RADIO COMMUNICATI0N SYSTEM, BASE srAiloNAPPARATUS, AND RADIO TERMINAL
[Technical Field][0001]This application relates to a radio communication system in which base stationscommunicate with the same radio terminal in their respective cells.[Background Art][0002]To improve deterioration in communication quality due to the recent rapid increase inmobile traffic and to achieve higher-speed communication, 3GPP lnng Term Evolution (LTE)specifies a carrier aggregation (CA) function to allow a radio base station (eNode B (eNB)) and aradio terminal (User Equipment (UE) to communicate with each other using a plurality of cells.The cells which can be used by the UE in the CA are limited to cells of one eNB (i.e., cells thatare served or managed by the eNB). The cells used by the UE in the CA are classified into aprimary cell (PCell) that is already used as a serving cell when the CA is started and a secondarycell(s) (SCell(s)) that is used additionally or subordinately. In the PCell, Non Access Stratum(NAS) mobility information (NAS mobility information) and security information (securityinput) is sent and received during radio connection (re)-establishment (RRC ConnectionEstablishment, RRC Connection Re-establishment) (see Section 7.5 inNon-Patent Literature l).[0003]In the CA, SCell configuration information transmitted from the eNB to the UE includesSCell radio resourc€ configuration information common to UEs(RadioResourceConfigCommonSCell) and SCell radio resource configuration informationdedicated to a specific UE (RadioResourceConfigDedicatedSCell). The latter informationmainly indicates a dedicated configuration @hysicalConfigDedicated) for a physical layer.When cells (carriers) having different transmission timings (Timing Advance: TA) areaggregated in an uplink, configuration information (MAC-MainConfigSCell) about a MediumAccess Control (MAC) sublayer is also transmitted from the eNB to the UE. However, theconfiguration information about the MAC sublayer includes only an STAG-Id, which is an indexof TA Group (TAG) representing a set of cells included in the same TA (see Section 5.3.10.4 inNon-Patent Literature 2). The other configurations for the MAC sublayer in the SCell are the same as those in the PCell.[0004]One of the ongoing study items in the LTE standardization related mainly to aHeterogeneous Network (HetNet) environment is dual connectivity in which the UE performscommunication using a pluralityof wlls of a plurality of eNBs (see Non Patent-Literature 3).Dual connectivity is a process to allow an UE to perform communication simultaneously usingboth radio resources (i.e., cells or carriers) provided (or managed) by a main base station (masterbase station, Master eNB (MeNB)) and a sub base station (secondary base station, SecondaryeNB (SeNB)). Dual connectivity enables inter-eNB CA in which the UE aggregates a pluralityof cells managed by different eNBs. Since the UE aggregates radio resources managed bydifferent nodes, dual connectivity is also called "inter-node radio resource aggregation". TheMeNB is connected to the SeNB through an inter-base-station interface called Xn. The MeNBmaintains, for the UE in dual connectivity, the connection (Sl-MME) to a mobility managementapparatus (Mobility Management Entity (MME)) in a core network (Evolved Packet Core(EPC)). Accordingly, the MeNB can be called a mobility management point (or mobilityanchor) of the UE. For example, the MeNB is a Macro eNB, and the SeNB is a Pico eNB orLow Power Node (LPN).[0005]Further, in dual connectivity, a bearer split for splitting a network bearer (EPS bearer)over the MeNB and the SeNB has been studied. The term "network bearer (EPS Bearer)" usedin this specification means a virtual connection that is configured between a UE and an endpoint(i.e., Packet Data Network Gateway (P-GW)) in a core network (EPC) for each service providedto the UE. In an alternative of the bearer split, for example, both a radio bearer (RB) in a cell ofthe MeNB and a radio bearer in a cell of the SeNB are mapped to one network bearer. Theradio bearer (RB) described herein refers mainly to a data radio bearer (DRB). The bearer splitwill contribute to a further improvement in user throughput.[Citation List][Non Patent Literature][0006][Non-Patent Literature I ] 3GPP TS 36.300 Vl 1 .5.0 (2013-03), "3rd Generation PartnershipProject; Technical Specification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN);Overall description; Stage 2 (Release I l)", March,2013fNon-Patent Literature 2l 3GPP TS 36.331 Vl I .4.0 (2013-06), "3rd Generation Partnershipl5202530
l0Japanese Patent Application No. 2013-227472 ^Project; Technical Specification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification (Release I 1)",June, 2013fNon-Patent Literature 3] 3GPP TR 36.842 V0.2.0 (2013-05), "3rd Generation PartnershipProject; Technical Specification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA); Study on Small Cell Enhancements for E-UTRA and E-UTRAN -Higher layer aspects (Release l2)",May,2013[Summary of Invention][Technical Problem][0007]An adequate control procedure for starting dual connectivity involving a bearer split hasnot been established. Accordingly, an object to be achieved by embodiments disclosed in thespecification is to provide a control procedure or signalling necessary for starting dualconnectivity involving a bearer split. Other objects and novel features will become apparentfrom the following description and the accompanying drawings.ISolution to Problem][0008]In an embodiment, a radio communication system includes a radio access network and aradio terminal. The radio access network includes a first base station that manages a first celland a second base station that manages a second cell. The radio terminal supports dualconnectivity involving a bearer split in which a network bearer between the radio terminal and acore network is split over the first base station and the second base station. The radio accessnetwork is configured to transmit, to the radio terminal, first control information relates to anaccess stratum and is necessary for the dual connectivity involving the bearer split.[000e]In an embodiment, a base station apparatus includes a communication control unitconfigured to control dual connectivity involving a bearer split in which a network bearerbetween a radio terminal and a core network is split over the base station apparatus and aneighbor base station. The communication control unit is configured to transmit, to the radioterminal, first control information that relates to an access stratum and is necessary for the dualconnectivity involving the bearer split.[0010]In an embodiment, a radio terminal includes a communication control unit configured tocontrol dual connectivity involving a bearer split in which a network bearer between the radiol5202530
4' Japnese Patent Application No. 2013-227472terminal and a core network is split over first and second base stations. The communicationcontrol unit is configured to receive, from the first or second base station, first controlinformation that relates to an access stratum and is necessary for the dual connectivity involvingthe bearer split, determine whether the bearer split is required based on the first control5 information, and control eommunication employing the dual connectivity in accordance with thefirst control information.[00] 1]In an embodiment, a control method includes transmitting, from a first base station to aradio terminal, first control information that relates to an access stratum and is necessary for dual10 connectivity involving a bearer split in which a network bearer between the radio terminal and acore network is split over the first base station and a second base station.[0012]In an embodiment, a control method that is performed by a radio terminal includes: (a)receiving, from a first or second base station, first control information that relates to an accessl5 stratum and is necessary for dual connectivity involving a bearer split in which a network bearerbetween the radio terminal and a core network is split over the first and second base stations; and(b) determining whether the bearer split is required based on the first control information, andcontrolling communication employing the dual connectivity in accordance with the first controlinformation.20 [0013]In an embodiment, a program includes instructions (software codes) for causing acomputer to perform the above-described control method when the program is loaded into thecomputer.[Advantageous Effects of Invention]25 [0014]According to the embodiments described above, it is possible to provide a controlprocedure or signalling necessary for starting dual connectivity involving a bearer split.IBrief Description of Drawings][0015]30 Fig. 1A is a diagram showing an example of a user plane protocol stack of LTE Layer-2related to dual connectivity involving a bearer split;Fig. lB is a diagram showing another example of the user plane protocol stack of LTELayer-Z related to dual connectivity involving a bearer split;Fig. 2 is a diagram showing a configuration example of a radio communication system
