Abstract:
The present invention relates to a method of selecting a public land mobile network (PLMN) for network sharing, and a method of communicating at a base station according to one embodiment of the present invention may include: receiving from a core network a handover request message including information on whether to support network sharing of user equipment (UE); selecting a PLMN identification (ID) by using information on whether to support network sharing of the UE; and transmitting the selected PLMN ID to the UE. According to one embodiment of the present invention, since a source base station, a target base station or a core network node may select a correct PLMN depending on the situation of UE when carrying out a handover, it is possible to decrease unnecessary signaling and errors in a network sharing situation.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a continuation application of prior application Ser. No. 14/407,317, filed on Dec. 11, 2014, which will issue as U.S. Pat. No. 9,467,908 on Oct. 11, 2016, and which is a U.S. National Stage application under 35 U.S.C. §371 of an International application filed on Jun. 14, 2013 and assigned application number PCT/KR2013/005280, which claimed the benefit under 35 U.S.C. §119(e) of a U.S. Provisional application filed on Jun. 14, 2012 in the U.S. Patent and Trademark Office and assigned Ser. No. 61/659,623, the entire disclosure of which is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a Public Land Mobile Network (PLMN) selection method for network sharing. 
       BACKGROUND 
       [0003]    Network sharing is a concept introduced to allow operators to share a Radio Access Network (RAN) node (i.e. RAN sharing). With the popularization of Long Term Evolution (LTE), it has become necessary for the operators who removed the 2G/3G infrastructures to share the RAN node (or cell under control of a base station) on account of the legacy 2G/3G terminal users. The base station supporting the network sharing may broadcast a Public Land Mobile Network Identifier (PLMN ID) of the operators sharing the base station. 
         [0004]      FIG. 1  is a schematic diagram illustrating a network sharing concept according to a conventional technology. 
         [0005]    Referring to  FIG. 1 , there may be supporting User Equipment (UE) having PLMN selection function capable of selecting one of PLMN IDs broadcast by 2G/3G network and non-supporting UE having no PLMN selection function in the network sharing mode. In this case, in order to assist the non-supporting UE to operate normally in the network sharing mode, the base stations (or the cells under the control of the base stations)  120  and  125  may broadcast a common PLMN ID  130  and  135  determined through negotiation among the operators  111 ,  113 , and  115 . If the base stations  120  and  125  broadcast the common PLMN ID  130  and  135 , the other PLMN IDs which are called additional PLMN IDs  141 ,  143 , and  145  can be used only by the supporting UEs. 
       SUMMARY 
       [0006]    The present invention has been proposed to fulfil the above necessity and aims to provide a PLMN selection method capable of allowing a handover source or target base station or a core network node to select a PLMN correctly in adaptation to the status of the UE so as to reduce unnecessary signaling and error in a network sharing situation. 
         [0007]    The objects of the present invention are not limited to the aforesaid, and other objects not described herein with be clearly understood by those skilled in the art from the descriptions below. 
         [0008]    In accordance with an aspect of the present invention, the communication method of a base station includes receiving a handover request message including network sharing capability information of a terminal from a core network, selecting a Public Land Mobile Network (PLMN) Identifier (ID) based on the terminal network sharing capability information, and transmitting the selected PLMN ID to the terminal. 
         [0009]    Preferably, selecting the PLMN ID includes determining whether the terminal is a network sharing supporting terminal and selecting, when the terminal is not the network sharing supporting terminal, a common PLMN ID. 
         [0010]    Preferably, selecting the PLMN ID includes determining, when the terminal is the network sharing supporting terminal, whether the PLMN ID allocated to the terminal before receiving the handover request message is identical with the common PLMN ID and selecting, when the PLMN ID allocated to the terminal before receiving the handover request message is identical with the common PLMN ID, the common PLMN ID. 
         [0011]    Preferably, selecting the PLMN ID includes selecting, when the PLMN ID allocated to the terminal before receiving the handover request message is identical not with the common PLMN ID, an additional PLMN ID. 
         [0012]    Preferably, selecting the PLMN ID includes determining whether the PLMN ID allocated to the terminal before receiving the handover request message is identical with an additional PLMN ID and selecting, when the PLMN ID allocated to the terminal before receiving the handover request message is identical with an additional PLMN ID, the additional PLMN ID. 
         [0013]    In accordance with another aspect of the present invention, a communication method of a base station includes determining whether handover of a terminal is required, receiving terminal network sharing capability information from a core network, selecting a Public Land Mobile Network (PLMN) Identifier (ID) based on the terminal network sharing capability information, and transmitting the selected PLMN ID to the core network. 
         [0014]    In accordance with another aspect of the present invention, a communication method of a core network includes receiving terminal network sharing capability information from a terminal, selecting a Public Land Mobile Network (PLMN) Identifier (ID) based on the terminal network sharing capability information, and transmitting the selected PLMN ID to a base station. 
         [0015]    In accordance with another aspect of the present invention, a base station includes a communication unit which communicates with a base station and a core network and a control unit which controls receiving a handover request message including network sharing capability information of a terminal from a core network, selecting a Public Land Mobile Network (PLMN) Identifier (ID) based on the terminal network sharing capability information, and transmitting the selected PLMN ID to the terminal. 
