KR20150035283A - Method and apparatus for performing change of serving cell in wireless communication system using dual connectivity - Google Patents

Abstract

The present invention relates to a method and an apparatus for changing a serving cell in a wireless communication system using a dual connectivity method. According to the present invention, the method for changing a cell in a wireless communication system using a dual connectivity method comprises the following steps of: performing admission control to change a secondary serving cell with a targeted secondary eNB; transmitting a radio resource control (RRC) connectivity reconfiguration message to change the secondary serving cell to a terminal; and transmitting, to a serving secondary eNB, a secondary serving cell deactivation order to instruct that the secondary cell be deactivated.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and apparatus for changing a serving cell in a wireless communication system using a dual-

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for performing a handover or a change of a secondary serving cell (or a secondary base station) when a terminal is dual connected through two or more different base stations in a wireless communication system.

In a wireless communication system, a terminal can perform wireless communication through two or more base stations among the base stations constituting at least one serving cell. This is called Dual Connectivity. In other words, a dual connection is an operation in which a terminal set to an RRC connection state with at least two different network points consume radio resources provided by the network points can do. Herein, at least two or more different network points may be physically or logically divided into a plurality of base stations, one of which is a master eNB (MeNB) and the other base stations are a secondary base station (SenB) Lt; / RTI >

In the dual connection, each base station transmits downlink data through a bearer configured for one terminal and receives uplink data. At this time, one bearer may be configured through one base station, or may be configured through two or more different base stations. Also, in the dual connection, each base station may have at least one serving cell (Serving Cell), and each serving cell may be operated in an activated or deactivated state. In this case, a primary serving cell (PCell: Primary cell) configured in a conventional CA (Carrier Aggregation) scheme is configured in the master base station, a secondary serving cell (SCell: Cell). Here, carrier aggregation is a technique for efficiently using a fragmented small band, in which one base station bundles a plurality of physically continuous or non-continuous bands in the frequency domain to form a logically large band So as to have the same effect as using a band.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for performing a handover or a change of a secondary serving cell (or secondary base station) when a terminal is dual-connected through two or more different base stations.

According to an aspect of the present invention, there is provided a method of performing a cell change by a master base station (eNB) in a wireless communication system using a dual connection scheme.

The method includes performing admission control for changing a secondary serving cell together with a target secondary secondary Node B, performing radio resource control (RRC) for changing the secondary serving cell, Transmitting a connection reconfiguration message to the UE, and transmitting a secondary serving cell release command indicating the release of the secondary serving cell to the serving secondary base station.

The ambiguity of sequence number (SN) status forwarding / data forwarding from the serving secondary base station to the target secondary base station can be removed when the UE performs a cell change or a change of the secondary base station in the dual connection state.

1 is a diagram showing a network structure of a wireless communication system.
2 is a block diagram illustrating a wireless protocol structure for a user plane.
3 is a block diagram illustrating a wireless protocol structure for a control plane.
4 is a diagram showing a structure of a bearer service in a wireless communication system.
5 is a diagram showing a dual connection situation of a terminal.
6 is a view showing a structure of a user plane for a double connection.
7 to 11 are diagrams illustrating a protocol structure of base stations in downlink transmission of user plane data.
12 and 13 are flow charts illustrating SNST and DF procedures in a dual connection 2A according to one embodiment.
14 and 15 are flowcharts showing SNST and DF procedures in a dual connection 2C according to another embodiment
16 and 17 are flowcharts illustrating SNST and DF procedures in a dual connection 1A according to yet another embodiment.
18 is an illustration of possible handover scenarios in a dual connection environment to which the present invention is applied.
19 and 20 are flow charts illustrating handover SNST and DF procedures in dual connections 1A and 2A according to one embodiment.
FIGS. 21 and 22 are flowcharts illustrating handover SNST and DF procedures in a dual connection 2C according to another embodiment.
23 is a block diagram illustrating a master base station and a secondary base station according to an example of the present invention.

Hereinafter, the contents related to the present invention will be described in detail with reference to exemplary drawings and embodiments, together with the contents of the present invention. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

In addition, the present invention will be described with respect to a wireless communication network. The work performed in the wireless communication network may be performed in a process of controlling a network and transmitting data by a system (e.g., a base station) Work can be done at a terminal connected to the network.

1 is a diagram showing a network structure of a wireless communication system.

FIG. 1 shows a network structure of an evolved-universal mobile telecommunications system (E-UMTS) system as an example of a wireless communication system. The E-UMTS system may be an Evolved-UMTS Terrestrial Radio Access (E-UTRA) or a Long Term Evolution (LTE) or an LTE-A (advanced) system. The wireless communication system can be classified into a Code Division Multiple Access (CDMA), a Time Division Multiple Access (TDMA), a Frequency Division Multiple Access (FDMA), an Orthogonal Frequency Division Multiple Access (OFDMA), a Single Carrier- , OFDM-TDMA, and OFDM-CDMA.

Referring to FIG. 1, an Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) includes a Base Station (BS) providing a control plane (CP) and a user plane (UP) (eNB: evolved NodeB, 20).

A user equipment (UE) 10 may be fixed or mobile and may be a mobile station, an AMS (advanced MS), a user terminal (UT), a subscriber station (SS), a wireless device It can be called another term.

The base station 20 generally refers to a station that communicates with the terminal 10 and includes a base station (BS), a base transceiver system (BTS), an access point, a femto-eNB, A pico-eNB, a home eNB, a relay, or the like. The base stations 20 are physically connected through an optical cable or a DSL (digital subscriber line), and can exchange signals or messages with each other via the Xn interface. In FIG. 1, for example, the base stations 20 are connected through an X2 interface.

In the following, the description of the physical connection is omitted and the logical connection is described. As shown in FIG. 1, the base station 20 is connected to an evolved packet core (EPC) 30 through an S1 interface. More specifically, the base station 20 is connected to an MME (Mobility Management Entity) through an S1-MME interface and is connected to an S-GW (Serving Gateway) through an S1-U interface. The base station 20 exchanges context information of the MME with the terminal 10 and information for supporting the mobility of the terminal 10 through the S1-MME interface. And sends and receives data to be served to the S-GW and each terminal 10 through the S1-U interface.

