WO2014098390A1

WO2014098390A1 - Method for controlling bearer extension in heterogeneous network wireless communication system and apparatus for same

Info

Publication number: WO2014098390A1
Application number: PCT/KR2013/011125
Authority: WO
Inventors: 허강석; 권기범; 안재현; 정명철
Original assignee: 주식회사 팬택
Priority date: 2012-12-20
Filing date: 2013-12-03
Publication date: 2014-06-26
Also published as: KR20140080278A

Abstract

The present invention relates to a method for controlling a bearer extension in a heterogeneous network wireless communication system and an apparatus for same. The present invention discloses a method for supporting a modification of an extended EPS bearer, comprising the steps of: receiving from a macro base station first uplink transmission starting information and first uplink transmission withholding information; receiving from the macro base station a parameter for configuring a radio bearer, which is mapped onto a second extended EPS bearer to be formed between user equipment and a second small base station, and second uplink transmission withholding information; and receiving from the macro base station third uplink transmission withholding information and second uplink transmission starting information.

Description

Bearer extension control method and apparatus therefor in heterogeneous network wireless communication system

The present invention relates to wireless communications, and more particularly, to a method and apparatus for controlling bearer expansion in a heterogeneous network wireless communication system.

A multiple component carrier system refers to a wireless communication system capable of supporting carrier aggregation. Carrier aggregation is a technique for efficiently using fragmented small bands. A base station uses a logically large band by grouping a plurality of physically continuous or non-continuous bands in the frequency domain. It is intended to produce the same effect. The multi-component carrier system supports a plurality of component carriers (CCs) distinguished in the frequency domain. The component carrier includes an uplink component carrier used for uplink and a downlink component carrier used in downlink. One serving cell may be configured by combining the downlink component carrier and the uplink component carrier. Alternatively, one serving cell may be configured only with a downlink component carrier.

In particular areas, such as hot spots inside the cell, there is a great demand for communication, and in certain areas such as cell edges or coverage holes, the reception sensitivity of radio waves may be reduced. With the development of wireless communication technology, small cells, such as pico cells, within a macro cell for the purpose of enabling communication in areas such as hot spots, cell boundaries, and coverage holes. (Pico Cell), femto cell (Femto Cell), micro cell (Micro Cell), remote radio head (RRH), relay (relay), repeater (repeater) is installed together. Such a network is called a heterogeneous network (HetNet). In a heterogeneous network environment, a macro cell is a large coverage cell, and a small cell such as a femto cell and a pico cell is a small coverage cell. Coverage overlap occurs between multiple macro cells and small cells in a heterogeneous network environment.

A terminal connected to a network may communicate with any cell according to a channel environment or a mobile state, and may perform cell change. In the case of cell change, a handover may be performed to solve a problem of call disconnection that occurs when moving to an adjacent cell. Handover refers to a new call channel of an adjacent communication service area when the terminal moves out of the current communication service area (source cell) and moves to an adjacent communication service area (target cell). It is a function that automatically tunes to a traffic channel to maintain a call state continuously. That is, a terminal communicating with a specific base station is linked to another neighboring base station (target base station) when the signal strength of the specific base station (hereinafter referred to as a source base station) is weakened. . For example, the terminal may be disconnected from the macro cell and connected to another macro cell or pico cell due to a deterioration of the channel state while being connected to the macro cell. Alternatively, as the terminal moves in a state of being connected with the macro cell, the terminal may be disconnected from the macro cell and connected to another macro cell or pico cell.

The terminal may perform wireless communication through any one of base stations constituting at least one serving cell. In a heterogeneous network environment, a terminal that is connected to one base station constituting a macro cell may be serviced by the other base station without a handover procedure even when the signal quality of the other base station constituting the small cell is excellent and the radio resource utilization is low. Is not provided. In addition, even if the UE is connected to the base station constituting the small cell through a handover procedure, there is a problem that the handover occurs frequently as the UE moves because the coverage of the small cell is relatively small. This is also the case when the terminal supports the multi-component carrier. Accordingly, there is a need for a method for distributing an excessive load or a load requiring a specific QoS to a small cell without a handover procedure in a heterogeneous network environment and efficiently transmitting data.

An object of the present invention is to provide a method and apparatus for setting and operating a bearer extension in a wireless communication system.

An apparatus and method for replacing an extended EPS bearer of one small cell with an extended EPS bearer of another small cell is provided.

Another technical problem of the present invention is to provide a method for efficient transmission of data to a terminal without generating unnecessary load on a cell in a heterogeneous network environment.

Another technical problem of the present invention is to efficiently transmit data to a terminal through an extension of a radio bearer (RB).

Another technical problem of the present invention is to provide specific data through a small cell to the terminal connected to the macro cell.

Another technical problem of the present invention is to provide a service through a small cell suitable for service operation of a specific Quality of Service (QoS).

Another technical problem of the present invention is to prevent frequent handover of a terminal and provide data seamlessly.

According to an aspect of the present invention, a heterogeneous network system (Heterogeneous Network System) including a plurality of small base station (HeNB) provides a method for supporting the change of the extended EPS (Evolved Packet System) bearer by the terminal. The method includes first uplink transmission start information indicating start of uplink transmission using an EPS bearer of a macro cell formed between the terminal and the macro base station, and a first extended EPS bearer formed between the terminal and the first small base station. Receiving first uplink transmission reservation information indicating reservation for uplink transmission from the macro base station, a radio bearer mapped to a second extended EPS bearer to be formed between the terminal and the second small base station; Receiving a second uplink transmission reservation information from the macro base station, indicating that the uplink transmission using the second extended EPS bearer is reserved, and the EPS bearer of the macro cell. A third uplink transmission reservation information indicating that the uplink transmission is reserved and the second extended EPS bearer; And receiving, from the macro base station, second uplink transmission start information indicating that uplink transmission is started.

According to another aspect of the present invention, a terminal supporting a change of an extended EPS bearer in a heterogeneous network system including a plurality of small base stations is provided. The terminal includes first uplink transmission start information indicating start of uplink transmission using an EPS bearer of a macro cell formed between the terminal and the macro base station, and a first extended EPS bearer formed between the terminal and the first small base station. First uplink transmission reservation information indicating reservation for uplink transmission of a parameter, a parameter for configuring a radio bearer mapped to a second extended EPS bearer to be formed between the terminal and the second small base station, and the second extended EPS bearer Second uplink transmission reservation information indicating the reservation of uplink transmission using the third uplink transmission reservation information indicating the reservation of uplink transmission using the EPS bearer of the macro cell, and the second extended EPS Receive second uplink transmission start information indicating that uplink transmission is started using a bearer from the macro base station And performing uplink transmission to the macro base station based on the terminal receiver, and the first uplink transmission start information and the first uplink transmission reservation information, and performing the third uplink transmission reservation information and the second uplink. And a terminal processor configured to perform uplink transmission using the second extended EPS bearer based on link transmission start information.

According to another aspect of the present invention, there is provided a method for supporting a change of an extended Evolved Packet System (EPS) bearer by a macro base station in a heterogeneous network system including a plurality of small base stations. . The method includes first uplink transmission start information indicating that uplink transmission is started using an EPS bearer of a macro cell formed between the terminal and the macro base station, and a first extended EPS bearer formed between the terminal and the first small base station. Transmitting first uplink transmission reservation information indicating reservation for uplink transmission in a radio bearer mapped to a second extended EPS bearer to be formed between the terminal and a second small base station; Transmitting to the terminal a parameter for configuring a signal and second uplink transmission reservation information indicating reservation for uplink transmission using the second extended EPS bearer, and uplink using the EPS bearer of the macro cell. Start uplink transmission using the third uplink transmission reservation information indicating that the transmission is reserved and the second extended EPS bearer. A second uplink transmission start information indicating a transmitting to the mobile station.

According to still another aspect of the present invention, there is provided a macro base station supporting a change of an extended EPS bearer in a heterogeneous network system including a plurality of small base stations. The macro base station includes first uplink transmission start information indicating start of uplink transmission using an EPS bearer of a macro cell formed between the terminal and the macro base station, and a first extended EPS bearer formed between the terminal and the first small base station. First uplink transmission reservation information indicating reservation for uplink transmission in S2, a parameter for configuring a radio bearer mapped to a second extended EPS bearer to be formed between the terminal and the second small base station, and the second extended EPS Second uplink transmission reservation information indicating suspension of uplink transmission using a bearer, third uplink transmission reservation information indicating suspension of uplink transmission using an EPS bearer of the macro cell, and the second extension Transmitting second uplink transmission start information indicating that uplink transmission is started using an EPS bearer; And a base station transmitter, and performs uplink reception based on the first uplink transmission start information and the first uplink transmission reservation information, and performs the uplink reception reservation information and the second uplink transmission start information. And a base station processor configured to perform uplink reception using the second extended EPS bearer based thereon.

From the viewpoint of the macro cell, the data of the user plane with a large amount of data is continuously transmitted and received through the small cell, thereby distributing the load of the macro cell. In addition, since the terminal does not move to the handover between the small cells, it is possible to reduce the burden or overhead of the handover, it is possible to change the service between the small cells faster than the handover.

1 shows a wireless communication system to which the present invention is applied.

