Abstract:
Disclosed is a method for performing switching between a macro evolved Node B (eNB) and a home eNB (HeNB) in a mobile communication system including broadcasting, by the HeNB, a length of an HeNB ID to a UE; notifying, by the UE, an HeNB indication information containing the length of the HeNB ID to the macro eNB; transmitting, by the macro eNB, a switching request message to a mobile station mobility management entity, the message including a target ID; finding, by the MME, the HeNB or an HeNB gateway according to the target ID, and performing a switching process from the macro eNB to the HeNB. With the described switching method for the mobile communication system, UE can move between the macro eNB and the HeNB.

Description:
PRIORITY 
       [0001]    This application claims priority under 35 U.S.C. §119(a) to a Chinese Patent Application filed Aug.  20 , 2008, assigned Serial No. 200810211062.1, and to PCT/KR2009/004586 filed Aug. 17, 2009, the disclosure of each of which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to mobile communications, especially to a method and an apparatus for performing switching in a mobile communication system. 
         [0004]    2. Description of the Related Art 
         [0005]    An existing structure of the 3rd Generation Mobile Communication System Partnership Project (3GPP) is shown in  FIG. 1 . 
         [0006]    User Equipment  101  (UE) is a mobile terminal device used to receive data. Node B  102  is a node for radio receiving/transmitting in an Radio Network Subsystem (RNS). Control Radio Network Controller  103  (CRNC) is a radio network controller that controls Node B directly. An interface between a radio network controller (RNC) and the UE is provided via an wireless interface. A Serving Radio Network Controller  104  (SRNC) is used as the RNC to control bearer information such as a Radio Resource Control (RRC) information. The interface between SRNC and CRNC is an Iur interface. Gateway General Packet Radio Service (with General Packet Radio Service referred to as GPRS) Supporting Node  106  (with Gateway GPRS Supporting Node referred to as GGSN) and Service GPRS Supporting Node  105  (SGSN) provide routing for data transmission. An interface between SGSN and RNC is a lu interface. An External Public Data Network (E-PDN)  107  for providing data resources. 
         [0007]    A system structure of Service Architecture Evolution (SAE) is illustrated in  FIG. 2 . Referring to  FIG. 2 , UE  201  is a terminal device used to receive data. EUTRAN  202 , also called evolved Node B (eNB), is a radio access network of the LTE SAE, for providing an interface through which a Long Term Evolution (LTE) mobile station will access the radio network. 
         [0008]    Through the interface S 1 , eNB  202  connects to the mobile station Mobility Management Entity (MME)  203  and the user plane entity Serving Gateway (Serving GW)  204 . MME  203  is used for managing a mobile context and a session context for the UE, and saving user security information. Serving GW  204  primarily provides a function of user plane for delivering information from user. An interface S 1 -MME is used for establishing radio access bearer for UE and forwarding messages from the UE  201  to the MME  203  through a wireless access network. The combined function of MME  203  and Serving GW  204  is similar to that of the original SGSN  206 . Both the MME and the Serving Gateway can be located at the same physical entity. Public Data Network (PDN) Gateway  205  is used for functions like accounting, legal monitoring, etc. Both the Serving Gateway and the PDN Gateway can be located at the same physical entity. SGSN  206  provides routing for data transmission for existing Universal Mobile Telephone Service (UMTS). The existing SGSN finds a corresponding GGSN according to an Access Point Name (APN). A Home Subscription Sub-system (HSS)  207  is provided for the UE, for storing user information that includes a current location of the UE, an address of the serving node, security related information for the user, and an activated Packet Data Protocol (PDP) context for the UE. Policy and Charging Rules Function (PCRF)  208  provides a Quality of Service (QoS) policy and accounting rules through an interface S 7 . 
         [0009]    In general, a user data stream arrives at the Serving GW  204  through PDN Gateway  205 . Then, through the GPRS Tunnel Protocol (GTP) channel, data is transmitted by the Serving Gateway to the eNB where the UE locates, and transmitted by the eNB to a corresponding UE. 
