KR20150020510A - Method for providing dual connectivity in wireless communication system - Google Patents

Abstract

The present invention relates to a method for providing dual connectivity in a wireless communication system. The present invention provides a method for dual connection, changing a base station of dual connection, changing a wireless resource of the dual connection, and releasing dual connection including the steps of: determining a different base station to be connected dually to a terminal; setting the different base station; and reconfiguring RRC connection of the terminal for the different base station.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for providing dual connectivity of a wireless communication system,

The present invention relates to a method for providing dual connectivity in a wireless communication system.

3GPP RAN2 determines three deployment scenarios for small cell enhancement (SCE) and discusses technical issues for each scenario.

Scenario 1 is a case where a macro cell and a small cell connected by a non-ideal backhaul use the same intra-frequency. Scenario 2 is the case where macro cells and small cells connected by non-ideal backhaul use different carrier frequencies. Scenario 3 is a case where a plurality of small cells using at least one carrier frequency are connected by an unrealized backhaul and the mobility of the user equipment (UE) is low or medium.

Table 1 shows the technical requirements of SCE deployment scenarios according to the results of May 2013 R2-82.

Scenario
Technical issues Scenario # 1 Scenario # 2 Scenario # 3 Mobility robustness X X UL (Uplink) / DL (Downlink) Power Imbalance Increased signaling load due to frequent handover X X X Difficult ot improve system capacity (per-user throughput) by utilizing radio resources in more than one eNB X Network planning and configuration effort Small cell discovery X
(HetNet WI) X
(HetNet WI) X
(HetNet WI)

In order to satisfy the above-mentioned system requirements, it is necessary to invent a method in which a base station of a macro cell and a base station of a small cell can communicate with one terminal at the same time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for providing dual connectivity between two base stations and a single terminal connected to a non-ideal backhaul.

According to an aspect of the present invention, there is provided a method for a base station connected to a terminal to dual-link the base station and another base station. The dual linking method may include determining a first base station among a plurality of base stations, reconfiguring an RB connection with the terminal and the first base station, and performing communication based on the dual connection with the terminal and the first base station .

The step of determining in the double connection method may comprise setting up a first base station to the SeNB for the terminal.

The determining in the double connection method may include determining a first base station in consideration of a load state of the base station.

The step of setting up in the dual connection method may include transmitting an SeNB setup message to the first base station and receiving a response to the SeNB setup message from the first base station.

In the dual connection method, the SeNB setup message may include at least one of C-RNTI information of the UE, attribute information of a bearer to be configured, or UE capability information.

The response to the SeNB setup message in the dual connection method may include a result code generated after the subscription control procedure for whether to set up the bearer is performed.

The reconfiguring in the dual connection method may include instructing the terminal to connect to the first base station, and receiving a completion response to the connection indication from the terminal.

The duplexing method may further include, after the reconstructing step, transmitting an SeNB setup complete message to the first base station.

The reconfiguring in the dual connection method may include reconfiguring the RB connection using the RRC connection reconfiguration message to the terminal.

The dual connection method may further comprise, after the reconstructing step, updating the RRC state for the first base station.

The dual connection method may further comprise receiving a measurement result report from a terminal for a plurality of base stations prior to the determining step.

The measurement result report in the dual connection method may include information on a small cell to which the terminal can connect.

According to another embodiment of the present invention, there is provided a method for changing a secondary base station in a wireless communication system in which a master base station and a secondary base station are dual-connected to a terminal. The base station changing method includes: determining a change of a secondary base station from a source base station to a target base station, setting up a target base station, setting a radio bearer (RB) Reconfiguring the connection, and performing communication based on the dual connection with the terminal and the target base station.

The base station changing method may further comprise buffering downlink data of a radio bearer for the mobile station after the step of setting up.

The base station changing method may further include a step of releasing radio resources set in the source base station after the step of reconfiguring.

The base station changing method may further include transmitting a SeNB setup complete message to the target base station after the reconfiguration step.

The base station changing method may further include updating the RRC state for the target base station after the reconstructing step.

The step of setting up in the base station changing method may include transmitting a SeNB setup message to the target base station, and receiving a response to the SeNB setup message from the target base station.

The reconfiguring in the base station changing method may include reconfiguring the RB using the RRC connection reconfiguration message for the target base station to the terminal and receiving the RRC connection reconfiguration completion message for the target base station from the terminal .

According to another embodiment of the present invention, there is provided a method for changing a radio resource allocated to a secondary base station in a wireless communication system in which a master base station and a secondary base station are dual-connected to a terminal. The radio resource changing method includes a step of changing a radio resource allocated to a secondary base station, a step of reconfiguring an RB connection to a secondary base station of the terminal, and a step of informing the secondary base station of the completion of the change of the radio resource.

The radio resource change method may further include a step of, after the reconfiguring step, updating the RRC context for the secondary base station.

The changing step in the radio resource changing method includes transmitting a SeNB reconfiguration message instructing a change of radio resources to a secondary base station and receiving a SeNB reconfiguration response message from the secondary base station informing that the radio resource has been changed can do.

In the radio resource alteration method, the SeNB reconfiguration message may include a parameter used for reconfiguration of the radio bearer and a radio bearer identifier.

The reconfiguring in the radio resource change method may include reconfiguring a radio bearer connection using an RRC connection reconfiguration message, and receiving an RRC connection reconfiguration completion message for the secondary base station from the terminal.

According to another embodiment of the present invention, there is provided a method for changing a radio resource allocated to a secondary base station in a wireless communication system in which a master base station and a secondary base station are dual-connected to a terminal. The radio resource alteration method includes receiving an SeNB reconfiguration command instructing a secondary base station to change a radio resource, reconfiguring an RB connection to a secondary base station of the terminal, and transmitting a SeNB reconfiguration completion message to the secondary base station .

The radio resource change method includes a step of receiving a message requesting information on a radio resource setting state from a secondary base station before a receiving step and transmitting a response message including information on a radio resource setting state to a secondary base station Step < / RTI >

The radio resource changing method may further include, after receiving the reconfiguration command, determining whether to change the radio resource based on the information on the radio resource.

The radio resource changing method may further include transmitting information on the radio resources to the secondary base station periodically or when a change occurs in the radio resources.

The reconfiguring in the radio resource change method may include reconfiguring a radio bearer connection using an RRC connection reconfiguration message and receiving an RRC connection reconfiguration completion message for the secondary base station from the terminal.

According to another embodiment of the present invention, there is provided a method for releasing a connection between a secondary base station and a terminal in a wireless communication system in which a master base station and a secondary base station are connected to a terminal. The method of releasing a base station includes determining a connection release to a secondary base station, releasing radio resources allocated to the secondary base station, and releasing the RB connection to the secondary base station of the terminal.

The method may further include receiving a measurement result report including the wireless connection information or the radio channel information of the UE from the UE prior to the determining step, Lt; RTI ID = 0.0 > a < / RTI >

Wherein the step of releasing the base station further comprises the step of receiving a measurement result report including the wireless connection information or the radio channel information of the terminal from the terminal before the determining step, Transmitting a SeNB release message requesting release of the radio resource to the secondary base station, and receiving an SeNB release response message informing that the radio resource has been released from the secondary base station.

The step of releasing the RB connection in the base station releasing method includes the steps of transmitting an RRC connection reconfiguration message to the terminal indicating the release of the RB connection, and receiving an RRC reconfiguration completion message from the terminal, .

According to another embodiment of the present invention, there is provided a method for releasing a connection between a secondary base station and a terminal in a wireless communication system in which a master base station and a secondary base station are connected to a terminal. The method of releasing a base station includes receiving an SeNB release command from a secondary base station, releasing an RB connection between the terminal and a secondary base station, and updating a radio resource control state (RRC context) for the secondary base station.

The step of releasing the RB connection in the base station releasing method includes the steps of transmitting an RRC connection reconfiguration message to the terminal indicating the release of the RB connection, and receiving an RRC reconfiguration completion message from the terminal, .

According to another embodiment of the present invention, there is provided a method for releasing a connection between a secondary base station and a terminal in a wireless communication system in which a master base station and a secondary base station are connected to a terminal. The base station releasing method includes: determining a connection release to a secondary base station; updating an RRC context for the secondary base station; releasing an RB connection to the secondary base station of the terminal; And releasing the radio resources.

The step of releasing the RB connection in the base station releasing method includes the steps of transmitting an RRC connection reconfiguration message to the terminal indicating the release of the RB connection, and receiving an RRC reconfiguration completion message from the terminal, .

Wherein the step of releasing the base station further comprises the step of receiving a measurement result report including the wireless connection information or the radio channel information of the terminal from the terminal before the determining step, Transmitting an SeNB release message requesting release of the radio resource to the secondary base station, and receiving an SeNB release response message indicating that the radio resource is released from the secondary base station.

According to another embodiment of the present invention, there is provided a method of dual linking a terminal connected to a base station with a first base station different from the base station. The dual connection method includes reconfiguring an RRC connection with a first base station determined by the base station as SeNB, and performing communication based on the dual connection with the base station and the first base station.

The reconfiguring in the dual linking method may include receiving a reconfiguration indication from the base station for the RRC connection with the first base station, and performing uplink synchronization with the first base station.

The dual connection method may further include setting up an RB for the first base station based on the reconfiguration indication after performing the uplink synchronization.

In the dual connection method, the reconfiguration indication includes advance information related to random access to the first base station, and performing the uplink synchronization may include performing a contention-based random access to the first base station .

The step of performing uplink synchronization in the dual connection method may include performing a contention-based random access to the first base station.

The reconfiguring in the dual connection method may further include transmitting an RRC connection reconfiguration complete message to the base station.

Receiving a measurement indication from the base station to discover the first base station and periodically performing measurements to discover the first base station prior to the step of reconstructing in the dual connection method.

The measurement indication may include setting conditions for the first base station, and reporting the measurement result to the base station when the base station satisfies the set conditions.

According to another embodiment of the present invention, there is provided a method for a terminal to change a secondary base station in a wireless communication system in which a master base station and a secondary base station are dual-connected to a terminal. The base station changing method comprises the steps of: releasing an RB for a first base station connected as a SeNB, reconfiguring an RB for a second base station to be connected as a SeNB, and performing communication based on a dual connection with the master base station and the second base station .

The reconfiguring in the base station change method may include receiving an SeNB change indication from the master base station to the second base station.

The change indication in the base station change method may include information on the second base station and a list of secondary cells included in the coverage of the second base station.

Wherein the reconfiguring in the base station changing method further comprises buffering uplink data to be transmitted to the first base station and performing uplink synchronization with the second base station, To the second base station.

According to an embodiment of the present invention, a terminal can be connected (double-connected) to at least one base station at the same time to receive a service. At this time, the base station that is connected to the terminal is divided into a master base station and a secondary base station. The secondary base station can be connected to the terminal and bearer, and can be changed and released according to the control of the master base station. In particular, even when the RRC and PDCP functions are not included in the secondary base station, the terminal can receive services through the secondary base station according to the RRC and PDCP functions of the master base station.

1 is a diagram illustrating a wireless communication system supporting dual connection according to an embodiment of the present invention.
2 is a diagram illustrating control plane functions (RRC and RRM) performed by the MeNB and the SeNB in the candidate structure 1 providing a dual connection according to an embodiment of the present invention.
3 is a diagram illustrating a user plane downlink protocol stack of a wireless communication system providing a dual connection according to an embodiment of the present invention.
4 is a diagram illustrating a user plane uplink protocol stack of a wireless communication system providing a dual connection according to an embodiment of the present invention.
5 is a diagram illustrating a case where a BM according to an embodiment of the present invention is operated as an OM.
6 is a diagram illustrating an OM PDU and a TM PDU according to an operation of a BM according to an embodiment of the present invention.
7 is a view showing an interlocking structure of a BM according to an embodiment of the present invention.
8 is a diagram illustrating a channel mapping structure for double connection of an SeNB of a candidate structure 1 according to an embodiment of the present invention.
9 is a diagram illustrating a buffer management structure of a UE according to an embodiment of the present invention.
10A and 10B are flowcharts illustrating a SeNB access procedure of candidate structure 1 according to an embodiment of the present invention.
11 is a flowchart illustrating a SeNB access method in candidate structure 1 according to another embodiment of the present invention.
12A, 12B, and 13 are flowcharts illustrating a method of changing SeNB according to an embodiment of the present invention.
14 is a flowchart illustrating a SeNB reconstruction method of candidate structure 1 according to an embodiment of the present invention.
15 is a flowchart illustrating a SeNB release method of candidate structure 1 according to an embodiment of the present invention.
16 is a flowchart illustrating a method of reporting SeNB buffer status of candidate structure 1 according to an embodiment of the present invention.
17 is a diagram illustrating a connection of MeNB, SeNB, and UE in candidate structure 1 according to an embodiment of the present invention.
18 is a diagram illustrating an interlocking structure of a control plane according to an embodiment of the present invention.
19 is a view showing an interlocking structure of a user plane according to an embodiment of the present invention.
20 is a diagram illustrating a wireless communication system supporting dual connection according to another embodiment of the present invention.
21 is a diagram showing the functions and structure of the RRC and RRM in the control plane of the candidate structure 2 for providing a double connection.
22 is a diagram illustrating a user plane downlink protocol stack of a wireless communication system providing a dual connection according to another embodiment of the present invention.
23 is a diagram illustrating a user plane uplink protocol stack of a wireless communication system providing dual connection according to another embodiment of the present invention.
FIG. 24 is a diagram illustrating an uplink / downlink channel mapping structure of an SeNB according to another embodiment of the present invention.
25 is a diagram illustrating a buffer management structure of a UE according to another embodiment of the present invention.
26 is a flowchart illustrating a SeNB access procedure of candidate structure 2 according to another embodiment of the present invention.
FIG. 27 is a flowchart illustrating a method of changing a SeNB according to another embodiment of the present invention.
28 is a flowchart illustrating a SeNB reconstruction method of candidate structure 2 according to another embodiment of the present invention.
29 is a flowchart illustrating a method of sharing radio resource allocation information of a candidate structure 2 according to another embodiment of the present invention.
30 is a flowchart illustrating a SeNB release method of candidate structure 2 according to another embodiment of the present invention.
31 is a diagram illustrating a connection of MeNB, SeNB, and UE in candidate structure 2 according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, a mobile station (MS) is referred to as a terminal, a mobile terminal (MT), an advanced mobile station (AMS), a high reliability mobile station (HR- A subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), a user equipment (UE) , HR-MS, SS, PSS, AT, UE, and the like.