         [0016]    In accordance with another aspect of the present invention, a base station includes a communication unit which communicates with a terminal and a core network and a control unit which determines whether handover of a terminal is required and controls receiving terminal network sharing capability information from a core network, selecting a Public Land Mobile Network (PLMN) Identifier (ID) based on the terminal network sharing capability information, and transmitting the selected PLMN ID to the core network. 
         [0017]    In accordance with still another aspect of the present invention, a core network includes a communication unit which communicates with a terminal and a base station and a control unit which controls receiving terminal network sharing capability information from a terminal, selecting a Public Land Mobile Network (PLMN) Identifier (ID) based on the terminal network sharing capability information, and transmitting the selected PLMN ID to a base station. 
         [0018]    The PLMN selection method of the present invention is advantageous in terms of allowing a handover source or target base station or a core network node to select a PLMN correctly in adaptation to the status of the UE so as to reduce unnecessary signaling and error in a network sharing situation. 
         [0019]    The advantages of the present invention are not limited to the aforesaid, and other advantages not described herein be clearly understood by those skilled in the art from the descriptions below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a schematic diagram illustrating a network sharing concept according to a conventional technology. 
           [0021]      FIG. 2  is a diagram illustrating the network sharing procedure. 
           [0022]      FIG. 3  is a diagram illustrating a network sharing procedure according to an embodiment of the present invention, and  FIG. 4  is a flowchart illustrating a PLMN allocation procedure according to an embodiment of the present invention. 
           [0023]      FIGS. 5, 6, 7, 8, 9, and 10  are schematic diagrams illustrating PLMN allocation procedures according to the embodiments of the present invention. 
           [0024]      FIG. 11  is a flowchart illustrating a PLMN allocation procedure according to an embodiment of the present invention. 
           [0025]      FIGS. 12 and 13  are schematic diagrams illustrating PLMN allocation procedures according to the embodiments of the present invention. 
           [0026]      FIG. 14  is a block diagram illustrating a configuration of the UE according to an embodiment of the present invention. 
           [0027]      FIG. 15  is a block diagram illustrating a configuration of the base station according to an embodiment of the present invention. 
           [0028]      FIG. 16  is a block diagram illustrating a configuration of the core network according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Detailed description of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention. Exemplary embodiments of the present invention are described with reference to the accompanying drawings in detail. Further, the following terms are defined in consideration of the functionality in the present invention, and may vary according to the intention of a user or an operator, usage, etc. Therefore, the definition should be made on the basis of the overall content of the present specification. 
         [0030]      FIG. 2  is a diagram illustrating the network sharing procedure. 
         [0031]    Referring to  FIG. 2 , the source base station  220  broadcasts the PLMN X  230  as a common PLMN ID. There are the network sharing supporting UE  250  and the network sharing non-supporting UE  260  which use the common PLMN X  230 . The network sharing supporting UE may also be referred to as ‘supporting UE,’ and the network sharing non-supporting UE AS ‘non-supporting UE.’ The two UEs  250  and  260  may hand over to a neighboring base station  225 , i.e. target base station  225 , using the PLMN X  230  as the additional PLMN ID and the PLMN Y  237  as the common PLMN ID. At this time, it is preferred for the supporting UE  250  to use the PLMN X  235  to avoid unnecessary complex inter-PLMN handover. However, the non-supporting UE  260  has to use the common PLMN, i.e. the common PLMN Y  237 . 
         [0032]    However, unlike in the idle state where they select the PLMN broadcast by the base station, the UEs  250  and  260 , in the middle of the handover procedure, receives the information on target Radio Access Network (RAN)  225  from the source RAN instead of listening to the broadcast information and thus the PLMN selection procedure is omitted. There are three approaches for PLMN selection of the UEs  250  and  260  in the handover procedure. First, the target RAN  225  selects the PLMN for use of the UEs  250  and  260  (the first approach). Second, the source RAN  220  selects the PLMN which the UEs  250  and  260  are to be used under the control of the target RAN  225  after handover (the second approach). Finally, the Core Network (CN) node  210  selects the PLMN which the UEs  250  and  260  are to use under the control of the target RAN  225 . 
         [0033]    In order for the source RAN  220  or target RAN  225  to select the PLMN on behalf of the UEs  250  and  260 , it is necessary to know whether each of the UEs  250  and  260  is a supporting UE or a non-supporting UE. 
         [0034]    A description is made of the method for the target RAN to select the PLMN for by a UE according to the first approach hereinafter. 
         [0035]      FIG. 3  is a diagram illustrating a network sharing procedure according to an embodiment of the present invention, and  FIG. 4  is a flowchart illustrating a PLMN allocation procedure according to an embodiment of the present invention. 