Although not shown in FIG. 1, the EPC 30 includes an MME, an S-GW, and a packet data network-gateway (P-GW). The MME has information on the connection information of the terminal 10 and the capability of the terminal 10. This information is mainly used for managing the mobility of the terminal 10. [ The S-GW is a gateway having an E-UTRAN as an end point, and the P-GW is a gateway having a PDN (Packet Data Network) as an end point.

The E-UTRAN and the EPC 30 may be combined to form an EPS (Evolved Packet System). The traffic flow from the wireless link to the base station 20 to the PDN that connects the terminal 10 to the service entity (Internet Protocol).

The wireless interface between the terminal 10 and the base station 20 is referred to as a "Uu interface ". The layers of the radio interface protocol between the terminal 10 and the network are divided into a first layer L1 defined by a 3rd Generation Partnership Project (3GPP) series wireless communication system (UMTS, LTE, LTE-Advanced, etc.) A second layer L2 and a third layer L3. Among them, the physical layer belonging to the first layer provides an information transfer service using a physical channel, and the RRC (Radio Resource Control) layer located at the third layer exchanges RRC messages, (10) and the network.

FIG. 2 is a block diagram illustrating a radio protocol architecture for a user plane, and FIG. 3 is a block diagram illustrating a radio protocol structure for a control plane. The user plane is a protocol stack for transmitting user data, and the control plane is a protocol stack for transmitting control signals.

Referring to FIGS. 2 and 3, a physical layer (PHY (physical layer) of a terminal and a base station provide an information transfer service to an upper layer using a physical channel, respectively. The physical layer is connected to a medium access control (MAC) layer, which is an upper layer, through a transport channel. The data is transmitted between the MAC layer and the physical layer through a transmission channel. The transport channel is classified according to how the data is transmitted over the air interface. Further, data is transmitted through physical channels between different physical layers (i.e., between the physical layer of the terminal and the base station). The physical channel can be modulated by an Orthogonal Frequency Division Multiplexing (OFDM) scheme, and uses time, frequency, and space generated by a plurality of antennas as radio resources.

For example, a physical downlink control channel (PDCCH) of a physical channel notifies a UE of resource allocation of a paging CHannel (DLH), a downlink shared channel (DL-SCH), and Hybrid Automatic Repeat Request (HARQ) And an uplink scheduling grant informing the UE of the resource allocation of the uplink transmission. The Physical Control Format Indicator CHannel (PCFICH) informs the UE of the number of OFDM symbols used for PDCCHs and is transmitted every subframe. Also, the PHICH (Physical Hybrid ARQ Indicator CHannel) carries HARQ ACK / NAK signals in response to the uplink transmission. Also, the Physical Uplink Control CHannel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request and CQI for downlink transmission. Also, the Physical Uplink Shared CHannel (PUSCH) carries UL-SCH (Uplink Shared CHannel). If necessary, the PUSCH may include CSI (Channel State Information) information such as HARQ ACK / NACK and CQI according to the setup and request of the base station.

The MAC layer can perform multiplexing or demultiplexing into a transport block provided on a physical channel on a transport channel of a MAC SDU (Service Data Unit) belonging to a logical channel and a mapping between a logical channel and a transport channel. The MAC layer provides service to the Radio Link Control (RLC) layer through a logical channel. The logical channel can be divided into a control channel for transferring control area information and a traffic channel for transferring user area information. For example, there are data transmission or radio resource allocation as services provided from the MAC layer to the upper layer.

The function of the RLC layer includes concatenation, segmentation and reassembly of the RLC SDUs. The RLC layer includes a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (AM) to guarantee various QoSs required by a radio bearer (RB) Acknowledged Mode).

In general, transparent mode is used to set the initial connection. The unacknowledged mode is for data streaming or real-time data transmission such as Voice over Internet Protocol (VoIP), and is a speed-focused mode rather than a data reliability. On the other hand, the acknowledged mode is a mode that focuses on the reliability of data and is suitable for data transmission which is less sensitive to large data transmission or transmission delay. The base station determines the mode of the RLC in the RB corresponding to each EPS bearer based on the Quality of Service (QoS) information of each EPS bearer connected to the UE and configures the parameters in the RLC so as to satisfy the QoS.

RLC SDUs are supported in various sizes, and may be supported on a byte basis, for example. RLC Protocol Data Units (PDUs) are defined only when a transmission opportunity from a lower layer (eg, the MAC layer) is notified and forwarded to the lower layer. The transmission opportunity may be notified with the size of the total RLC PDUs to be transmitted. In addition, the transmission opportunity and the size of the total RLC PDUs to be transmitted may be separately reported.

The functions of the Packet Data Convergence Protocol (PDCP) layer in the user plane include delivery of user data, header compression and ciphering, and delivery of control plane data and encryption / integrity protection.

Referring to FIG. 3, the RRC layer is responsible for controlling logical channels, transport channels, and physical channels in connection with configuration, re-configuration and release of RBs. A radio bearer (RB) refers to a logical path provided by a first layer (PHY layer) and a second layer (MAC layer, RLC layer, PDCP layer) for data transmission between a UE and a network. The configuration of the RB means a process of defining characteristics of a radio protocol layer and a channel to provide a specific service, and setting each specific parameter and an operation method. RB may be classified into SRB (Signaling RB) and DRB (Data RB). The SRB is used as a path for transmitting the RRC message and the NAS (Non-Access Stratum) message in the control plane, and the DRB is used as a path for transmitting the user data in the user plane.

The non-access stratum (NAS) layer located at the top of the RRC layer performs functions such as session management and mobility management. When there is an RRC connection between the RRC layer of the UE and the RRC layer of the E-UTRAN, the UE is in an RRC connected state. Otherwise, the UE is in an RRC idle state do.

In order for a terminal to transmit user data (e.g., IP packets) to an external Internet network or to receive user data from an external Internet network, it is necessary for the terminal to exist between the mobile communication network entities existing between the terminal and the external Internet network. The resource must be assigned to multiple paths. A path in which resources are allocated between mobile communication network entities and data transmission / reception is possible is called a bearer.

4 is a diagram showing a structure of a bearer service in a wireless communication system.

FIG. 4 shows a path in which an end-to-end service is provided between a terminal and the Internet network. Here, the term end-to-end service refers to a service (UE Bearer) between the UE and the P-GW, a P-GW, and an external bearer to the outside for an Internet network and data service . Here, the external path is a bearer between the P-GW and the Internet network.