J4arests'PatentApplicatio nNo.20l3-22t472 5according to first to third embodiments;Fig. 3 is a sequence diagram showing an example of a control procedure for startingdual connectivity involving a bearer split according to the first embodiment;Fig. 4 is a sequence diagram showing another example of the control procedure for5 starting dual connectivity involving a bearer split according to the first embodiment;Fig. 5 is a sequence diagram showing an example of the control procedure for startingdual connectivity involving a bearer split according to the second embodiment;Fig. 6 is a sequence diagram showing an example of the control procedure for startingdual connectivity involving a bearer split according to the third embodiment;l0 Fig. 7 is a block diagram showing a configuration examplc of an MeNB according tothe first to third embodiments;Fig. 8 is a block diagram showing a configuration example of an SeNB according to thefirst to third embodiments; andFig. 9 is a block diagram showing a configuration example of a UE according to the firstl5 to third embodiments.[Description of Embodiments][0016]Specific embodiments will hereinafter be described in detail with reference to thedrawings. The same or coresponding elements are denoted by the same reference symbols20 throughout the drawings, and repeated descriptions thereof are omitted as appropriate for clarityof the explanation.[0017]A plurality of embodiments below will mainly be described with reference to anEvolved Packet System (EPS). However, these embodiments are not limited to the EPS, and25 can be applied to other mobile communication networks or systems, such as a 3GPP UniversalMobile Telecommunications System (UMTS), a 3GPP2 CDMA2000 system (lxRTT, High RatePacket Data (HRPD)), a global system for mobile communications (GSM)/General packet radioservice (GPRS) system, and a WiMAX system.[0018]30 First EmbodimentFirst, with regard to some embodiments including this exemplary embodiment, severalexamples of dual connectivity involving a bearer split are described. Figs. lA and lB showtwo alternatives of a user plane protocol stack of LTELayer-2 relatcd to dual connectivity (e.g.,inter-node radio resource aggregation) involving a bearer split. In the bearer split, a network
IO1520256' laparese' Patent Appl ication N o. 20 1 3 -227 47 2bearer (EPS bearer) configured between a UE and an endpoint (i.e., P-GW) of a core network(EPC) is split over an MeNB 11 and an SeNB 12. In the alternatives shown in Figs. lA and lB,an EPS bearer #2 is split over the MeNB I I and the SeNB 12. An EPS bearer #l shown in Figs.I A and I B is a normal bearer which is not subjected to a bearer split. Accordingly, the EPSbearer #1 is mapped in a one-to-one correspondence to the radio bearer in a cell of the MeNB I 1.[001e]In the alternatives shown in Figs. lA and I B, one data radio bearer (DRB), which has aone-to-one association with the'EPS'bearer #2 is split over the MeNB I 1 and the SeNB 12 in aPacket Data Convergence Protocol (PDCP) sublayer, a Radio Link Control (RLC) sublayer, or aMAC sublayer of Layer-2. Specifically, in the alternative shown in Fig. 1A, a PDCP entity ofthe MeNB I I terminates the S I -U of the EPS bearer #2. In other words, one S 1 bearer and onedata radio bearer (DRB) which are mapped to the EPS bearer #2 are terminated at the PDCPsublayer of the MeNB I l. Fufther, in the alternative shown in Fig. lA, the MeNB 1 I and theSeNB 12have independent RLC entities for bearer split, and one DRB (or PDCP bearer)terminated at the MeNB I I is split into the RLC bearer of the MeNB 11 and the RLC bearer ofthe SeNB 12. Note that, the term "PDCP bearer" means a connection terminated at the PDCPsublayers of the eNB and the UE. The PDCP bearer can also be called a PDCP Protocol DataUnit (PDCP PDU). In the example shown in Fig. lA, there is one PDCP bearer related to theEPS bearer #2 tobe split, and this PDCP bearer is terminated at the MeNB I I and the UE 2.On the other hand, the term "RLC bearer" means a connection terminated at the RLC sublayersof the eNB and the UE. The RLC bearer can also be called an RLC PDU or a logical channel.In the example shown in Fig. l, there are two independent RLC bearers associated with the EPSbearer #2. One of the two RLC bearers is terminated at the MeNB I I and the UE 2, andtheother one is terminated at the SeNB 12 and the UE 2. Accordingly, in the architecture shown inFig. 1A, the UE 2 is required to have two independent RLC entities associated with the EPSbearer #2 to be split.[0020]Like in the alternative shown in Fig. lA, in the altemative shown in Fig. 1B, a PDCPentity of the MeNB I I terminates the Sl-U of the EPS bearer #2. Further, as for the EPS bearer#2 to be split, the MeNB 1 I has a master RLC entity and the SeNB 12 has a slave RLC entity.In the alternative shown in Fig. 1B, the UE 2 is required to have only one RLC entity associatedwith the EPS bearer #2 to be split. In the downlink, the slave RLC entity of the SeNB l2receives, from the master RLC entity of the MeNB 11, RLC PDUs that has already beengenerated by the master RLC entity and allocated to the slave RLC for transmission.30
t0' Japanese Patent Application No. 2013 -227 472[0021]The following description is based on an assumption that a cell of the MeNB I I can becalled a PCell and a cell of the SeNB 12 can be called an SCell from the viewpoint of theconventional Carrier Aggregation (CA). However, the scope of this embodiment is not limitedto this. For example, when the radio terminal (UE) performs the CA (lntra-SeNB CA) on aplurality of cells of the SeNB 12 (i.e., at least a plurality of downlink Component Carriers (CCs))during dual connectivity, one of the cells of the SeNB l2 subjected to the CA may be defined asa PCell or a pseudo PCell which functions similarly to a PCell. The pseudo PCell can also becalled an Anchor cell, a Master cell, a Control cell, or the like. In the CA of the cells of theSeNB 12,the fonner cell (the PCell of the SeNB 12) has a role similar to that of the PCell in theconventional CA. In the PCell of the SeNB 12,for example, the eNB (SeNB) carries out SCellconfiguration or SCell activation/deactivation for the CA, and the UE carries out Radio LinkMonitoring @LM)/Radio Link Failure (RLF) detection. Further, the UE may perform, forexample, transmissionof LllL2 control information (e.g., CQI, CSI, HARQ feedback,Scheduling Request) in an uplink control channel (PUCCH), transmission of (a preamble of) aContention-based Random Access Channel (RACH), and reception of a response (RandomAccess Response (RAR)) to the RACH Preamble. The laffer cell (the Pseudo PCell of theSeNB 12) has a role as a cell having a PCell function regarding the control of a User Plane (UP)in the conventional CA. In the Pseudo PCell of the SeNB 12,the UE may perform, for example,transmission of LllL2 control information in the uplink control channel (PUCCH), transmissionof (a preamble of) a Contention-based RACH, and reception of a response (RAR) to the RACHPreamble. Furthermore, in the UE, the cells of the MeNB I I and the cells of the SeNB l2 neednot necessarily have a hierarchical relationship (PCell and SCell) or a master-slave relationship.[00221The user plane protocol stack for dual connectivity involving a bearer split is not limitedto the altematives shown in Figs. 1A and 18. In the bearer split, for example, two radio bearersmay be mapped to one network bearer (EPS bearer). When the tenns in Figs. lA and 1B areused, it can be expressed that the EPS bearer #2 is mapped to both the radio bearer (RB) in thecell (PCell) of the MeNB 1l and the radio bearer in the cell (SCell) of the SeNB 12. Forconvenience of explanation, the radio bearer in the cell (PCell) of the MeNB I I is defined hereinas a Primary RB (P-RB) and the radio bearer (RB) in the cell (SCell) of the SeNB is definedherein as a Secondary RB (S-RB). Since the bearer split is mainly applied to data radio bearers(DRBs), the P-RB and the S-RB can also be called P-DRB and S-DRB, respectively. Forexample,theMeNB ll mayterminatetheSl-UoftheEPSbearer#2,andtheMeNB ll andthet5202530
l08Japanese Patent Application No. 2013-227472SeNB 12 may have independent PDCP entities. Further, in a new layer higher than the PDCPentity of the MeNB I l, a downlink S1-U packet stream of the EPS bearer #2 may be split overthe PDCP entity of the MeNB I I and the PDCP entity of the SeNB 12. In this case, there aretwo independent PDCP bearers related to the EPS bearer #2. One of the two PDCP bearers isterminated at the MeNB I I and the UE 2, and the other one is terminated at the SeNB l2 and theUE 2.[0023]Fig.2 shows a configuration example of a radio communication system according tosome embodiments including this embodiment. The radio communication system includes aradio access network (RAN) l, a radio terminal (UE)2, and a core network 3. In the EPS, theRAN I is an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), and the corenetwork 3 is an Evolved Packet Core (EPC). The E-UTRAN I includes base stations (evolvedNodeBs (eNBs)) lL and 12. The eNB I I manages a cell 110, and the eNB l2 manages a cell120. The UE 2 is connected to the eNBs l l and 12 by means of a radio access technology.The EPC 3 is accessed from the UE 2 through the E-UTRAN 1, and provides the UE 2 with aconnection service (e.g., Intemet Protocol (IP) connection service) for connecting to an externalnetwork (Packet Data Network (PDN)). In addition, Fig.2 shows a HetNet environment.Specifically, the cell 1 10 shown in Fig. 2has a coverage area larger than that of the cell 120.Fig.2 also shows a hierarchical cell configuration in which the cell 120 is located within the cell110. However, the cell configuration shown in Fig. 2 is merely an example. For example, thecells 1 1 0 and 120 may have the same degree of coverage. In other words, the radiocommunication system according to this embodiment may be applied to a homogeneous networkenvironment.[0024)The E-UTRAN I and the UE 2 according to this embodiment support dual connectivityinvolving a bearer split. Specifically, while using the cell 110 of the eNB (i.e., MeNB) I I as aprimary cell (PCell), the UE 2 can use the cell 120 of the eNB (i.e., SeNB) 12 as a secondary cell(SCell). The UE 2 can receive and/or transmit data of one EPS bearer subjected to a bearersplit through the PCell I l0 and the SCell 120.[0025]To start dual connectivity involving a bearer split, the E-UTRAN I and the UE 2according to this embodiment camy out a control procedure or signalling as described below.The E-UTRAN 1 is configured to transmit, to the UE2, first control information that relates toan access stratum and is necessary for dual connectivity involving a bearer split. The UE 2 isl5202530