2 shows a structure of a bearer service in a wireless communication system to which the present invention is applied.

3 is a conceptual diagram illustrating a connection configuration between a macro base station and a small base station according to an example of the present invention.

4 is a conceptual diagram illustrating a connection configuration between a macro base station and a small base station according to another embodiment of the present invention.

5 is a flowchart illustrating signaling between a terminal, a macro base station, a first small base station, a second small base station, and a core network according to an embodiment of the present invention.

6 is an operation flowchart of a terminal according to an example of the present invention.

7 is a flowchart illustrating an operation of a macro base station according to an exemplary embodiment of the present invention.

8 is an operation flowchart of a second small base station according to an example of the present invention.

9 is a block diagram illustrating a terminal, a macro base station and a second small base station according to the present invention.

Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings and examples, together with the contents of the present disclosure. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used as much as possible even though they are shown in different drawings. In addition, in describing the embodiments of the present specification, when it is determined that a detailed description of a related well-known configuration or function may obscure the gist of the present specification, the detailed description thereof will be omitted.

In addition, the present specification describes a wireless communication network, the operation performed in the wireless communication network is performed in the process of controlling the network and transmitting data in the system (for example, the base station) that is in charge of the wireless communication network, or the corresponding wireless Work may be done at the terminal coupled to the network.

1 shows a wireless communication system to which the present invention is applied. This may be a network structure of an Evolved-Universal Mobile Telecommunications System (E-UMTS). The E-UMTS system may be referred to as Long Term Evolution (LTE) or LTE-A (Advanced) system. Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, and the like.

On the other hand, there is no limitation on the multiple access scheme applied to the wireless communication system. Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA For example, various multiple access schemes such as OFDM-CDMA may be used.

Here, the uplink transmission and the downlink transmission may use a time division duplex (TDD) scheme that is transmitted using different times, or may use a frequency division duplex (FDD) scheme that is transmitted using different frequencies. .

Referring to FIG. 1, the E-UTRAN includes a base station (BS) 20 that provides a control plane and a user plane to a user equipment (UE). The user plane is a protocol stack for user data transmission, and the control plane is a protocol stack for control signal transmission. The terminal 10 may be fixed or mobile and may be called by other terms such as mobile station (MS), advanced MS (AMS), user terminal (UT), subscriber station (SS), and wireless device (Wireless Device). .

The base station 20 generally refers to a station communicating with the terminal 10, and includes an evolved-NodeB (eNodeB), a Base Transceiver System (BTS), an Access Point, an femto-eNB, It may be called other terms such as a pico-eNB, a home eNB, and a relay. The base station 20 may provide at least one cell to the terminal. The cell may mean a geographic area where the base station 20 provides a communication service or may mean a specific frequency band. The cell may mean a downlink frequency resource and an uplink frequency resource. Alternatively, the cell may mean a combination of a downlink frequency resource and an optional uplink frequency resource.

The base stations 20 may be connected to each other through an X2 interface. The base station 20 is connected to a Serving Gateway (S-GW) through an MME (Mobility Management Entity) and an S1-U through an Evolved Packet Core (EPC) 30, more specifically, an S1-MME through an S1 interface. The S1 interface exchanges OAM (Operation and Management) information for supporting the movement of the terminal 10 by exchanging signals with the MME.

EPC 30 includes MME, S-GW and P-GW (Packet Data Network-Gateway). The MME has access information of the terminal 10 or information on the capability of the terminal 10, and this information is mainly used for mobility management of the terminal 10. The S-GW is a gateway having an E-UTRAN as an endpoint, and the P-GW is a gateway having a PDN (Packet Data Network) as an endpoint.

Integrating the E-UTRAN and the EPC 30 may be referred to as an EPS (Evoled Packet System), and the traffic flows from the radio link that the terminal 10 accesses the base station 20 to the PDN connecting to the service entity are all IP. It works based on (Internet Protocol).

The radio interface between the terminal and the base station is called a Uu interface. Layers of the radio interface protocol between the terminal and the network are based on the lower three layers of the Open System Interconnection (OSI) reference model, which is widely known in communication systems. L2 (second layer), L3 (third layer) can be divided into a physical layer belonging to the first layer of the information transfer service (Information Transfer Service) using a physical channel (Physical Channel), The RRC (Radio Resource Control) layer located in the third layer plays a role of controlling radio resources between the terminal and the network. To this end, the RRC layer exchanges an RRC message between the terminal and the base station.

A physical layer (PHY) layer provides an information transfer service to a higher layer by using a physical channel. The physical layer is connected to the upper layer Medium Access Control (MAC) layer through a transport channel. Data is moved between the MAC layer and the physical layer through the transport channel. Transport channels are classified according to how and with what characteristics data is transmitted over the air interface. Data moves between the physical layers, that is, between the physical layers of the transmitter and the receiver. The physical channel may be modulated by an orthogonal frequency division multiplexing (OFDM) scheme and utilizes time and frequency as radio resources. There are several physical control channels. The physical downlink control channel (PDCCH) informs the terminal of resource allocation of a paging channel (PCH) and downlink shared channel (DL-SCH) and hybrid automatic repeat request (HARQ) information related to the DL-SCH. The PDCCH may carry an uplink scheduling grant informing the UE of resource allocation of uplink transmission. The physical control format indicator channel (PCFICH) informs the UE of the number of OFDM symbols used for PDCCHs and is transmitted every subframe. PHICH (physical Hybrid ARQ Indicator Channel) carries a HARQ ACK / NAK signal in response to uplink transmission. Physical uplink control channel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request, and CQI for downlink transmission. Physical uplink shared channel (PUSCH) carries an uplink shared channel (UL-SCH).

The functions of the MAC layer include mapping between logical channels and transport channels and multiplexing / demultiplexing into transport blocks provided as physical channels on transport channels of MAC service data units (SDUs) belonging to the logical channels. The MAC layer provides a service to a Radio Link Control (RLC) layer through a logical channel. The logical channel may be divided into a control channel for transmitting control region information and a traffic channel for delivering user region information.

Functions of the RLC layer include concatenation, segmentation, and reassembly of RLC SDUs. In order to guarantee the various quality of service (QoS) required by the radio bearer (RB), the RLC layer has a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (Acknowledged Mode). Three modes of operation (AM). AM RLC provides error correction through an automatic repeat request (ARQ).

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

The RRC layer is responsible for the control of logical channels, transport channels, and physical channels in connection with configuration, re-configuration, and release of RBs. RB means a logical path provided by the first layer (PHY layer) and the second layer (MAC layer, RLC layer, PDCP layer) for data transmission between the terminal and the network. The configuration of the RB means a process of defining characteristics of a radio protocol layer and a channel to provide a specific service, and setting each specific parameter and operation method. The RB may be further classified into a signaling RB (SRB) and a data RB (DRB). SRB is used as a path for transmitting RRC and NAS messages in the control plane, and DRB is used as a path for transmitting user data in the user plane.

The non-access stratum (NAS) layer located above the RRC layer performs functions such as session management and mobility management.

If there is an RRC connection between the RRC layer of the UE and the RRC layer of the E-UTRAN, the UE is in an RRC connected state, otherwise it is in an RRC idle state. do.

In order for a terminal to transmit user data (eg, an IP packet) to an external internet network or to receive user data from an external internet network, the terminal exists between mobile communication network entities existing between the terminal and the external internet network. Resources must be allocated to different paths. Thus, a path in which resources are allocated between mobile communication network entities and data transmission and reception is possible is called a bearer.

Referring to FIG. 2, an end-to-end service is provided between a terminal and an internet network. Here, the end-to-end service refers to a service that requires a path between the terminal and the P-GW (EPS Bearer) and a P-GW and an external bearer for the Internet network and data service. Here, the external path is a bearer between the P-GW and the Internet network.

In order for the terminal to transmit data to the external internet network, the terminal first transmits data to the base station eNB through the RB on the radio. The base station then transmits data to the S-GW through the S1 bearer. S-GW transmits data to P-GW through S5 / S8 bearer, and finally through external bearer to destinations in P-GW and external internet network.

Similarly, in order to transmit data from the external Internet network to the terminal, the data can be delivered to the terminal through each bearer in the reverse direction as described above.

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

The bearers provided by the wireless communication system are collectively called an Evolved Packet System (EPS) bearer. An EPS bearer is a delivery path established between a UE and a P-GW for transmitting IP traffic with a specific QoS. The P-GW may receive IP flows from the Internet or send IP flows to the Internet. Each EPS bearer is set with QoS decision parameters that indicate the nature of the delivery path. One or more EPS bearers may be configured per UE, and one EPS bearer uniquely represents a concatenation of one E-RAB and one S5 / S8 bearer.

The S5 / S8 bearer is a bearer of the S5 / S8 interface. Both S5 and S8 are bearers present at the interface between the S-GW and the P-GW. The S5 interface exists when the S-GW and the P-GW belong to the same operator, and the S8 interface belongs to the provider (Visited PLMN) roamed by the S-GW, and the P-GW has subscribed to the original service (Home). PLMN).

