Patent Publication Number: US-9844095-B2

Title: Mobile communication system, base station, and user terminal

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation Application of U.S. patent application Ser. No. 15/252,649, filed Aug. 31, 2016, which is a Continuation Application of International Patent Application No. PCT/JP2015/058582, filed Mar. 20, 2015, which claims benefit of Japanese Patent Application No. 2014-058040, filed Mar. 20, 2014, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a mobile communication system into which a group communication function is introduced. 
     BACKGROUND ART 
     In 3rd Generation Partnership Project (3GPP) that is a mobile communication system standardization project, a Multimedia Broadcast Multicast Service (MBMS) has been established (see Non-Patent Literature 1). In the MBMS, a plurality of user terminals receives an MBMS service that is provided from a network in a multicast or broadcast manner. For example, the MBMS service is a broadcast video delivery. 
     In 3GPP, standardization for newly introducing a group communication function is scheduled to be conducted in Release 12. For example, the group communication is a group call (voice over Internet protocol (VoIP)) based on packet communication. In the group communication, basically, unicasting is applied to uplink communication, and unicasting or multicasting is applied to downlink communication. 
     CITATION LIST 
     Non Patent Literature 
     Non patent Literature 1: 3GPP Technical Specification “TS36.300 V12.0.0, ” Jan. 10, 2014 
     SUMMARY 
     In an embodiment according to the present disclosure, a user terminal is configured to communicate with a base station and comprises a controller configured to execute a first discontinuous reception (DRX) operation and a second DRX operation, where the first DRX operation is an operation of discontinuously monitoring first control information, which is transmitted from the base station via a physical downlink control channel (PDCCH), using a cell-radio network temporary identifier (C-RNTI) that uniquely identifies the user terminal in a cell of the base station. The second DRX operation is an operation of discontinuously monitoring second control information, which is transmitted from the base station via the PDCCH, using a group RNTI assigned to a terminal group including the user terminal. The controller is configured to monitor the first control information in a first ON duration for the first DRX operation, and to monitor the second control information in a second ON duration for the second DRX operation, the second ON duration being independent of the first ON duration. The controller is further configured to execute a process of receiving third control information, which is transmitted from the base station via the PDCCH, using a fixed RNTI that predefined in a system, wherein the third control information includes information indicating allocation of PDSCH resources. The PDSCH resources include a plurality of service identifiers, where each service identifier identifies a multicast service provided by the base station; and plural pieces of scheduling information corresponding to the service identifiers on a one-to-one basis. The controller is further configured to receive the service identifiers and the plural pieces of scheduling information, based on the third control information received using the fixed RNTI. 
     In another embodiment according to the present disclosure, a device to be equipped in a user terminal is configured to communicate with a base station and comprises at least one processor communicatively coupled to a memory, the at least one processor configured to execute a first discontinuous reception (DRX) operation and a second DRX operation. The first DRX operation is an operation of discontinuously monitoring first control information, which is transmitted from the base station via a physical downlink control channel (PDCCH), using a cell-radio network temporary identifier (C-RNTI) that uniquely identifies the user terminal in a cell of the base station. The second DRX operation is an operation of discontinuously monitoring second control information, which is transmitted from the base station via the PDCCH, using a group RNTI assigned to a terminal group including the user terminal. The at least one processor is configured to monitor the first control information in a first ON duration for the first DRX operation, and to monitor the second control information in a second ON duration for the second DRX operation, the second ON duration being independent of the first ON duration. The at least one processor is further configured to execute a process of receiving third control information, which is transmitted from the base station via the PDCCH, using a fixed RNTI that predefined in a system, wherein the third control information includes information indicating allocation of PDSCH resources. The PDSCH resources include a plurality of service identifiers, where each service identifier identifies a multicast service provided by the base station; and plural pieces of scheduling information corresponding to the service identifiers on a one-to-one basis, and the at least one processor is further configured to receive the service identifiers and the plural pieces of scheduling information, based on the third control information received using the fixed RNTI. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram illustrating an LTE system according to first to third embodiments. 
         FIG. 2  is a block diagram illustrating a UE according to the first to third embodiments. 
         FIG. 3  is a block diagram illustrating an eNB according to the first to third embodiments. 
         FIG. 4  is a protocol stack diagram of a radio interface according to the first to third embodiments. 
         FIG. 5  is a diagram illustrating a radio frame according to the first to third embodiments. 
         FIGS. 6( a ) and 6( b )  are diagrams for describing an operation according to the first embodiment. 
         FIG. 7  is a sequence diagram illustrating an operation when an eNB allocates a GC-RNTI according to the first embodiment. 
         FIG. 8  is a sequence diagram illustrating an operation when an EPC allocates a GC-RNTI according to the first embodiment. 
         FIG. 9  is a sequence diagram illustrating a group communication operation according to the first embodiment. 
         FIGS. 10( a ) and 10( b )  are diagrams illustrating a first operation pattern according to a first modified example of the first embodiment. 
         FIGS. 11( a ) and 11( b )  are diagrams illustrating a second operation pattern according to a first modified example of the first embodiment. 
         FIGS. 12( a ) to 12( c )  are timing charts illustrating an operation according to a second modified example of the first embodiment. 
         FIGS. 13( a ) and 13( b )  are diagrams for describing an operation according to the second embodiment. 