l09' 'Japanese Patent Application No. 2013-227472configured to receive the first control information from the E-UTRAN l, determine whether thebearer split is required based on the first control information (i.e., based on the decoding result ofthe first control information), and control communication employing the dual connectivityinvolving the bearer split in accordance with the first control information. In order to determinewhether the bearer split is required based on the first control information, the UE 2 may consider,for example, whether configuration information related to the bearer split is included or not,whether an explicit indication (e.g., a flag) to instruct performing the bearer split is included ornot, or whether radio resource control information necessary for execution of the bearer split isincluded or not. The first control information relating to the access stratum to be transmiffedfrom the E-UTRAN I to the UE 2 may include at least one of the following information items(l) to (s):(l) Radio bearer (RB) configuration information about P-RB and S-RB;(2) Control information about Scheduling Request (SR);(3) Control information about uplink (UL) transmission power control;(4) Control information about generation of uplink (UL) MAC PDUs; and(5) Control information about a terminal measurement report (UE measurement report).[0026](l) RB configuration information about P-RB and S-RBThe information items (1) to (5) will be sequentially described below. The RBconfiguration information about the P-RB and the S-RB indicates mapping of the two RBs (i.e.,P-RB and S-RB) in the PCell I l0 and the SCell 120 to one EPS beaner. This RB configurationinformation is effective in the architecture in which one EPS bearer is mapped to both the P-RBin the PCell I l0 and the S-RB in the SCell 120. The RB configuration information about theP-RB and the S-RB may indicate that an EPS bearer identity in comrnon with the P-RB is alsoset to the S-RB. For example, the RB configuration information may indicate that the EPSbearer identity associated with the EPS Radio Bearer identity (or DRB-identity) of the P-RB isalso associated with the EPS Radio Bearer identity (or DRB-identity) of the S-RB.Alternatively, the RB configuration information may indicate that the EPS bearer identity andthe EPS Radio Bearer identity (or DRB-identity) which are the same as those of the P-RB are setto the S-RB.10027)The differences between the RB configuration information about the P-RB and theS-RB and the SCell configuration information in the normal CA (intra-eNB CA) will now bedescribed. In the normal CA (intra-eNB CA), the eNB transmits the SCell configuration to receive the first control information from the E-UTRAN l, determine whether thebearer split is required based on the first control information (i.e., based on the decoding result ofthe first control information), and control communication employing the dual connectivityinvolving the bearer split in accordance with the first control information. In order to determinewhether the bearer split is required based on the first control information, the UE 2 may consider,for example, whether configuration information related to the bearer split is included or not,whether an explicit indication (e.g., a flag) to instruct performing the bearer split is included ornot, or whether radio resource control information necessary for execution of the bearer split isincluded or not. The first control information relating to the access stratum to be transmiffedfrom the E-UTRAN I to the UE 2 may include at least one of the following information items(l) to (s):(l) Radio bearer (RB) configuration information about P-RB and S-RB;(2) Control information about Scheduling Request (SR);(3) Control information about uplink (UL) transmission power control;(4) Control information about generation of uplink (UL) MAC PDUs; and(5) Control information about a terminal measurement report (UE measurement report).[0026](l) RB configuration information about P-RB and S-RBThe information items (1) to (5) will be sequentially described below. The RBconfiguration information about the P-RB and the S-RB indicates mapping of the two RBs (i.e.,P-RB and S-RB) in the PCell I l0 and the SCell 120 to one EPS beaner. This RB configurationinformation is effective in the architecture in which one EPS bearer is mapped to both the P-RBin the PCell I l0 and the S-RB in the SCell 120. The RB configuration information about theP-RB and the S-RB may indicate that an EPS bearer identity in comrnon with the P-RB is alsoset to the S-RB. For example, the RB configuration information may indicate that the EPSbearer identity associated with the EPS Radio Bearer identity (or DRB-identity) of the P-RB isalso associated with the EPS Radio Bearer identity (or DRB-identity) of the S-RB.Alternatively, the RB configuration information may indicate that the EPS bearer identity andthe EPS Radio Bearer identity (or DRB-identity) which are the same as those of the P-RB are setto the S-RB.10027)The differences between the RB configuration information about the P-RB and theS-RB and the SCell configuration information in the normal CA (intra-eNB CA) will now bedescribed. In the normal CA (intra-eNB CA), the eNB transmits the SCell configuration to thel5202530
l0l52025t0' ' Japanese Patent Application No. 2013-227472UE through the PCell, and the UE executes the SCell configuration. The SCell configuration inthe normal CA includes dedicated (per-UE) radio resource configuration information for SCell(RadioResourceConfigDedicatedSCell). The configuration information in the normal CAincludes SCell physical channel configuration information, but does not include any informationabout the radio bearer (RB). This is because the unique functions necessary for the SCell in thenormal CA are only the functions of a PHY layer and a MAC sublayer (i.e., the RLC sublayerand the PDCP sublayer of the SCell are in common with those of the PCell), and accordingly, theradio bearer configuration ofthe SCell (i.e., mapping between the EPS bearer and the radiobearer) is unnecessary.[0028]On the other hand, the architecture in which one EPS bearer is mapped to both the P-RB'in the PCell 110 and the S-RB in the SCell 120 requires information indicating that one EPSbearer is mapped to radio bearers of different eNBs (MeNB I I and SeNB l2). In other words,since the SCell configuration method employed in the normal CA (intra-eNB CA) lacks a radiobearer configuration procedure for the SCell, it is difficult to apply the SCell configurationmethod in the normal CA to the SCell configuration in the architecture in which one EPS beareris mapped to both the P-RB in the PCell 110 and the S-RB in the SCell 120. Accordingly, asdescribed herein, new RB configuration information different from that of the normal CA isrequired. Note that, the new RB configuration information is configuration informationespecially about the S-RB and thus can also be called S-RB configuration information.1002e)(2) Control information about SRWhen there is data to be transmitted to the UE2, a Scheduling Request (SR) istransmitted from the UE to an eNB to request allocation of an uplink radio resource. The UEtransmits the SR in a Physical Uplink Control Channel (PUCCH), or by using a Random AccessProcedure using a Random Access Channel (RACH). When data for transmission of the EPSBearer subjected to a bearer split is available in the UE 2, control information about the SRindicates either a cell (e.g., the PCell 110) of the MeNB 1l or a cell (e.g., the SCell 120) of theSeNB 12 to which the SR is to be transmitted. For example, the control information about theSR may explicitly indicate one of the MeNB I I (PCell I l0) and the SeNB 12 (SCell 120) towhich the SR (or an RACH for transmitting the SR) is to be transmitted. Altematively, thecontrol information about the SR may indicate that the UE 2 is allowed to select the destinationof the SR (or an RACH for transmifting the SR). Specifically, the control information about theSR may specify signalling which enables selection of the destination of the SR (or an RACH for30