When the UE transmits data to the external Internet network, the UE transmits data to the eNB through the RB. Then, the base station transmits the data received from the terminal to the S-GW through the S1 bearer. The S-GW carries the data received from the base station through the S5 / S8 bearer to the P-GW, and finally the data is transmitted to the destination existing in the P-GW and the external internet network through the external bearer.

Likewise, in order for data to be transmitted from the external Internet network to the mobile station, the mobile station can transmit data to the mobile station via the bearers in the reverse direction.

As described above, in the wireless communication system, each bearer is defined for each interface to ensure independence between interfaces. The bearer at each interface will be described in more detail as follows.

The bearer provided by the wireless communication system is collectively referred to as an evolved packet system (EPS) bearer. The EPS bearer is a delivery path established between the UE and the P-GW to transmit IP traffic with a specific QoS. The P-GW may receive IP flows from the Internet or may transmit IP flows over the Internet. Each EPS bearer is set with QoS decision parameters indicating the characteristics of the propagation path. An EPS bearer may be configured for one or more UEs per UE, and one EPS bearer uniquely represents a concatenation of one E-RAB and one S5 / S8 bearer.

The radio bearer (RB) exists between the UE and the base station and delivers the packets of the EPS bearer. A specific RB has a one-to-one mapping relationship with the corresponding EPS Bearer / E-RAB (E-UTRAN Radio Access Bearer).

The S1 bearer carries the E-RAB packet as a bearer existing between the S-GW and the base station.

The S5 / S8 bearer is the bearer of the S5 / S8 interface. Both S5 and S8 are bearers present at the interface between the S-GW and the P-GW. S5 interface exists when the S-GW and P-GW belong to the same service provider. The S8 interface belongs to the Visited PLMN roaming S-GW and the P- RTI ID = 0.0 > PLMN). ≪ / RTI >

The E-RAB uniquely represents the concatenation of the S1 bearer and its corresponding RB. When there is one E-RAB, a one-to-one mapping is established between the corresponding E-RAB and one EPS bearer. That is, one EPS bearer corresponds to one RB, S1 bearer, and S5 / S8 bearer, respectively. The S1 bearer is the bearer at the interface between the base station and the S-GW.

RB means two kinds of data RB (data radio bearer) and signaling RB (signaling radio bearer). However, in the present invention, RB is a DRB provided in a Uu interface to support a user service . Therefore, the RB that is expressed separately is distinguished from the SRB. RB is a path through which user plane data is transmitted, and SRB is a path through which control plane data such as an RRC layer and a NAS control message are transmitted. There is a one-to-one mapping between RB, E-RAB and EPS bearer. The base station maps DRBs and S1 bearers to one-to-one and stores them in order to generate a DRB that bundles both uplink and downlink. The S-GW maps the S1 bearer to the S5 / S8 bearer one-to-one and stores it in order to create the S1 bearer and the S5 / S8 bearer that bind both the uplink and downlink.

EPS bearer types include a default bearer and a dedicated bearer. When the terminal accesses the wireless communication network, the terminal is allocated an IP address and generates a PDN connection and a default EPS bearer at the same time. That is, the default bearer is first created when a new PDN connection is created. If a user uses a service (eg, the Internet) via a default bearer and uses a service (eg, VoD, etc.) that is not properly provided with QoS as the default bearer, A dedicated bearer is created. In this case, the dedicated bearer can be set to a different QoS from the bearer that has already been set. The QoS decision parameters applied to the dedicated bearer are provided by the Policy and Charging Rule Function (PCRF). When generating the dedicated bearer, the PCRF can receive the subscription information of the user from the Subscriber Profile Repository (SPR) and determine QoS determination parameters. Up to 15 dedicated bearers can be created, for example, up to 15, and in the LTE system, four out of the 15 are not used. Therefore, up to 11 dedicated bearers can be created.

The EPS bearer includes QoS Class Identifier (QCI) and Allocation and Retention Priority (ARP) as basic QoS decision parameters. EPS bearer is divided into GBR (Guaranteed Bit Rate) bearer and non-GBR bearer according to QCI resource type. The default bearer is always set to a non-GBR bearer, and the dedicated bearer can be set to a GBR or non-GBR bearer. In addition to QCI and ARP, the GBR type bearer has GBR and MBR (Maximum Bit Rate) as QoS decision parameters. After QoS defined by the wireless communication system as a whole is defined as an EPS bearer, QoS is determined for each interface. Each interface establishes a bearer according to the QoS it should provide.

5 is a diagram illustrating an example of a dual connection situation of a terminal.

5, the terminal 550 includes a service area of the macro cell F2 provided by the master base station 500 and a service area of the small cell F1 provided by the secondary base station 510 overlaid area.

In this case, the network forms a dual connection to the terminal 550 in order to support additional data service through the small cell F1 while maintaining the existing wireless connection and data service connection through the macro cell F2. Accordingly, the user data arriving at the master base station 500 can be transmitted to the terminal through the secondary base station 510. Specifically, the F2 frequency band is allocated to the master base station 500, and the F1 frequency band is allocated to the secondary base station 510. [ The terminal 550 can receive the service from the master base station 500 through the frequency band F2 and receive the service from the secondary base station 510 via the frequency band F1. In the above example, the master base station 500 uses the F2 frequency band and the secondary base station 510 uses the F1 frequency band. However, the present invention is not limited to this, and the master base station 500 and the secondary base station 510 510) may use the same F1 or F2 frequency band.

6 is a view showing a structure of a user plane for a double connection.

Referring to FIG. 6, a dual connection is composed of an arbitrary terminal, a master base station (MeNB), and at least one secondary base station (SeNB). The double connection can be divided into three options as shown in FIG. 6 depending on how the user plane data is divided. In Fig. 6, the concept of the above three options for downlink transmission of user plane data is shown as an example.

The first option is when the S1-U interface has an end point not only in the master base station but also in the secondary base station. In this case, each of the base stations MeNB and SeNB transmits downlink data through an EPS bearer (EPS bearer # 1 for the master base station and EPS bearer # 2 for the secondary base station) configured for one UE. Since the user plane data is splitted in the core network (CN), this is called a CN split.

Second option: The case where the S1-U interface has an end point only in the master base station. In this case, the S1-U interface has an end point only at the master base station, but the bearer does not differentiate and only one bearer is mapped for each base station.