         FIGS. 14( a ) and 14( b )  are diagrams for describing an operation according to the third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     [Overview of Embodiments] 
     A user terminal according to an embodiment is configured to communicate with a base station. The user terminal includes a controller configured to execute a first discontinuous reception (DRX) operation and a second DRX operation. The first DRX operation is an operation of discontinuously monitoring first control information, which is transmitted from the base station via a physical downlink control channel (PDCCH), using a cell-radio network temporary identifier (C-RNTI) that uniquely identifies the user terminal in a cell of the base station. The second DRX operation is an operation of discontinuously monitoring second control information, which is transmitted from the base station via the PDCCH, using a group RNTI assigned to a terminal group including the user terminal. The controller is configured to monitor the first control information in a first ON duration for the first DRX operation, and to monitor the second control information in a second ON duration for the second DRX operation, the second ON duration being independent of the first ON duration. 
     In an embodiment, the second control information is allocated in a common search space of the PDCCH. 
     In an embodiment, the controller is further configured to execute a process of receiving third control information, which is transmitted from the base station via the PDCCH, using a fixed RNTI that predefined in a system. 
     In an embodiment, the third control information includes information indicating allocation of physical downlink shared channel (PDSCH) resources. A plurality of service identifiers and plural pieces of scheduling information are allocated in the PDSCH resources, the plural pieces of scheduling information corresponding to the service identifiers on a one-to-one basis. 
     In an embodiment, the controller is further configured to receive the service identifiers and the plural pieces of scheduling information, based on the third control information received using the fixed RNTI. 
     In an embodiment, the controller is further configured to execute a process of receiving, from the base station, a message including a plurality of service identifiers and a plurality of group RNTIs, the group RNTIs corresponding to the service identifiers on a one-to-one basis. The message is transmitted to a plurality of user terminals including the user terminal. 
     In an embodiment, a device to be equipped in a user terminal configured to communicate with a base station, includes at least one processor configured to execute a first discontinuous reception (DRX) operation and a second DRX operation. The first DRX operation is an operation of discontinuously monitoring first control information, which is transmitted from the base station via a physical downlink control channel (PDCCH), using a cell-radio network temporary identifier (C-RNTI) that uniquely identifies the user terminal in a cell of the base station. The second DRX operation is an operation of discontinuously monitoring second control information, which is transmitted from the base station via the PDCCH, using a group RNTI assigned to a terminal group including the user terminal. The at least one processor is configured to monitor the first control information in a first ON duration for the first DRX operation, and to monitor the second control information in a second ON duration for the second DRX operation, the second ON duration being independent of the first ON duration. 
     In an embodiment, a user terminal includes a controller configured to execute a process of receiving control information, which is transmitted from a base station via a PDCCH, using a fixed RNTI that predefined in a system. The control information includes information indicating allocation of physical downlink shared channel (PDSCH) resources. A plurality of service identifiers and plural pieces of scheduling information are allocated in the PDSCH resources, the plural pieces of scheduling information corresponding to the service identifiers on a one-to-one basis. The controller is further configured to receive the service identifiers and the plural pieces of scheduling information, based on the control information received using the fixed RNTI. 
     In an embodiment, a device to be equipped in a user terminal, includes at least one processor configured to execute a process of receiving control information, which is transmitted from a base station via a PDCCH, using a fixed RNTI that predefined in a system. The control information includes information indicating allocation of physical downlink shared channel (PDSCH) resources. A plurality of service identifiers and plural pieces of scheduling information are allocated in the PDSCH resources, the plural pieces of scheduling information corresponding to the service identifiers on a one-to-one basis. The at least one processor is further configured to receive the service identifiers and the plural pieces of scheduling information, based on the control information received using the fixed RNTI. 
     In an embodiment, a base station includes a controller configured to execute a process of transmitting control information, which is transmitted to user terminals via a PDCCH, using a fixed RNTI that predefined in a system. The control information includes information indicating allocation of physical downlink shared channel (PDSCH) resources. The controller allocates a plurality of service identifiers and plural pieces of scheduling information into the PDSCH resources, the plural pieces of scheduling information corresponding to the service identifiers on a one-to-one basis. 
     In an embodiment, a device to be equipped in a base station includes at least one processor configured to execute a process of transmitting control information, which is transmitted to user terminals via a PDCCH, using a fixed RNTI that predefined in a system. The control information includes information indicating allocation of physical downlink shared channel (PDSCH) resources. The at least one processor allocates a plurality of service identifiers and plural pieces of scheduling information into the PDSCH resources, the plural pieces of scheduling information corresponding to the service identifiers on a one-to-one basis. 
     [First Embodiment] 
     Hereinafter, exemplary embodiments when the present disclosure is applied to an LTE system that is a mobile communication system based on the 3GPP standard will be described. 
     (1) System Configuration 
     A system configuration of an LTE system according to the first embodiment will be described below.  FIG. 1  is a configuration diagram illustrating the LTE system according to the first embodiment. 