Also, a base station (BS) is an advanced base station (ABS), a high reliability base station (HR-BS), a base station B, an evolved node B, eNodeB), an access point (AP), a radio access station (RAS), a base transceiver station (BTS), a mobile multihop relay (MMR) a relay station (RS) serving as a base station, an RN serving as a base station, an advanced relay station (ARS) serving as a base station, a high reliability relay station (HR) A femto BS, a home Node B, a HNB, a pico BS, a metro BS, a micro BS, ), A master eNB (MeNB), a secondary eNB (SeNB), or the like, and may be referred to as an ABS, a base station B, an eNodeB P, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, and the like.

1 is a diagram illustrating a wireless communication system supporting dual connection according to an embodiment of the present invention.

1 shows a candidate structure (Alternative Architecture, Alt. Arch.) 1 of a wireless communication system supporting dual connection.

1, the MeNB 100 of the candidate structure 1 includes a mobility management entity (MME), a serving gateway (S-GW), a control plane interface (S1-MME) S1-U, respectively. In FIG. 2, MeNB 100, SeNB 200, and UE 300 include the same protocol stack. The protocol stacks included in the MeNB 100, the SeNB 200 and the UE 300 include a radio resource control (RRC) protocol, a packet data aggregation protocol (PDCP), a radio link control (RLC) Protocol, a media access control (MAC) protocol, and a physical layer (PHY) protocol.

In FIG. 1, radio resource control (RRC) of the MeNB 100 and RRC of the SeNB 200 perform a control plane protocol function for dual connection. In the present invention, both MeNB 100 and SeNB 200 have a 2-layer protocol as a user plane protocol. In the present invention, the MeNB 100 and the SeNB 200 can provide a carrier aggregation (CA) function using a plurality of component carriers (CCs). Accordingly, each eNB manages a primary cell and a secondary cell. At this time, a set of cells managed by the MeNB 100 is called a master cell group (MCG), and a set of cells managed by the SeNB 200 is called a secondary cell group.

First, the function and structure of the RRC and the radio resource management (RRM) that perform the control plane function of the candidate structure 1 will be described. In the control plane of the candidate structure 1, the RRC protocol function is divided into MeNB 100 and SeNB 200.

2 is a diagram showing control plane functions (RRC and RRM) performed by the MeNB 100 and the SeNB 200 in a candidate structure 1 providing a dual connection according to an embodiment of the present invention.

Table 2 shows the RRC functions provided by the MeNB 100 and the SeNB 200 in the RRC_CONNECTED state. Table 2 excludes functions related to inter radio access technology (Inter-RAT) among the RRC functions. In Table 2, 'X' indicates that the corresponding RRC function exists in the MeNB 100 or the SeNB 200.

RRC Functions MeNB SeNB System information broadcast NAS information X Information for UEs in RRC_CONNECTED X X RRC
connection
control Paging X Establish / modification /
release of RRC connection Assignment / modification of UE identity X Establishment / modification / release of SRB1 and SRB2 X X Access barring X Initial security activation Initial configuration of AS integrity protection (SRBs) X X AS ciphering (SRBs, DRBs) X X RRC connection mobility Intra-frequency and inter-frequency handover X Security handling
(key / algorithm change) X RRC context information transfer X Establish / modification /
Release of DRBs X X Radio configuration control Assignment / modification of ARQ configuration X X HARQ configuration X X DRX configuration X X QoS control Assignment / modification of SPS configuration X Assignment / modification of parameters for UL rate control in UE X X Recovery from radio link failure X Measurement configuration and reporting Establishment / modification / release of measurement X Setup and release of measurement gaps X Measurement reporting X Other functions Transfer of dedicated NAS information and non-3GPP dedicated information X Transfer of UE radio access capability information X

Referring to Table 2, system information broadcasted in the RRC function includes information of a non-access stratum (NAS), information of an NAS (access information), and an idle state of an access stratum (AS) (idle) and the UE 300 in RRC_CONNECTED state. Therefore, the NAS information transmitted through the S1-MME is transmitted using the MeNB 100, and the following information can be considered for transmission of information related to the AS.

A system for transmitting system information related to the AS of the SeNB 200 to the UE 300 using the MeNB 100: a method for transmitting a dedicated radio bearer-based RRC And transmits system information using a message. This scheme is advantageous in that it is easy to manage the system information received by the UE 300, but signal information is transmitted on the basis of the dedicated radio bearer, so that signaling increases and additional use of radio resources is inevitable .

A method of transmitting system information related to the AS of the SeNB 200 to the UE 300 using the SeNB 200. The method of transmitting system information broadcasted by the MeNB 100 and the SeNB 200 to the UE 300 independently Respectively. This scheme is advantageous in that signaling based on the dedicated radio bearer is not required for the transmission of the system information, but there is a disadvantage that the UE 300 must interwork with each eNB in order to acquire system information.

In the candidate structure 1 according to the embodiment of the present invention, system information of the SeNB 200 is transmitted to the UE 300 through dedicated signaling at the MeNB 100 when the SeNB 200 is initially attached, The terminal receives the information broadcast by the SeNB 200 and acquires the system information of the SeNB 200.

Referring to Table 2, since the dual link structure of the radio communication system relates to an operation procedure for the UE 300 in the RRC_CONNECTED state, the setting, change and release of the RRC connnection can be performed mainly in the MeNB 100. [ However, since the RRC protocol procedure for a specific data radio bearer (DRB) in the candidate structure 1 is performed in the SeNB 200, a signaling radio bearer (SRB) (mainly SRB1) Setting, changing, and releasing may also be performed in the SeNB 200. [

Also, as shown in Table 2, initial security activation is a procedure for integrity protection and ciphering control of SRB and DRB. Initial security activation may be performed in the MeNB 100 and the SeNB 200 in which the SRB and DRB are set. The initial security activation of the evolved UMTS terrestrial radio access network (E-UTRAN) is through an exchange procedure of the RRC messages SecurityModeCommand message and SecurityModeComplete message. That is, the eNB forwards the SecurityModeCommand message including the integrity protection / encryption algorithm to be used for the AS communication to the UE 300, and the RRC of the UE 300 that has received the SecurityModeCommand message transmits the PDCP using the information provided through the SecurityModeCommand message. After setting, it sends a SecurityModeComplete message to the eNB as a response message. The AS security key information used in the UE 300 and the eNB are K _eNB , K _RRCint , K _{RR Cenc} , and K- _UPenc , can be generated based on K _ASME derived from the key included in the authentication center (AuC). K _ASME is activated at the time of setting the NAS security mode before setting up the AS security mode and the UE 300 and the eNB derive the K _eNB which is the AS security key based on the K _ASME , K _RRCint , K _RRCenc , and K- _UPenc can be derived using a key derivation function.

In the candidate structure 1 providing dual connectivity according to an embodiment of the present invention, a method related to security activation may be considered as follows.

The security control information exchange through the interworking of the MeNB 100 / SeNB 200,

- MeNB 100 _{derives the} next hop (NH) based on K _enb of _MeNB 100 and derives K _{enb *} of _SeNB 200 based on SeNB information (PCI, DL carrier frequency) Step

- transmitting K _{enb *} of _SeNB 200 derived from MeNB (100)

- SeNB (200) is by using the key derivation function from K _{* enb} deriving _RRCint K, K _RRCenc, K _UPenc

- the SeNB 200 exchanges an integrity protection / encryption algorithm with the UE 300 through an RRC Connection Reconfiguration procedure, and

- Establishing the PDCP using the AS security related information exchanged through the RRC connection reconfiguration procedure by the SeNB 200 and the UE 300

Lt; / RTI >

Referring to Table 2, the mobility of the RRC connection is managed in the MeNB 100 considering mobile robustness and the like. The management (setting, changing, and releasing) of the DRB can be performed in the MeNB 100 or the SeNB 200 under the control of the MeNB 100. That is, since the DRB is a radio bearer for transmitting / receiving user traffic, the DRB can be performed in the MeNB 100 or the SeNB 200 under the control of the MeNB 100 according to the state of the enb and a service request of the UE 300 .

In Table 2, radio configuration control relates to setting control of the sub-layer 2 protocol of the eNB. In the candidate structure 1, the radio configuration control operates according to the request of the RRC and can be performed in the MeNB 100 and the SeNB 200 in which the SRB and DRB are set.

The QoS control includes a function of setting Semi Persistent Scheduling (SPS) and a rate control function of the uplink of the UE 300. The SPS is used to schedule packet services with small size sizes with a constant inter-arrival time, such as Voice over Internet Protocol (VoIP). In the candidate structure 1, the service using the SPS is provided through the MeNB 100, which facilitates ensuring quality of service (QoS) without interruption due to SeNB change and the like. The uplink speed control function of the UE 300 may be set in units of radio bearers. In the candidate structure 1, this function may be provided by the MeNB 100 or the SeNB 200.

A radio link failure (RLF) is a state in which a radio link is lost due to an error in RLC, MAC, and PHY, and can be recovered through an RRC connection re-establishment procedure. In the candidate structure 1, the parameter setting function for RLF detection can be performed through the system information provided by the MeNB 100 and the SeNB 200, and when the RLF is generated, the UE 300 can access the MeNB 100 or the SeNB 200 ) And the RRC connection re-establishment procedure.

The measurement setup and reporting procedure of the UE 300 may be controlled by the MeNB 100 performing mobility management functions to ensure mobility of the UE 300. [ The MeNB 100 instructs the UE 300 to set measurement related to the MeNB 100 and the SeNB 200 and the UE 300 that has received the measurement setup performs measurement according to an instruction from the MeNB 100. [ When a specific event occurs as a result of the measurement of the UE 300, the UE 300 reports information on the generated specific event to the MeNB 100 (measurement report). The MeNB 100 receiving the measurement report from the UE 300 controls the operation procedure appropriate to the reported event.

Referring to Table 2, the exchange of UE 300 capabilities information for dedicated NAS (dedicated NAS) information exchange, non-3GPP related dedicated information exchange, and E-UTRAN sharing is performed by MME and UE 300, it can be performed in the MeNB 100. [

Table 3 defines the RRM functions excluding the inter-RAT related functions in the control plane of candidate structure 1.

Main functions MeNB SeNB Radio Bearer Control Establishment, maintenance, and release of Radio Bearers X X Radio Admission Control Admission or Rejection of the establishment requests for new Radio Bearers X X Connection Mobility Control Management of radio resources in connection with idle and connected mode mobility X Dynamic Resource Allocation Allocation and de-allocation of resource to user and control plane packets X X Inter-cell Interference Coordination Management of radio resources such as inter-cell interference is kept under control X X Load Balancing Handling of uneven distribution of traffic over multiple cells X

FIG. 3 is a diagram illustrating a user plane downlink protocol stack of a wireless communication system providing a dual connection according to an embodiment of the present invention. FIG. 4 is a diagram illustrating a protocol stack of a wireless communication Figure 5 shows a protocol stack of a user plane uplink of the system.

In the user plane of the candidate structure 1, the layer 2 protocol (PDCP, RLC, MAC) and the physical layer (PHY) may be located independently of MeNB 100 and SeNB 200. Therefore, in this candidate structure 1, the dividing point of the user plane for providing the double connection can be the upper layer (PDCP) of the PDCP.

In order to transfer user traffic between the MeNB 100 and the SeNB 200 in the candidate structure 1, the user traffic must be divided or merged in the upper layer of the PDCP according to control of the control plane. For this purpose, in the embodiment of the present invention, And a bearer management (BM) function that performs the same functions as the bearer management (BM) function.

First, BM functions performed by MeNB 100 will be described. MeNB 100 processes a service data unit (SDU) received from S1-U to generate a downlink BM packet data unit (PDU), and transmits the generated PDU to MeNB 100 To the radio bearer of the SeNB 200. In addition, the MeNB 100 may process the uplink BM PDU received from the radio bearer of the MeNB 100 or the SeNB 200 and transmit the processed uplink BM PDU to S1-U. The MeNB 100 may buffer and forward the user plane downlink BM PDU according to the SeNB change procedure. In the case of bearer split, the order of the uplink BM PDUs can be rearranged and transmitted in sequence. Also, it is possible to route the downlink packet according to the flow control setting information.

The BM function performed by the UE 300 will now be described. The UE 300 may process the SDU received from the application to generate an uplink BM PDU and forward it to the radio bearer of the MeNB 100 or the SeNB 200. [ In addition, the UE 300 can forward the downlink BM PDU received from the radio bearers of the MeNB 100 or the SeNB 200 to the application. The UE 300 can buffer and forward the user plane uplink PDU according to the SeNB change procedure. In the case of the bearer split, the UE 300 can reorder the order of the downlink BM PDUs and perform in-sequence delivery. In addition, the UE 300 may route the uplink packet according to the flow control setting information.

In one embodiment of the present invention, when a bearer (EPS bearer) of one Evolved Packet System (EPS) is divided into a plurality of radio bearers, reordering and sequential transmission of received BM PDUs the following BM method can be considered for in-sequence delivery. FIG. 5 is a diagram illustrating a case where a BM according to an embodiment of the present invention is operated as an OM, and FIG. 6 is a diagram illustrating an OM PDU and a TM PDU according to an operation of a BM according to an embodiment of the present invention.