         [0010]      FIG. 3  shows a structure of interface S 1  in SAE, where Evolved Packet Core (EPC) is the LTE core network. Here, each eNB  301  connects with several MMEs  312  in the MME pool. Each eNB  301  also connects to several S-GWs  311  in the S-GW Pool. 
         [0011]    A Home Network B (HNB), which includes 3G HNB, LTE HNB and HNBs for the other access systems, refers to a Node B applied in a home. It also can be applied in sites such as a university, a company and so on. HNB is Plug-and-Play. HNB includes an open-typed HNB and the close user group-typed HNB. A difference between the close user group-typed HNB and a common macro eNB lies in that usually not all UE can access the HNB. For example, only the UEs in the home of a user or other UEs specifically allowed to access the HNB can access the corresponding HNB. For the HNB in a company, only a company&#39;s staff and allowed partners can access the HNB. The HNB group, for example, an HNB in a company, bearing the same access subscriber cluster is called a Closed Subscriber Group (CSG). 
         [0012]    The structure of the 3G HNB is illustrated in  FIG. 4 . A UTRAN  400  includes a 3G HNB  401  and a 3G HNB GW  402 . The HNB and the HNB GW form an HNB RAN. 3G HNB performs the functions of original NodeB and some functions of RNC, such as RRC, RLC, MAC, etc. The 3G HNB GW is a node connecting to the core network, including a function of NAS Node Selection Function (NNSF). The interface between HNB and HNB GW is the Iuh interface. 3G HNB GW accesses the core network through the lu interface. 
         [0013]    No conclusion is made on the structure of LTE HNB (HeNB). A solution is that MME and S-GW are directly connected to the HeNB. Another solution is that a structure similar to 3G HNB, and HeNB accesses the core network through the HeNB GW. 
         [0014]    When UE switches between eNBs, an existing MME relocation process is illustrated in  FIGS. 5A and 5B . If no relocation is performed by the Serving GW, the source Serving GW in  FIG. 5A  functions as a target Serving GW. 
         [0015]    In step  501 , the source eNB  520  decides to initiate an S 1  switching process. This process can be triggered when no X 2  interface exists between the source eNB  520  and the target eNB  530 , triggered by an error indication from the target eNB  530  when an unsuccessful X 2  switch is performed, or triggered by the dynamic information obtained by the source eNB  520 . 
         [0016]    In step  502 , the source eNB  520  transmits a “Switching Request” message to the source MME  540 . The message includes an indicator indicating whether data can be directly forwarded between the source eNB  520  and the target eNB  530 . The “Switching Request” message includes message elements of:
       MME UE S 1 AP ID (MME UE S 1  application layer identifier).   eNB UE S 1 AP ID (eNB UE S 1  application layer identifier).   Switch type, including IntraLTE (within LTE), LTE to UTRAN (from LTE to UTRAN), LTE to GERAN (from LTE to GERAN).   Cause for switching.   Source ID. The same method for setting the source ID can be applied in the configuration of both the source ID and the target ID. For example, the ID may include a TAI (Tracking Area Identity) and a unique eNB ID in a Public Land Mobile Network (PLMN), i.e. a global land mobile network, or a PLMN ID, which is a unique eNB ID and the MME group ID under PLMN.   Target ID, which can be either the PLMN ID or the unique eNB ID under PLMN. For the sake of routing between MMEs, the target ID can also include the TAI and the MME group ID. If the TAI is included for the sake of routing between different MMEs, the target ID includes the TAI and the unique eNB ID under PLMN, since the TAI has already contained the PLMN ID.   Availability on direct data forwarding.   Intra-LTE-switch information list request, which is enabled when there happens IntraLTE switching, and includes a transparent container from the source eNB to the target eNB.   LTE-UTRAN-switching information list request, which is enabled when LTE to UTRAN switching occurs.   LTE-GERAN-switch information list request, which is enabled when LTE to GERAN switching occurs.       
