RAN node method, wireless terminal and wireless terminal method

Abstract

The present application relates to a method of a RAN node, a wireless terminal and a method of a wireless terminal. The secondary base station (2) receives a SeNB addition request message (302) from a second main base station (3) while providing a secondary cell group (SCG) used for a DC that cooperates with a first main base station (1) to a wireless terminal (4). If the SeNB addition request message (302) explicitly or implicitly indicates that the main base station of the DC used by the wireless terminal (4) is changed from the first main base station (1) to the second main base station (3), the secondary base station (2) considers that the SeNB addition request message (302) requests a modification of the configured SCG. Thus, for example, a change process of a main base station for dual connectivity (DC) can be facilitated by using existing inter-base station interface procedures and inter-base station signaling messages.

Description

[0001] This application is a divisional application of an application with a filing date of June 21, 2016, application number 201680045190.6, and invention name “Base station device and method thereof”. Technical Field

[0002] The present invention relates to wireless communication networks, and in particular to Dual Connectivity (DC). Background Art

[0003] The 3GPP Release 12 specification defines Dual Connectivity (DC) (e.g., see non-patent documents 1 and 2). DC is similar to but different from the coordinated multi-point (CoMP) introduced in the 3GPP Release 11 specification. In particular, in DC, different carrier frequencies are used for macro cells and small cells (pico cells), the wireless terminal (i.e., user equipment (UE)) executes two medium access control (MAC) entities (i.e., the UE uses wireless resources provided by two independent schedulers, one of which is in the primary base station (i.e., primary eNodeB (MeNB)) and the other is in the secondary base station (i.e., secondary eNB (SeNB))), and the UE needs to support the simultaneous use of at least two UL carriers.

[0004] In DC of 3GPP version 12, the UE is connected to one MeNB and one SeNB. A UE configured with DC (DC UE) uses two MAC entities and at least two radio link control (RLC) entities for each data flow on the MeNB and the SeNB. The MeNB in ​​DC is the eNB that terminates the S1-MME used by the DC UE. The SeNB in ​​DC provides additional radio resources to the DC UE. The one or more service cells provided by the MeNB to the UE are referred to as the primary cell group (MCG), and the one or more service cells provided by the SeNB to the UE are referred to as the secondary cell group (SCG). The MCG is one or more service cells associated with the MeNB, and includes a primary cell (PCell) and optionally one or more secondary cells (SCell). The SCG includes one or more service cells associated with the SeNB, and includes a primary secondary cell (PSCell) and optionally one or more secondary cells (SCell). In DC of 3GPP version 12, the PSCell is a special cell in the SCG, and is different from a normal SCell in that the PSCell is configured with an uplink (i.e., PUCCH) used by the UE.

[0005] In the control plane architecture used for DC, there is only one S1-MME for each DC UE. The S1-MME is defined between the MeNB and the Mobility Management Entity (MME), and the MeNB terminates the S1-MME. The signaling interface between eNBs (i.e., X2-C) is used for signaling between the MeNB and SeNB related to DC UEs.

[0006] For DC, two user plane architectures are allowed. In one architecture, S1-U terminates only in the MeNB, and the MeNB forwards the user plane data to the SeNB using X2-U. In the other architecture, S1-U also terminates in the SeNB.

[0007] Therefore, three types of radio bearers are defined for DC, namely MCG bearer, split bearer and SCG bearer. Regarding MCG bearer, MeNB terminates the S1-U connection with the serving gateway (S-GW), and the radio protocol of MCG bearer is only configured in MeNB to use MeNB resources. Therefore, SeNB does not participate in transmitting user plane data of MCG bearer on Uu interface.

[0008] Regarding the split bearer, the MeNB terminates the S1-U connection with the S-GW and transmits packet data convergence protocol (PDCP) data (i.e., PDCP protocol data unit (PDCP PDU)) between the MeNB and the SeNB. Thus, both the MeNB and the SeNB participate in transmitting the user plane data of the split bearer over the Uu interface.

[0009] Regarding the SeNB bearer, the SeNB terminates the S1-U connection with the S-GW, and the radio protocol of the SeNB bearer is only configured in the SeNB to use SeNB resources. Therefore, the MeNB does not participate in transmitting the user plane data of the SCG bearer on the Uu interface.

[0010] Some overall processes related to DC are defined in Non-Patent Document 1 (eg, see Section 10.1.2.8 of Non-Patent Document 1).

[0011] SeNB adding process:

[0012] This process is initiated by the MeNB to establish a UE context at the SeNB. This process is used to add at least the first cell (ie, PSCell) in the SCG. In this process, at least one bearer (split bearer or SCG bearer) is always configured in the SCG.

[0013] SeNB modification process:

[0014] This procedure is used to modify the SCG within the SeNB and is initiated by the MeNB or SeNB. This procedure is used to modify, establish or release bearer contexts within the same SeNB, transfer bearer contexts relative to the SeNB or modify other attributes of the UE context. The MeNB uses this procedure to add or release SCG SCells, SCG bearers, and the SCG portion of a split bearer. The MeNB also uses this procedure to trigger a PSCell change involving a PSCell release.

[0015] SeNB release process:

[0016] This procedure is initiated by the MeNB or SeNB and is used to initiate the release of the UE context at the SeNB.

[0017] Change process within MeNB:

[0018] This process is used to perform handover within the same MeNB while maintaining the SCG within the same SeNB.

[0019] SeNB change process:

[0020] This procedure is used to change SCG between SeNBs (inter-SeNB). This procedure is initiated by MeNB and is used to transfer UE context from source SeNB to target SeNB and change SCG configuration in UE for each SeNB. This procedure is basically implemented by a combination of SeNB addition procedure and SeNB release procedure.

[0021] MeNB to eNB change process:

[0022] This process is initiated by the MeNB and is used to transmit context data from the source MeNB and the source SeNB to the target eNB.

[0023] The signaling and transmission of user plane data between the MeNB and SeNB in ​​the DC is performed via the X2 interface. Therefore, the following X2 procedures used by the DC are defined (for example, see Section 8.6 and Section 9.1.3 of Non-Patent Document 2). Some of the above overall procedures use these X2 procedures used by the DC.

[0024] -SeNB adding preparation process

[0025] -SeNB modification preparation process initiated by MeNB

[0026] -SeNB modification process initiated by SeNB

[0027] -SeNB release process initiated by MeNB

[0028] -SeNB release process initiated by SeNB

[0029] In 3GPP Release 12, when the UE switches from a MeNB to another eNB (target eNB), the above-mentioned MeNB to eNB change procedure is used. In this process, the SeNB (SCG) is completely released. Therefore, in the case where SCG is required after the switch, the target eNB should perform the SeNB addition procedure again after the switch is completed. That is, in addition to the normal switching procedure, the MeNB to eNB change procedure also requires the same signaling as the SeNB change procedure (that is, a combination of the SeNB release procedure and the SeNB addition procedure is required). In addition, with respect to the SCG bearer, data forwarding from the SeNB to the source MeNB and data forwarding from the source MeNB to the target eNB are required.

[0030] In 3GPP Release 13, support for inter-MeNB handover from source MeNB to target MeNB without SeNB change or inter-MeNB handover involving SeNB addition procedure is being discussed. If these procedures are supported, the target eNB may not need to perform SeNB addition procedure to configure SCG again at SeNB. In addition, data forwarding related to SCG bearers from SeNB to source MeNB and from source MeNB to target eNB may become unnecessary.

[0031] Patent document 1 also discloses some processes of switching a wireless terminal from a first master base station to a second master base station during dual connection. In one process disclosed in patent document 1, when a wireless terminal in dual connection switches from a first master base station to a second master base station, the first master base station requests the secondary base station to suspend providing services in the SCell, and then the secondary base station suspends providing services in the SCell and maintains communication status information related to the SCell. In addition, in this process, after the switch, the second master base station sends an indication for resuming communication to the secondary base station, and in response to the indication, the secondary base station resumes the service in the SCell based on the communication status information related to the SCell maintained in the secondary base station. The communication status information related to the SCell includes, for example, at least one of the following: (a) the sending or receiving status of user data (user plane (U plane)), (b) service information, (c) bearer information, and (d) wireless resource configuration information.