- Rewordering and in-sequence delivery based on ordering mode (OM): A method for transmitting / receiving up / down data through a BM PDU to which header information including a sequence number is added to an SDU transmitted to BM, Can be used. This method is disadvantageous in that all BM PDUs are transmitted including a BM header, which requires additional radio resources and increases transmission overhead.

- Reordering and in-sequence delivery based on Transparent Mode (TM): It is a method to transmit / receive up / down data without adding header information to the SDU transferred to BM and can be used when bearer split does not occur . This method is advantageous in that the BM PDU is transmitted without including the BM header, so that no additional radio resources are required.

In one embodiment of the present invention, the BM may be operated as an OM for in-sequence delivery of BM PDUs delivered to the MeNB 100 and the SeNB 200 when a bearer split occurs in the MeNB 100, The TM can be operated. When the BM is operated as an OM, the MeNB 100 or the UE 300 transmits a sliding window method ordering and in-sequence delivery using a sequence number of BM PDUs. ) Procedure. When the BM operates as a TM, the MeNB 100 or the UE 300 does not perform reordering and in-sequence delivery procedures.

7 is a view showing an interlocking structure of a BM according to an embodiment of the present invention.

Referring to FIG. 7, the BM is located in an upper layer of the PDCP of the MeNB 100 and the UE 300. That is, the BM of the MeNB 100 is interworked with the PDCP of the MeNB 100 or the PDCP of the SeNB 200, and the BM of the UE 300 can be interworked with the PDCP of the UE 300. [

Since the MeNB 100 and the SeNB 200 independently include the PDCP in the candidate structure 1 according to the embodiment of the present invention, it is necessary to define the operation procedure of the PDCP related to the security, The method described in the RRC function described in < RTI ID = 0.0 > U. < / RTI > When the method described in the RRC function is used, the MeNB 100 transmits the key (K _{enb *} ) of the SeNB 200 for the dual link radio bearer to the SeNB 200, and the SeNB 200 receiving the key K _{enb *} Select a protection and encryption algorithm. After selecting the integrity protection and encryption algorithm, the SeNB 200 performs an RRC connection reconfiguration procedure with the UE 300 and then performs a security related PDCP setup procedure using the RRC function of the SeNB 200. [ The SeNB 200 processes the data of the radio bearer to support dual connectivity.

Meanwhile, the candidate structure 1 according to the embodiment of the present invention includes independent MAC protocols for the MeNB 100 and the SeNB 200. A technical issue related to the MAC for the dual connection in the candidate structure 1 is the procedure related to the channel mapping structure and the uplink / downlink radio resource allocation.

8 is a diagram illustrating a channel mapping structure for double connection of the SeNB 200 of the candidate structure 1 according to the embodiment of the present invention.

Referring to FIG. 8, a dedicated control channel, a dedicated traffic channel, and a broadcast channel may be supported in the downlink. Also, a dedicated control channel, a dedicated traffic channel, and a random access channel may be supported in the uplink.

The MeNB 100 and the SeNB 200, which provide a dual connection, operate independently in an independent scheduler that performs uplink and downlink radio resource allocation functions, and can operate in the following manner.

- Downlink Radio Resource Allocation and Scheduling: For the downlink radio resource allocation, the MAC layer of the MeNB 100 and the SeNB 200 receives the information of the downlink buffer and the downlink channel status information reported from the UE 300 As shown in FIG. The MeNB 100 and the SeNB 200, which provide double connection in the candidate structure 1 according to the embodiment of the present invention, include an independent MAC protocol and a scheduler, and have a downlink buffer state and an RLC- (CSI) such as channel quality information (CQI), a precoding matrix index (PMI) and a rank index (RI) received from the UE 300, ; CQI, PMI, RI) to perform the downlink radio resource allocation procedure.

Uplink Radio Resource Allocation: In order to allocate uplink radio resources of the UE 300, a scheduling request (SR), a remaining power amount report (PHR), and a buffer status report (Buffer Status Report , BSR) are required.

The SR procedure is a procedure in which the UE 300 requests the eNB for radio resource allocation for a new uplink transmission. To this end, the UE 300 transmits a Physical Uplink Control Channel (PUCCH) including an SR to the eNB (MeNB 100 or SeNB 200) in which the RRC is located.

In the candidate structure 1 according to the embodiment of the present invention, the MAC of each UE can transmit SR to MeNB or SeNB.

The PHR procedure is a procedure in which the UE 300 transmits a difference between a maximum transmission power of the UE 300 and a power estimation value required for uplink transmission to the eNB. To this end, the UE 300 performs a PHR procedure with the MeNB 100 and the SeNB 200. The PHR information (V _PHR ) reported to the eNB at this time is a power estimate (P _m ) for the UL-SCH and the PUCCH transmission of the MeNB 100 and the UL-SCH of the SeNB 200 at the maximum transmission power (P _max ) And the power estimate (P _s ) for PUCCH transmission. At this time, the PHR information can be transmitted to the eNB using a MAC Control Element. The PHR information transmitted in the uplink through the PHR procedure can be defined as follows.

The BSR procedure is a procedure for transmitting the uplink buffer state of the UE 300 to the eNB.

9 is a diagram illustrating a buffer management structure of a UE according to an embodiment of the present invention.

Referring to FIG. 9, the UE 300 transmits a MAC CE including BSR information to an eNB (MeNB 100 or SeNB 200) where an RRC that sets up a corresponding radio bearer is located for a BSR procedure. In the candidate structure 1 according to an embodiment of the present invention, the UE 300 transmits a Radio Bearer / Logical Channel (RBO) configured in units of the MeNB 100 or the SeNB 200 for the BSR procedure for the dual connection And manages a logical channel group (LCG) based on the logical channel group and performs a procedure of a BSR (short BSR, long BSR, or truncated BSR) with the MeNB 100 or the SeNB 200.

Logical Channel Prioritization (LCP): The UE 300, which has been allocated uplink radio resources through an uplink scheduling procedure, constructs a MAC PDU through an LCP procedure. The LCP procedure for the dual connection is performed based on the radio bearer allocated to each MeNB 100 or the SeNB 200 according to the prioritized bit rate (PBR) and the bucket size duration Bucket Size Duration, BSD). The UE 300 generates an uplink MAC PDU through the LCP procedure.

Meanwhile, the downlink data traffic (e.g., traffic transmitted from the S-GW via S1-U) of the candidate structure 1 according to the embodiment of the present invention is transmitted to the MeNB 100 according to the RRC / And may be transmitted to the UE 300 using the downlink radio resources of the BS 100 or the SeNB 200. [ The uplink data traffic for the dual connection can be transmitted to the MeNB 100 or the SeNB 200 by using the uplink radio resource according to the control of the RRC / BM of the UE 300. [ Therefore, a data transmission function and a flow control function between the MeNB 100 and the SeNB 200 are required in the downlink of the wireless communication system supporting the dual connectivity, and a flow control function is required in the uplink.

In a wireless communication system supporting dual connection according to an embodiment of the present invention, the MeNB 100 and the SeNB 200 operate in cooperation with the UE 300 using an independent 2-layer protocol. In particular, the MeNB 100 and the SeNB 200 allocate upstream and downstream radio resources using an independent MAC scheduler. The MAC scheduler located in each eNB assigns the DL and grants the UL based on the information of the RLC buffer and the state of the radio channel of the UE 300 and the eNB. In the candidate structure 1, The amount of traffic between the MeNB 100 and the SeNB 200 can be variably adjusted in consideration of the change of the radio channel state between the MeNB 100 and the SeNB 200 and the UE 300. [ .

In order to solve the downlink traffic flow control problem, the MeNB 100 and the SeNB 200 perform flow control for traffic transmission between the MeNB 100 and the SeNB 200 through the following methods and procedures, Can be performed. The downlink traffic flow control is performed when data is transmitted using the SeNB 200 regardless of the bearer split.

- Downlink flow control method D1: Using the control plane protocol

And the RRC of the MeNB 100 performs flow control for traffic transfer between the MeNB 100 and the SeNB 200. [ In this method, when the radio bearer is set, the RRC of the MeNB 100 sets a flow control initial value for the radio bearer for the BM, and during the service, The RRC performs flow control dynamically through the control of the BM. When this method is performed, a flow control related protocol procedure between MeNB 100 and SeNB 200 is performed through Xn-CP.

- Downlink flow control method D2: Using user plane protocol

The BM of the MeNB 100 performs flow control for traffic transfer between the MeNB 100 and the SeNB 200. [ In this method, when the RRC sets up a radio bearer, the MeNB 100 sets a flow control initial value for the radio bearer to the BM, and during the service, the BM of the MeNB 100 according to the downlink buffer status report of the SeNB 200 To perform flow control dynamically. When this method is performed, a flow control related protocol procedure between the MeNB 100 and the SeNB 200 is performed through Xn-UP.

Hereinafter, a method for performing flow control for traffic transmission between the MeNB 100 and the SeNB 200 using the 'DL flow control method D1' will be described.

First, when a downlink radio bearer for dual connection is established, the RRC of the MeNB 100 sets an initial value for flow control of a packet transmitted to the BM 100 and the SeNB 200 to the BM step). At this time, the initial value is set in consideration of the QoS characteristics of the radio bearers set in the MeNB 100 and the SeNB 200, and the like. The BM processes the downlink packet using the packet flow set value set at the initial setting of the radio bearer. At this time, the packet flow setting value can be set by the following method. For the flow control of the downlink packet, the set values of the MeNB 100 and the SeNB 200 may be defined as fcm.d or fcs.d, and the sum of these values is set to one. The BM can derive the amount of packets to be transmitted to the MeNB 100 and the SeNB 200 by multiplying the value of fcm.d or fcs.d by the RRC with the maximum data rate transmitted by the corresponding radio bearer. The MeNB 100 and the SeNB 200 can transmit the packet using the derived amount of the packet.

Then, the SeNB 200 reports the buffer status of the downlink to the MeNB 100 (DL buffer status reporting step). That is, after the radio bearer is set, the RRCs of the MeNB 100 and the SeNB 200 periodically or when an event occurs, the state of the downlink PDCP transmission buffer is checked. In order to perform this procedure, the RRC performs the configuration procedure related to the status report of the PDCP and the transmission buffer when setting up the radio bearer, and this setting can be divided into periodic report or event report based on the upper / lower threshold of the transmission buffer . In addition, the RRC located in the SeNB 200 for the downlink buffer status report transmits the status of the downlink PDCP transmission buffer received from the PDCP to a protocol message on the Xn-CP (for example, using Resource Status Update Lt; RTI ID = 0.0 > RRC < / RTI >

The next MeNB 100 and the SeNB 200 re-establish the flow control function in accordance with the change of the downlink buffer state (flow control function resetting step). That is, the RRC, which has reported the status of the downlink packet buffers of the MeNB 100 and the SeNB 200, determines a set value for controlling the flow of packets transmitted to the MeNB 100 and the SeNB 200 through the BM reconfiguration procedure Reset. After performing the BM reconfiguration procedure of the RRC, the BM processes the downlink packet using the newly set packet flow setting value.

Next, a method for performing flow control for traffic transmission between the MeNB 100 and the SeNB 200 using the 'method D2' described above will be described.

First, when establishing the downlink radio bearer for the dual connection, the initial setting of the BM is the same as the first step of the 'method D1'. However, in 'Method D1', the dynamic reconfiguration of fcm.d or fcs.d values is performed by the RRC BM reconstruction procedure, but in 'Method D2', the BM autonomously performs the flow control procedure according to the report of SeNB (200) Can be performed.

Next, the SeNB 200 reports the status of the downlink buffer to the MeNB 100 (downlink buffer status report step). After the radio bearer is set, the Xn-UP of the MeNB 100 and the SeNB 200 periodically or when an event occurs, checks the state of the downlink PDCP transmission buffer. In order to perform this procedure, the RRC of each eNB performs a setup procedure related to reporting of the transmission buffer status to the PDCP when setting up the radio bearer. In accordance with the method D2, the PDCP of the SeNB 200 periodically or transits the state of the transmission buffer to the Xn-UP of the SeNB 200 based on the threshold. The Xn-UP of the SeNB 200 receiving the status of the transmission buffer delivers the corresponding information to the MeNB 100 through a management message. The MeNB 100 receiving the Xn-UP management message transmits the downlink buffer status information to the BM. For example, when a general packet radio service tunneling protocol (GTP) -U (user plane) is used as a user plane protocol for data transmission between the MeNB 100 and the SeNB 200, D2 'GTP-U management message for reporting the status of the downlink buffer is newly defined, and information can be exchanged using the GTP-U management message.

Thereafter, the MeNB 100 and the SeNB 200 re-establish the flow control function in accordance with the change of the downlink buffer state (flow function resetting step). BMs that have reported the status of the downlink packet buffers of the MeNB 100 and the SeNB 200 dynamically reset the set values for flow control of the packets transmitted to the MeNB 100 and the SeNB 200. [ Then, the BM processes the downlink packet using the newly set packet flow setting value after changing the set value for the packet flow control.

Meanwhile, to solve the uplink traffic flow control problem, the UE 300 can perform flow control for uplink traffic delivery through the following method and procedure. The flow control of the uplink traffic may be performed when a bearer split occurs, that is, when the uplink traffic transmission path of the UE 300 includes both the MeNB 100 or the SeNB 200. [

- Uplink flow control method U1: Using control plane protocol

This method is a method in which the RRC of the UE 300 performs flow control for uplink traffic delivery. According to this method, when the RRC sets up a radio bearer, the RRC of the UE 300 sets a flow control initial value for the corresponding radio bearer for the BM, controls the BM according to the uplink buffer status report during the service, Control procedures can be performed.

- Uplink flow control method U2: Using user plane protocol

This method is a form in which the BM of the UE 300 performs a flow control for uplink traffic delivery. According to this method, when the RRC sets up the radio bearer, the flow control initial value for the corresponding radio bearer is set for the BM, and during the service, the flow control can be dynamically performed through the BM control according to the uplink buffer status report have.

Hereinafter, a method of performing the flow control for uplink traffic delivery by the UE 300 using the 'method U1' will be described.