Option 3: The S1-U interface has an endpoint only in the MeNB. In this case, since the bearer is differentiated, it is called a bear split. The bearer split is divided into two flows (or more flows) because one bearer is differentiated into a plurality of base stations. We call bearer splits as multi-flow, multiple-node (eNB) transmission, inter-eNB carrier aggregation, etc. in that information is transmitted through multiple flows. Also.

On the other hand, if the end point of the S1-U interface is the master base station (i.e., the second or third option) in terms of the protocol structure, the protocol layer in the secondary base station must support the segmentation or refinement process. This is because the physical interface and subdivision processes are closely related to each other, and when using non-ideal backhaul, the subdivision or subdivision process must be the same as the node transmitting the RLC PDU. Therefore, considering the protocol structures for dual connection in the RLC layer and above, the following is considered.

A. It is the case that the PDCP layer exists independently in each base station. This is also referred to as an independent PDCP type. In this case, each base station can use the operation of the existing LTE layer 2 protocol in the bearer as it is. This can be applied to both the first option and the third option.

B. The case where the PDCP layer exists in a master-slave form.

C. It is the case that the RLC layer exists independently in each base station. This is also referred to as an independent RLC type. In this case, the S1-U interface makes the master base station an end point, and the PDCP layer exists only in the master base station. In the case of the bearer split (third option), the RLC layer is separated in both the network and the UE side, and there exists an independent RLC bearer for each RLC layer.

D. The RLC layer is divided into the 'master RLC' layer of the master base station and the 'slave RLC' layer of the secondary base station. This is also referred to as master-slave RLC type. In this case, the S1-U interface has a master base station as an end point. In the master base station, a part of the PDCP layer and the RLC layer (the master RLC layer) exists and the secondary base station has a part of the RLC layer (the slave RLC layer). In the UE, there is only one RLC layer forming a pair with the master RLC layer and the slave RLC layer.

Thus, the double connection can be distinguished as shown in FIG. 7 by the combination of the above-described options and types. For example, 1A indicates a dual connection in which the CN splits and the PDCP layer exists independently in each base station. The term " 2A " means a dual connection in which two bearers are differentiated from the master base station and the PDCP layer exists independently. 2C means a dual connection in which the PDCP layer exists only in the master base station while the two bearers are differentiated from the master base station.

7 to 11 are diagrams illustrating a protocol structure of base stations in downlink transmission of user plane data.

First, referring to FIG. 7, an S1-U interface has an end point not only in a master base station but also in a secondary base station, and a PDCP layer exists independently in each base station (1A dual connection). In this case, the PDCP layer, the RLC layer and the MAC layer exist in the master base station and the secondary base station, respectively, and each base station transmits downlink data through each EPS bearer configured for the terminal.

In this case, the master base station does not need to buffer or process packets transmitted by the secondary base station, and has the advantage that there is little or no impact on the RDCP / RLC and GTP-U / UDP / IP. Since there is no need for backhaul link between the master base station and the secondary base station and there is no need to control the flow between the master base station and the secondary base station, the master base station does not need to route all the traffic, Can support local break-out and content caching at the same time.

Referring to FIG. 8, a case where the S1-U interface has an end point only in the master base station and not in the bearer split, and the PDCP layer exists independently in each base station (2A dual connection) is shown. In this case, the PDCP layer, the RLC layer and the MAC layer exist in the master base station and the secondary base station, respectively, but the PDCP layer of the master base station is connected to the PDCP layer of the secondary base station via the Xn interface. Here, the Xn interface may be an X2 interface defined between base stations in the LTE system.

In this case, there is an advantage that the mobility of the secondary base station is hidden in the core network, and there is little or no effect on the RDCP / RLC and GTP-U / UDP / IP and only the packet is routed to the secondary base station without buffering .

9, the S1-U interface has an end point only in the master base station, not bearer split, and the RLC layer exists independently in each base station (2C dual connection). In this case, the master base station includes the PDCP layer, the RLC layer, and the MAC layer, but only the RLC layer and the MAC layer exist in the secondary base station. The PDCP layer of the master base station is separated into a bearer level, and one of the PDCP layers is connected to the RLC layer of the secondary base station through the Xn interface.

In this case, the mobility of the secondary base station is hidden in the core network, and there is no security effect that the ciphering is required in the master base station. Also, there is an advantage that the master base station can transfer RLC processing to the secondary base station, and has little or no effect on the RLC.

Referring to FIG. 10, there is shown a case where the S1-U interface has end points only in the master base station, bearer split, and RLC layers exist independently in each base station (3C dual connection). In this case, the master base station has the PDCP layer, the RLC layer, and the MAC layer, and only the RLC layer and the MAC layer exist in the secondary base station. The PDCP layer, the RLC layer, and the MAC layer of the master base station are separated into bearer levels, and one PDCP layer is connected to one of the RLC layers of the master base station and is connected to the RLC layer of the secondary base station through the Xn interface.

In this case, there is no security effect that the mobility of the secondary base station is hidden in the core network, encryption is required in the master base station, and data forwarding between the secondary base stations is not necessary when the secondary base station is changed. In addition, the master base station can transfer RLC processing to the secondary base station, and can utilize radio resources through the master base station and the secondary base station for the same bearer when there is no or little influence on the RLC, There is an advantage in that the requirement for the mobility of the secondary base station is small since it is possible to use the master base station.

11, if the S1-U interface has an end point only in the master base station and is bearer split, and the RLC layer of the master base station is the master RLC layer and the secondary base station RLC layer is the slave RLC layer (3B double connection) Respectively. In this case, the master base station has the PDCP layer, the RLC layer, and the MAC layer, and only the RLC layer and the MAC layer exist in the secondary base station. In addition, the PDCP layer, the RLC layer and the MAC layer of the master base station are separated into bearer levels, and one RLC layer is connected to the RLC layer (slave RLC layer) of the secondary base station through the Xn interface as the master RLC layer.

In this case, there is no security effect that the mobility of the secondary base station is hidden in the core network, encryption is required in the master base station, and data forwarding between the secondary base stations is not necessary when the secondary base station is changed. In addition, if there is no influence on the RLC, and if it is possible to do so, it is possible to utilize radio resources for the same bearer through the master base station and the secondary base station, and since the master base station can be used during the movement of the secondary base station, The advantage is that there are few things. In addition, there is an advantage that the packet loss between the master base station and the secondary base station can be covered by the ARQ of the RLC.