[0032] Prior art literature

[0033] Patent Literature

[0034] Patent Document 1: International Patent Publication No. WO2014 / 103145

[0035] Non-patent literature

[0036] Non-patent document 1: 3GPP TS 36.300V12.6.0 (2015-06), "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release12)", June 2015

[0037] Non-patent document 2: 3GPP TS 36.423V12.6.0 (2015-06), "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2applicationprotocol (X2AP) (Release 12)", June 2015 Summary of the invention

[0038] Problem that the invention aims to solve

[0039] It is preferable to use the existing X2 procedures and X2 messages related to DC defined in the 3GPP Release 12 specification to implement a MeNB change (or inter-MeNB handover) from a first MeNB to a second MeNB without a SeNB change, or a MeNB change (or inter-MeNB handover) involving SeNB addition. However, in these MeNB change procedures, the SeNB is required to perform operations different from those in the SeNB addition procedure and SeNB release procedure of 3GPP Release 12.

[0040] One of the purposes to be achieved by the embodiments disclosed in this specification is to provide the following apparatus, method and program, wherein the apparatus, method and program facilitate, during the provision of dual connectivity to a wireless terminal (UE), a master base station (MeNB) change procedure without the release of a secondary base station (SeNB) or a master base station (MeNB) change procedure involving the addition of a secondary base station (SeNB) by using an existing inter-base station interface (X2 interface) procedure and an inter-base station signaling message (X2 message). Note that this purpose is only one of the purposes to be achieved by the embodiments disclosed herein. Other features or problems and novel features will become apparent through the description in the following specification and the accompanying drawings.

[0041] Solutions for solving problems

[0042] In a first aspect, a base station device comprises: at least one wireless transceiver; and at least one processor connected to the at least one wireless transceiver, wherein the at least one processor is configured to, when the base station device provides a wireless terminal with a secondary cell group, i.e., an SCG, for dual connectivity in cooperation with a first main base station and receives a SeNB add request message from a second main base station, if the SeNB add request message includes a first information element that explicitly or implicitly indicates that the main base station for the dual connectivity used by the wireless terminal is to be changed from the first main base station to the second main base station, then the SeNB add request message is considered to request modification of the configuration related to the SCG.

[0043] In a second aspect, a method in a secondary base station comprises the following steps:

[0044] (a) receiving a SeNB addition request message from a second master base station during a period in which a secondary cell group (SCG) used for dual connectivity in cooperation with a first master base station is provided to a wireless terminal; and

[0045] (b) If the SeNB add request message includes a first information element that explicitly or implicitly indicates that the dual-connected primary base station used by the wireless terminal is to be changed from the first primary base station to the second primary base station, the SeNB add request message is deemed to request modification of the configuration related to the SCG.

[0046] In a third aspect, a program comprises instructions (software codes), which, when loaded into a computer, cause the computer to perform the method according to the second aspect.

[0047] In a fourth aspect, a wireless terminal comprises: at least one wireless transceiver for communicating with a first main base station, a second main base station and a secondary base station; and at least one processor, wherein the secondary base station is configured to, when providing the wireless terminal with a secondary cell group, i.e., SCG, for dual connectivity in cooperation with the first main base station and receiving a SeNB add request message from the second main base station, if the SeNB add request message includes a first information element that explicitly or implicitly indicates that the dual-connected main base station used by the wireless terminal is to be changed from the first main base station to the second main base station, then the SeNB add request message is considered to request modification of the configuration related to the SCG, and the at least one processor is configured to communicate with the first main base station and the second main base station, and change the dual-connected main base station from the first main base station to the second main base station while maintaining the connection to the SCG of the secondary base station.

[0048] Effects of the Invention

[0049] According to the above aspects, the following device, method and program can be provided, wherein the device, method and program facilitate, during the provision of dual connectivity to a wireless terminal (UE), performing a master base station (MeNB) change procedure that does not involve the release of a secondary base station (SeNB) or a master base station (MeNB) change procedure that involves the addition of a secondary base station (SeNB) by using an existing inter-base station interface (X2 interface) procedure and an inter-base station signaling message (X2 message). BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a diagram showing an example of the structure of a wireless communication network according to some embodiments.

[0051] Figure 2A is a sequence diagram illustrating an example of the overall process of MeNB change (inter-MeNB handover) according to some embodiments.

[0052] Figure 2B is a sequence diagram illustrating an example of the overall process of MeNB change (inter-MeNB handover) according to some embodiments.

[0053] Figure 3 is a sequence diagram for explaining the operation of the SeNB according to the first embodiment.

[0054] Figure 4 is a flowchart showing an example of the operation of the SeNB according to the first embodiment.

[0055] Figure 5 is a sequence diagram for explaining the operation of the SeNB according to the second embodiment.

[0056] Figure 6 is a flowchart for explaining the operation of the SeNB according to the second embodiment.

[0057] Figure 7 is a sequence diagram for explaining the operation of the SeNB according to the third embodiment.

[0058] Figure 8 is a block diagram showing a structural example of a base station according to some embodiments.

[0059] Fig. 9 is a block diagram showing an example of the structure of a wireless terminal according to some embodiments. DETAILED DESCRIPTION

[0060] The specific embodiments will be described in detail below with reference to the accompanying drawings. In the entire drawings, the same reference numerals are used to represent the same or corresponding elements, and for the sake of clarity, repeated descriptions will be omitted as needed.

[0061] The following description of the embodiments mainly focuses on the Evolved Packet System (EPS) that accommodates LTE and SAE (System Architecture Evolution). However, these embodiments are not limited to EPS and can be applied to other mobile communication networks or systems, such as 3GPP UMTS, 3GPP2 CDMA 2000 system (1xRTT, High Rate Packet Data (HRPD), Global System for Mobile Communications (GSM (registered trademark)) / General Packet Radio Service (GPRS) and WiMAX system, etc.

[0062] Figure 1 An example of the structure of a wireless communication network according to some embodiments is shown. Figure 1 In the example of FIG, a wireless communication network includes a base station (eNB) 1, a base station (eNB) 2, a base station (eNB) 3, and a wireless terminal (UE) 4. eNB 1 and eNB 2 are respectively used as MeNB and SeNB for dual connectivity (DC) to UE 4. UE 4 is configured with DC by MeNB 1, and uses an MCG including a cell 11 provided by MeNB 1 and an SCG including a cell 21 provided by SeNB 2.

[0063] like Figure 1As shown, some embodiments provide a MeNB change 101, wherein in the MeNB change 101, during the period when SeNB 2 provides the SCG used for the DC cooperating with eNB (MeNB) 1 to UE 4, the MeNB in ​​the DC used by UE 4 is changed from eNB 1 to eNB 3. After the MeNB change, UE 4 is configured with DC by MeNB3, while using the MCG including the cell 31 provided by MeNB 3 and the SCG including the cell 21 provided by SeNB 2. The MeNB change may also be referred to as an inter-MeNB handover. Hereinafter, eNB 1, which is the MeNB before the MeNB change (or inter-MeNB handover), is referred to as a source MeNB (S-MeNB), and eNB 3, which is the MeNB after the MeNB change (or inter-MeNB handover), is referred to as a target MeNB (T-MeNB).

[0064] Figure 1 The eNBs 1 to 3 shown may each be a baseband unit (BBU) used in a centralized radio access network (C-RAN) architecture. Figure 1 Each eNB shown may be a RAN node to be connected to one or more remote radio heads (RRHs). In some implementations, eNBs 1 to 3 as BBUs are each responsible for control plane processing and digital baseband signal processing for the user plane. On the other hand, each RRH is responsible for analog radio frequency (RF) signal processing (e.g., frequency conversion and signal amplification). C-RAN is also referred to as cloud RAN. BBU is also referred to as radio equipment controller (REC) or data unit (DU). RRH is also referred to as radio equipment (RE), radio unit (RU) or remote radio unit (RRU).

[0065] Figure 2A and 2B An example of the overall process of MeNB change (or inter-MeNB handover) according to some embodiments is shown (process 200). As described later, the inter-MeNB handover process 200 includes a process corresponding to the SeNB addition process of 3GPP Release 12 (i.e., steps 202 and 203). That is, process 200 is a MeNB change (or inter-MeNB handover) process involving the addition of SeNB when providing dual connectivity to UE 4. In other words, process 200 is a MeNB change (or inter-MeNB handover) process that does not involve the release of SeNB 2 when providing dual connectivity to UE 4.