First, the RRC of the UE 300 sets an initial value for flow control of a packet to be transmitted to the MeNB 100 and the SeNB 200 with respect to the BM when the uplink radio bearer for dual connection is established (BM initial setting step). At this time, the PDCP setup scheme for performing this procedure is the same as the downlink setup scheme, and uplink parameters (fc _{m .u} , fc _{s .u} ) can be used.

Next, the UE 300 reports the uplink buffer status to the BM (uplink buffer status reporting step). After the RB is established, the RRC of the UE 300 periodically checks the state of the uplink PDCP transmission buffer according to an event occurrence. The PDCP setup method for performing this procedure is the same as the downlink setup method.

Then, the UE 300 resets the flow control function according to the change of the UL buffer state (flow control function resetting step). The BM of the RRC that has received the status of the uplink packet buffer resets the set value for controlling the flow of packets transmitted in the uplink through the BM reconfiguration procedure. After performing the BM reconfiguration procedure of the RRC, the BM processes the uplink packet using the newly set packet flow setting value.

Hereinafter, a method for performing the flow control for uplink traffic delivery of the UE 300 using the 'uplink flow control method U2' described above will be described. First, in the uplink radio bearer setup, the initial setup step of BM is the same as the first step of 'method U1'.

Next, the UE 300 reports the uplink buffer status to the BM (uplink buffer status reporting step). That is, after the initial setting of the RB, the PDCP of the UE 300 reports the status of the uplink PDCP transmission buffer to the BM periodically or when an event occurs.

Then, the UE 300 reconfigures the flow control function according to the change of the uplink buffer state (flow control function reconstruction step). That is, the BM, which has reported the status of the uplink packet buffer, reestablishes the setting value for controlling the flow of the packet transmitted through the uplink through the reconfiguration procedure. After performing the BM reconstruction procedure, the BM processes the UL packet using the newly set packet flow setting value.

Next, data transmission between the MeNB 100 and the SeNB 200 of a wireless communication system supporting dual connectivity according to an embodiment of the present invention will be described.

The downlink BM PDU generated in the BM of the MeNB 100 is delivered to the PDCP of the MeNB 100 or the PDCP of the SeNB 200 according to the control of the RRC. In particular, when a downlink BM PDU is transmitted using a radio bearer set in the SeNB 200, a mechanism for data transfer between the MeNB 100 and the SeNB 200 is needed. Also, similar to the transmission of the downlink BM PDU, the uplink BM PDU is also transmitted through the MeNB 100 or the SeNB 200. In particular, when the uplink BM PDU is transmitted through the radio bearer set in the SeNB 200, 100) and the SeNB 200 is needed.

In the candidate structure 1 according to the embodiment of the present invention, the GTP-U + added with the additional function for the dual connection to the GTP-U protocol used in the existing Rel-11 is used as the Xn-UP protocol and the MeNB 100 and the SeNB 200). ≪ / RTI >

The Xn-UP protocol must have a mechanism for guaranteeing QoS (QoS parameters at E-RAB (E-RAB) level) according to bearer characteristics for traffic transmission between MeNB 100 and SeNB 200 Xn-CP is used as a method of setting this.

The operation procedure of the wireless communication system for the dual connection will be described below using the control plane and the user plane structure of the candidate structure 1 through FIGS. 10 to 16. FIG. The operational procedure of the candidate structure 1 according to an embodiment of the present invention includes an SeNB attach procedure, a SeNB change procedure, a SeNB reconfiguration procedure, a SeNB detach procedure, and a SeNB buffer status report procedure.

In the present invention, the RRC_CONNECTED state of the UE 300 is divided into a single connectivity state and a dual connectivity state. In the present invention, when the UE 300 communicates with the DRB of the SeNB 200, the UE 300 can be defined as a dual link state regardless of the presence or absence of the DRB of the MeNB 100. This is because the SRB exists even if DRB does not exist in the MeNB 100.

First, a procedure of attaching the SeNB 200 will be described.

10A and 10B are flowcharts illustrating a SeNB access procedure of candidate structure 1 according to an embodiment of the present invention.

The connection procedure of the SeNB 200 is a procedure of providing the double connection to the UE 300 by adding the SeNB 200 under the control of the MeNB 100. [ In the candidate structure 1, there are two access procedures according to the RRC message transmission scheme for connection with the SeNB 200. [

Method A1: RRC connection reconfiguration with SeNB

Method A2: RRC connection reconfiguration related message exchange using MeNB and SeNB

10A and 10B illustrate method A1 wherein method A1 allows MeNB 100 to perform uplink / downlink synchronization to UE 300 for connection of SeNB 200 providing a dual connection, The SeNB 200 can be added through the protocol between the RRC of the SeNB 200 and the RRC of the UE 300. [

First, the UE 300 is communicating with the MeNB 100 based on single connectivity with the MeNB 100. That is, the UE 300 is in the RRC_connected state. In this state, the UE 300 performs the initial connection with the MeNB 100 and receives the service through the MeNB 100 (single connection-based communication step) (S1001) .

Next, the MeNB 100 instructs the UE 300 to measure the discovery of the SeNB 200 through an RRC Connection Reconfiguration procedure. The UE 300, which is instructed to measure from the MeNB 100, periodically performs a measurement procedure (SeNB measurement instruction step) (S1002).

According to the setting of the MeNB 100, the UE 300 periodically performs measurement and reports it to the MeNB 100 when the condition set by the MeNB 100 is satisfied. In this step, the UE 300 can search / discover and report a small cell that operates at the same frequency or neighboring frequency that can be accessed through the measurement procedure. Also, the UE 300 can transmit channel state information between the cell included in the MeNB and the UE 300 to the MeNB 100 (measurement reporting step) (S1003).

Then, the MeNB 100 determines whether to add the SeNB 200 considering the load state of the MeNB 100 or the like. This procedure may be performed by the UE 300 to set up a new bearer or to change the path of a bearer previously established in the UE 300 or to simultaneously transmit a plurality of bearers (SeNB addition decision step) (S1004).

The MeNB 100 requests the SeNB 200 to establish SeNB based on the SeNB 200 search result of the UE and the SeNB 200 addition decision of the MeNB 100. [ At this stage, the MeNB 100 transmits the Cell-Radio Network Temporary Identifier (C-RNTI) information of the UE 300 providing the dual connection, the bearer attribute information (SRB or DRB) And the UE 300 radio access capability to the SeNB 200. The SeNB 200 transmits the SeNB setup message to the SeNB 200, The SeNB 200 receiving the SeNB setup message from the MeNB 100 performs an admission control procedure on whether to set up the bearer requested through the Radio Admission Control (RAC) function of the RRM And transmits the SeNB setup Ack message including the result code to the MeNB 100 (SeNB Setup requesting step) (S1005).

Then, the MeNB 100 transmits a SeNB attach message for uplink synchronization to the UE 300. The SeNB connect message includes information for non-contention based random access and cause information for SeNB connection for uplink synchronization. At this time, the cause information included in the SeNB connection message is an initial setup. If contention based random access is indicated, dictionary information related to random access is not included in this message (SeNB connection step) (S1006).

The UE performs a random access procedure with the SeNB 200 using the information for non-contention-based random access included in the SeNB attach message, and secures uplink synchronization. If the contention-based random access is indicated in the SeNB access step, the UE 300 may perform a random access procedure according to the standard of 3GPP TS 36.321 (uplink synchronization step) (S1007).

The UE 300 that has performed the uplink synchronization acquisition procedure with the SeNB 200 transmits a connection response message to the MeNB 100 (SeNB connection response step) (S1008).

After the uplink / downlink synchronization acquisition of the UE is completed, the MeNB 100 informs the SeNB 200 of user plane protocol (egXn-U) setup information for transmitting and receiving packets between the MeNB 100 and the SeNB 200, And transmits a SeNB attach indication message including key (K _{enb *} ) information for setting a security mode. The SeNB 200 receiving the message starts the radio resource setting procedure of the SeNB 200 (SeNB connection instruction step) (S1009).

The SeNB 200 receiving the SeNB connection instruction from the MeNB 100 performs the radio resource setup step of the UE 300 and the SeNB 200 using the RRC Connection Reconfiguration procedure. Through this procedure, requested radio bearer-related attribute information and security-related algorithm information and the like can be exchanged when performing the SeNB setup request step. In particular, the radio bearer-related attribute information delivered at the SeNB setup request stage is SRB information for transmitting the RRC message and DRB information for conveying the user traffic, and using these information, the protocol message between the SeNB 200 and the UE 300 An SRB setup procedure for exchange and a radio resource setup procedure for a DRB (Data Radio Bearer) may be performed. The SeNB 200 that has completed the radio resource setup procedure between the SeNB 200 and the UE 300 transmits the packet transmission message between the MeNB 100 and the SeNB 200 using the Xn-U configuration information received through the SeNB connection indication message. / Set up a user plane protocol for reception (radio resource setting step for SeNB connection) (S1010).

 Then, the SeNB 200 performs RRC Connection Reconfiguration procedure and then transmits a SeNB Setup complete message to the MeNB 100 (SeNB setup completion stage) (S1011).

After receiving the SeNB setup completion message from the SeNB 200, the MeNB 100 transits the RRC state of the UE 300 to the dual link state (RRC state update step) (S1012).

Finally, the UE 300 performs a communication procedure through a radio bearer established through the SeNB 200 and a radio bearer established through the MeNB 100 (dual connection-based communication step) (S1013).

11 is a flowchart illustrating a SeNB access method in candidate structure 1 according to another embodiment of the present invention.

That is, FIG. 11 illustrates method A2. 11, a single connection-based communication step (S1101), a SeNB measurement instruction step (S1102), a measurement reporting step (S1103), and a single connection-based communication step (S1101) are performed in the connection method (method A2) of the SeNB 200 according to another embodiment of the present invention. The SeNB addition decision step (S1104) may proceed in the same manner as the method A1.

Then, the MeNB 100 requests the SeNB 200 to set up SeNB based on the SeNB search result of the UE 300 and the SeNB addition decision of the MeNB 100. [ For this step, the MeNB 100 transmits C-RNTI information, Xn-U setting information, key (K _{enb *} ) information for security mode setting of the UE 300 providing a dual connection, And transmits the SeNB setup message including the attribute information of the SeNB 200 to the SeNB 200. The SeNB 200 receiving the SeNB setup message from the MeNB 100 performs an admission control procedure on whether to set up the bearer requested through the RAC of the RRM and transmits the RRC And generates a RRC Connection Configuration message. The RRC connection configuration message generated by the SeNB 200 may be transmitted to the MeNB 100 as a SeNB setup Ack message including a result code (SeNB additional setup request step) (S1105).

The SeNB 200 that has transmitted the SeNB setup Ack message to the MeNB 100 then performs the radio resource setup procedure of the SRB and the DRB of the SeNB 200 when the requested SeNB connection is accepted. Upon receiving the SeNB setup Ack message for SeNB connection from the SeNB 200, the MeNB 100 extracts the RRC Connection Reconfiguration message included in the corresponding message and transmits the RRC Connection Reconfiguration message to the UE 300. [ The UE 300 that has received the RRC connection reconfiguration message for the SeNB connection from the MeNB 100 performs the uplink synchronization procedure and then performs the radio resource setup procedure of the UE 300 and performs RRC Connection Reconfiguration Complete ) Message to the SeNB 200 (radio resource setting step for SeNB connection) (S1106).

Thereafter, the setup of the SeNB 200 is completed, and the same steps (SeNB setup completion phase, RRC status update phase and dual connection based communication phase) (S1107 to S1109) as in the method A1 can be performed in the method A2.

12A, 12B, and 13 are flowcharts illustrating a method of changing the SeNB 200 according to an embodiment of the present invention.

The SeNB changing procedure of the candidate structure 1 according to an embodiment of the present invention relates to a change of the SeNB 200 providing the dual connection of the UE 300 under the control of the MeNB 100. [ In the candidate structure 1, the following two methods can be applied according to the transmission method of the RRC message for changing the SeNB in the same manner as the connection procedure of the SeNB 200.

Method C1: RRC Connection Reconfiguration message exchange with SeNB

Method C2: RRC connection reconfiguration message exchange with MeNB and SeNB

According to the method C1, the MeNB 100 causes the UE 300 to perform uplink / downlink synchronization for connection of the SeNB 200 providing the double connection, and the uplink / downlink synchronization of the UE 300 is performed The protocol procedure is performed between the RRC of the SeNB 200 and the RRC of the UE 300, and the SeNB 200 can be added.

12A and 12B are flowcharts showing a SeNB changing method C1 in candidate structure 1 according to an embodiment of the present invention.

12A and 12B, communication is performed through a radio bearer established through the radio resources of the SeNB 200 and a radio bearer established through the radio resources of the MeNB 100 (dual connection based communication step) (S1201 ).

Then, the UE 300 transmits a measurement report to the MeNB 100 (measurement report step) (S1202), and the MeNB 100 transmits the measurement report to the channel 300 of the SeNB 200 measured and reported by the UE 300 (SeNB change decision step) (S1203).

Then, the MeNB 100 requests SeNB setup with a new SeNB 210, the target SeNB 210 performs admission control, and then the SeNB 210 transmits an SeNB And transmits a setup response (ACK) (target SeNB setup request step) (S1204).

The MeNB 100 receiving the SeNB setup response from the target SeNB 210 buffers the downlink data for the corresponding radio bearer. If bearer splitting is possible, the MeNB 100 may perform a service using the corresponding bearer after performing a downlink radio bearer change procedure set in the MeNB 100 (downlink data buffering step) (S1205 ).

Then, the MeNB 100 forwards the SeNB attach message to the target SeNB 210 to the UE 300. At this time, the cause information included in the SeNB connect message is SeNB Change (target SeNB connecting step) (S1206).