     The LTE system according to the first embodiment includes user equipments (UEs)  100 , an evolved-UMTS terrestrial radio access network (E-UTRAN)  10 , and an evolved packet core (EPC)  20  as illustrated in  FIG. 1 . 
     The UE  100  corresponds to a user terminal. The UE  100  is a mobile communication apparatus, and performs radio communication with a cell (a serving cell). A configuration of the UE  100  will be described later. 
     The E-UTRAN  10  corresponds to a radio access network. The E-UTRAN  10  includes evolved Node-Bs (eNBs)  200 . The eNB  200  corresponds to a base station. The eNBs  200  are connected to one another via an X2 interface. A configuration of the eNB  200  will be described later. 
     The eNB  200  manages one or more cells, and performs radio communication with the UE  100  that has established a connection with its own cell. The eNB  200  has a radio resource management (RRM) function, a user data routing function, a measurement control function for mobility control/scheduling, and the like. A “cell” is used as not only a term indicating a minimum unit of a radio communication area but also a term indicating a function of performing radio communication with the UE  100 . 
     The EPC  20  corresponds to a core network. The EPC  20  includes a mobility management entity (MME)/serving-gateway (S-GW)  300 . The MME performs various kinds of mobility controls on the UE  100 . The SGW performs user data transfer control. The MME/S-GW  300  is connected with the eNB  200  via an S1 interface. The E-UTRAN  10  and the EPC  20  constitute a network of the LTE system. 
       FIG. 2  is a block diagram illustrating the UE  100 . The UE  100  includes a plurality of antennas  101 , a radio transceiver  110 , a user interface  120 , a global navigation satellite system (GNSS) receiver  130 , a battery  140 , a memory  150 , and a processor  160  as illustrated in  FIG. 2 . The memory  150  and the processor  160  constitute a controller. The UE  100  may not include the GNSS receiver  130 . The memory  150  may be integrated with the processor  160 , and this set (that is, a chip set) may be used as the processor  160 ′. 
     The antennas  101  and the radio transceiver  110  are used for transmission and reception of radio signals. The radio transceiver  110  converts a baseband signal (a transmission signal) output from the processor  160  into a radio signal and transmits the radio signal through the antennas  101 . The radio transceiver  110  converts a radio signal received through the antennas  101  into a baseband signal (a reception signal) and outputs the baseband signal to the processor  160 . 
     The user interface  120  is an interface with the user who carries the UE  100 , and includes, for example, a display, a microphone, a speaker, various kinds of buttons, and the like. The user interface  120  receives an operation from the user, and outputs a signal indicating content of the operation to the processor  160 . In order to obtain position information indicating a geographical position of the UE  100 , the GNSS receiver  130  receives a GNSS signal and outputs the received signal to the processor  160 . The battery  140  accumulates electric power to be supplied to the respective blocks of the UE  100 . 
     The memory  150  stores a program executed by the processor  160  and information used for a process performed by the processor  160 . The processor  160  includes a baseband processor that perform, for example, modulation, demodulation, encoding, and decoding of the baseband signal and a central processing unit (CPU) that performs various kinds of processes by executing the program stored in the memory  150 . The processor  160  may include a codec that encodes and decodes audio and video signals. The processor  160  executes various kinds of processes which will be described later and various kinds of communication protocols. 
       FIG. 3  is a block diagram illustrating the eNB  200 . The eNB  200  includes a plurality of antennas  201 , a radio transceiver  210 , a network interface  220 , a memory  230 , and a processor  240  as illustrated in  FIG. 3 . The memory  230  and the processor  240  constitute a controller. The memory  230  may be integrated with the processor  240 , and this set (that is, a chip set) may be used as a processor. 
     The antenna  201  and the radio transceiver  210  are used for transmission and reception of radio signals. The radio transceiver  210  converts a baseband signal (a transmission signal) output from the processor  240  into a radio signal and transmits the radio signal through the antenna  201 . The radio transceiver  210  converts a radio signal received by the antenna  201  into a baseband signal (a reception signal), and outputs the baseband signal to the processor  240 . 
     The network interface  220  is connected with a neighboring eNB  200  via the X2 interface and connected with the MME/S-GW  300  via the S1 interface. The network interface  220  is used for communication performed on the X2 interface and communication performed on the S1 interface. 
     The memory  230  stores a program executed by the processor  240  and information used for a process performed by the processor  240 . The processor  240  includes a baseband processor that perform, for example, modulation, demodulation, encoding, and decoding of the baseband signal and a CPU that performs various kinds of processes by executing the program stored in the memory  230 . The processor  240  executes various kinds of processes which will be described later and various kinds of communication protocols. 
       FIG. 4  is a protocol stack diagram of a radio interface in the LTE system. A radio interface protocol is classified into first to third layers of an OSI reference model, and the first layer is a physical (PHY) layer as illustrated in  FIG. 4 . The second layer includes a medium access control (MAC) layer, a radio link control (RLC) layer, and a packet data convergence protocol (PDCP) layer. The third layer includes a radio resource control (RRC) layer. 
     The PHY layer performs encoding/decoding, modulation/demodulation, antenna mapping/demapping, and resource mapping/demapping. User data and control information are transmitted through a physical channel between the PHY layer of the UE  100  and the PHY layer of the eNB  200 . 
     The MAC layer performs preferential control of data, a retransmission process by hybrid ARQ (HARQ), a random access sequence, and the like. User data and control information are transmitted through a transport channel between the MAC layer of the UE  100  and the MAC layer of the eNB  200 . The MAC layer of the eNB  200  includes a scheduler for deciding transport formats (a transport block size and a modulation and coding scheme (MCS)) of an uplink and a downlink and a resource block to be allocated to the UE  100 . 