         [0036]    According to an embodiment of the present invention, after knowing that the UEs  350  and  360  are the supporting and non-supporting UEs respectively, the target RAN  325  determines, based on this information, the PLMN  340  to be notified to the UEs  350  and  360  in the handover procedure. That is, for the supporting UE  350 , the target RAN  325  allocates, if necessary, an additional PLMN to prevent the supporting UE  350  from performing unnecessary inter-PLMN handover. For the non-supporting UE  360 , the target RAN  325  allocates the common PLMN. 
         [0037]    Similarly to the exemplary case of  FIG. 2 , the source RAN  320  may broadcast only the PLMN X  330  as the common PLMN while the target RAN  325  may user the PLMN Y as an additional PLMN and the PLMN X as the common PLMN. In this case, the target RAN  325  may allocate the PLMN X as an additional PLMN to the supporting UE  350 . The target RAN  325  also may allocate the PLMN Y as a common PLMN to the non-supporting UE  360 . 
         [0038]    According to an embodiment, when it is not explicit to the core network  310  whether the UE  350  (or  360 ) is a network sharing supporting UE or a network sharing non-supporting UE, the recipient may regard the UE AS a non-supporting UE. According to an embodiment, if it is not explicit whether the UE supports network sharing in the procedure of exchanging the information on network sharing supportability of the UE among the core network  310  and the base stations  320  and  325 , the recipient regards the corresponding UE is a non-supporting UE. 
         [0039]      FIG. 4  is a flowchart illustrating the PLMN allocation procedure of the target base station according to an embodiment of the present invention. 
         [0040]    Referring to  FIGS. 3 and 4 , the target RAN  325  receives a handover request from the core network at step  410 . Next, the target RAN  325  determines whether the UE is a supporting UE at step  420 . 
         [0041]    If it is determined that the UE is not a supporting UE at step  420 , the target RAN  325  allocates the common PLMN at step  430 . 
         [0042]    If it is determined that the UE is a supporting UE at step  420 , the target eNB  325  determines whether the PLMN used under the control of the previous base station, i.e. the source base station  320 , is identical with the common PLMN of the current base station, i.e. target base station  325  at step  440 . 
         [0043]    If the previous PLMN used under the control of the source base station  320  is identical with the common PLMN of the target base station  325 , the target base station  325  allocates the common PLMN to the UE at step  430 . 
         [0044]    Otherwise, if the previous PLMN used under the control of the source base station  320  is different from the common PLMN of the target base station  325 , the target base station  325  allocates an additional PLMN to the UE at step  450 . At this time, if there is any additional PLMN of the target base station  325  which is identical with the PLMN used in the previous base station  320 , the target base station  325  allocates the same PLMN to the UE. In this way, it is possible to avoid unnecessary inter-PLMN handover procedure. 
         [0045]    A description is made of the PLMN allocation method according to the first approach with reference to detailed embodiments. 
         [0046]      FIGS. 5 to 10  are schematic diagrams illustrating PLMN allocation procedures according to the embodiments of the present invention. 
         [0047]      FIG. 5  shows a NAS-based solution in the Packet Switched (PS) core network (NAS-based solution-PS). 
         [0048]    Referring to  FIG. 5 , the UE  550  sends the Packet-Switched (PS) Core Network (CN)  510  an attach/Tracking Area Update (TAU)/Routing Area Update (RAU) request message including the information indicating whether it is a network sharing supporting UE or a network sharing non-supporting UE at step  530 . At this time, the information indicating whether the UE is a network sharing supporting UE or a network sharing non-supporting UE may be a network sharing capability indicator of the UE. 
         [0049]    The PS CN  510  stores the network sharing capability indicator of the UE  550 . Afterward, a handover required message is transmitted from the source RAN  520  to the PS CN  510  according to the necessity of handover of the UE at step  533 , and the PS CN  510  sends the target RAN  525  a PS handover request message at step  535 . At step  535 , the PS CN  510  sends the target RAN  525  the PS handover request message including the network sharing capability indicator of the UE  550 . 
         [0050]    According to an embodiment, the PS handover request message is as follows. 
         [0051]    PS HANDOVER REQUEST (message from Mobile Switching Center (MSC) to target Global System for Mobile communications (GSM)/Enhanced Data rates for GSM evolution and enhanced data rates for global evolution (EDGE) Radio Access Network (GERAN) through A/Gb interface: Using GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability). 
         [0052]    At step  537 , the target RAN  525  selects a PLMN based on the network sharing capability indicator included in the PS handover request message received at step  535 . That is, in the case that the UE  550  is a non-supporting UE, the common PLMN of the target RAN  525  is allocated to the UE  550 . In the case that the UE  550  is a supporting UE, if the PLMN used at the source RAN  520  is identical with the common PLMN of the target RAN  525 , the target RAN  525  allocates the common PLMN to the UE  550 . Otherwise if the PLMN used at the source RAN  520  is not identical with the common PLMN of the target RAN  525 , the target RAN  525  allocates an additional PLMN to the UE  550 . 
         [0053]    Steps  530  to  537  may be applied to a Circuit-Switched (CS) CN domain in the same manner. 
         [0054]      FIG. 6  shows a NAS-based solution in the Circuit-Switched Core Network (NAS-based solution-CS). 
