Method and apparatus for handover using X2 interface based on closed subscriber group in mobile communication system

A method for handover of User Entity (UE) by a source Base Station (BS) is provided. The method includes determining whether to handover the UE using an X2 interface, transmitting a handover request message to a target BS, the handover request message including Closed Subscriber Group (CSG) information of the target BS, and receiving a handover request acknowledgement message from the target BS, wherein the determining of whether to handover the UE using the X2 interface includes, if there is the X2 interface between the source BS and the target BS, and if the target BS does not support a CSG or the target BS supports a same CSG supported by the source BS, determining to perform the handover of the UE using the X2 interface, and obtaining the CSG information of the target BS through an X2 interface set up procedure.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a Chinese patent application filed on Apr. 28, 2010 in the Chinese Intellectual Property Office and assigned Serial No. 201010159953.4 and a Chinese patent application filed on Apr. 29, 2010 in the Chinese Intellectual Property Office and assigned Serial No. 201010168721.5, the entire disclosures of all of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a handover method and apparatus using an X2 interface in the mobile communication system.

2. Description of the Related Art

Long Term Evolution (LTE) is an evolution technology of the third Generation (3G) mobile communication system, and has several advantages, such as enhancing the capacity of cells and reducing the system delay.

FIG. 1is a schematic diagram illustrating an architecture of a LTE system according to the related art.

Referring toFIG. 1, the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) of the LTE system typically includes radio resource management entities, such as evolved Node Bs (eNBs) and Home eNBs (HeNBs), and may further include HeNB GateWays (GWs). When the HeNB GWs are not included, the HeNBs may directly connect with Mobile Management Entities (MMEs) of the core network. When the HeNB GWs are included, the HeNBs connect with the MMEs through the HeNB GW. The MMEs are important network entities of the core network, and are responsible for functions such as, radio access bearer establishment and mobility management.

In the mobile communication system, in order to provide better services for particular users, as for a particular group, a Closed Subscriber Group (CSG) is usually needed to be formed with multiple radio resource management entities. For example, all users of a company or campus form a particular user group. A CSG is formed for this user group with multiple radio resource management entities to provide specialized access services.

The radio resource management entities of the LTE include eNB101and HeNB103. The radio resource management entities of the LTE may further include HeNB GW103. Each eNB101is connected with each other through an X2 interface. Each eNB101is directly connected with MME104in a Core Network (CN) through an S1 interface. HeNB102may connect with HeNB GW103through the S1 interface, and then HeNB GW103may connect with MME104through the S1 interface. HeNB102may also directly connect with MME104through the S1 interface. When there is no HeNB GW103deployed in the system, HeNB102directly connects with MME104through S1 interface. Both eNB101and HeNB102may connect with multiple MMEs104in the CN.

In order to provide richer access services, the radio resource management entities of the LTE system shown inFIG. 1usually include more types. For example, the HeNBs are classified into open HeNBs, hybrid HeNBs, and CSG HeNBs. The open HeNBs denote HeNBs which are not directed against any particular user group, and to which any User Entity (UE) may access. The CSG HeNBs denote HeNBs in the CSG user group, and only permit the access of UEs in the particular group served by the CSG HeNBs. The hybrid HeNBs denote the HeNBs which support the function of the CSG, permit the access of UEs in the particular user group served by the hybrid HeNBs, and also permit the access of the UEs in a general user group.

The UE may move among different HeNBs and between a HeNB and eNB. The movement of UE is implemented through S1 handover. The S1 handover represents handover using an S1 interface.

FIG. 2is a schematic diagram illustrating an S1 handover procedure according to the related art. Suppose each of HeNBs connects with the MME through the HeNB GW.

Referring toFIG. 2, a source HeNB217sends a handover required message to a HeNB GW219in step201a. How to send a measurement report to the source HeNB217from the UE216and how to initiate the handover by the source HeNB217is not introduced here.

In step201b, the HeNB GW219sends the handover required message to the MME (220).

In step202a, the MME220sends a handover request message to the HeNB GW219, and in the step202b, the HeNB GW219sends the handover request message to the target HeNB. The source HeNB217denotes the HeNB at which the UE216is originally located. The target HeNB218refers to the HeNB to which the UE performs handover.

In step203, the target HeNB218allocates resources for the UE216, and in step203a, sends a handover request acknowledgement message to the HeNB GW219. In step203b, the HeNB GW219sends the handover request acknowledgement message to the MME220.

In step205a, the MME220sends a handover command message to the HeNB GW219. In step205b, The HeNB GW219sends the handover command message to the source HeNB217.

In step206, the source HeNB217sends a Radio Resource Control (RRC) connection re-configuration message to the UE216.

In step207, the UE216synchronizes to the target cell, and in step208, sends the RRC connection re-configuration completion message to the target HeNB218.

In step209a, the target HeNB218sends a handover notify message to the HeNB GW219. In step209b, the HeNB GW219sends the handover notify message to the MME220.

In step210, the MME220sends a modify bearer request message to a Service-Gateway/Packet Data Network Gateway (S-GW/PDN GW)225. The S-GW is mainly used for providing a user plane function. The PDN GW is mainly used for functions, e.g., charging and lawful interception. In step211, the S-GW and PDN GW may be set in a same physical entity, or be two entities. This step omits the signaling interactions between the S-GW and PDN GW.