[0066] In step 201, S-MeNB 1 requests T-MeNB 3 to perform inter-MeNB handover of UE 4. The handover request message in step 201 may also be referred to as a MeNB change request message.

[0067] In step 202, in response to receiving the handover request message in step 201, T-MeNB 3 sends a SeNB add request message to SeNB 2. The SeNB add request message may be referred to as an SCG add request message. The SeNB add request message indicates the characteristics of a radio access bearer (i.e., an E-UTRAN radio access bearer (E-RAB)) and requests SeNB 2 to allocate radio resources used by a specific E-RAB. The characteristics of the E-RAB, for example, indicate an E-RAB identifier (E-RAB ID) and a bearer type (i.e., an SCG bearer or a split bearer). The bearer type is also referred to as a DRB type. The SeNB add request message may also include information required for SCG configuration (SCG-ConfigInfo) including MCG configuration and UE capabilities.

[0068] In response to receiving the SeNB Add Request message from T-MeNB 3, SeNB 2 prepares radio resources and control plane (C-plane) resources and prepares transport network resources related to the SCG bearer. Then, SeNB 2 sends a response message (i.e., SeNB Add Request Confirmation) containing SCG configuration (SCG-Config) to T-MeNB 3 (step 203). SCG-Config may include, for example, RadioResourceConfigDedicatedSCG IE containing pSCellToAddMod IE.

[0069] In step 204, T-MeNB 3 sends a response message (i.e., handover request confirmation) indicating acceptance of the handover request to S-MeNB 1. In step 205, in response to receiving the handover request confirmation message, S-MeNB 1 sends a SeNB release request message to SeNB 2. The SeNB release request message may be referred to as an SCG release request message.

[0070] In step 206, S-MeNB 1 requests UE 4 to reconfigure the radio resource control (RRC) connection in the PCell (e.g., cell 11) within the MCG. The RRC connection reconfiguration message in step 206 includes: mobility control information (mobility control Info) and MCG configuration related to T-MeNB 3; and configuration information related to the SCG in SeNB 2 (SCG configuration, i.e., scg-ConfigPartMCG (e.g., scg-Counter) and scg-ConfigPartSCG). In this way, UE 4 believes that UE 4 is instructed to perform an inter-eNB handover to change the primary base station in DC from S-MeNB 1 to T-MeNB 3 while maintaining a connection to the SCG in SeNB 2 (i.e., at least one bearer (SCG bearer or split bearer)). For example, upon receiving the RRC connection reconfiguration message, UE 4 resets the MAC entity on the MCG side (MCG MAC) and the MAC entity on the SCG side (SCG MAC). Then, UE 4 establishes a PDCP entity on the MCG side (MCG PDCP), and in the case of SCG bearer, also establishes a PDCP entity on the SCG side (SCG PDCP). After that, UE 4 establishes an RLC entity on the MCG side (MCG RLC) and an RLC entity on the SCG side (SCGRLC).

[0071] In steps 207 and 208, UE 4 performs a random access procedure to acquire synchronization with T-MeNB 3, and then sends an RRC connection reconfiguration complete message to T-MeNB 3 to notify T-MeNB 3 of the completion of the RRC reconfiguration including handover confirmation and modification (or change) of the MCG configuration and SCG configuration.

[0072] In step 209 , UE 4 performs a random access procedure to acquire synchronization with SeNB 2 according to the new SCG configuration (including the mobility control InfoSCG) received through the RRC connection reconfiguration message in step 206 .

[0073] In step 210 , in response to receiving the RRC connection reconfiguration message from the UE 4 (step 208 ), the T-MeNB 3 notifies the SeNB 2 that the SeNB reconfiguration has been completed (SeNB reconfiguration complete message).

[0074] In step 211, S-MeNB 1 sends a report of the data communication status related to MCG (i.e., SN status transfer message) to T-MeNB 3. The SN status transfer message includes, for example, numbers related to MCG bearers, where these numbers include uplink PDCP sequence number (SN), uplink hyperframe number (HFN), downlink PDCP sequence number and downlink hyperframe number. The SN status transfer message may include the PDCP sequence number and hyperframe number related to the split bearer. In step 212, S-MeNB 1 starts forwarding the buffered downlink user data received from S-GW 5 to T-MeNB 3.

[0075] In step 213, T-MeNB 3 initiates the S1 path switching process. In the S1 path switching process of steps 213 to 217, one or more S1 bearers for MCG bearers (and optional split bearers) are configured between S-GW 5 and T-MeNB 3 (215), and one or more S1 bearers for SCG bearers are configured between S-GW 5 and SeNB 2 (216). If there is no modification of the SCG bearer (E-RAB), the configuration of the S1 bearer (216) between S-GW 5 and SeNB 2 can be the same as the configuration before initiating the inter-MeNB handover. For example, the S1 path switching process can be omitted.

[0076] In step 218, T-MeNB 3 sends a UE context release message to S-MeNB 1 to initiate the UE context release procedure. Upon receiving the UE context release message from T-MeNB 3 (step 218), S-MeNB 1 is allowed to release the radio resources and C-plane resources associated with the UE context. In step 219, in response to receiving the UE context release message from T-MeNB 3, S-MeNB 1 sends a UE context release message to SeNB 2.

[0077] Some embodiments will be described below. These embodiments can be used alone, or two or more of these embodiments can be appropriately combined with each other. These embodiments are provided for illustrative purposes.

[0078] First embodiment

[0079] Figure 2A and 2B The MeNB change procedure shown implements the MeNB change procedure involving the addition of SeNB (or the MeNB change procedure not involving the release of SeNB 2) by using the existing SeNB addition procedure and SeNB release procedure. Figure 2A and 2BIn the process shown, SeNB 2 must distinguish the SeNB add request message from T-MeNB 3 in step S202 from the existing (usual) SeNB add request message. This is because the SeNB add request message in step 202 is used to change the MeNB and MCG associated with the SCG (or E-RAB) configured in SeNB 2 from S-MeNB 1 to T-MeNB 3. Therefore, the SeNB add request message in step 202 may have a different role from the existing (usual) SeNB add request message.

[0080] This embodiment provides a specific example of the operation and message structure of S-MeNB 1, SeNB 2 and T-MeNB 3 to Figure 2A The SeNB add request message (step 202) shown is distinguished from existing (normal) messages.

[0081] Figure 3 An example of a process (process 300 ) is shown in which SeNB 2 receives a SeNB add request message from other eNB (T-MeNB) 3 during provision of SCG for DC cooperating with MeNB (S-MeNB) 1 to a specific UE 4 . Figure 3 Steps 301 and 302 shown are similar to Figure 2A The steps 201 and 202 shown correspond to each other. That is, in step 301, S-MeNB1 sends a handover request message for requesting inter-MeNB handover of UE 4 to T-MeNB 3. The handover request message includes, for example, the MCG SCG configuration before the handover.

[0082] The handover request message (step 301) also includes one or more additional information elements for explicitly or implicitly indicating from the S-MeNB 1 to the T-MeNB 3 that this is a MeNB change involving maintaining the SeNB (or the SCG or the bearer in the SCG (SCG bearer or split bearer)). Therefore, when the T-MeNB 3 receives the handover request from the S-MeNB 1, it can be considered that the T-MeNB 3 is requested to perform a MeNB change (or inter-MeNB handover) involving maintaining the SeNB (or the SCG or the bearer in the SCG (SCG bearer or split bearer)).

[0083] In some implementations, such as Figure 3As shown, in order to implicitly indicate the change of the MeNB in ​​the DC used by UE 4, the additional information element included in the handover request message (step 301) may include a wireless terminal identifier (i.e., SeNB UE X2AP ID) allocated by SeNB2 to uniquely identify UE 4 on the inter-base station interface (i.e., X2 interface) between S-MeNB 1 and SeNB 2. The additional information element may also include one or more bearer identifiers (e.g., a network bearer identifier (i.e., E-RAB ID or eps-bearer identity), an identifier of a data radio bearer (DRB) (i.e., DRB identity) or a combination thereof) used by UE4 that has been configured in SeNB 2 for the DC that cooperates with S-MeNB 1.

