Abstract:
A method and apparatus for controlling inter-PLMN handover based on CSG lists of equivalent PLMNs is provided. A method for receiving subscriber information of a terminal at a Mobility Management Entity (MME) includes transmitting an update location request message for the terminal to a Home Subscriber Server (HSS), and receiving an update location acknowledgement message with the subscriber information of the terminal from the HSS, wherein the update location request message comprises a list of equivalent Public Land Mobile Networks (PLMNs) among which the MME supports inter-PLMN handover of the terminal. The method and apparatus for controlling inter-plan handover to a CSG cell according to the present invention is characterized in that a control apparatus of a core network acquires the allowed CSG lists for determining a User Equipments (UEs) capability of access to a CSG cell and determines whether to permit inter-PLMN handover based on the allowed CSG lists.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation application of prior application Ser. No. 13/440,300, filed on Apr. 5, 2012, and claimed the benefit under 35 U.S.C §119(a) of a Korean patent application filed on Apr. 5, 2011, in the Korean Intellectual Property Office and assigned Serial number 10-2011-0031360, the entire disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for controlling inter-Public Land Mobile Network (PLMN) handover to a Closed Subscriber Group (CSG) cell. More particularly, the present invention relates to a method and apparatus for controlling inter-PLMN handover based on CSG lists of equivalent PLMNs. 
     2. Description of the Related Art 
     A Closed Subscriber Group (CSG) is a limited set of users permitted to access a specific cell (i.e., a CSG cell assigned a CSG ID). In other words, only those users included in the CSG list are permitted to access the specific cell. For example, when a femtocell is deployed for use in a specific location, such as a user&#39;s home, it can be configured in CSG mode in which it is assigned a CSG ID. In that case, the CSG ID is added to the allowed CSG list of the family members&#39; terminals so as to allow access to the femto cell. 
     The control nodes of a network including a Home evolved Node B (HeNB) that are assigned a CSG ID can be configured as shown in  FIGS. 1 and 3 . 
       FIG. 1  is a diagram illustrating a configuration of network control nodes including an HeNB having a CSG ID according to the related art.  FIG. 3  is a diagram illustrating another configuration of network control nodes having a CSG ID according to the related art. 
     Referring to  FIG. 1 , macro eNB1  17  and macro eNB2  20  having no CSG ID and HeNBs  15 ,  16 ,  18 , and  19  having a CSG ID are respectively connected to a Mobility Management Entity (MME)  11  and  12 , which are in turn each connected to Home Subscriber Server (HSS)  10 . The connection to the MME can be achieved via an HeNB Gateway (GW)  13  and  14 , as used by the HeNBs  15 ,  16 , and  18 , or without involvement of an HeNB GW as in the case of the HeNB  19 . Because the fact of whether the HeNB is connected to the MME through the HeNB GW does not influence the procedure related to the present invention, a detailed description thereof is omitted 
     Similarly, referring to  FIG. 3 , both macro eNBs  37  and  40  having no CSG ID and HeNBs  35 ,  36 ,  38  and  39  having a CSG ID are connected to an MME  31  and  32 , respectively, which are in turn each connected to HSS  30 . The connection to an MME can be achieved via an HeNB GW  33  and  34 , as used by the HeNBs  35 ,  36 , and  38 , or without involvement of an HeNB GW as in the case of the HeNB  39 . Because the fact of whether the HeNB is connected to the MME through the HeNB GW does not influence the procedure related to the present invention, a detailed description thereof is omitted. 
     Problems that may arise in the networks configured as shown in  FIGS. 1 and 3  are described with reference to  FIGS. 2 and 4 , respectively. 
       FIG. 2  is a signaling diagram illustrating a handover procedure in the network configured as shown in  FIG. 1  according to the related art. 