In step212, the S-GW/PDN GW221sends a modify bearer response message to the MME220.

In step213, the UE216initiates a Tacking Area Update (TAU) process.

In step213a, The MME220sends a UE context release command message to the HeNB GW219. In step213b, the HeNB GW219sends the UE context release command message to the source HeNB217.

In step214a, the source HeNB217sends the UE216context release completion message to the HeNB GW219. In the214b, the HeNB GW219sends the UE216context release completion message to the MME220.

Although the above process may implement the handover procedure, taking the large number of HeNBs and the often handover of UE into consideration, if each handover is implemented through the S1 handover, the burden of the core network is heavily aggravated and the efficiency of the handover is reduced. Similarly, the above issues also exist when the UE moves between the HeNB and eNB, and between eNB and eNB.

In the related art as described above, movement of UE between HeNB and eNB is also achieved through S1 handover. From above analysis, it can be seen that movement of UE between HeNBs through S1 handover is achieved via the CN, which includes handover preparation and data forwarding. If each movement of UE between HeNBs is achieved through S1 handover, a very heavy load will be brought for the CN due to the huge number of HeNB. The handover efficiency may be reduced.

However, handover preparation and data forwarding in prior X2 handover process are not necessary to be performed through the MME. Thus, the X2 handover process may be applied for the movement of UE between HeNBs.

FIGS. 3A-3Care a connection schematic diagram illustrating applying X2 handover to an HeNB according to the related art.FIG. 3Ais a connection schematic diagram illustrating movement (300) of a UE between HeNBs305aand305bthrough X2 handover.FIG. 3Bis a connection schematic diagram illustrating movement (310) of a UE from HeNB315to eNB320through X2 handover.FIG. 3Cis a connection schematic diagram illustrating movement (325) of UE from eNB330to HeNB335through X2 handover.

Referring toFIGS. 3A-3C, since the HeNB GW possesses Non-Access-Stratum (NAS) Node Selection Function (NNSF), the HeNB GW will select a serving MME for a UE under the HeNB when the HeNB accesses the MME through the HeNB GW. However, the HeNB doesn't learn of the MME selected by the HeNB GW for the UE. Accordingly, when executing the X2 handover, the source HeNB cannot inform the target HeNB about the serving MME of the UE. Subsequently, the target HeNB, or the eNB, or the target HeNB GW will not learn to which MME the path switch request message should be sent. The handover process will be unsuccessful if the message has been sent to other MME instead of the MME initially accessed by the UE.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a handover method using an X2 interface in the mobile communication system.

Another aspect of the present invention is to provide that a Mobile Management Entity (MME) identifier of a MME accessed by a User Entity (UE) to perform X2 handover is provided to a target evolved Node B (eNB)/Home eNB (HeNB) or target HeNB GateWay (GW) during the X2 handover.

In accordance with an aspect of the present invention, a method for handover of a User Entity (UE) by a source Base Station (BS) is provided. The method includes determining whether to handover the UE using an X2 interface, transmitting a handover request message to the target BS, the handover request message including Closed Subscriber Group (CSG) information of a target BS, and receiving a handover request acknowledgement message from the target BS, wherein the determining of whether to handover the UE using the X2 interface includes, if there is X2 interface between the source BS and the target BS, and if the target BS doesn't support a CSG or the target BS supports the same CSG supported by the source BS, determining to perform the handover of the UE using the X2 interface, and obtaining the CSG information of the target BS through an X2 interface set up procedure.

In accordance with another aspect of the present invention, a method for handover of a User Entity (UE) by a target Base Station (BS) is provided. The method includes receiving a handover request message from a source BS, the handover request message including CSG information of a target BS, if the CSG information includes a first CSG IDentifier (ID), determining whether the first CSG ID and a second CSG ID are the same, and obtaining the second CSG ID from CSG information broadcasted from the target cell, if the first CSG ID and the second CSG ID are the same, transmitting a handover request acknowledgement message to the source BS, and receiving a Radio Resource Control (RRC) re-configuration message from the UE, transmitting a path switch request message including the second CSG ID to Mobility Management Entity (MME), and if a path switch request acknowledgement message is received from the MME, transmitting an UpLink (UL) context release message to the source a BS.

In accordance with another aspect of the present invention, a method for handover of a User Entity (UE) by a Mobility Management Entity (MME) is provided. The method includes receiving a path switch request message from a target BS, the path switch request message including CSG information of the target BS, if the CSG information indicates that the target BS is a CSG BS supporting a specific CSG, transmitting a bearer update request message including user CSG information to a user plane entity, and receiving a bearer update response message, and transmitting a path switch request acknowledgement message to the target BS, wherein the CSG information of the target BS or CSG information broadcast from the target cell includes an access mode indicating that the target BS is CSG BS supporting a specific CSG or hybrid BS supporting the specific CSG and UEs not included the specific CSG, if the target BS is the CSG BS or the hybrid BS, the CSG information includes a CSG ID of the specific CSG, and if the target BS supports the same CSG supported by the source BS, the CSG information includes an identifier indicating that the target BS supports the same CSG.