[0084] Additionally or optionally, in some implementations, in order to implicitly indicate the change of the MeNB in ​​the DC used by UE 4, the additional information element included in the handover request message (step 301) may include a terminal identifier (e.g., a cell radio network temporary identifier (C-RNTI)) allocated by SeNB 2 to UE 4 to uniquely identify the UE 4 within the SCG. In this case, the additional information element may also include one or more bearer identifiers (e.g., E-RAB ID or eps-bearer identity, or DRB identity, or a combination thereof) used by UE 4 that have been configured in SeNB 2 for the DC that cooperates with S-MeNB 1. In this case, the E-RAB ID may be sent as an information element of the X2 message, and the eps-bearer identity and the DRB identity may be included as information elements in the RRC layer within the container (i.e., the MeNB to SeNB container) contained in the X2 message.

[0085] Additionally or optionally, in some implementations, the additional information element included in the handover request message (step 301) may explicitly indicate that the MeNB in ​​the DC used by UE 4 is to be changed from MeNB (S-MeNB) 1 to MeNB (T-MeNB) 3. In this case, the additional information element may indicate that there is no change in the bearer identifier (e.g., E-RAB ID or eps-bearer identity, or DRB identity, or a combination thereof) used by UE 4 that has been configured in SeNB 2 for the DC that cooperates with MeNB 1.

[0086] In step 302, in response to receiving the handover request message in step 301, T-MeNB 3 sends a SeNB add request message to SeNB 2. The SeNB add request message indicates the characteristics of the radio access bearer (i.e., E-UTRAN radio access bearer (E-RAB)) and requests SeNB 2 to allocate radio resources used by a specific E-RAB. The characteristics of the E-RAB, for example, indicate an E-RAB identifier (E-RAB ID) and a bearer type (i.e., SCG bearer or split bearer). The bearer type is also referred to as a DRB type. The SeNB add request message may also include information required for SCG configuration including MCG configuration and UE capabilities (SCG-ConfigInfo). In addition, T-MeNB 3 may specify in SCG-ConfigInfo a network bearer identifier (e.g., eps-bearer identity) and a data radio bearer identifier (e.g., DRB identity) having the same value as the identifier used in the DC between S-MeNB 1 and SeNB 2. Likewise, T-MeNB 3 may specify a logical identifier of cell 21 (eg, sCellIndex or ServCellIndex) having the same value as that of the identifier used in the DC between S-MeNB 1 and SeNB 2.

[0087] The SeNB add request message (step 302) further includes one or more additional information elements for explicitly or implicitly indicating to the SeNB 2 that the MeNB is to be changed from the S-MeNB 1 to the T-MeNB 3 while maintaining the SeNB (or the SCG, or the bearer (SCG bearer or split bearer) used by the SCG). The one or more additional information elements may be the same as the corresponding additional information elements included in the handover request message (step 301), or may be derived from the corresponding additional information elements.

[0088] Specifically, in some implementations, such as Figure 3 As shown, in order to implicitly indicate the change of the MeNB in ​​the DC used by UE 4, the additional information element included in the SeNB add request message (step 302) may include a wireless terminal identifier (i.e., SeNB UE X2AP ID) allocated by SeNB 2 to uniquely identify the UE 4 on the inter-base station interface (i.e., X2 interface) between S-MeNB 1 and SeNB 2. In this case, the additional information element may also include one or more bearer identifiers (e.g., E-RAB ID or eps-bearer identity, or DRB identity, or a combination thereof) used by UE 4 that has been configured in SeNB 2 for the DC that cooperates with S-MeNB 1.

[0089] Additionally or optionally, in some implementations, in order to implicitly indicate the change of the MeNB in ​​the DC used by the UE 4, the additional information element included in the SeNB add request message (step 302) may include a terminal identifier (e.g., C-RNTI) allocated by the SeNB 2 to the UE 4 to uniquely identify the UE 4 within the SCG. In this case, the additional information element may also include one or more bearer identifiers (e.g., E-RAB ID or eps-bearer identity, or DRB identity, or a combination thereof) used by the UE 4 that have been configured in the SeNB 2 for the DC that cooperates with the S-MeNB 1.

[0090] Additionally or optionally, in some implementations, the additional information element included in the SeNB add request message (step 302) may explicitly indicate that the MeNB in ​​the DC used by UE 4 is to be changed from MeNB (S-MeNB) 1 to MeNB (T-MeNB) 3. For example, the SeNB add request message may include an SCG change indication IE. In addition, a new cause value (e.g., "inter-MeNB switching" or "SeNB (SCG) stored switching") may be defined for the SCG change indication IE, and the SeNB add request message may specify the cause value. In addition, in this case, the additional information element may indicate that there is no change in the bearer identifier (e.g., E-RAB ID or eps-bearer identity, or DRB identity, or a combination thereof) used by UE 4 that has been configured in SeNB 2 for the DC that cooperates with MeNB 1.

[0091] In step 303, SeNB 2 is configured to, when receiving a SeNB add request message (step 302) including the above-mentioned additional information element during providing a specific UE 4 with an SCG used for a DC cooperating with MeNB (S-MeNB) 1, deem that the SeNB add request message requests a modification (or change) of the configuration related to the SCG configured for the DC cooperating with S-MeNB 1. The modification (or change) of the configuration related to the SCG, for example, includes at least one of the following: (a) modification (or change) of the configuration of the MeNB associated with the SCG (e.g., MeNB UE X2AP ID); (b) modification (or change) of the configuration of the MCG or MCG bearer associated with the SCG; (c) modification (or change) of the SeNB security key (S-KeNB); and (d) modification (or change) of the configuration of the SCG or SCG bearer or split bearer. As a more specific example, if the E-RAB to be added list IE included in the SeNB add request message includes a wireless terminal identifier (e.g., SeNB UE X2AP ID) having the same value as the value of the identifier configured for UE 4 that is currently conducting DC with S-MeNB1, and also includes an E-RAB ID having the same value as the value configured for UE 4, then SeNB 2 regards the SeNB add request as a request for modification (or change) of the configuration corresponding to the E-RAB or a request for reconfiguration of the SCG including the E-RAB.

[0092] In step 304, SeNB 2 creates a new SCG configuration (SCG-Config) based on the information (e.g., SCG-ConfigInfo) included in the SeNB Add Request message (step 302) from T-MeNB 3, and sends a response message (i.e., SeNB Add Request Ack) containing the new SCG configuration to T-MeNB 3. The new SCG configuration may include a terminal identifier (C-RNTI) allocated by SeNB 2 to UE 4 to uniquely identify UE 4 within the SCG. In addition to the case of SCG establishment, SeNB 2 may also always add C-RNTI to the "MobilityControlInfoSCG" information element within the SCG configuration in the case of SCG modification (or change) caused by MeNB change, SCG re-establishment, or SCG relocation (or SCG relocated).

[0093] In with Figure 3Under abnormal conditions related to the process shown, SeNB 2 and T-MeNB 3 may operate as described below. If UE 4 is not uniquely identified on the inter-base station interface (i.e., X2 interface) between S-MeNB 1 and SeNB 2 using the wireless terminal identifier (i.e., SeNB UE X2AP ID) identified using the SeNB add request message (step 302), SeNB 2 may send a SeNB add request reject message instead of a SeNB add request confirm message (step 304). The SeNB add request reject message indicates that the SeNB add request message (step 302) cannot be accepted. The SeNB add request reject message may include a cause value indicating that the requested wireless terminal identifier (i.e., SeNB UE X2AP ID) is inappropriate (e.g., "inappropriate X2APID"). Optionally, if SeNB 2 does not support the function required for inter-eNB handover of DC UE while maintaining SCG, the SeNB add request reject message may include a cause value indicating that the function is not supported (e.g., "bearer maintenance option not supported" or "bearer maintenance handover not supported").

[0094] In response to receiving the SeNB add request rejection message, T-MeNB 3 may send a response message indicating that the handover cannot be accepted (i.e., a handover preparation failure message) to S-MeNB 1. Optionally, T-MeNB3 may include the E-RAB ID of the bearer (SCG bearer or split bearer) in the SeNB in ​​the "E-RABs Not Admitted List" IE included in the handover request confirmation message. In this case, S-MeNB 1 may release the SCG or change the SCG bearer to an MCG bearer before sending the handover command (i.e., RRC connection reconfiguration including mobility control Info) to UE 4 or after stopping (pausing) the handover.