     Referring to  FIG. 2 , User Equipment (UE)  21  is configured with the allowed CSG lists of {(PLMN A, (CSG1, CSG2)), (PLMN B, (CSG1, CSG3))} at step  100  which is the same CSG list of the HSS  10 . Here, PLMN A and PLMN B are equivalent PLMNs. In this state, if the UE  21  sends an ATTACH or a TRACKING AREA UPDATE (TAU) request to the MME1  11  of the PLMN A at step  101 , the MME1  11  processes the ATTACH or the TAU request and sends a Location Update Request to the HSS  10  so as to register itself as the serving MME of the corresponding UE  21  and acquire the subscription information of the UE  21  at step  101 . a . The subscription information includes the CSG list of the PLMN A as the registered PLMN and is delivered to the MME1  11  at step  101 . b . After the registration process has completed, the CSG list of the PLMN B is updated. In this case, the CSG1 may be unintentionally deleted in the CSG list at step  103 . Such a CSG list update situation of the HSS  10  is delivered through Open Mobile Alliance (OMA) Device Management (DM). However, since the allowed CSG list update execution timing in the UE  21  using the OMA-DM is not synchronized with the HSS  10  update timing accurately, the allowed CSG list of the UE  21  is in the un-synchronized state for a certain time period until the OMA-MD is executed, even though the allowed CSG list of the HSS  10  has been updated. In such a situation, the UE  21  may approach the HeNB3  18  at step  102 . If the UE  21  moves towards the HeNB3  18  in the state that in which its allowed CSG list is un-synchronized, the measurement report is performed based on the old allowed CSG list which has not been updated yet. That is, the UE  21  determines whether the CSG ID of the HeNB3  18  exists in the PLMN&#39;s allowed CSG list stored in the UE  21 . Since the CSG ID of the HeNB3  18  is CSG1 and the PLMN B&#39;s CSG list of the UE  21  includes the CSG1, the determination result is true such that the UE  21  reports the CS cell (i.e., the HeNB3&#39;s cell) to the eNB1  17  as the current serving cell at step  104 . If the report is received, the eNB1  17  evaluates the information on the equivalent PLMN and the CSG membership reported by the UE  21  to determine inter-PLMN handover to the target CSG cell of a different PLMN, resulting in a handover decision for the UE  21  to the CSG1 of the PLMN B and sending a Handover Required message to the MME1  11  (PLMN A) at step  105 . If the Handover Required message is received, the MME1  11  determines handover based on the allowed CSG list of the PLMN A which is received from the HSS  10  at step  101 . b  other than the allowed CSG list of the target PLMN B. Since the CSG1 as the CSG ID of the target cell exists in the allowed CSG list of the PLMN A, the MME1  11  determines that the UE  21  has access rights to the CSG1 and, as a consequence, determines that the PLMN B is the equivalent PLMN of the PLMN A. In that case, the MME1  11  executes the handover by sending a forward relocation required message to the MME2  12  as the target MME at step  106 . Since the MME2  12 , as the target MME, is the equivalent PLMN of the source PLMN, it performs the handover preparation procedure at step  107  and the handover execution procedure entirely such that the UE  21  completes the handover to the HeNB3  18  at step  108 . Since the TA is changed due to the change of the PLMN after the completion of the handover, the UE  21  sends a TAU message to the MME2  12  as the new MME at step  109 . If the TAU message is received, the MME2  12  sends a location update request to the HSS  10  at step  110  for the TAU to register the MME2  12  as the serving MME of the UE  21  and receives the subscription data including the PLMN B&#39;s allowed subscription list of CSG3 at step  111 . At this time, the MME2  12  determines that the UE  21  is not authorized for CSG1 in step  112 . That is, the received PLMN B&#39;s allowed CSG list does not include CSG1. Accordingly, the TAU request of the UE  21  is rejected at step  113  and the UE  21  enters the unregistered state. Thus, if the procedure depicted in  FIG. 2  is executed in the network configured as shown in  FIG. 1 , a problem is caused in that the UE  21  completes the handover and then loses network connection. 
       FIG. 4  is a signaling diagram illustrating a handover procedure in the network configured as shown in  FIG. 3 . 