In accordance with another aspect of the present invention, a source Base Station (BS) for handover of User Entity (UE) is provided. The source BS includes a controller for determining whether to handover the UE using an X2 interface, a transmitter for transmitting a handover request message to a target BS, the handover request message including CSG information of the target BS, and a receiver for receiving a handover request acknowledgement message from the target BS, wherein if there is an X2 interface between the source BS and the target BS, and if the target BS doesn't support a CSG or the target BS supports a same CSG supported by the source BS, the controller determines to perform the handover of the UE using the X2 interface, and obtains the CSG information of the target BS through an X2 interface set up procedure.

In accordance with another aspect of the present invention, a target Base Station (BS) for handover of User Entity (UE) is provided. The target BS includes a receiver for receiving a handover request message comprising CSG information of a target BS from a source BS, a controller for determining, if the CSG information includes a first CSG ID, whether the first CSG ID and a second CSG ID are the same, and for obtaining the second CSG ID from CSG information broadcasted from the target cell, and if the first CSG ID and the second CSG ID are the same, the transmitter transmits a handover request acknowledgement message to the source BS, the receiver receives a Radio Resource Control re-configuration message from the UE, the transmitter transmits a path switch request message including the second CSG ID to a Mobility Management Entity (MME), and wherein if a path switch request acknowledgement message is received by the receiver from the MME, the transmitter transmits a UL context release message to the source a BS.

In accordance with another aspect of the present invention, a Mobility Management Entity (MME) method for handover of a User Entity (UE) is provided. The MME method includes receiving a path switch request message from a target BS, the path switch request message including CSG information of the target BS, if the CSG information indicates that the target BS is a CSG BS supporting a specific CSG, transmitting a bearer update request message including user CSG information to a user plane entity, wherein, if the a bearer update response message is received, transmitting a path switch request acknowledgement message to the target BS, and wherein the CSG information of the target BS or CSG information broadcast from the target cell includes an access mode indicating that the target BS is CSG BS supporting a specific CSG or hybrid BS supporting the specific CSG and UEs not included the specific CSG, wherein if the target BS is the CSG BS or the hybrid BS, the CSG information includes a CSG ID of the specific CSG, and wherein if the target BS supports the same CSG supported by the source BS, the CSG information includes an identifier indicating that the target BS supports the same CSG.

Adopting the technical scheme of the present invention, when the preset condition is satisfied, for instance, the UE moves in a same CSG, or the UE moves into an open cell, or the UE moves into a hybrid cell, the X2 handover is adopted. Compared with S1 handover, the X2 handover procedure requires fewer steps for performing the signaling interaction with the MME. Thus, the processing burden of the core network is reduced, and the handover efficiency is improved.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiment of the present invention provide a handover scheme using X2 interface for reducing processing burden of the core network in the mobile communication system. When the User Entity (UE) moves in the same Closed Subscriber Group (CSG), or the UE moves into an open cell (may be a cell covered by a HeNB, or a cell covered by an eNB), or moves into a hybrid cell, X2 handover is adopted. Since fewer steps for interacting with a Mobile Management Entity (MME) are needed in the X2 handover process, the processing burden of the core network is reduced, and the handover efficiency is improved according to first and second exemplary embodiments of the present invention. Under a few circumstances, such as when the UE moves from one CSG to another CSG, S1 handover may still be adopted.

According to a third exemplary embodiment of the present invention, when a UE connects to a network through an HeNB, an MME or an HeNB GW sends the MME identifier of the UE's MME to the HeNB. When performing the X2 handover, the HeNB may send the MME identifier to the target eNB/HeNB to which the UE should handover, to enable the target eNB/HeNB to successfully send a path switch request message to the MME serving the UE. When the target HeNB accesses the MME through HeNB GateWay (GW), the target HeNB sends the MME identifier to the destination HeNB GW, to enable the destination HeNB GW to successfully send the path switch request message to the MME serving the UE, and to reduce frequent interactions with a Core Network (CN) during an S1 handover process when ensuring a successful X2 handover. Thus, influence of the handover process on the CN is reduced, and handover delay is reduced.

The scheme of an exemplary embodiment of the present invention may be implemented on the basis of the network structure illustrated inFIG. 4.

FIG. 4is a schematic diagram illustrating a connection structure when performing X2 handover through an HeNB in accordance with an exemplary embodiment of the present invention.

Referring toFIG. 4, both of the HeNB400aand the HeNB400band the eNB410connect with the MME415in the core network through the S1 interfaces and adopt an S1 protocol stack. Each HeNB400aand400balso connects with the HeNB GWs405aand405bthrough the S1 interface and adopts the S1 protocol stack. Each HeNB405aand405bconnect with another HeNB, and each HeNB405aand405bconnects with an eNB410through an X2 interface and adopts an X2 protocol stack. Depending on the arrangement of the operator, the HeNB GWs405aand405bmay, or may not exist. If the HeNB GW does not exist, the HeNB directly connects with the MME415through the S1 interface.

The first exemplary embodiment of the present invention may apply to the following situations involving X2 handover, including when the UE moves between HeNBs, when the UE moves between the HeNB and eNB, and when the UE moves between eNBs. X2 handover is performed in these situations. In addition, the scheme of an exemplary embodiment of the present invention may also apply to the scheme in which the UE moves among different Base Stations (BSs), HeNBs, eNBs, and between the HeNB in the 3rdGeneration (3G) network.