[0095] Figure 4 4 is a flowchart showing an example of the operation (operation 400) of SeNB 2. In block 401, during the provision of the SCG used for the DC cooperating with MeNB (S-MeNB) 1 to a specific UE 4, SeNB 2 receives a SeNB add request message from another eNB (T-MeNB) 3. In block 402, in the case where the SeNB add request message (block 401) contains a UE ID (e.g., SeNB UE X2AP ID) configured by SeNB 2 in order to uniquely identify the specific UE 4 in the DC with S-MeNB 1, SeNB 2 regards the SeNB add request message as a request for modifying (changing) the configured SCG (or SCG Config or bearer (e.g., E-RAB)).

[0096] As can be understood from the above description, according to reference Figure 3 and 4 In the example described above, when SeNB 2 receives a SeNB add request message from another eNB (T-MeNB) 3 while providing a specific UE 4 with an SCG used for a DC that cooperates with MeNB (S-MeNB) 1, SeNB 2 is able to distinguish the SeNB add request message from an existing (or common) SeNB add request message. Therefore, it is possible to avoid erroneously determining that the SeNB add request message received from T-MeNB 3 is an error, thereby avoiding erroneously ignoring the message or erroneously releasing the SCG (or bearer).

[0097] When receiving the SeNB add request message from the T-MeNB 3, the SeNB 2 may also operate as described below. In some implementations, the SeNB 2 may be configured to replace the SCG configuration used by the DC cooperating with the S-MeNB 1 with the modified (or newly configured) SCG configuration used by the DC cooperating with the T-MeNB 3 in response to sending the SeNB add request confirmation message to the T-MeNB 3.

[0098] Optionally, SeNB 2 may be configured to replace the SCG configuration used by the DC cooperating with S-MeNB 1 with the modified (or newly configured) SCG configuration used by the DC cooperating with T-MeNB 3 in response to receiving a SeNB release request message from S-MeNB 1 (step 205).

[0099] In some implementations, the SeNB 2 may be configured to stop either or both of transmission and reception of user data with respect to the UE 4 in response to receiving the SeNB add request message from the T-MeNB 3 .

[0100] Second embodiment

[0101] exist Figure 2A and 2BIn the process shown, SeNB 2 must distinguish the SeNB release request message from S-MeNB 1 in step 205 from the existing (or common) SeNB release request message, and must also distinguish the UE context release message from S-MeNB 1 in step 219 from the existing (or common) UE context release message. This is because these SeNB release request messages and UE context release messages in steps 205 and 219 allow SeNB 2 to release only a portion of the resources associated with the UE context of UE 4. Therefore, these SeNB release request messages and UE context release messages in steps 205 and 219 have different functions from the existing (or common) SeNB release request messages and UE context release messages.

[0102] This embodiment provides a specific example of the operation and message structure of S-MeNB 1, SeNB 2 and T-MeNB 3 to Figure 2A and 2B The SeNB release request message (step 205) and the UE context release message (step 219) shown are distinguished from existing (or common) messages.

[0103] Figure 5 An example of the following process is shown (process 500 ): SeNB 2 receives a SeNB release request message from S-MeNB 1 after receiving a SeNB add request message from T-MeNB 3 . Figure 5 Steps 501 to 504 shown are similar to Figure 3 The steps 301 to 304 shown are the same. Figure 5 Steps 505 and 506 are shown in FIG. Figure 2A The steps 204 and 205 shown correspond to each other. That is, in step 505, T-MeNB3 sends a response message (ie, handover request confirmation) indicating that the handover request in step 501 is received to S-MeNB1.

[0104] In step 506, in response to receiving the handover request confirmation message, S-MeNB 1 sends a SeNB release request message to SeNB 2. The SeNB release request message triggers SeNB 2 to release resources related to UE 4 (eg, UE context) used by SeNBs in the DC of S-MeNB 1.

[0105] In step 507, after receiving the SeNB add request from T-MeNB 3 (step 502) and receiving the SeNB release request message from S-MeNB 1 (step 506), SeNB 2 considers that part of the resources associated with the UE context of UE 4 can be released, but the remaining resources should be maintained.

[0106] In other words, when SeNB 2 receives a SeNB add request (step 503) from T-MeNB 3 that is regarded as a request to modify the SCG or bearer (E-RAB) used by the DC of UE 4 before receiving the SeNB release request message (step 506) from S-MeNB 1, SeNB 2 considers that part of the resources associated with the UE context of UE 4 can be released, but the remaining resources should be maintained.

[0107] In other words, before SeNB 2 receives the SeNB release request message from S-MeNB 1 (step 506), when T-MeNB 3 explicitly or implicitly notifies that the MeNB of the DC used by UE 4 is to be changed from S-MeNB 1 to T-MeNB 3 (step 502), SeNB 2 considers that part of the resources associated with the UE context of UE4 can be released, but the remaining resources should be maintained.

[0108] In some implementations, in response to receiving a SeNB release request message from S-MeNB 1 (step 506), SeNB 2 may consider that part of the radio resources and control plane resources associated with the UE context of UE 4 may be released, but the remaining resources should be maintained. The part of the resources that can be released, for example, includes one or more identifiers of the inter-base station connection (i.e., X2 interface connection) between S-MeNB 1 and SeNB 2 associated with UE 4 (e.g., MeNB UE X2APID allocated by S-MeNB). The remaining resources that should not be released, for example, include the bearer configuration in the SCG associated with UE 4. The bearer configuration, for example, includes a bearer identifier (e.g., E-RAB ID or eps-bearer identity), a DRB identity or a combination thereof), a logical channel configuration, and a radio link control (RLC) configuration. The bearer configuration may be a bearer configuration updated based on the SeNB add request from T-MeNB 3.

[0109] Additionally or optionally, in some implementations, in response to receiving the SeNB release request message from the S-MeNB 1 (step 506), the SeNB 2 may consider that even when data forwarding from the SeNB 2 to the S-MeNB 1 (or the T-MeNB 3) is not required, the status related to the user data of the UE 4 should be maintained. The status related to the user data includes, for example, at least one of a Packet Data Convergence Protocol (PDCP) status (e.g., PDCP SN and HFN) and a Radio Link Control (RLC) status related to the user data of the UE 4.

[0110] Figure 66 is a flowchart showing an example (process 600) of the operation of SeNB 2. In block 601, during the provision of the SCG used for the DC cooperating with MeNB (S-MeNB) 1 to a specific UE 4, SeNB 2 receives a SeNB release request message from S-MeNB 1. In block 602, before SeNB 2 receives the SeNB release request message from S-MeNB 1 (step 601), in the case where a SeNB add request from T-MeNB 3, which is regarded as a request to modify (or change) the SCG or bearer (E-RAB) used for the DC of UE 4, is received, SeNB 2 regards the SeNB release request message as a request for triggering the release of only a part of the resources related to the specific UE 4. For example, in the case where the E-RAB to be released list IE included in the received SeNB release request message includes a bearer identifier (e.g., E-RABID) having the same value as the bearer identifier requested to be added by T-MeNB 3 (i.e., specified using the SeNB add request message) and accepted by SeNB2 (i.e., its addition is accepted by SeNB 2), SeNB 2 regards the SeNB release message as a request for triggering the release of only a portion of the resources of the corresponding E-RAB (related to UE 4).

[0111] As can be understood from the above description, according to reference Figure 5 and 6 In the example described above, when SeNB 2 receives a SeNB release request message from MeNB (S-MeNB) 1 while providing the SCG used by the DC cooperating with S-MeNB 1 to a specific UE 4, SeNB 2 can determine the resources that can be released upon reception of the SeNB release request based on whether SeNB 2 has received the SeNB add request from T-MeNB 3. Therefore, when MeNB change (or inter-MeNB switching) is performed while maintaining SeNB (or SCG or bearer of SCG (SCG bearer or split bearer)), it is possible to avoid erroneously releasing (or removing) the resources to be continuously used by the DC cooperating with T-MeNB 3.

[0112] Third embodiment

[0113] This embodiment provides a variation of the second embodiment. Instead of or in addition to the case where SeNB 2 receives a SeNB release request message from S-MeNB 1, refer to Figure 5 and 6 The process and operation may also be performed when SeNB 2 receives a UE context release message from S-MeNB 1. Figure 7 An example of the following process is shown (process 700 ): after receiving the SeNB Add Request message from the T-MeNB 3 , the SeNB 2 receives the SeNB UE Context Release message from the S-MeNB 1 . Figure 7 Steps 701 to 704 shown are similar to Figure 3 The steps 301 to 304 shown are the same as those shown in FIG. Figure 5 The steps 501 to 504 shown are the same.