 
         [0027]    In step  503 , the source MME  540  selects a target MME  550  and transmits a “Forward relocation request” message. Detailed description on MME selecting is omitted here for conciseness. The “forward relocation request” message includes the MME UE context. The MME UE context includes a PDN GW  580  address and TEIDs for uplink data transmission, which corresponds to the interfaces S 5  and S 8  of GTP, and a Serving GW address and TEIDs for uplink data transmission. The message also includes an indicator indicating whether data can be forwarded directly or any bearer has been established in the source side for indirect data forwarding. The message further includes a switching type, a switching cause, and a container from source eNB  520  to target eNB  530  since it is the switching inside the LTE. 
         [0028]    In step  504 , the target MME  550  verifies whether the source Serving GW  560  can still serve the UE  500 . If not, the target MME  550  selects a new Serving GW, a detailed description of which is omitted here for conciseness. The target MME  550  transmits an “establishing bearer request” message to the target Serving GW  570 . If the source Serving GW  560  still serves for the UE  500 , it also acts as the target Serving GW. In this case, the message in this step is not necessary. The “establishing bearer request” message includes a bearer context, such as the PDN GW address and the TEIDs, which corresponds to interfaces S 5  and S 8  of GTP. The target Serving GW allocates the S-GW address and TEIDs for uplink data transmission through interface S 1 . 
         [0029]    In step  504 A, the target Serving GW  570  transmits an “establishing bearer response” message to the target MME  550 . This message includes a Serving GW address and uplink TEIDs. 
         [0030]    In step  505 , the target MME  550  transmits a “switching request” message to the target eNB  530 . This message includes the Serving GW address and the uplink TEIDs. After the target eNB  530  receives this message, it establishes the UE context including the bearer and the security context. In the message, the switch type is set as IntraLTE. The “switching request” message includes information elements of: MME UE S 1 AP ID (MME UE S 1  application layer identifier); Switch type, including IntraLTE (within LTE), LTE to UTRAN (from LTE to UTRAN), LTE to GERAN (from LTE to GERAN); Cause for switching; SAE bearer list to be established; intra-LTE-switch (within LTE) information list request, which is enabled when there happens IntraLTE switching, and includes the transparent container from the source eNB to the target eNB; UTRAN-to-LTE switching information list request, which is enabled when there happens UTRAN to LTE switching; GERAN-to-LTE switch information list request, which is enabled when there happens GERAN to LTE; a serving PLMN; and a switching constraint list. 
         [0031]    In step  505 A, the target eNB  530  transmits a “switching request ACK” message to the target MME  550 . The message includes the address and the TEIDs allocated by the target eNB  530  for downlink data transmission through interface S 1 . 
         [0032]    In step  506 , if an indirect data forwarding mode is applied here, the target MME  550  specifies forwarding parameters for the target Serving GW  570 . 
         [0033]    In step  507 , the target MME  550  transmits a “forwarding relocation response” message to the source MME  540 . The message includes an indicator indicating whether any change takes place in the Serving GW. If a change does take place, a new Serving GW is indicated. If the indirect data forwarding mode is applied here, the message also includes the Serving GW address and the TEIDs for data forwarding. 
         [0034]    In step  508 , if the indirect data forwarding mode is applied here, the source MME  540  updates the source Serving GW&#39;s channel for data forwarding. If the Serving GW has been relocated, the “establishing bearer request” message also includes an index of the channel between the source and the target Serving GWs. 
