIG. 8  shows an example of a frame structure upon using MBES. 
         FIG. 9  is a diagram illustrated to describe an overview of information associated with an MBMS session. 
         FIG. 10  is a schematic sequence diagram illustrating an example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to the present embodiment. 
         FIG. 11  is a diagram illustrated to describe an overview of beam sweeping. 
         FIG. 12  is a diagram illustrated to describe an overview of beam sweeping. 
         FIG. 13  is a schematic sequence diagram illustrating an example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to the present embodiment. 
         FIG. 14  is a schematic sequence diagram illustrating an example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to a first modification. 
         FIG. 15  is a schematic sequence diagram illustrating another example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to the first modification. 
         FIG. 16  is a schematic sequence diagram illustrating another example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to the first modification. 
         FIG. 17  is a schematic sequence diagram illustrating an example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to a second modification. 
         FIG. 18  is a flowchart illustrating an example of a processing procedure in a base station  100  in the communication system according to the second modification. 
         FIG. 19  is a schematic sequence diagram illustrating an example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to a third modification. 
         FIG. 20  is a schematic sequence diagram illustrating another example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to the third modification. 
         FIG. 21  is a block diagram illustrating a first example of a schematic configuration of an eNB. 
         FIG. 22  is a block diagram illustrating a second example of the schematic configuration of the eNB. 
         FIG. 23  is a block diagram illustrating an example of a schematic configuration of a smartphone. 
         FIG. 24  is a block diagram illustrating an example of a schematic configuration of a car navigation apparatus. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a preferred embodiment of the present disclosure will be described in detail with reference to the appended drawings. Note that, in this specification and the appended drawings, structural elements that have substantially the same function and structure are denoted with the same reference numerals, and repeated explanation of these structural elements is omitted. 
     Note. that description will be provided in the following order.
         1. Configuration example   1.1. Configuration example of system   1.2. Configuration example of base station   1.3. Configuration example of terminal apparatus   2. MBMS   3. Technical features   4.1. Application examples   4.1. Application examples for base station device   4.2. Application examples for terminal apparatus   5. Concluding remarks       

     1. Configuration Example 
     1.1. Configuration Example of System 
     An example of a schematic configuration of a system  1  according to an embodiment of the present disclosure is now described with reference to  FIG. 1 .  FIG. 1  is a diagram illustrated to describe an example of a schematic configuration of the system  1  according to an embodiment of the present disclosure. As illustrated in  FIG. 1 , the system  1  includes a wireless communication apparatus  100 , a terminal apparatus  200 , and an MEC server  300 . The terminal apparatus  200  herein is also called a user. The user can also be called a UE. In other words, the above-described UE  200  can correspond to the terminal apparatus  200  illustrated in  FIG. 1 . The wireless communication apparatus  100 C is also called UE-relay. The UE herein can be a UE defined in LTE or LTE-A, and the UE-relay can be the Prose-UE-to-Network relay, which is under development in 3GPP and can refer to more typically communication equipment. 
     (1) Wireless Communication Apparatus  100   
     The wireless communication apparatus  100  is an apparatus that provides a subordinate device with a wireless communication service. In one example, the wireless communication apparatus  100 A is a base station of a cellular system (or a mobile communication system). The base station  100 A establishes wireless communication with a device located within a cell  10 A (e.g., the terminal apparatus  200 A) of the base station  100 A. In one example, the base station  100 A transmits a downlink signal to the terminal apparatus  200 A and receives an uplink signal from the terminal apparatus  200 A. 
     The base station  100 A establishes a logical connection with other base statons over, in one example, the X2 interface, and is capable of transmitting and receiving control information or the like. In addition, the base station  100 A establishes a logical connection with a core network  40  over, in one example, the S1 interface, and is capable GT transmitting and receiving control information or the like. Moreover, communication between these apparatuses can be relayed through various devices physically. 
     In this description, the wireless communication apparatus  100 A illustrated in  FIG. 1  is a macrocell base station, and the cell  10  is a macrocell. On the other hand, the wireless communication apparatuses  100 B and  100 C are master devices that operate the small cells  10 B and  10 C, respectively. As an example, the master device  100 B is a fixedly installed small cell base station. The small cell base station  100 B establishes a wireless backhaul link with the macrocell base station  100 A and establishes an access link with one or more terminal. apparatuses (e.g., the terminal apparatus  200 B) within the small cell  10 B. Moreover, the wireless communication apparatus  100 B can be a relay node defined by 3GPP. The master device  100 C is a dynamic access point (AP). The dynamic AP  100 C is a mobile device that dynamically operates the small cell  10 C. The dynamic AP  100 C establishes a wireless backhaul link with the macrocell base station  100 A and establishes an access link with one or more terminal apparatuses (e.g., the terminal apparatus  200 C) within the small cell  10 C. The dynamic AP  100 C can be, in one example, a terminal apparatus equipped with hardware or software operable as a base station or a wireless access point. In this case, the small cell  10 C is a dynamically configured localized network (virtual cell). 
     The cell  10  can he operated, in one example, in accordance with any wireless communication scheme such as LTE, LTE-Advanced (LTE-A), GSM (registered trademark), UMTS, W-CDMA, CDMA200, WiMAX, WiMAX2, IEEE802.16, and the like. 
     Moreover, the small cell is a concept that can include various types of cells (e.g., such as femtocells, nanocells, picocells, and microcells) that are smaller than the macrocell and are arranged to overlap or not to overlap with the macrocell. In one example, a small cell is operated by a dedicated base station. In another example, a small cell is operated by a terminal acting as a master device that temporarily operates as a small cell base station. It is also possible for a so-called relay node to be considered as a form of small cell base station. A wireless communication. apparatus functioning as a master station of a relay node is also called a donor base station. The donor base station can mean a DeNB in LTE, and can more generally refer to a master station of a relay node. 
     (2) Terminal Apparatus  200   
     The terminal apparatus  200  is capable of performing communication in a cellular system (or a mobile communication system). The terminal apparatus  200  performs wireless communication with a wireless communication apparatus of the cellular system (e.g., the base station  100 A and the master device  100 B or  100 C). In one example, the terminal apparatus  200 A receives a downlink signal from the base station  100 A and transmits an uplink signal to the base station  100 A. 
     (3) Application Server  60   
     An application server  60  is a device that provides a user with a service. The application server  60  is connected to a packet data network (PDN)  50 . On the other hand, the bae station  100  is connected to the core network  40 . The core network  40  is connected to the PDN  50  via a gateway device (P-GW in  FIG. 8 ). Thus, the wireless communication apparatus  100  provides the MEC server  300  and the user with the service provided by the application server  60 , via the packet. data network  50 , the core network  40 , and the wireless on channel. 
     (4) NEC Server  300   
     The MEC server  300  is a service-providing device that provides a user with a service (such as application and content). The MEC server  300  can he provided in the wireless communication apparatus  100 . In this case, the wireless communication apparatus  100  provides the user with the service provided by the MEC server  300  via the wireless communication channel. The MEC server  300  can be implemented as a logical functional entity or can be configured integrally with the wireless communication apparatus  100  or the like as illustrated in  FIG. 1 . 
     In one example, the base station  100 A provides the terminal apparatus  200 A connected. to the macrocell  10  with the service provided by the MEC server  300 A. In addition, the base station  100 A provides the terminal apparatus  200 B connected to the small cell  10 B, via the master device  100 B, with the service provided by the MEC server  300 A. 
     Further, the master device  100 B provides the terminal apparatus  200 B connected to the small  10 B with the service provided by the MEC server  300 B. Similarly, the master device  100 C provides the terminal apparatus  200 C connected to the small cell  10 C with the service provided by the server  300 C. 
     (5) Supplement 
     Although the schematic configuration of the system  1  is described above, the present technology is not limited to the example illustrated in  FIG. 1 . Examples of the configuration of the system  1  can employ a configuration with no master device, a configuration of a small cell enhancement (SCE), a configuration of a heterogeneous network (HetNet), a configuration of a machine-type communication (MTC) network, or the like. 
     1.2. Configuration Example of Base Station 
     A configuration of the base station  100  according to an embodiment of the present disclosure is now described with reference to  FIG. 2 .  FIG. 2  is a block diagram illustrating an example of a configuration of the base station  100  according to an embodiment of the present disclosure. Referring to  FIG. 2 , the base station  100  includes an antenna unit  110 , a wireless communication unit  120 , a network communication unit  130 , a storage unit  140 , and a processing unit  150 . 
     (1) Antenna Unit  110   
     The antenna unit  110  radiates a signal output by the wireless communication unit  120  into space as a radio wave. In addition, the antenna unit  110  converts a radio wave in space into a signal and outputs the signal to the wireless communication unit  120 . 
     (2) Wireless Communication Unit  120   
     The wireless communication unit  120  transmits and receives a signal. In one example, the wireless communication unit  120  transmits a downlink signal to a terminal apparatus and receives an uplink signal from a terminal apparatus. 
     (3) Network Communication Unit  130   
     The network communication unit  130  transmits and receives information. In one example, the network communication unit  130  transmits and receives information to and from other nodes. In one example, the above-mentioned other nodes nodes include other base stations and core network nodes. 
     Moreover, as described above, in the system  1  according to the present embodiment, the terminal apparatus operates as a relay terminal to relay communication between a remote terminal and a base station in some cases. In such a case, in one example, the wireless communication apparatus  100 C corresponding to the relay terminal is not necessarily provided with the network communication unit  130 . 
     (4) Storage Unit  140   
     The storage unit  140  temporarily or permanently stores various data and a program necessary for operating the base station  100 . 
     (5) Processing Unit  150   
     The professing unit  150  allows the base station  100  to perform various functions. The processing unit  150  includes a communication control unit  151 , an information acquisition unit  153 , and a notification. unit  155 . Moreover, the processing unit  150  can further include other components than these components. In other words, the processing unit  150  can perform other operations than the operations of these components. 
     The operations of the communication control unit  151 , the information acquisition unit  153 , and the notification unit  15 . 5  will be described later in detail. 
     1.3. Configuration Example of Terminal Apparatus 
     An example of a configuration of the terminal apparatus  200  according to an embodiment of the present disclosure is now described with reference to  FIG. 3 .  FIG. 3  is a block diagram illustrating an example of a configuration of the terminal apparatus  200  according to an embodiment of the present disclosure. As illustrated in  FIG. 3 , the terminal apparatus  200  includes an antenna unit  210 , a wireless communication unit  220 , a storage unit  230 , and a processing unit  240 . 
     (1) Antenna Unit  210   
     The antenna unit  210  radiates a signal output by the wireless communication unit  220  into space as a radio wave. In addition, the antenna unit  210  converts a radio wave in space into a signal and outputs the signal to the wireless communication unit  220 . 
     (2) Wireless Communication Unit  220   
     The wireless communication unit  220  transmits and receives a signal. In one example, the wireless communication unit  220  receives a downlink signal from a base station and transmits an uplink signal to a base station. 
     Further, as described above, in the system  1  according to the present embodiment, the terminal apparatus can operate as a relay terminal to relay communication between a remote terminal and the base station in some cases. In such a case, in one example, the wireless communication unit  220  in the terminal apparatus  200 C operating as a remote terminal can transmit and receive a side-link signal to and from the relay terminal. 
     (3) Storage Unit  230   
     The storage unit  230  temporarily or permanently stores various data and a program necessary for operating the terminal apparatus  200 . 
     (4) Processing Unit  240   
     The processing unit  240  allows the terminal apparatus  200  to perform various functions. For example, the processing unit  240  includes a communication control unit  241 , an information acquisition unit  243 , a measuring unit  245 , and a notification unit  247 . Moreover, the processing unit  240  can further include other components than these components. In other words, the processing unit  240  can perform other operations than the operations of these components. 
     The operations of the communication control unit  241 , the information acquisition unit  243 , the measuring unit  245 , and the notification unit  247  will be described later in detail. 
     2. MBMS 
     A description of MBMS is now given. The MBMS is a technique for delivering content such as text, music, still images, and moving images to each terminal apparatus using a wireless network and is officially referred to as “multimedia broadcast multicast services”. Moreover, a description of an overview of broadcast and multicast is given below to make the characteristics of the communication system according to an embodiment of the present disclosure easier to understand. 
     The broadcast is a unidirectional point-to-multipoint downlink transmission. The broadcast is unnecessary to communicate with a network in providing the service, even in a power-saving state not connected to the network, such as a so-called “RRC idle” state, the terminal apparatus is capable of receiving the delivery of a broadcast service. In other words, the terminal apparatus is capable of, even in the RRC idle state, receiving content that is broadcast from the base station and presenting the content to the user. 