FIG. 5Ais a flowchart illustrating an X2 handover method according to a first exemplary embodiment of the present invention. As shown inFIG. 5A, the following steps are included. The UE moves among different BSs (a source BS and target BS), but the scheme of an exemplary embodiment of the present invention may also apply to the scheme in which the UE moves between apparatuses connected the X2 interface. The apparatuses include HeNBs and eNBs.

Referring toFIG. 5A, a source BS502makes a handover decision in step507.

In step508, the source BS502determines that an X2 handover procedure is adopted. For example, the source BS502determines whether there is an X2 interface between itself and the target BS503. If there is not an X2 interface, the S1 handover flow of the related art is executed; otherwise, the source BS502further determines whether the target cell is an open cell, or whether the source cell and the target cell belong to a same CSG. If so, the X2 handover is performed, i.e., step509is performed.

The S1 handover flow is described above. In addition, the source cell and the target cell being located at a same CSG indicates that both the source cell and the target cell are CSG cells, and that they have the same CSG identifier.

The source BS502may be a HeNB or an eNB. The target BS503may also be the HeNB or eNB. According to different network configurations, there may or may not be an X2 interface between the source BS502and the target BS503.

In addition, in step508, the source BS502may obtain the CSG IDentifier (ID) and an access mode of the target cell from the UE501, through the X2 setup procedure, according to the configuration of the operator, and/or through other fashions. The access mode refers to the type of the target cell, for instance, the hybrid or CSG cell. If the CSG ID does not exist, the target cell is considered as an open cell, or the target cell may be explicitly denoted as the open cell. Whether the source cell and the target belong to a same CSG can be determined according to the CSG ID of the target cell.

The method for obtaining the CSG ID and access mode of the target cell from the UE501includes obtaining the CSG ID and access mode from an Automatic Neighbor Relation (ANR), or from a measurement report sent for the purpose of handover. The specific implementations are well known, and any specific implementation may be employed. In addition, when initially accessing the network, the BS and partial other BSs may execute the X2 interface setup procedure. The BSs, with which the BS executes the X2 interface setup procedure, are determined according to the configuration of the operator and so on. The source BS502may obtain the CSG ID and access mode of the target cell with this method.

FIG. 5Bis a schematic diagram illustrating an X2 interface setup procedure in accordance with a first exemplary embodiment of the present invention.

Referring toFIG. 5B, the BS15000sends an X2 setup request message to the BS25005in step5011. The X2 setup request message includes information of serving cells belonging to BS15000. The information includes the CSG ID and Physical Cell Identifier (PCI) of each of the serving cells, and may further include the access mode of each the serving cells, etc. for indicating whether the cell is a hybrid cell or CSG cell. When the access mode of each of the serving cells is the hybrid cell, the X2 setup request message includes the access mode for indicating that the cell is the hybrid cell. When the cell is the CSG cell, the X2 setup request message does not include the access mode. This method is used for implicitly indicating that the access mode is the CSG type. Alternatively, the access mode is not carried in the X2 setup request message, but is determined according to the scope of the PCI of the cell.

In step5012, the BS2sends an X2 setup response message to the BS1. The X2 setup response message includes information of target cells belonging to the BS25005. The information includes the CSG ID and PCI of each of the target cells, and may further include an access mode of the each of the target cells, etc. for indicating whether the cell is a hybrid cell or a CSG cell. When the cell is the hybrid cell, the X2 setup response message includes the access mode for indicating that each of the target cells is the hybrid cell. When one of the target cells is the CSG cell, the X2 setup response message does not include the access mode. This method is used for implicitly indicating that the access mode is the CSG type. If the access mode is not carried in the X2 setup response message, the access mode may be determined according to the scope of the PCI of the cell.

The BS15000illustrated inFIG. 5Bmay be an eNB, or a HeNB. Similarly, the BS25005may be an eNB or a HeNB. As shown inFIG. 5B, the source BS502obtains the CSG ID and the access mode of the target cell, and the source BS502determines X2 handover for the UE501, and proceeds to step509.

In step509, the source BS502sends the handover request message to the target BS503. If a target cell serviced by the target BS (503) is a CSG cell, the CSG ID of the target cell may be carried in the handover request message. In addition, if the CSG ID of the target is obtained through the X2 interface setup procedure as shown inFIG. 5B, the CSG ID of the target cell may not be carried. Since it is considered that the CSG ID of the target cell obtained through this mode is correct, it is unnecessary to perform the verification as shown in step510.

In step510, the target BS503verifies the CSG ID included in the handover request message of the target cell. The target BS503verifies whether the CSG ID of the target cell included in the handover request message is correct. The target BS503compares the CSG ID of the target cell included in the handover request message with the CSG ID broadcast by the target cell to determine whether the two CSG IDs are the same. If they are not the same, the X2 handover is rejected, and the CSG ID broadcast by the target cell, i.e. the correct CSG ID of the target cell is carried in a handover preparation failure message and sent to the source BS502; otherwise, step405is performed.

Step510is optional. If the handover request message sent from the source BS502to the target BS503in step509does not include the CSG ID of the target cell, execution of step510is not needed.

In step511, the target BS503sends a handover request acknowledgement message to the source BS502.