The UE 300 receiving the SeNB connect message for changing the SeNB from the MeNB 100 to the target SeNB 210 buffers the uplink data for the corresponding radio bearer (uplink data buffering step) (S1207). If bearer splitting is possible, the UE 300 may perform a procedure for changing the uplink radio bearer set in the MeNB 100 and then perform a service using the corresponding radio bearer.

Then, the UE 300 synchronizes the uplink with the target SeNB 210 (uplink synchronization step) (S1208), and the UE 300 acquiring the uplink synchronization with the target SeNB 210 transmits the SeNB connection response (SeNB attach ACK) message to the MeNB 100 (SeNB connection response step) (S1209). The MeNB 100 receiving the SeNB connection response from the UE 300 transmits a SeNB attach indication message to the target SeNB 210 (SeNB connection indication step) (S1210). That is, the 'uplink synchronization step', the 'SeNB connection response step' and the 'SeNB connection confirmation step' of the SeNB change procedure are the same as those of the SeNB connection procedure shown in FIG.

After receiving the SeNB attach response message from the UE 300, the MeNB 100 transmits a Packet Transfer message requesting forwarding of the packet transmitted / received to the existing SeNB (SeNB, SeNB # 1) . The source SeNB 200 receiving the Packet Transfer message from the MeNB 100 transmits the buffered downlink packet to the target SeNB 210 (traffic passing step) (S1211).

Then, the UE 300 sets a radio resource with the target SeNB 210 (radio resource setting step for SeNB connection) (S1212). This step can be performed simultaneously with the 'traffic forwarding step'. Then, the SeNB transmits a SeNB Setup complete message to the MeNB 100 (SeNB setup completion step) (S1213). The 'radio resource setting step for SeNB connection' and the 'SeNB setup completion step' shown in FIG. 12 are the same as those of the SeNB access procedure shown in FIG.

After completing the radio resource setting procedure of the target SeNB 210, the MeNB 100 requests a radio resource release procedure of the source SeNB 200, and the source SeNB 200 releases the set radio resources SeNB releasing step) (S1214). Then, the MeNB 100 updates the RRC status (RRC status update step) by changing the information of the dual-connected SeNB to the information related to the target SeNB 210 (S1215).

Then, the UE 300 can perform duplex connection-based communication with the MeNB 100 and the target SeNB 210 (duplex connection-based communication step) (S1216).

According to the method 2, the MeNB 100 relays the RRC Connection Reconfiguration message to the UE 300 for the SeNB Change by relaying the RRC Connection Reconfiguration message to the target SeNB 210. After the UE 300 receives the RRC Connection Reconfiguration Complete message from the target SeNB 210, the UE 300 performs uplink / downlink synchronization with the target SeNB 210 and transmits a RRC Connection Reconfiguration Complete message to the target SeNB 210, have. 'Method 2' differs from 'Method C1' in that an RRC message for change of SeNB is exchanged with UE 300 through MeNB 100 and SeNB.

13 is a flowchart illustrating a SeNB changing method C2 of the candidate structure 1 according to another embodiment of the present invention.

Referring to FIG. 13, in the SeNB changing method of the candidate structure 1, the double connection based communication is performed through the first MeNB 100 and the source SeNB 200 (S1301) in the same manner as the SeNB changing method of FIG. 12 , The measurement report step S1302, the SeNB change decision step S1303, and the target SeNB setup request step S1304 may be performed in the same manner as the 'method C1' shown in FIG. At this time, the cause information included in the SeNB setup message is SeNB change.

Then, the MeNB 100 receiving the SeNB setup ACK from the SeNB performs buffering on the uplink / downlink data for SeNB change. In addition, the MeNB 100 extracts an RRC connection reconfiguration message included in the received ACK and transmits the RRC connection reconfiguration message to the UE 300. At this time, the cause information included in the RRC connection reconfiguration message is SeNB change. When the MeNB 100 receives the setup ACK from the target SeNB 210, it buffers the data for the corresponding radio bearer. When the UE 300 receives the RRC connection reconfiguration message from the MeNB 100, Buffer. If bearer splitting is possible, a service can be provided through the modified radio bearer after the procedure of changing the radio bearer set in the MeNB 100 is performed. After that, the UE 300 synchronizes the uplink with the target SeNB 210, sets radio resources (Radio Resource Configuration), and then transmits an RRC Connection Reconfiguration Complete message to the target SeNB 210 (Radio resource setting step for SeNB change) (S1305).

The target SeNB 210 completes the reconfiguration of the RRC connection with the UE 300 and transmits a SeNB setup complete message to the MeNB 100 (step SeNB setup completion) (S1306).

Then, the MeNB 100 receiving the SeNB attach response message from the UE 300 delivers a Packet Transfer message requesting delivery of the packet transmitted / received to the source SeNB 200. The source SeNB 200 receiving the Packet Transfer message from the MeNB 100 transmits the buffered downlink packet to the target SeNB 210 (traffic forwarding step) (S1307). The 'traffic forwarding step' is the same as the SeNB changing procedure of FIG. 12 according to method C1.

Thereafter, the MeNB 100 releases the radio resources set in the source SeNB 200 and the source SeNB 200 (SeNB release step) (S1308), and updates the RRC status with respect to the target SeNB 210 Update step) (S1309). Then, the UE 300 can perform double connection based communication with the MeNB 100 and the target SeNB 210 (dual connection based communication step) (S1310). That is, the 'SeNB release step', the 'RRC state update step', and the 'dual connection based communication step' according to the method C2 are the same as the SeNB changing procedure according to the method C1 shown in FIGS. 12A and 12B.

Next, a method of reconstructing SeNB according to an embodiment of the present invention will be described.

14 is a flowchart illustrating a SeNB reconstruction method of candidate structure 1 according to an embodiment of the present invention.

In the present invention, the SeNB reconfiguration method is for changing the radio resource setting of the SeNB 200 according to the control of the MeNB 100 or the request of the SeNB 200. [

Referring to FIG. 14, the MeNB 100 first determines whether to change the radio resource setting information of the SeNB 200 considering the channel information of the SeNB 200, which is measured and reported by the UE 300. Then, the MeNB 100 transmits a SeNB reconfiguration message including a parameter for reconfiguring the radio bearer of the SeNB and a radio bearer identifier to the SeNB (step Se130).

The SeNB 200 receiving the SeNB reconfiguration message from the MeNB 100 determines whether to accept the SeNB reconfiguration request through the radio bearer control (RBC) function of the RRM.

On the other hand, when the SeNB 200 itself reconfigures the radio resource setting information of the SeNB 200, the SeNB reconfiguration request step is not performed. The SeNB 200 can determine the change of the radio resource setting information of the radio bearer of the SeNB 200 (SeNB reconfiguration determination step) (S1402) by requesting the SeNB 200 sub-layer protocol. This step is not performed when the SeNB reconfiguration procedure is started in the MeNB 100 (SeNB reconfiguration request step). That is, the SeNB reconfiguration request step and the SeNB reconfiguration determination step may be selectively performed.

When the SeNB 200 accepts the SeNB reconfiguration request of the MeNB 100 or determines the SeNB reconfiguration, the SeNB 200 changes the radio resource configuration (radio resource configuration), and performs RRC Connection Reconfiguration (RRC reconfiguration) for SeNB reconfiguration ) Message to the UE 300. [ The UE 300 that has received the RRC connection reconfiguration message from the SeNB 200 changes the radio resource configuration and transmits a RRC Connection Reconfiguration Complete message to the SeNB 200 (SeNB reconfiguration step) S1403).

The SeNB 200 that has reconfigured the radio resource setting of the SeNB 200 transmits the SeNB reconfiguration response to the MeNB 100 requesting the SeNB reconfiguration. In this case, when the SeNB 200 requests reconfiguration of the SeNB 200 by the MeNB 100, the SeNB 200 transmits the SeNB reconfiguration ACK to the MeNB 100, and when the SeNB 200 determines the SeNB reconfiguration, Transmits a SeNB reconfiguration complete message to the MeNB 100 (SeNB reconfiguration response step) (S1404).

Thereafter, the MeNB 100 updates the RRC state including the attribute of the corresponding radio bearer (RRC state update step) (S1405).

Next, the release method of the SeNB 200 according to the embodiment of the present invention will be described.

15 is a flowchart illustrating a SeNB release method of candidate structure 1 according to an embodiment of the present invention.

The SeNB releasing procedure is a procedure for controlling the MeNB 100 or releasing the connection of the SeNB 200 to the terminal according to a request from the SeNB 200. [

15, the UE 300 performs communication through a bearer established through radio resources of the SeNB 200 and a bearer established through a radio resource of the MeNB 100 (dual connection based communication step) (S1501). The UE 300 periodically performs measurement according to the setting of the MeNB 100 and reports the measurement result to the MeNB 100 and the MeNB 100 if the condition set by the MeNB 100 is satisfied. Receives a measurement report of the UE 300 (measurement report step) (S1502). That is, it is the same as the measurement report step of the SeNB connection procedure.

Thereafter, the MeNB 100 determines whether to release the SeNB 200 in consideration of the channel information of the SeNB 200, which is measured and reported by the UE 300 (SeNB release decision step) (S1503). Then, based on the SeNB channel measurement information of the UE 300, the MeNB 100 requests the SeNB 200 to release the SeNB (SeNB release request step) (S1504). For this procedure, the MeNB 100 may transmit a SeNB Release Request message including the C-RNTI information of the UE 300 providing the double connection to the SeNB 200. [

The SeNB 200 that has received the SeNB release request message from the MeNB 100 performs the SeNB release procedure.

The SeNB 200 transmits an RRC Connection Reconfiguration message to the UE 300 in order to release the SeNB. Upon receiving the RRC Connection Reconfiguration message, the UE 300 releases the established radio resources and transmits a RRC Connection Reconfiguration Complete message to the SeNB 200. [ The SeNB 200 that has received the release response of the requested RRC connection releases the set radio resource (radio resource release step for SeNB release) (S1505). This procedure is performed when the SeNB release request message is received from the MeNB 100 in the case of the SeNB release procedure starting from the MeNB 100. When the SeNB detach procedure starting from the SeNB 200 is performed, Lt; RTI ID = 0.0 > RRM < / RTI >

The SeNB 200 that has completed the radio resource release procedure of the SeNB 200 transmits a SeNB release ACK message to the MeNB 100 (SeNB release response step) (S1506).

The MeNB 100 that has received the SeNB release ACK message from the SeNB 200 transits the RRC state of the UE 300 to the single connectivity state (step 1507).

Then, the UE 300 performs a communication procedure through the established radio bearer with the MeNB 100 (single connection-based communication step) (S1508).

16 is a flowchart illustrating a method of reporting SeNB buffer status of candidate structure 1 according to an embodiment of the present invention.

In the present invention, the SeNB buffer state reporting means reporting the PDCP transmission buffer state of the SeNB 200 to the MeNB 100.

Referring to FIG. 16, the SeNB 200 may transmit a Resource Status Update message to the MeNB 100 according to a condition set by control of the RRC. The resource status update message includes indicating the status of the downlink transmission buffer, and the delivery condition of the resource status update message can be defined periodically or by the RRC according to the occurrence of a specific event.

The following describes the information exchanged between the MeNB 100, the SeNB 200 and the UE 300 and the way of exchanging the information, in order to provide a double connection through the candidate structure 1.

17 is a diagram illustrating a connection of MeNB, SeNB, and UE in candidate structure 1 according to an embodiment of the present invention.

17, a reference point between the MeNB 100 and the SeNB 200 is defined as Xn, and the information of the control plane and the information of the user plane exchanged at the reference point are defined as Xn-CP (control plane) exchange information And Xn-UP (user plane) exchange information. Also, a reference point between the MeNB 100 and the UE 300 is defined as Uu / m, and a reference point between the SeNB 200 and the UE 300 is defined as Uu / s.

18 is a diagram illustrating an interlocking structure of a control plane according to an embodiment of the present invention.

Referring to FIG. 18, the control plane interface Xn-CP between the MeNB 100 and the SeNB 200 for providing a dual connection can provide the following functions.

* SeNB management function

- SeNB setup, SeNB change, SeNB release,

- SeNB Reconfiguration

- SeNB buffer status report (buffer status report)

- Flow control between MeNB and SeNB: When downlink traffic is controlled through the control plane protocol (performed using method D1)

* Xn-UP management

- Traffic bearer management function between MeNB and SeNB (setup, change, release)

* RLF Reporting from SeNB to MeNB (Reporting)

Referring to FIG. 18, the Xn-CP is similar to the X2-CP in terms of the application level that operates based on a stream control transmission protocol / internet protocol (SCTP / IP) Signaling protocol.

Uu / m, which is a control plane interface between the MeNB 100 and the UE 300 to provide a dual connection, and Uu / s, which is a control plane interface between the SeNB 200 and the UE 300, provide the following functions.

* RRC function for dual connectivity for dual connection

- SeNB request and response

- RRC connection reconfiguration

SeNB setup, SeNB Change, SeNB release,

SeNB reconfiguration

- Measurement configuration and reporting

Purpose of SeNB Management

Table 4 defines the messages exchanged with Xn-CP and Uu when providing a double connection through candidate structure 1.