     The multicast is similar to the broadcast in that it provides a plurality of terminal apparatuses with a service. However, the multicast differs from the broadcast in that the terminal apparatus, upon receiving a service, is necessary to indicate to the network that the terminal apparatus attempts to receive the service. In other words, in the multicast, the terminal apparatus necessitates communication with the network to receive a service. 
     Moreover, in 5G, a high frequency of 6 GHz or more is usable, but a high-frequency band has higher propagation loss. Thus, to compensate for propagation loss, a higher antenna gain is obtained by giving directivity to radio waves (wireless signals) by beam forming. For this reason, the directivity is directed to a particular terminal apparatus by beam forming, so it is desirable to indicate that the terminal apparatus desires to receive the service corresponding to MBMS. In other words, in applying MBMS to the 5G mobile communication system, it is more important to implement the delivery of content by multicast. Moreover, in the following description, the service corresponding to MBMS is also referred to as “MBMS service”. 
     (MBMS Network Architecture) 
     An overview of the MBMS network architecture is now described with reference to  FIG. 4 .  FIG. 4  is a diagram illustrated to describe an overview of the MBMS network architecture. 
     As illustrated in  FIG. 4 , the MBMS network architecture includes a core network (CN) and a radio access network (RAN). In addition, the CN includes various entities. Examples of the entities included in the CN include mobility management entity (MME), home subscriber server (HSS), serving gateway (S-GW), packet data network gateway (P-GW), MBMS gateway, broadcast multicast service center (BM-SC), content server, and the like. In addition, in the MBMS network architecture, an example on the side of the RAN includes multi-cell/multicast coordination entity (MCE). Moreover, among these entities, MCE, MBMS gateway, BM-SC, and content server are entities specific to MBMS, and the other entities are similar to the entities used for unicast communication in LTE. In addition, the content to be provided in the MBMS service can be provided from inside the operator&#39;s network or can be provided from the Internet network. Moreover, an entity in the CN (particularly, an MBMS gateway or a BM-SC) corresponds to an example of an “upper node” of the base station. In addition, the MME corresponds to an example of a “predetermined node that manages a session”. 
     An overview of each of the entities specific to the MBMS, that is, the MCE, the MBMS gateway, the BM-SC, and the content server is now described. 
     (MCE) 
     A description of MCE is first given. As illustrated in  FIG. 4 , the MCE is classified as an entity on the side of the PAN. The MCE can be located in each base station (eModeB) or can be located outside the base station. Examples of the role of the MCE include three functions of “allocation of time and frequency resources for MBMS”, “decision of modulation and coding scheme (MOS)”, and “counting function”. Moreover, the MCS corresponds to a modulation scheme or coding rate. In addition, the counting function corresponds to a function of collecting how much the user is interested in the service. The counting function makes it possible, in one example, for the base station to allocate time and frequency resources for MBMS or stop the allocation depending on the number of interested users (i.e., the number of terminal apparatuses desiring to deliver content). 
     Moreover, in LTE, an omnidirectional beam is used, so it is difficult to control the MCS individually for each terminal apparatus. On the other hand, in 5G, it is possible to allocate a beam individually to each terminal apparatus, so in one example, it is also possible to provide content (e.g., content corresponding to MBMS) using different MCSs for each terminal apparatus. 
     In other words, in 5G, in one example, a situation can be assumed in which an MBMS service is provided to each terminal apparatus using a UE-specific beam. Even in a case where the handling between the base station and the terminal apparatus is used like unicast (strictly speaking, it is multicast because similar content is delivered to a plurality of terminal apparatuses), the content is delivered using multicast (multicast for the IP layer) between the content server and the base station. Thus, a function called counting is important to specify which base station to perform multicasting. 
     For reference, an example of the existing procedure for performing the counting is now described with reference to  FIG. 5 .  FIG. 5  is a diagram illustrated to describe an example of a procedure for performing counting. 
     As illustrated in  FIG. 5 , at first, an MCE  400  transmits an MBMS service counting request to the base station  100  (S 101 ). The base station  100  receives the MBMS service counting request from the MCE  400  and replies an MBMS service counting response to the MCE  400  (S 103 ). Then, the base station  100  transmits an MBMS service counting request to the terminal apparatus  200  (S 105 ). The terminal apparatus  200  receives the MBMS service counting request from the base station  100  and replies an MBMS service counting response to the base station  100  (S 107 ). Then, the base station  100 , when receiving the MBMS service counting response from the terminal apparatus  200 , transmits an MBMS service results report to the MCE  400  (S 109 ). The procedure as described above makes it possible for the MCE  400  to recognize the number of terminal apparatuses that desire to provide the MBMS service, in one example, on the basis of the report (the MBMS service results report) transmitted from the base station  100 . 
     (MBMS Gateway) 
     Subsequently, a description of the MBMS gateway is given. As illustrated in  FIG. 4 , the MBMS gateway is an entity located in the CN. The MBMS gateway has a function of sending a packet to a corresponding base station (eNodeB) using Internet protocol (IP) multicast address as a key. In LTE, MBMS is assumed only to use broadcast and does not support multicast. This means that the service does not support multicast. On the other hand, multicast is used for the IP layer. Specifically, in order for the service to be broadcast to a plurality of terminal apparatuses, the previous signaling between the plurality of base stations and the MBMS gateway allows at least some of the base stations to be specified and to be transferred only to the specified base station. Thus, a multicast address is used in the IP layer. 
     In one example,  FIG. 6  is a diagram illustrating an example of a protocol stack of the M1 interface between the MBMS gateway and the base station. Among the protocols illustrated in  FIG. 6 , the layers of DASH, HTTP, TPC/UDP, and IP located on the upper side are not explicitly described in the standard, but it is presumed that the configuration illustrated in  FIG. 6  will be obtained in a case similar to the ordinary unicast. In addition, the layers of GTPv1-U, UDP, IP, L2, and L1 located on the lower side are similar to the S1 interface in the unicast. Moreover, the IP layer used to transfer a packet to a plurality of base stations on the basis of the multicast address is an IP layer located on the lower side. 
     In LTE, as described above, a packet is multicast from the MBMS gateway to a plurality of base stations, and the plurality of base stations transmit packets received in synchronization with each other to a terminal apparatus through wireless communication. On the other hand, in 5G, an MBMS service is provided to each terminal apparatus using a UE-specific beam. Thus, a cache function is provided for the base station, and the terminal apparatus is capable of optionally selecting the time for receiving the MBMS service within a certain fixed period. 
     In 5G MBMS, caching of the content corresponding to MBMS (hereinafter also referred to as “MBMS content”) in a base station makes it possible to provide a terminal apparatus with a service more flexibly, resulting in expecting an effect of further reducing the CN traffic. In addition, it is possible to further reduce resource consumption by MBMS on the side of RAN, by transmitting content for each terminal apparatus using the UE-specific beam instead of transmitting content by the existing broadcast or multicast on the side of RAN. 
     (BM-SC) 
     Subsequently, a description of BM-SC is given. The BM-SC corresponds to the entry point of MBMS content. The BM-SC has the functions as described below. As the first function, the BM-SC performs MBMS session management. Specifically, the BM-SC manages the start and end of the MBMS service. As the second function, the BM-SC allocates an ID called a temporary mobile group identity (TMGI) to each MBMS session. As the third function, the BM-SC allocates QoS to an MBMS session. As the fourth function, the BM-SC provides the terminal apparatus with information regarding broadcasting such as a program guide at the application level (TS29.061). 
     In LTE, the MBMS traffic and the unicast traffic are separated into sub frames. Specifically, a radio frame having a length of 1 ms is divided into ten sub frames having a length of 0.1 ms, and an MBMS service is provided in some of the sub frames. Thus, MBMS and unicast are separate networks, and even if the unicast traffic increases, the situation where the MBMS traffic is affected is extremely limited, in one example, as in the case or the like where the sub frames allocated to MBMS are semi-statically changed. In a case where the MBMS service is provided by unicast using a UE-specific beam, it can be assumed that there is a possibility that at least one of the ordinary unicast or the unicast of the MBMS service affects the other. 
     (Content Server) 
     Subsequently, a description of the content server is given. The content server is a server that provides content. The content server can be located both inside and outside the operator&#39;s network. 
     (Session Start Procedure) 
     Subsequently, an example of an MBMS session start procedure in LTE is described for reference to make the characteristics of the communication system according to the present embodiment more understandable. In one example,  FIG. 7  is a sequence diagram illustrating an example of the MBMS session start procedure in LTE. 
     As illustrated in  FIG. 7 , the MBMS session start procedure starts from an MB-SC. Specifically, at first, an MB-SC  460  transmits a request to start (Start Request) an MBMS session to an MBMS gateway  440  (S 121 ). In this case, in one example, information such as a service area, QoS, and a mobile group identity (MGI) is notified through the request. The MBMS gateway  440  replies a response to the request (Start Response) from the MB-SC  460  (S 123 ). 
     Subsequently, the MBMS gateway  440  transmits a request to start (Start Request) the MBMS session to the MME  420  (S 12 S). The MME  420 , when receiving the request from the MBMS gateway  440 , transmits a request to start (Start Request) an MBMS session to the MCE  400  (S 127 ). The MCE  400 , when receiving the request from the MME  420 , replies a response (Start Response) to the MME  420  (S 129 ). The MME  420 , when receiving the response from the MCE  400 , replies, to the MBMS gateway  440 , a response (Start Response) to the request from the MBMS gateway  440  (S 131 ). 
     Subsequently, the MCE  400  transmits a request to start (Start Request) the MBMS session to the base station  100  that is the service area (S 133 ), In addition, the MCE  400  notifies the base station  100  of information regarding the schedule of the MBMS session (Scheduling Info) (S 135 ). The base station  100  replies, to the MCE  400 , a response (Start Response) to the request from the MCE  400  (S 137 ). In addition, the base station  100 , when receiving the notification of the information regarding the schedule of the MBMS session from the MCE  400 , replies a response (Scheduling Info Response) to the MCE  400  (S 139 ). 
     Subsequently, the base station  100 , on the basis of the information notified from the MCE  400 , transmits an MCCH change notification to the terminal apparatus  200  within the communication range (S 141 ) and then transmits MCCH/MCH/PMCH to the terminal apparatus  200  (S 143 ). Moreover, the details of MCCH, MCH, and PMCH will be separately described later. 
     Subsequently, the target MBMS content is transferred from the MB-SC  460  to the MBMS gateway  440 , and the MBMS content is IP multicast from the MBMS gateway  440  to the base station  100  (S 145 ). The base station  100 , when receiving the MBMS content from the MBMS gateway  440 , transmits MCCH/MCH/PMCH to the terminal apparatus  200 . In other words, the base station  100  broadcasts the received MBMS content (S 147 ). 
     The example of the MBMS session start procedure in LTE is described above with. reference to  FIG. 7  On the other hand, there is a possibility that, in 5G NB, a procedure for starting a session from the terminal apparatus is added to the existing session start procedure. This is because it s possible to change the content delivery time for each terminal apparatus in the MBMS service provided using the UE-specific beam. 
     (Radio Access Network of MBMS) 
     Subsequently, the characteristics of the MBMS in the RAN now described. 
     (1) Logical Channel for MBMS 
     The multimedia broadcast multicast service (MBMS) is provided over two logical channels of multicast transport channel (MTCH) and multicast control channel (MCCH). These two channels are mapped to PMCH (PHY Multicast Channel) as physical channels. In the PMCH, both the MCCH and the MTCH are sent, and scheduling information for mapping between the MBMS session and the PMCH generated as MAC signaling is also sent. This Mac signaling is sent in the header of the PMCH. 
     (2) Physical Channel for MBMS 
     The PMCH uses a cyclic prefix having a relatively long CP length called extend CP. This is to constitute a single-frequency network for combining signals from a plurality of base stations. In LTE, one radio frame has 10 sub frames of which sub frames in which MBMS single-frequency network (MBSFN) is usable are designated semi-statically to be used. In one example,  FIG. 8  illustrates an example of a frame structure in a case of using the MBMS. In  FIG. 8 , the marked sub frames schematically show sub frames in which the MBSFN is usable. In addition, the marked frames schematically show a frame including a sub frame in which the MBSFN is usable. 
     Some of the sub frames for MBSFN are used for PDCCH and PDSCH, but the PDCCH is used not for MBMS but for transmission of uplink scheduling information necessary for ordinary unicast traffic. Thus, the PDSCH portion in the sub frames for MBSFN is used for MBMS, and the PMCH is transmitted by the PDSCH. 