l0ltJapanese Patent Application No. 2013-227472transmitting the SR), or may instruct the UE 2 to select the destination of the SR. Through thiscontrol, the UE 2 can appropriately determine the destination of the SR even during execution ofthe bearer split.[0030](3) Control information about UL transmission power controlDuring execution of the bearer split, an upper limit of total transmission power foruplink transmission in a cell (e.g., the PCell 110) of the MeNB 1l and a cell (e.g., the SCell 120)of the SeNB 12 may be specified. The control information about UL transmission powercontrol may be applied to the procedure for controlling uplink transmission power in the UE 2when the UE 2 is scheduled for uplink transmission in the PCell I l0 and uplink transmission inthe SCell 120 in the same subframe (LTE subframe) (i.e., when the UE 2 receives UL grants forboth the PCell I l0 and the SCell 120). Alternatively, the control information about ULtransmission power control may be applied to the procedure for controlling uplink transmissionpower in the UE 2 when data or control information to be transmitted in the uplink is available inboth the PCell 110 and the SCell 120. The control information may indicate, for example,maximum transmission power applied to the total transmission power for uplink transmission inthe PCell I l0 and the SCell 120. The UE 2 may first determine the transmission power in thePCell I l0 and then determine the transmission power in the SCell 120. In other words, the UE2may perform uplink transmission in the SCell 120 by using surplus transmission power that isnot used for uplink transmission in the PCell I 10. Alternatively, the IJE 2 may perform uplinktransmission in the PCell I l0 by using surplus transmission power that is not used for uplinktransmission in the SCell 120. Through this control, the UE 2 can appropriately perform theUL transmission power control even during execution of the bearer split.[003r]Altematively, during execution of the bearer split, an upper limit of transmission powermay be specified for each of uplink transmission in the PCell I l0 and uplink transmission in theSCell 120. In this case, the control information about UL transmission power control mayindicate first and second maximum transmission power applied to uplink transmission in thePCell I l0 and uplink transmission in the SCell 120, respectively. The control information mayindicate a configuration value ofthe first maximum transmission power, and an offset value (apositive or negative value) for obtaining the second maximum transmission power. A valueobtained by adding the offset value to the configuration value of the first maximum transmissionpower may be used as the second maximum transmission power applied to uplink transmissionin the SCell 120. Through this control, the UE 2 can appropriately perform the ULl5202530
1012' Japanebel Patent Application N o. 20 13'227 47 2transmission power control even during execution of the bearer split.[0032](4) Control information about generation of UL MAC PDUsEven during execution of the bearer split, the UE 2 should generate MAC PDUs inconsideration of an EPS bearer QoS (QoS class identifier (QCI), a guaranteed bit rate (GBR), anaggregate maximum bit rate (AMBR), etc.) for each of all EPS bearers including bearers whichare subjected to a bearer split and bearers which are not subjected to a bearer split. One MACPDU can also be called a transport block. Accordingly, the control information aboutgeneration of UL MAC PDUs is applied to the procedure for generating a first MAC PDU foruplink transmission in the PCell I l0 and a second MAC PDU for uplink transmission in theSCell 120 in the UE 2, when the UE 2 is scheduled for uplink transmission in the cell (e.g., thePCell I l0) of the MeNB 1 1 and uplink transmission in the cell (e.g., the SCell 120) of the SeNBl2 in the same subframe (LTE subframe).[0033]The control information about generation of UL MAC PDUs may indicate, for example,a first Prioritized Bit Rate (PBR) applied to generation of the first MAC PDU and a second PBRapplied to generation of the second MAC PDU for one logical cannel of the EPS bearersubjected to the bearer split. In other words, the information may specify two PBRs, i.e., thefirst PBR for transmission in the PCell I 10 and the second PBR for transmission in the SCell 120,for one logical channel of the EPS bearer subjected to the bearer split. In this case, the first andsecond PBRs may be configured so that the total (arithmetic sum) of the first and second PBRsbecomes a PBR appropriate for one logical channel of the EPS bearer subjected to the bearersplit. This control can prevent transmission of an excessive amount of uplink data of the EPSbearer subjected to the bearer split (i.e., prevent an excessive amount of uplink data of the EPSbearer subjected to the bearer split from being included in the MAC PDU), as compared with theuplink data of EPS bearers which are not subjected to the bearer split.[0034]The control information about the generation of the UL MAC PDU may indicate eitherthe first MAC PDU or the second MAC PDU for which the Prioritized Bit Rate (PBR) applied tothe logical channel of the EPS bearer subjected to the bearer split is should be preferentiallysecured. It may be desirable for the tJE 2 to preferentially use the uplink resources allowed inthe PCell 1 10 for transmission of EPS bearers which are not subjected to the bearer split. Thisis because uplink transmission of the EPS bearer subjected to the bearer split can use the uplinkresources allowed in the SCell 120. Accordingly, the control information about generation ofl520t'2530
l0Japanese Patent Application No. 2\t3-22i472 13UL MAC PDUs may indicate that the PBR applied to the logical channel of the EPS bearersubjected to the bearer split should be preferentially secured for the second MAC PDU. Thiscontrol can suppress transmission of an excessive amount of uplink data of the EPS bearersubjected to the bearer split, as compared with uplink data of EPS bearers which are notsubjected to the bearer split.[003s]The control information about generation of UL MAC PDUs may include aconfiguration value (weighting factor) used for weighting a PBR applied to the PCell I l0 (firstMAC PDU) and a PBR applied to the SCell 120 (second MAC PDU) during execution of thebearer split. Further, the control information may include a configuration value (weightingfactor) for weighting a PBR applied to the logical channel of the EPS bearer subjected to thebearer split and a PBR applied to a logical channel of an EPS bearer which is not subjected to thebearer split.[0036](5) Control information about a terminal measurement report (UE measurement report)LTE specifies the following events that trigger a terminal measurement report (UEMeasurement Report).- Event Al (Serving becomes better than threshold)- Event ,{2 (Serving becomes worse than threshold)- Event A3 (Neighbour becomes offset better than PCell)- Event ,{4 (Neighbour becomes better than threshold)- Event 45 (PCell becomes worse than thresholdl and neighbour becomes better thanthreshold2)- Event ,46 (Neighbour becomes offset better than Scell)[0037]The term "Serving (cell)" represents each cell configured and activated by a network(i.e., eNB) so that the UE 2 can use the cell for data communication. For example, when theUE 2 uses two cells in the conventional CA, each of the two cells is a serving cell, and the cell ofinterest (i.e., the serving cell to be compared) may be determined depending on the cell in whichthe measurement report configuration is performed. That is, the cell to which the configurationis transmiffed (the cell in which the UE 2 receives the configuration) may be considered as theserving cell. On the other hand, the term "neighbour (cell)" is basically a cell other than theserving cell. However, in Events A.3 and ,A.5, a serving cell other than the serving cell ofinterest (i.e., a comparison reference) may also be considered as one of the neighbor cells.15202530
l0l4' ,Japanese Patent Application No. 2013-227472[0038]The control information about the terminal measurement report may indicate any one ormore of the above-mentioned events, or may indicate an event newly defined for the bearer split.When the control information indicates any one or more of the above-mentioned events, thePCell may be the cell 110 of the MeNB l1 or the cell 120 of the SeNB 12. Fufther, the SCell(s)may be a cell(s) other than the cell I l0 of the MeNB 1 I (if the cell(s) is configured), the cell 120of the SeNB 72, or a cell(s) other than the cell 120 of the SeNB 12 (if the cell(s) is configured).Examples of the new event may include the following events A7-Al0 (the numbers assigned tothe events are only illustrative and are not limited thereto):- Event A7 (Neighbour becomes offset better than Pseudo PCell);- Event A8 (Pseudo PCell becomes worse than thresholdl and neighbour becomes better thanthreshold2);- Event A'9 (Neighbour of SeNB becomes better than threshold); and- Event A10 (Neighbour of SeNB becomes offset better than SCell).[003e]Next, several examples of the control procedure for starting dual connectivity (e.g.,inter-node radio resource aggregation) involving a bearer split are described. Fig. 3 is asequence diagram showing an example of the control procedure for starting dual connectivityinvolving a bearer split. In the example shown in Fig. 3, dual connectivity involving a bearersplit is configured during a procedure in which the UE 2 transitions from an RRC_IDLE state toan RRC_CONNECTED state to start a service (e.g., FTP download). Upon determining that abearer split is necessary (or effective) for the llB 2, the E-UTRAN I initiates configuration of thebearer split. Further, in the example shown in Fig. 3, one EPS Bearer is mapped to both thePrimary RB (P-RB) in the PCell I l0 and the Secondary RB (S-RB) in the SCell 120. In theexample shown in Fig. 3, the UE 2 first establishes the P-RB in the PCell I 10, and thenestablishes the S-RB in the SCell 120.[0040]In step S I l, the UE 2 executes a Connection Establishment procedure with theE-UTRAN 1. In the Connection Establishment procedure of step Sl 1, an RRC connection isfirst established between the MeNB 1 I and the UE 2 (step l), and then initial security activationand establishment of a DRB (i.e., P-RB) are carried out (step 2). Step I includes transmissionof an RRC Connection Request message from the UE 2 to the MeNB I l, transmission of anRRC Connection Setup message from the MeNB I I to the UE2, and transmission of an RRCConnection Setup Complete message from the UE 2tothe MeNB 1 l. Step 2 includesl5202530
