Patent Description:
When an enhanced Node B (eNB) is newly or additionally installed, the eNB executes a self-configuration process. Self-configuration is an automated function for identifying a neighbor eNB, registering relationship setup, and setting up a connection to the core network in an eNB's initial bootup process and a pre-operation phase. In other words, the self-configuration process is a method of self-collecting/analyzing the parameters needed for an eNB's initial operation.

In the self-configuration operation process, after an eNB is powered on and connected to a transport link, the eNB may perform self-detection functions after the basic self-hardware verification. The self-detection functions may include functions of detecting the transport type and the length of an antenna cable, and automatically adjusting the path of a receiver. After performing the self-detection function, the eNB may set up a physical transfer link, and acquire information about its Internet Protocol (IP) address and an IP address to a relevant service or to relevant equipment such as a serving gateway, a Mobility Management Entity (MME), a configuration server, and the like, through a connection to a Dynamic Host Configuration Protocol (DHCP)/Domain Name System (DNS) server. Upon completion of this process, the eNB may create a secure tunnel to be used for S1 and X2 links in preparation for communication with a storage server, from which the eNB can obtain a new parameter set. Neighbor relations may be optionally set through the automated functions.

Automatic Neighbor Relation (ANR) aims to minimize or remove, if possible, the operations on neighbor information when installing a new eNB and optimizing the neighbor information. The ANR function may provide an automated method of acquiring and setting neighbor information to another eNB or a neighbor cell in an eNB or a cell, to which a User Equipment (UE) is currently connected. For the purpose of handover, the ANR function may automatically set an X2 interface that supports an interface between eNBs in Long Term Evolution (LTE).

An Evolved Universal Terrestrial Radio Access (EUTRA) Cell Global ID (ECGI), a Cell Global Identity (CGI), and a Global eNB ID (GEI) needed to set the X2 interface will be described with reference to the following table.

Table <NUM> illustrates relationships among the ECGI, CGI, and GEI.

The ECGI may include the CGI and the first Public Land Mobile Network ID (PLMN ID) in a Broadcast Public Land Mobile Network ID LIST (BPLMN ID LIST). The BPLMN LIST represents a list of PLMN IDs supported by the cell. Typically, the first PLMN ID may be a PLMN ID of a global eNB ID of an eNB managing the cell and the first PLMN ID may be defined as a Primary PLMN ID. The PLMN ID may include a mobile country code and a mobile network code. The CGI may include an eNB ID and a cell ID, and the cell ID and the eNB ID included in the CGI may be <NUM> bits and <NUM> bits in length, respectively. The GEI may include a PLMN ID and an eNB ID of the eNB.

For example, assuming that a first cell operates a first eNB and a se cond cell operates a second eNB, there is a need for a CGI included in an ECGI o f the second cell and a PLMN ID of the second eNB, in order for the first cell to add and manage the second cell as its neighbor cell.

<NPL>) analyses the issue of PLMN ID to be included in the Global eNB and ECGI from the point of view of a variety of possible network sharing cases, and then proposes RAN3 to first clarify the requirement for network sharing so that it is possible to judge whether the network sharing, described in the document, is supported. <NPL>) discloses that RAN3 has finalized the coding of the eNB identify and the Cell identity in RAN <NUM> specifications.

Recently, however, an operator sharing a cell may not broadcast information about a primary PLMN ID of the shared cell in order to exclusively use the allocated frequency band. In other words, the second cell broadcasts only its own PLMN ID for an ECGI except for a PLMN ID for a global eNB ID of the second eNB. Therefore, the first cell may acquire only the PLMN ID for the ECGI of the second cell and the first cell may fail a handover operation since the first cell may recognize the PLMN ID for ECGI of the second cell as the PLMN ID for the global eNB ID of the second eNB which is needed to achieve X2 setup. That is, the PLMN ID for the ECGI of the second cell may be mistaken for the PLMN ID for the global eNB ID of the second eNB.

Accordingly, there exists a need for an improved method and apparatus for acquiring cell identifiers (or a PLMN ID for a global eNB ID of an eNB) in a radio communication system.

The following aspects of the present disclosure in this Summary section relate to nonclaimed examples being useful for understanding the invention.

Aspects of the present disclosure are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present disclosure is to provide a method and apparatus for acquiring cell identifiers in a radio communication system.