Discussions have been focused on reducing the overload to the core network (for example, blind path changes in the core network), and the mobility to do so The structure of the user plane is studied. (Sequence Number) status transfer and data forwarding (SN) transfer in a user plane structure during a wide range of cell change including a change of a secondary base station and a handover between a master station and a base station, SNST and DF) have not yet been studied. However, SNST and DF are closely related to seamless cell changes, which is a very important factor in terms of robust communication.

In this embodiment, a procedure for performing SNST and DF is defined when a secondary base station (or serving cell) is changed in a dual connection 1A / 2A / 2C and when a master base station is changed (i.e., handover). A serving cell change command (or an RRC connection reconfiguration message instructing a cell change) is required in the procedure of performing SNST and DF at the time of changing the secondary base station (or the serving cell) or at the time of changing the master base station. This serving cell change command is transmitted to the terminal through the master base station. Although the SNST and DF procedures in the user plane are described only in terms of the downlink data processing process throughout the present specification, it goes without saying that the SNST and DF procedures can be similarly applied to the uplink data processing process.

1. Dual connection at 1A / 2A / 2C Secondary  Base station (or Secondary serving cell ) At the time of change SNST  And DF  step

(1) For double connection 2A

The double connection 2A is the same as the structure of Fig. Here, the master base station has the S1-MME, and the end point of the S1-U interface exists in the master base station. Accordingly, when the secondary base station (or serving cell) is changed, the path change to the core network is not required, and the SNST and DF procedures are performed through the X2 interface between the serving secondary base station SeNB1 and the target secondary base station SeNB2. Compared to the dual connection 1A, no path change occurs in the dual connection 2A because the secondary base station is anchored by the master base station.

12 and 13 are flow charts illustrating SNST and DF procedures in a dual connection 2A according to one embodiment. 12 is an operation in the control plane according to the SNST and DF procedures, and Fig. 13 is an operation in the user plane according to the SNST and DF procedures.

Referring to FIG. 12, the MS moves to the vicinity of the target secondary base station 2 (SeNB2) while being connected to the master base station MeNB and the serving secondary base station 1 (SeNB1). At this time, the secondary base station connected to the terminal can be changed from the existing serving secondary base station to the new target secondary base station.

The master base station performs a SeNB change admission control procedure for the SeNB2 and the secondary base station (or the serving cell (SCell)) (S1200).

Then, the master base station transmits an RRC connection reconfiguration message for changing the SeNB to the UE (S1205). Upon receiving the RRC connection reconfiguration message, the UE reestablishes the RRC connection to the existing serving secondary base station 1 (SeNB1) (S1205). At this time, all protocol layers below PDCP and RLC are reset. In this embodiment, transmission of an RRC connection reconfiguration message for SeNB change and RRC connection reconfiguration have been shown to occur at the same time, but this embodiment also includes embodiments that occur at different points in time considering the processing time in actual implementation .

When the terminal reestablishes the RRC connection, the dual connection is composed of the master base station / target secondary base station 2 (MeNB / SeNB2). That is, the change of the secondary base station is completed. At this time, data loss may occur if the user data and the SN state transmitted through the serving secondary base station 1 (SeNB1) are not transmitted and are changed to the target secondary base station 2 (SeNB2). Therefore, in order to provide continuous communication service, the residual data and the SN state must be transmitted to the target secondary base station 2 (SeNB2). This procedure is called SNST and DF. In the structure of the dual connection 2A, since the PDCP layer exists in the serving secondary base station 1 (SeNB1), the serving secondary base station 1 (SeNB1) can perform the SNST and DF procedures. However, it is impossible to know at what time the serving secondary base station 1 (SeNB1) should perform SNST and DF.

In order to clarify the SNST and the DF operation time, the master base station may provide some signaling to the secondary base station 1 (SeNB1). For example, the master base station transmits a secondary base station release order (SeNB release order) (S1210). The secondary base station release command may be referred to as a secondary serving cell release command. Alternatively, the secondary base station release command may be referred to as an SNST and DF command. This secondary base station release command is transmitted using a message structure defined in the Xn interface.

Upon receiving the secondary base station release command from the master base station, the serving secondary base station 1 (SeNB1) forwards the SN state and the data remaining in the buffer to the target secondary base station 2 (SeNB2) (S1215).

A specific example in which the user data is transmitted from the serving secondary base station 1 (SeNB1) to the target secondary base station 2 (SeNB2) in step S1215 is described in Fig.

Meanwhile, although not shown in FIG. 12, the MeNB may transmit the SeNB release order to the SeNB1 without transmitting the SeNB release order to the SeNB1.

Referring to FIG. 13, the serving secondary base station 1 (SeNB1) sequentially transmits packets 1, 2, 3 and 4 to the UE. After the serving secondary base station 1 (SeNB1) successfully receives the RLC ACK from the terminal only for the packet 1 and receives the secondary base station release command, the serving secondary base station 1 (SeNB1) does not transmit the packet 5 to the terminal.

On the other hand, packets 5, 6 and 7 are transmitted from the master base station to the serving secondary base station 1 (SeNB1) and then transmitted to the target secondary base station 2 (SeNB2) from the packet 8 due to the double connection change to the target secondary base station 2 (SeNB2) .

The serving secondary base station 1 (SeNB1) forwards the packets 2, 3, 4, ..., 7 after the packet 1 successfully received RLC ACK to the target secondary base station 2 (SeNB2). At this time, the terminal has already received the packets 3 and 4 from the serving secondary base station 1 (SeNB1), but also receives from the target secondary base station 2 (SeNB2) after the change of the secondary base station. That is, packets 3 and 4 become duplicated packets.

(2) For dual connection 2C

The double connection 2C is the same as that of Fig. Here, the master base station has the S1-MME, and the end point of the S1-U interface exists in the master base station. Therefore, when the secondary base station (or serving cell) is changed, the path change to the core network is not required, and the SNST and DF procedures are performed by the master base station (MeNB). This is because the secondary base station has no PDCP layer corresponding to the corresponding bearer.

14 and 15 are flowcharts illustrating SNST and DF procedures in a dual link 2C according to another embodiment. 14 is an operation in the control plane according to the SNST and DF procedures, and Fig. 15 is an operation in the user plane according to the SNST and DF procedures.