Protocol message
Protocol Message Explanation
Descriptions
RP IEs Remark SeNB Setup SeNB setup request message Xn-CP -Setup type
-Bearer attribute
-C-RNTI Method A1
Method C1 -Setup type
-Bearer attribute
-C-RNTI
-Xn -i info.
-Security Key Method A2
Method C2 SeNB Setup Ack SeNB Setup Response Message Xn-CP -Result code Method A1
Method C1 -Result code
-RRC message Method A2
Method C2 SeNB Setup Complete SeNB setup complete message Xn-CP SeNB attach SeNB connection request message Uu / m -Cause Method A1
Method C1 SeNB attach Ack SeNB connection response message Uu / m -Result code Method A1
Method C1 SeNB attach Ind SeNB connection confirmation message Xn-CP -Xn -i info.
-Security Key Method A1
Method C1 RRC Connection Reconfiguration Uu / m -SeNB Addition List
-Cause Method A1
Method C1 Uu / s -SeNB Addition List Method A2
Method C2 RRC Connection Reconfiguration Complete Uu / m Method A1
Method C1 Uu / s Method A2
Method C2 Packet Transfer Buffered packet delivery request message Xn-CP Packet Transfer Ack Packet Tranfer response message Xn-CP SeNB Release SeNB release request message Xn-CP SeNB Release Ack SeNB Release Response Message Xn-CP SeNB reconfiguration SeNB reconfiguration request message Xn-CP -RB id.
-SeNB Modification List SeNB reconfiguration Ack SeNB Reconfiguration Response Message Xn-CP -Result Code Resource Status Update SeNB's downlink buffer information reporting message Xn-CP -DL Buffer Status

Table 5 defines the information entities contained in the message exchanged with Xn-CP in Table 4. Table 4:

Information Element Descriptions Remarks Setup Type SeNB Setup Type
- Initial setup / SeNB Change - Bearer Attributes Properties of Radio Bearer Security Key K _{enB *} C-RNTI Cell-Radio Network Temporary Identifier Xn-U info. Information for setting Xn-U Result Code Result code
- Success / Fail RRC message RRC Connection Reconfiguration message Included in SeNB Setup Ack SeNB Addition List SeNB Setup Information SeNB Modification List SeNB modification information RB id. Radio Bearer Identifier DL Buffer Status The state of the downlink buffer
- Low / Medium / High / Overload

19 is a view showing an interlocking structure of a user plane according to an embodiment of the present invention.

Referring to FIG. 19, a user plane interface between the MeNB 100 and the SeNB 200 to provide a dual connection, Xn-UP, may provide the following functions.

* Traffic passing between MeNB and SeNB

- Flow control between MeNB and SeNB: When downlink traffic is controlled through user plane protocol (performed when using method D2)

The Xn-UP can operate based on a GPRS tunneling protocol / user datagram protocol (GTP-U / UDP) based transport network similar to the structure of the X2-UP.

UuUP / m, which is a user plane interface between the MeNB 100 and the UE 300 to provide a dual connection in the present invention, can provide the following functions.

* BM PDU management (management)

- PDCP PCU ordering, In-sequence delivery,

20 is a diagram illustrating a wireless communication system supporting dual connection according to another embodiment of the present invention.

20 shows a candidate structure 2 of a wireless communication system supporting dual connection.

Referring to FIG. 20, the MeNB 500 of the candidate structure 2 is connected to the MME and the S-GW, the control plane interface S1-MME, and the user plane interface S1-U, respectively. In addition, the MeNB 500 and the UE 300 of the candidate structure 2 include the RRC protocol, the PDCP, the RLC protocol, the MAC protocol, and the PHY protocol as in the candidate structure 1 of FIG. 1, PDCP is not included. That is, in terms of the user plane protocol, the MeNB 500 includes all the 2-layer protocols, but the SeNB 600 includes the 2-layer protocols except for the PDCD.

In the candidate structure 2 according to the embodiment of the present invention, the MeNB 500 and the SeNB 600 can provide a CA function using a plurality of CCs. Thus, the eNBs (MeNB 500 and SeNB 600) manage the primary and secondary cells. A set of cells managed by the MeNB 500 is referred to as a master cell group (MCG), and a set of cells managed by the SeNB 600 is referred to as a secondary cell group (SCG).

The functions and structure of the RRC and RRM that perform the control plane function of the candidate structure 2 will be described below.

In the candidate structure 2 according to the embodiment of the present invention, the function of the RRC protocol is performed in the MeNB 500. In the candidate structure 2, the SeNB 600 can operate according to the RRC control of the MeNB 500. [

That is, in the RRC_CONNECTED state of Table 2, all the RRC functions are located in the MeNB 500, and the execution of the 2-layer protocol according to the RRC operation and the setting of the physical layer are performed through the Xn interface between the MeNB 500 and the SeNB 600 .

First, the system information broadcast function among the RRC functions described in Table 2 will be described. The MeNB 500 transmits the system information of the SeNB 600 to the UE 300 in the dual connection state using the dedicated bearer based RRC message, . That is, the MeNB 500 determines whether the system information is changed by interworking with the SeNB 600, and when the system information of the SeNB 600 is changed, the MeNB 500 can transmit the changed system information to the UE 300 through the dedicated bearer . More specifically, the UE receives master information block (MIB) information from the SeNB and receives a system information block (SIB) from the MeNB using the dedicated bearer. This is for the UE to recognize the system frame number (SFN) and the sub-frame number (SN) of the MeNB and the SeNB. In addition, the UE may obtain the SFN difference between MenB and SeNB and report it to the MeNB so that this information can be used to set the discontinuous reception (DRX) and measurement of the MeNB.

In the candidate structure 2 according to the exemplary embodiment of the present invention, the RRC connection management function (i.e., RRC connection establishment / modification / release) among the RRC functions is performed by the MeNB 500 Lt; / RTI >

Since the PDCP responsible for the integrity protection / encryption function of the SRB and the DRB in the candidate structure 2 exists only in the MeNB 500, the key information (K _eNB , K _RRCint , K _RRCenc , K _UPenc ) exchange is not required. Therefore, the initial security activation procedure may be performed while the SecurityModeCommand message and the SecurityModeComplete message are exchanged between the MeNB 500 and the UE 300. [

In the candidate structure 2, the RRC connection mobility of the RRC connection is controlled in the MeNB 500 in consideration of mobile robustness and the like.

The DRB management, that is, the establishment / modification / release of the DRB, is performed by the MeNB 500 and the SeNB 600 according to the RRC procedure for DRB set in the MeNB 500 and the SeNB 600 . ≪ / RTI > For the DRB management, the MeNB 500 and the SeNB 600 can exchange parameters for DRB setting and perform an RRC operation procedure for DRB control based on the exchanged parameters.

In the candidate structure 2, the radio configuration control is performed in the MeNB 500, and the setting according to the control of the MeNB 500 is performed in the MeNB 500 or the SeNB 600. That is, the MeNB 500 performs a radio resource setting procedure for the radio bearer management of the RRC. In the second layer protocol and the physical layer located in the SeNB 600, operation parameters are set according to a radio resource setting procedure presented in the MeNB 500. [

In the candidate structure 2, the QoS control includes the setting of the SPS and the uplink rate control function of the UE 300, and the control of the corresponding function is performed in the MeNB 500.

In the candidate structure 2, the UE 300 sets a parameter for RLF detection using system information and configuration information provided by the MeNB 500, and operates in conjunction with the MeNB 500 when RLF is generated. That is, when the RLF for the radio link between the MeNB and the UE occurs, the RLF recovery procedure can be performed through the RRC connection re-establishment procedure. The RNC, the MAC, and the PHY of the SeNB 600 report information about the error to the RRC located in the MeNB 500 when the error occurs on the wireless link, and the MeNB 500 receiving the error reports the SeNB 600, Can be controlled. Therefore, the UE needs to define an RRC message that can detect the RLF occurrence of the SeNB and transmit the RLF message to the MeNB. In this patent, the message is defined as a secondary RLF indication message (Secondary-RLF Indication) message.

The measurement setup and reporting procedure of the UE 300 in the candidate structure 2 can be controlled in the MeNB 500.

In addition, dedicated NAS information, non-3GPP dedicated information, and UE 300 availability information for E-UTRAN sharing are information exchange procedures for an operation procedure between the MME and the UE 300, and thus can be performed in the MeNB 500 have.

Table 6 defines the RRM functions in the control plane of Candidate Structure 2, excluding Inter-RAT related functions.

Main functions MeNB SeNB Radio Bearer Control Establishment, maintenance, and release of Radio Bearers X X Radio Admission Control Admission or Rejection of the establishment requests for new Radio Bearers X X Connection Mobility Control Management of radio resources in connection with idle and connected mode mobility X Dynamic Resource Allocation Allocation and de-allocation of resource to user and control plane packets X X Inter-cell Interference Coordination Management of radio resources such as inter-cell interference is kept under control X X Load Balancing Handling of uneven distribution of traffic over multiple cells X

21 is a diagram showing the functions and structure of RRC and RRM in the control plane of candidate structure 2 for providing a double connection.

Referring to FIG. 21, in the SeNB 600, since the RRC protocol is not executed, the function corresponding to the RRC is not shown, and the RRM function is also limitedly displayed. Unlike the RRM of the MeNB 500, the RRM of the SeNB 600 excludes connection mobility control (CMC) and load balancing (LB) functions.

FIG. 22 is a diagram illustrating a user plane downlink protocol stack of a wireless communication system providing a dual connection according to another embodiment of the present invention. FIG. 23 is a diagram illustrating a protocol stack of a wireless communication Figure 5 shows a protocol stack of a user plane uplink of the system.

In the user plane of the candidate structure 2, a sub radio bearer including a master radio bearer (M-RB) and a secondary radio bearer (S-RB) Can be newly defined. That is, in the candidate structure 2, one radio bearer may be divided into M-RBs set in the MeNB 500 and S-RBs set in the SeNB 600 to provide a dual connection, and M-RBs and S- The RB may be located at a service access point (SAP) between the PDCP and the RLC.

In addition, the PDCP of the candidate structure 2 is required to divide user traffic according to the control plane control in the PDCP PDU step for the user traffic transmission between the MeNB 500 and the SeNB 600. Accordingly, the following functions may be additionally introduced into the PDCP of candidate structure 2.

The PDCP of the candidate structure 2 can perform routing and flow control between the MeNB 500 and the SeNB 600 (Routing and Flow control between MeNB 500 and SeNB 600). First, the PDCP can route uplink / downlink packets according to flow control setting information. The PDCP of the MeNB 500 may forward the downlink PDCP PDU to the subnetwork bearer of the MeNB 500 or the SeNB 600 and the PDCP of the UE 300 may transmit the uplink PDCP PDU to the subnetwork bearer ) Or SeNB 600).

The PDCP can also generate and exchange management messages for flow control. This is performed in a flow control using a user plane protocol, and a PDCP management message for flow control between the MeNB 500 and the SeNB 600 is newly defined and flow control can be performed through this message exchange.

In addition, PDCP can perform traffic rearrangement and in-sequence delivery in the case of a bearer split. When one EPS bearer is split into a plurality of radio bearers, the PDCP sequence number is rearranged and sequential delivery is performed. If a non-ideal backhaul between the MeNB (500) and the SeNB (600) is considered, a PDCP SN of a longer length (12 + x) needs to be used by extending the SN length presented in the existing Rel- The PDCP PDU format can be changed.

Finally, the PDCP can perform PDU buffering according to the SeNB 600 change. The PDCP of the MeNB 500 may buffer the downlink PDCP PDU and the PDCP of the UE 300 may buffer the uplink PDCP PDU.

Candidate structure 2 independently includes MAC functions of MeNB 500 and SeNB 600 similar to candidate structure 1. Therefore, when providing the double connection in the candidate structure 2, the MAC related characteristic is the same as the candidate structure 1 except for the channel mapping structure of the SeNB 600 and the data structure for the BSR.

FIG. 24 is a diagram illustrating an uplink / downlink channel mapping structure of an SeNB according to another embodiment of the present invention.

Referring to FIG. 24, the channel mapping structure of the SeNB 600 according to another embodiment of the present invention supports a dedicated traffic channel in a downlink, and a dedicated traffic channel and a random access channel access channel.

25 is a diagram illustrating a buffer management structure of a UE according to another embodiment of the present invention.

The procedure for the uplink radio resource allocation of the UE 300 in the candidate structure 2 is the same as the procedure of the MAC layer of the candidate structure 1 except for the data structure for the BSR. In the candidate structure 2, the UE 300 transmits an LCG based on a sub-radio bearer (M-RB or S-RB) and a logical channel set in units of MeNB 500 or SeNB 600 for BSR procedure And performs a procedure of MeNB (500) or SeNB (600) and BSR (short BSR, long BSR, or truncated BSR).

The downlink data traffic for providing the double connection in the candidate structure 2 can be controlled according to the following method.

The downlink data traffic (e.g., PDCP PDU) of the candidate structure 2 according to another embodiment of the present invention is transmitted to the MeNB 500 or the SeNB 600 in accordance with the RRC / PDCP control of the MeNB 500, And may be delivered to the UE 300 using resources. The uplink PDCP PDU of the candidate structure 2 may be transmitted to the MeNB 500 or the SeNB 600 by using the uplink radio resource according to the RRC / PDCP control of the UE 300. [

In order to efficiently provide the double connection in the candidate structure 2, it is necessary to transmit data according to the flow control between the MeNB 500 and the SeNB 600 like the flow control of the candidate structure 1.

In order to solve the downlink traffic flow control problem in the candidate structure 2, the MeNB 500 and the SeNB 600 perform flow control for traffic transmission between the MeNB 500 and the SeNB 600 through the following methods and procedures (Similar to the flow control method of candidate structure 1). The downlink traffic flow control can be performed when data is transmitted using the SeNB 600 regardless of the bearer split.

- Downlink flow control method D1: Using the control plane protocol

And the RRC of the MeNB 500 performs flow control for the traffic transfer between the MeNB 500 and the SeNB 600. According to this method, the RRC of the MeNB 500 sets a flow control initial value for the corresponding radio bearer to the PDCP when setting up the radio bearer, and sets the flow control initial value for the radio bearer to the MeNB 500 ) Can perform the flow control dynamically through the PDCP control. When this method is used, a flow control related protocol procedure between the MeNB 500 and the SeNB 600 can be performed through the Xn-CP.

- Downlink flow control method D2: Using user plane protocol

The PDCP of the MeNB 500 performs a flow control for traffic transfer between the MeNB 500 and the SeNB 600. [ According to this method, when the RRC of the MeNB 500 sets up a radio bearer, a flow control initial value for the corresponding radio bearer is set to the PDCP of the MeNB 500, and a downlink buffer The PDCP of the MeNB 500 can dynamically perform the flow control of the PDCP PDU according to the state. When this method is used, a flow control related protocol procedure between the MeNB 500 and the SeNB 600 can be performed through Xn-UP.