         [0055]    If the UE transmits the information indicating its network sharing capability to only one of PS and CS domains, this may cause a problem. For example, if the UE which is operating after transmitting its network sharing capability indicator to the PS domain releases the PS session so as to maintain only the CS session, the CS CN node has no way of supporting the network sharing. 
         [0056]    The problem can be solved in such a way that the UE  650  sends the CS CN  610  the information indicating whether it is a network sharing supporting UE or a network sharing non-supporting UE in the attach or location update procedure as described with reference to  FIG. 5 . 
         [0057]    According to an embodiment, the location update request message is as follows. 
         [0058]    LOCATION UPDATING REQUEST (message from UE to MSC for IMSI attach or location update): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0059]    The CS CN  610  stores the network sharing capability indicator of the UE  650 . A handover command is transmitted to the RAN  620  for the handover of the UE  650  at step  631 , and the source RAN  620  sends the CS CN  610  a handover required message at step  633 . The CS core network  610  sends the target RAN  525  a handover request message at step  635 . At step  635 , the CS CN  610  may send the target RAN  625  the network sharing capability indicator of the UE  650  in the handover request message. 
         [0060]    According to an embodiment, the handover request message is as follows. 
         [0061]    HANDOVER REQUEST (message from MSC to target GERAN through A/Gb interface): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0062]    At step  637 , the target RAN  625  selects a PLMN based on the network sharing capability indicator of the UE which is included in the handover request message received at step  635 . That is, in the case that the UE  650  is a non-supporting UE, the target RAN  625  allocates the common PLMN to the UE  650 . In the case that the UE  650  is a supporting UE, if the PLMN used in the source RAN  620  is identical with the common PLMN of the target RAN  625 , the target RAN  625  allocates the common PLMN to the UE  650 . Otherwise if the PLMN used in the source RAN  620  is not identical with the common PLMN of the target RAN  625 , the target RAN  625  allocates an additional PLMN to the UE  650 . 
         [0063]      FIG. 7  shows a NAS-based solution in the combination of the PS CN and CS CN (NAS-based solution-combined. 
         [0064]    As shown in  FIG. 7 , the UE  750  sends the CN  710  of the PS domain its network sharing capability information at step  730 . 
         [0065]    In this case, the PS domain CN node  710  and the CS domain CN node  715  are connected to each other. According to an embodiment, the PS domain CN node  710  may be a Mobility Management Entity (MME) or a Serving GPRS Support Node (SGSN). According to an embodiment, the CS domain CN node  715  may be a Mobile Switching Center (MSC) or a Visitor Location Register (VLR). In the case that the PS domain CN node  710  and the CS domain CN node  715  are connected to each other, it cause signaling overhead for the UE  750  to transmit its network sharing capability information to both the PS domain CN  710  and CS domain CN  715 . In order to solve this problem, the PS domain CN node  710  which received the UE network sharing capability information from the UE  750  forwards this information to the CS domain CN node  715  at step  731 . 
         [0066]    In detail, if it is possible to use Circuit Switched Fall-Back (CSFB) and thus a SGs interface exists or if Network Mode of Operation (NMO) 1 is configured and thus a Gs interface is available, the UE  750  performs a combined attach/TAU/RAU procedure at step  730 . At this time, the UE  750  may insert its UE network sharing capability information in the combined attach/TAU/RAU message which is transmitted to the PS CN  710 . The network sharing capability information of the UE  750  may be the UE network sharing capability indicator indicating whether the UE supports network sharing. 
         [0067]    According to an embodiment, the UE  750  may notify the PS domain CN node  710  of its network sharing capability using the following messages. 
         [0068]    ATTACH REQUEST (message from UE to MME/SGSN): MS network capability IE includes GERAN Network sharing capability bit (1-bit supporting/non-supporting indication) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0069]    TRACKING AREA UPDATE REQUEST (message from UE to MME): MS network capability IE includes GERAN network sharing capability bit (1-bit supporting/non-supporting indication) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0070]    ROUTING AREA UPDATE REQUEST (message from UE to SGSN): MS network capability IE includes GERAN network sharing capability bit (1-bit supporting/non-supporting indication) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0071]    If the UE network sharing capability information is received, the PS CN  710  transmits this information to the CS CN  715  in the location update procedure at step  731 . 
         [0072]    In detail, the Attach/TAU/RAU received by the PS domain CN node  710  may request for association with the CS domain CN node  715 . In this case, the UE  750  may send the CS domain CN node  715  the location update request message including the UE network sharing capability information instead of notifying the CS domain CN node directly whether it supports network sharing. 
         [0073]    According to an embodiment, the location update request message is as follows. 
         [0074]    SGsAP-LOCATION-UPDATE-REQUEST (message from MME to MSC/VLR): Including GERAN network sharing capability IE (1-bit supporting/non-supporting indication field) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0075]    LOCATION-UPDATE-REQUEST (message from SGSN MSC/VLR): Including GERAN network sharing capability IE (1-bit supporting/non-supporting indication field) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0076]    The subsequent procedure of notifying, when handover is triggered, the target RAN  725  of the UE network sharing capability information such that the target RAN  725  selects a PLMN based on the information and notifies the UE  750  of the selected PLMN is similar to the above described embodiments. 