     (3) MBMS Session 
     In the present disclosure, one program is also referred to as an MBMS session. In this case, the MBMS session is mapped to the PMCH (PHY Multicast Channel) that is the physical channel. In addition, the PMCH is mapped to a sub frame allocated for the MBMS. 
     (4) MBMS Service Area 
     The MBMS service area corresponds to an area where one MBMS service is provided. In addition, the MBSFN area corresponds to an area that constitutes a single-frequency network (SFN). In the MBSFN area, it is possible, to set up to eight areas for one base station. In a case where the SFN is configured, a plurality of base stations cooperates and transmits the same content. 
     Moreover, in 5G, it can be assumed that the MBMS session is provided to each terminal apparatus using the UE-specific beam. In the existing MBMS, the SFN technology described later is used, so it is not necessary to consider handover. On the other hand, in 5G, a mechanism corresponding to the MBMS handover is necessary due to the above-described characteristics. Thus, in one example, it can be necessary to notify the number of the MBMS session from the switching source base station to the switching destination base station. In this description, in a case where a beam necessary for beam recovery is provided from another base station (e.g., a base station in an adjacent cell), it is also possible to reduce the latency by including the MBMS session in a beam recovery request. 
     (5) SFN 
     The single-frequency network (SFN) is the technology in which the same signal is transmitted simultaneously at the same time and frequency from a plurality of base stations (eNodeBs) and the plurality of downlink signals is regarded as a reflected wave within the range of the cyclic prefix (CP), combined, and received, resulting in improving the signal strength. In the case of broadcasting, a wide reception range of the terminal apparatus is necessary, so the SFN can he used in some cases. 
     (6) MBMS Scheduling 
     In some cases, it is difficult for a terminal apparatus to receive a program without knowing where the base station (eNodeB) transmits the program. In such a case, the terminal apparatus is necessary to acquire scheduling information (i.e., information indicating where transmission is being performed). 
     The scheduling is performed in accordance with the procedure described below. The details of each procedure are described below with reference to  FIG. 9 .  FIG. 9  is a diagram illustrated to describe an overview of information associated with an MBMS session.
         Specifying radio frame and sub frame   MBSFN area configuration   Specifying MBMS session       

     (Specifying Radio Frame and Sub Frame) 
     The location of the MCCH is specified in the SIB 13 of the system information. Specifically, the location of a radio frame including the MCCH is specified by a period and an offset. Furthermore, it is specified which sub frame in each radio frame includes the MCCH. The location of the MCCH is actually the PMCH, so the MCCH is transmitted in the PDSCH portion of the MBSFN sub frame. 
     (MBSFN Area Configuration) 
     The MCCH includes the MBSFN area configuration. The MBSFN area configuration specifies which sub frame where the MBSFN is performed. The specifying of the sub frame is settable by a period and an offset of a radio frame. In this case, it is possible to set simultaneously eight types of different periods and offsets for the specifying of the sub frame. In addition, which sub frame in the radio frame is used is also set. Such an operation allows a sub frame usable for MBMS to be determined. In the sub frames for MBMS determined as described above, how to allocate the PMCH is also specified. The PMCH can set up to 16 channels 
     (Specifying of MBMS Session) 
     It is possible to set up to 30 MBMS sessions (i.e., programs) for 16 PMCHs determined as described above. As a specific example, MBMS sessions 0 and 1 can be set for PMCH0, and MBMS sessions 2, 3, 4, 5, and 6 can be set for PMCH1. 
     How to map the MBMS session to the PMCH is specified using the Mac signaling sent by the PMCH. The Mac signaling is a kind of RPC signaling in the SIB13, so it is said that the MBMS scheduling is performed by a combination of RPC signaling and Mac signaling. 
     In 5G, it is conceivable that the MBMS session can be provided to each terminal using the UE-specific beam. In this case, the SFN is not necessary to be used, and there is a possibility that the terminal apparatus is able to receive the delivery of television broadcast at the desired time. The content that is broadcast in the MBMS session is transmitted from the EM-SC to each base station (eNodeB) via the MBMS gateway. This content can be provided as a broadcast to the terminal apparatus at a time desired by the terminal apparatus as long as the content is held as a cache in the base station. In a case where the cache capacity has a physical limit, the expiration date can be given to the information of the MBMS session disclosed in the SIB. The location where the existing MBMS session is provided is disclosed on the PMCH specified by the information of the radio frame and sub frame and the location of the PMCH in the sub frame. On the other hand, in the case where the MBMS service is provided using the beam, it is also possible to disclose the information of the MBMS session as follows.
         Disclosure is performed as before by system information embedded in performing beam forming during beam management. Moreover, beam management is a procedure for identifying an appropriate beam between a base station and a terminal apparatus.   In a procedure after determining an appropriate beam between a base station and a terminal apparatus, the provision of MBMS information is notified on the downlink control channel (DCI).       

     (7) Entity for Receiving MBMS 
     The above-mentioned MBMS service can be provided to both the terminal apparatus in the RRC idle mode and the terminal apparatus in the RRC connected mode. Thus, it is also possible for a terminal in the RRC idle mode to receive the various information described above. 
     (8) MCS (Modulation Scheme) used in MBMS 
     As described above in connection with the network architecture, in the existing MBMS in LTE, the MCS can be changed by the MCE, but it is the broadcasting, so the frequency to be changed is small. Thus, in the existing MBMS in LTE, in one example, a common MCS that is preset for all terminal apparatuses is used. 
     On the other hand, in 5G, it is conceivable that the MBMS session is provided to each terminal apparatus using a UK-specific beam. In such a case, it is possible to provide the MBMS service by changing the MCS between the base station and the terminal apparatus. Furthermore, in a case where the beam is blocked by an obstacle such as a person or a car located between the base station and the terminal apparatus, it is necessary, in some cases, to switch the beam used for communication into that from another base station. In such a case, there is a possibility that an MCS different from the MCS used in the beam before the switching is used for the beam after the switching, and it can be assumed that the MCS before and after the switching is discontinuous. 
     (9) Feedback Information from Terminal Apparatus 
     The feedback information from a terminal apparatus is not specified in the MBMS in LTE at present. There is the mixed mode in which both ordinary LTE and MBMS are operated, but even in this case, feedback regarding the MBMS is not specified as a standard. 
     3. Technical Features 
     Technical features of the communication system according to an embodiment of the present disclosure are now described. 
     (Basic Configuration) 
     A basic configuration of the communication system according to an embodiment of the present disclosure is first described. In 5G, the beam forming technique that enables the concentration of radio wave energy in a particular direction is used to compensate for attenuation of radio wave propagation of a relatively high frequency in the 6 GHz to 100 GHz range. In a situation where a beam is emitted in a particular direction by applying the beam forming technique in this way, the number of terminal apparatuses existing within the range of the beam is considerably limited. In addition, among the limited terminal apparatuses that are present, in the area covered by the beam, the number of terminal apparatuses desiring to deliver the same program is also considerably limited. 
     Thus, in the 5G MBMS, the broadcasting content is transmitted to each base station by multicast during transmission in the core network, and in the subsequent radio access network (RAN), the broadcasting content (i.e., MBMS service) is provided to the terminal apparatus by multicast using a UE-specific beam (i.e., transmission by specifying a destination). 
     The procedure for delivering the MBMS content to the terminal apparatus by multicast, the MBMS content (i.e., the broadcasting content) transmitted by multicast to the base station using a UE-specific beam is, in one example, as follows. 
     The procedure for transmitting the MBMS content to the base station is similar to the procedure in LTE described with reference to  FIG. 7 . In this description, for the MBMS content transmitted from the MS-SC  460  to the base station  100  via the MBMS gateway  440 , the information indicating that the base station  100  is deliverable is provided from the base station  100  to the terminal apparatus  200  as system information. Moreover, the information indicating that the base station  100  is capable of delivering the MBMS content is provided to the terminal apparatus  200  after or before transmission of the MBMS content to the base station  100 . 
     The procedure of the communication system according to the present disclosure differs from the procedure in LTE described with reference to  FIG. 7  in that the base station  100  may necessarily not immediately deliver the multicast MBMS content to the terminal apparatus. An example of a procedure for providing a program to each terminal apparatus using a directional beam in the communication system according to an embodiment of the present disclosure is now described with reference to  FIG. 10 .  FIG. 10  is a schematic sequence diagram illustrating an example of a procedure for providing a program to each terminal apparatus using a directional beam in the communication system according to an embodiment of the present disclosure. Moreover, in  FIG. 10 , the steps denoted by reference numerals S 151  to S 169  are substantially similar to the steps denoted by reference numerals S 121  to S 139  in  FIG. 7 , respectively, and so detailed description thereof is omitted. 
     In a case where the target MBMS content is transferred (IP multicast) from the MB-SC  460  to the MBMS gateway  440 , the: MBMS content is IP multicast from the MBMS gateway  440  to the base station  100  (S 173 ). The base station  100  (the: notification unit  155 ) can provide the terminal apparatus  200  with information regarding the MBMS content using the system information before the MBMS content is IP multicast from the MBMS gateway  440  (S 171 ). In addition, as another example, the base station  100  (the notification unit  155 ) can provide the terminal apparatus  200  with information regarding the MBMS content using the system information after the MBMS content is IP multicast from the MBMS gateway  440  (S 175 ). 
     As described above with reference to  FIG. 10 , the base station  100  (the notification unit  155 ) notifies information indicating what kind of program (i.e., MBMS content) the relevant base station  100  can provide to the terminal apparatus  200  using information that is commonly notified to a plurality of terminal apparatuses  200 , such as system information. The system information is provided as a broadcast signal that all terminal apparatuses are receivable in the RRC idle state during beam sweeping. 
     An overview of beam sweeping is now described with reference to  FIGS. 11 and 12 .  FIGS. 11 and 12  are diagrams illustrated to describe the overview of beam sweeping. As illustrated in  FIG. 11 , the base station performs beam sweeping using a plurality of beams every predetermined period (e.g., 10 ms or 20 ms) as if it were a lighthouse light. Each beam transmitted by the beam sweeping includes, in one example, synchronization signal that is a signal for synchronization, system information, and the like, as illustrated in  FIG. 12 . Each of a plurality of beams transmitted from one base station by one time of beam sweeping (i.e., a plurality of beams belonging to the beam sweeping) includes system information indicating common contents. This is because it is not necessary to change the contents of system information for each beam due to the characteristics of providing information to an unspecified number of terminal apparatuses. Thus, information common to each beam is provided as information regarding the MBMS session provided in association with the system information (MBMS) session information). Moreover, although an example in which a beam including synchronization information is used is described above, in a case where the beam is used to provide common. information to a plurality of terminal apparatuses such as system information, the beam may not necessarily include a synchronization signal. 
     An example of a procedure for providing a program to each terminal apparatus using a directional beam in the communication system according to an embodiment of the present disclosure is now described in more detail with reference to  FIG. 13 .  FIG. 13  is a schematic sequence diagram illustrating an example of a procedure for providing a program to each terminal apparatus using a directional beam in the communication system according to an embodiment of the present disclosure. Moreover, in  FIG. 13 , the steps denoted by reference numerals S 201  to S 225  are similar to the steps denoted by reference numerals S 151  to S 175  in  FIG. 10 , respectively, and so detailed description thereof is omitted. 
     As illustrated in  FIG. 13 , the terminal apparatus  200  (the notification unit  247 ) delivers an MBMS session request to the MME  420  on the side of a network for the MBMS content desired to be delivered, on the basis of the information regarding the MBMS session associated with the system information (e.g., information regarding the MBMS session that is capable of being provided by the base station  100 ) (S 227 ). The HME  420 , when receiving the MBMS session request from the terminal apparatus  200 , replies an MBMS session confirmation to the terminal apparatus  200  (S 229 ). Moreover, it is possible for the communication between the terminal apparatus  200  and the HME  420  to be achieved by, in one example, the non-access stratum (NAS) signaling. 
     Subsequently, the MME  420  transmits an MBMS session start request for the UE to the base station  100  in which the terminal apparatus  200  that is the transmission source of the MBMS session request is placed in the communication range (cell) in response to the MBMS session request (S 231 ). The base station  100 , when receiving the MBMS session start request for the UE from the MME  420 , replies an MBMS session start confirmation for the UE to the MME  420  (S 233 ). Moreover, the MBMS session start request for the UE transmitted to the base station  100  corresponds to an example of a “request for content delivery”. 
     Further, the base station  100  transmits, to the terminal apparatus  200 , various types of information used to identify a beam used for delivering the MBMS content to the terminal apparatus  200  (S 235 ). Examples of the information include information regarding the resource of beam sweeping (hereinafter also referred to as “MBMS beam sweeping”) for delivering the MBMS content (CSI-RS resource configuration) and information regarding the settings for terminal apparatus  200  to report an observation result of a beam transmitted by the beam sweeping (beam report configuration). Then, the base station  100  performs MBMS beam sweeping (S 237 ). 