         [0035]    In step  509 , the source MME  540  transmits a “switching command” message to the source eNB  520 . The message includes a target address and TEIDs allocated by eNB for data forwarding. The switch command includes the information elements of: an MME UE S 1 AP ID, i.e. MME UE S 1  application layer identifier; an eNB UE S 1 AP ID, i.e. eNB UE S 1  application layer identifier; a Switch type, including IntraLTE (within LTE), LTE to UTRAN (from LTE to UTRAN), LTE to GERAN (from LTE to GERAN); a bearer list for data forwarding; an SAE bearer list to be released; an Intra-LTE-switch (within LTE) information list request, which is enabled when there happens IntraLTE switching, and includes the transparent container from the source eNB to the target eNB; an LTE-UTRAN-switching information list request, which is enabled when LTE to UTRAN switching occurs; and an LTE-GERAN-switch information list request, which is enabled when there happens LTE to GERAN. 
         [0036]    In step  510 , the source eNB  520  transmits the “switching command” message to UE. This message includes information on radio resource configuration of the target cell. 
         [0037]    In step  511 A, for the bearer for data forwarding, the source eNB  520  begins to forward downlink data to the target eNB  540 . Here, either a direct data forwarding mode (step  511 A) or the indirect data forwarding mode (step  511 B) can be applied here. 
         [0038]    As shown in  FIG. 5B , in step  512 , after UE  500  is synchronized to the target cell, the UE  500  transmits a “switching ACK” message to the target eNB  530 . The target eNB  530  can transmit the forwarded downlink data to UE  500 . Similarly, the UE  500  can transmit the uplink data. 
         [0039]    In step  513 , the target eNB  530  transmits a “switching notification” message to the target MME. 
         [0040]    In step  514 , the target MME  550  transmits a “forwarding relocation complete” message to the source MME  540 . The source MME  540  transmits a “relocation complete ACK” message to the target MME  550 . 
         [0041]    In step  515 , the target MME  550  transmits an “updating bearer request” message to the target Serving GW  570 . The message includes an eNB address and the TEIDs allocated by the target eNB  530  for downlink data transmission through interface S 1 , and the PDN GW address and the TEIDs for uplink data transmission (this case corresponds to the interfaces S 5  and S 8  of GTP). 
         [0042]    In step  516 , if the Serving GW is relocated, the target Serving GW  570  allocates addresses and TEIDs to PDN GW  580  for downlink data transmission. The target Serving GW  570  transmits the “updating bearer request” message to PDN GW  580 . The message includes the Serving GW address and the TEIDs. 
         [0043]    In step  516 B, PDN GW  580  updates the context information and transmits an “updating bearer response” message to the target Serving GW  570 . PDN GW  580  begins to transmit downlink data to the target Serving GW  570 . If the Serving GW has not yet been relocated, the message in this step is not necessary. Serving GW directly transmits data to the target eNB  530 . 
         [0044]    In step  517 , the target Serving GW  570  transmits the “updating bearer response” message to the target MME  550 . This message includes the PDN GW address and the TEIDs corresponding to interfaces S 5  and S 8  of GTP. 
         [0045]    In step  518 , UE  500  initializes a Track-Area-Updating (TAU) process, regarding which a detailed technical description is omitted here for conciseness. The target ID in the “switching request” message of step  502  of  FIG. 5A  facilitates the MME to obtain a downstream node, e.g., the HeNB or HeNB GW. 
         [0046]    However, a length of the HeNB ID or the HeNB GW ID possibly differs from that of the macro eNB, and the information on adjacent HeNBs is not saved in the macro eNB. When the target cell is a CSG cell, the manner of making the macro eNB learn about the eNB type or eNB ID of the target cell will not be solved. Thus, the process of switching from a macro eNB to an HeNB can not be implemented. 
       SUMMARY OF THE INVENTION 
       [0047]    The invention provides a method and an apparatus for performing switching in a mobile communication system. 
         [0048]    According to an aspect of the present invention, a method for performing switching between a macro eNB and an HeNB in a mobile communication system is provided that includes broadcasting, by the HeNB, a length of an HeNB ID to a UE; notifying, by the UE, an HeNB indication information containing a length of the HeNB ID to the macro eNB; transmitting, by the macro eNB, a switching request message to a MME, the message including a target ID; and finding, by the MME, the HeNB or an HeNB GW according to the target ID, and performing a switching process from the macro eNB to the HeNB. 