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

RB means two types of data RB (Data Radio Bearer (DRB)) and signaling RB (Signaling Radio Bearer (SRB)). However, in the present invention, the expression RB without distinction refers to data RB provided in the Uu interface to support a service of a user. to be. Therefore, an RB expressed without distinction is distinguished from a signaling radio bearer (SRB). The RB is a path through which data of the user plane is transmitted, and the SRB is a path through which data of the control plane, such as the RRC layer and NAS control messages, are delivered. One-to-one mapping is established between RB, E-RAB and EPS bearer.

EPS bearer types include a default bearer and a dedicated bearer. When the terminal accesses the wireless communication network, an IP address is assigned and a default EPS bearer is created while creating a PDN connection. That is, a default bearer is first created when a new PDN connection is created. When a user uses a service (for example, the Internet, etc.) through a default bearer, and uses a service (for example, VoD, etc.) that the default bearer cannot provide QoS properly, the user may be on-demand. A dedicated bearer is created. In this case, the dedicated bearer may be set to a different QoS from the bearer that is already set. QoS decision parameters applied to the dedicated bearer are provided by a Policy and Charging Rule Function (PCRF). Upon creation of a dedicated bearer, the PCRF may receive subscription information of a user from a Subscriber Profile Repository (SPR) to determine QoS determination parameters. Up to 15 dedicated bearers may be created, for example, and four of the 15 are not used in the LTE system. Therefore, up to 11 dedicated bearers can be created.

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

In general, since a small cell serves a smaller area than a macro cell, it is advantageous to a macro cell in terms of throughput that can be provided for a single terminal. However, in the current wireless communication system, even though the terminal connected to the macro cell is located in the service area of the small cell, the terminal cannot receive the service from the small cell without performing the handover. In addition, even if the UE is connected to the small cell through handover, the handover may occur frequently because the small cell coverage is small, which is not preferable in terms of network efficiency.

Hereinafter, embodiments of the present invention will be described in detail, and embodiments of the present invention can be applied to a heterogeneous network system including a macro cell and a small cell.

One embodiment includes a method of distributing a data service or a load through a first small cell to a second small cell while maintaining an EPS bearer including a wireless connection between a terminal and a macro cell in a heterogeneous network system. For example, the method may be applied when the terminal connected to the macro cell is located in an area over-laid with the service area of the macro cell, the service area of the first small cell and the second small cell. This method is referred to as a procedure for configuring multiple wireless connections. Alternatively, the method may be called an extended bearer establishment procedure or a bearer extension procedure.

More specifically, in the bearer extension mode, the control plane (RRC layer, NAS) for the terminal is provided by the macro cell, and the user plane is provided by the EPS bearer of the small cell.

Accordingly, in the second small cell area existing in an area overlapped with the first small cell, the UE disconnects the downlink signal from the first small cell or the second small cell without handover in a state of being connected to the macro cell. It can be received without, or the uplink signal can be transmitted without interruption. Here, the downlink signal includes data of the user plane transmitted through the downlink, and the uplink signal includes data of the user plane transmitted through the uplink. Data in the control plane is transmitted and received through the macro cell.

Referring to FIG. 3, data is transmitted from the packet data network 300 (eg, the Internet) to the P-GW 305, and the data is transmitted to the macro base station 320 via the S-GW 310. QoS for the data may be set at a particular level. The macro base station 320 and the terminal 340 are configured with an EPS bearer of the macro cell.

The macro base station 320 includes an RRC entity 321, a PDCP entity 322, an RLC entity 323, a MAC entity 324, and a PHY layer 325. The small base station 330 includes a PDCP entity 332, an RLC entity 333, a MAC entity 334, and a PHY layer 335.

In normal mode without bearer extension, macro base station 320 receives the data at PDCP entity 322, processes the data based on control of RRC entity 321, and the like, and performs RLC entity ( 323, the MAC entity 324 and the PHY layer 325 to the terminal 340. Although not shown in the figure, there are entities forming the EPS bearer of the macro cell in the terminal 340. For example, PDCP entity, RRC entity, RLC entity corresponding to PDCP entity 322, RRC entity 321, RLC entity 323, MAC entity 324, and PHY layer 325 of macro base station 320, respectively. The MAC entity and the PHY layer exist on the terminal 340 side.

On the other hand, when the terminal 340 exists in the macro cell only area and moves to the overlapped small cell area, when there is a large amount of traffic in the macro cell or the terminal needs to receive user data of good quality (QoS) In addition, extended EPS bearers for the small base station 330 and the terminal 340 may be generated. The creation of the extended EPS bearer is made by the above-described extended bearer setup procedure. An operation mode of the small base station 330 and the terminal 340 after the extended EPS bearer is generated is called a bearer extended mode.

In bearer extension mode, the S-GW 310 may forward the data to the PDCP entity 332 of the small base station 330 via the backhaul network. The RLC entity 333 of the small base station 330 then transmits it to the terminal 340 via the MAC entity 334 and the PHY layer 335. Although not shown in the figure, entities that form an extended EPS bearer are also created in the terminal 340. For example, PDCP entity, RRC entity, RLC entity, MAC entity and PHY layer corresponding to PDCP entity 332, RLC entity 333, MAC entity 334 and PHY layer 335 of small base station 330, respectively. This is present on the terminal 340 side.

In this case, the terminal 340 may receive the service through the EPS bearer of the small base station 330 that the service is provided through the EPS bearer of the macro base station 320. Here, the control plane (RRC layer, NAS) for the terminal is provided by the macro cell, the user plane is provided by the extended EPS bearer of the small cell.

As described above, in generating the extended EPS bearer, the present embodiment includes an operation of maintaining the EPS bearer of the macro cell without deleting it. According to this, the following effects are obtained.

First, if the EPS bearer of the macro cell is deleted while the extended EPS bearer is not completely completed in the radio section and the core network section, the user data exchanged between the terminal and the core network is transmitted to the base station or the core. There is a problem that a large amount of user data must be exchanged through the interface between the macro cell and the small cell or buffered at the network side. This problem can be solved.

Second, if the terminal frequently moves between the macro cell and the small cell for a short time in the boundary region of the macro cell and the small cell, such as a ping-pong phenomenon, the radio configuration such as handover is frequently changed. There is a problem that must be given. For example, when the UE moves from the macro cell to the overlapped region, the EPS bearer of the macro cell may be released, and again when the UE returns to the macro cell within a short time, the EPS bearer of the macro cell may be generated again. . However, this may cause signaling overhead between the terminal and the base station. However, according to the present embodiment, since the terminal can easily reuse it at any time while maintaining the EPS bearer of the macro cell until the terminal is completely determined as a macro cell or a small cell, it is possible to stably provide a data transmission / reception service of the terminal. For example, if the extended EPS bearer is deleted because the terminal is out of the coverage of the small cell (or the use of the extended EPS bearer is stopped), it can be quickly reused without resetting the radio configuration corresponding to the EPS bearer of the macro cell. have.

Third, the terminal does not need to perform a random access procedure accompanying the handover, and thus does not cause service interruption in the wireless section during random access. In addition, there is no need to exchange a large amount of UE context information of the X2 interface between the base station and the base station, which was necessary for performing the handover.

Fourth, when the terminal receives the user data through the small cell rather than the macro cell, it is possible to reduce the load of the macro cell while providing a better quality of service. Although FIG. 3 shows only data transmission in the downlink direction with an arrow, the technical content of FIG. 3 may be similarly applied to data transmission in the uplink direction.

Referring to FIG. 4, the transmission and reception of data in the control plane is provided by the macro base station 400 to the terminal 450 through the macro cell. The macro base station 420 includes an RRC entity 421, a PDCP entity 422, an RLC entity 423, a MAC entity 424, and a PHY layer 425. And unlike FIG. 3, two extended EPS bearers are supported. To this end, two

small base stations

430 and 440 which provide data of a user plane are disposed. The terminal 450 may use any one of two extended EPS bearers of two small cells for transmitting and receiving data of a user plane.

The first small base station 440, which provides the first extended EPS bearer to the terminal 450 through the small cell A, provides the PDCP entity 432, the RLC entity 433, the MAC entity 434, and the PHY layer 435. Include. The second small base station 440, which provides the second extended EPS bearer to the terminal 450 through the small cell B, provides the PDCP entity 442, the RLC entity 443, the MAC entity 444, and the PHY layer 445. Include.

In transmitting or receiving data of the user plane, the terminal 450 uses the first extended EPS bearer of the small cell A, and changes the service to the second extended EPS bearer of the small cell B, which is of higher quality as it moves. Can be provided. An example of a scenario in which the change of the extended EPS bearer occurs includes the case where the terminal 450 exists in the area of the small cell A and subsequently moves to the area of the small cell B adjacent thereto.

Accordingly, when the first extended EPS bearer is used, the S-GW 410 may forward data of the user plane to the PDCP entity 432 of the first small base station 430 through the backhaul network. Thereafter, the RLC entity 433 of the first small base station 430 transmits it to the terminal 450 through the MAC entity 434 and the PHY layer 435. Although not shown in the figure, entities 450 forming the first extended EPS bearer together with the first small base station 430 are generated in the terminal 450.