In step512, the source BS502sends a Radio Resource Control (RRC) connection re-configuration message to the UE501.

In step513, the UE501sends a RRC connection re-configuration completion message to the target BS503.

In step514a, the target BS503sends a path switch request message to the gateway. If the target cell is a CSG cell, the CSG ID of the target cell is carried in the path switch request message. If the target cell is a CSG cell, the target cell can determine that this handover adopts the X2 handover according to steps509-514a, and the target cell knows the principle of X2 handover, i.e. under what circumstances X2 handover is adopted. Accordingly, the target cell may determine that both the source cell and target cell are CSG cells, and that they have the same CSG ID. Thus, the path switch request message may include the same CSG ID indication, indicating that the source cell and the target have the same CSG ID. In this situation, the CSG ID of the target may not be carried. In addition, if the source cell and target are HeNBs, the gateway is the HeNB GW.

In step514b, the gateway504sends the path switch request message to the MME505. The content of the path switch request message in this step are identical with the content of the path switch request message in step514a. If the gateway504is not configured, steps514aand514bmay be merged into one step, in which the target BS503sends the path switch request message to the MME505.

In step515a, the MME505sends a bearer update request message to a user plane entity, i.e. Service-Gateway/Packet Data Network Gateway (S-GW/PDN GW)506. The signaling interactions between the S-GW and PDN GW are omitted here.

According to the received path switch request message, the MME505can determine that the target cell to which the UE501moves is a CSG cell or an open cell. For example, if the path switch request message includes the CSG ID of the target cell, it can be determined that the target cell of the UE501is the CSG cell. If the CSG ID of the target cell is not carried, it can be determined that the target cell is an open cell. If the received path switch request message includes the same CSG ID indication, it can be determined that the target cell and the source cell locate at a same CSG. In addition, the MME505knows the CSG ID and access mode of the source cell. Accordingly, the MME505can know the CSG ID and access mode of the target cell. If the PDN GW has requested the user CSG information of the UE (determined according to the UE context), under the circumstance that the target cell is the CSG cell, the bearer update request message sent from the MME505to the S-GW/PDN GW506includes the user CSG information.

The user CSG information includes the CSG ID of the target cell, the access mode of the target cell, and CSG membership indication of the target cell (the MME itself can make the judgment). The CSG membership indication indicates that the UE is joined to a CSG supported by the target cell, so that the PDN GW may charge the UE501according to the corresponding mode. In addition, if the PDN GW has requested the location information of the UE501, the modify bearer request message sent from the MME505to the S-GW/PDN GW506further includes the location information of the UE501, for example, the Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) Cell Global Identifier (ECGI) and/or the Tracking Area Identity (TAI), etc. How the PDN GW requests the MME (505) for reporting the location information of the UE and/or the user CSG information is well known and is omitted herein for brevity.

In step515b, the S-GW/PDN GW sends a bearer update response message to the MME.

In step516a, the MME505sends a path switch request acknowledgement message to the gateway504.

In step516b, the gateway504sends the path switch request acknowledgement message to the target BS503. If the gateway is not configured, steps516aand516bmay be merged into one step, in which the MME505sends the path switch request acknowledgement message to the target BS503.

In step517, the target BS503sends a UE context release message to the source BS502.

FIG. 6is a flowchart illustrating a handover method according to a second exemplary embodiment of the present invention.

Referring toFIG. 6, a source BS602makes a handover decision in step607.

In step608, the source BS602determines that an X2 handover is adopted. For example, the source BS602determines whether there is an X2 interface between itself and the target BS603. If there is not an X2 interface, the S1 handover process is executed; otherwise, the source BS602further determines whether the target cell is a hybrid cell. If yes, X2 handover is performed, i.e., step609is performed. Alternatively, the X2 handover may be adopted when the target cell is hybrid cell and the source cell and target cell have the same CSG ID. The S1 handover is adopted when they have different CSG IDs. The source BS602may be a HeNB or an eNB. The target BS (603) may also be the HeNB or eNB.

In addition, in step608, the source BS602may obtain the CSG ID and an access mode of the target cell from the UE601, through the X2 interface setup procedure, according to the configuration of the operator, and the like. The method for obtaining the CSG ID and the access mode is identical with that described above in step402, and is unnecessary to be described again here.

In step609, the source BS602sends the handover request message to the target BS. The handover request message may include the CSG ID of the target cell, and may further include a member indication for indicating whether the UE601is a subscribed or non-subscribed member of the target cell.

If the CSG ID of the target cell is obtained through the X2 interface setup procedure, the CSG identifier of the target cell may be omitted from the handover request message. In addition, the handover request message may include the member indication only under certain circumstances, such as when both the source cell and target cell are the hybrid cells, and have the same CSG ID.

In step610, the target BS603verifies the received CSG ID of the target cell. The target BS603verifies whether the CSG ID of the target cell carried in the handover request message is correct. The target BS603compares the CSG ID of the target cell carried in the handover request message with the CSG ID broadcast by the target cell to determine whether the two CSG IDs are the same. If they are not the same, but the target cell is a hybrid cell, this handover is accepted, i.e. step611is executed. Under this circumstance, as an implementation mode, the UE601may first be processed as a non-signed member. If they are the same CSG ID, step611is performed.