         [0049]    According to another aspect of the present invention, an apparatus is provided for performing switching in a mobile communication system, the apparatus including: an HeNB broadcasting a length of an HeNB ID to a UE; a macro eNB receiving an HeNB indication information containing the length of the HeNB ID from the UE, transmitting a switching request message including a target ID; and a MME receiving the switching request message from the macro eNB, finding the HeNB or an HeNB GW according to the target ID, and transmitting the switching request message to the HeNB or the HeNB GW. 
         [0050]    With the switching method proposed in present invention for the mobile communication system, UE can move between the macro eNB and the HeNB. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0051]    The objects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0052]      FIG. 1  shows a structure of an existing 3GPP system; 
           [0053]      FIG. 2  shows a structure of a SAE system network; 
           [0054]      FIG. 3  shows a structure of an interface S 1 ; 
           [0055]      FIG. 4  shows a structure of a 3G HNB; 
           [0056]      FIGS. 5A and 5B  provide a flow diagram of an MME relocation process when the UE switches between eNBs; 
           [0057]      FIG. 6  shows a first embodiment of a method for performing S 1  switching with that HeNB directly accessing the core network; 
           [0058]      FIG. 7  shows a second embodiment of a method for performing S 1  switching with the HeNB directly accessing the core network; 
           [0059]      FIG. 8  shows a third embodiment of a method for performing S 1  switching with the HeNB accessing a core network through HeNB GW; 
           [0060]      FIG. 9  shows a fourth embodiment of a method for performing S 1  switching with the HeNB accessing a core network through HeNB GW; 
           [0061]      FIG. 10  shows a method for HeNB GW obtaining an HeNB serving cell ID; 
           [0062]      FIG. 11  shows an MME relocation process when the UE switches between the macro eNB and the HeNB; and 
           [0063]      FIG. 12  shows an MME relocation process when the UE switches between one macro eNB and another macro eNB. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0064]    Herein, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted to avoid obscuring the subject matter of the present invention. 
         [0065]    In the following, an LTE system is taken as an example for description. The method proposed in present invention can also be applied in HeNB of any other access system. The case in which a UE moves from a macro eNB to a HeNB is taken as an example for description. The method proposed in present invention is also suitable when the UE moves from one HeNB to another HeNB. 
         [0066]    On condition that the access system has different types of access network node equipment, and the lengths of the IDs of the different types of access network node equipments are different, the method proposed in present invention can be normally operated. 
         [0067]      FIG. 6  shows a first embodiment that performs S 1  switching. In this embodiment, no HeNB GW exists in the HeNB structure. The length of HeNB ID can be the same (e.g., 28-bit) or be different. 
         [0068]    In step  601  of  FIG. 6 , HeNB  630  transmits an indicator through BCCH, indicating that it is a HeNB. At present, disagreement remains on HeNB classification. However, the agreement that the eNB applied in a home is a HeNB can be reached. Some companies consider the eNB applied in a small company as a HeNB, and some consider the eNB as a macro eNB with the function of close-user-cluster. The eNB applied in a shop or restaurant can be either an open HeNB or a macro eNB, e.g., a pico eNB. If an open eNB, e.g., as applied in a shop or restaurant, is a macro eNB, the eNB bears the same ID length as that of a macro eNB. The indication function of HeNB can then also be realized by CSG, i.e., what HeNB  630  needs to do is to transmit a CSG indicator through BCCH. In this case, HeNB and CSG are consistent. 
         [0069]    If the eNB in a shop or restaurant is a HeNB with a CSG function, it is necessary for HeNB to transmit the HeNB indicator through BCCH, indicating that it is a HeNB. If the eNB in a small company functions as a macro eNB with CSG function, which in this case the eNB shares the same ID length with the macro eNB, some overlap exists between the concept of CSG and that of HeNB. In this case, it is also necessary to transmit separate HeNB indicator through BCCH. Therefore, the indication of HeNB can be realized by CSG indicator or individual information element, depending on the application scenario for the HeNB and the definition of the HeNB. 