         [0077]    That is, if the UE network sharing capability information is received in the handover situation, the CS CN node  715  sends the target RAN  725  the handover request message including the UE network sharing capability information. 
         [0078]    In detail, in the state that the CS CN  715  retains the network sharing capability information of the UE  750 , the source RAN  720  transmits a handover command for handover of the UE  750  at step  733  and transmits a handover required message to the CS CN  715  at step  735 . The CS CN  715  transmits a handover request message to the target RAN  725  at step  737 . At this time, the CS CN  715  inserts the retained network sharing capability indicator of the UE  750  into the handover request message which is transmitted to the target RAN  725 . 
         [0079]    At step  739 , the target RAN  725  selects a PLMN using the UE network sharing capability indicator included in the handover request message received at step  737 . That is, in the case that the UE  750  is a non-supporting UE, the common PLMN of the target RAN  725  is allocated to the UE  750 . In the case that the UE  750  is a supporting UE, if the PLMN used at the source RAN  720  is identical with the common PLMN of the target RAN  725 , the target RAN  725  allocates the common PLMN to the UE  750 . Otherwise if the PLMN used at the source RAN  720  is not identical with the common PLMN of the target RAN  725 , the target RAN  725  allocates an additional PLMN to the UE  750 . 
         [0080]      FIG. 8  shows a NAS-based solution via Home Subscriber Server (HSS) (NAS-based solution-via HSS). 
         [0081]    In the embodiment of  FIG. 7 , it is possible to prevent the UE from transmitting its network sharing capability information to both the PS and CS domains. However, such an embodiment can be applied only when the SGs/Gs connection is established. In the case of passing through the HSS/HLR as shown in  FIG. 8 , however, it is possible to prevent the UE from transmitting its network sharing capability information to both the PS and CS domains with establishment of SGs/Gs connection. 
         [0082]    Referring to  FIG. 8 , in the case that the UE  850  is attached to the PS domain first, the UE  850  sends the CN  810  of the PS domain its UE network sharing capability information at step  830 . That is, the UE  850  may perform the combined attach/TAU/RAU procedure at step  830 . At this time, the UE  850  inserts its network sharing capability information into the combined attach/TAU/RAU message which is transmitted to the PS CN  810 . The network sharing capability information of the UE  850  may be the UE network sharing capability indicator informing whether the UE supports network sharing. 
         [0083]    The PS CN  810  may store the UE network sharing capability information. The PS CN  810  may insert the UE network sharing capability information in the update location request message which is transmitted to the HSS  813  at step  831 . 
         [0084]    According to an embodiment of the present invention, the update location request message is as follows. 
         [0085]    UPDATE LOCATION REQUEST (message from MME/SGSN to HSS): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0086]    If the update request message including the UE network sharing capability information is received at step  831 , the HSS  813  stores the UE network sharing capability information. Afterward, if the UE  850  attempts IMSI attach to the CS domain, the HSS  813  sends the CS domain CN node  815  the Location Update Accept message including the UE network sharing capability information to the CS domain CN node  815  at step  833 . 
         [0087]    According to an embodiment, the Location Update Accept message is as follows. 
         [0088]    LOCATION UPDATE ACCEPT (message from HSS/HLR to MSC/VLR): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0089]    The subsequent procedure of notifying, when handover is triggered, the target RAN  825  of the UE network sharing capability information such that the target RAN  825  selects a PLMN based on the information and notifies the UE  850  of the selected PLMN is similar to the above described embodiments. 
         [0090]    That is, in the case of performing handover of the UE  850  after receiving the UE network sharing capability information from the HSS  813 , the CS domain CN node  815  may insert the UE network sharing capability information in the handover request message which is transmitted to the target RAN  825 . 
         [0091]    In detail, in the state that the CS CN  815  retains the network sharing capability information of the UE  850 , the source RAN  820  transmits a handover command for handover of the UE  850  at step  834  and transmits a handover required message to the CS CN  815  at step  835 . The CS CN  815  transmits a handover request message to the target RAN  825  at step  837 . At this time, the CS CN  815  inserts the retained network sharing capability indicator of the UE  850  into the handover request message which is transmitted to the target RAN  725 . 
         [0092]    At step  839 , the target RAN  825  selects a PLMN using the UE network sharing capability indicator included in the handover request message received at step  837 . That is, in the case that the UE  850  is a non-supporting UE, the common PLMN of the target RAN  825  is allocated to the UE  850 . In the case that the UE  850  is a supporting UE, if the PLMN used at the source RAN  820  is identical with the common PLMN of the target RAN  825 , the target RAN  825  allocates the common PLMN to the UE  850 . Otherwise if the PLMN used at the source RAN  820  is not identical with the common PLMN of the target RAN  825 , the target RAN  825  allocates an additional PLMN to the UE  850 . 
         [0093]    In the case that the UE  850  is attached to the CS domain first, the CS domain CN node  815  may send the HS S/HLR  813  the UE network sharing capability information. The HSS/HLR  813  may forward the UE network sharing capability information to the PS domain CN node  810 . 