. 'gapahese Patent Application No. 2013-227472 15transmission of an RRC Connection Reconfiguration message from the MeNB l l to the tJE2,and transmission of an RRC Connection Reconfiguration Complete message from the lJE2tothe MeNB I l. The configuration information about the P-RB is included in the RRCConnection Reconfiguration message in step 2.s [004r]In step S12, the E-UTRAN I transmits an S-RB configuration (Bearer SplitConfiguration) to the UE 2. The S-RB configuration may be transmitted by the MeNB 11, orby a combination of the MeNB 1l and the SeNB 12. In other words, apart of the S-RBconfiguration may be transmiffed from the MeNB I I to the lJE2, and the rest of the S-RBl0 configuration may be transmitted from the SeNB l2 to the UE2. The S-RB configuration maybe transmitted using an RRC Connection Reconfiguration message as shown in Fig. 3.[0042)In step Sl3, the UE 2 reports completion ofthe S-RB configuration to the E-UTRAN l.The UE 2 may report the completion of the S-RB configuration to the MeNB I I or the SeNB 12,l5 or to both of them. The completion ofthe S-RB configuration may be transmitted using anRRC Connection Reconfiguration Complete message as shown in Fig. 3.[0043]In step S14, the E-UTRAN I notifies the UE 2 aboutthe start of using the S-RB (BearerSplit Activation). The notification of the start of using the S-RB may be transmitted from the20 MeNB I I or the SeNB 12. Note that step Sl4 may be omitted. In this case, the use of theS-RB may be started upon completion of step Sl3.[0044]The S-RB configuration (Bearer Split Configuration) transmitted from the E-UTRAN Ito the UE 2 in step S12 of Fig. 3 corresponds to the first control information relating to an access25 stratum described above. The S-RB configuration (Bearer Split Configuration) is a genericterm (logical term) for configuration elements included in the following four messages:- DRB-ToAddMod_Sbearer;- RadioResourceConfi gCommon_Sbearer;- RadioResourceConfi gDedicated_Sbearer; and30 -BearerSplitResourceConfig.These configuration elements may be transmiffed to the UE 2 as one informationelement (IE) or as a plurality of information elements (IEs).[004s]DRB-ToAddMod Sbearer indicates the S-RB configuration (e.g., eps-Bearerldentity,drb-ldentity, pdcp-Config, and rlc-Config). As described above, eps-Bearerldentity anddrb-ldentity of the S-RB may be the same as eps-Bearerldentity and drb-ldentity of the P-RB.However, drb-ldentity of the P-RB may be different from that of the P-RB.[0046]RadioResourceConfigCommon_sbearer indicates a resource configuration (e.g.,prach-Confi g, pdsch-Confi gCommon, pusch-Confi gCommon, pucch-Confi gCommon,uplinkPoweControlCommon, and tdd-Config, dl-Bandwidth) of the S-RB. In other words,RadioResourceConfigCommon-sbearer includes common radio resource information about thecell in which the S-RB is configured (established).[0047)RadioResourceConfigDedicated_Sbearer indicates a resource configuration (e.g.,physicalConfigDedicated and mac-MainConfig) of the S-RB. In other words,RadioResourceConfigDedicated_sbearer includes dedicated radio resource information aboutthe cell in which the S-RB is configured (established). The above-mentionedDRB-ToAddMod_Sbearer may be transmitted as one element contained in this IE.[0048]BearerSplitResourceConfig indicates specific configurations of the bearer split. Thespecific configuration of the bearer split includes control parameters related to functions usedduring execution of the bearer split. These control parameters can be used for configuringfunctions that require a configuration for the bearer split different from that when no bearer splitis executed, or for configuring a new (special) function that is used only during execution of thebearer split. As described above, these control parameters may include at least one of: (a)control information about a scheduling request (SR) and a random access channel (RACH); (b)control information about UL transmission power control (UL power control); and (c) controlinformation about generation of UL MAC PDUs (e.g., control information about logical channelprioritization (LCP)).[004e]Fig. 4 is a sequence diagram showing another example of the control procedure forstarting dual connectivity involving a bearer split. The example shown in Fig. 4 is differentfrom the example shown in Fig. 3 in that the P-RB and the S-RB are simultaneously configuredduring the procedure in which the UE 2 transitions from the RRC IDLE state to theRRC_CONNECTED state.[0050]15202530In steps 52l to S25, the UE 2 executes a Connection Establishment procedure with the
l0l7Japanese Patent Application No. 2013-227472E-UTRAN l. That is, steps S2l to S25 correspond to step S1 I shown in Fig. 3. Steps S21 toS23 correspond to an RRC connection establishment procedure (step I ), and steps S24 and S25correspond to a DRB establishment procedure (step 2).[0051]In step 52l, the UE 2 transmits an RRC Connection Request message to the E-UTRANl. In step S22,the E-UTRAN I transmits an RRC Connection Setup message to the UE 2.This RRC Connection Setup message contains both a configuration of the PCell I l0 and aconfiguration of the SCell 120. In step S23, the UE 2 transmits an RRC Connection SetupComplete message to the E-UTRAN 1. This RRC Connection Setup Complete messageindicates the completion of the configuration of the PCell 110 and the SCell 120.[00s2]In step S24, the E-UTRAN I transmits an RRC Connection Reconfiguration message tothe UE 2 to establish DRBs (i.e., both the P-RB and the S-RB). This RRC ConnectionReconfiguration message contains both a configuration of the P-RB and a configuration of theS-RB. In step S25, the UE 2 transmits an RRC Connection Reconfiguration Complete messageto the E-UTRAN l. This RRC Connection Reconfiguration Complete message indicates thecompletion ofthe configuration of the P-RB and the S-RB.[00s3]In step S25, the E-UTRAN 1 notifies the UE 2 about the start of using the S-RB (Bearersplit Activation). Similar to step Sl4 shown in Fig. 3, step S25 may be omitted.[0054]In the procedure shown in Fig. 4, apart (e.g., BearerSplitResourceConfig) of the SCellconfiguration may be transmitted in step S24 instead of step S22.[0055]The processing by the E-UTRAN 1 in the procedure shown in Fig. 4 may be performedby the MeNB I l, or may be performed by a combination of the MeNB I I and the SeNB 12.[0056]Figs. 3 and 4 show examples of the control or signalling for starting dual connectivityinvolving a bearer split is carried out when the UE 2 transitions from the RRC_IDLE state to theRRC_CONNECTED state. However, the control or signalling for starting dual connectivityinvolving a bearer split may be carried out when the UE 2 is already in the RRC_CONNECTEDstate in the PCell I l0 and is in the ECM-CONNECTED state with the EPC 3 and when the UE 2is receiving a service from the EPC 3 through the PCell I l0 (i.e., when the EPS Bearer is alreadyconfigured).l5202530
l0l8Japanese Patent Application No. 2013-227472[0057]As can be understood from the above description, according to this embodiment, it ispossible to provide a control procedure or signalling necessary for starting dual connectivityinvolving a bearer split.[0058]Second EmbodimentIn this embodiment, a modification of the first embodiment is described. Aconfiguration example of a radio communication system according to this embodiment is similarto that shown in Fig. 2. In this embodiment, the MeNB 1l exchanges signalling messages withthe SeNB 12 through an inter-base-station interface (e.g., Xn interface), and applies aconfiguration of dual connectivity (e.g., inter-node radio resource aggregation) involving abearer split to the SeNB I2. For example, the MeNB I I may send, to the SeNB 12, secondcontrol information necessary for starting dual connectivity involving a bearer split (i.e.,configuration information of the bearer split). At this time, the SeNB 12 may determinewhether the second control information (bearer split configuration information) received fromthe MeNB l1 is acceptable. If the second control information is not acceptable, the SeNB 12may notify the MeNB 11 that the second control information is not acceptable, or may suggestan acceptable alternative configuration to the MeNB I 1. At least apart of the content of thesecond control information (configuration information of the bearer split) may be the same as apart of the content of the first control information described above. The MeNB I I and theSeNB 12 may exchange signalling messages through an X2 interface or an S I interface, insteadof using the Xn interface.[005e]Fig. 5 is a sequence diagram showing an example of the control procedure for startingdual connectivity involving a bearer split in this embodiment. Like in the example shown inFig. 3, in the example shown in Fig. 5, dual connectivity involving a bearer split is configuredduring the procedure in which the UE 2 transitions from the RRC_IDLE state to theRRC_CONNECTED state to start a service (e.g., FTP download). Upon determining that abearer split is necessary (or effective) for the UE 2, the MeNB I I initiates configuration of thebearer split. Like in the example shown in Fig. 3, in the example shown in Fig. 5, one EPSBearer is mapped to both the Primary RB (P-RB) in the PCell 110 and the secondary RB (S-RB)in the SCell 120. Like in the example shown in Fig. 3, in the example shown in Fig. 5, the UE2 first establishes the P-RB in the PCell 1 10, and then establishes the S-RB in the SCell 120.[0060]l5202530