         [0070]    In step  602 , UE  600  moves to an area close to its HeNB  630 , and requests a sounding gap from the macro eNB. UE  600  transmits a “sounding gap request” message to the macro eNB  620 . According to footprint information, UE  600  detects arrival at the area close to its HeNB  630 . For example, UE  600  arrives at the macro cell where the HeNB  630  is located, or UE  600  arrives at the TA of the macro cell where the HeNB  630  is located. In this case, it will be confirmed that UE  600  arrives at the area close to its HeNB  630 . 
         [0071]    In step  603 , the macro eNB  620  transmits a “sounding gap response” message to UE  600 . It includes a sounding gap allocated to UE  600 . 
         [0072]    In step  604 , UE  600  receives the broadcast information from HeNB  630 . 
         [0073]    In step  605 , UE  600  transmits a sounding report to the macro eNB  620 . In this message, the cell information corresponding to the HeNB  630  includes the HeNB indicator and the CGI, the global cell identifier. CGI includes the PLMN, i.e. the global land mobile network, identifier and the unique Cell Identifier (CI) under PLMN. The message also includes a TAI where HeNB cell is located. The CI includes the eNB ID and the cell ID for the eNB. For a CSG, the CI includes the HeNB ID and the cell ID of the HeNB. For a typical HeNB, e.g. applied in a home, the CI can equal the HeNB ID, with a HeNB having only one cell. All these concepts are suitable for following embodiments. 
         [0074]    The message can also include a CGI, a TAI and a sounding result for the UE  600 . 
         [0075]    The macro eNB  620  determines whether to performing switching according to the sounding result for the UE. If the macro eNB  620  determines to switch UE  600  to the HeNB cell, in step  606 , the macro eNB  620  transmits the “switching request” message to MME  640 . If the switching is implemented between different MMEs, the MME is a source MME. When a length of the HeNB ID is unique, the Target ID in the message includes a PLMN ID and a unique HeNB ID under PLMN. According to the CI in the CGI reported from UE and the length of the HeNB ID, the macro eNB finds the HeNB ID (viz., the first n bits in CI where n refers to the length of HeNB ID). When switching between different MMEs, the source MME transmits the “forwarding relocation request” message to the target MME after receiving the “switching request” message. In subsequent embodiments, the way the source MME finds the target MME will be given. When switching between different MMEs, the MME mentioned later in the present embodiment refers to the target MME. With the “S 1  establishment request” message, MME  640  obtains the HeNB ID to which it connects during the process of establishing S 1 . MME  640  finds the target HeNB according to the PLMN ID and the HeNB ID. 
         [0076]    When a HeNB  630  has two lengths of IDs, if UE  600  hopes to switch to the HeNB  630 , the Target ID in the “switching request” message includes the PLMN ID and the identifier CI for the target cell. According to the length of the target ID, MME knows that the target eNB is not a macro eNB. And according to the length of the HeNB ID, MME extracts the target HeNB ID out from CI. For example, the HeNB ID is 24-bit or 28-bit in length. The value of the first 24 bits in the 28-bit long HeNB ID is different from that of the 24-bit HeNB ID. Therefore, MME respectively determines the matched 24-bit HeNB ID or 28-bit HeNB ID. Or according to the first 24 bits, the MME knows to which category the HeNB ID length belongs. Then, the MME obtains the target HeNB ID from CI according to the length of the HeNB ID. The MME finds the target eNB according the PLMN ID and the target HeNB ID. 
         [0077]    In step  607 , MME  640  transmits the “switching request” message to the HeNB  630 . 
         [0078]    In step  608 , subsequent operation flow of S 1  switching is the same as that in existing technique, with a detailed technical description omitted for conciseness. 