[0114] Figure 7 Steps 705 and 706 are shown in FIG. Figure 2B The steps 218 and 219 shown correspond to each other. That is, in step 705, T-MeNB 3 sends a UE context release message to S-MeNB 1. In step 706, in response to receiving the UE context release message from T-MeNB 3, S-MeNB 1 sends a UE context release message to SeNB 2.

[0115] In step 707, after SeNB 2 receives the SeNB add request from T-MeNB 3 (step 702) and receives the UE context release message from S-MeNB 1 (step 706), SeNB 2 considers that part of the resources associated with the UE context of UE 4 can be released, but the remaining resources should be maintained.

[0116] In other words, when SeNB 2 receives a SeNB add request (step 703) from T-MeNB 3 that is considered as a request to modify the SCG or bearer (E-RAB) used by the DC of UE 4 before receiving the UE context release message (step 706) from S-MeNB 1, SeNB 2 considers that part of the resources associated with the UE context of UE 4 can be released, but the remaining resources should be maintained.

[0117] In other words, before SeNB 2 receives the UE context release message from S-MeNB 1 (step 706), when T-MeNB 3 explicitly or implicitly notifies that the MeNB of the DC used by UE 4 is to be changed from S-MeNB 1 to T-MeNB 3 (step 702), SeNB 2 considers that part of the resources associated with the UE context of UE4 can be released, but the remaining resources should be maintained.

[0118] According to reference Figure 7In the example described, when SeNB 2 receives a UE context release message from MeNB (S-MeNB) 1 while providing a specific UE 4 with an SCG used by a DC that cooperates with S-MeNB 1, SeNB 2 can determine resources that can be released upon reception of the UE context release message based on whether SeNB 2 has received a SeNB add request from T-MeNB 3. Therefore, when a MeNB change (or inter-MeNB handover) is performed while maintaining the SeNB (or SCG or a bearer of the SCG (SCG bearer or split bearer)), it is possible to avoid erroneously releasing (or removing) resources to be continuously used by a DC that cooperates with T-MeNB 3.

[0119] In reference Figure 5 and 6 In the described example, S-MeNB 1 may include in the SeNB release request message or the UE context release message an information element that explicitly indicates that the MeNB of the DC used by the UE is to be changed from S-MeNB 1 to T-MeNB 3. Additionally or optionally, S-MeNB 1 may include in the SeNB release request message or the UE context release message an information element indicating the release of a portion of the resources associated with the UE context of UE 4 (i.e., a partial SeNB release request or a partial UE context release). Each of these information elements may be a cause information element indicating the cause of the release message (i.e., the SeNB release request message or the UE context release message). For example, a new cause value / cause name indicating "inter-MeNB handover", "optimized handover" or "control plane release" may be defined. In this way, SeNB 2 can easily distinguish the SeNB release request message or the UE context release message including these information elements from the existing (or usual) SeNB release request message or the UE context release message.

[0120] Finally, a configuration example of the eNB 1, eNB 2, eNB 3, and UE 4 according to the above-described embodiment will be described. Figure 8 is a block diagram showing a structural example of SeNB 2. S-MeNB 1 and T-MeNB 3 may each have Figure 8 The structure shown is the same as the structure shown in the reference Figure 8, SeNB 2 includes an RF transceiver 801, a network interface 803, a processor 804, and a memory 805. The RF transceiver 801 performs analog RF signal processing to communicate with the UE. The RF transceiver 801 may include a plurality of transceivers. The RF transceiver 801 is connected to an antenna 802 and a processor 804. The RF transceiver 801 receives modulation symbol data (or OFDM symbol data) from the processor 804, generates a transmit RF signal, and supplies the transmit RF signal to the antenna 802. In addition, the RF transceiver 801 generates a baseband receive signal based on the receive RF signal received by the antenna 802, and supplies the baseband receive signal to the processor 804.

[0121] The network interface 803 is used to communicate with network nodes (eg, other eNBs, MMEs, and S-GWs). The network interface 803 may, for example, include a network interface card (NIC) compliant with the IEEE 802.3 series.

[0122] The processor 804 performs digital baseband signal processing (i.e., data plane processing) and control plane processing for wireless communication. For example, in the case of LTE and Advanced LTE, the digital baseband signal processing performed by the processor 804 may include signal processing of the PDCP layer, the RLC layer, the MAC layer, and the PHY layer. In addition, the signal processing performed by the processor 804 may include signal processing of the GTP-U UDP / IP layer used by the X2-U interface and the S1-U interface. In addition, the control plane processing performed by the processor 804 may include processing of the X2AP protocol, the S1-MME protocol, and the RRC protocol.

[0123] The processor 804 may include a plurality of processors. The processor 804 may include, for example, a modem processor (e.g., DSP) for performing digital baseband signal processing, a processor (e.g., DSP) for performing signal processing of the GTP-U UDP / IP layer used for the X2-U interface and the S1-U interface, and a protocol stack processor (e.g., CPU or MPU) for performing control plane processing.

[0124] The memory 805 includes a combination of volatile memory and non-volatile memory. The memory 805 may include physically independent multiple memory devices. The volatile memory is, for example, a static random access memory (SRAM), a dynamic RAM (DRAM), or a combination thereof. The non-volatile memory may be a mask read-only memory (MROM), an electrically erasable programmable ROM (EEPROM), a flash memory, a hard disk drive, or any combination thereof. The memory 805 may include a memory configured separately from the processor 804. In this case, the processor 804 may access the memory 805 via the network interface 803 or an I / O interface not shown.

[0125] The memory 805 may store software modules (computer programs) including instructions and data used for the processing of the SeNB 2 described in the above embodiments. In some implementations, the processor 804 may be configured to load the software module from the memory 805 and execute the loaded software module, thereby performing the processing of the SeNB 2 described in the above embodiments.

[0126] Fig. 9 901 is a block diagram showing a structural example of UE 4 according to the above-mentioned embodiment. A radio frequency (RF) transceiver 901 performs analog RF signal processing to communicate with eNB 2. The analog RF signal processing performed by the RF transceiver 901 includes up-conversion, down-conversion, and amplification. The RF transceiver 901 is connected to an antenna 902 and a baseband processor 903. That is, the RF transceiver 901 receives modulation symbol data (or OFDM symbol data) from the baseband processor 903, generates a transmission RF signal, and supplies the transmission RF signal to the antenna 902. In addition, the RF transceiver 901 generates a baseband reception signal based on the reception RF signal received by the antenna 902, and supplies the baseband reception signal to the baseband processor 903.

[0127] The baseband processor 903 performs digital baseband signal processing (i.e., data plane processing) and control plane processing for wireless communication. Digital baseband signal processing includes (a) data compression / decompression, (b) data segmentation / concatenation, (c) generation / decompression of a transmission format (transmission frame), (d) transmission channel coding / decoding, (e) modulation (symbol mapping) / demodulation, and (f) generation of OFDM symbol data (baseband OFDM signal) using inverse fast Fourier transform (IFFT), etc. On the other hand, control plane processing includes communication management in layer 1 (e.g., transmission power control), communication management in layer 2 (e.g., radio resource management and hybrid automatic repeat request (HARQ) processing), and communication management in layer 3 (e.g., signaling related to attachment, mobility, and call management).

[0128] For example, in the case of LTE and Advanced LTE, the digital baseband signal processing performed by the baseband processor 903 may include signal processing in a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, a MAC layer, and a PHY layer. In addition, the control plane processing using the baseband processor 903 may include processing of a non-access stratum (NAS) protocol, an RRC protocol, and a MAC CE.

[0129] The baseband processor 903 may include a modem processor (e.g., a digital signal processor (DSP)) for performing digital baseband signal processing and a protocol stack processor (e.g., a central processing unit (CPU) or a microprocessor unit (MPU)) for performing control plane processing. In this case, the protocol stack processor for performing control plane processing may be integrated with the following application processor 904.

[0130] The application processor 904 is also referred to as a CPU, an MPU, a microprocessor, or a processor core. The application processor 904 may include a plurality of processors (a plurality of processor cores). The application processor 904 loads a system software program (operating system (OS)) and various application programs (e.g., a call application, a WEB browser, a mail program, a camera operation application, a music playback application) from the memory 906 or from other memories (not shown), and executes these programs, thereby providing various functions of the UE 4.