     The RLC layer transmits data to an RLC layer of a reception side using the functions of the MAC layer and the PHY layer. User data and control information are transmitted through a logical channel between the RLC layer of the UE  100  and the RLC layer of the eNB  200 . 
     The PDCP layer performs header compression/decompression and encryption/decryption. 
     The RRC layer is defined only in a control plane in which control information is dealt with. Control information (an RRC message) for various kinds of settings is transmitted between the RRC layer of the UE  100  and the RRC layer of the eNB  200 . The RRC layer controls the logical channel, the transport channel, and the physical channel in response to establishment, re-establishment, and release of the radio bearer. When there is a connection (an RRC connection) between the RRC of the UE  100  and the RRC of the eNB  200 , the UE  100  is in an RRC connected state, and otherwise, the UE  100  is in an RRC idle state. 
     A non-access stratum (NAS) layer positioned above the RRC layer performs session management, mobility management, and the like. 
       FIG. 5  is a diagram illustrating a radio frame used in the LTE system. In the LTE system, Orthogonal Frequency Division Multiplexing Access (OFDMA) is applied for downlink, and Single Carrier Frequency Division Multiple Access (SC-FDMA) is applied for uplink. 
     A radio frame is configured with 10 subframes arranged in a time direction as illustrated in  FIG. 5 . Each subframe is configured with two slots arranged in the time direction. A length of each subframe is 1 ms, and a length of each slot is 0.5 ms. Each subframe includes a plurality of resource blocks (RBs) in a frequency direction and includes a plurality of symbols in the time direction. Each resource block includes a plurality of sub carriers in the frequency direction. One resource element (RE) is configured with one symbol and one sub carrier. Among radio resources (time and frequency resources) allocated to the UE  100 , the frequency resources can be specified by resource blocks, and the time resources can be specified by subframes (or slots). 
     In the downlink, an interval of several symbols at the head of each subframe is a control region used as a physical downlink control channel (PDCCH) for transmitting control information mainly. The remaining interval of each subframe is a data region that can be used as a physical downlink shared channel (PDSCH) for transmitting user data mainly. 
     The eNB  200  transmits information (L1/L2 control information) for notifying of downlink and uplink resource allocation results to the UE  100  through the PDCCH. Each PDCCH occupies resources configured with one or more control channel elements (CCEs). One CCE is configured with a plurality of REs. One of 1, 2, 4, and 8 is set as the number of CCEs occupied by the PDCCH (an aggregation level). 
     The eNB  200  transmits a plurality of pieces of control information. The eNB  200  includes CRC bit scrambled using an identifier (Radio Network Temporary ID (RNTI)) of the UE  100  of a transmission destination in control information in order to identify the UE  100  of the transmission destination of each control information. 
     For a plurality of pieces of control information that may be directed to its own UE, each of the UEs  100  performs descrambling on the CRC bits using the RNTI of its own UE, performs blind decoding on the PDCCH, and detects the control information directed to its own UE. 
     In order to reduce the number of blind decodings, a CCE serving as a blind decoding target is limited. A CCE region serving as the blind decoding target is referred to as “search space.” The search space will be described later in detail. 
     (2) Operation According to First Embodiment 
     The LTE system according to the first embodiment supports group communication. An operation for appropriately controlling the group communication according to the first embodiment will be described below. 
     (2.1) Operation Overview 
       FIGS. 6( a ) and 6( b )  are diagrams for describing an operation according to the first embodiment.  FIG. 6( a )  illustrates a downlink subframe according to the first embodiment, and  FIG. 6( b )  illustrates an operation environment according to the first embodiment. 
     As illustrated in  FIGS. 6( a ) and 6( b ) , the LTE system according to the first embodiment includes an eNB  200  that manages a cell and transmits control information in a control region (a PDCCH region) in a downlink subframe and a plurality of UEs  100  that constitute a terminal group (hereinafter, referred to simply as a “group”) that perform the group communication in the cell. Each group is identified by a service identifier (hereinafter, referred to as a “GC service ID”).  FIGS. 6( a ) and 6( b )  illustrate an example in which UEs  100 - 1  to  100 - 3  belong to a group A, and UEs  100 - 4  to  100 - 6  belong to a group B. 
     Each of the UEs  100  is in the RRC connected state, and a different identifier (cell RNTI (C-RNTI)) is allocated from the eNB  200  to each UE  100  in the cell. 
     A group communication identifier (a group communication RNTI (GC-RNTI)) is allocated to each of the UEs  100  that perform the group communication. In the first embodiment, a different GC-RNTI is allocated to each of the UEs  100  for each group. In  FIGS. 6( a ) and 6( b ) , a GC-RNTI(A) is allocated to the UEs  100 - 1  to  100 - 3  belonging to the group A, and a GC-RNTI(B) is allocated to the UEs  100 - 4  to  100 - 6  belonging to the group B. An operation of allocating the GC-RNTI will be described later. 
     The PDCCH region includes a common search space (CSS) in which control information common to all the UEs  100  in the cell is arranged and a UE specific search space (USS) in which control information specific to each of the UEs  100  in the cell is arranged. The control information common to all the UEs  100  in the cell is, for example, allocation information related to a broadcast signal and a paging signal. The control information specific to each of the UEs  100  in the cell is, for example, allocation information related to downlink user data. The USS is set according to the C-RNIT, a subframe number, and the like. 
     In the first embodiment, the PDCCH region further includes a group communication search space (GCSS) in which group communication control information related to the group communication (hereinafter, referred to as “GC control information”) is arranged. The GC control information is, for example, allocation information (information of an allocation resource block) related to downlink user data (group communication data). The GC control information may include information of the MCS. When semi-persistent scheduling is performed, information indicating a duration of an allocation resource block may be included. The GCSS is set according to the GC-RNTI, the subframe number, and the like. In the first embodiment, since the GC-RNTI differs according to each group, the GCSS differs according to each group as well. In  FIGS. 6( a ) and 6( b ) , the GCSS corresponding to the group A and the GCSS corresponding to the group B are individually set. 