When the UE moves to the small cell B, an EPS bearer or a second extended EPS bearer of the macro cell may be used instead of the first extended EPS bearer. That is, replacement (or replacement) of the extended EPS bearer may occur. When the second extended EPS bearer is used due to the replacement of the extended EPS bearer, the S-GW 410 may forward the data of the user plane to the PDCP entity 442 of the second small base station 440 via the backhaul network. . The RLC entity 443 of the second small base station 440 then transmits it to the terminal 450 via the MAC entity 444 and the PHY layer 445. Although not shown in the figure, entities 450 forming the second extended EPS bearer together with the second small base station 440 are generated in the terminal 450.

In this case, from a macro cell point of view, for a relatively short time from the data of the user plane with a large amount of data until the change is completed from the use of the first extended EPS bearer of small cell A to the use of the second extended EPS bearer of small cell B. After the EPS bearer of the macro cell is used and the change is completed, the macro cell load is distributed by continuously transmitting and receiving through the small cell. In addition, since the terminal 450 does not move to the handover between the small cells, it is possible to reduce the burden or overhead of the handover, it is possible to change the service between the small cells faster than the handover. This is because there is no service interruption in the radio section that occurs during the execution of the random access procedure. Here, the overhead of handover includes a random access procedure required for handover and the exchange of a large amount of UE context information through the X2 interface between the base station and the base station.

Referring to FIG. 5, small cell A is a small cell provided by a first small base station, and small cell B is a small cell provided by a second small cell. Currently, the terminal uses a first extended EPS bearer that provides data of a user plane by a first small base station.

The terminal measures the signal strength of the macro cell, small cell A, small cell B, and transmits a measurement report (measurement report) to the macro base station if the measured signal strength satisfies a specific criterion (S500). For example, if the measured signal strength satisfies a specific criterion, the signal strengths of the macro cell and the small cell B should be as small as the threshold while the signal strength of the macro cell is as large as the threshold. In addition to the above conditions, other conditions that may determine that the UE is located in the macro cell and move from the small cell A to the small cell B are possible.

The macro base station analyzes the signal strength according to the measurement report. If the signal strength of the macro cell is greater than the signal strengths of the small cell A and the small cell B and the signal strength of the small cell B is greater than the signal strength of the small cell A, the macro base station determines that the terminal is within the coverage of the small cell A. It can be determined from the small cell B to move from.

In this case, the macro base station determines to generate a second extended EPS bearer to use in place of the first extended EPS bearer in the small cell B. Here, the condition that the macro base station determines to generate the second extended EPS bearer is, for example, the signal of the small cell B is greater than a certain value greater than the signal of the small cell A, or the signal strength of the small cell B is greater than the specific threshold. It can be time.

If the macro base station decides to create and use a second extended EPS bearer without using the first extended EPS bearer anymore, the first base station indicates to start uplink transmission using the EPS bearer of the suspended macro cell. The RRC connection reconfiguration message is transmitted to the terminal (S505). The reason for using the EPS bearer of the macro cell, which has been discontinued for data of the user plane, is to reuse the EPS bearer of the macro cell until the second extended EPS bearer is completed. This is because the UE needs the EPS bearer for uplink transmission until the generation of the second extended EPS bearer is completed in both the radio period and the core network period. In addition, when the generation of the second extended EPS bearer is not completely completed in the wireless section and the core network section, when transmitting and receiving using the second extended EPS bearer of the small cell B, the user data exchanged between the terminal and the core network is transmitted to the macro base station. This is because there is a problem that a large amount of data must be exchanged through buffering in the core network or through an interface between the macro cell and the small cell. Step S505 is not signaling to directly generate a second extended EPS bearer, but is performed as a preliminary step.

Meanwhile, as data of the user plane is transmitted and received through the EPS bearer of the macro cell, uplink transmission in the existing first extended EPS bearer should be stopped. In this sense, the first RRC connection reconfiguration message may indicate an interruption of uplink transmission in the existing first extended EPS bearer.

As a first embodiment, the first RRC connection reconfiguration message may include UL Tx reservation information (ULTxStopInfo) indicating to stop uplink transmission using the first extended EPS bearer. In other words, the first RRC connection reconfiguration message may include UL Tx reservation information meaning that no uplink transmission is performed using the first extended EPS bearer. This is because the creation of the second extended EPS bearer is not completed in all sections from the terminal to the core network.

As a second embodiment, the first RRC connection reconfiguration message may include UL TX start information (ULTxStartInfo) indicating that uplink transmission is started using the EPS bearer of the macro cell.

As a third embodiment, the first RRC connection reconfiguration message may include a UE identifier, an EPS bearer identifier of a macro cell, and a first extended EPS bearer identifier. The terminal identifier is an identification number for identifying the terminal and may include a Cell-Radio Network Temporary Identifier (C-RNTI), an International Mobile Subscriber Identity (IMSI), a Globally Unique Temporary Identity (GUTI), and the like.

In addition, the first RRC connection reconfiguration message may include information according to the combination of the first embodiment and the second embodiment, may include information according to the combination of the first embodiment and the third embodiment, and the second embodiment. It may include information according to a combination of an example and a third embodiment, or may include information according to a combination of the first to third embodiments.

This embodiment is not limited to the transmission of the UL Tx reservation information or the UL TX start information included in the first RRC connection reconfiguration message. That is, the UL Tx reservation information and the UL TX start information may be transmitted independently of the first RRC connection reconfiguration message.

Upon receiving the first RRC connection reconfiguration message, the UE no longer uses the first extended EPS bearer when transmitting uplink data (ie, suspends uplink transmission using the first extended EPS bearer), and the macro cell of the macro cell. EPS bearers can be used.

The macro base station transmits EPS bearer control information to the core network (MME, S-GW, P-GW) (S510). The P-GW finally receives EPS bearer control information. Downlink data of the user plane received from the UE is transmitted to the terminal using the EPS bearer of the macro cell instead of the first extended EPS bearer The EPS bearer control information may be, for example, the terminal identifier, the EPS bearer identifier of the macro cell, and the first. It may include at least one of the extended EPS bearer identifier.

The terminal completes the radio configuration based on the first RRC connection reconfiguration message, and transmits the first RRC connection reconfiguration complete message to the macro base station (S515). Step S515 may be performed before step S505.

The terminal may provide a smooth service to the terminal by reusing the EPS bearer of the macro cell based on the first RRC connection reconfiguration message and the EPS bearer control information. For example, even when the signal strength of the small cell A deteriorates rapidly in the process of generating the second extended EPS bearer, the terminal may receive a stable service through the EPS bearer of the macro cell.

Apart from reusing the EPS bearer of the macro cell, the UE must create a second extended EPS bearer. This is a bearer extension procedure, and the macro base station transmits a bearer extension request message to the second small base station (S520). The bearer extension request message may be transmitted from the macro base station to the second small base station through the X2 interface. Receiving the bearer extension request message, the second small base station interprets the second extended EPS bearer to be used in place of the first extended EPS bearer indicated by the extended EPS bearer identifier in the bearer extension request message to satisfy the given QoS information. do.

The bearer extension request message may include at least one information element (IE). For example, the information element may be a UE identifier or an EPS bearer identifier of a macro cell, a first extended EPS bearer identifier of a small cell A, or a QoS decision parameter.

The terminal identifier is an identification number for identifying the terminal and may include a Cell-Radio Network Temporary Identifier (C-RNTI), an International Mobile Subscriber Identity (IMSI), a Globally Unique Temporary Identity (GUTI), and the like.

The EPS bearer identifier of the macro cell is information for identifying the EPS bearer of the macro cell formed between the macro base station and the terminal.

The first extended EPS bearer identifier of the small cell A is information for identifying the EPS bearer of the small cell A formed between the small base station A and the terminal.

The QoS determination parameter is a parameter used to determine the QoS to be expected for the extended EPS bearer or the QoS applied to the EPS bearer of the macro cell. QoS determination parameters include, for example, values that can characterize QoS, such as QoS Class Identifiers (QCI), Guaranteed Bit Rate (GBR) QoS information, and Maximum Bit Rate (MBR).

QCI is a scalar that is used as a reference to access node-specific parameters that control bearer level packet forwarding treatment, and the scalar value is assigned to an operator owning a base station. Pre-configured by For example, the scalar may be preconfigured with any one of integer values 1 to 9. The main purpose of ARP is to determine whether a bearer's establishment / modification request is accepted or needs to be rejected in case of resource limitations. ARP may also be used to determine which bearer (s) to drop by the base station at exceptional resource limitations, for example at handover.

GBR means that fixed resources are allocated for each bearer (bandwidth guarantee). On the other hand, non-GBR has an aggregated maximum bit rate (AMBR) as a QoS decision parameter in addition to QCI and ARP, and instead of not being allocated resources per bearer, it is allocated the maximum bandwidth that can be used like other non-GBR bearers. Means.

Upon receiving the bearer extension request message, the second small base station extracts information elements included in the bearer extension request message. And the second small base station is configured to satisfy the QoS determination parameter by the terminal identified by the terminal identifier instead of the EPS bearer identified by the EPS bearer identifier of the macro cell or instead of the first extended EPS bearer of small cell A. 2 prepare a procedure for generating an extended EPS bearer with the core network side (S525).