If the handover request message does not include the CSG ID of the target cell, the verification does not need to be performed. In addition, if the source cell and the target cell are different hybrid cells, but have different CSG IDs, the target cell may first process the UE601as the non-subscribed member after receiving the handover request message sent from the source BS. For the subscribed member and non-subscribed member, the target BS may provide services of different Quality of Service (QoS).

In step611, the target BS603sends a handover request acknowledgement message to the source BS602.

If the verification in step610fails, the CSG ID broadcast by the target cell, i.e., the CSG ID of the correct target cell may be carried in the handover request acknowledgement message. Even if the CSG ID of the target cell received by the target BS603from the source BS (602) is not in accordance with the CSG ID broadcast by the target cell, this handover may also be accepted. Accordingly, the target BS603sends the correct CSG ID of the target cell to the source BS602.

In step612, the source BS602sends a RRC connection re-configuration message to the UE601.

In step613, the UE601sends a RRC connection re-configuration completion message to the target BS603.

In step614a, the target BS603sends a path switch request message to the gateway604. The path switch request message includes the CSG ID and the access mode of the target cell, for indicating whether the target cell is a hybrid cell or a CSG cell. When the access mode is a CSG type, the path switch request message does not include the access mode, but only includes the CSG ID. This method is adopted for implicitly indicating that the target cell is a CSG cell. The target cell may be the hybrid type.

In addition, if the target cell receives member indication sent from the source BS602, the target cell may determine that its CSG ID is identical with that of the source cell. Correspondingly, the target BS603may include the same CSG ID indication or member indication in the path switch request message. In this case, the CSG ID and access mode may or may not be carried in the path switch request message.

In step614b, the gateway sends the path switch request message to the MME. The content of the path switch request message in this step is the same as that of the path switch request message in step614a. If the gateway is not configured, steps614aand614bmay be merged into one step, in which the target BS603sends the path switch request message to the MME605.

In step615, the MME605determines whether the UE (601) is a subscribed or non-subscribed member of the target cell. In step615, the MME605determines whether the UE601is a subscribed or non-subscribed member only when the target cell is a hybrid cell. The determination may be made using any appropriate technique.

In step616, the MME605sends a bearer update request message to an S-GW/PDN GW606. The signaling interactions between the S-GW and PDN GW are omitted here.

According to the CSG ID and access mode of the target cell carried by the received path switch request message, the MME605knows the CSG ID and access mode of the target cell. In addition, if the path switch request message does not include the CSG ID and access mode, but includes the same CSG identifier indication, since the MME605knows the CSG ID and access mode of the source cell, the MME605knows the CSG ID and access mode of the target cell. If the path switch request message does not include the CSG ID, but does include the member indication, the MME605may acquiesce in that under this circumstance, the source cell and the target cell have the same CSG ID, and may also know the CSG ID and access mode of the target cell. In addition, the MME605has determined whether the UE (601) is a subscribed or non-subscribed member of the target cell in step615. Accordingly, if the PDN GW has requested for the user CSG information determined from context of the UE601, the MME includes the user CSG information in the bearer update request message sent to the S-GW/PDN GW606.

The user CSG information includes the CSG ID of the target cell, access mode (i.e. hybrid cell), and CSG membership indication of the target cell, so that the PDN GW may charge the UE according to the corresponding mode. In addition, if the PDN GW has requested for the location information of the UE, the modify bearer request message sent from the MME605to the S-GW/PDN GW606further includes the location information of the user, for instance, the ECGI and/or the TAI, etc. How the PDN GW requests the MME605for reporting the location information of the UE601and/or the user CSG information may be implemented using any appropriate technique.

In step616b, the S-GW/PDN GW sends a bearer update response to the MME601.

In step617a, the MME601sends a path switch request acknowledgement message to the gateway604. The path switch request acknowledgement message may include the member indication indicating whether the UE601is a subscribed or non-subscribed member of the target cell. In addition, if the path switch request message received by the MME605in step509includes the member indication, and the result of whether the UE601is a subscribed member determined by the MME in step615is identical with the received member indication, the path switch request acknowledgement message in this step may not include the member indication; otherwise, the path switch request acknowledgement message includes the member indication.

The MME605may also notify the target BS603of the member indication through an S1 message, such as the UE context modification request message. Accordingly, the member indication does not need to be carried in the path switch request acknowledgement message in this step.

In step617b, the gateway604sends the path switch request acknowledgement message to the target BS603. The member indication may be carried in the path switch request acknowledgement message. If the gateway is not configured, steps617aand617bmay be merged into one step, in which the MME604sends the path switch request acknowledgement message to the target BS603.

In step618, the target BS603sends a UE context release message to the source BS602.

X2 handover in accordance with a third exemplary embodiment of the present invention is described below with respect toFIGS. 7 and 8.

FIG. 7is a working flow diagram of accessing a network by UE through an HeNB, when using the connection structure shown inFIG. 4in accordance with an exemplary embodiment of the invention. Detailed descriptions about steps outside the scope of the present exemplary embodiment are omitted.

In step706a, the UE701sends a Non-Access Stratum (NAS) message, e.g., an Attach message, a service request message, or the like, to a source HeNB702. In steps706band706c, the source HeNB702sends the NAS message received from the UE701to the HeNB GW704through S1 Access Protocol (AP) message, and the HeNB GW704sends the S1 AP message to the MME705. If the source HeNB702requested to be accessed by the UE701is CSG-HeNB or hybrid-HeNB, the S1 AP message further includes CSG identifier of the source HeNB cell704. In step707, after receiving the NAS message, the MME705performs the NAS authentication/security process with the UE701.