Another aspect of the present disclosure is to provide a method and apparatus for acquiring cell identifiers in an environment where multiple operators share cells, in a radio communication system.

Another aspect of the present disclosure is to provide a method and apparatus for registering neighbor relationships by acquiring cell identifiers in an environment where multiple operators share cells, in a radio communication system.

In accordance with an aspect of the present disclosure, a method for acquiring a cell identifier by a source cell in a radio communication system is provided. The method includes receiving information about a new cell from a User Equipment (UE) in the source cell, acquiring an Evolved Universal Terrestrial Radio Access (EUTRA) Cell Global Identifier (ECGI) of the new cell from the UE, if it is determined based on the information about the new cell that there is no neighbor relationship with the new cell, determining whether a Public Land Mobile Network (PLMN) Identifier (ID) (PLMN ID) in the ECGI is included in a mapping table between a primary PLMN ID and a shared PLMN ID, and acquiring an X2 Internet Protocol (IP) address of the new cell from an Evolved Packet Core (EPC) according to the determination results.

In accordance with another aspect of the present disclosure, a method for supporting a source cell to acquire a cell identifier by a UE in a radio communication system is provided. The method includes detecting a new cell, and reporting information about the new cell to the source cell to allow the source cell to acquire a cell identifier.

In accordance with still another aspect of the present disclosure, a method for supporting a source cell to acquire a cell identifier by an EPC in a radio communication system is provided. The method includes determining whether a PLMN ID in an ECGI of a new cell different from the source cell is included in a mapping table between a primary PLMN ID and a shared PLMN ID, and providing an X2 IP address of the new cell to the source cell according to the determination results.

In accordance with yet another aspect of the present disclosure, a source cell in a radio communication system is provided. The source cell includes a receiving unit configured to receive information about a new cell from a UE in the source cell, a control unit configured to acquire an ECGI of the new cell from the UE, if it is determined based on the information about the new cell that there is no neighbor relationship with the new cell, determine whether a PLMN ID in the ECGI is included in a mapping table between a primary PLMN ID and a shared PLMN ID, and acquire an X2 IP address of the new cell from an EPC according to the determination results.

In accordance with still another aspect of the present disclosure, a UE that supports a source cell to acquire a cell identifier in a radio communication system is provided. The UE includes a control unit configured to detect a new cell, and report information about the new cell to the source cell to allow the source cell to acquire a cell identifier.

In accordance with still another aspect of the present disclosure, an EPC that supports a source cell to acquire a cell identifier in a radio communication system is provided. The EPC includes a control unit configured to determine whether a PLMN ID in an ECGI of a new cell different from the source cell is included in a mapping table between a primary PLMN ID and a shared PLMN ID, and to provide an X2 IP address of the new cell to the source cell according to the determination results.

Further advantegeous embodiments of the invention are defined in the dependent claims.

The above and other aspects, features and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:.

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims. Accordingly, those of ordinary skilled in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope of the present disclosure.

In this disclosure, it will be assumed that a cell can be managed to have a different PLMN ID for an ECGI from a PLMN ID for a global eNB ID.

The present disclosure provides a method and apparatus for acquiring cell identifiers in a radio communication system.

In addition, the present disclosure provides a method and apparatus for acquiring cell identifiers in an environment where multiple operators share cells, in a radio communication system.

Moreover, the present disclosure provides a method and apparatus for registering neighbor relationships by acquiring cell identifiers in an environment where multiple operators share cells, in a radio communication system.

Although the cell identifier acquisition method and apparatus proposed in the present disclosure will be applied to a Long Term Evolution Advanced (LTE-A) mobile communication system in the following description, it is to be understood that this is merely by way of example and that the proposed cell identifier acquisition method and apparatus may be used not only in the LTE-A mobile communication system, but also in other cellular radio communication systems such as a High Speed Downlink Packet Access (HSDPA) mobile communication system, a High Speed Uplink Packet Access (HSUPA) mobile communication system, a Long Term Evolution (LTE) mobile communication system, a <NUM>rd Generation Project Partnership <NUM> (3GPP2) High Rate Packet Data (HRPD) mobile communication system, an Institute of Electrical and Electronics Engineers (IEEE) <NUM> mobile communication system, and the like.

In the first example and in the embodiment of the present disclosure, a source cell will be referred to as a first cell, and a new cell (or target cell) will be referred to as a second cell.