[0131] In some implementations, such as Fig. 9 As shown by the dashed line (905) in FIG. 1 , the baseband processor 903 and the application processor 904 may be integrated on a single chip. In other words, the baseband processor 903 and the application processor 904 may be implemented on a system on chip (SoC) device 905. SoC devices are sometimes referred to as system large scale integration (LSI) or chipsets.

[0132] The memory 906 is a volatile memory or a non-volatile memory or a combination thereof. The memory 906 may include a plurality of physically independent memory devices. The volatile memory is, for example, a static random access memory (SRAM), a dynamic RAM (DRAM), or a combination thereof. The non-volatile memory may be a mask read-only memory (MROM), an electrically erasable programmable ROM (EEPROM), a flash memory, a hard disk drive, or any combination thereof. The memory 906 may include an external memory device accessible from the baseband processor 903, the application processor 904, and the SoC 905. The memory 906 may include an internal memory device integrated in the baseband processor 903, the application processor 904, or the SoC 905. The memory 906 may also include a memory in a universal integrated circuit card (UICC).

[0133] The memory 906 may store software modules (computer programs) including instructions and data used for the processing of the UE 4 described in the above embodiments. In some implementations, the baseband processor 903 or the application processor 904 may be configured to load the software module from the memory 906 and execute the loaded software module, thereby performing the processing of the remote UE 4 described in the above embodiments.

[0134] As reference Figure 8 and9 As described, the processors included in the eNB 1, eNB 2, eNB 3 and UE 4 according to the above-mentioned embodiments execute one or more programs including instructions for causing the computer to perform the algorithm described with reference to the accompanying drawings. Any type of non-transitory computer-readable medium can be used to store these programs and provide these programs to the computer. Non-transitory computer-readable media include any type of tangible storage media. Examples of non-transitory computer-readable media include: magnetic storage media (such as floppy disks, tapes, and hard disk drives, etc.); optical magnetic storage media (for example, magneto-optical disks, etc.); compact disk read-only memory (CD-ROM); CD-R; CD-R / W; and semiconductor memory (such as mask ROM, programmable ROM (PROM), erasable PROM (EPROM), flash ROM, and random access memory (RAM)). Any type of temporary computer-readable medium can be used to store these programs and provide these programs to the computer. Examples of temporary computer-readable media include electrical signals, optical signals, and electromagnetic waves. Temporary computer-readable media can provide programs to the computer via wired communication lines (for example, wires and optical fibers) or wireless communication lines.

[0135] Other embodiments

[0136] The description of the above embodiments mainly focuses on LTE / LTE-Advanced and its extensions. However, the above embodiments can be applied to other wireless communication networks or systems. The eNBs 1 to 3 described in the above embodiments can each also be referred to as a wireless station. The wireless station in this specification may include a control node with a wireless resource management function (e.g., a radio network controller (RNC) in UMTS or a base station controller (BSC) in a GSM system) and a wireless transmission node (e.g., a NodeB in UMTS or a base transceiver station (BTS) in a GSM system).

[0137] In addition, the above-described embodiments are merely examples of applications of the technical concepts obtained by the present inventors. These technical concepts are not limited to the above-described embodiments, and various changes and modifications can be made to these technical concepts.

[0138] For example, all or part of the embodiments disclosed above may be described as, but not limited to, the following supplementary descriptions.

[0139] (Supplementary Note A1)

[0140] A base station device, comprising:

[0141] at least one wireless transceiver; and

[0142] at least one processor connected to the at least one wireless transceiver,

[0143] In which, the at least one processor is configured to receive a SeNB add request message from a second main base station during the period when the base station device provides a secondary cell group (SCG) used for dual connectivity in cooperation with a first main base station to a wireless terminal, and if the SeNB add request message includes a first information element that explicitly or implicitly indicates that the main base station for the dual connectivity used by the wireless terminal is to be changed from the first main base station to the second main base station, then the SeNB add request message is considered to request a modification of the configuration related to the SCG.

[0144] (Supplementary Note A2)

[0145] The base station device according to Supplementary Note A1, wherein the first information element includes a wireless terminal identifier to implicitly indicate a change in a dual-connection primary base station used by the wireless terminal,

[0146] The wireless terminal identifier is an identifier allocated by the base station device and used to uniquely identify the wireless terminal on an inter-base station interface between the first main base station and the base station device.

[0147] (Supplementary Note A3)

[0148] The base station device according to Supplementary Note A2, wherein the wireless terminal identifier comprises a SeNB UE X2AP ID allocated by the base station device.

[0149] (Supplementary Note A4)

[0150] The base station device according to Supplementary Note A2 or A3, wherein the first information element further includes a bearer identifier of a network bearer configured in the base station device for dual connectivity in cooperation with the first primary base station.

[0151] (Supplementary Note A5)

[0152] The base station device according to Supplementary Note A1, wherein the first information element explicitly indicates that a dual-connection master base station used by the wireless terminal is to be changed from the first master base station to the second master base station.

[0153] (Supplementary Note A6)

[0154] The base station device according to Supplementary Note A5, wherein the SeNB add request message includes information for specifying a combination of an identifier of a network bearer and a bearer identifier of a data radio bearer, wherein the identifier of the network bearer and the bearer identifier of the data radio bearer are dual-connected in collaboration with the first main base station and have been configured in the base station device.

[0155] (Supplementary Note A7)

[0156] According to the base station device described in any one of supplementary instructions A1 to A6, wherein the at least one processor is configured to, in response to sending a response message to the SeNB add request message to the second main base station, replace the SCG configuration used for the dual connection cooperating with the first main base station with the modified or newly configured SCG configuration used for the dual connection cooperating with the second main base station.

[0157] (Supplementary Note A8)

[0158] According to the base station device described in any one of supplementary instructions A1 to A6, wherein the at least one processor is configured to, in response to receiving a SeNB release request message from the first main base station, replace the SCG configuration used for the dual connection cooperating with the first main base station with the modified SCG configuration used for the dual connection cooperating with the second main base station.

[0159] (Supplementary Note A9)

[0160] According to the base station device described in any one of supplementary notes A1 to A8, the at least one processor is configured to suspend one or both of sending and receiving user data relative to the wireless terminal in response to receiving the SeNB add request message from the second main base station.

[0161] (Supplementary Note A10)

[0162] According to the base station device described in any one of supplementary instructions A1 to A9, wherein the at least one processor is configured to, after receiving the SeNB add request message from the second main base station, when receiving a release message from the first main base station to trigger the release of the context of the wireless terminal used for the dual connection, consider that a part of the wireless resources and control plane resources associated with the context of the wireless terminal can be released, but the remaining resources of the wireless resources and the control plane resources should be maintained.

[0163] (Supplementary Note A11)

[0164] The base station device according to supplementary note A10, wherein the portion of resources includes one or more identifiers of an inter-base station interface connection between the first main base station associated with the wireless terminal and the base station device.

[0165] (Supplementary Note A12)

[0166] The base station device according to supplementary note A10 or A11, wherein the remaining resources include configuration of a bearer associated with the wireless terminal.

[0167] (Supplementary Note A13)

[0168] The base station device according to Supplementary Note A12, wherein the configuration of the bearer includes an identifier of the bearer, a logical channel configuration, and a radio link control (RLC) configuration.

[0169] (Supplementary Note A14)

[0170] The base station device according to supplementary note A12 or A13, wherein the configuration of the bearer is updated based on the SeNB adding request from the second master base station.

[0171] (Supplementary Note A15)

[0172] According to a base station device described in any one of supplementary instructions A1 to A14, wherein the at least one processor is configured to, after receiving the SeNB add request message from the second main base station, when receiving a release message from the first main base station to trigger the release of the context of the wireless terminal used for the dual connection, consider that a condition related to user data of the wireless terminal should be maintained even when data forwarding from the base station device to the first main base station or the second main base station is not required.

[0173] (Supplementary Note A16)

[0174] According to the base station device described in Supplementary Note A15, the status related to the user data includes at least one of a Packet Data Convergence Protocol (PDCP) status related to the user data of the wireless terminal and a Radio Link Control (RLC) status related to the user data of the wireless terminal.

[0175] (Supplementary Note A17)

[0176] The base station device according to any one of supplementary instructions A10 to A16, wherein the release message is an SCG release request message indicating the release of the SCG or a context release message indicating the release of the context of the wireless terminal.