     Hereinafter, a region in which the CSS is set in the PDCCH region is referred to as a “CSS region,” a region in which the USS is set is referred to as a “USS region,” and a region in which the GCSS is set is referred to as a “GCSS region.” 
     The eNB  200  arranges the GC control information in the GCSS region according to the GC-RNTI. Specifically, the eNB  200  performs mapping of the GC control information for the group A in the GCSS corresponding to the group A, and performs mapping of the GC control information for the group B in the GCSS corresponding to the group B. The eNB  200  scrambles the GC control information for the group A using the GC-RNTI(A) allocated to the group A, and scrambles the GC control information for the group B using the GC-RNTI(B) allocated to the group B. 
     Each of the UEs  100  acquires the GC control information arranged in the GCSS according to the GC-RNTI allocated to its own UE  100 . Specifically, each of the UEs  100  performs blind decoding (monitoring) of the GCSS corresponding to the group to which its own UE  100  belongs using the GC-RNTI allocated to its own UE  100 . Then, each of the UEs  100  acquires the GC control information for the group to which its own UE  100  belongs through the blind decoding. For example, the UE  100 - 1  acquires the GC control information for the group A through the blind decoding of the GCSS corresponding to the group A. On the other hand, the UE  100 - 4  acquires the GC control information for the group B through the blind decoding of the GCSS corresponding to the group B. 
     As described above, in the first embodiment, since the GC-RNTI differs according to each group, the GC control information is transmitted within the PDCCH region. As a result, for example, a flexible (dynamic) radio resource allocation can be performed according to the number of groups, the group communication data amount, and the like for each group. 
     (2.2) GC-RNTI Allocation Operation 
     Next, a GC-RNTI allocation operation according to the first embodiment will be described. 
     (2.2.1) First Operation Pattern 
     In the first operation pattern, the eNB  200  or the core network (the EPC  20 ) decides the GC-RNTI according to a request from the UE  100  that attempts to start the group communication. The eNB  200  notifies the UE  100  of the request source of the decided GC-RNTI. For example, the eNB  200  transmits the GC-RNTI through an individual RRC message in the unicast manner. In this case, the GC-RNTI may be included in group communication setting information (Configuration). 
       FIG. 7  is a sequence diagram illustrating an operation when the eNB  200  allocates the GC-RNTI. 
     As illustrated in  FIG. 7 , in step S 11 , the UE  100  establishes an RRC connection with the eNB  200 . 
     Thereafter, the UE  100  performs a group communication initiation process. In step S 12 , the UE  100  transmits a GC-RNTI allocation request (a GC control request) to the eNB  200 . The GC control request includes the GC service ID of the group communication that the UE  100  desires to join. 
     In step S 13 , the eNB  200  that has received the GC control request derives the GCRNTI from the GC service ID included in the GC control request. The eNB  200  is assumed to receive a GC service ID list from the EPC  20  and associate the GC-RNTI with each group communication. For example, an association timing is a timing at which the GC service ID list is received from the EPC  20  or a timing at which the GC control request is received from the UE  100 . 
     In step S 14 , the eNB  200  transmits a response (a GC control response) including the GC-RNTI corresponding to the GC service ID to the UE  100 . 
     The UE  100  acquires and holds the GC-RNTI included in the GC control response. The UE  100  starts the blind decoding as the GC-RNTI is held. 
       FIG. 8  is a sequence diagram illustrating an operation when the EPC  20  allocates the GC-RNTI. When the EPC  20  allocates the GC-RNTI, a plurality of eNBs  200  can operate in collaboration with one another. Here, an example in which an MME  300  in the EPC  20  allocates the GC-RNTI is illustrated. 
     As illustrated in  FIG. 8 , in step S 21 , the UE  100  establishes an RRC connection with the eNB  200 . 
     Thereafter, the UE  100  performs a group communication initiation process. In step S 22 , the UE  100  transmits the GC-RNTI allocation request (the GC control request) to the eNB  200 . The GC control request includes the GC service ID of the group communication that the UE  100  desires to join. 
     When the eNB  200  holds an association between the GC service ID and the GC-RNTI, the eNB  200  may allocates the GC-RNTI based on the association. Here, the eNB  200  is assumed not to hold the association. In step S 23 , the eNB  200  transfers the GC control request transmitted from the UE  100  to the MME  300 . 
     In step S 24 , the MME  300  that has received the GC control request derives the GCRNTI from the GC service ID included in the GC control request. 
     In step S 25 , the MME  300  transmits a response (the GC control response) including the GC-RNTI corresponding to the GC service ID to the eNB  200 . 
     In step S 26 , the eNB  200  that has received the GC control response transfers the GC control response to the UE  100 . Further, when the GC-RNTI allocated by the MME  300  is identical to an RNTI allocated by its own eNB  200 , the eNB  200  may request the MME  300  to change the allocation of the GC-RNTI. 
     The UE  100  acquires and holds the GC-RNTI included in the GC control response. The UE  100  starts the blind decoding as the GC-RNTI is held. 
     (2.2.2) Second Operation Pattern 
     In the first operation pattern, the eNB  200  notifies the UE  100  of the GC-RNTI in the unicast manner but may notify of the GC-RNTI in the broadcast manner. 
     In the second operation pattern, the eNB  200  transmits a message including a plurality of GC service IDs that differ according to each group and a plurality of GC-RNTIs corresponding to the plurality of GC service IDs within the cell in the broadcast manner. This message may be a common RRC message (for example, a system information block). 
     In the second operation pattern, the UE  100  that has received the message acquire the GC-RNTI corresponding to the GC service ID of the group communication that it desires to join from the message and holds the GC-RNTI. The UE  100  starts the blind decoding as the GC-RNTI is held. 
     (2.2.3) Range of GC-RNTI 
     Table 1 illustrates available RNTIs in the current specification and ranges of values thereof. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Value  
                   