It will be assumed in <FIG> and <FIG> that first and second cells <NUM> and <NUM> and first and second eNBs <NUM> and <NUM> have the same Public Land Mobile Network Identifier (PLMN ID)=A, the first cell <NUM> has an ID=<NUM>, and the first eNB <NUM> has an ID=<NUM>. Therefore, a Cell Global Identity (CGI) of the first cell <NUM> is <NUM> that includes the first eNB's ID=<NUM> and the first cell's ID=<NUM>, and an Evolved Universal Terrestrial Radio Access (EUTRA) Cell Global Identifier (ECGI) is A. <NUM> that includes the first PLMN ID=A in a Broadcast Public Land Mobile Network ID LIST (BPLMN LIST) and the CGI=<NUM>.

In the same way, if it is assumed that an ID of the second cell <NUM> is <NUM> and an ID of the second eNB <NUM> is <NUM>, a CGI of the second cell <NUM> is <NUM> that includes the second eNB's ID=<NUM> and the second cell's ID=<NUM>, and an ECGI thereof is A. <NUM> that includes the first PLMN ID (i.e., a primary PLMN ID)=A in the BPLMN LIST, and the CGI=<NUM>.

In addition, a Global eNB ID (GEI) of the first eNB <NUM> is A. <NUM> that includes the primary PLMN ID=A and the first eNB's ID=<NUM>, and a GEI of the second eNB <NUM> is A. <NUM> that includes the primary PLMN ID=A and the second eNB's ID=<NUM>.

<FIG> illustrates relationships among an ECGI, a CGI and a GEI according to a first example of the present disclosure.

Referring to <FIG>, a communication system may include the first cell <NUM>, the first eNB <NUM>, the second cell <NUM>, the second eNB <NUM>, a Mobility Management Entity (MME) <NUM>, and a UE existing in the first cell <NUM>. If the UE corresponds to the first cell <NUM> operated by the first eNB <NUM>, the UE may newly discover the second cell <NUM> and acquire cell information that includes System Information (SI). Since the second cell <NUM> broadcasts its own cell information to broadcast the currently available BPLMN LIST=(A,B) and a CGI that includes the second cell's ID=<NUM> and the second eNB's ID=<NUM>, the UE, upon receiving the BPLMN LIST, may transmit the CGI=<NUM> and the first PLMN ID=A to the first cell <NUM>. Therefore, the first eNB <NUM> may recognize a GEI of the second eNB <NUM> as A. <NUM>, determining that an ECGI of the second cell <NUM> is A. <NUM> (ECGI=A. Thereafter, the first eNB <NUM> may request X2 setup, using the PLMN ID=A of the second eNB <NUM>, which is included in the recognized GEI=A.

<FIG> illustrates an operation process of a system according to the first example of the present disclosure.

Referring to <FIG>, in operation <NUM>, a terminal <NUM> connected to the first cell <NUM> may determine or detect the presence of the second cell <NUM>, for different cells between which an inter-eNB neighbor relationship is not set.

The second cell <NUM> may broadcast its own cell information that includes SI. In operation <NUM>, the UE <NUM> may transmit, to the first cell <NUM>, a Physical Cell ID (PCI), which is received through the cell information and represents a cell identifier in a physical layer.

In operation <NUM>, the first cell <NUM> may send, to the UE <NUM>, an SI request for acquiring an ECGI of the second cell <NUM> to additionally manage the second cell <NUM> as its neighbor cell, determining that a PCI for the second cell <NUM> is not present in a database managed by the first cell <NUM>.

In operation <NUM>, the UE <NUM> may receive a CGI that includes a second eNB's ID and a second cell's ID, and a BPLMN LIST supported by the second cell <NUM>, by analyzing the cell information broadcasted by the second cell <NUM>.

In operation <NUM>, the UE <NUM> may transmit, to the first cell <NUM>, the CGI that includes the second eNB's ID and the second cell's ID, and the ECGI that includes a PLMN ID supporting the second cell <NUM>.

In operation <NUM>, the first cell <NUM> may attempt to acquire an X2 IP address by transmitting, to an Evolved Packet Core (EPC) <NUM>, a GEI that includes the second eNB's ID and a primary PLMN ID, which are acquired in operation <NUM>. The process of attempting to acquire an IP address may use setup transfer (or SlAP ENB CONFIGURATION TRANSFER).

In operation <NUM>, the EPC <NUM> may transmit the relevant IP address acquisition information to the second eNB <NUM> using the received GEI.