         [0079]      FIG. 7  shows a second embodiment for performing S 1  switching, corresponds to the case that no HeNB GW exists in the structure of HeNB, with a detailed description provided below. 
         [0080]    In step  701 , HeNB  730  transmits the indicator of the HeNB ID length or the net HeNB ID length through BCCH. For example, if the length of the HeNB ID can be  22 , or  25  or  28 , the numbers 0, 1 and 2 can be adopted to indicate the length of  22 ,  25  and  28 , respectively. If the HeNB ID is 24 or 28 bits long, numbers 0 and 1 can be adopted to indicate the length of 24 and the length of 28, respectively. 
         [0081]    In step  702 , UE  700  moves to the area close to its HeNB  730 , it requests a sounding gap from the macro eNB  720 . UE  700  transmits the “sounding gap request” message to the macro eNB  720 . According to the footprint information, UE  700  knows when it arrives at the area close to its HeNB  730 . For example, UE  700  arrives at the macro cell where the HeNB  730  is located, or UE  700  arrives at the TA of the macro cell where the HeNB  730  is located. In this case, it will be confirmed that the UE  700  arrives at the area close to its HeNB  730 . 
         [0082]    In step  703 , the macro eNB  720  transmits the “sounding gap response” message to UE  700 , including the sounding gap allocated to UE  700 . 
         [0083]    In step  704 , UE  700  receives the broadcast information from HeNB  730 . 
         [0084]    In step  705 , UE  700  transmits a sounding report to the macro eNB  720 , including the HeNB ID length indicator or the net HeNB ID length. The message can also include CGI, TAI and the UEs sounding result. 
         [0085]    The macro eNB  720  determines whether to perform switching according to the sounding result for the UE  700 . If the macro eNB  720  determines to switch UE  700  to the HeNB cell, in step  706 , it transmits the “switching request” message to MME  740 , if the switching is implemented between different MMEs, the MME is a source MME. The macro eNB  720  includes the PLMN ID and the HeNB ID in the target ID in the message. The macro eNB  720  extracts the target HeNB ID from CI (viz., the first n bits where n refers to the length of HeNB ID), which includes the PLMN ID and CI, according to the HeNB ID length indicator or the net HeNB ID length reported by UE  700 . 
         [0086]    When switching between different MMEs, the source MME transmits the “forwarding relocation request” message to the target MME after receiving the “switching request” message. In subsequent embodiments, the way in which the source MME finds the target MME will be given. When switching between different MMEs, the MME mentioned later in present embodiment refers to the target MME. With the “S 1  establishment request” message, MME  740  obtains the ID of the HeNB  730  to which it connects during the process of establishing S 1 . MME  740  finds the target HeNB according to the HeNB ID. 
         [0087]    In step  707 , MME  740  transmits the “switching request” message to the HeNB. 
         [0088]    In step  708 , subsequent operation flow of S 1  switching is the same as that in existing technique, and a detailed technical description is omitted here for conciseness. 
         [0089]      FIG. 8  shows a third embodiment for performing S 1  switching, corresponding to an HeNB consists of HeNB GW, which has fixed length, with a, detailed description provided below. 
         [0090]    In step  801 , HeNB  830  transmits the HeNB indicator through BCCH, indicating that it is an HeNB. At discussed above, some disagreement remains on HeNB classification. This disagreement is discussed above and is not repeated here for conciseness. 
         [0091]    In step  802 , UE  800  moves to the area close to its HeNB  830  and requests the macro eNB for a sounding gap. UE  800  transmits the “sounding gap request” message to the macro eNB  820 . And according to footprint information, UE  800  knows that it arrives at the area close to its HeNB  830 . For example, UE  800  arrives at the macro cell where the HeNB  830  is located, or UE  800  arrives at the TA of the macro cell where the HeNB  830  is located. In this case, it will be confirmed that UE  800  arrives at the area close to its HeNB  830 . 