Hereinafter, a method for performing flow control for traffic transmission between the MeNB 500 and the SeNB 600 using the 'DL Flow Control Method D1' will be described.

First, when setting up a radio bearer for dual connection (including M-RB and S-RB), the RRC of the MeNB 500 transmits an initial value to the PDCP for controlling the flow of packets to be transmitted to the MeNB 500 and the SeNB 600 (PDCP initial setting step). This value can be set in consideration of the QoS characteristics of the radio bearers set in the MeNB 500 and the SeNB 600, and the like. The PDCP can process the downlink packet using the packet flow set value set at the initial setting of the radio bearer. The parameters used in the flow of the PDCP can be used in the same way as fc _{m .d} or fc _{s .d} of candidate structure 1.

Next, the RRC of the MeNB 500 periodically or after an event occurs, after the radio bearer is set up, checks the state of the downlink RLC transmission buffer (downlink buffer state reporting step). In order to perform this procedure, the RRC may perform a setup procedure related to reporting the transmission buffer status to the RLC when setting up the RB. And the settings associated with the transmission buffer status report may include periodic reporting or reporting of events based on the upper bound threshold of the transmission buffer and the lower bound threshold. At this time, the RLC located in the SeNB 600 transmits the status of the downlink RLC transmission buffer to the MeNB 600 using a protocol message (for example, a resource status update message) on the Xn-CP in order to report the downlink buffer status. (500).

The RRC that has reported the status of the downlink RLC packet buffers of the MeNB 500 and the SeNB 600 receives the packet transmitted from the MeNB 500 and the SeNB 600 according to the downlink buffer status change through the reconfiguration procedure of the PDCP, (The flow control function resetting step). After performing the BM reconfiguration procedure of the RRC, the PDCP can process the downlink packet using the newly set packet flow setting value.

Next, a method of performing flow control for traffic transmission between the MeNB 500 and the SeNB 600 using the 'DL flow control method D2' described above will be described.

The initial step of initializing the PDCP when setting up the downlink radio bearer is the same as the first step of the 'method D1'.

After the radio bearer is established, the RLCs of the MeNB 500 and the SeNB 600 periodically report the status of the downlink RLC transmission buffer according to the setting of the RRC or when an event occurs (downlink buffer status reporting step). To this end, the RLC of the MeNB 500 transmits information on the downlink buffer state to the PDCP using a local primitive, and the RLC of the SeNB 600 transmits information on the downlink buffer state using the Xn-UP To the PDCP of the MeNB 500.

The PDCP of the MeNB 500 that has received the status of the downlink packet buffers of the MeNB 500 and the SeNB 600 transmits a flow of packets transmitted to the MeNB 500 and the SeNB 600 according to the downlink buffer state change, And dynamically resets the setting values for the control (flow control function resetting step). The PDCP of the MeNB 500 may process the downlink packet using the newly set packet flow setting value after changing the set value for packet flow control.

Hereinafter, a method for solving the flow control problem for the uplink traffic will be described. The UE 300 can perform flow control for uplink traffic delivery through the following method. The flow control of the uplink traffic may be performed when a bearer split occurs, i.e., when the uplink traffic transmission path of the UE 300 is directed to both the MeNB 500 and the SeNB 600. [

- Uplink flow control method U1: Using control plane protocol

This method is a method in which the RRC of the UE 300 performs flow control for uplink traffic delivery. According to this method, when the RRC sets up a radio bearer, the RRC of the UE 300 sets a flow control initial value for the corresponding radio bearer to the PDCP, controls the PDCP according to the uplink buffer status report during the service, Procedure can be performed.

- Uplink flow control method U2: Using user plane protocol

This method is a method in which the PDCP of UE 300 performs flow control for uplink traffic delivery. According to this method, when the RRC sets up a radio bearer, the PDCP of the UE 300 sets a flow control initial value for the corresponding radio bearer to the BM, and when the PDCP of the UE 300 is in service, According to the buffer status report, it is possible to control the flow dynamically through the control of the PDCP.

Hereinafter, a method of performing flow control for uplink traffic delivery of the UE 300 using the 'UL flow control method U1' will be described.

When setting up a radio bearer for a dual connection, the RRC of the UE 300 sets an initial value for flow control of packets transmitted to the MeNB 500 and the SeNB 600 with respect to the PDCP (initial setting step of BM). At this time, the PDCP setup scheme for performing this procedure is the same as the downlink setup scheme, and uplink parameters (fc _{m .u} , fc _{s .u} ) can be used.

Next, after the RB is established, the RRC of the UE 300 periodically or when an event occurs, checks the state of the uplink RLC transmission buffer (uplink buffer state reporting step). At this time, the RLC setting method is the same as the downlink setting method (periodic reporting or reporting when an event occurs).

Upon receipt of the uplink packet buffer status, the RRC reestablishes the set value for controlling the flow of the packet transmitted in the uplink through the reconfiguration procedure of the PDCP according to the change of the uplink buffer state (step of resetting the flow control function). After the RRC performs the PDCP reconfiguration procedure, the PDCP can process the uplink packet using the newly set packet flow setting value.

Hereinafter, a method for performing the flow control for uplink traffic delivery of the UE 300 using the 'uplink flow control method U2' described above will be described.

First, when setting uplink radio bearers, the initial setting step of BM is the same as the first step of 'method U1'.

Next, after the initial setting of the RB, the RLC of the UE 300 periodically reports the state of the uplink RLC transmission buffer to the PDCP according to the occurrence of the event (uplink buffer state reporting step).

After receiving the status of the uplink packet buffer, the PDCP reestablishes the set value for flow control of the packet transmitted in the uplink through the reconfiguration procedure according to the uplink buffer state change (flow control function reconfiguration step). After performing the reconfiguration procedure of the PDCP, the PCPC can process the uplink packet using the newly set packet flow setting value.

Data between the MeNB 500 and the SeNB 600 in the candidate structure 2, that is, the PDCP PDU generated from the PDCP of the MeNB 500, is transmitted to the RLC of the MeNB 500 or the RLC of the SeNB 600. In particular, when a PDCP PDU is transmitted through a sub-radio bearer set in the SeNB 600, as a mechanism for data transmission between the MeNB 500 and the SeNB 600, the GTP-U + proposed in the user plane interworking structure of the candidate structure 1 Xn-UP protocol.

Hereinafter, the operation procedure of the wireless communication system for the dual connection will be described using the control plane and the user plane structure of the candidate structure 2 with reference to FIG. 26 through FIG. The operation procedure of the candidate structure 2 according to another embodiment of the present invention includes an SeNB attach procedure, a SeNB change procedure, a SeNB reconfiguration procedure, a SeNB detach procedure, and a SeNB buffer status report procedure.

First, the connection procedure of the SeNB in the candidate structure 2 will be described.

26 is a flowchart illustrating a SeNB access procedure of candidate structure 2 according to another embodiment of the present invention.

Referring to FIG. 26, the 'single connection-based communication step S2601', the 'SeNB measurement instruction step S2602' and the 'measurement report step S2603' correspond to the SeNB access method of the candidate structure 1 shown in FIG. same.

Then, the MeNB 500 determines whether to add the SeNB 600 considering the load state of the MeNB 500 or the like (SeNB addition decision step) (S2604). At this time, the RBC function located in the MeNB 500 may be used as the radio bearer control of the SeNB 600 in the candidate structure 2.

Based on the SeNB search result of the UE 300 and the SeNB addition decision of the MeNB 500, the MeNB 500 requests the SeNB 600 to configure the SeNB. At this stage, the MeNB 500 transmits the cell-radio network temporary identifier (C-RNTI) information of the UE 300 providing the double connection and the bearer attribute information (SRB or DRB And a UE radio access capability of the UE 300 to the SeNB 600. The SeNB 600 transmits the SeNB setup message to the SeNB 600, The SeNB 600, which has received the SeNB setup message from the MeNB 500, performs an admission control procedure on whether to set up the bearer requested through the Radio Admission Control (RAC) of the RRM, To the MeNB 500 (SeNB setup request step) (S2605). At this time, in the candidate structure 2, the SeNB 600 performs only the RAC function for the bearer requested by the MeNB 500.

Thereafter, when the SeNB 600 accepts the SeNB Setup request received from the MeNB 500, the SeNB 600 transmits the bearer attribute information for the dual connection included in the SeNB Setup Request message to the SeNB 600 ) (Step S2606). In step S2606, the wireless resources of the SeNB are set. The radio resources established in the SeNB 600 through this procedure can be activated when the RRC Connection Reconfiguration procedure between the MeNB 500 and the UE 300 is successful.

Thereafter, the MeNB 500 may instruct the UE 300 to establish a SeNB connection for the dual connection (RRC connection reconfiguration request step for connection with the SeNB) (S2607) using the RRC connection reconfiguration message. At this time, the RRC connection reconfiguration message transmitted from the MeNB 500 to the UE 300 may include configuration information for the PHY, MAC, and RLC connection between the UE 300 and the SeNB 600. [ If the MeNB 500 indicates contention based random access to the UE 300, advance information related to the random access is not included in the present message.

The UE 300 that has received the SeNB connection request from the MeNB 500 performs a non-contention-based or contention-based random access procedure and acquires uplink synchronization (uplink synchronization step) (S2608) . If contention based random access is indicated in the 'RRC connection reconfiguration request step for SeNB connection', a random access procedure according to the standard of 3GPP TS 36.321 may be performed.

The UE 300 which has acquired the uplink synchronization can set the radio resource using the information included in the RRC connection reconfiguration message received from the MeNB 500 in the 'RRC connection reconfiguration request step for SeNB connection' Setting step) (S2609). That is, the UE 300 can establish a radio bearer connection with the SeNB 600.

After the radio resource setting procedure of the UE is completed, the UE 300 transmits to the MeNB 500 that the SeNB connection is completed, and uses the RRC Connection Reconfiguration Complete message (RRC Connection Reconfiguration Complete message for SeNB connection) Step S2610.

Upon receiving a response to the SeNB connection from the UE, the MeNB 500 transmits a SeNB Setup Complete message to the SeNB 600 (SeNB setup completion step) (S2611). The SeNB setup completion message is transmitted from the MeNB 500 to the SeNB 600 because the subject indicating the SeNB Seup in the candidate structure 2 is the MeNB 500. This is different from the procedure in the structure of the candidate structure 1. [

Thereafter, the MeNB 500 updates the RRC status (RRC status update step) S2612 and the dual connection-based communication step (dual connection based communication step) S2613 of the UE 300, Is the same as candidate structure 1.

FIG. 27 is a flowchart illustrating a method of changing a SeNB according to another embodiment of the present invention.

The SeNB changing method of the candidate structure 2 according to another embodiment of the present invention relates to a change of the SeNB 600 providing the dual connection of the UE 300 under the control of the MeNB 500. [

27, the 'double connection based communication step S2701', the 'measurement report step S2702', and the 'SeNB change decision step S2703' are the same as the SeNB change method C1 of the candidate structure 1.

The 'target SeNB setup request step S2704' and the 'target SeNB wireless resource setup step S2705' are the same as the 'SeNB setup request step' and the 'SeNB wireless resource setup step' '.

Hereinafter, the 'downlink data buffering step S2706' of the MeNB 500 is the same as the 'downlink data buffering step' of the SeNB changing method C1 of the candidate structure 1.

Hereinafter, the 'RRC connection reconfiguration request step S2707 for connection to the target SeNB' is the same as the 'RRC connection reconfiguration request step for SeNB connection' of the SeNB connection method of FIG. That is, the RRC connection reconfiguration message transmitted from the MeNB 500 to the UE 300 may include configuration information for the PHY, MAC, and RLC connection between the UE 300 and the SeNB 600. [ At this time, in the RRC Connection Reconfiguration message transmitted by the MeNB 500 to change the SeNB to the UE 300, in the relation with the UE 300, the base station to operate as a new SeNB and the secondary A list of secondary cells may be included.

Hereinafter, the 'uplink data buffering step (S2708)' is the same as the 'uplink data buffering step' of the SeNB changing method C1 of the candidate structure 1.

Thereafter, the uplink synchronization step S2709 of the UE 300, the radio resource setting step S2710 of the UE 300, the RRC connection reconfiguration response step S2711 for the target SeNB connection, SeNB setup completion step (S2712) 'is the same as the SeNB connection method in Fig.

Finally, the 'source SeNB release step S2713', 'RRC status update step S2714' and 'dual connection based communication step S2715' are the same as SeNB change method C1 of candidate structure 1.

28 is a flowchart illustrating a SeNB reconstruction method of candidate structure 2 according to another embodiment of the present invention.

In the present invention, the SeNB reconfiguration method is for changing the radio resource setting allocated to the SeNB according to the control of the MeNB 500 or the request of the SeNB 600. [

First, the MeNB 500 determines whether to change the radio resource setting information of the SeNB 600 in consideration of the channel information of the SeNB 600 measured and reported by the UE 300 (SeNB reconfiguration determination step). Then, the MeNB 500 transmits a SeNB reconfiguration message including a parameter for radio bearer reconfiguration of the SeNB 600 and a radio bearer identifier to the SeNB 600 (S2801a). Upon receiving the SeNB reconfiguration message from the MeNB 500, the SeNB 600 determines whether to accept the request through the RBC function of the RRM, and then transmits a SeNB reconfiguration ACK message to the MeNB 500. [

S2801 (b) is a step for starting the SeNB reconstruction in the SeNB 600. Fig. At this stage, the SeNB 600 transmits a reconfiguration command of the SeNB 600 to the MeNB 500. [ At this time, the SeNB 600 transmits a parameter for the radio bearer reconfiguration of the SeNB 600 to the MeNB 500 through the RRM function of the SeNB 600. When performing this procedure, the SeNB 600 starts the SeNB reconfiguration using the independent RRM, so that the procedure of exchanging the radio resource configuration information with the MeNB 500 needs to be preceded. SeNB can allocate radio resources for dual connection based on the UE availability information and the radio resource allocation information set by the MeNB.