In operation <NUM>, the second eNB <NUM> may transmit an IP address for its X2 to the EPC <NUM>, if the second eNB <NUM> supports the first cell <NUM>. In this case, SlAP ENB CONFIGURATION TRANSFER and MME CONFIGURATION TRANSFER may be used.

In operation <NUM>, the first cell <NUM> may acquire an IP of the second eNB <NUM> operating the second cell <NUM>, through the EPC <NUM>. In operation <NUM>, the first cell <NUM> may request X2 setup using the acquired X2 IP address of the second eNB <NUM>. In operation <NUM>, the first cell <NUM> may complete its operation if the second cell <NUM> responds to the request.

Referring to <FIG> and <FIG>, an embodiment is described. In the embodiment, it will be assumed that a PLMN ID for a global eNB ID of a second eNB <NUM> is different from a PLMN ID for an ECGI of a second cell <NUM> in the network, and as to its broadcast cell information, the second cell <NUM> broadcasts only its (i.e., the second cell's) own PLMN ID for the ECGI.

It will be assumed in <FIG> and <FIG> that a first cell <NUM> has an ID=<NUM>, a first eNB <NUM> has an ID=<NUM>, and the first cell <NUM> and the first eNB <NUM> have a PLMN ID for an ECGI=A. Therefore, a CGI is <NUM> that includes an ID=<NUM> of the first eNB <NUM> and an ID=<NUM> of the first cell <NUM>; a GEI is A. <NUM> that includes an ID=<NUM> of the first eNB <NUM> and a PLMN ID for a global eNB ID=A of the first eNB <NUM>; and an ECGI is A. <NUM> that includes a PLMN ID for the ECGI=A of the first cell <NUM> and the CGI=<NUM>.

In the same way, it will be assumed that the second cell <NUM> has an ID=<NUM>, the second eNB <NUM> has an ID=<NUM>, the second cell <NUM> has a PLMN ID for an ECGI=B, and the second eNB <NUM> has a PLMN ID for a global eNB ID=A. Therefore, a CGI is <NUM> that includes an ID=<NUM> of the second eNB <NUM> and an ID=<NUM> of the second cell <NUM>; a GEI is A. <NUM> that includes an ID=<NUM> of the second eNB <NUM> and a PLMN ID for the global eNB ID=A of the second eNB <NUM>, and an ECGI is B. <NUM> that includes a PLMN ID for the ECGI=B of the second cell <NUM> and the CGI=<NUM>.

In addition, it will be assumed that a third eNB <NUM> has an ID=<NUM> and a GEI=B.

<FIG> illustrates relationships among an ECGI, a CGI and a GEI according to an embodiment of the present disclosure.

Referring to <FIG>, the system may include the first cell <NUM>, the first eNB <NUM>, the second cell <NUM>, the second eNB <NUM>, the third eNB <NUM>, an MME <NUM>, and a UE existing in the first cell <NUM>.

For example, a process of performing X2 setup by the first cell <NUM> and the second cell <NUM> will be described below.

If the UE corresponds to the first cell <NUM> of the first eNB <NUM>, the UE may newly discover the second cell <NUM> and perform SI request. Thereafter, upon receiving a BPLMN ID LIST=B that the second cell <NUM> is currently broadcasting, the UE may transmit a CGI=<NUM> and a PLMN ID=B to the first eNB <NUM>. In this case, the first eNB <NUM> may recognize even a GEI of the second eNB <NUM> as B. <NUM>, determining that an ECGI of the second cell <NUM> is B. As a result, the first eNB <NUM> may send an X2 setup request not to the second eNB <NUM>, but to the third eNB <NUM>. The X2 setup request may include a process in which the first cell <NUM> acquires an X2 IP address of the second cell <NUM>.

Therefore, the first cell <NUM> may use a mapping table as defined in Table <NUM>. The mapping table may represent mapping relationships between a primary PLMN (or a primary PLMN for Global eNB ID) and a shared PLMN (or a shared PLMN ID for EUTRA CGI).