For example, the second small base station and the core network determine an identifier of the second extended EPS bearer and an E-RAB identifier associated with the second extended EPS bearer identifier. Then, a preparation operation necessary for using the newly created second extended EPS bearer and the E-RAB in place of the first extended EPS bearer is performed.

The second small base station transmits a bearer extension response message including radio configuration parameter values satisfying QoS of the second extended EPS bearer and the associated E-RAB to the macro base station (S530). The bearer extension response message is a message informing the UE of the availability or activation of the second extended EPS bearer. This may include messages coming from the core network. The X2 interface may be used for delivery of the bearer extension response message.

In a first embodiment, the radio configuration parameter values included in the bearer extension response message are parameters configuring an RB, and may include system information, PHY, and MAC layer information necessary to provide a service to a terminal on a small cell B. have.

As a second embodiment, the bearer extension response message includes a terminal identifier, system information of small cell B, physical layer information of small cell B, information of MAC layer of small cell B, EPS bearer identifier of macro cell, and second extended EPS bearer. It may include at least one of the identifier.

As a third embodiment, the bearer extension response message includes parameters for DRB configuration, for example, DRB identifier (drb-Identity), PDCH configuration information (pdcp-Config), RLC configuration information (rlc-Config), and second extension. It may further include at least one of the EPS bearer identifier.

In addition, the bearer extension response message may include information according to the combination of the first embodiment and the second embodiment, may include information according to the combination of the first embodiment and the third embodiment, and The information according to the combination of the third embodiment may be included, or the information according to the combination of the first to third embodiments may be included.

The macro base station transmits to the terminal a second RRC connection reconfiguration message indicating the radio resource configuration of the terminal using the values received through the bearer extension response message (S535). The second RRC connection reconfiguration message includes control information required between the second small base station and the terminal to complete the second extended EPS bearer.

As a first embodiment, the second RRC connection reconfiguration message may include UL Tx reservation information (ULTxSuspendInfo) indicating suspending uplink transmission using the second extended EPS bearer. In other words, the second RRC connection reconfiguration message may include UL Tx reservation information meaning that no uplink transmission is performed using the second extended EPS bearer. This is because when the creation of the second extended EPS bearer is not completed in the entire period from the terminal to the core network, when the second extended EPS bearer is used, the user data exchanged between the terminal and the core network is buffered at the macro base station or core network side. This may be a problem because a large amount of data must be exchanged through an interface between the macro base station and the second small base station. However, the uplink transmission may not include transmission of PUCCH and HARQ ACK / NACK information. In other words, despite the UL Tx reservation information, the terminal may transmit the PUCCH and HARQ ACK / NACK information.

As a second embodiment, the second RRC connection reconfiguration message may include all radio configuration parameter values of the bearer extension response message and an identifier of the second extended EPS bearer.

As a third embodiment, the second RRC connection reconfiguration message may include detailed information indicating availability or activation of a second extended EPS bearer formed between the second small base station and the terminal.

As a fourth embodiment, the second RRC connection reconfiguration message includes a dedicated NAS list (dedicatedInfoNASList) information element used for transferring UE specific NAS layer information between the core network and the terminal. The dedicated NAS list information element may include detailed information indicating availability or activation of a second extended EPS bearer formed between the second small base station and the terminal.

In addition, the second RRC connection reconfiguration message may include information according to the combination of the first embodiment and the second embodiment, may include information according to the combination of the first embodiment and the third embodiment, and the first embodiment. It may include information according to a combination of an example and a fourth embodiment, may include information according to a combination of a second embodiment and a third embodiment, and may include information according to a combination of a second embodiment and a fourth embodiment. In addition, the information according to the combination of the third and fourth embodiments may be included, and the information according to the combination of the first to fourth embodiments may be included.

This embodiment is not limited to the transmission of the UL Tx reservation information (ULTxSuspendInfo) included in the second RRC connection reconfiguration message. That is, the UL Tx reservation information may be transmitted independently of the second RRC connection reconfiguration message.

The terminal completes the radio configuration with the second small base station based on the second RRC connection reconfiguration message, and the macro base station receives a second RRC connection reconfiguration complete message indicating that the radio configuration corresponding to the second extended EPS bearer has been successfully completed. It transmits to (S540).

The terminal receiving the UL Tx reservation information may transmit and process uplink (UL) data through the EPS bearer of the macro cell since the second extended EPS bearer is not yet completed in the core network. That is, in the preparation preparation step of generating the second extended EPS bearer, the terminal performs uplink transmission using the EPS bearer of the macro cell remaining without being deleted. However, the UE may transmit PUCCH and HARQ ACK / NACK information using the second extended EPS bearer as an exception. The UE can receive and process downlink (DL) data through the EPS bearer of the macro cell.

As such, although the radio configuration is completed in the terminal (that is, the RB configuration is completed) and the second extended EPS bearer can be used, the reason why the uplink transmission is still performed through the EPS bearer of the macro cell is to ensure the reliability of the uplink transmission. to be. This is because the UE may move to the small cell B and then move to the area of the small cell A or the macro cell only.

The macro base station transmits an RB generation complete message indicating that generation of the RB is completed between the terminal and the second small base station to the second small base station (S545). The RB creation complete message is a message transmitted through the X2 interface. Upon receiving the RB generation complete message, the second small base station may confirm that the configuration of the RB corresponding to the second extended EPS bearer is successfully completed. Finally, generation of the RB is completed between the terminal and the second small base station (S550).

The second small base station completes generation of the second extended EPS bearer for the core network (S555). After the second extended EPS bearer is created in the core network, among the components of the core network, the P-GW starts to transmit user data coming from the PDN through the P-GW toward the terminal to the terminal using the second extended EPS bearer. do. Then, the second small base station transmits the user data flowing through the P-WG to the terminal using a second extended EPS bearer (S560). Since generation of the RB is completed between the second small base station and the terminal, the second small base station has no problem in transmitting the user data to the terminal through the second extended EPS bearer, and the terminal also transmits the user data through the second extended EPS bearer. There is no problem to receive.

If it is confirmed that generation of the second extended EPS bearer for the core network is completed, the macro base station transmits a third RRC connection reconfiguration message to the UE indicating that the second extended EPS bearer starts uplink transmission (S565). ). Accordingly, the UE can perform uplink transmission using the second extended EPS bearer (S570).

As an example, the third RRC connection reconfiguration message indicates UL Tx reservation information (ULTxSuspendInfo) indicating that the uplink transmission is suspended in the EPS bearer of the macro cell and uplink transmission is started in the second extended EPS bearer. UL Tx start information (ULTxStartInfo) is included.

As another example, the third RRC connection reconfiguration message may include UL Tx reservation information indicating that the uplink transmission is suspended in the EPS bearer of the macro cell, and UL indicating that the uplink transmission is started in the second extended EPS bearer. It may include Tx start information (ULTxStartInfo), an identifier of the EPS bearer of the macro cell, and an identifier of the second extended EPS bearer.

This embodiment is not limited to the UL Tx reservation information and the UL Tx start information (ULTxStartInfo) included in the third RRC connection reconfiguration message and transmitted. That is, the UL Tx reservation information and the UL Tx start information may be transmitted independently of the third RRC connection reconfiguration message.

The first small base station and the core network perform an operation for releasing the first long EPS bearer (S575).

Although the signaling between the terminal, the macro base station, the first and the second small base station according to the embodiment of FIG. 5 has been described as including step S565, another embodiment of the present invention instead of transmitting the third RRC connection reconfiguration message of step S565. May include transmission of the PDCCH. That is, the terminal may receive downlink assignment information (downlink assignment) from the small base station through the PDCCH, the terminal may determine that uplink transmission is also possible. Therefore, when uplink transmission is required, the UE may perform uplink transmission through the second extended EPS bearer.

6 is an operation flowchart of a terminal according to an example of the present invention. Here, small cell A is a small cell provided by the first small base station, and small cell B is a small cell provided by the second small cell. It is currently assumed that the terminal uses a first extended EPS bearer that provides data of a user plane by a first small base station.

Referring to FIG. 6, the terminal measures signal strengths of the macro cell, the small cell A, and the small cell B, and transmits a measurement report to the macro base station when the measured signal strength satisfies a specific criterion (S600). For example, if the measured signal strength satisfies a specific criterion, the signal strengths of the macro cell and the small cell B should be as small as the threshold while the signal strength of the macro cell is as large as the threshold. In addition to the above conditions, other conditions that may determine that the UE is located in the macro cell and move from the small cell A to the small cell B are possible.

If the macro base station decides to create and use the second extended EPS bearer without using the first extended EPS bearer anymore, the terminal indicates that the uplink transmission is started using the EPS bearer of the suspended macro cell. The first RRC connection reconfiguration message is received from the macro base station (S605). Step S605 is not signaling to directly generate a second extended EPS bearer, but is performed as a preliminary step.

As a first embodiment, the first RRC connection reconfiguration message may include UL Tx reservation information (ULTxSuspendInfo) indicating reservation for uplink transmission using the first extended EPS bearer. In other words, the first RRC connection reconfiguration message may include UL Tx reservation information meaning that no uplink transmission is performed using the first extended EPS bearer. This is because the creation of the second extended EPS bearer is not completed in all sections from the terminal to the core network.