     Referring to  FIG. 4 , UE  41  is configured with the allowed CSG lists of {(PLMN A, (CSG1, CSG2)), (PLMN B, (CSG2, CSG3))} in step  200  which is the same CSG list of the HSS  30 . Here, PLMN A and PLMN B are equivalent PLMNs. In this state, if the UE  41  sends an ATTACH or a TAU request to the MME1  31  of the PLMN A at step  201 , the MME1  31  processes the ATTACH or TAU request and sends a Location Update Request to the HSS  30  at step  201 . a  so as to register itself as the serving MME of the corresponding UE  41  and acquire the subscription information of the UE  41  at step  201 . b . The subscription information includes the CSG list of the PLMN A as the registered PLMN and is delivered to the MME1  31 . In this situation, the UE may approach the HeNB4  38  at step  202 . In that case, the UE  41  performs a measurement report based on its allowed CSG list. That is, the UE  41  determines whether the CSG ID of the HeNB4  38  exists in the corresponding PLMN&#39;s allowed CSG list stored in the UE  41 . Since the CSG ID of the HeNB4  38  is CSG3 and the CSG3 exists in the corresponding PLMN&#39;s CSG list of the UE  41 , the determination result is true such that the UE  41  reports the CSG3 as a cell of the HeNB4  38  to the eNB1  37  as the current serving cell at step  204 . If the report is received, the eNB1  37  makes an inter-PLMN handover decision to a CSG cell of another PLMN using the membership information and equivalent PLMN information reported by the UE  41  and sends a Handover Required message to the MME1  31  (PLMN A) at step  205 . If the Handover Required message is received, the MME1  31  makes a handover decision at step  206  based on the allowed CSG list of the PLMN A which is received from the HSS  30  at step  201 . b  other than the allowed CSG list of the target PLMN B. If the CSG3 as the CSG ID of the target cell does not exist in the allowed CSG list of the PLMN A, it is determined that the UE  41  has no access right to the CSG3 such that the handover is rejected at step  207 , even though the UE can actually make a handover to the CSG 3. As a result, although it is possible to be served by the HeNB4  38  having a good channel condition, the UE  41  is being served by the eNB1  37  having a poor channel condition. 
     That is, the procedure shown in  FIG. 4  that is executed in the network configuration of  FIG. 3  causes a problem in that the UE fails to perform a handover to the best cell available, resulting in a potential failure of the communication. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention are to address at least the above-mentioned problem and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an access control method and apparatus that is capable of preventing a handover decision from being made to an inappropriate network or the handover from being blocked. 
     In accordance with an aspect of the present invention, a method for receiving subscriber information of a terminal at a Mobility Management Entity (MME) is provided. The method includes transmitting an update location request message for the terminal to a Home Subscriber Server (HSS), and receiving an update location acknowledgement message with the subscriber information of the terminal from the HSS, wherein the update location request message comprises a list of equivalent Public Land Mobile Network (PLMNs) among which the MME supports inter-PLMN handover of the terminal. 
     In accordance with another aspect of the present invention, a method for transmitting subscriber information of a terminal at an HSS is provided. The method includes receiving an update location request message for the terminal from an MME, and transmitting an update location acknowledgement message including the subscriber information of the terminal to the MME, wherein the update location request message comprises a list of equivalent PLMNs among which the MME supports inter-PLMN handover of the terminal. 
     In accordance with another aspect of the present invention, an MME for receiving subscriber information of a terminal is provided. The MME includes a transceiver which communicates with at least one of a base station and an HSS, and a controller which controls transmitting an update location request message for the terminal to an HSS and receiving an update location acknowledgement message with the subscriber information of the terminal from the HSS, wherein the update location request message comprises a list of equivalent PLMNs among which the MME supports inter-PLMN handover of the terminal. 
     In accordance with still another aspect of the present invention, an HSS for transmitting subscriber information of a terminal is provided. The HHS includes a transceiver which communicates with an MME, and a controller which controls receiving an update location request message for the terminal from an MME and transmitting a update location acknowledgement message including the subscriber information of the terminal to the MME, wherein the update location request message comprises a list of equivalent PLMNs among which the MME supports inter-PLMN handover of the terminal. 
     Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram illustrating a configuration of network control nodes including a Home evolved Node B (HeNB) having a Closed Subscriber Group Identifier (CSG ID) according to the related art; 
         FIG. 2  is a signaling diagram illustrating a handover procedure in the network of  FIG. 1  according to the related art; 
         FIG. 3  is a diagram illustrating another configuration of network control nodes having a CSG ID according to the related; 
         FIG. 4  is a signaling diagram illustrating a handover procedure in the network of  FIG. 3  according to the related art; 
         FIG. 5  is a diagram illustrating a configuration of a network according to an exemplary embodiment of the present invention; 
         FIGS. 6 to 8  are signaling diagrams illustrating handover procedures according to exemplary embodiments of the present invention; 
         FIG. 9  is a signaling diagram illustrating a handover procedure modified from the handover procedure of  FIG. 8  according to an exemplary embodiment of the present invention; 
         FIG. 10  is a flowchart illustrating a Mobility Management Entity (MME) procedure in a handover control method according to an exemplary embodiment of the present invention; and 
         FIG. 11  is a flowchart illustrating a Home Subscriber Server (HSS) procedure in a handover control method according to an exemplary embodiment of the present invention. 
     
    
    
     Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
     The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
     In the following description, the term “equivalent Public Land Mobile Networks (PLMNs)” refers to a PLMN belonging to a set of PLMNs among which a certain Mobility Management Entity (MME) supports handover of a certain User Equipment (UE). In the following description, the term “inter-PLMN handover” refers to a handover between two equivalent PLMNs. 
     It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
       FIG. 5  is a diagram illustrating a configuration of a network according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , the communication network includes a Home Subscriber Server (HSS)  56  having allowed Closed Subscriber Groups (CSGs) of {(PLMN A, (CSGID1, CSGID2)), (PLMN B, (CSGID2, CSGID3)), (PLMN C, (CSGID1, CSGID2)), (PLMN D, (CSGID1, CSGID2)), (PLMN E, (CSGID1, CSGID2))}. The communication network further includes MME1  53 , and an evolved Node B1 (eNB1)  52  which may provide service to a UE  51 . The communication network also includes MME2  54  and a Home evolved Node B (HeNB4)  55  that may provide service to the UE  51  if the UE  51  moves into the service coverage area of the HeNB4  55  or when the HeNB4  55  is otherwise selected. As illustrated in  FIG. 5 , the connection between the HeNB4  55  and the MME2  54  may include an HeNB GateWay (GW). However, as the HeNB GW is a connection that does not affect the following description, its connection is shown as a dotted line and is not further explained. 
       FIGS. 6 to 8  are signaling diagrams illustrating handover procedures according to exemplary embodiments of the present invention. 
     Referring to  FIG. 6 , when the UE1  51  is performing an Attach/Tracking Area Update (TAU) procedure, the HSS  56  transmits all CSG lists stored in the HSS  56 . That is, in the Attach and TAU procedure of the UE  51  at step  301 , if the MME1  53  sends an update location request message to the HSS  56  at step  301 . a , the HSS  56  sends the allowed CSG lists of all PLMNs that are stored in the UE  51  subscription data to the MME1  53  at step  301 . b . In such a situation, the UE  51  may approach the HeNB4  55  at step  303 . In that case, the UE  51  reports the CSGID of the HeNB4 cell to the eNB1  52  as the current serving cell at step  304 . After receiving the allowed CSG lists, if a handover required message is received from the eNB1  52  at step  305 , the MME1  53  determines whether, among the allowed CSG lists, the list corresponding to the target PLMN includes the target CSG ID at step  306 . If so, the MME1  53  performs a handover procedure to the MME2  54  and HeNB2  55  at step  307 . b  and, otherwise, rejects the handover at step  307 . a.    