When using the mapping table, the first cell <NUM> may determine whether the PLMN ID in the ECGI is included in the mapping table between the primary PLMN and the shared PLMN, and map the PLMN IDs depending on the determination results. Since the second cell <NUM> broadcasts only the currently available BPLMN ID LIST=B, the first eNB <NUM> may recognize a GEI of the second eNB <NUM> as A. <NUM> by mapping the PLMN ID=B of the second cell <NUM> to A. Thereafter, based on the GEI, the first eNB <NUM> may recognize the second eNB <NUM> and request X2 setup. If a PLMN ID for a global eNB ID of a neighbor eNB does not coincide with a PLMN ID for an ECGI of the neighbor eNB's cell, the first eNB <NUM> may map PLMN IDs for global eNB IDs of the neighbor eNB and the cells corresponding to the neighbor eNB using the mapping table, thereby preventing errors from occurring in X2 setup.

The X2 setup request corresponds to a process in which a source cell acquires an X2 IP address of a new cell. The process of acquiring an X2 IP address will be described with reference to an operation process of <FIG> according to the second embodiment of the present disclosure.

<FIG> illustrates an operation process according to the embodiment of the present disclosure.

Referring to <FIG>, in operation <NUM>, a terminal <NUM> connected to the first cell <NUM> may determine or detect the presence of the second cell <NUM>, for different eNBs between which an inter-eNB neighbor relationship is not set.

The second cell <NUM> may broadcast information about its cell. In operation <NUM>, the UE <NUM> may transmit, to the first cell <NUM>, a PCI that the UE <NUM> has received based on the information. In other words, the UE <NUM> may provide information about a new cell to a source cell so that the source cell may acquire an identifier of the new cell. The information about a cell may include the cell's PCI and the system information.

Thereafter, in operation <NUM>, determining that a PCI for the second cell <NUM> is not present in a database managed by the first cell <NUM>, the first cell <NUM> may transmit, to the UE <NUM>, a cell information request for acquiring an ECGI of the second cell <NUM> in order to additionally manage the second cell <NUM> as a neighbor cell.

In operation <NUM>, the UE <NUM> may receive a CGI and a BPLMN ID LIST supporting the second cell <NUM> by analyzing cell information that is broadcasted by the second cell <NUM>. In operation <NUM>, the UE <NUM> may transmit, to the first cell <NUM>, an ECGI that includes the CGI and the PLMN ID=B supporting the second cell <NUM>.

In operation <NUM>, the first cell <NUM> may determine whether the PLMN ID=B in the received ECGI is present in the mapping table. The mapping table may represent mapping relationships between a primary PLMN ID and a PLMN ID for shared cells in the eNB.

In operation <NUM>-<NUM>, if the PLMN ID in the ECGI received at the first cell <NUM> is included in the PLMN LIST for shared cells, which is included in the mapping table, the first cell <NUM> may acquire a GEI by mapping the PLMN ID to the primary PLMN ID in the mapping table. In other words, the source cell may acquire a GEI of a new cell by changing the PLMN ID in the ECGI to a primary PLMN ID in the mapping table.

However, if the PLMN ID in the received ECGI is not included in the PLMN LIST for shared cells, which is included in the mapping table, the first cell <NUM> may determine in operation <NUM>-<NUM> whether the PLMN ID is present in the primary PLMN ID in the mapping table, and acquire a GEI by mapping the PLMN ID to the primary PLMN ID, if the PLMN ID is present in the primary PLMN ID in the mapping table. In other words, a source cell may determine whether the PLMN ID in the ECGI is included in the primary PLMN LIST in the mapping table, and acquire a GEI of a new cell using the PLMN ID in the ECGI, if it is determined that the PLMN ID in the ECGI is included in the primary PLMN LIST in the mapping table.

In operation <NUM>-<NUM>, if the PLMN ID in the received ECGI is not mapped to an item in the mapping table, the first cell <NUM> may terminate the ANR function, disregarding the ECGI. In other words, if the PLMN ID in the ECGI is not included in the mapping table, the source cell may terminate the ANR function, discarding information about the new cell.

In operation <NUM>, the first eNB <NUM> may attempt to acquire an X2 IP address to the EPC using the GEI that is acquired in operation <NUM>-<NUM> or <NUM>-<NUM>. Operation <NUM> may use SlAP ENB CONFIGURATION TRANSFER. In operation <NUM>, the EPC may transmit IP address acquisition information for the second cell <NUM> to the second eNB <NUM> using the received GEI. In operation <NUM>, the second eNB <NUM> may transmit, to the EPC, an X2 IP address for the second eNB <NUM>, if the second eNB <NUM> supports the first cell. In operation <NUM>, the EPC may transmit an X2 IP address of the second eNB <NUM> managing the second cell <NUM>, to the first eNB <NUM>. In operation <NUM>, the first eNB <NUM> may request X2 setup using the acquired X2 IP address of the second eNB <NUM>. In operation <NUM>, the first eNB <NUM> may end the operation if the second eNB <NUM> responds to the request.