               
               
                   
                 (hexa-decimal) 
                 RNTI 
               
               
                   
                   
               
             
            
               
                   
                 0000 
                 N/A 
               
               
                   
                 0001-003C 
                 RA-RNTI, C-RNTI,  
               
               
                   
                   
                 Semi-Persistent; 
               
               
                   
                   
                 Scheduling C-RNTI, 
               
               
                   
                   
                 Temporary C-RNTI,  
               
               
                   
                   
                 TPC-PUCCH-RNTI and  
               
               
                   
                   
                 TPC-PUSCH-RNTI (see note) 
               
               
                   
                 003D-FFF3 
                 C-RNTI, Semi-Persistent  
               
               
                   
                   
                 Scheduling C-RNTI, 
               
               
                   
                   
                 Temporary C-RNTI,  
               
               
                   
                   
                 TPC-PUCCH-RNTI and 
               
               
                   
                   
                 TPC-PUSCH-RNTI 
               
               
                   
                 FFF4-FFFC 
                 Reserved for future use 
               
               
                   
                 FFFD 
                 M-RNTI 
               
               
                   
                 FFFE 
                 P-RNTI 
               
               
                   
                 FFFF 
                 SI-RNTI 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 1, an RNTI value has a range of 0000-FFFF. A “FFF4-FFFC” region reserved for the future use may be used as the range of the GC-RNTI value. Alternatively, a part of a “0001-003C” or “003D-FFF3” region may be allocated for the group communication. Alternatively, when a “0001-003C” or “003D-FFF3” region is used, it may be dynamically used, or a part may be cut for the GC-RNTI in advance. 
     (2.3) Group Communication Operation 
     Next, a group communication operation according to the first embodiment will be described. As described above, the eNB  200  allocates downlink radio resources for the group communication using, the GC-RNIT. 
       FIG. 9  is a sequence diagram illustrating a group communication operation according to the first embodiment. In  FIG. 9 , the UEs  100 - 1  to  100 - 3  are assumed to belong to the same group (the group A), and the GC-RNIT is assumed to have been allocated. The eNB  200  starts to allocate the downlink radio resources for the group communication according to a group communication delivery request transmitted from the EPC  20 . 
     As illustrated in  FIG. 9 , in step S 31 , the eNB  200  performs mapping of the GC control information for the group A in the GCSS corresponding to the group A, and scrambles the GC control information for the group A using the GC-RNTI allocated to the group A. As described above, the GC control information is, for example, the allocation information (the information of the allocation resource block) related to the group communication data. The GC control information may include information of the MCS. 
     In step S 32 , the eNB  200  transmits the GC control information and the group communication data. When the dynamic resource allocation (dynamic scheduling) is performed, the group communication data is arranged in a resource block in a data region of a downlink subframe in which the GC control information is arranged. However, the eNB  200  may perform a semi-persistent resource allocation (semi-persistent scheduling). 
     In step S 33 , each of the UEs  100  acquires the GC control information arranged in the GCSS corresponding to the group A according to the GC-RNTI allocated to its own UE  100 . Specifically, each of the UEs  100  performs the blind decoding (monitoring) of the GCSS corresponding to the group to which its own UE  100  belongs using the GC-RNTI allocated to its own UE  100 . Each of the UEs  100  acquires the GC control information for the group to which its own UE  100  belongs through the blind decoding. 
     In step S 34 , each of the UEs  100  receives the group communication data based on the acquired GC control information. Specifically, each of the UEs  100  demodulates and decodes the group communication data arranged in the resource block indicated by the GC control information. 
     (3) Conclusion of First Embodiment 
     In the first embodiment, the eNB  200  arranges the GC control information in the GCSS region according to the GC-RNTI. Each of the UEs  100  acquires the GC control information arranged in the GCSS according to the GC-RNTI allocated to its own UE  100 . As a result, the dynamic scheduling in the group communication can be implemented. 
     Further, it is possible to collectively allocate the resource blocks to a plurality of UEs  100  belonging to one group and collectively transmit (that is, multicast) the group communication data to a plurality of UEs  100  through the resource blocks. Thus, the radio resources can be efficiently used. 
     [First Modified Example of First Embodiment] 
     The first embodiment has been described in connection with the example in which the GC-RNTI differs according to each group. In this case, it is necessary to secure a plurality of GC-RNTIs and a plurality of GCSSs, and resources are likely to be tight. Thus, one GC-RNTI may be shared by the respective groups instead of causing the GC-RNTI to differ according to each group. 
     In the first modified example of the first embodiment, the GC-RNTI is a fixed value that is specified on a system in advance. Thus, the GC-RNTI is common to all groups. In this case, the GC control information includes information for receiving radio resources included in the data region other than the PDCCH region in the downlink subframe. This information includes the information of the allocation resource block, the information of the MCS, and the like. When the semi-persistent scheduling is performed, information indicating the duration of the allocation resource block may be further included. 