         [0094]      FIG. 9  is shows a procedure of transferring UE network sharing capability information to a new core network for Inter-Core Network update. 
         [0095]    Referring to  FIG. 9 , the Inter-core network node mobility/Tracking Area Update (TAU)/Routing Area Update (RAU)/Location Area Update (LAU) occurs due to the mobility of the UE  8 = 950 . In this case, the old network node to which the UE  950  has connected may retain the network sharing capability information of the UE  950  as described in the above embodiments. 
         [0096]    The new core network  910  to which the UE connects to newly sends a Context Request to the old core network  915  at step  935 . 
         [0097]    In response to the request, the old core network node  915  sends the new core network  910  the information on the network sharing, i.e. RAN sharing, capability reported by the UE  950  at step  937 . At this time, the old core network  915  may send the new core network  910  the UE a Context Response including network sharing capability information. 
         [0098]    According to an embodiment, the context response message is as follows. 
         [0099]    CONTEXT REPONSE (message from Old CN node to New CN node: Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0100]    The new CN node  910  may retain the received UE network sharing capability information and sends, when a handover is triggered afterward, the UE network sharing capability information to the target RAN node (not shown). 
         [0101]      FIG. 10  shows a procedure of transferring the UE network sharing capability information to a new core network according to the Forward Relocation in handover. 
         [0102]    Referring to  FIG. 10 , in the case that it is required to change the serving core network node of the UE in the middle of handover at step  1030 , the old core network node  1010  to which the UE (now shown) has connected may include the UE network sharing capability information as described in the above embodiments. 
         [0103]    The old core network node  1010  may send the new core network node  1015  the UE network sharing capability information using the UE context. The old core network node  1010  also may send the network core network the UE network sharing capability information using the Forward Relocation Request message. 
         [0104]    According to an embodiment, the Forward Relocation Request message is as follows. 
         [0105]    FORWARD RELOCATION REQUEST (message from Old CN node to New CN node): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0106]    The new core network node  1015  may retain the receive UE network sharing capability information and send, when handover is triggered afterward, the UE network sharing capability information to the target RAN node. 
         [0107]    Hereinabove, a description has been made of the method for the target RAN to select the PLMN for use by a UE according to the first embodiment hereinabove. 
         [0108]    A description is made of the method for the source RAN to select the PLMN for use by a UE according to the second approach hereinafter. 
         [0109]      FIG. 11  is a flowchart illustrating a PLMN allocation procedure according to an embodiment of the present invention. 
         [0110]    Unlike the first approach described with reference to  FIGS. 3 to 10 , the second approach is capable of allowing the source RAN to select the PLMN for use by the UE after handover depending on whether the UE is a network sharing supporting UE or a network sharing non-supporting UE. 
         [0111]    Referring to  FIG. 11 , the source RAN determines whether a handover is required at step  1110 . Afterward, the source RAN determines whether the UE is a supporting UE at step  1120 . 
         [0112]    If it is determined that the UE is a non-supporting UE at step  1120 , the source RAN allocates a common PLMN to the UE among the PLMN supported by the handover target RAN at step  1130 . 
         [0113]    If it is determined that the UE is a supporting UE at step  1120 , the source RAN notifies a source core network node of the PLMN which has been allocated to the UE before handover such that the PLMN is not changed as far as possible. 
         [0114]    In detail, if the UE is a supporting UE at step  1120 , the source RAN determines whether the old PLMN used in association with the RAN before handover, i.e. the source RAN, is identical with the common PLMN of the new RAN, i.e. the target RAN, at step  1140 . 
         [0115]    If the old PLMN used in association with the source RAN is identical with the common PLMN of the target RAN, the source RAN allocates the common PLMN to the UE among the PLMNs of the target RAN at step  1130 . 
         [0116]    Otherwise if the old PLMN used in association with the source RAN is different from the common PLMN of the target RAN, the source RAN allocates an additional PLMN to the UE among the PLMNs of the target RAN at step  1150 . At this time, if any additional PLMN of the target RAN is identical with the PLMN used in the old RAN, the target RAN selection the identical PLMN for allocation to the UE. 
         [0117]    In order to apply the second approach, the source RAN has to know the PLMNs supported by the neighboring RANs and which is the common PLMN among the PLMNs. In order to accomplish this, the base stations may exchange the information on the PLMNs supported and common PLMN whenever a new base station is deployed or periodically. If there is no direct connection among the RAN nodes, this information may be exchanged through a third node (e.g. SGSN). At this time, a message structured as follows may be used. 
         [0118]    SNA (Shared Network Area) IE 
         [0119]    Authorised PLMNs (1 to multiple)
       -&gt;PLMN Identity, Common PLMN flag       
 
         [0121]    Or 
         [0122]    SNA (Shared Network Area) IE 
         [0123]    Authorised PLMNs ( 1  to multiple)
       -&gt;PLMN Identity       
 
         [0125]    Common PLMN (1)
       -&gt;PLMN Identity       
 
         [0127]    A description is made of the PLMN allocation method according to the second approach with reference to detailed embodiments. 