This embodiment is not limited to the transmission of the UL Tx reservation information or the UL TX start information included in the first RRC connection reconfiguration message. That is, the UL Tx reservation information and the UL TX start information may be received independently of the first RRC connection reconfiguration message.

The terminal completes the radio configuration based on the first RRC connection reconfiguration message, and transmits the first RRC connection reconfiguration complete message to the macro base station (S610).

The terminal receives from the macro base station a second RRC connection reconfiguration message indicating the radio resource configuration of the terminal using the values received through the bearer extension response message (S615). The second RRC connection reconfiguration message includes control information required between the second small base station and the terminal to complete the second extended EPS bearer.

The terminal completes the radio configuration with the second small base station based on the second RRC connection reconfiguration message, and the macro base station receives a second RRC connection reconfiguration complete message indicating that the radio configuration corresponding to the second extended EPS bearer has been successfully completed. Transmit to (S620).

When the second small base station confirms that the configuration of the RB corresponding to the second extended EPS bearer is successfully completed, the generation of the RB is completed between the terminal and the second small base station. When the generation of the second extended EPS bearer until the core network is completed, the terminal starts receiving the user data coming in through the P-GW from the PDN toward the terminal using the second extended EPS bearer (S625). Since generation of the RB is completed between the second small base station and the terminal, the second small base station has no problem in transmitting the user data to the terminal through the second extended EPS bearer, and the terminal also transmits the user data through the second extended EPS bearer. There is no problem to receive.

When generation of the second extended EPS bearer for the core network is completed, the terminal receives a third RRC connection reconfiguration message from the macro base station instructing the terminal to start uplink transmission in the second extended EPS bearer (S630). Accordingly, the UE may perform uplink transmission using the second extended EPS bearer (S635).

As another example, the third RRC connection reconfiguration message may include UL Tx reservation information indicating that the uplink transmission is reserved by the EPS bearer of the macro cell, and UL Tx start information indicating that the uplink transmission is started by the second extended EPS bearer. (ULTxStartInfo), the identifier of the EPS bearer of the macro cell, and the identifier of the second extended EPS bearer.

Although the signaling between the UE, the macro base station, and the first and second small base stations according to the embodiment of FIG. 6 has been described as including step S635, another embodiment of the present invention instead of receiving the third RRC connection reconfiguration message of step S635. May include the reception of a PDCCH. That is, the terminal may receive downlink assignment information (downlink assignment) from the small base station through the PDCCH, the terminal may determine that uplink transmission is also possible. Therefore, when uplink transmission is required, the UE may perform uplink transmission through the second extended EPS bearer.

Referring to FIG. 7, when the signal strengths of the macro cell, the small cell A, and the small cell B satisfy a specific criterion, the macro base station receives a measurement report from the terminal (S700). For example, if the measured signal strength satisfies a specific criterion, the signal strengths of the macro cell and the small cell B should be as small as the threshold while the signal strength of the macro cell is as large as the threshold. In addition to the above conditions, other conditions that may determine that the UE is located in the macro cell and move from the small cell A to the small cell B are possible.

If the macro base station decides to create and use a second extended EPS bearer without using the first extended EPS bearer anymore, the first base station indicates to start uplink transmission using the EPS bearer of the suspended macro cell. The RRC connection reconfiguration message is transmitted to the terminal (S705). The reason for using the EPS bearer of the macro cell, which has been discontinued for data of the user plane, is to reuse the EPS bearer of the macro cell until the second extended EPS bearer is completed. This is because the terminal needs the EPS bearer for uplink transmission until the generation of the second extended EPS bearer is completed. Also, if the EPS bearer of the macro cell is deleted while the creation of the second extended EPS bearer is not completed in the wireless section and the core network section, the user data exchanged between the terminal and the core network is buffered at the macro base station or core network side. Or a large amount of data must be exchanged through an interface between the macro cell and the small cell. Step S505 is not signaling to directly generate a second extended EPS bearer, but is performed as a preliminary step.

The macro base station transmits EPS bearer control information to the core network (MME, S-GW, P-GW) (S710). The P-GW finally receives EPS bearer control information. Downlink data of the user plane received from the UE is transmitted to the terminal using the EPS bearer of the macro cell instead of the first extended EPS bearer The EPS bearer control information may be, for example, the terminal identifier, the EPS bearer identifier of the macro cell, and the first. It may include at least one of the extended EPS bearer identifier.

The macro base station receives a first RRC connection reconfiguration complete message from the terminal (S715). Step S715 may be performed before step S705.

Apart from reusing the EPS bearer of the macro cell, a second extended EPS bearer must be created. This is a bearer extension procedure, and the macro base station transmits a bearer extension request message to the second small base station (S720). The bearer extension request message may be transmitted from the macro base station to the second small base station through the X2 interface. Receiving the bearer extension request message, the second small base station interprets the second extended EPS bearer to be used in place of the first extended EPS bearer indicated by the extended EPS bearer identifier in the bearer extension request message to satisfy the given QoS information. do.

The bearer extension request message may include at least one information element (IE). For example, the information element may be a UE identifier or an EPS bearer identifier of a macro cell, a first extended EPS bearer of a small cell A, or a QoS decision parameter.

The macro base station receives from the second small base station a bearer extended response message including radio configuration parameter values satisfying QoS of the second extended EPS bearer and the associated E-RAB (S725). The bearer extension response message is a message informing the UE of the availability or activation of the second extended EPS bearer. This may include messages coming from the core network. The X2 interface may be used for delivery of the bearer extension response message.

The macro base station transmits to the terminal a second RRC connection reconfiguration message indicating the radio resource configuration of the terminal using the values received through the bearer extension response message (S730). The second RRC connection reconfiguration message includes control information required between the second small base station and the terminal to complete the second extended EPS bearer.

The macro base station receives a second RRC connection reconfiguration complete message from the terminal (S735).

Since the second extended EPS bearer is not yet completed in the core network, the macro base station may receive and process uplink (UL) data from the terminal through the EPS bearer of the macro cell. That is, in the preparation for generating the second extended EPS bearer, the macro base station performs uplink reception using the EPS bearer of the macro cell which is not deleted.

The macro base station transmits, to the second small base station, an RB generation complete message indicating that generation of the RB is completed between the terminal and the second small base station (S740). The RB creation complete message is a message transmitted through the X2 interface. Upon receiving the RB generation complete message, the second small base station may confirm that the configuration of the RB corresponding to the second extended EPS bearer is successfully completed. Finally, generation of the RB is completed between the terminal and the second small base station.

If it is confirmed that the generation of the second extended EPS bearer for the core network is completed, the macro base station transmits a third RRC connection reconfiguration message to the UE indicating that the second extended EPS bearer starts uplink transmission (S745). ). As a result, the UE may perform uplink transmission using the second extended EPS bearer.

Referring to FIG. 8, apart from reusing the EPS bearer of the macro cell, the terminal should generate the second extended EPS bearer. This is a bearer extension procedure, and the second small base station receives a bearer extension request message from the macro base station (S800). The bearer extension request message may be transmitted from the macro base station to the second small base station through the X2 interface. Receiving the bearer extension request message, the second small base station interprets the second extended EPS bearer to be used in place of the first extended EPS bearer indicated by the extended EPS bearer identifier in the bearer extension request message to satisfy the given QoS information. do.

Upon receiving the bearer extension request message, the second small base station extracts information elements included in the bearer extension request message. And the second small base station generates, with the core network side, a second extended EPS bearer that satisfies the QoS determination parameter, instead of the EPS bearer whose terminal identified by the terminal identifier is identified by the EPS bearer identifier of the macro cell. Prepare a procedure to perform (S805).

The second small base station transmits a bearer extension response message including radio configuration parameter values satisfying QoS of the second extended EPS bearer and the associated E-RAB to the macro base station (S810). The bearer extension response message is a message informing the UE of the availability or activation of the second extended EPS bearer. This may include messages coming from the core network. The X2 interface may be used for delivery of the bearer extension response message.

An RB generation complete message indicating that generation of the RB is completed between the terminal and the second small base station is received from the macro base station (S815). The RB creation complete message is a message transmitted through the X2 interface. When receiving the RB generation complete message, the second small base station can confirm that the configuration of the RB corresponding to the second extended EPS bearer was successfully completed. Finally, generation of the RB is completed between the terminal and the second small base station (S820).

The second small base station completes generation of the second extended EPS bearer for the core network (S825). After the second extended EPS bearer is created in the core network, among the components of the core network, the P-GW starts to transmit user data coming from the PDN through the P-GW toward the terminal to the terminal using the second extended EPS bearer. do. Then, the second small base station transmits the user data flowing through the P-WG to the terminal using a second extended EPS bearer (S830). Since generation of the RB is completed between the second small base station and the terminal, the second small base station has no problem in transmitting the user data to the terminal through the second extended EPS bearer, and the terminal also transmits the user data through the second extended EPS bearer. There is no problem to receive.

If it is confirmed that the generation of the second extended EPS bearer for the core network is completed, the macro base station transmits a third RRC connection reconfiguration message to the terminal indicating that the uplink transmission is started in the second extended EPS bearer. Accordingly, the UE may perform uplink transmission using the second extended EPS bearer (S835).