The performance of the NAS authentication/security process may be implemented using any appropriate implementation. When there is no UE context for the UE701in the network, when there is no integrity protection for the Attach request in steps706aand706b, or when the integrity authentication has failed, the integrity protection is activated with authentication and NAS security and the NAS encryption is performed. Otherwise, the process is optional. When the NAS security algorithm changes, the NAS security is established.

If the MME705supports unauthenticated International Mobile Subscriber Identification (IMSI) with emergent Attach, and the Attach type indicated by the UE501is emergent, the MME705will omit the authentication and security establishment process or the MME705will continue the Attach process when accepting the failed authentication.

In step708aand708b, the MME705sends an initial context setup request message to the HeNB GW704, and the HeNB GW704sends the initial context setup request message to the source HeNB702. The initial context setup request message includes the MME identifier of the MME705to service the UE701. The MME identifier may be included in the initial context setup request message sent by the MME to the HeNB GW704, may be included in the initial context setup request message sent by the HeNB GW704to the source HeNB702, or the MME705identifier may be included only in the initial context setup request message sent by the HeNB GW704to the source HeNB702. Any implementation may be employed.

In step709, after receiving the initial context setup request message, the source HeNB702establishes the radio bearer with the UE701.

In steps710aand710b, after establishing the radio bearer with the UE701, the source HeNB702sends an initial context setup response message to the HeNB GW704. The HeNB GW704sends the initial context setup response message to the MME705.

Until now, the whole working flow for accessing a network by UE (701) through HeNB in accordance with an exemplary embodiment of the invention has been completed.

After establishing the radio bearer between the UE701and the source HeNB702in accordance with the present exemplary embodiment, the X2 handover may be performed through the HeNBs. An exemplary embodiment is described below with respect toFIG. 8.

FIG. 8is a working flow diagram of X2 handover achieved with an HeNB in accordance with a third exemplary embodiment of the present invention. As shown inFIG. 8, detailed descriptions about steps outside the scope of the present exemplary embodiment are omitted.

In step807, the source HeNB802makes a handover decision.

In step808a, the source HeNB802sends a handover request message to a target HeNB803. The handover request message includes an MME identifier of a MME805serving the UE801.

In step808b, the target HeNB803sends a handover request acknowledge message to the source HeNB802.

In step809a, the source HeNB802sends an RRC connection reconfiguration message to the UE801, to request the UE801to X2 handover.

In step809b, after handover, the UE801sends an RRC connection reconfiguration completion message to the target HeNB803.

In step810a, the target HeNB803sends a path switch request message to the HeNB GW804, and the HeNB GW804sends the path switch request message to the MME805. The path switch request message includes an MME identifier of the MME805serving the UE801.

The path switch request message may further include a CSG identifier of the target HeNB803. Furthermore, the path switch request message may further include access mode of the target HeNB803, e.g. hybrid, etc. The value of the access mode may further include a CSG type, or the existence of CSG identifier may be used to implicitly demonstrate the CSG type of the target HeNB803when there is no access mode. When the target HeNB803accesses the MME805without going through the HeNB GW804, the path switch request message is directly sent by the target HeNB803to the MME805.

In step811a, the MME805sends a bearer update request message to S-GW/PDN GW806. The MME805may learn of the CSG identifier and the access mode of the destination cell, according to the CSG identifier and access mode information about the destination cell carried in received path switch request message. If the destination cell is hybrid, the MME805may determine whether the UE801is a subscribed member or a non-subscribed member of the destination cell according to the CSG identifier of the destination cell. Accordingly, if the PDN GW requests the user CSG information about the UE (which may be learned according to the UE context), the MME may includes the user CSG information in the bearer update request message which is sent to the S-GW/PDN GW806. The user CSG information includes the CSG identifier and access mode of the destination cell, as well as whether the UE801is a subscribed member or a non-subscribed member of the destination cell, so as to facilitate subsequent charging performed by the PDN GW for the UE801according to a corresponding mode. The requesting of the MME805to report the user CSG information by the PDN GW may be implemented using any known technique.

In step811b, after modifying the UE801's bearer, the S-GW/PDN GW806sends a modify bearer response message to the MME805.

In steps812aand812b, the MME805sends a path switch request acknowledge message to the HeNB GW805, and the HeNB GW805sends the path switch request acknowledge message to the target HeNB803. When the target HeNB803accesses the MME805without going through the HeNB GW804, the path switch request acknowledge message is directly sent by the MME805to the target HeNB803.

In step813, after receiving the path switch request acknowledge message, the target HeNB803sends a UE context release message to the source HeNB802.

Until now, the whole working flow for performing the X2 handover through the HeNB in accordance with an exemplary embodiment of the invention is completed.

The exemplary embodiments illustrated withFIGS. 7 and 8are only described in examples in which X2 handover is performed between HeNBs. In practical applications, the above handover process may also be applicable to the X2 handover process between an eNB and an HeNB accessed a CN through the HeNB GW. The specific process is as above, which will not be repeated here.