     In the first modified example of the first embodiment, the user data or the control information is arranged in the radio resources indicated by the GC control information together with the GC service ID. In other words, the GC control information is common to the respective groups and cut for each group based on the GC service ID in the data region. 
       FIGS. 10( a ) and 10( b )  are diagrams illustrating a first operation pattern according to the first modified example of the first embodiment. In the first operation pattern, the user data is arranged in the radio resources indicated by the GC control information together with the GC service ID. 
     As illustrated in  FIGS. 10( a ) and 10( b ) , the eNB  200  arranges the GC control information in the GCSS region according to the GC-RNTI. The GC-RNTI is common to the groups A and B, and thus the GCSS is also common to the groups A and B. The eNB  200  scrambles the GC control information using the GC-RNTI. 
     The eNB  200  allocates the radio resources in the data region to the UEs  100  belonging to the groups A and B. In the first operation pattern, the eNB  200  arranges the GC service ID of the group A, the GC service ID of the group B, the group communication data of the group A, and the group communication data of the group B in the radio resources. Here, the group communication data of the group A is associated with the GC service ID of the group A. The group communication data of the group B is associated with the GC service ID of the group B. For example, a corresponding GC service ID is added to the head of the group communication data. 
     The UE  100  acquires the GC control information in the GCSS using the GC-RNIT allocated to its own UE  100 . The UE  100  specifies allocation radio resources in the data region based on the GC control information, acquires the GC service ID included in the specified radio resources, and detects the GC service ID corresponding to the group communication in which its own UE  100  is taking part. Then, the UE  100  acquires the group communication data associated with the detected GC service ID. 
       FIGS. 11( a ) and 11( b )  are diagrams illustrating a second operation pattern according to the first modified example of the first embodiment. In the second operation pattern, the control information is arranged in the radio resources indicated by the GC control information together with the GC service ID. 
     As illustrated in  FIGS. 11( a ) and 11( b ) , the eNB  200  arranges the GC control information in the GCSS region according to the GC-RNTI. The GC-RNTI is common to the groups A and B, and thus the GCSS is also common to the groups A and B. The eNB  200  scrambles the GC control information using the GC-RNTI. 
     In the second operation pattern, the eNB  200  allocates radio resources in which the control information is arranged, radio resources in which the group communication data of the group A is arranged, and radio resources in which the group communication data of the group B is arranged in the data region. 
     The eNB  200  arranges control information (A) including the GC service ID of the group A and control information (B) including the GC service ID of the group B in the radio resources in which the control information is arranged. The control information (A) is scheduling information related to the radio resources in which the group communication data of the group A is arranged. The control information (B) is scheduling information related to the radio resources in which the group communication data of the group B is arranged. The control information (A) and (B) may include the information of the MCS. Further, when the semi-persistent scheduling is performed, the control information (A) and (B) may further include information the duration of the allocation resource block. 
     The UE  100  acquires the GC control information in the GCSS using the GC-RNIT allocated to its own UE  100 . The UE  100  specifies the radio resources in the data region based on the GC control information, and acquires the control information included in the specified radio resources. Here, the UE  100  detects the control information including the GC service ID corresponding to the group communication in which its own UE  100  is taking part. Then, the UE  100  specifies the radio resources indicated by the detected control information, and acquires the group communication data included in the specified radio resources. 
     [Second Modified Example of First Embodiment] 
     In the second modified example of the first embodiment, an example in which the UE  100  that performs the group communication performs a discontinuous reception (DRX) operation is assumed. The UE  100  that performs the DRX operation monitors control information in a first ON period in which control information different from the GC control information is received, and monitors the GC control information in a second ON period in which the GC control information is received. 
       FIGS. 12( a ) to 12( c )  are timing charts illustrating an operation according to the second modified example of the first embodiment. 
     As illustrated in  FIG. 12( a ) , the UE  100  that performs the DRX operation monitors the control information different from the GC control information such as the control information transmitted using the C-RNTI in an ON period of a DRX cycle. Specifically, the receiver (the radio transceiver  110 ) is turned at intervals of the DRX cycles, and the blind decoding of the PDCCH region is performed using the C-RNTI. 
     Here, when the group communication is allocated discontinuously (periodically), the UE  100  needs to turn on the receiver in the ON period in which the GC control information is received as well as the ON period illustrated in  FIG. 12( a )  as illustrated in  FIG. 12( b ) . Thus, as illustrated in  FIG. 12( c ) , the UE  100  performs control the receiver is turned on in the ON period illustrated in  FIG. 12( a )  and the ON period illustrated in  FIG. 12( b ) . 
     [Second Embodiment] 
     A second embodiment will be described focusing on a difference with the first embodiment. A system configuration according to the second embodiment is the same as in the first embodiment. 