Referring to FIG. 14, the MS moves to the vicinity of the target secondary base station 2 (SeNB2) while being connected to the master base station MeNB and the serving secondary base station 1 (SeNB1). At this time, the secondary base station connected to the terminal can be changed from the existing serving secondary base station to the new target secondary base station.

The master base station performs a SeNB change admission control procedure for the target secondary base station 2 (SeNB2) and the secondary base station (or serving cell) (S1400).

Then, the master base station transmits an RRC connection reconfiguration message for changing the SeNB to the UE (S1405). Upon receiving the RRC connection reconfiguration message, the UE reestablishes the RRC connection to the existing serving secondary base station 1 (SeNB1). At this time, all protocol layers below PDCP and RLC are reset. In this embodiment, transmission of an RRC connection reconfiguration message for SeNB change and RRC connection reconfiguration have been shown to occur at the same time, but this embodiment also includes embodiments that occur at different points in time considering the processing time in actual implementation .

When the terminal reestablishes the RRC connection, the dual connection is configured by the master base station / target secondary base station. That is, the change of the secondary base station is completed. At this time, data loss may occur if the user data and the SN state transmitted through the serving secondary base station 1 (SeNB1) are not transmitted and are changed to the target secondary base station 2 (SeNB2). Therefore, in order to provide continuous communication service, the residual data and the SN state must be transmitted to the target secondary base station 2 (SeNB2). This procedure is called SNST and DF.

The master base station transmits a secondary base station release order (SeNB release order) (S1410). The secondary base station release command may be referred to as a secondary serving cell release command. Alternatively, the secondary base station release command may be referred to as an SNST and DF command. This secondary base station release command is transmitted using a message structure defined in the Xn interface.

In the dual connection 2C structure, the PDCP layer does not exist in the serving secondary base station 1 (SeNB1) but exists only in the master base station. Therefore, the master base station can perform SNST and DF. However, if the RLC ACK / NACK information is not properly notified from the serving secondary base station 1 (SeNB1), it can not be determined from which SN packet to be transmitted to the target secondary base station. For example, as shown in FIG. 15, packets 1, 2, 3, and 4 are transmitted to the mobile station. Assume that RLC ACK is received only for packet 1. In this case, if the RLC ACK is not transmitted to the master base station, the master base station can not know to which packet the terminal normally received, and therefore, it is unclear from which packet to forward to the target secondary base station.

Accordingly, the present embodiment includes a step in which the serving secondary base station 1 (SeNB1) appropriately provides the RLC ACK / NACK information to the master base station (S1415).

Here, if the RLC ACK / NACK information is not sufficiently provided to the master base station, the buffer of the master base station for data forwarding may overflow during the change of the secondary base station. On the other hand, if the RLC ACK / NACK information is frequently transmitted, it can serve as an overhead for the Xn interface. Therefore, the report of the RLC ACK / NACK information should be able to be provided from the serving secondary base station to the master base station as an appropriate frequency at the appropriate timing.

As an example of the signaling scheme, the ACK / NACK information may be transmitted from the SeNB 1 to the MeNB whenever an ACK / NACK status report is generated in the RLC layer of the SeNB 1.

In another embodiment, a period value (Period) for updating the corresponding ACK / NACK information may be set in SeNB1 from MeNB. The latest ACK / NACK status report value from the MeNB to the corresponding time point can be periodically transmitted to the SeNB 1 according to the period value.

A specific example in which the user data is transmitted from the master base station to the target secondary base station is described in Fig.

Referring to FIG. 15, the serving secondary base station 1 (SeNB1) sequentially transmits packets 1, 2, 3, and 4 to the UE. After the serving secondary base station 1 successfully receives the RLC ACK from the terminal only for the packet 1 and then receives the secondary base station release command, the serving secondary base station 1 does not transmit the packet 5 to the terminal.

On the other hand, packets 5, 6, and 7 are transmitted from the master base station to the serving secondary base station 1, and then from packet 8 to the target secondary base station 2 due to the change of the secondary base station.

The serving secondary base station 1 forwards the packets 2, 3, 4, ..., 7 after the packet 1 successfully received RLC ACK to the target secondary base station 2. At this time, the terminal receives the packets 3 and 4 from the serving secondary base station 1, but also receives the packet 3 and 4 from the target secondary base station 2 after the change of the secondary base station. That is, packets 3 and 4 become duplicated packets.

(3) For double connection 1A

The double connection 1A is the same as that of Fig. Here, both the master base station and the secondary base station have the S1-MME, and the end points of the S1-U interface exist in both the master base station and the secondary base station. Therefore, when the secondary base station (or the serving cell) is changed, a path change to the core network is required, and the SNST and DF procedures are performed through the X2 interface between the serving secondary base station SeNB1 and the target secondary base station SeNB2.

16 and 17 are flowcharts illustrating SNST and DF procedures in a dual connection 1A according to yet another embodiment. 16 is an operation in the control plane according to the SNST and DF procedures, and Fig. 17 is an operation in the user plane according to the SNST and DF procedures.

Referring to FIG. 16, the MS moves to the vicinity of the target secondary base station 2 (SeNB2) while being connected to the master base station MeNB and the serving secondary base station 1 (SeNB1). At this time, the secondary base station connected to the terminal can be changed from the existing serving secondary base station to the new target secondary base station.

The master base station performs a SeNB change admission control procedure for the target secondary base station 2 and the secondary base station (or serving cell) (S1600).

Then, the master base station transmits an RRC connection reconfiguration message for changing the SeNB to the UE (S1605). Upon receiving the RRC connection reconfiguration message, the terminal reestablishes the RRC connection to the existing serving secondary base station 1. At this time, all protocol layers below PDCP and RLC are reset. In this embodiment, transmission of an RRC connection reconfiguration message for SeNB change and RRC connection reconfiguration have been shown to occur at the same time, but this embodiment also includes embodiments that occur at different points in time considering the processing time in actual implementation .

When the terminal reestablishes the RRC connection, the dual connection is configured by the master base station / target secondary base station 2. That is, the change of the secondary base station is completed. At this time, if the user data and the SN state transmitted through the serving secondary base station 1 are changed to the target secondary base station 2 without being transmitted, data loss may occur. Therefore, in order to provide continuous communication service, the residual data and the SN state must be transmitted to the target secondary base station 2. This procedure is called SNST and DF. In the structure of the dual connection 2A, since the PDCP layer exists in the serving secondary base station 1, the serving secondary base station 1 can perform the SNST and DF procedures. However, it is impossible to know at what point the serving secondary base station 1 should perform SNST and DF.