[0177] (Supplementary Note A18)

[0178] A base station device according to any one of supplementary instructions A10 to A17, wherein the release message includes one or both of a second information element and a third information element, wherein the second information element explicitly indicates that the dual-connected main base station used by the wireless terminal is to be changed from the first main base station to the second main base station, and the third information element indicates a partial release of resources associated with the context of the wireless terminal.

[0179] (Supplementary Note A19)

[0180] The base station device according to supplementary note A18, wherein at least one of the second information element and the third information element includes a reason information element indicating a reason for the release message.

[0181] (Supplementary Note B1)

[0182] A base station device, comprising:

[0183] at least one wireless transceiver; and

[0184] at least one processor connected to the at least one wireless transceiver,

[0185] The at least one processor is configured to receive, from the first primary base station, a release message for triggering release of a context of the wireless terminal used for the dual connection during providing a secondary cell group (SCG) used for the dual connection in cooperation with the first primary base station to the wireless terminal, and

[0186] The at least one processor is configured to, if, before receiving the release message, the second main base station explicitly or implicitly notifies the at least one processor that the dual-connected main base station used by the wireless terminal is to be changed from the first main base station to the second main base station, then, upon receiving the release message, consider that a portion of the wireless resources and control plane resources associated with the context of the wireless terminal can be released, but the remaining resources of the wireless resources and the control plane resources should be maintained.

[0187] (Supplementary Note B2)

[0188] The base station device according to Supplementary Note B1, wherein the portion of resources includes one or more identifiers of an inter-base station interface connection between the first main base station associated with the wireless terminal and the base station device.

[0189] (Supplementary Note B3)

[0190] The base station device according to supplementary note B1 or B2, wherein the remaining resources include configuration of a bearer associated with the wireless terminal.

[0191] (Supplementary Note B4)

[0192] The base station device according to supplementary note B3, wherein the configuration of the bearer includes an identifier of the bearer, a logical channel configuration, and a radio link control (RLC) configuration.

[0193] (Supplementary Note B5)

[0194] The base station device according to supplementary note B3 or B4, wherein the configuration of the bearer is updated based on the SeNB adding request from the second master base station.

[0195] (Supplementary Note B6)

[0196] A base station device, comprising:

[0197] at least one wireless transceiver; and

[0198] at least one processor connected to the at least one wireless transceiver,

[0199] The at least one processor is configured to receive, from the first primary base station, a release message for triggering release of a context of the wireless terminal used for the dual connection during providing a secondary cell group (SCG) used for the dual connection in cooperation with the first primary base station to the wireless terminal, and

[0200] The at least one processor is configured to, if, before receiving the release message, the second main base station explicitly or implicitly notifies the at least one processor that the dual-connected main base station used by the wireless terminal is to be changed from the first main base station to the second main base station, then, when receiving the release message, consider that the status related to the user data of the wireless terminal should be maintained even when data forwarding to the first main base station or the second main base station is not required.

[0201] (Supplementary Note B7)

[0202] The base station device according to supplementary note B6, wherein the status related to the user data includes at least one of a packet data convergence protocol (PDCP) status and a radio link control (RLC) status related to the user data of the wireless terminal.

[0203] (Supplementary Note B8)

[0204] The base station device according to any one of supplementary notes B1 to B7, wherein the release message is an SCG release request message indicating the release of the SCG or a context release message indicating the release of a context related to the wireless terminal.

[0205] (Supplementary Note B9)

[0206] A base station device according to any one of supplementary instructions B1 to B8, wherein the release message includes one or both of a second information element and a third information element, wherein the second information element explicitly indicates that the dual-connected main base station used by the wireless terminal is to be changed from the first main base station to the second main base station, and the third information element indicates a partial release of wireless resources and control plane resources associated with the context of the wireless terminal.

[0207] (Supplementary Note B10)

[0208] The base station device according to supplementary note B9, wherein at least one of the second information element and the third information element includes a reason information element indicating a reason for the release message.

[0209] This application is based upon and claims the benefit of priority from Japanese patent application No. 2015-152735, filed on Jul. 31, 2015, the entire contents of which are incorporated herein by reference.

[0210] Description of Reference Numerals

[0211] 1-3 Base Station (eNB)

[0212] 4 Wireless Terminal (UE)

[0213] 801 RF Transceiver

[0214] 804 processor

[0215] 805 Memory

Claims

1. A method in a secondary radio access network node, i.e., a secondary RAN node, the method comprising: Operate the secondary cell group, i.e. SCG; communicating with a wireless terminal configured to perform dual connectivity using the SCG and a master cell group (MCG) operated by a first master RAN node; During a handover process of the wireless terminal from the first primary RAN node to a second primary RAN node, receiving a secondary RAN node adding request message from the second primary RAN node, wherein the secondary RAN node adding request message includes a secondary RAN node user equipment identifier, i.e., a secondary RAN node UE ID; and in a case where the secondary RAN node UE ID included in the secondary RAN node add request message is not used to uniquely identify any wireless terminal on an interface between the first primary RAN node and the secondary RAN node, rejecting a secondary RAN node add request procedure corresponding to the secondary RAN node add request message by using a secondary RAN node add request reject message, The secondary RAN node adding request rejection message includes a reason indicating that the secondary RAN node UE ID included in the secondary RAN node adding request message is inappropriate.

2. The method according to claim 1, wherein: The secondary RAN node adding request message includes the secondary RAN node UE ID to implicitly indicate the change of the primary RAN node in the dual connectivity used by the wireless terminal.

3. The method according to claim 1 or 2, further comprising: In response to receiving a secondary RAN node release request message from the first primary RAN node, replacing the SCG configuration for dual connectivity in cooperation with the first primary RAN node with a modified SCG configuration for dual connectivity in cooperation with the second primary RAN node.

4. A wireless terminal, comprising: at least one wireless transceiver configured to communicate with a first primary radio access network node, i.e. a first primary RAN node, a second primary RAN node, and a secondary RAN node; as well as At least one processor configured to: communicating with the first primary RAN node and the secondary RAN node via the at least one wireless transceiver to perform dual connectivity using a primary cell group (MCG) operated by the first primary RAN node and a secondary cell group (SCG) operated by the secondary RAN node; as well as while maintaining the connection to the SCG in the secondary RAN node, changing the primary RAN node in the dual connection from the first primary RAN node to the second primary RAN node, Wherein, the secondary RAN node is configured as: During a handover process of the wireless terminal from the first primary RAN node to the second primary RAN node, receiving a secondary RAN node adding request message from the second primary RAN node, wherein the secondary RAN node adding request message includes a secondary RAN node user equipment identifier, i.e., a secondary RAN node UE ID; and rejecting a secondary RAN node add request procedure corresponding to the secondary RAN node add request message by using a secondary RAN node add request reject message, in case the secondary RAN node UE ID included in the secondary RAN node add request message is not used to uniquely identify any wireless terminal on an interface between the first primary RAN node and the secondary RAN node, and The secondary RAN node adding request rejection message includes a reason indicating that the secondary RAN node UE ID included in the secondary RAN node adding request message is inappropriate.

5. A method in a wireless terminal, the method comprising: communicating with a first master radio access network node, i.e. a first master RAN node, and a secondary RAN node to perform dual connectivity using a primary cell group, i.e. an MCG, operated by the first master RAN node and a secondary cell group, i.e. an SCG, operated by the secondary RAN node; as well as while maintaining the connection to the SCG in the secondary RAN node, changing the primary RAN node in the dual connection from the first primary RAN node to a second primary RAN node, Wherein, the secondary RAN node is configured as: During a handover process of the wireless terminal from the first primary RAN node to the second primary RAN node, receiving a secondary RAN node adding request message from the second primary RAN node, wherein the secondary RAN node adding request message includes a secondary RAN node user equipment identifier, i.e., a secondary RAN node UE ID; and rejecting a secondary RAN node add request procedure corresponding to the secondary RAN node add request message by using a secondary RAN node add request reject message, in case the secondary RAN node UE ID included in the secondary RAN node add request message is not used to uniquely identify any wireless terminal on an interface between the first primary RAN node and the secondary RAN node, and The secondary RAN node adding request rejection message includes a reason indicating that the secondary RAN node UE ID included in the secondary RAN node adding request message is inappropriate.

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