     The terminal apparatus  200  (measuring unit  245 ) measures a predetermined signal (e.g., a reference signal) in the beam transmitted by the MBMS beam sweeping, and identifies a beam desired for receiving the MBMS content depending on a result of the measurement. Then, the terminal apparatus  200  (notification unit  247 ) reports information corresponding to the result obtained by identifying the beam to the base station  100  (S 239 ). 
     The base station  100  identifies a beam used for delivering the MBMS content to the terminal apparatus  200  in response to the report from the terminal apparatus  200  (S 241 ). Then, the base station  100  (the communication control unit  241 ) delivers (e.g., Multicast) the MBMS content that is previously multicast from the MBMS gateway  440  to the terminal apparatus  200  using the UE-specific beam (i.e., the identified beam) (S 243 ). 
     Moreover, in the example described above, the MBMS content is provided using a beam different from the beam used in ordinary unicast by performing beam sweeping for MBMS and beam reporting for MBMS. This is because it can be assumed that a beam having a wider beam width than the above-mentioned unicast beam is used for providing content (e.g., MBMS content) as a beam for broadcasting. In other words, this is because, in a case where such a condition is assumed, it can be more desirable to obtain a beam for MBMS by a procedure different from a beam used for or unicast. 
     It is natural that a case where it is difficult to use a beam for MBMS separately from a beam for ordinary unicast can be assumed. In such a situation, in a case where there is a beam for unicast being previously in use, the beam can be used for another purpose as a beam for MBMS. In this case, the procedure for newly identifying a beam can be omitted. 
     A description of the difference between a case where unicast is performed in all of a series of paths through which MBMS content is transmitted and a case where MBMS content is transmitted through the series of paths in the communication system according to the present embodiment is now given. Moreover, the case where unicast is performed in all of the series of paths corresponds to, specifically, a case where unicast is used for transmitting MBMS content in both core network (CN) and radio access network (RAN). In the communication system according to the present embodiment as described above, the transmission of MBMS content from the MB-SC to the base station via the MBMS gateway is performed using multicast. Thus, this makes it possible to reduce the amount of signaling for the transmission and reduce an increase in traffic, as compared to a case where the transmission of the MBMS content on the path is performed using unicast. 
     Moreover, it is expected that a new MBMS session request and a beam sweeping procedure dedicated to MBMS are necessary to implement the mechanism as described above. As described above, it can be assumed that different beam widths are set for the ordinary unicast beam and the MBMS beam. Thus, it is desirable to manage the beam for MBMS separately from the beam for ordinary unicast in some cases. Such management can be necessary, even in the case where the terminal apparatus to which the beam for MBMS is once allocated makes a transition to the RRC idle state, so that the beam for MBMS is receivable in the RRC idle state. Moreover, the details of a technique for enabling the terminal apparatus to receive the beam for MBMS in the PRC idle state (i.e., enabling reception of the MBMS content) will be described separately later as a modification. 
     First Modification 
     Subsequently, a modification of the communication system according to an embodiment of the present disclosure is described. Moreover, the present modification is also referred to as a “first modification”. 
     In LTE, it is possible to receive the DL MBMS service without allowing the terminal apparatus to perform signaling to the base station. Thus, in LTE, even in the RRC idle state in which the terminal apparatus is not registered in the base station (i.e., the communication between the terminal apparatus and the base station is not established), it is possible for the terminal apparatus to receive the MBMS content. On the other hand, in the case where the MBMS content is delivered to the terminal apparatus by multicast using a UE-specific beam as described above, the terminal apparatus may be necessary to be in a state registered in the base station, that is, in the RRC connected state. On the other hand, the increase in the number of terminal apparatuses in the RRC connected state may consume the memory area of the base station. In addition, the UL or DL signaling Is necessary to keep the RRC connected state, so there is a possibility to increase the signaling overhead 
     In view of the above situation, the present modification provides the technology enabling the terminal apparatus to keep the beam for MBMS provided in the RRC connected state, even in the case of making the state transition to the RRC idle state. 
     For example,  FIG. 14  is a schematic sequence diagram illustrating an example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to the present modification. Moreover, the procedure illustrated in  FIG. 14  is executed after the provision of MBMS content using a UE-specific beam to a particular terminal apparatus is started by the procedure described with reference to  FIG. 13 . Specifically, the steps denoted by reference numerals. S 301  and S 303  correspond to the steps denoted by reference numerals S 221  and S 223  in  FIG. 13 , respectively. Moreover, the steps denoted by reference numerals S 305  to S 321  correspond to the steps denoted by reference numerals S 227  to S 243  in  FIG. 13 , respectively. Therefore, detailed description of the steps denoted by reference numerals S 301  to S 321  is omitted. 
     As illustrated in  FIG. 14 , after the provision of the MBMS content using the UE-specific beam is started, the terminal apparatus  200  (the notification unit  247 ) transmits a detach request to the MME  420  to make the transition to the RRC idle state. At this time, in the communication system according to the present modification, the terminal apparatus  200  can indicate the intention to continue receiving the provision of the MBMS service using the beam set at this time (that is, receiving the MBMS content) in response to the Detach request (S 323 ). The MME  420 , when receiving the Detach request transmitted from the terminal apparatus  200 , notifies the terminal apparatus  200  that the Detach request is confirmed and the provision of the MBMS service continues (S 325 ). 
     Moreover, a state or mode in which communication used for notification of information from the terminal apparatus  200  to the base station  100 , such as the RRC idle state, is restricted corresponds to an example of a “first mode”. On the other hand, a state or mode in which the communication used for notification of information from the terminal apparatus  200  to the base station  100 , such as the RRC connected state, is established corresponds to an example of a.“second mode”. Moreover, the communication restricted in the first mode corresponds to an example of “first wireless communication”. In addition, as described above, in the communication system according to the present modification, even in the case of making the state transition to the RRC idle state (i.e., the, first mode), the communication for providing the MBMS service is kept in response to the request from the terminal apparatus. The communication kept in response to the request from the terminal apparatus even in the case of making the state transition to the first mode, that is, the communication for providing the MBMS service corresponds to an example of “second wireless communication”. In other words, in the communication system according to the present modification, even in a case where the above-mentioned first wireless communication and second wireless communication are set and make a transition to the first mode (e.g., the RRC idle state), the first wireless communication is restricted. However, the second wireless communication is kept in response to a request from the terminal apparatus. In addition, in the example illustrated in  FIG. 14 , the MME  420  corresponds to an example of a “device that manages a transition between the first mode and the second mode”. 
     Moreover, in the communication system according to the present modification, in order to continue to provide the MBMS service, the control can be performed such that the terminal apparatus  200  makes a transition to the RRC connected state again within a predetermined period (e.g., every hour) and transmits an MBMS session request to the MME  420 . In this case, in one example, in a case where the MME  420  receives the detach request indicating that the terminal apparatus  200  attempts to continue to receive the provision of the MBMS service, the MME  420  starts timing for a predetermined period by a timer (S 327 ). Then, if the MBMS session request is not transmitted from the terminal apparatus  200  before the expiration of the timer (S 329 ), the MME  420  instructs the base station  100  to stop providing the corresponding MBMS service (S 331 ). 
     For the above-described control, in one example, the beam width of the beam used for providing the MBMS service is wider than the beam used for ordinary unicast, the coverage area is relatively wide, and the affinity with the situation where the terminal apparatus  200  moves less (ideally, the terminal apparatus  200  does not move) is high. 
     Moreover, the above description is given focusing on the case where the terminal apparatus  200  makes a transition to the RRC idle state. On the other hand, even in a case where the terminal apparatus  200  makes a transition to the inactive mode, it is also possible to control in such a way that the provision of the MBMS service continues during the relevant mode on the basis of a similar concept to the example described with reference to  FIG. 14 . For example,  FIG. 15  is a schematic sequence diagram illustrating another example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to the present modification. Specifically,  FIG. 15  illustrates an example of a procedure for controlling the provision of the MBMS service to the terminal apparatus to continue even in the case where the terminal apparatus  200  makes a transition to the inactive mode. Moreover, the steps denoted by reference numerals S 351  to S 371  correspond to the steps denoted by reference numerals S 301  to S 321  in  FIG. 14 , respectively. Therefore, detailed description of the steps denoted by reference numerals S 351  to S 371  is omitted. 
     As illustrated in  FIG. 15 , the terminal apparatus  200  (the notification unit  247 ), when making at transition to the inactive mode, transmits an inactive mode request to the base station  200 . At this time, in the communication system according to the present modification, the terminal apparatus  200  can indicate the intention to continue receiving the provision of the MBMS service using the beam set at this time (that is, receiving the MBMS content) in response to the inactive mode request S 373 ). In other words, the terminal apparatus  200  requests the base station  100  to make a transition to a mode in which the operation relating to transmission and reception other than the operation of receiving the provision of the MBMS service (i.e., the reception of the MBMS content) is stopped. The base station  100  (the notification unit  155 ), when receiving the inactive mode request transmitted from the terminal apparatus  200 , notifies the terminal apparatus  200  that the inactive mode request is confirmed and the provision of the MBMS service continues (S 375 ). 
     Further, in the example illustrated in  FIG. 15 , the provision of the MBMS service .o the terminal apparatus  200  that makes a transition to the inactive mode can be managed by a timer on the basis of a similar concept to the example described with reference to  FIG. 14 . In other words, in this case, the base stations  100  (the communication control unit  155 ), when receiving, from the terminal apparatus  200 , the inactive mode request indicating that the user intends to continue to receive the MBMS service, starts timing for a predetermined period using a timer (S 377 ). Then, if the base station  100  (the communication control unit  155 ) does not receive the notification of the MBMS session request from the terminal apparatus  200  via the MME  420  before the expiration of the timer (S 379 ), the base station  100  stops providing the MBMS service to the terminal apparatus  200  (S 361 ). Moreover, in the example illustrated in  FIG. 15 , the inactive mode corresponds to an example of the “first mode”. In other words, in the example illustrated in  FIG. 15 , the base station  100  corresponds to an example of a “device that manages a transition between the first mode and the second mode”. 
     A supplementary description is now given of the case where the signaling from the terminal apparatus to the base station occurs again in the communication system according to the present modification. In one example, even if the terminal apparatus moves less, in some cases, it is desirable to change the modulation and coding scheme (MCS) applied when the terminal apparatus  200  receives the content due to the fluctuation of the channel. Thus, in one example, in a case where the reception quality of the MBMS content (e.g., reference signal received power (RSRP) or reference signal received quality (RSRQ)) fluctuates by a certain value or more, the terminal apparatus can request the base station to change the MCS for the beam used for delivering the relevant MBMS content. Moreover, examples of the index of the reception quality of the MBMS content include the reception power of channel state information reference signal (CSI-RS) included in the beam used for delivering the relevant MBMS content, the amount of interference by other signals, and the like. In addition, the terminal apparatus, when requesting the base station to change the MCS, makes a transition to the RRC connected state. 
     For example,  FIG. 13  is a schematic sequence diagram illustrating another example of a procedure for providing a program to each terminal apparatus using a directional beam in a communication system according to the present modification. Specifically,  FIG. 16  illustrates an example of a procedure for the terminal apparatus  200  to request the base station  100  to change the MCS. Moreover, the steps denoted by reference numerals S 601  to S 621  correspond to the steps denoted by reference numerals S 351  to S 371  in  FIG. 15 , respectively. Therefore, detailed description of the steps denoted by reference numerals S 601  to S 621  is omitted. 
     As illustrated in  FIG. 16 , the terminal apparatus  200  (the notification unit  247 ), when making a transition to the inactive mode, transmits an inactive mode request to the base station  200 . At this time, the terminal apparatus  200  can indicate the intention to continue receiving the provision of the MBMS service using the beam set at this time (that is, receiving the MBMS content) in response to the inactive mode request (S 623 ). This is similar to the example described with reference to  FIG. 15 . Moreover, the terminal apparatus  200  can determine whether or not to be necessary to modify a beam used for providing an MBMS service by using a state that can be determined in response to a wireless signal transmitted from the base station  100  (e.g., the quality of a transmitted beam) as a trigger (S 625 ). 
     The base station  100  (the notification unit  155 ), when receiving the inactive mode request transmitted from the terminal apparatus  200 , notifies the terminal apparatus  200  that the inactive mode request is confirmed and the provision of the MBMS service continues (S 627 ). In addition, the base station  100  (the communication control unit  155 ), when receiving, from the terminal apparatus  200 , the inactive mode request indicating the intention to continue to receive the MBMS service, can start timing for a predetermined period by a timer (S 629 ). These steps are similar to the steps denoted by reference numerals S 375  and S 377  in  FIG. 15 . 