' : Japanese PatentApplication No. 2013-227472 19The processing of step 53l may be performed between the MeNB I I and the UE 2 inthe same manner as the processing of step Sl l shown in Fig. 3. In step S32 of Fig. 5, theMeNB I I sends a request for (execution or configuration of) a bearer split to the SeNB 12. Instep S33, the SeNB 12 sends, to the MeNB I l, a response as to whether the (execution or5 configuration of) bearer split is accepted or not. If the (execution or configuration of) bearersplit is accepted in the SeNB 12,the processing of steps S34 to 536 is carried out. Theprocessing of steps S34 to 536 may be performed between the MeNB I I and the UE 2 in thesame manner as the processing of steps Sl2 to Sl4 shown in Fig. 3.[0061]l0 The configuration information of the bearer split may also be sent when the request forthe bearer split is sent from the MeNB I I to the SeNB 12 in step S32 shown in Fig. 5. Theconfiguration information ofthe bearer split indicates, for example, mapping between the S-RBand the EPS bearer subjected to the bearer split. The configuration information of the bearersplit may include the EPS bearer identity of the EPS bearer subjected to the bearer split and thel5 Radio Bearer identity (DRB-identity) of the S-RB. Altematively, the configuration informationof the bearer split may include the EPS bearer identity of the EPS bearer, and may not includethe Radio Bearer identity (DRB-identity) of the S-RB. In this case, the SeNB 12 maydetermine the Radio Bearer identity (DRB-identity) of the S-RB, and may notiff the MeNB I Iof the determined Radio Bearer identity (DRB-identity) ofthe S-RB in step S33.20 [0062]The configuration information of the bearer split, which is sent from the MeNB I I tothe SeNB 12 in step S32 shown in Fig. 5, may include at least one of the following informationitems, which are transmitted in step S12 shown in Fig. 3 (and step S34 shown in Fig. 5):- DRB-ToAddMod_Sbearer;25 - ldentification information about a cell of the SeNB subjected to a bearer split (e.g., ECGIand/or PCI);- RadioResourceConfi gCommon_Sbearer;- RadioResourceConfi gDedicated_Sbearer; and- BearerSplitResourceConfi g.30 [0063]In addition to or in place of these information items, the configuration information ofthe bearer split may include at least one of:- Identification information of the UE2 (e.9., C-RNTI and/or TMSI);- Information about security; and
1020" -Xapanese Patent Appl icati on N o. 20 1 3 -227 47 2- Information about radio resource use.[0064]Examples of the information about security includes KeNB, KeNB*,NextHopChainingCount, and SecurityAlgorithmConfig. However, the information aboutsecurity may include other security information of an access stratum (AS) layer. Examples ofthe information about radio resource use include a request for reporting the use status (ResourceStatus) of resources in the SeNB 12, andlor the cycle of the report.[006s]As can be understood from the above description, according to this embodiment, it ispossible to provide a control procedure or signalling between the MeNB 1 I and the SeNB 12that is necessary for starting dual connectivity involving a bearer split.[0066]Third EmbodimentIn this embodiment, a modification of the first and second embodiments is described.A configuration example of a radio communication system according to this embodiment issimilar to that shown in Fig. 2. Like in the second embodiment, the MeNB l1 according to thisembodiment exchanges signalling messages with the SeNB 12 through an inter-base-stationinterface (e.g., Xn interface), and applies a configuration of dual connectivity involving a bearersplit to the SeNB 12.[0067]Fig. 6 is a sequence diagram showing an example of the control procedure for startingdual connectivity involving a bearer split in this embodiment. Like in the example shown'inFig. 4, in the example shown in Fig. 6, the P-RB and the S-RB are simultaneously configuredduring the procedure in which the UE 2 transitions from the RRC IDLE state to theRRC_CONNECTED state.[0068]The processing of steps 541 to S43 may be performed between the MeNB 11 and theUE 2 in the same manner as the processing of steps 52l to S23 shown in Fig. 4. In step S44shown in Fig. 6, the MeNB l l performs NAS Service Setup with the EPC 3, and configures theEPS Bearer (NAS connection establishment). At this time, the MeNB I I may send a requestfor a bearer split, a notification to perform a bearer split, or the like to the EPC 3 (specifically,MME).[006e]The processing of steps S45 and 546 may be performed between the MeNB I 1 and thel5202530
l02l. "' " Sapercse?atent Application No. 2013-227472SeNB 12 in the same manner as the processing of steps S32 and S33 shown in Fig. 5.Specifically, in step S45, the MeNB I I requests the SeNB l2 to execute (configure) a bearersplit. In step 546, the SeNB 12 sends, to the MeNB I l, a response as to whether the execution(configuration) ofa bearer split is accepted or not.[0070]The processing of steps S47 to S49 may be performed between the MeNB 1l and theUE 2 in the same manner as the processing of steps S24 to 526 shown in Fig. 4. If theexecution (configuration) of a bearer split is accepted in the SeNB l2 in the procedure of stepsS45 and 546, the MeNB I I transmits to the UE 2 an RRC Connection Reconfiguration messagecontaining both the P-RB configuration and the S-RB configuration in step S47. On the otherhand, if the execution (configuration) of a bearer split is denied in the SeNB 12, in step S47, theMeNB I I transmits to the UEZ an RRC Connection Reconf,rguration message which containsthe P-RB configuration and does not contain the S-RB configuration.[0071]As can be understood from the above description, according to this embodiment, it ispossible to provide a control procedure or signalling between the MeNB I I and the SeNB 12that is necessary for starting dual connectivity involving a bearer split.[0072]Next, configuration examples of the MeNB I l, the SeNB 12, and the UE 2 according tothe first to third embodiments are described. Fig.7 is a block diagram showing a configurationexample of the MeNB 11. A radio communication unit 1l I receives an uplink signaltransmitted from the UE 2 via an antenna. A received data processing unit I l3 recovers thereceived uplink signal. Obtained received data is transferred to other network nodes, such asServing Gateway (S-GW) or MME of the EPC 3, or another eNB, via a communication unit I14.For example, uplink user data received from the UE 2 is transferred to the S-GW within the EPC3. NAS control data contained in control data received from the UE 2 is transferred to theMME within the EPC 3. Furtheq the received data processing unit I l3 receives control data tobe sent to the SeNB 12 from a communication control unit I15, and sends the received controldata to the SeNB 12 via the communication unit I 14.[0073]A transmission data processing unit I l2 receives user data addressed to the UE 2 fromthe communication unit I 14, and performs error correction coding, rate matching, interleaving,or the like, to thereby generate a transport channel. Further, the transmission data processingunit I l2 adds control information to a data sequence of the transport channel, to thereby generatel5202530
l0l5202522'Japarese' Pdent Application No. 2013 -227 472a transmission symbol sequence. The radio communication unit I I I generates a downlinksignal by performing processing including carrier wave modulation based on the transmissionsymbol sequence, frequency conversion, and signal amplification, and transmits the generateddownlink signal to the UE 2. The transmission data processing unit I l2 receives control data tobe transmitted to the UE 2 finm the communication control unit 1 15, and transmits the receivedcontrol data to the UE 2 viathe radio communication unit I I l.100741The communication control rmit 1 15 controls dual connectivity involving a bearer split.The communication control unit I l5 is configured to transmit, the first control information,which relates to the access stratum and is necessary for dual connectivity involving a bearer split,to the IJE 2 via the transmission data processing unit I 12 and the radio communication unit 1 I 1.In the second and third embodiments, the communication control unit 115 is configured to sendthe radio bearer (RB) configuration information, which indicates mapping between the S-RB andthe EPS bearer subjected to the bearer split, to the SeNB 12 via the communication unit I 14.[0075]Fig. 8 is a block diagram showing a configuration example of the SeNB 12. Thefunctions and operations of a radio communication unit 121, a transmission data processing unit122, areceived data processing unit 123, and a communication unit 124, which are shown in Fig.8, are the same as those of the corresponding elements, i.e., the radio communication unit I I l,the transmission data processing unit 112, the received data processing unit 113, and thecommunication unit 114 in the MeNB l1 shown in Fig. 7.[0076]A communication control unit 125 ofthe SeNB l2 controls dual connectivity involvinga bearer split. In the second and third embodiments, the communication control unit 125 isconfigured to receive the radio bearer (RB) configuration information, which indicates mappingbetween the S-RB and the EPS bearer subjected to the bearer split, from the MeNB I I via thecommunication unit I 24.[00771Fig. 9 is a block diagram showing a configuration example of the UE2. A radiocommunication unit 2l is configured to support dual connectivity and to communicatesimultaneously in a plurality of cells (PCell 110 and SCell 120) served by different eNBs (MeNBI I and SeNB l2). Specifically, the radio communication unit 21 receives a downlink signalfrom one or both of the MeNB I I and the SeNB 12 via an antenna. A received data processingunit22 recovers received data from the received downlink signal, and sends the recovered data30