     In the first embodiment, the GC control information is arranged in the GCSS region. On the other hand, in the second embodiment, the GC control information is arranged in the CSS region without disposing the GCSS region. 
       FIGS. 13( a ) and 13( b )  are diagrams for describing an operation according to the second embodiment. 
     As illustrated in  FIGS. 13( a ) and 13( b ) , the eNB  200  arranges the GC control information related to the group communication in the CSS according to the GC-RNTI allocated to each group. Here, the eNB  200  scrambles the GC control information using the GC-RNTI. 
     Specifically, the eNB  200  performs mapping of the GC control information for the group A in the CSS corresponding to the group A, and performs mapping of the GC control information for the group B in the CSS corresponding to the group B. The eNB  200  scrambles the GC control information for the group A using the GC-RNTI(A) allocated to the group A, and scrambles the GC control information for the group B using the GC-RNTI(B) allocated to the group B. 
     The eNB  200  also arranges the control information common to all the UEs  100  in the cell in the CSS. The eNB  200  scrambles the common control information, for example, using an SI-RNTI and/or a P-RNTI. 
     Each of the UEs  100  acquires the GC control information arranged in the CSS according to the GC-RNTI allocated to its own UE  100 . Specifically, each of the UEs  100  performs the blind decoding (monitoring) of the GCSS corresponding to the group to which its own UE  100  belongs using the GC-RNTI allocated to its own UE  100 . Then, each of the UEs  100  acquires the GC control information for the group to which its own UE  100  belongs through the blind decoding. 
     The remaining points are similar to those in the first embodiment. Specifically, in the second embodiment, the GC-RNTI differs according to each group in which the group communication is performed in the cell. 
     The eNB  200  or the core network decides the GC-RNTI according to the request of the UE  100  that desires to start the group communication. The eNB  200  notifies the UE  100  of the request source of the decided GC-RNTI. 
     Alternatively, the eNB  200  transmits a message including a plurality of GC service IDs that differ according to each group and a plurality of GC-RNTIs corresponding to the plurality of GC service IDs within the cell in the broadcast manner. 
     [Modified Example of Second Embodiment] 
     The second embodiment has been described in connection with the example in which the GC-RNTI differs according to each group. However, similarly to the first modified example of the first embodiment, one GC-RNTI may be shared by the respective groups. 
     [Third Embodiment] 
     A third embodiment will be described focusing on a difference with the first embodiment. A system configuration according to the second embodiment is the same as in the first embodiment. 
     In the first embodiment, the GC control information is arranged in the GCSS region. On the other hand, in the third embodiment, the GC control information is arranged in the USS region without disposing the GCSS region. 
       FIGS. 14( a ) and 14( b )  are diagrams for describing an operation according to the third embodiment. 
     As illustrated in  FIGS. 14( a ) and 14( b ) , the eNB  200  arranges the GC control information related to the group communication in the USS according to the GC-RNTI allocated to each group. Here, the eNB  200  scrambles the GC control information using the GC-RNTI. 
     Specifically, the eNB  200  performs mapping of the GC control information for the group A in the USS corresponding to the group A, and performs mapping of the GC control information for the group B in the USS corresponding to the group B. The eNB  200  scrambles the GC control information for the group A using the GC-RNTI(A) allocated to the group A, and scrambles the GC control information for the group B using the GC-RNTI(B) allocated to the group B. 
     Each of the UEs  100  acquires the GC control information arranged in the USS according to the GC-RNTI allocated to its own UE  100 . Specifically, each of the UEs  100  performs the blind decoding (monitoring) of the GUSS corresponding to the group to which its own UE  100  belongs using the GC-RNTI allocated to its own UE  100 . Then, each of the UEs  100  acquires the GC control information for the group to which its own UE  100  belongs through the blind decoding. 
     The remaining points are similar to those in the first embodiment. Specifically, in the third embodiment, the GC-RNTI differs according to each group in which the group communication is performed in the cell. 
     The eNB  200  or the core network decides the GC-RNTI according to the request of the UE  100  that desires to start the group communication. The eNB  200  notifies the UE  100  of the request source of the decided GC-RNTI. 
     Alternatively, the eNB  200  transmits a message including a plurality of GC service IDs that differ according to each group and a plurality of GC-RNTIs corresponding to the plurality of GC service IDs within the cell in the broadcast manner. 
     [First Modified Example of Third Embodiment] 
     The third embodiment has been described in connection with the example in which the GC-RNTI differs according to each group. However, similarly to the first modified example of the first embodiment, one GC-RNTI may be shared by the respective groups. 
     [Second Modified Example of Third Embodiment] 
     In the third embodiment, similarly to the second modified example of the first embodiment, the UE  100  that performs the DRX operation monitors control information in the first ON period in which control information different from the GC control information is received, and monitors the GC control information in the second ON period in which the GC control information is received. 
     [Other Embodiments] 
     The above embodiments have been described in connection with the example in which each of the UEs  100  belongs to one group, but one UE  100  may belong to a plurality of groups. In this case, one UE  100  may hold a plurality of GC-RNTIs. 
     In the above embodiments, the LTE system has been described as an example of the mobile communication system, but the present disclosure is not limited to the LTE system and may be applied to any other system than the LTE system.