9, the terminal 900 includes a terminal receiver 905, a terminal processor 910, and a terminal transmitter 915. The macro base station 930 includes a macro transmitter 935, a macro receiver 940, and a macro processor 945. The second small base station 960 includes a small transmitter 965, a small receiver 970, and a small processor 975.

Although not shown in the figure, the first small base station provides a small cell A, and the second small base station 960 provides a small cell B. Currently, the terminal 900 uses a first extended EPS bearer that provides data of a user plane by a first small base station.

The terminal processor 910 measures the signal strengths of the macro cell, the small cell A, and the small cell B, generates a measurement report when the measured signal strength satisfies a specific criterion, and the terminal transmitter 915 includes the macro base station ( 930) the measurement report. For example, if the measured signal strength satisfies a specific criterion, the signal strengths of the macro cell and the small cell B should be as small as the threshold while the signal strength of the macro cell is as large as the threshold. In addition to the above conditions, other conditions that may determine that the UE is located in the macro cell and move from the small cell A to the small cell B are possible.

When the macro receiver 940 receives the measurement report, the macro processor 945 analyzes the signal strength based on the measurement report. If the signal strength of the macro cell is greater than the signal strengths of the small cell A and the small cell B and the signal strength of the small cell B is greater than the signal strength of the small cell A, the macro processor 945 determines that the terminal 900 of the macro cell is the signal strength of the macro cell. It may be determined that the cell is moving from the small cell A within the coverage to the small cell B.

In this case, the macro processor 945 decides to generate a second extended EPS bearer to use in place of the first extended EPS bearer in the small cell B. Here, the condition that the macro processor 945 determines to generate the second extended EPS bearer may be, for example, that the signal of the small cell B is larger than the signal of the small cell A by a certain value or the signal strength of the small cell B is specific. May be greater than the threshold.

If the macro processor 945 decides to generate and use the second extended EPS bearer without using the first extended EPS bearer anymore, it instructs to start uplink transmission using the EPS bearer of the suspended macro cell. The first RRC connection reconfiguration message is generated, and the macro transmitter 935 transmits the first RRC connection reconfiguration message to the terminal 900. The reason for using the EPS bearer of the macro cell, which has been discontinued for the data of the user plane, is because there is a delay of negotiation with the core network for generating the second extended EPS bearer. 2 Until the extended EPS bearer is created, the EPS bearer of the macro cell is first reused. This is because the terminal 900 needs the EPS bearer for uplink transmission until the generation of the second extended EPS bearer is completed. Also, if the EPS bearer of the macro cell is deleted while the generation of the second extended EPS bearer is not completed in the wireless section and the core network (not shown), the user data exchanged between the terminal 900 and the core network This is because there is a problem that a large amount of data must be exchanged through buffering at the macro base station or core network side or through an interface between the macro cell and the small cell.

As a first embodiment, the first RRC connection reconfiguration message may include UL Tx reservation information (ULTxSsuspendInfo) indicating that the uplink transmission using the first extended EPS bearer is suspended. In other words, the first RRC connection reconfiguration message may include UL Tx reservation information meaning that no uplink transmission is performed using the first extended EPS bearer. This is because the generation of the second extended EPS bearer is not completed in the entire period from the terminal 900 to the core network.

As a third embodiment, the first RRC connection reconfiguration message may include a UE identifier, an EPS bearer identifier of a macro cell, and a first extended EPS bearer identifier. The terminal identifier is an identification number for identifying the terminal 900 and may include C-RNTI, IMSI, GUTI, and the like.

This embodiment is not limited to the transmission of UL Tx interruption information or UL TX start information included in the first RRC connection reconfiguration message. That is, the UL Tx stop information or the UL TX start information may be transmitted independently of the first RRC connection reconfiguration message.

When the terminal receiver 905 receives the first RRC connection reconfiguration message, the terminal processor 910 no longer uses the first extended EPS bearer when transmitting uplink data (that is, uplink using the first extended EPS bearer). Stop link transmission), and use the EPS bearer of the macro cell.

The macro processor 945 generates EPS bearer control information, and the macro transmitter 935 transmits EPS bearer control information to the core network (MME, S-GW, P-GW). The P-GW is an EPS bearer. Finally, the P-GW forwards downlink data of the user plane received from the PDN to the terminal 900 using the EPS bearer of the macro cell instead of the first extended EPS bearer. The control information may include, for example, at least one of a terminal identifier, an EPS bearer identifier of a macro cell, and a first extended EPS bearer identifier.

The terminal processor 910 completes the radio configuration based on the first RRC connection reconfiguration message and generates a first RRC connection reconfiguration complete message. The terminal transmitter 915 transmits the first RRC connection reconfiguration complete message to the macro base station 930.

The terminal 900 may provide a smooth service to the terminal by reusing the EPS bearer of the macro cell based on the first RRC connection reconfiguration message and the EPS bearer control information. For example, even when the signal strength of the small cell A deteriorates rapidly in the process of generating the second extended EPS bearer, the terminal 900 may receive a stable service through the EPS bearer of the macro cell.

Apart from reusing the EPS bearer of the macro cell, the terminal 900 must create a second extended EPS bearer. This is a bearer extension procedure. The macro processor 945 generates a bearer extension request message, and the macro transmitter 935 transmits a bearer extension request message to the second small base station 960. The bearer extension request message may be transmitted from the macro base station 930 to the second small base station 960 through the X2 interface.

The small processor 975 receiving the bearer extension request message means to make a second extended EPS bearer to use in place of the first extended EPS bearer indicated by the extended EPS bearer identifier in the bearer extension request message to satisfy the given QoS information. Interpret The bearer extension request message may include at least one information element. For example, the information element may be a terminal identifier or an EPS bearer identifier or QoS determination parameter of a macro cell.

Upon receiving the bearer extension request message, the small processor 975 extracts information elements included in the bearer extension request message. In addition, the small processor 975 is configured to core the second extended EPS bearer that satisfies the QoS determination parameter instead of the EPS bearer whose terminal 900 is identified by the terminal identifier. Prepare the procedure to create with the side.

For example, the small processor 975 determines the identifier of the second extended EPS bearer along with the core network and determines the E-RAB identifier associated with the second extended EPS bearer identifier. Then, a preparation operation necessary for using the newly created second extended EPS bearer and the E-RAB in place of the first extended EPS bearer is performed.

The small processor 975 generates a bearer extension response message that includes radio configuration parameter values that satisfy the QoS of the second extended EPS bearer and its associated E-RAB, and sends it to the macro base station 930. This may include messages coming from the core network. The X2 interface may be used for delivery of the bearer extension response message.

In a first embodiment, the radio configuration parameter values included in the bearer extension response message are parameters for configuring an RB, and provide system information, PHY, and MAC layer information necessary for providing a service to a terminal 900 on a small cell B. It may include.

The macro processor 945 generates a second RRC connection reconfiguration message indicating a radio resource configuration of the terminal using the values received through the bearer extension response message, and the macro transmitter 935 generates a second RRC connection reconfiguration message. Transmit to the terminal 900. The second RRC connection reconfiguration message includes control information required between the second small base station 960 and the terminal 900 to complete the second extended EPS bearer.

As a first embodiment, the second RRC connection reconfiguration message may include UL Tx reservation information (ULTxSuspendInfo) indicating suspending uplink transmission using the second extended EPS bearer. In other words, the second RRC connection reconfiguration message may include UL Tx reservation information meaning that no uplink transmission is performed using the second extended EPS bearer. This means that if the second extended EPS bearer is used while the generation of the second extended EPS bearer is not completed in the entire period from the terminal 900 to the core network, the user data exchanged between the terminal 900 and the core network is macro. This is because a problem may occur that a large amount of data is exchanged through the interface between the macro base station 930 and the second small base station 960 or buffered at the base station or the core network. However, the uplink transmission may not include transmission of PUCCH and HARQ ACK / NACK information. In other words, despite the UL Tx reservation information, the terminal may transmit the PUCCH and HARQ ACK / NACK information.

In a third embodiment, the second RRC connection reconfiguration message may include detailed information indicating availability or activation of a second extended EPS bearer formed between the second small base station 960 and the terminal 900. It may include.

As a fourth embodiment, the second RRC connection reconfiguration message includes a dedicated NAS list (dedicatedInfoNASList) information element used for transferring UE specific NAS layer information between the core network and the terminal 900. The dedicated NAS list information element may include detailed information indicating availability or activation of the second extended EPS bearer formed between the second small base station 960 and the terminal 900.

When the terminal receiver 905 receives the second RRC connection reconfiguration message, the terminal processor 910 completes the radio configuration with the second small base station 960 based on the second RRC connection reconfiguration message, and the second extended EPS. A second RRC connection reconfiguration complete message is generated indicating that the radio configuration corresponding to the bearer has been successfully completed. The terminal transmitter 915 transmits a second RRC connection reconfiguration complete message to the macro base station 930.

The terminal 900 receiving the UL Tx reservation information may transmit and process uplink (UL) data through the EPS bearer of the macro cell since the second extended EPS bearer is not yet completed in the core network. That is, in the generation preparation step of generating the second extended EPS bearer, the terminal processor 910 performs uplink transmission using the EPS bearer of the macro cell which is not deleted. However, the UE processor 910 may transmit the PUCCH and HARQ ACK / NACK information using the second extended EPS bearer as an exception. The terminal processor 910 is capable of receiving and processing downlink (DL) data through an EPS bearer of a macro cell.