In the present invention, the availability information of the UE 300 included in the SeNB setup message of the SeNB access procedure may be used to exchange radio resource configuration information between the MeNB 500 and the SeNB 600, and the following three types of A radio resource setting information sharing scheme can be considered.

FIG. 29 is a flowchart illustrating a method of sharing radio resource setting information of a candidate structure 2 according to another embodiment of the present invention.

- Alt.1: two-way handshake before reconfiguration

In this method, when the SeNB 600 performs an RRM decision for reconfiguration, the MeNB 500 transmits a message (Radio Status Request) requesting information on the current radio resource setting state of the UE 300 And receives a response message (Radio Status Response) from the MeNB 500 to share radio resource setting information. According to this method, the SeNB 600 determines the radio resource state of the UE 300 received from the MeNB 500 at the time of reconfiguration of the SeNB 600 and the radio access capability of the UE 300 The RRM procedure can be performed. However, in the case of starting the SeNB reconfiguration procedure in the SeNB 600 according to the present method, a signaling procedure between the SeNB 600 and the MeNB 500 for obtaining the radio resource allocation information of the UE 300 is always performed before the reconfiguration procedure is performed And a delay may occur.

- Alt 2: One-way indication during modification when exceeding UE (300) capability if the availability of UE 300 is exceeded.

In this method, the SeNB 600 transmits a reconfiguration command, and the MeNB 500 receiving the reconfiguration command transmits a reconfiguration command to the SeNB 600 based on the information of the radio resources currently set in the UE 300, Radio resource reconfiguration) is allowed. If the SeNB reconfiguration is allowed through this method, the MeNB 500 performs SeNB reconfiguration through the RRC reconfiguration procedure, and if not, the MeNB 500 forwards the message to the SeNB 600 to reject the request. The Rejection Rejection message transmitted to the SeNB 600 may include the cause and the radio resource allocation information between the current MeNB 500 and the UE 300. The SeNB 600 receiving the message may transmit the received radio resource allocation information Determines whether to re-run the SeNB reconfiguration procedure or stop the reconfiguration procedure. The method can be reconfigured without additional signaling between the MeNB 500 and the SeNB 600 if the reconfiguration requested by the SeNB 600 does not exceed the current availability of the UE 300, The delay caused by the signaling procedure is reduced. However, if the reconfiguration requested by the SeNB 600 exceeds the availability of the UE 300, a response message for the reconfiguration is transmitted from the MeNB 500 to the SeNB 600, And a signaling procedure may be required.

- Alt 3: one-way reporting at arbitrary time.

In this method, when the MeNB 500 changes periodically to the SeNB 600 or to the radio resource setting of the UE 300 set in the MeNB 500, the radio resource allocation information of the UE 300 And transmits it to the SeNB 600 using the Xn interface. According to this method, the SeNB 600 can perform an RRM decision function for the SeNB reconfiguration procedure using the radio resource allocation information of the UE 300 received from the MeNB 500. [ This method has an advantage that an additional signaling procedure between the SeNB 600 and the MeNB 500 is not required when the SeNB 600 is reconfigured. However, this method is disadvantageous in that the load due to signaling for sharing radio resource use information between the MeNB 500 and the SeNB 600 increases when the radio resource information of the UE 300 changes dynamically frequently.

Referring again to FIG. 28, when a change to the radio resource allocated to the SeNB 600 is determined, the MeNB 500 requests the UE 300 to reconfigure the RRC connection (S2802). At this time, the RRC connection reconfiguration message transmitted from the MeNB 500 to the UE 300 may include configuration information for the PHY, MAC, and RLC connection between the UE 300 and the SeNB 600. [ Thereafter, when the UE 300 reconfigures the radio resource and transmits an RRC connection reconfiguration completion message to the MeNB 500 (S2803), the MeNB 500 transmits a SeNB reconfiguration completion message to the SeNB 600 and updates the RRC status (S2804).

30 is a flowchart illustrating a SeNB release method of candidate structure 2 according to another embodiment of the present invention.

The SeNB releasing procedure is a procedure for releasing the connection to the terminal of the SeNB 600 according to the control of the MeNB 500 or the request of the SeNB 600. [

First, the 'double connection based communication step (S3001)' and the 'measurement reporting step (S3002)' are the same as the SeNB releasing method of candidate structure 1.

Thereafter, when the MeNB 500 determines to release the SeNB 600, the MeNB 500 releases radio resources of the bearer set in the SeNB 600 (SeNB release request step). In the present invention, the following three types can be considered.

In step S3003 (a), the MeNB 500 determines to release the SeNB 600 and requests release of the radio resources set in the SeNB 600. [ The MeNB 500 requests the SeNB 600 to release the radio resources of the SeNB 600 according to the measurement result received from the UE 300 and transmits the request to the SeNB 600, After releasing the radio resource for the bearer, a response message may be transmitted to the MeNB 500.

Step S3003 (b) is a step for the SeNB 600 to issue a radio resource release command. At this stage, the SeNB 600 instructs the MeNB 500 to release the radio resources of the SeNB 600 according to the result determined by the RRM, and the MeNB 500, which receives the SeNB release command, The radio resources of the base station 300 can be released. Thereafter, the MeNB 500 forwards the RRC Connection Reconfiguration message to the UE 300 for SeNB release. At this time, the RRC connection reconfiguration message transmitted from the MeNB 500 to the UE 300 may include configuration information for releasing the radio bearer of the UE 300 and the SeNB 600. Upon receiving the RRC connection reconfiguration message from the MeNB 500, the UE 300 releases the established radio resource (radio bearer) and transmits a RRC Connection Reconfiguration Complete message to the MeNB 500 (S3004) .

In step S3003 (c), unlike steps S3003a and S3003b, the MeNB 500 arbitrarily releases the radio resources of the SeNB 600 and performs an 'RRC status update step'. Thereafter, the MeNB 500 releases radio resources of the UE 300 for the SeNB 600, and then notifies the SeNB 600 of radio resource release.

The SeNB 600 recognizes that the radio resource is released through the SeNB release message received from the MeNB 500 and performs a radio resource release procedure and then transmits a SeNB Release ACK message to the MeNB 500 do.

Thereafter, the MeNB 500 updates the RRC status (RRC status update step) (S3005), and the UE 300 can perform a single connection-based communication with the MeNB 500 (single connection-based communication step) S3006).

In the candidate structure 2, the buffer status report of the SeNB 600 may follow the SeNB buffer status reporting method of candidate structure 1.

In the following, information exchanged between the MeNB 500, the SeNB 600 and the UE 300 and a method of exchanging the information will be described in order to provide a double connection through the candidate structure 2.

31 is a diagram showing a connection of MeNB 500, SeNB 600 and UE 300 of candidate structure 2 according to another embodiment of the present invention.

31, reference points between MeNB 500 and SeNB 600 are Xn-CP and Xn-UP, and reference points between MeNB 500 and UE 300 are Uu / m, SeNB 600) and UE 300 is Uu / s.

The control plane interface of MeNB (500) and SeNB (600) in the control plane of candidate structure 2 to provide dual connection can provide the following functions.

* SeNB radio resource configuration function to provide dual connection

- SeNB resource setup, SeNB resource change, SeNB resource release

- SeNB resource reconfiguration

- SeNB buffer status reporting

- Flow control between MeNB and SeNB: This function can be performed during flow control using control plane protocol.

* Xn-UP management

- Traffic bearer management function between MeNB and SeNB (that is, setting, changing and releasing of traffic bearer)

* Reporting RLF from SeNB to MeNB

Xn-CP is an application-level signaling protocol that operates based on a SCTP / IP-based transport network similar to X2-CP, and has the same structure as FIG.

Uu / m, which is the control plane interface between the MeNB 500 and the UE 300 to provide a dual connection, can provide the following functions.

* RRC function for dual connection

- RRC connection reconfiguration

SeNB Setup, SeNB Change, and SeNB Release

SeNB reconstruction

- Measurement configuration and reporting

Management for SeNB

Table 7 shows the messages exchanged in Xn-CP and Uu when the dual connection is provided through candidate structure 2.

Protocol Message Descriptions RP IEs Remark SeNB Setup SeNB setup request message Xn-CP -Setup type
-Bearer attribute
-C-RNTI
- Xn-U info.
-Security Key SeNB Setup Ack SeNB Setup Response Message Xn-CP -Result code SeNB Setup Complete SeNB setup complete message Xn-CP RRC Connection Reconfiguration Uu / m -SeNB Addition List
-Cause RRC Connection Reconfiguration Complete Uu / m Packet Transfer Buffered packet delivery request message Xn-CP Packet Transfer Ack Packet Tranfer response message Xn-CP SeNB Release SeNB release request message Xn-CP SeNB Release Ack SeNB Release Response Message Xn-CP SeNB reconfiguration SeNB reconfiguration request message Xn-CP -RB id.
-SeNB Modification List add list SeNB reconfiguration Ack SeNB Reconfiguration Response Message Xn-CP Result Code Resource Status Update SeNB's downlink buffer information reporting message Xn-CP -DL Buffer Status

The information entities included in the messages exchanged in the Xn-CP in Table 7 are in accordance with the information entity definitions in Table 5. [

The user plane interface of the MeNB 500 and the SeNB 600 in the user plane of the candidate structure 2 for providing a double connection, Xn-UP, can provide the following functions.

* Traffic passing between MeNB and SeNB

- Flow control between MeNB and SeNB: This function can be performed during flow control using user plane protocol

Also, Xn-UP operates on the basis of GTP-U / UDP based transmission network similar to X2-UP, and has the same structure as in FIG.

The user plane interface Uu-UP / m between the MeNB 500 and the UE 300 in the user plane of the candidate structure 2 for providing a double connection can provide the following functions.

PDCP PDU management

- ordering and in-sequence delivery of PDCP PDUs;

As described above, according to the embodiment of the present invention, a terminal can be simultaneously connected (double-connected) with at least one base station to receive a service. In this case, the base station that is connected to the terminal is divided into a master base station and a secondary base station. The secondary base station can be connected to, changed, and released from the terminal under the control of the master base station. In particular, even when the RRC and PDCP functions are not included in the secondary base station, the terminal can receive services through the secondary base station according to the RRC and PDCP functions of the master base station.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (20)

There is provided a method for a base station connected to a mobile terminal,
Determining a first one of the plurality of base stations,
Reconfiguring a radio bearer (RB) connection to the terminal and the first base station, and
Performing communication based on the dual connection with the terminal and the first base station
≪ / RTI > The method of claim 1,
Wherein the determining comprises:
Setting up the first base station with a secondary eNB (SeNB) for the terminal
≪ / RTI > 3. The method of claim 2,
Wherein the determining comprises:
Determining the first base station in consideration of a load state of the base station
/ RTI > 3. The method of claim 2,
The step of setting up,
Forwarding an SeNB setup message to the first base station, and
Receiving a response to the SeNB setup message from the first base station
/ RTI > 5. The method of claim 4,
The SeNB setup message includes:
Comprising at least one of C-RNTI information, C-RNTI information, UE bearer attribute information, or UE radio access capability information, How to provide a connection. 5. The method of claim 4,
The response to the SeNB setup message includes:
And a result code generated after a subscription control procedure for whether or not the bearer is set up is performed. The method of claim 1,
Wherein the reconstructing comprises:
Instructing the terminal to connect to the first base station; and
Receiving a completion response to the connection instruction from the terminal
/ RTI > The method of claim 1,
Transmitting a SeNB setup complete message to the first base station after the reconfiguring step
The method further comprising: A method for dual linking a terminal connected to a base station with a first base station different from the base station,
Reconfiguring a radio resource control connection (RRC) connection with the first base station determined by the base station as a secondary eNB (SeNB); and
Performing communication based on the dual connection with the base station and the first base station
≪ / RTI > The method of claim 9,
Wherein the reconstructing comprises:
Receiving a reconfiguration indication from the base station for an RRC connection with the first base station, and
Performing uplink synchronization with the first base station
≪ / RTI > 11. The method of claim 10,
(B) setting up a radio bearer (RB) for the first base station based on the reconfiguration indication after performing the uplink synchronization;
≪ / RTI > 11. The method of claim 10,
Wherein the reconfiguration indication includes advance information associated with random access to the first base station,
The step of performing uplink synchronization comprises:
Performing non-contention-based random access to the first base station
≪ / RTI > 11. The method of claim 10,
The step of performing uplink synchronization comprises:
Performing a contention-based random access to the first base station
≪ / RTI > 11. The method of claim 10,
Wherein the reconstructing comprises:
Transmitting an RRC connection reconfiguration completion message to the base station
≪ / RTI > The method of claim 9,
Prior to the reconstructing step,
Receiving a measurement indication from the base station to discover the first base station, and
Periodically performing a measurement to find the first base station
≪ / RTI > 16. The method of claim 15,
Wherein the measurement instruction includes a setting condition for the first base station,
Reporting the measurement result to the base station if the base station satisfies the set condition
≪ / RTI > A method for changing a secondary base station in a wireless communication system in which a master base station (master eNB, MeNB) and a secondary base station (secondary eNB, SeNB)
Releasing a radio bearer (RB) for the first base station connected as the SeNB and reconfiguring the RB for the second base station to be connected as the SeNB, and
Performing communication based on the dual connection with the master base station and the second base station
/ RTI > The method of claim 17,
Wherein the reconstructing comprises:
Receiving an SeNB change instruction from the master base station to the second base station
/ RTI > The method of claim 18,
Wherein the change indication comprises information about the second base station and a list of secondary cells included in the coverage of the second base station. The method of claim 18,
Wherein the reconstructing comprises:
Buffering uplink data to be transmitted to the first base station, and
Performing uplink synchronization with the second base station
Further comprising:
Wherein the performing the communication comprises transmitting the buffered data to the second base station
/ RTI >

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