In other words, the EPC may provide the X2 IP address of a new cell to a source cell depending on whether a PLMN ID in an ECGI of the new cell different from the source cell is included in the mapping table between the primary PLMN and the shared PLMN.

Although not illustrated in the drawings, the source cell may include a receiving unit, a transmitting unit, a control unit, and a storage unit. The control unit may control the overall operation of the source cell, and the receiving unit may receive various messages from a UE, a new cell and an EPC. The transmitting unit may send various messages to the UE, the new cell and the EPC, and the storage unit may store various messages received by the receiving unit, and various programs needed to operate the source cell. For the source cell, the receiving unit, the transmitting unit, the control unit and the storage unit may be separately implemented, or the receiving unit, the transmitting unit, the control unit and the storage unit may be implemented in a single combined unit.

In addition, although not illustrated in the drawings, the new cell may include a receiving unit, a transmitting unit, a control unit, and a storage unit. The control unit may control the overall operation of the new cell, and the receiving unit may receive various messages from a UE, a source cell and an EPC. The transmitting unit may send various messages to the UE, the source cell and the EPC, and the storage unit may store various messages received by the receiving unit, and various programs needed to operate the new cell. For the new cell, the receiving unit, the transmitting unit, the control unit and the storage unit may be separately implemented, or the receiving unit, the transmitting unit, the control unit and the storage unit may be implemented in a single combined unit.

Further, although not illustrated in the drawings, the EPC may include a receiving unit, a transmitting unit, a control unit, and a storage unit. The control unit may control the overall operation of the EPC, and the receiving unit may receive various messages from a source cell and a new cell. The transmitting unit may send various messages to the source cell and the new cell, and the storage unit may store various messages received by the receiving unit, and various programs needed to operate the EPC. For the EPC, the receiving unit, the transmitting unit, the control unit and the storage unit may be separately implemented, or the receiving unit, the transmitting unit, the control unit and the storage unit may be implemented in a single combined unit.

Moreover, although not illustrated in the drawings, the UE may include a receiving unit, a transmitting unit, a control unit, and a storage unit. The control unit may control the overall operation of the UE, and the receiving unit may receive various messages from a source cell and a new cell. The transmitting unit may send various messages to the source cell and the new cell, and the storage unit may store various messages received by the receiving unit, and various programs needed to operate the UE. For the UE, the receiving unit, the transmitting unit, the control unit and the storage unit may be separately implemented, or the receiving unit, the transmitting unit, the control unit and the storage unit may be implemented in a single combined unit.

Claim 1:
A method, performed by a first eNB (<NUM>), for acquiring an identifier of a new cell (<NUM>) of a second eNB (<NUM>) and connecting the first eNB (<NUM>) to the second eNB (<NUM>), comprising:
receiving (<NUM>) a Physical Cell ID, PCI, from a UE (<NUM>);
determining whether the received PCI is not present in a database managed by the first eNB (<NUM>);
transmitting (<NUM>) a cell information request for acquiring an Evolved universal terrestrial radio access Cell Global Identifier, ECGI, of the new cell to the UE;
receiving (<NUM>) an ECGI from the UE;
acquiring a proper Public Land Mobile Network IDentifier, PLMN ID, based on the received ECGI;
transmitting (<NUM>), to an Evolved Packet Core, EPC, (<NUM>), an eNB configuration transfer message which includes a global eNB identifier, GEI, for acquiring an X2 address of the second eNB (<NUM>), said GEI being acquired by using the acquired proper PLMN ID; and
receiving (<NUM>), from the EPC (<NUM>), a MME configuration transfer message which includes the X2 address of the second eNB (<NUM>) for connecting the first eNB (<NUM>) to the second eNB (<NUM>),
wherein the proper PLMN ID is one of:
if the PLMN ID in the received ECGI is included in a shared PLMN ID list of a mapping table, a corresponding PLMN ID in a primary PLMN ID list of the mapping table; and
if the PLMN ID in the received ECGI is not included in the shared PLMN ID list but is included in the primary PLMN ID list, the PLMN ID in the received ECGI.