         [0128]      FIGS. 12 and 13  are schematic diagrams illustrating PLMN allocation procedures according to the embodiments of the present invention.  FIG. 12  shows a NAS-based solution. 
         [0129]    The Packet Switched (PS)/Circuit Switched (CS) domain core network node operation for determining whether the UE is a supporting UE or a non-supporting node in the embodiments described with  FIGS. 3 to 10  in association with the first approach can be applied to the second approach without modification. 
         [0130]    Unlike the first approach, the second approach is characterized in that the source RAN determines the PLMN to be used in the target RAN. In order to accomplish this, the core network node stores the UE network sharing capability information as in the embodiments described with reference to  FIGS. 3 to 10 . The core network node notifies the source RAN of the stored UE network sharing capability information such that the source RAN selects a PLMN based thereon. 
         [0131]    Referring to  FIG. 12 , the UE  1250  notifies the core network node  1210  that it is a non-supporting UE at step  1230 . The node  1250  may send the core network node  1210  the network sharing capability information in a similar manner to the embodiments of  FIGS. 3 to 10 . Detailed description thereof is omitted herein for convenience purpose. 
         [0132]    Whenever the RAN node changes and thus the UE  1250  enters the active state due to the mobility of the UE  1250 , the core network node  1210  sends the RAN node the UE network sharing capability information along with the UE context at step  1233 . 
         [0133]    According to an embodiment, the following messages can be used. 
         [0134]    INITIAL CONTEXT SETUP REQUEST (message from MME to eNB): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0135]    COMMON ID (message from SGSN/MCS to Radio Network Controller (RNC): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0136]    DL-UNIDATA (message from SGSN to Base Station Controller (BSC): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0137]    CREATE-BSS-PFC (message from SGSN to BSC): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0138]    ASSIGNMENT REQUEST (message from MSC to BSC): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0139]    COMMON ID (message from MSC to BSC): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0140]    As described above, the RAN node having information on whether the UE is a supporting UE or a non-supporting UE uses this information to select the PLMN to be use in the target cell  1225 . That is, if the UE  1250  is a non-supporting UE, the source RAN node  1220  selects the common PLMN. Otherwise if the UE is a supporting UE, the source RAN node  1220  selects the same PLMN for the UE  1250  without PLMN change as far as possible. The source RAN node  1220  selects the core network node  1210  belonging to the PLMN of the core network node  1210  to which the UE  1220  connects according to the selected PLMN, and sends the core network node  1210  a message notifying of the selected PLMN at step  1235 . At this time, a Tracking Area Identifier (TAI), Routing Area Identifier (RAI), or a Location Area Identifier (LAI) may be used instead of the selected PLMN ID. 
         [0141]    According to an embodiment, the selected PLMN information may be carried in the following messages. 
         [0142]    HANDOVER REQUIRED (message from eNB to MME): Including selected PLMN Identifier or TAI/RAI/LAI. 
         [0143]    PS HANDOVER REQUIRED (message from BSC to SGSN): Including selected PLMN Identifier or TAI/RAI/LAI. 
         [0144]    HANDOVER REQUIRED (message from BSC to MSC): Including selected PLMN Identifier or TAI/RAI/LAI. 
         [0145]    RELOCATION REQUIRED (message from RNC to SGSN/MSC): Including selected PLMN Identifier or TAFRAI/LAI. 
         [0146]      FIG. 13  shows a procedure of transmitting the UE network sharing capability information to a new core network according to the Forward Relocation in handover. 
         [0147]    Revering to  FIG. 13 , if the core network node is changed in the middle of handover, the source core network node  1310  receives the selected PLMN information (including TAI/RAI or LAI) from the source RAN  1320  at step  1330 . The source core network node  1310  forwards the received PLMN information (including TAI/RAI or LAI) to the target core network node  1315 . 
         [0148]    According to an embodiment, the selected PLMN information (including TAI/RAI or LAI) may be carried in the following messages. 
         [0149]    FORWARD RELOCATION REQUEST (message from source CN node to target CN node): Including the selected PLMN identifier or TAI/RAI/LAI). 
         [0150]    Afterward, the target core network node  1315  may notify the target RAN  1325  of the selected PLMN using the Handover Request message. 
         [0151]    According to an embodiment, the handover request message is as follows. 
         [0152]    HANDOVER REQUEST (message from MME to eNB): Including Selected PLMN identifier or TAI/RAI/LAI. 
         [0153]    PS HANDOVER REQUEST (message from SGSN to BSC): Including Selected PLMN identifier or TAI/RAI/LAI. 
         [0154]    HANDOVER REQUEST (message from MSC to BSC): Including Selected PLMN identifier or TAI/RAI/LAI. 
         [0155]    RELOCATION REQUEST (message from MSC/SGSN to RNC): Including selected PLMN identifier or TAI/RAI/LAI 
         [0156]    Although not depicted, according to another embodiment of the present invention, the UE may notify the core network node whether it is a GERAN sharing supporting UE or GERAN sharing non-supporting UE in order for the core network node to select a PLMN based thereon. In the present embodiment, the UE may send its network sharing capability information to the RAN node directly. The UE notifies the base station whether it is a supporting UE or a non-supporting UE when establishing a connection with the RAN node. The base station retains this information and, when handover is triggered, selects a PLMN for use in the target RAN based on this information. 