As such, although the radio configuration is completed in the terminal 900 (that is, the RB configuration is completed) and the second extended EPS bearer can be used, the reason why the uplink transmission is still performed through the EPS bearer of the macro cell is that the reliability of the uplink transmission is reduced. To ensure. This is because the terminal 900 may move to the small cell B and then move to the area of the small cell A or the macro cell only.

The macro processor 945 generates an RB generation complete message indicating that generation of the RB has been completed between the terminal 900 and the second small base station 960, and the macro transmitter 935 generates a second small RB generation message. Transmit to base station 960. The RB creation complete message is a message transmitted through the X2 interface.

When the small receiver 970 receives the RB generation complete message, the small processor 975 may confirm that the configuration of the RB corresponding to the second extended EPS bearer is completed successfully. At this time. Finally, generation of the RB is completed between the terminal 900 and the second small base station 960.

The small processor 975 completes the creation of the second extended EPS bearer for the core network. After the second extended EPS bearer is generated in the core network, the P-GW among the components of the core network uses the second extended EPS bearer for user data coming in through the P-GW from the PDN toward the terminal 900. 900). The small transmitter 965 transmits the user data introduced through the P-WG to the terminal 900 using the second extended EPS bearer. Since the generation of the RB is completed between the second small base station 960 and the terminal 900, the small transmitter 965 has no problem in transmitting the user data to the terminal 900 through the second extended EPS bearer and the terminal ( 900 also has no problem receiving the user data via a second extended EPS bearer.

When the generation of the second extended EPS bearer for the core network is completed, the macro processor 945 sends a third RRC connection reconfiguration message indicating to the terminal 900 that the uplink transmission starts from the second extended EPS bearer. The macro transmitter 935 generates and transmits a third RRC connection reconfiguration message to the terminal 900. As a result, the terminal 900 may perform uplink transmission using the second extended EPS bearer.

This embodiment is not limited to the UL Tx reservation information and the UL Tx start information (ULTxStartInfo) included in the third RRC connection reconfiguration message and transmitted. That is, the UL Tx holding information and the UL Tx start information may be transmitted independently of the third RRC connection reconfiguration message.

The first small base station and the core network perform an operation for releasing the first extended EPS bearer.

In the exemplary system described above, the methods are described based on a flowchart as a series of steps or blocks, but the invention is not limited to the order of steps, and certain steps may occur in a different order or concurrently with other steps than those described above. Can be. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

The above-described embodiments include examples of various aspects. While not all possible combinations may be described to represent the various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, the invention is intended to embrace all other replacements, modifications and variations that fall within the scope of the following claims.

Claims

A method for supporting a change of an extended EPS (Evolved Packet System) bearer by a UE in a heterogeneous network system including a plurality of small eNBs,

First uplink transmission start information indicating that uplink transmission is started using an EPS bearer of a macro cell formed between the terminal and the macro base station, and an uplink in the first extended EPS bearer formed between the terminal and the first small base station; Receiving first uplink transmission reservation information indicating reservation for link transmission from the macro base station;

A parameter for configuring a radio bearer mapped to a second extended EPS bearer to be formed between the terminal and the second small base station, and a second indicating that the uplink transmission using the second extended EPS bearer is reserved. Receiving uplink transmission reservation information from the macro base station; And

Third uplink transmission reservation information indicating that the uplink transmission using the EPS bearer of the macro cell is reserved and second uplink transmission starting indicating the uplink transmission using the second extended EPS bearer is started. Receiving information from the macro base station.
The method of claim 1,

Performing uplink transmission for the macro base station after receiving the first uplink transmission start information and the first uplink transmission reservation information; And

And after receiving the second uplink transmission reservation information and the second uplink transmission start information, performing uplink transmission by using the second extended EPS bearer. How to support change.
The method of claim 1,

The first uplink transmission start information, the first uplink transmission reservation information, the second uplink transmission reservation information, the third uplink transmission reservation information and the second uplink transmission start information are included in an RRC connection reconfiguration message. Characterized in that it is included and received.
The method of claim 1,

When generation of the radio bearer is completed between the second small base station and the terminal based on the parameter, and generation of the second extended EPS bearer between the second small base station and the core network is completed,

Starting to perform downlink reception using the second extended EPS bearer.
A terminal for supporting a change of an extended EPS bearer in a heterogeneous network system including a plurality of small base stations,

First uplink transmission start information indicating that uplink transmission is started using an EPS bearer of a macro cell formed between the terminal and the macro base station, and an uplink in a first extended EPS bearer formed between the terminal and the first small base station; First uplink transmission reservation information indicating reservation for transmission, a parameter for configuring a radio bearer mapped to a second extended EPS bearer to be formed between the terminal and the second small base station, and an uplink using the second extended EPS bearer Using second uplink transmission reservation information indicating suspension of link transmission, third uplink transmission reservation information indicating suspension of uplink transmission using the EPS bearer of the macro cell, and using the second extended EPS bearer Number of UEs receiving second uplink transmission start information from the macro base station indicating that uplink transmission is started priest; And

Perform uplink transmission to the macro base station based on the first uplink transmission start information and the first uplink transmission reservation information, and perform the uplink transmission on the third uplink transmission reservation information and the second uplink transmission start information. And a terminal processor configured to perform uplink transmission based on the second extended EPS bearer.
The method of claim 5, wherein the terminal receiving unit,

The RRC connection reconfiguration message includes the first uplink transmission start information, the first uplink transmission reservation information, the second uplink transmission reservation information, the third uplink transmission reservation information, and the second uplink transmission start information. Receiving through, the terminal.
The method of claim 5,

When generation of the radio bearer is completed between the second small base station and the terminal based on the parameter, and generation of the second extended EPS bearer between the second small base station and the core network is completed,

And the terminal processor starts downlink reception using the second extended EPS bearer.
A method of supporting a change of an extended Evolved Packet System (EPS) bearer by a macro base station in a heterogeneous network system including a plurality of small base stations,

First uplink transmission start information indicating that uplink transmission is started using an EPS bearer of a macro cell formed between the terminal and the macro base station, and an uplink in the first extended EPS bearer formed between the terminal and the first small base station; Transmitting first uplink transmission reservation information indicating reservation for link transmission to the terminal;

A parameter for configuring a radio bearer mapped to a second extended EPS bearer to be formed between the terminal and the second small base station, and a second indicating that the uplink transmission using the second extended EPS bearer is reserved. Transmitting uplink transmission reservation information to the terminal; And

Third uplink transmission reservation information indicating that the uplink transmission using the EPS bearer of the macro cell is reserved and second uplink transmission starting indicating the uplink transmission using the second extended EPS bearer is started. And transmitting the information to the terminal.
The method of claim 8,

Performing uplink reception after transmitting the first uplink transmission start information and the first uplink transmission reservation information; And

And after transmitting the second uplink transmission reservation information and the second uplink transmission start information, performing uplink reception using the second extended EPS bearer. How to support change.
The method of claim 8,

The first uplink transmission start information, the first uplink transmission reservation information, the second uplink transmission reservation information, the third uplink transmission reservation information and the second uplink transmission start information are included in an RRC connection reconfiguration message. Method for supporting a change of an extended bearer, characterized in that the transmission is included.
The method of claim 8,

When generation of the radio bearer is completed between the second small base station and the terminal based on the parameter, and generation of the second extended EPS bearer between the second small base station and the core network is completed,

Starting to perform downlink transmission using the second extended EPS bearer.
A macro base station supporting a change of an extended EPS bearer in a heterogeneous network system including a plurality of small base stations,

First uplink transmission start information indicating that uplink transmission is started using an EPS bearer of a macro cell formed between the terminal and the macro base station, and an uplink in a first extended EPS bearer formed between the terminal and the first small base station; First uplink transmission reservation information indicating reservation for transmission, a parameter for configuring a radio bearer mapped to a second extended EPS bearer to be formed between the terminal and the second small base station, and an uplink using the second extended EPS bearer Using second uplink transmission reservation information indicating suspension of link transmission, third uplink transmission reservation information indicating suspension of uplink transmission using the EPS bearer of the macro cell, and using the second extended EPS bearer A base station transmitter which transmits second uplink transmission start information indicating to start uplink transmission to the terminal; And

Uplink reception is performed based on the first uplink transmission start information and the first uplink transmission reservation information, and the second uplink is based on the third uplink transmission reservation information and the second uplink transmission start information. And a base station processor for performing uplink reception using an extended EPS bearer.
The method of claim 12, wherein the base station transmitter,

The RRC connection reconfiguration message includes the first uplink transmission start information, the first uplink transmission reservation information, the second uplink transmission reservation information, the third uplink transmission reservation information, and the second uplink transmission start information. Macro base station, characterized in that through the transmission.
The method of claim 12,

When generation of the radio bearer is completed between the second small base station and the terminal based on the parameter, and generation of the second extended EPS bearer between the second small base station and the core network is completed,

And the base station processor starts performing downlink transmission using the second extended EPS bearer.