l0Japanese PatentApplication No. 2013-227472 23to a data control unit 23. The data control unit23uses the received data according to theintended use. A transmission data processing unit24 and the radio communication unit 2lgenerate an uplink signal by using data for transmission supplied from the data control unit 23,and transmit the generated uplink signal to one or both of the MeNB I I and the SeNB 12.[0078]A communication control unit 25 of the UE 2 controls dual connectivity involving abearer split. As described in the first embodiment, the communication control unit 25 receivesfrom the E-UTRAN I (MeNB I I or SeNB 12) the first control information, which relates to anaccess stratum and is necessary for dual connectivity involving a bcarer split, and controlscommunication of dual connectivity involving a bearer split based on the first controlinformation.[007e]Other EmbodimentsThe communication control processes in the MeNB I l, the SeNB 12, andthe UE 2 inassociation with dual connectivity involving a bearer split as described in the first to thirdembodiments may be implemented by a semiconductor processing device including anApplication Specific Integrated Circuit (ASIC). These processes may be implemented bycausing a computer system including at least one processor (e.g., a microprocessor, a MicroProcessing Unit (MPU), or a Digital Signal Processor (DSP) to execute a program.Specifically, one or more programs including instructions for causing the computer system toperform algorithms described above with reference to sequence diagrams and the like may becreated, and the program(s) may be supplied to a computer.[0080]The program(s) can be stored and provided to a computer using any type ofnon-transitory computer readable media. Non-transitory computer readable media include anytype of tangible storage media. Examples of non-transitory computer readable media includemagnetic storage media (such as flexible disks, magnetic tapes, hard disk drives, etc.), opticalmagnetic storage media (e.g. magneto-optical disks), Compact Disc Read Only Memory(CD-ROM), CD-R, CD-R/W, and semiconductor memories (such as mask ROM, ProgrammableROM (PROM), Erasable PROM (EPROM), flash ROM, Random Access Memory (RAM), etc.).The program(s) may be provided to a computer using any type of transitory computer readablemedia. Examples of transitory computer readable media include electric signals, optical signals,and electromagnetic waves. Transitory computer readable media can provide the program to acomputer via a wired communication line, such as electric wires and optical fibers, or a wirelessl5202530
24Japanese Patent Application No. 2013-227472communication line.[0081]In the first to third embodiments, the LTE system is mainly described. However, asdescribed above, these embodiments may be applied to radio communication systems other than5 the LTE system, such as a 3GPP UMTS, a 3GPP2 CDMA2000 system (1xRTT, HRPD), aGSM/GPRS system, or a WiMAX system.[0082]The above embodiments are only illustrative of the application of the technical ideaobtained by the present inventor. That is, the technical idea is not limited only to the above10 embodiments and can be modified in various ways as a matter of course.[Reference Signs List][0083]1 EVOLVED UTRAN (E-UTRAN)2 USER EQUIPMENT (UE)l5 3 EVOLVED PACKET CORE (EPC)11 MASTER eNodeB (MeNB)12 SECONDARY eNodeB (SeNB)25 COMMUNICATION CONTROL TINIT110 PRIMARY CELL (PCell)20 120 SECONDARY CELL (SCell)I 15 COMMUNICATION CONTROL UNIT125 COMMUNICATION CONTROL UNIT144 FEC DECODER
Claimsl. A radio communication system comprisinga radio access network including first and second base stations that manage a first celland a second cell, respectively; and5 a radio terminal that supports dual connectivity involving a bearer split in which anetwork bearer between the radio terminal and a core network is split over the first base stationand the second base station,wherein the radio access network is configured to transmit, to the radio terminal, firstcontrol information that relates to an access stratum and is necessary for the dual connectivityl0 involving the bearer split.2. The radio communication system according to Claim l, wherein the radio terminalis configured to receive the first control information, determine whcther the bearer split isrequired based on the first control information, and control communication employing the duall5 connectivity in accordance with the first control information.3. The radio communication system according to Claim I or 2, whereinin the bearer split, a first radio bearer in the first cell and a second radio bearer in thesecond cell are both mapped to the network bearer, and20 the first control information includes radio bearer configuration information indicatingmapping of the first and second radio bearers to the network bearer.4. The radio communication system according to any one of Claims I to 3, whereinthe first base station is configured to transmit the first control infonrnation to the radio terminal,25 and to transmit, to the second base station, second control information that relates to an accessstratum and is necessary for the dual connectivity involving the bearer split.5. The radio communication system according to Claim 4, whereinin the bearer split, a first radio bearer in the first cell and a second radio bearer in the30 second cell are mapped to the network bearer, andthe second control information includes radio bearer configuration informationindicating mapping between the second radio bearer and the network bearer.6. The radio communication system according to Claim 4 or 5, wherein the second
t0' iJapahesd Patent App I icat io n N o. 20 I 3 -221 47 2control information includes configuration information about a bearer split.7. The radio communication system according to any one of Claims I to 6, whereinthe first base station is configured to instruct the radio terminal and the second base station toexecute the bearer split.8. The radio communication system according to any one of Claims I to 7, whereinthe first control informati'on'inficates either the first or second base station to which the radioterminal should transmit a Scheduling Request or a Random Access Channel (RACH) forrequesting allocation of an uplink radio resource when data for transmission of the networkbearer is available in the radio terminal.9. The radio communication system according to any one of Claims I to 8, whereinthe first control information includes Layer-1 configuration information applied to a procedurefor controlling uplink transmission power in the radio terminal when the radio terminal isscheduled for uplink transmission in the first cell and uplink transmission in the second cell inthe same subframe.10. The radio communication system according to Claim 9, wherein the Layer-lconfiguration information indicates maximum transmission power applied to total transmissionpower of uplink transmission in the first cell and the second cell.11. The radio communication system according to Claim 9, wherein the Layer-lconfiguration information indicates first maximum transmission power applied to uplinktransmission in the first cell and second maximum transmission power applied to uplinktransmission in the second cell.12. The radio communication system according to Claim 11, wherein the Layer-lconfiguration information includes a configuration value of the first maximum transmissionpower and an offset value from the configuration value for obtaining the second maximumtransmission power.13. The radio communication system according to any one of Claims I to 12, whereinthe first control information includes Layer-2 configuration information applied to a procedurel5202530
l03Japanese Patent Application No. 2013-227472for generating, in the radio terminal, a first Medium Access Control Protocol Data Unit (MACPDU) for uplink transmission in the first cell and a second MAC PDU for uplink transmission inthe second cell when the radio terminal is scheduled for the uplink transmission in the first celland the uplink transmission in the second cell in the same subframe.14. The radio communication system according to Claim 13, wherein theLayer-2configuration information indicates a first Prioritized Bit Rate (PBR) applied to a logical channelof the network bearer during generation of the first MAC PDU, and a second PBR applied to thelogical channel during generation of the second MAC PDU.15. The radio communication system according to Claim 13, wherein theLayer-2configuration information indicates either the first or second MAC PDU for which a PrioritizedBit Rate (PBR) applied to a logical channel of the network bearer should be preferentiallysecured.l516. A base station apparatus comprising:a communication control unit that controls dual connectivity involving a bearer split inwhich a network bearer between a radio terminal and a core network is split over the base stationapparatus and a neighbor base station,20 wherein the communication control unit is configured to transmit, to the radio terminal,first control information that relates to an access stratum and is necessary for the dualconnectivity involving the bearer split.L7. The base station apparatus according to Claim 16, wherein25 in the bearer split, a first radio bearer in a first cell managed by the base stationapparatus and a second radio bearer in a second cell managed by thc neighbor radio station areboth mapped to the network bearer, andthe first control information includes radio bearer configuration information indicatingmapping of the first and second radio bearers to the network bearer.3018. The base station apparatus according to Claim 16 or 17, wherein thecommunication control unit is configured to transmit, to the neighbor base station, secondcontrol information that relates to an access stratum and is necessary for the dual connectivityinvolving the bearer split.