     In an alternative embodiment, the subscription data transmitted from the HSS to the MME may be reduced. In order to reduce the data amount, it can be considered to eliminate the transmission of the unnecessary allowed CSG lists. Since the inter-PLMN handover takes place between the equivalent PLMNs, the allowed CSG lists of the non-equivalent PLMNs are unnecessary information and thus it is more efficient for the HSS to transmit only the equivalent PLMNs&#39; allowed CSG lists to the MME. This exemplary procedure is described with reference to  FIG. 7 . 
     Referring to  FIG. 7 , during the UE  51  Attach or TAU procedure at step  401 , the MME1  53  sends an update location request message including parameters of equivalent PLMNs to the HSS  56  at step  401 . a . If the equivalent PLMN list is received, the HSS  56  sends the allowed CSG lists of the equivalent PLMNs among all of the allowed CSG lists of the PLMNs that are stored in the UE  51  subscription data at step  401 . b . Among the allowed CSG lists of {(PLMN A, (CSGID1, CSGID2)), (PLMN B, (CSGID2, CSGID3)), (PLMN C, (CSGID1, CSGID2)), (PLMN D, (CSGID1, CSGID2)), (PLMN E, (CSGID1, CSGID2))} retained in the HSS  56 , the allowed CSG lists of the PLMN A and PLMN B as equivalent PLMNs, i.e., {(PLMN A, (CSGID1, CSGID2)), (PLMN B, (CSGID2, CSGID3))} are transmitted to the MME1  53 . In such a situation, the UE  51  may approach the HeNB4  55  at step  403 . In that case, the UE  51  reports the CSGID of the HeNB4 cell to the eNB1  52  as the current serving cell at step  404 . After receipt of the allowed CSG lists of the equivalent PLMNs, if a handover required message is received from the eNB1  52  at step  405 , the MME1  53  determines whether, among the allowed CSG lists received at step  401 . b , the target PLMN&#39;s allowed CSG list includes the target CSG ID at step  406 , and, if so, performs handover at step  407 . b . Otherwise, the MME1  53  rejects the handover at step  407   a.    
     Although the exemplary embodiment of  FIG. 7  reduces the amount of subscription data transmitted from the HSS to the MME as compared to the exemplary embodiment of  FIG. 6 , there may be additional room for reducing the redundant data in transmitting the CSG lists of the equivalent PLMNs in identical configuration. In case that the same allowed CSG list is configured for the equivalent PLMNs, it can be considered to transmit only a flag. That is, when the allowed CSG lists of the equivalent PLMNs that allow inter-PLMN handover are configured identically among each other, the HSS can provide only the allowed CSG list of the registered PLMN and equivalent flag. If the allowed CSG list of the registered PLMN is received along with the flag, the MME makes the inter-PLMN handover decision and otherwise, without a flag, rejects the inter-PLMN handover. This procedure is described with reference to  FIG. 8 . 
     Referring to  FIG. 8 , when the UE1  51  is performing Attach/TAU procedure at step  501 , the MME1  53  sends an update location request message to the HSS  56  with the parameters of equivalent PLMNs at step  501 . a . If an equivalent PLMN list is received, the HSS  56  determines the allowed CSG lists of the equivalent PLMNs among all allowed CSG lists stored in the UE  51  subscription data and sends a flag indicating whether the allowed CSG list of the PLMN A as registered PLMN and the allowed CSG list of the equivalent PLMNs are identical with each other at step  501 . b . After comparing the allowed CSG lists of the PLMN A and PLMN B as the equivalent PLMNs among the allowed CSG lists={(PLMN A, (CSGID1, CSGID2)), (PLMN B, (CSGID2, CSGID3)), (PLMN C, (CSGID1, CSGID2)), (PLMN D, (CSGID1, CSGID2)), (PLMN E, (CSGID1, CSGID2))} as shown in  FIG. 5 , the HSS  56  sends the flag indicating the result of comparison with the allowed CSG list of the PLMN A as the registered PLMN to the MME1  53 . In such a situation, the UE  51  may approach the HeNB4  55  at step  503 . In that case, the UE  51  reports the CSGID of the HeNB4 cell to the eNB1  52  as the current serving cell at step  504 . After the receipt of the flag, if a handover required message is received from the eNB1  52  at step  506 , the MME1  53  determines the information received form the HSS  56  at step  507 . That is, when the handover is targeted to the CSG cell of another PLMN, if the flag is set to false, the handover is rejected at step  508 . a . Otherwise, if the flag is set to true, the MME1  53  progresses with the handover only when the CSG ID of the target cell is in the allowed CSG list retained by the MME  53  at step  508 . b.    