     In this stage, it is assumed that the fluctuation (e.g., decrease in reception quality) of the reception quality (e.g., RSRP/RSPQ) of the MBMS content in the terminal apparatus  200  exceeds a threshold (S 631 ). In this case, the terminal apparatus  200  (the notification unit  247 ) can request the base station  100  to change he MCS for the beam used for delivering the MBMS content by performing beam reporting for a new beam to the base station  100  (S 633 ). 
     The control as described above in the present modification makes it possible for the terminal apparatus to continue to keep the beam for the MBMS provided in the RPC connected state even in the case of making a transition to the RPC idle state or the inactive mode. In other words, the communication system according to the present modification makes it possible to limit the number of terminal apparatuses in the RRC connected state among the terminal apparatuses to which the MBMS content is delivered depending on the conditions. Thus, the communication system according to the present modification makes it possible to reduce the consumption of the memory area of the base station. In addition, in the communication system according to the present modification, it is possible to decrease the UL and DL signaling for keeping the RRC connected state, resulting in expecting an effect of reducing signaling overhead. 
     Second Modification 
     Subsequently, a modification of the communication system according to another embodiment of the present disclosure is described. Moreover, the present modification is also referred to as a “second modification”, 
     In 5G, the beam forming technique, that enables the concentration of radio wave energy in a particular direction is used to compensate for attenuation of radio wave propagation of a high frequency from 6 GHz to 100 GHz. The use of the beam forming technique allows the beam width of a beam emitted in a particular direction to be limited, so the area covered by the beam is limited compared to the case where the beam forming technique is not used. Under such circumstances, the number of terminal apparatuses that present within the range covered by the beam radiated in a particular direction may be more limited than the case where the beam forming technique is not used. In addition, the area covered by the beam is limited, so there is a possibility that the number of terminal apparatuses that desire to deliver the same program among the terminal apparatuses that present in the area can be further limited. In view of such a situation, in the 5G MBMS, a case can be assumed in which a delivery scheme capable of more efficiently delivering the program content (e.g., MBMS content) differs depending on the conditions at each time. Examples of an option of the method of delivering the Program content include broadcast, multicast, unicast, and the like in the past employed in LTE or the like in addition to the multicast using the UP-specific beam described above. Moreover, in the following description, broadcast, multicast, and unicast employed in the past in LTE or the like can be referred to as “ordinary broadcast”, “ordinary multicast”, and “ordinary unicast”, respectively. 
     To apply selectively delivery means that are more suitable from among the above-described examples as delivery means of broadcast content in a radio access network. (RAN), the base station is important, in one example, to recognize which program content is delivered using which beam for each terminal apparatus. For the base station to grasp such a situation, in one example, it is possible to use the above-described. counting function. Moreover, in LTE, a function similar to the, counting function is defined. Specifically in LTE, as described with reference to  FIG. 5 , the MCE  400  collects information from each terminal apparatus  200  by transmitting a counting request to the terminal apparatus  200  via the base station  100 . 
     On the other hand, in the 5G MBMS. only by collecting information regarding a program that each terminal apparatus  200  desires to deliver, it is difficult for the base station to select the delivery means for delivering the content corresponding to the. program in a more suitable manner. In other words, as described above, to apply selectively a more suitable delivery means, in one example, it is important to recognize which program content is delivered using which beam for each terminal apparatus. 
     Moreover, as described above with reference to  FIG. 13 , the base station is capable of recognizing an ID (MBMS session ID) of the MBMS content that the terminal apparatus desires to deliver on the basis of a request (the MBMS session start request for the US) from. the MME in response to the MBMS session request from the terminal apparatus to the MME. In addition, the base station is capable of recognizing a beam used for delivering the MBMS content on the basis of a report (beam report for MBMS beam sweeping) from the terminal apparatus. In other words, the base station is capable of determining whether or not it is possible to merge beam resources used for delivering the MBMS content with, respect to at least some of two or more terminal apparatuses among the plurality of terminal apparatuses by using these pieces of information. 
     The determination by the base station as described above can be achieved by the implementation of the base station. Moreover, in this case, it is important what kind of modulation and coding scheme is used to deliver the broadcast content (MBMS content). The terminal apparatus is capable of notifying what type of modulation and coding scheme is desired to be applied using the channel quality indication (CQI). Moreover, it can be said that the CQI indicates the MCS. Thus, in the following description, it is assumed that the terminal apparatus notifies the base station of what type of MCS (i.e., the modulation and coding scheme) is desired to be applied. 
     In a case where the MCSs are approximately equal among a plurality of terminal apparatuses, in one example, the broadcast content can be provided to each of the plurality of terminal apparatuses by applying the MCS having lower communication quality. On the other hand, even in a case where the direction of the beam allocated to each of the plurality of terminal apparatuses is the same and the programs that each of the plurality of terminal apparatuses desires to deliver are the same, if the difference between the MCSs is large (e.g., the threshold or more), the base on can make a selection not to merge the beams. Moreover, in this case, the MCS corresponds to an example of “wireless communication settings” between the base station and the terminal apparatus. 
     An example of a procedure of a series of processing steps of the communication system according to the present modification is now be described with reference to  FIG. 17 .  FIG. 17  is a schematic sequence diagram illustrating an example of a procedure for providing a program to each terminal apparatus using a directional beam in the communication system according to the present modification. Moreover, in the example illustrated in  FIG. 17 , it is assumed that each of the terminal apparatuses  200 A and  200 B desires to deliver common MBMS content. 
     As illustrated in  FIG. 17 , the base station  100  transmits various types of information (e.g., such as CSI-RS resource configuration or beam report configuration) for identifying a beam used to deliver the MBMS content to the terminal apparatus  200 B, to the terminal apparatus  200 B (S 401 ), and performs the MBMS beam sweeping (S 403 ). The terminal apparatus  200 B measures a predetermined signal (e.g., a reference signal) in the beam transmitted by the MBMS beam sweeping, and identifies a beam desired for receiving the MBMS content depending on a result of the measurement. Then, the terminal apparatus  200 B reports information corresponding to the result obtained by identifying the beam to the base station  100  (S 405 ). In this case, the terminal apparatus  200 B can associate information regarding the MCS desired to be applied at the time of delivering the MBMS content with the report depending on the result of the measurement. 
     Similarly, the base station  100  transmits various types of information for identifying a beam used to deliver the MBMS content to the terminal apparatus  200 A, to the terminal apparatus  200 A (S 407 ), and performs the MBMS beam sweeping (S 409 ). The terminal apparatus  200 A measures a predetermined signal (e.g., a reference signal) in the beam transmitted by the MBMS beam sweeping, and identifies a beam desired for receiving the MBMS content depending on a result of the measurement. Then, the terminal apparatus  200 A reports information corresponding to the result obtained by identifying the beam to the base station  100  (S 411 ). In this case, the terminal apparatus  200 A can associate information regarding the MCS desired to be applied at the time of delivering the MBMS content with the report depending on the result of the measurement. 
     Subsequently, the base station  100  decides whether or not to merge the beams used for delivering the MBMS content to the terminal apparatuses  200 A and  200 B between the terminal apparatuses  200 A and  200 B depending on the report from the terminal apparatuses  200 A and  200 B (S 413 ). Moreover, in this stage, it is assumed that base station  100  decides to merge beams between terminal apparatuses  200 A and  200 B. In addition, an example of the procedure of a series of processing steps relating to the above decision by the base station  100  will be described later in detail. 
     The base station  100 , when deciding to merge beams between the terminal apparatuses  200 A and  200 B, decides the MCS to be applied to the delivery of the MBMS content to each of the terminal apparatuses  200 A and  200 B (S 415 ). In this case, the base station  100  can decide the MCS to be applied to the delivery of the MBMS content to each of the terminal apparatuses  200 A and  200 B, in one example, depending on the information notified from the terminal apparatuses  200 A and  200 B. Then, the base station  100  delivers common MBMS content to each of the terminal apparatuses  200 A and  200 B by using the decided common beam (S 4 I 7 ). 
     Subsequently, an example of the procedure of a series of processing steps for determining whether or not the base station  100  merges beams among the plurality of terminal apparatuses  200  in the example illustrated in  FIG. 17  is described with reference to  FIG. 18 .  FIG. 18  is a flowchart illustrating an example of the procedure of processing of the base station  100  in the communication system according to the present modification and illustrates an example of the procedure of processing for determining whether or not the base station  100  merges beams among a plurality of terminal apparatuses  200 . 
     As illustrated in  FIG. 18 , the base station  100  determines whether or not a plurality of terminal apparatuses  200  desire to deliver content (i.e., MBMS content) for the same MBMS session (S 451 ). In addition, the base station  100  determines whether or not the plurality of terminal apparatuses  200  desire to use the same beam or a beam having approximately equal direction, as the beam used for delivering the content corresponding to the MBMS session (S 453 ). In addition, the base station  100  determines whether or not the plurality of terminal apparatuses  200  desire to deliver the content corresponding to the MBMS session in the approximately equal MCS (S 455 ). In a case where the plurality of terminal apparatuses  200  use, for the content corresponding to the same MBMS session (YES in S 451 ), the same beam or beams having approximately equal direction (YES in S 453 ) and desire the delivery with approximately equal MCS (YES in S 455 ), the base station  100  delivers (broadcast or multicast) the content to the plurality of terminal apparatuses  200  using a common beam (S 457 ). 
     On the other hand, if each of the plurality of terminal apparatuses  200  desires to deliver the content corresponding to different MBMS sessions from each other (NO in S 451 ), the base station  100  delivers individually to each of the plurality of terminal apparatuses  200  using the UE-specific beam (S 4 S 8 ). The same applies to a case where the plurality of terminal apparatuses  200  desire to use different beams as beams used for delivering content corresponding to the MBMS session (NO in S 453 ), or a case where the plurality of terminal apparatuses  200  desire to deliver content corresponding to the MBMS session in different MCSs (NO in S 455 ). 
     A supplementary description is now given of the difference between the case where the MBMS service is provided to a plurality of terminal apparatuses using a common beam (directional beam) as described above and the case where the MBMS service is provided to a plurality of terminal apparatuses using a cell-specific beam. In the case of using the cell-specific beam, the beam does not include control information for each terminal apparatus  200 . On the other hand, in the case where the MBMS service is provided to a plurality of terminal apparatuses using a common beam (UE-specific beam), the beam includes control information for each terminal apparatus  200  individually. In other words, in this case, the settings of the beam are also performed for each terminal apparatus  200 . Moreover, even in the case where the control, information is included for each terminal apparatus  200 , common information is used for a data portion (e.g., a portion corresponding to MBMS content data), so it is desirable that the modulation scheme or the like are set to be common among the plurality of terminal apparatuses  200 . 
     As described above, in the present modification, the base station merges the resources of the beam used for delivering the MBMS content with respect to at least some of two or more of the plurality of terminal apparatuses depending on the conditions. Such control makes it also possible to switch selectively the delivery schemes of delivering the program content (e.g., the MBMS content) to each terminal apparatus depending on the conditions at each time by using the communication system according to the present modification. Thus, the communication system according to the present modification enables the efficiency of resource utilization in the entire system to be improved, resulting in expecting an effect of improving the throughput in the entire system. 
     Third Modification 
     Subsequently, a modification of the communication system according to another embodiment of the present disclosure is described. Moreover, the present modification is also referred to as a “third modification”. 
     As described above, the MBMS content is transmitted by multicast from the content server to the base station in the CN and is transmitted by multicast using the UE-specific beam from the base station to the terminal apparatus in the RAN. In the case where the MBMS session is provided from a base station to each terminal apparatus using the UE-specific beam (i.e., the case of delivering the MBMS content), the UE-specific beam corresponding to each terminal apparatus is transmitted at a different time in some cases. This is because, in order to provide the MBMS session to each of a plurality of terminal apparatuses using the same time resource, in one example, each of the plurality of terminal apparatuses is necessary to be arranged at a spatially separable position. In other words, in a case where a plurality of terminal apparatuses are located in an area where spatial separation is difficult (e.g., a case where a plurality of terminal apparatuses are located in the same area), the UE-specific beam corresponding to each of the plurality of terminal apparatuses uses different time/frequency resources from each other. Due to such characteristics, it can be difficult, in some cases, to deliver the same information to each of a plurality of terminal apparatuses at the same timing. 