In order to clarify the SNST and DF operation time, the master base station can provide any signaling to the secondary base station 1. For example, the master base station transmits a secondary base station release command (SeNB release order) for starting SNST and DF (S1610). The secondary base station release command may be referred to as a secondary serving cell release command. Alternatively, the secondary base station release command may be referred to as an SNST and DF command. This secondary base station release command is transmitted using a message structure defined in the Xn interface.

Upon receiving the secondary base station release command from the master base station, the serving secondary base station 1 forwards the SN state and the data remaining in the buffer to the target secondary base station 2 (S1615).

Then, in order to change the route, the target secondary base station 2 transmits a route change request to the MME (S1620). Upon receiving the route change request, the MME transmits a bearer modify request to the gateway (S1625).

A specific example in which user data is transmitted from the serving secondary base station to the target secondary base station according to this embodiment is described in Fig.

Referring to FIG. 17, the serving secondary base station SeNB1 sequentially transmits packets 1, 2, 3 and 4 to the UE. After the serving secondary base station only successfully receives the RLC ACK for the packet 1 from the terminal and receives the secondary base station release command, the serving secondary base station does not transmit the packet 5 to the terminal.

On the other hand, packets 5, 6, and 7 are transmitted from the gateway to the serving secondary base station 1, and then from the packet 8 to the target secondary base station 2 due to the change of the secondary base station.

The serving secondary base station forwards the packets 2, 3, 4, ..., 7 to the target secondary base station 2 after the packet 1 successfully received the RLC ACK. At this time, the terminal receives the packets 3 and 4 from the serving secondary base station 1, but also receives the packet 3 and 4 from the target secondary base station 2 after the change of the secondary base station. That is, packets 3 and 4 become duplicated packets.

2. When the master base station is changed (handover) in dual connection 1A / 2A / 2C SNST  And DF  step

18 is an illustration of possible handover scenarios in a dual connection environment to which the present invention is applied.

Referring to FIG. 18, (A) shows a scenario in which a terminal performs a handover in a dual connection state and a dual connection is released. Since a handover region includes only macro cell coverage, a terminal having a dual connection can not maintain a dual connection after a handover. Thus, under the dual connection, the radio bearers provided by the serving secondary base station and the master base station can be combined and then only provided by the target master base station.

(B) shows a first scenario in which a terminal performs handover in a dual connection state and a dual connection is maintained. The neighboring macro cell overlaps with the adjacent small cell in the area where the terminal performs handover. Therefore, the terminal having the dual connection can maintain the double connection after the handover. However, since the handover occurs, the UE must perform a dual cell change.

(C) shows a second scenario in which a terminal performs handover in a dual connection state and a dual connection is maintained. The neighboring macro cell and the current serving small cell are overlapped in the area where the UE handover. Therefore, the terminal having the dual connection can maintain the double connection after the handover. However, since the handover occurs, the terminal changes the master base station while maintaining the connection with the secondary base station.

In these various scenarios, two approaches are possible. One is to prevent double connection in the area where the master base station is changed. This means that the connection with the secondary base station is canceled before the macro cell handover. The other is to define a new handover procedure under a dual connection.

The following describes possible handover procedures under each duplexing scheme. Here, it is assumed that the inter-base station (inter MeNB) handover operation is allowed. It is also assumed that scenario (A) of FIG. 18 is representative of SNST and DF during handover. In scenario B, SNST and DF may occur between secondary base stations or between master base stations. The SNST and DF between the master base stations can follow the existing handover procedure. In scenario (C), SNST and DF may occur between the master base stations. Therefore, SNST and DF between the master base stations can follow the conventional handover procedure even in this case.

(1) For double connection 1A / 2A

The double connection 1A is the same as that of Fig. 7, and 2A is the same as that of Fig. 1A and 2A, each of the master base station and the secondary base station has an independent PDCP layer. Therefore, when the master base station is changed by handover, SNST and DF are transmitted to the target master base station along each path in a dual forwarding manner.

19 and 20 are flow charts illustrating handover SNST and DF procedures in dual connections 1A and 2A according to one embodiment. Fig. 19 is an operation in the control plane according to the SNST and DF procedures applied to both of the double connections 1A and 2A, and Fig. 20 is an operation in the user plane according to the SNST and DF procedures applied to the dual connection 2A.

Referring to FIG. 19, the UE moves to the vicinity of the target master base station MeNB2 while being doubly connected to the serving base station MeNB1 and the serving secondary base station SeNB. At this time, the dual connection configured in the terminal is released and handover to the target master base station can be performed.

The serving master base station performs a handover admission control procedure with the target master base station (@ t1).

Then, the serving master base station transmits an RRC connection reconfiguration message for handover to the UE (@ t2). Upon receiving the RRC connection reconfiguration message, the terminal reestablishes the RRC connection to the existing serving master base station and the serving secondary base station (@ t2). At this time, all protocol layers below PDCP and RLC are reset. In this embodiment, transmission of an RRC connection reconfiguration message for handover and RRC connection reconfiguration have been shown to occur at the same time, but this embodiment also includes embodiments that occur at different points of time in consideration of processing time in actual implementation .

When the terminal reestablishes the RRC connection, the dual connection is released, and the terminal hands over to the target master base station. At this time, data loss may occur if the user data and the SN state transmitted through the serving master base station and the serving secondary base station are handed over to the target master base station without being transmitted. Therefore, in order to provide seamless communication service, the residual data and the SN state of the serving master base station and the serving secondary base station must be transmitted to the target master base station. The SNST and the DF are referred to as dual SNST and DF in the case where two or more base stations by dual connection perform SNST and DF.

The double SNST and DF are performed according to the following procedure. First, the serving master base station performs SNST and DF (@ t3).

On the other hand, in the structure of the dual connection 1A, since the PDCP layer exists in the serving secondary base station, the serving secondary base station can also perform the SNST and DF procedures. However, it is not known at what point the serving secondary base station should perform SNST and DF.

In order to clarify the SNST and DF operation time, the serving master base station may provide some signaling to the secondary base station. For example, the serving master base station transmits a secondary base station release order (@ t4). The secondary base station release command may be referred to as a secondary serving cell release command. Alternatively, the secondary base station release command may be referred to as an SNST and DF command. This secondary base station release command is transmitted using a message structure defined in the Xn interface.