         [0157]    According to an embodiment, the message transmitted from the UE to the base station may be as follows. 
         [0158]    RRC CONNECTION REQUEST (message from UE to RAN): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0159]    RRC CONNECTION REQUEST (message from UE to RAN): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0160]    RRC CONNECTION SETUP COMPLETE (message from UE to RAN): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0161]    INFORMATION TRANSFER (message from UE to RAN): Including GERAN network sharing capability IE (1-bit field indicating supporting/non-supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0162]    CAPABILITY INFORMATION (message from UE to RAN): Including GERAN network sharing capability IE (1-bit field indicating supporting/non- supporting capability) or GERAN network sharing capability bit in Mobile Station Classmark 1, 2, or 3. 
         [0163]    If necessary, the UE network sharing capability information received by the RAN node according to the above embodiments may be transferred to another network entity. For example, the RAN node may transmit the received information to a core network node such as SGSN/MME/MSC or another RAN node. If handover is triggered, the RAN node may send the target RAN node the UE network sharing capability information using a transparent container. 
         [0164]    Hereinabove, a description has been made of the method for the source RAN to select the PLMN for use by a UE according to the second approach. 
         [0165]    A description is made of the method for the core network to select a PLMN for use by a UE according to the third approach. 
         [0166]    According to the embodiments of the first and second approaches that are described with  FIGS. 3 to 13 , the core network node may know whether the UE is a supporting UE or a non-supporting UE. Detailed description thereof is omitted herein. 
         [0167]    The source RAN may select a PLMN and notify the core network node of the selected PLMN or sends the core network node a handover request without selecting any PLMN. In this case, if the UE is a non-supporting UE, the core network node selects the common PLMN as the PLMN for use in the target RAN and, otherwise, selects a PLMN, which is not changed as far as possible, and notifies the target RAN node of the selected PLMN. If it is required to change the PLMN depending on whether the UE supports the network sharing function even though the source RAN selected a PLMN and notified of the selected PLMN, the core network node may change the PLMN for the UE. The core network node may notify the target RAN node of the selected PLMN using the handover request message. Since how to notify the target RAN node of the selected PLMN has been described, detailed description thereof is omitted herein. 
         [0168]      FIG. 14  is a block diagram illustrating a configuration of the UE according to an embodiment of the present invention. 
         [0169]    Referring to  FIG. 14 , the control unit  1410  controls the UE to perform at least one of the operations of the above described embodiments. For example, the control unit  1410  may control the UE to transmit the UE network sharing capability information to the base station or the core network. The base station or the core network may select a PLMN identifier based on the UE network sharing capability information. 
         [0170]    The communication unit  1420  communicates signal according to one of the operations of the above described embodiments. For example, the communication unit  1420  may transmit the UE network sharing capability information to the base station or the core network. The communication unit  1420  also may receive the selected PLMN identifier from the base station. 
         [0171]      FIG. 15  is a block diagram illustrating a configuration of the base station according to an embodiment of the present invention. 
         [0172]    Referring to  FIG. 15 , the control unit  1510  controls the base station to perform on of the operations of the above-described embodiments. For example, the control unit  1510  may control the base station to receive the handover request message including the UE network sharing capability information from the core network, selects the common PLMN ID based on the UE network sharing capability information, and sends the selected PLMN ID to the UE. The control unit  1510  also may determine whether it is necessary to hand over the UE and control the base station to receive the UE network sharing capability information, select PLMN ID based on the UE network sharing capability information, and transmit the selected PLMN ID to the core network. 
         [0173]    The communication unit  1520  transmits/receives signals according to one of the operations of the above-described embodiments. For example, the communication unit  1520  may receive the UE network sharing capability information from the core network. The communication unit  1520  also may transmit the selected PLMN ID to the core network or the UE. 
         [0174]      FIG. 16  is a block diagram illustrating a configuration of the core network according to an embodiment of the present invention. 
         [0175]    Referring to  FIG. 16 , the control unit  1610  controls the core network to perform on of the operations of the above-described embodiments of the present invention. For example, the control unit  1610  controls the core network to receive the UE network sharing capability information, select a PLMN ID based on the UE network sharing capability information, and transmit the selected PLMN ID to the base station. 
         [0176]    The communication unit  1620  may transmit/receive signals according to one of the operations of the above-described embodiments. For example, the communication unit  1620  may receive the UE network sharing capability information. The communication unit  1620  also may transmit the selected PLMN ID to the base station. 
         [0177]    Although preferred embodiments of the invention have been described using specific terms, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense in order to help understand the present invention. It is obvious to those skilled in the art that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention. 
         [0178]    Therefore, a detailed description of the above should not be construed as limited in all respects but as considered exemplarily. The scope of the present invention is to be determined by a reasonable interpretation of the appended claims and include all the changes within the equivalent range of the present invention.