     Further, it is demanded to introduce a mechanism that allows a user holding a terminal apparatus to specify a time for viewing broadcast content through the terminal apparatus. In such a case, in one example, in the case where the terminal apparatus receives the provision of the MBMS session, there is a possibility to be necessary to introduce a mechanism capable of specifying the time at which the provision is performed. In other words, in order to deliver the MBMS content to each of a plurality of terminal apparatuses at different timings by multicast using the UE-specific beam, a different response from the ordinary multicast that is capable of delivering the content to a plurality of terminal apparatuses at the same time is necessitated. 
     In view of such a situation, in the communication system according to the present modification, a buffer provided in the base station absorbs a difference) i.e., a time lag) in the delivery timing of the MBMS content between a plurality of terminal apparatuses, and the information regarding the allowable time difference is notified to each of the plurality of terminal apparatuses. Moreover, the notification can be performed only by using, in one example, system information or dedicated signaling. Thus, an example of the procedure of a series of processing steps of the communication system according to the present modification is now described with reference to  FIG. 19 , by particularly focusing on a mechanism for absorbing the time difference.  FIG. 19  is a schematic sequence diagram illustrating an example of a procedure for providing a program to each terminal apparatus using a directional beam in the communication system according to the present modification. Moreover, the steps denoted by reference numerals S 501  to S 519  correspond to the steps denoted by reference numerals S 201  to S 219  in  FIG. 13 , respectively. Thus, a detailed description of the steps denoted by reference numerals S 501  to S 519  is omitted. 
     As illustrated in  FIG. 19 , in a case where the MBMS content is transferred (IF multicast) from the MB-SC  460  to the MBMS gateway  440 , the MBMS content is IF multicast from the MBMS gateway  440  to the base station  100  (S 521 ). 
     The base station  100  (the communication control unit  151 ) holds (buffers) the data of the MBMS content subjected to the IP multicast from the MBMS gateway  440  in a predetermined storage area (S 523 ). In this case, the base station  100  calculates a period during which the acquired data of MBMS content can be held (buffered) on the basis of, in one example, the communication speed for providing the MBMS session (i.e., delivering the MBMS content) and the capacity (buffer amount) of the storage area available to itself. Then, the base station  100  (the notification unit  155 ) notifies the terminal apparatus  200 , by using broadcast or dedicated signaling as system information, of the information regarding the calculated period, that is, the information regarding the period in which the MBMS content can be buffered (S 525 ). 
     The terminal apparatus  200  receives the notification of the information regarding the period in which the MBMS content can be buffered from the base station  100  and performs a procedure for setting the UE-specific beam for receiving the MBMS content by specifying a destination (e.g., unicast or multicast) for itself within the period (S 527  to S 539 ). In addition, the base station  100  identifies a beam to be used for delivering the MBMS content to the terminal apparatus  200  (S 541 ), in response to the report from the terminal apparatus  200  in the procedure (S 539 ). Then, the base station  100  (the communication control unit  241 ) delivers (e.g., Multicast) the MBMS content held in the predetermined storage area to the terminal apparatus  200  using the UE-specific beam (i.e., the identified beam) (S 543 ). Moreover, the above processing steps denoted by reference numerals S 527  to S 543  are substantially similar to the steps denoted by reference numerals S 227  to S 243  in  FIG. 13 , respectively. 
     Further, the base station  100  is capable of adjusting the timing to start holding (buffering) the data of the MBMS content depending on the information regarding the timing at which the MBMS content notified from the terminal apparatus  200  is desired to be delivered. Moreover, the information regarding the timing at which the terminal apparatus  200  desires to deliver the MBMS content can be notified from the terminal apparatus  200  to the base station  100  before the timing. In addition, the terminal apparatus  200  can notify the base station  100  that the MBMS content is currently desired to he delivered. 
     Moreover, the association of the information regarding the. timing at which the terminal apparatus  200  desires to deliver the MBMS content with the information notified from the terminal apparatus  200  to the base station  100  for counting makes it possible for the base station  100  to recognize the timing. In other words, the base station  100  can adjust the timing to start holding (buffering) the data of the MBMS content depending on the timing recognized on the basis of the information notified from the terminal apparatus  200 . In one example,  FIG. 20 . is a schematic sequence diagram illustrating another example of a procedure for providing a program to each terminal apparatus using a directional beam in the communication system according to the present modification. In other words,  FIG. 20  illustrates an example of a procedure for adjusting the timing at which the base station  100  starts holding (buffering) the data of the MBMS content. Moreover, the steps denoted by reference numerals S 701  to S 719  are similar to the steps denoted by reference numerals S 501  to S 519  in  FIG. 19 , respectively, and so a detailed description thereof will be omitted. 
     As illustrated in  FIG. 20 , the base station  100  (the notification unit  155 ) notifies the terminal apparatus  200  of a counting request to perform the counting (S 721 ). The terminal apparatus  200  (the notification unit  247 ), when receiving the counting request from the base station  100 , replies information to the base station  100  regarding the desired timing of the providing for the MBMS session desired to be provided (i.e., the MBMS content desired to be delivered) (S 723 ). 
     The base station  100  (the communication control unit  151 ) decides the timing to start providing the corresponding MBMS session on the basis of the information notified from the terminal apparatus  200  (S 725 ). Then, the base station  100  (the notification: unit  155 ) notifies the MB-SC  460  of a request for starting delivering the content (i.e., MBMS content) corresponding to the MBMS session depending on the decided timing (S 727 ). The MB-SC  460 , when receiving the notification, transfers (IP multicast) the corresponding HEMS content to the MB MS gateway  440 . In addition, the MBMS gateway  440  performs IP multicast of the HEMS content transferred from the MB-SC  460  to the base station  100  (S 727 ). The base station  100  (the communication control unit  151 ) holds (buffers) the data of the MBMS content subjected to the IP multicast from the MBMS gateway  440  in a predetermined storage area (S 731 ). 
     Moreover, the subsequent steps, that is, the steps denoted by reference numerals S 733  to S 751  are similar to the steps denoted by reference numerals S 525  to S 543  in  FIG. 19 , respectively, and so a detailed description thereof will be omitted. 
     The control as described above makes it possible for the base station  100  to control the timing at which the terminal apparatus  200  starts holding (buffering) data of content corresponding to the MBMS service depending on the timing at which the terminal apparatus  200  desires to provide the MBMS service. 
     A description of the relationship between the technology according to the present modification and a technology called mobile edge computing (MEC) is now given. The MEC is a technology that allows a base station to hold data of an application executed on the side of a server, thereby reducing the latency between the application and a terminal apparatus. In view of such characteristics, in the communication system according to the present modification, the technology causing the base station to hold the data of the MBMS content and delivering the MBMS content from the base station to the terminal apparatus on the basis of the data can be regarded as a type of the MEC. 
     Moreover, the communication system according to the present modification is a service assuming provision of broadcast content, and it differs from a typical MEC in that the period in which data to be delivered (i.e., MBMS content) is held at the side of a base station is finite. In addition, in the communication system according to the present modification, there is a high possibility that strictly speaking a request for improvement in latency or response is not provided, as compared to the typical MEC. In other words, in the communication system according to the present modification, in providing a service as broadcasting, in order to absorb the reception timing between the terminal apparatuses, the characteristic point is that the content data is held (buffered) by the base station. 
     4. Application Examples 
     The technology according to the present disclosure can be applied to various products. For example, the base station  100  may be realized as any type of evolved Node B (eNB) such as a macro eNB or a small eNB. The small eNB may be an eNB that covers a cell, such as a pico eNB, a micro eNB, or a home (femto) eNB, smaller than a macrocell. Instead, the base station  100  may be realized as another type of base station such as a NodeB or a base transceiver station (BTS). The base station  100  may include a main entity (also referred to as a base station device) that controls wireless communication and one or more remote radio heads (RRHs) disposed at different locations from the main entity. Further, various types of terminals to be described below may operate as the base station  100  by performing a base station function temporarily or semi-permanently. Further, at least one of constituent elements of the base station  100  may be realized in the base station device or a module for the base station device. 
     Further, for example, the terminal apparatus  200  may be realized as a mobile terminal such as a smartphone, a tablet personal computer (PC), a notebook PC, a portable game terminal, a portable/dongle mobile router or a digital camera, or an in-vehicle terminal such as a car navigation apparatus. Further, the terminal apparatus  200  may be realized as a terminal that performs machine to machine (M2M) communication (also referred to as a machine type communication (MTC) terminal). Further, the terminal apparatus  200  may be realized as a so-called “low cost terminal”, such as an MTC terminal, an eMTC terminal, or an NB-IoT terminal. Moreover, at least a part of the constituent elements of the terminal apparatus  200  may be realized in a module mounted on the terminal (for example, an integrated circuit module configured on one die). 
     4.1. Application Examples for Base Station Device 
     (First Application Example) 
       FIG. 21  is a block diagram illustrating a first example of a schematic configuration of an eNB to which the technology according to the present disclosure may be applied. An eNB  800  includes one or more antennas  810  and a base station device  820 . Each antenna  810  and the base station device  820  may be connected to each other via an RF cable. 
     Each of the antennas  810  includes a single or a plurality of antenna elements (e.g., a plurality of antenna elements constituting a MIMO antenna) and is used for the base station device  820  to transmit, and receive a wireless signal. The eNB  800  may include the plurality of the antennas  810  as illustrated in  FIG. 21 , and the plurality of antennas  810  may, for example, correspond to a plurality of frequency bands used by the eNB  800 . It should be noted that while  FIG. 21  illustrates an example in which the eNB  300  includes the plurality of antennas  810 , the eNB  800  may include the single antenna  610 . 
     The base station device  820  includes a controller  821 , a memory  822 , a network interface  823 , and a wireless communication interface  825 . 
     The controller  821  may be, for example, a CPU or a DSP, and operates various functions of an upper layer of the base station device  820 . For example, the controller  821  generates a data packet from data in a signal processed by the wireless communication interface  325 , and transfers the generated packet via the network interface  823 . The controller  321  may generate a bundled packet by bundling data from a plurality of base band processors to transfer the generated bundled packet. Further, the controller  821  may also have a logical function of performing control such as radio resource control, radio bearer control, mobility management, admission control, and scheduling. Further, the control may be performed in cooperation with a surrounding eNB or a core network node. The memory  822  includes a RAM and a ROM, and stores a program executed by the controller  821  and a variety of control data (such as, for example, terminal list, transmission power data, and scheduling data). 
     The network interface  823  is a communication interface for connecting the base station device  820  to the core network  824 . The controller  821  may communicate with a core network node or another eNB via the network interface  823 . In this case, the eNB  800  may be connected to a core network node or another eNB through a logical interface (e.g., S1 interface or X2 interface). The network interface  823  may be a wired communication interface or a wireless communication interface for wireless backhaul. In the case where the network interface  323  is a wireless communication interface, the network interface  823  may use a higher frequency band for wireless communication than a frequency band used by the wireless communication interface  825 . 
     The wireless communication interface  825  supports a cellular communication system such as long term evolution (LTE) or LIE-Advanced, and provides wireless connection to a terminal located within the cell of the eNB  800  via the antenna  810 . The wireless communication interface  825  may typically include a base band (SB) processor  826 , an RF circuit  827 , and the like. The BB processor  826  may, for example, perform encoding/decoding, modulation/demodulation, multiplexing/demultiplexing, and the like, and performs a variety of signal processing on each layer (e.g., L1, medium access control (MAC), radio link control (RLC), and packet data convergence protocol (PDCP)). The BB processor  826  may have part or all of the logical functions as described above instead of the controller  821 . The BB processor  826  may be a module including a memory having a communication control program stored therein, a processor to execute the program, and a related circuit, and the function of the BB processor  826  may be changeable by updating the program. Further, the module may be a card or blade to be inserted into a slot of the base station device  820 , or a chip mounted on the card or the blade. Meanwhile, the RF circuit  827  may include a mixer, a filter, an amplifier, and the like, and transmits and receives a wireless signal via the antenna  810 . 
     The wireless communication interface  825  may include a plurality of the BB processors  826  as illustrated in  FIG. 21 , and the plurality of BB processors  826  may, for example, correspond to a plurality of frequency bands used by the eNB  300 . Further, the wireless communication interface  825  may also include a plurality of the RF circuits  827 , as illustrated in  FIG. 21 , and the plurality of RF circuits  327  may, for example, correspond to a plurality of antenna elements. Note that  FIG. 21  illustrates an example in which the wireless communication interface  825  includes the plurality or BB processors  826  and the plurality of RF circuits  827 , but the wireless communication interface  825  may include the single BB processor  826  or the single RF circuit  827 . 