Upon receiving the secondary base station release command from the serving master base station, the serving secondary base station forwards the SN state and the data remaining in the buffer to the target master base station (@ t5).

Upon receiving the data from the serving master base station and the serving secondary base station, the target master base station transmits a route change request to the MME (@ t6), and the MME transmits a bearer modify request (@ t7).

In SNST and DF, SNST and DF at each base station occur at different points of time. However, since SNST and DF are applied to independent radio bearers according to separate PDCP layers, there is no effect on terminals.

Referring to FIG. 20, until t7 (see FIG. 19), the serving master base station MeNB1 receives data via two bearers from the gateway. Here, one bearer is provided to the terminal by the serving secondary base station (SeNB) anchored to the serving master base station.

However, since t7, the two bearers are provided by one master base station (i.e., target master base station MeNB2), and data is transmitted on each bearer.

(2) For dual connection 2C

The double connection 2C is the same as that of Fig. 1C, only the master base station has the PDCP layer.

FIGS. 21 and 22 are flowcharts illustrating handover SNST and DF procedures in a dual connection 2C according to another embodiment. Fig. 21 is an operation in the control plane according to the SNST and DF procedures, and Fig. 22 is an operation in the user plane according to the SNST and DF procedures.

Referring to FIG. 21, the UE moves to the vicinity of the target master base station MeNB2 while being doubly connected to the serving base station MeNB1 and the serving secondary base station SeNB. At this time, the dual connection configured in the terminal is released and handover to the target master base station can be performed.

The serving master base station performs a handover admission control procedure with the target master base station (@ t1).

Then, the serving master base station transmits an RRC connection reconfiguration message for handover to the UE (@ t2). Upon receiving the RRC connection reconfiguration message, the terminal reestablishes the RRC connection to the existing serving master base station and the serving secondary base station (@ t2). At this time, all protocol layers below PDCP and RLC are reset. In this embodiment, transmission of an RRC connection reconfiguration message for handover and RRC connection reconfiguration have been shown to occur at the same time, but this embodiment also includes embodiments that occur at different points of time in consideration of processing time in actual implementation .

The serving master base station performs SNST and DF (@ t3). Since the serving secondary base station serves as an anchor for the serving secondary base station, the serving secondary base station must transmit its data to the serving master base station. However, the time point for this can not be known by the serving secondary base station. Therefore, in order to clarify the SNST and the DF operation time, the serving master base station may provide any signaling to the secondary base station. For example, the serving master base station transmits a secondary base station release order (@ t4). The secondary base station release command may be referred to as a secondary serving cell release command. Alternatively, the secondary base station release command may be referred to as an SNST and DF command. This secondary base station release command is transmitted using a message structure defined in the Xn interface.

On the other hand, when the master base station is changed by the handover in the dual connection 2C, the serving secondary base station can not directly perform SNST and DF with respect to the target master base station, and SNST and DF are performed only in the serving master base station serving as the anchor .

However, if the RLC ACK / NACK information is not properly notified from the serving secondary base station, the serving master base station can not determine from which SN packet to forward to the target master base station. That is, from which packet to forward to the target master base station.

Therefore, the present embodiment includes a step in which the serving secondary base station appropriately provides the RLC ACK / NACK information to the master base station (@ t4 '). Upon receiving the secondary base station release command from the serving master base station, the serving secondary base station forwards the SN state and the data remaining in the buffer to the target master base station (@ t4 ').

Here, if the RLC ACK / NACK information generated between the mobile station and the serving secondary base station is not sufficiently provided to the serving master base station, the buffer of the master base station for data forwarding may overflow during the change of the secondary base station. On the other hand, if the RLC ACK / NACK information is frequently transmitted, it can serve as an overhead for the Xn interface. Therefore, the report of the RLC ACK / NACK information should be able to be provided from the serving secondary base station to the master base station as an appropriate frequency at the appropriate timing.

Upon receiving data from the serving master base station and the serving secondary base station, the target master base station transmits a route change request to the MME (@ t5), and the MME transmits a bearer modify request (@ t6).

In SNST and DF, SNST and DF at each base station occur at different points of time. However, since SNST and DF are applied to independent radio bearers according to separate PDCP layers, there is no effect on terminals.

Referring to FIG. 22, until t6 (see FIG. 21), the serving master base station MeNB1 receives data via two bearers from the gateway. Here, one bearer is provided to the terminal by the serving secondary base station (SeNB) anchored to the serving master base station.

From t6, however, the two bearers are provided by one master base station (i.e., the target master base station MeNB2), and data is transmitted on each bearer.

23 is a block diagram illustrating a master base station and a secondary base station according to an example of the present invention.

23, the master base station 2350 includes a transmitting unit 2355, a receiving unit 2360, and a control unit 2370.

The control unit 2370 may perform operations of the master base station MeNB as described generally herein. For example, both the SNST and the DF procedures can be performed at the time of change or handover of the secondary base station in the dual connection. Specifically, a SeNB release command is generated and sent to the transmission unit 2355.

The transmitting unit 2355 transmits an SeNB release command to the secondary base station 2300.

The receiver 2360 can receive the RLC ACK / NACK information required for SNST and DF from the secondary base station.

The secondary base station 2300 includes a receiving unit 2305, a control unit 2310, and a transmitting unit 2315.

The receiving unit 2305 receives the SeNB release command from the master base station 2350 and sends it to the controller 2310.

In response to the SeNB release command, the control unit 2310 prepares and executes forwarding for the data in the buffer, and sends the SN state and data to the transfer unit 2315. [

The transmitting unit 2315 transmits the RLC ACK / NACK information to the master base station 2350. The transmitting unit 2315 may also transmit the SN state and data to the master base station 2350. [ Also, although not shown in the figure, the transmitting unit 2315 may transmit the SN state and data to another master base station or another secondary base station.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders or simultaneously . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (1)

A method for performing a cell change by a master eNB in a wireless communication system using a dual connection method,
Performing admission control for changing a secondary serving cell together with a target secondary eNB;
Transmitting a radio resource control (RRC) connection reconfiguration message for changing the secondary serving cell to the UE; And
And transmitting a secondary serving cell release command instructing release of the secondary serving cell to the serving secondary base station.

Images