l0Japanese Patent Application No. 2013-22747219. The base station apparatus according to Claim 18, whereinin the bearer split, a first radio bearer in a first cell managed by the base stationapparatus and a second radio bearer in a second cell managed by the neighbor base station aremapped to the network bearer, andthe second control information includes radio bearer configuration informationindicating mapping between the second radio bearer and the network bearer.20. The base station apparatus according to Claim 1 8 or 19, wherein the secondcontrol information includes configuration information about a bearer split.21 . The base station apparatus according to any one of Claims 16 to 19, wherein thecommunication control unit is configured to instruct the radio terminal and the neighbor basestation to execute the bearer split.22. The base station apparatus according to any one of Claims l6 to 21, wherein thefirst control information indicates either the base station apparatus or the neighbor base station towhich the radio terminal should transmit a Scheduling Request or a Random Access Channel(RACH) for requesting allocation of an uplink radio resource when data for transmission of thenetwork bearer is available in the radio terminal.23. The base station apparatus according to any one of Claims l6 to 22, wherein thefirst control information includes Layer-1 configuration information applied to a procedure forcontrolling uplink transmission power in the radio terminal when the radio terminal is scheduledfor uplink transmission in a first cell managed by the base station apparatus and uplinktransmission in a second cell managed by the neighbor base station in the same subframe.24. The base station apparatus according to Claim 23, wherein the Layer-lconfiguration information indicates maximum transmission power applied to total transmissionpower of uplink transmission in the first cell and the second cell.25. The base station apparatus according to Claim 23, wherein the Layer-lconfiguration information indicates first maximum transmission power applied to uplinktransmission in the first cell and second maximum transmission power applied to uplinkl5202530
'' Japanese Patent Application No. 2013-22747btransmission in the second cell.26. The base station apparatus according to Claim 25, wherein the Layer-lconfiguration information includes a configuration value of the first maximum transmission5 power and an offset value from the second value for obtaining the second maximum transmissionpower.27 . The base station apparatus according to any one of Claims l6 to 26, wherein thefirst control information includes Layer-2 configuration information applied to a procedure forl0 generating, in the radio terminal, a first Medium Access Control Protocol Data Unit (MAC PDU)for uplink transmission in the first cell and a second MAC PDU for uplink transmission in thesecond cell when the radio terminal is scheduled for uplink transmission in a first cell managedby the base station apparatus and uplink transmission in a second cell managed by the neighborbase station in the same subframe.l528. The base station apparatus according to Claim 27 , wherein the Layer-2configuration information indicates a first Prioritized Bit Rate (PBR) applied to a logical channelof the network bearer during generation of the first MAC PDU, and a second PBR applied to thelogical channel during generation of the second MAC PDU.2029. The base station apparatus according to Claim 27, wtrereinthe Layer-Zconfiguration information indicates either the first or second MAC PDU for which a PrioritizedBit Rate (PBR) applied to a logical channel of the network bearer.should be preferentiallysecured.2530. A radio terminal comprising:a communication control unit that controls dual connectivity involving a bearer split inwhich a network bearer between the radio terminal and a core network is split over a first basestation and a second base station,30 wherein the communication control unit is configured to receive, from the first orsecond base station, first control information that relates to an access stratum and is necessary forthe dual connectivity involving the bearer split, determine whether the bearer split is requiredbased on the first control information, and control communication employing the dualconnectivity in accordance with the first control information.
l0Japanese Patent Application No. 2013-22747231. The radio terminal according to Claim 30, wheretnin the bearer split, a first radio bearer in a first cell managed by the first base station anda second radio bearer in a second cell managed by the second base station are both mapped to thenetwork bearer, andthe first control information includes radio bearer configuration information indicatingmapping of the first and second radio bearers to the network bearer.32. The radio terminal according to Claim 30 or 31, wherein the first controlinformation indicates either the first or second base station to which the radio terminal shouldtransmit a Scheduling Request or a Random Access Channel (RACH) for requesting allocationof an uplink radio resource when data for transmission of the network bearer is available in theradio terminal.33. The radio terminal according to any one of Claims 30 to 32, wherein the firstcontrol information includes Layer-1 configuration information applied to a procedure forcontrolling uplink transmission power in the radio terminal when the radio terminal is scheduledfor uplink transmission in a first cell managed by the first base station and uplink transmission ina second cell managed by the second base station in the same subframe.34. The radio terminal according to Claim 33, wherein the Layer-l configurationinformation indicates maximum transmission power applied to total transmission power ofuplink transmission in the first cell and the second cell.35. The radio terminal according to Claim 33, wherein the Layer-l configurationinformation indicates first maximum transmission power applied to uplink transmission in thefirst cell and second maximum transmission power applied to uplink transmission in the secondcell.36. The radio terminal according to Claim 35, wherein the Layer-l configurationinformation includes a configuration value of the first maximum transmission power and anoffset value from the configuration value for obtaining the second maximum transmission power.l520253037. The radio terminal according to any one of Claims 30 to 36, wherein the first
l07Japanese Patent Application No. 2013-227 472control information includes Layer-2 configuration information applied to a procedure forgenerating, in the radio terminal, a first Medium Access Control Protocol Data Unit (MAC PDU)for uplink transmission in the first cell and a second MAC PDU for uplink transmission in thesecond cell when the radio terminal is scheduled for uplink transmission in a first cell managedby the first base station and uplink transmission in a second cell managed by the second basestation in the same subframe.38. The radio terminal according to Claim 37, wherein theLayer-2 configurationinformation indicates a first Prioritized Bit Rate (PBR) applied to a logical channel of thenetwork bearer during generation of the first MAC PDU, and a second PBR applied to thelogical channel during generation of the second MAC PDU.39. The radio terminal according to Claim 37, wherein tlreLayer-2 configurationinformation indicates either the first or second MAC PDU for which a Prioritized Bit Rate (PBR)applied to a logical channel of the network bearer should be preferentially secured.40. A control method comprising:transmitting, from a first base station to a radio terminal, first control information thatrelates to an access stratum and is necessary for dual connectivity involving a bearer split inwhich a network bearer between the radio terminal and a core network is split over the first basestation and a second base station.41. The control method according to Claim 40, whereinin the bearer split, a first radio bearer in a first cell managed by the first base station anda second radio bearer in a second cell managed by the second base station are both mapped to thenetwork bearer, andthe first control information includes radio bearer configuration information indicatingmapping of the first and second radio bearers to the network bearer.42. The control method according to Claim 40 or 41, wherein the first controlinformation indicates either the first base station or the second base station to which the radioterminal should transmit a Scheduling Request or a Random Access Channel (RACH) forrequesting allocation of an uplink radio resource when data for transmission of the networkbearer is available in the radio terminal.
The control method according to any one of Claims 40 to 42, wherein the firstcontrol information includes Layer-1 configuration information applied to a procedure forcontrolling uplink transmission power in the radio terminal when the radio terminal is scheduled5 for uplink transmission in a first cell managed by the first base station and uplink transmission ina second cell managed by the second base station in the same subframe.44. The control method according to any one of Claims 40 to 43, wherein the firstcontrol information includes Layer-2 configuration information applied to a procedure forl0 generating a first Medium Access Control Protocol Data Unit (MAC PDU) for uplinktransmission in the first cell and a second MAC PDU for uplink transmission in the second cellwhen the radio terminal is scheduled for uplink transmission in a first cell managed by the firstbase station and uplink transmission in a second cell managed by the second base station in thesame subframe.l545. A control method that is performed in a radio terminal, the control methodcomprising:receiving, from a first base station or a second base station, first control information thatrelates to an access stratum and is necessary for dual connectivity involving a bearer split in20 which a network bearer between the radio terminal and a core network is split over the first basestation and the second base station; anddetermining whether the bearer split is required based on the first control informationand controlling communication employing the dual connectivity in accordance with the firstcontrol information.2546. A program for causing a computer to perform the method according to any one ofClaims 40 to 45.
Japanese Patent Application No. 20 I 3 -227 472[Name of Document] Abstract[Abstract][Problem] Providing a control procedure or signalling necessary for starting dualconnectivity involving a bearer split5 [Solution to Problem] A radio communication system includes a radio access network (l)and a radio terminal (2). The radio access network (l) includes a first base station (l l) thatmanages a first cell (110) and a second base station (12)thatmanages a second cell (120). Theradio terminal (2) supports dual connectivity involving a bearer split in which a network bearerbetween the radio terminal (2) and a core network (3) is split over the first base station (l l) and10 the second base station (12). The radio access network (l) is configured to transmit, to theradio terminal (2), first control information that relates to an access stratum and is necessary forthe dual connectivity involving the bearer split.[Selected Drawing] Fig.2