     In the eNB  800  illustrated in  FIG. 21 , one or more constituent elements (for example, at least one of the communication control unit  151 , the information acquisition unit  153 , or the notification unit  155 ) included in the processing unit  150  described with reference to  FIG. 2  may be implemented in the wireless communication interface  325 . Alternatively, at least some of the constituent elements may be implemented in the controller  821 . As one example, a module including a part (for example, the BB processor  826 ) of or the whole of the wireless communication interface  825  and/or the controller  821  may be implemented on the eNB  800 . The one or more constituent elements in the module may be implemented in the module. In this case, the module may store a program causing a processor to function as the one or more constituent elements (in ether words, a program causing the processor to execute operations of the one or more constituent elements) and execute the program. As another example, a program causing the processor to function as the one or more constituent elements may be installed in the eNB  800 , and the wireless communication interface  825  (for example, the BB processor  826 ) and/or the controller  821  may execute the program. In this way, the eNB  800 , the base station device  820 , or the module may be provided as a device including the one or more constituent elements and a program causing the processor to function as the one or more constituent elements may be provided. In addition, a readable recording medium on which the program is recorded may be provided. 
     Further, in the eNB  800  illustrated. in  FIG. 21 , the wireless communication. unit  120  described with reference to  FIG. 2  may be implemented in the wireless communication interface  825  (for example, the. RF circuit  027 ). Further, the antenna unit  110  may be implemented in the antenna  818 . In addition, the network communication unit  130  may be implemented in the controller  821  and/or the network interface  823 . Further, the storage unit  140  may be implemented in the memory  822 . 
     Second Application Example 
       FIG. 22  block diagram illustrating a second example of a schematic configuration o an eNB to which the technology according to the present disclosure may be applied. An eNB  830  includes one or more antennas  840 , base station device  850 , and an RRH  860 . Each of the antennas  840  and the RRH  860  may be connected to each other via an RE cable. Further, the base: station device  850  and the RRH  860  may be connected to each other by a high speed line such as optical fiber cables. 
     Each of the antennas  840  includes a single or at plurality of antenna elements (e.g., antenna elements constituting a MIMO antenna), and is used for the RRH  860  to transmit and receive a wireless signal. The eNB  830  may include a plurality of the antennas  840  as illustrated in  FIG. 22 , and the plurality of antennas  840  may, for example, correspond to a plurality of frequency beads used by the eNB  830 . Note that  FIG. 22  illustrates an example in which the eNB  830  includes the plurality of antennas  840 , but the eNB  830  may include the single antenna  848 . 
     The base station device  850  includes a controller  851 , a memory  852 , a network interface  853 , a wireless communication interface  855 , and a connection interface  857 . The controller  851 , the memory  852 , and the network interface  853  are similar to the controller  821 , the memory  822 , and the network interface  823  described with reference to  FIG. 21 . 
     The wireless communication interface  855  supports a. cellular communication system such as LTE and LTE-Advanced, and provides wireless connection to a terminal located in a sector corresponding to the RRH  860  via the RRE  860  and the antenna  840 . The wireless communication interface  855  may typically include a BB processor  856  or the like. The BB processor  856  is similar to the BB processor  826  described with reference to  FIG. 21  except that the BB processor  856  is connected to an RF circuit  864  of the RRH  860  via the connection interface  857 . The wireless communication interface  855  may include a plurality of the BB processors  856 , as illustrated in  FIG. 21 , and the plurality of BB processors  856  may, for example, correspond to a plurality of frequency bands used by the eNB  830 . Note that  FIG. 22  illustrates an example in which the wireless communication interface  855  includes the plurality of BB processors  856 , but the wireless communication interface  855  may include the single BB processor  856 . 
     The connection interface  857  is an interface for connecting the base station device  850  (wireless communication interface  855 ) to the RRH  860 . The connection interface  857  may be a communication module for communication on the high speed line which connects the base station device  850  (wireless communication interface  855 ) to the RRH  860 . 
     Further, the RRH  860  includes a connection interface  861  and a wireless communication interface  863 . 
     The connection interface  861  is an interface for connecting the RRH  860  (wireless communication interface  863 ) to the base station device  850 . The connection interface  861  may be a communication module for communication on the high speed line. 
     The wireless communication interface  863  transmits and receives a wireless signal via the antenna  840 . The wireless communication interface  863  may typically include the RF circuit  864  or the like. The RF circuit  864  may include a mixer, a filter, an amplifier and the like, and transmits and receives a wireless signal via the antenna  840 . The wireless communication interface  863  may include a plurality of the RF circuits  864  as illustrated in  FIG. 22 , and the plurality of RF circuits  864  may, for example, correspond to a plurality of antenna elements. Note that  FIG. 22  illustrates an example in which the wireless communication interface  863  includes the plurality of RF circuits  864 , but the wireless communication interface  863  may include the single RF circuit  864 . 
     In the eNB  830  illustrated in  FIG. 22 , one or more constituent elements (at least one of the communication control unit  153 , the information acquisition unit  153 , or the notification unit  155 ) included in the processing unit  150  described with reference to  FIG. 2  may be implemented in the wireless communication interface  855  and/or the wireless communication interface  863 . Alternatively, at least some of the constituent elements may be implemented in the controller  851 . As one example, a module including a part, (for example, the BB processor  356 ) of or the whole of the wireless communication interface  855  and/or the controller  351  may be implemented on the eNB  330 . The one or more constituent elements in the module may be implemented in the module. In this case, the module may store a program causing a processor to function as the one or more constituent elements (in other words, a program causing the processor to execute operations of the one or more constituent elements) and execute the program. As another example, a program causing the processor to function as the one or more constituent elements may be installed in the eNB  830 , and the wireless communication interface  855  (for example, the BB processor  856 ) and/or the controller  851  may execute the program. In this way, the eNB  830 , the base station device  650 , or the module may be provided as a device including the one or more constituent elements and a program causing the processor to function as the one or more constituent elements may be provided. In addition, a readable recording medium on which the program is recorded may be provided. 
     Further, in the eNB  830  illustrated in  FIG. 22 , for example, the wireless communication unit  120  described with reference to  FIG. 2  may be implemented in the wireless communication interface  883  (for example, the RF circuit  864 ). Further, the antenna unit  110  may be implemented in the antenna  840 . In addition, the network communication unit  130  may be implemented in the controller  851  and/or the network interface  853 . Further, the storage unit  140  may be implemented in the memory  852 . 
     4.2. Application Examples for Terminal Apparatus 
     (First Application Example) 
       FIG. 23  is a block diagram illustrating an example of a schematic configuration of a smartphone  900  to which the technology according to the present disclosure may be applied. The smartphone  900  includes a processor  901 , a memory  902 , a storage  903 , an external connection interlace  904 , a camera  906 , a sensor  907 , a microphone  908 , an input device  909 , a display device  910 , a speaker  911 , a wireless communication interface  912 , one or more antenna switches  915 , one or more antennas  916 , a bus  917 , a battery  918 , and an auxiliary controller  919 . 
     The processor  901  may be, for example, a CPU or a system on chip (SoC) and controls the functions of an application layer and other layers of the smartphone  900 . The memory  902  includes a RAM and a ROM, and stores a program executed by the processor  901  and data. The storage  903  may include a storage medium such as semiconductor memories and hard disks. The external connection interface  904  is an interface for connecting the smartphone  500  to an externally attached. device such as memory cards and universal serial bus (USB) devices. 
     The camera  906  includes, for example, an image sensor such as charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS), and generates a captured image. The sensor  907  may include a sensor group including, for example, a positioning sensor, a gyro sensor, a geomagnetic sensor, an acceleration sensor and the like. The microphone  906  converts a sound that is input into the. smartphone  900  to an audio signal. The input device  909  includes, for example, a touch sensor which detects that a screen of the display device  910  is touched, a key pad, a keyboard, a button, a switch or the like, and accepts an operation or an information input from a user. The display deice  910  includes a screen such as liquid crystal displays (LCDs) and organic light emitting diode (OLED) displays, and displays an output image of the smartphone  900 . The speaker  911  converts the audio signal that is output from the smartphone  900  to a sound. 
     The wireless communication interface  912  supports a cellular communication system such as LTE or LTE-Advanced, and performs wireless communication. The wireless communication interface  912  may typically include the BB processor  913 , the RF circuit  914 , and the like. The, BB processor  913  may, for example, perform encoding/decoding, modulation/demodulation, multiplexing/demultiplexing, and the like, and performs a variety of types of signal processing for wireless communication. On the other hand, the RF circuit.  914  may include a mixer, a filter, an amplifier, and the like, and transmits and receives a wireless signal via the antenna  916 . The wireless communication interface  912  may be a one-chip module in which the BB processor  913  and the RF circuit  914  are integrated. The wireless communication interface  912  may include a plurality of BB processors  913  and a plurality of RF circuits  914  as illustrated in  FIG. 23 . Note that  FIG. 23  illustrates an example in which the wireless communication interface  912  includes a plurality of BB processors  913  and a plurality of RF circuits  914 , but the wireless communication interface  912  may include a single BB processor  913  or a single RF circuit  914 . 
     Further, the wireless communication interface  912  may support other types of wireless communication system such as a short range wireless communication system, a near field communication system, and a wireless local area network (LAN) system in addition to the cellular communication system, and in this case, the wireless communication interface  912  may include the BB processor  913  and the RE circuit  914  for each wireless communication system. 
     Each antenna switch  915  switches a connection destination of the antenna  916  among a plurality of circuits (for example, circuits for different wireless communication systems) included in the wireless communication interface  912 . 
     Each of the antennas  916  includes one or more antenna elements (for example, a plurality of antenna elements constituting a MIMO antenna) and is used for transmission and reception of the wireless signal by the wireless communication interface  912 . The smartphone  900  may include a plurality of antennas  916  as illustrated in  FIG. 23 . Note that  FIG. 23  illustrates an example in which the smartphone  900  includes a plurality of antennas  916 , but the smartphone  900  may include a single antenna  916 . 
     Further, the smartphone  900  may include the antenna  916  for each wireless communication system. In this case, the antenna switch  915  may be omitted from a configuration of the smartphone  900 . 
     The bus  917  connects the processor  901 , the memory  902 , the storage  903 , the external connection interface  904 , the camera  906 , the sensor  907 , the microphone  908 , the input device  909 , the display device  910  the speaker  911 , the wireless communication interface  912 , and the auxiliary controller  919  to each other. The batter  918  supplies electric power to each block of the smartphone  900  illustrated in  FIG. 23  via a feeder line that is partially illustrated in the figure as a dashed line. The auxiliary controller  919 , for example, operates a minimally necessary function of the smartphone  900  in a sleep mode. 
     In the smartphone  900  illustrated in  FIG. 23 , one or more constituent elements included in the processing unit  240  (at least one of the communication control unit  241 , the information acquisition unit  243 , the measuring unit  245 , or the notification unit  247 ) described with reference to  FIG. 3  may be implemented in the wireless communication interface  912 . Alternatively, at least some of the constituent elements may be implemented in the processor  901  or the auxiliary controller  919 . As one example, a module including a part (for example, the BB processor  913 ) of or the whole of the wireless communication interface  912 , the processor  901 , and/or the auxiliary controller  919  may be implemented on the smartphone  900 . The one or more constituent elements in the module may be implemented in the module. In this case, the module may store a program causing a processor to function as the one or more constituent elements (in other words, a program causing the processor to execute operations of the one or more constituent elements) and execute the program. As another example, a program causing the processor to function as the one or more constituent elements may be installed in the smartphone  900 , and the wireless communication interface  912  (for example, the BB processor  913 ), the processor  901 , and/or the auxiliary controller  919  may execute the program. In this way, the smartphone  900  or the module may be provided as a device including the one or more constituent elements and a program causing the processor to function as the one or more constituent elements may be provided. In addition, a readable recording medium on which the program is recorded may be provided. 
     Further, in the smartphone  900  illustrated in  FIG. 23 , for example, the wireless communication unit  220  described with reference to  FIG. 3  may be implemented in the wireless communication interface  912  (for example, the RF circuit  914 ). Further, the antenna unit  210  may be implemented in the antenna  916 . Further, the storage unit  230  may be implemented in the memory  902 . 
     Second Application Example 
       FIG. 24  is a block diagram illustrating an example of a schematic configuration of a car navigation apparatus  920  to which the technology according to the present disclosure may be applied. The car navigation apparatus  220  includes a processor  921 , a memory  922 , a global positioning system (GPS) module  924 , a sensor  925 , a data interface  926 , a content player  927 , a storage medium interface  926 , an input device  929 , a display device  930 , a speaker  931 , a wireless communication interface  933 , one or more antenna switches  936 , one or more antennas  937 , and a battery  938 . 