In the method for performing X2 handover through HeNB adopted by the third exemplary embodiment of the invention, when the UE accesses a network through the HeNB, the MME or the HeNB GW sends an MME identifier of an MME serving the UE to the HeNB. When performing the X2 handover, the HeNB may send the MME identifier to the target eNB/HeNB to which the UE needs to handover, to enable the target eNB/HeNB to successfully send the path switch request message to the MME serving the UE. When the target HeNB accesses the MME through the HeNB GW, the target HeNB sends the MME identifier to the destination HeNB GW, to enable the destination HeNB GW to successfully send the path switch request message to the MME serving the UE, and to reduce frequent interactions with the CN during an S1 handover process when ensuring a successful X2 handover. Thus, influence of the handover process on the CN is reduced, and handover delay is reduced.

The foregoing are only exemplary embodiments of the invention, which is not used for limiting the invention. Any modifications, equivalent substitutions, improvements, etc, within the spirit and principle of the invention, should be covered by the scope of the invention.

FIG. 9is a block diagram illustrating a structure of an HeNB/eNB or BS according to an exemplary embodiment of the present invention.

Referring toFIG. 9, each HeNB/eNB and BS operates as source HeNB/eNB and BS or target HeNB/eNB or BS, and a HeNB/eNB900includes a receiver902, a controller904, and a transmitter906. The controller904determines handover of the UE using an X2 interface.

For example, when the HeNB/eNB900operates as a source HeNB/eNB or BS. according to the first and second embodiment of the present invention, the controller904determines handover of the UE using X2 interface. If there is an X2 interface between the source BS and the target BS, and if the target BS doesn't support a CSG or the target BS supports a same CSG supported by the source BS, the controller904determines to perform the handover of the UE using the X2 interface, and obtains the CSG information of the target BS through an X2 interface set up procedure.

The transmitter906transmits a handover request message comprising (CSG) information of the target BS to the target BS. The receiver902receives a handover request acknowledgement message from the target BS. The CSG information includes an access mode indicating that the target BS is CSG BS supporting a specific CSG or hybrid BS supporting the specific CSG and UEs not included the specific CSG. If the target BS is the CSG BS or the hybrid BS, the CSG information includes a CSG ID of the specific CSG. If the target BS supports the same CSG supported by the source BS, the CSG information includes an identifier indicating that the target BS supports the same CSG. If the target BS is the hybrid BS, a membership identifier indicating whether the UE is joined to a CSG supported the hybrid BS.

In the X2 interface set up procedure, the transmitter906transmits a X2 setup request message comprising a CSG (ID) and a PCI for each serving cell of the source BS to the target BS, and the receiver902receives a X2 setup response message from target BS comprising a CSG ID and a PCI for each serving cells of the target BS.

According to the third exemplary embodiment of the present invention, if a MME identifier of MME serving the UE from MME or BS gateway, the transmitter906transmits the handover request message further comprising the MME identifier to the target BS by controlling of the controller (904).

For example, when the HeNB/eNB or BS900operates as a target source HeNB/eNB or BS according to the first and second exemplary embodiments of the present invention, the receiver902receives a handover request message comprising CSG information of a target BS from a source BS.

If the CSG information includes a first CSG ID, the controller904determines whether the first CSG ID and a second CSG ID are the same, and obtains the second CSG ID from CSG information broadcasted from the target cell. If the first CSG ID and the second CSG ID are the same, the transmitter906transmits a handover request acknowledgement message to the source BS, and the receiver902receives a RRC re-configuration message from the UE. The transmitter906transmits a path switch request message including the second CSG ID to MME. If a path switch request acknowledgement message is received by the receiver902from the MME, the transmitter906transmits an UpLink UL context release message to the source a BS.

When the HeNB/eNB or BS900operates as a target source HeNB/eNB or BS according to the third exemplary embodiment of the present invention, if the controller904obtains a MME ID of a MME serving the UE from the handover request message, the transmitter906transmits a path switch request message comprising the MME ID to the MME corresponding to the MME ID by controlling of the controller.

FIG. 10is a block diagram illustrating a structure of an MME according to an exemplary embodiment of the present invention.

The receiver1002receives a path switch request message comprising CSG information of a target BS from the target BS. If the CSG information indicates that the target BS is a CSG BS supporting a specific CSG, the transmitter1006transmits a bearer update request message including user CSG information to a user plane entity. If the receiver1002receives a bearer update response message, the transmitter1006transmits a path switch request acknowledgement message to the target BS by controlling of the controller (1004). The CSG information of the target BS or CSG information broadcast from the target cell includes an access mode indicating that the target BS is CSG BS supporting a specific CSG or hybrid BS supporting the specific CSG and UEs not included the specific CSG. If the target BS is the CSG BS or the hybrid BS, the CSG information includes a CSG ID of the specific CSG, and if the target BS supports the same CSG supported by the source BS, the CSG information includes an identifier represents that the target BS supports the same CSG.

According to an exemplary embodiment of the present invention, the processing burden of the core network can be reduced, and handover efficiency is improved.

The foregoing are only exemplary embodiments of the present invention. The protection scope of the present invention, however, is not limited to the above description. Any change or substitution, easily occurring to those skilled in the art, should be covered by the protection scope of the present invention.