       FIG. 9  is a signaling diagram illustrating a handover procedure modified from the handover procedure of  FIG. 8  according to an exemplary embodiment of the present invention. 
     The exemplary embodiment of  FIG. 9  includes an option to that of the exemplary embodiment of  FIG. 8 . Unlike the exemplary embodiment of  FIG. 8  in which the MME determines handover rejection, the exemplary embodiment of  FIG. 9  is characterized in that the MME transmits the flag for inter-PLMN to CSG cell to the eNB in the initial UE Context Setup request message for installing the UE context according to the result transmitted by the HSS such that the eNB determines whether to initiate the handover to a target CSG cell belonging to another PLMN. 
     Referring to  FIG. 9 , in the Attach/TAU process at step  601 , the MME1  53  forwards the flag received from the HSS  56  at step  601 . b  to the eNB1  52  at step  601 . c  such that, although the UE1  51 , which may move close to the HeNB cell at step  603 , reports to the HeNB cell at step  604 , the eNB1  52  rejects handover if the flag is set to false and if the target cell is a CSG cell belonging to another PLMN, and initiates handover if the flag received from the MME1  53  is set to true and if the target cell is a CSG cell belonging to another PLMN at step  605 . The procedure following step  605  is substantially identical with that of  FIG. 8 . That is, steps  606 ,  607 ,  608 . a  and  608 . b  are substantially identical with steps  506 ,  507 ,  508 . a  and  508 . b.    
     In order to address the backward compatibility of the exemplary embodiments of  FIGS. 6 to 9  with the legacy method in which an HSS transmits the allowed CSG list of the registered PLMN, if there is no additional information, i.e., if only the allowed CSG of the registered PLMN is transmitted, the MME determines that the inter-PLMN handover to the CSG cell is not supported and thus rejects the inter-PLMN handover. 
       FIG. 10  is a flowchart illustrating an MME procedure in a handover control method according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 10 , an MME receives an ATTACH or TAU request message from a UE at step  1010 . The MME transmits an Update location request message to an HSS at step  1020 . As above described, the Update location request message may include parameters of the PLMNs. 
     The MME receives an Update location ACK from the HHS at step  1030 . In an exemplary implementation, the Update location ACK can include the allowed CSG lists of the equivalent PLMNs. 
     If a Handover request message is received from the eNB at step  1040 , the MME determines whether, among the received allowed CSG lists, the list corresponding to the target PLMN includes the target CSG ID at step  1050 . If the allowed CSG list of the target PLMN includes the target CSG ID, the MME continues the handover procedure in step  1060  and, otherwise, rejects the handover at step  1070 . 
       FIG. 11  is a flowchart illustrating an HSS procedure in a handover control method according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 11 , an HSS receives an Update location request message transmitted by the MME at step  1110 . In an exemplary implementation, the Update location request message may include the parameters of the equivalent PLMNs. 
     The HSS transmits an Update location ACK message to the MME at step  1120 . In an exemplary implementation, the Update location ACK message may include the allowed CSG lists of the equivalent PLMNs. 
     According to exemplary embodiments of the present invention, in the handover of a UE to an HeNB having CSG ID of a different PLMN, an MME receives subscription information in the UE&#39;s attach/tracking update procedure and makes a correct handover decision so as to prevent handover failure and improve successful handover probability. 
     While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.