     The processor  921  may be, for example, a CPU or an SoC, and controls the navigation function and the other functions of the car navigation apparatus  920 . The memory  922  includes a RAM and a ROM, and stores a program executed by the processor  921  and data. 
     The GPS module  924  uses a GPS signal received from a GPS satellite to measure the position (e.g., latitude, longitude, and altitude) of the car navigation apparatus  920 . The sensor  925  may include a sensor group including, for example, a gyro sensor, a geomagnetic sensor, a barometric sensor and the like. The data interface  926  is, for example, connected to an in-vehicle network  941  via a terminal that is not illustrated, and acquires data such as vehicle speed data generated on the vehicle side. 
     The content player  927  reproduces content stored in a storage medium (e.g., CD or DVD) inserted into the storage medium interface  928 . The input device  929  includes, for example, a touch sensor which detects that a screen of the display device  930  is touched, a button, a switch or the like, and accepts operation or information input from a user. The display device  930  includes a screen such as LCDs and OLED displays, and displays an image of the: navigation function or the reproduced content. The speaker  931  outputs a sound of the navigation function or the reproduced content. 
     The wireless communication interface  933  supports a cellular communication system such as LTE or LTE-Advanced, and performs wireless communication. The wireless communication interface  933  may typically include the BB processor  934 , the RE circuit  935 , and the like. The BB processor  934  may, for example, perform encoding/decoding, modulation/demodulation, multiplexihg/demultiplexing, and the like, and performs a variety of types of signal processing for wireless communication. On the other hand, the RE circuit  935  may include a mixer, a filter, an amplifier, and the like, and transmits and receives a wireless signal via the antenna  937 . The wireless communication interface  933  may be a one-chip module in which the BB processor  934  and the RF circuit  935  are integrated. The wireless communication interface  933  may include a plurality of BB processors  934  and a plurality of RF circuits  935  as illustrated in  FIG. 24 . Note that  FIG. 24  illustrates an example in which the wireless communication interface  933  includes a plurality of BB processors  934  and a plurality of RF circuits  935 , but the wireless communication interface  933  may include a single BB processor  934  or a single RF circuit  935 . 
     Further, the wireless communication interface  933  may support other types of wireless communication system such as a short range wireless communication system, a near field communication system, and a wireless LAN system in addition to the cellular communication system, and in this case, the wireless communication interface  933  may include the BB processor  934  and the RF circuit  935  for each wireless communication system. 
     Each antenna switch  936  switches a connection destination of the antenna  937  among a plurality of circuits (for example, circuits for different wireless communication systems) included in the wireless communication interface  933 . 
     Each of the antennas  937  includes one or more antenna elements (for example, a plurality of antenna elements constituting a MIMO antenna) and is used for transmission and reception of the wireless signal by the wireless communication interface  933 . The car navigation apparatus  920  may include a plurality of antennas  937  as illustrated in  FIG. 24 . Note that  FIG. 24  illustrates an example In which the car navigation apparatus  920  includes a plurality of antennas  937 , but the car navigation apparatus  920  may include a single antenna  937 . 
     Further, the car navigation apparatus  920  may include the antenna  937  for each wireless communication system. In this case, the antenna switch  936  may be omitted from a configuration of the car navigation apparatus  920 . 
     The battery  938  supplies electric power to each block of the car navigation apparatus  920  illustrated in  FIG. 24  via a feeder line that is partially illustrated in the figure as a dashed line. Further, the battery  938  accumulates the electric power supplied from the vehicle. 
     In the car navigation apparatus  920  illustrated in  FIG. 24 , one or more constituent elements included in the processing unit  240  (at least one of the communication control unit  241 , the information acquisition unit  243 , the measuring unit  245 , or the notification unit  247 ) described with reference to  FIG. 3  may be implemented in the wireless communication. interface  933 . Alternatively, at least some of the constituent elements may be implemented in the processor  921 . As one example, a module including a part of (for example, the BB processor  934 ) of or the whole of the wireless communication interface  933  and/or the processor  921  may be implemented on the car navigation apparatus  920 . The one or more constituent elements in the module may be implemented in the module. In this case, the module may store a program causing a processor to function as the one or more constituent elements (in other words, a program causing the processor to execute operations of the one or more constituent elements) and execute, the program. As another example, a program causing the processor to function as the one or more constituent elements may be installed in the car navigation apparatus  920 , and the wireless communication interface  933  (for example, the BB processor  934 ) and/or the processor  921  may execute the program. In this way, the car navigation apparatus  920  or the module may be provided as a device including the one or more constituent elements and a program causing the processor to function as the one or more constituent elements may be provided. In addition, a readable recording medium on which the program is recorded may be provided. 
     Further, in the car navigation apparatus  920  illustrated  FIG. 24 , for example, the wireless communication unit  220  described with reference to  FIG. 3  may be implemented in the wireless communication interface  933  (for example, the RF circuit  935 ). Further, the antenna unit  210  may be implemented in the antenna  937 . Further, the storage unit  230  may be implemented in the memory  922 . 
     The technology of the present disclosure may also be realized as an in-vehicle system (or a vehicle)  940  including one or more blocks of the car navigation apparatus  920 , the in-vehicle network  941 , and a vehicle module  942 . In other words, the in-vehicle system (or the vehicle)  940  may be provided as a device including at least one of the communication control unit  241 , the information acquisition unit  243 , the measuring unit  245 , or the notification unit  247 . The vehicle module  942  generates vehicle data such as vehicle speed, engine speed, and trouble information, and outputs the generated data to the in-vehicle network  941 . 
     5.Concluding Remarks 
     As described above, in the communication system according to an embodiment of the present disclosure, the base station delivers the MBMS content that is multicast from the upper node (e.g., the MBMS gateway) to the terminal apparatus using at least a part of the directional beams (i.e., UE-specific beam) allocated to the terminal apparatus from the plurality of directional beams. The configuration as described above makes it possible to deliver efficiently so-called broadcast content (e.g., MBMS content) to each terminal apparatus even under such a situation that the wireless communication between the base station and each terminal apparatus is spatially separated by using the directional beam. As described above, according to the communication system according to an embodiment of the present disclosure, it is possible to implement the delivery of content to a terminal apparatus using a directional beam more suitably. 
     The preferred embodiment of the present disclosure has been described above with reference to the accompanying drawings, whilst the present disclosure is not limited to the above examples. A person skilled in the art may find various alterations and modifications within the scope of the appended claims, and it should be understood that they will naturally come under the technical scope of the present disclosure. 
     Further, the effects described in this specification are merely illustrative or exemplified effects, and are not limitative. That is, with or in the place of the above effects, the technology according to the present disclosure may achieve other effects that are clear to those skilled in the art from the description of this specification. 
     Additionally, the present disclosure may also be configured as below. 
     (1) 
     A communication apparatus comprising: 
     a communication unit configured to perform wireless communication; and 
     a control unit configured to control in such a way as to deliver content subjected to multicast from an upper node to a terminal apparatus using at least a part of a plurality of directional beams allocated to the terminal apparatus from the directional beams used for the wireless communication. 
     (2) 
     The communication apparatus according to (1), wherein the control unit controls in such a way as to deliver the content to the terminal apparatus by specifying as a destination the terminal apparatus to which the at least part of the directional beams is allocated. 
     (3) 
     The communication apparatus according to (2), further comprising: 
     an acquisition unit configured to acquire a request for delivering the content for each program, 
     wherein the control unit controls, depending on a condition of the request for each of the programs, a delivery scheme of the content corresponding to the program. 
     (4) 
     The communication apparatus according to (3), wherein the control unit selects any one of broadcast, multicast, and unicast as the delivery scheme of the content depending on the number of terminal apparatuses desiring to deliver the content for each of the programs. 
     (5) 
     The communication apparatus according to (3), wherein the control unit controls, depending on settings of wireless communication with each of a plurality of the terminal apparatuses, in such a way as to deliver the content used in common by specifying each of the plurality of terminal apparatuses as a destination through the directional beam used in common. 
     (6) 
     The communication apparatus according to (5), 
     wherein the acquisition unit acquires information regarding settings of wireless communication with the terminal apparatus from each of one or more of the terminal apparatuses, and 
     the control unit controls in such a way as to deliver the content used in common by specifying each of a plurality of the terminal apparatuses as a destination through the directional beam used in common depending on the acquired information. 
     (7) 
     The communication apparatus according to any one of (3) to (6), further comprising: a notification unit configured to notify the terminal apparatus of information regarding a period in which the content is held. 
     (8) 
     The communication apparatus according to (7), 
     wherein the acquisition unit acquires information regarding a timing at which the terminal apparatus desires to deliver the content from a predetermined node managing a session, and 
     the notification unit transmits a request for delivering the content to the upper node depending on the timing. 
     (9) 
     The communication apparatus according to any one of (1) to (8), 
     wherein the control unit 
     sets, separately from first wireless communication used for notification of information from the terminal apparatus, second wireless communication used for delivering the content, and 
     restricts the first wireless communication and maintains the second wireless communication depending on a request for maintaining the second wireless communication during a first mode restricting the first wireless communication, the request being associated with a request, which is notified from the terminal apparatus and is for making a transition to the first mode. 
     (10) 
     A communication apparatus comprising: 
     a communication unit configured to perform wireless communication; and 
     a control unit configured to control in such a way to receive content subjected to multicast from an upper node to a base station and delivered from the base station using at least a part of directional beams allocated from a plurality of directional beams. 
     (11) 
     The communication apparatus according to (10), further comprising: 
     a notification unit configured to notify a predetermined node managing a session of a request for delivering the content, 
     wherein the control unit, after notification of the request, controls in such a way to receive the content to be delivered using the allocated at least part of the directional beams. 
     (12) 
     The communication apparatus according to (11), 
     wherein second wireless communication used for delivering the content is set separately from first, wireless communication used for notification of information to the base station, and 
     the notification unit notifies a predetermined device configured to manage a transition between a first mode and a second mode of a request for making a transition to the first mode restricting the first wireless communication in association with a request for maintaining the second wireless communication during the first mode. 
     (13) 
     The communication apparatus according to (12), 
     wherein the second wireless communication uses the allocated at least, part of the directional beams, 
     the control unit controls in such a way to make a transition from the first mode to the second mode capable of performing the first wireless communication depending on a condition relating to the at least part of the directional beams in the first mode, and 
     the notification unit, after the transition to the second mode, notifies the base station of a request for settings of communication using the at least part of the directional beams. 
     (14) 
     The communication apparatus according to any one of (11) to (13), wherein the notification unit notifies the base station of information regarding a timing at which the content is desired to be delivered. 
     (15) 
     A communication method executed by a computer, the method comprising: 
     performing wireless communication; and 
     controlling in such a way as to deliver content subjected to multicast from an upper node to a terminal apparatus using at least a part of a plurality of directional beams allocated to the terminal apparatus from the directional beams used for the wireless communication. 
     (16) 
     A communication method executed by a computer, the method comprising: 
     performing wireless communication; and
         controlling in such a way to receive content subjected to multicast from an upper node to a base station and delivered from the base station using at least a part of directional beams allocated from a plurality of directional beams.
 
(17)
       

     A program causing a computer to execute: 
     performing wireless communication; and 
     controlling in such a way as to deliver content subjected to multicast from an upper node to a terminal apparatus using at least a part of a plurality of directional beams allocated to the terminal apparatus from the directional beams used for the wireless communication. 
     (10) 
     A program causing a computer to execute: 
     performing wireless communication; and 
     controlling in such a way to receive content subjected to multicast from an upper node to a base station and delivered from the base station using at least a part of directional beams allocated from a plurality of directional beams. 
     REFERENCE SIGNS LIST 
       1  SYSTEM 
       10  CELL 
       40  CORE NETWORK 
       50  PACKET DATA NETWORK 
       60  APPLICATION SERVER 
       100  RASE STATION 
       110  ANTENNA UNIT 
       120  WIRELESS COMMUNICATION UNIT 
       130  NETWORK COMMUNICATION UNIT 
       140  STORAGE UNIT 
       150  PROCESSING UNIT 
       151  COMMUNICATION CONTROL UNIT 
       153  INFORMATION ACQUISITION UNIT 
       155  NOTIFICATION UNIT 
       200  TERMINAL APPARATUS 
       210  ANTENNA UNIT 
       220  WIRELESS COMMUNICATION UNIT 
       230  STORAGE UNIT 
       240  PROCESSING UNIT 
       241  COMMUNICATION CONTROL UNIT 
       243  INFORMATION ACQUISITION UNIT 
       245  MEASURING UNIT 
       247  NOTIFICATION UNIT 
       300  MEC SERVER