         [0092]    In step  803 , the macro eNB  820  transmits the “sounding gap response” message to UE  800 . This message includes the sounding gap allocated to UE  800 . 
         [0093]    In step  804 , UE  800  receives the broadcast information from HeNB  830 . 
         [0094]    In step  805 , UE  800  transmits a sounding report to the macro eNB  820 . In this message, the cell information corresponding to the HeNB  830  includes the HeNB indicator or the CSG indicator, CGI and the sounding result for the UE. The message further includes the identifier of the TA where the HeNB cell is located. 
         [0095]    The macro eNB  820  determines whether to perform switching according to the sounding result for the UE. If the macro eNB  820  determines to switch UE  800  to the HeNB cell, in step  806 , it transmits the “switching request” message to MME  840 , and if the switching is implemented between different MMEs, the MME is a source MME. The macro eNB  820  includes the PLMN ID and the unique HeNB GW ID in the information element Target ID in the message. HeNB GW ID is included in CI. The macro eNB  820  obtains the HeNB GW ID by extracting corresponding number of bits (viz., the first n bits in CI where n refers to the length of HeNB GW ID) according to the length of the HeNB GW ID. When switching between different MMEs, the source MME transmits the “forwarding relocation request” message to the target MME after receiving the “switching request” message. In subsequent embodiments, the manner for the source MME finding the target MME will be given. When switching between different MMEs, the MME mentioned later in present embodiment refers to the target MME. With the “S 1  establishment request” message, MME  840  obtains the HeNB GW IDs of all HeNB GWs to which it connects during the process of establishing S 1 . MME  840  finds the target HeNB GW according to the HeNB GW ID. The container of transparent transmission from source eNB to target eNB in the “switching request” message includes the target cell&#39;s CGI or CI. 
         [0096]    In step  807 , MME  840  transmits the “switching request” message to HeNB GW  870 . 
         [0097]    In step  808 , HeNB GW  870  finds the HeNB  830  according to the CGI or CI in the container of transparent transmission from source eNB to target eNB. The ID for the HeNB serving cell can be allocated by HeNB GW  870 . Then, it is transmitted from HeNB GW  870  to HeNB  830  with the HeNB registration process or an S 1 -h establishing process, as described in regard to  FIG. 10 . The ID for the HeNB serving cell can also be allocated by the operation and maintenance center. It is transmitted from HeNB  830  to HeNB GW  870  with the S 1 -h establishing process. The method for HeNB GW  870  to obtain the ID for the HeNB cell from HeNB  830  is illustrated in  FIG. 9 . 
         [0098]    In step  809 , subsequent operation flow of S 1  switching is the same as that in existing technique, with a detailed technical description omitted here for conciseness. 
         [0099]      FIG. 9  shows a fourth embodiment for performing S 1  switching. This embodiment corresponds to the case that HeNB consists of HeNB GW, further to the following detailed description. 
         [0100]    In step  901 , HeNB  920  transmits the indicator of the HeNB ID length or the length of the HeNB ID through BCCH. For example, if the length of the HeNB ID can be 22, or 25 or 28, the numbers 0, 1 and 2 can be adopted to indicate the length of 22, 25 and 28, respectively. 
         [0101]    In step  902 , UE  900  moves to the area close to its HeNB  930 , it requests a sounding gap from macro eNB  920 . UE  900  transmits the “sounding gap request” message to the macro eNB  920 . According to the footprint information, UE  900  knows that it arrives at the area close to its HeNB  930 . For example, UE  900  arrives at the macro cell where the HeNB  930  is located, or UE  900  arrives at the TA of the macro cell where the HeNB  930  is located. In this case, it will be confirmed that UE  900  arrives at the area close to its HeNB  930 . 
         [0102]    In step  903 , the macro eNB  920  transmits the “sounding gap response” message to UE  900 . The message includes the sounding gap allocated to UE  900 . 
         [0103]    In step  904 , UE  900  receives the broadcast information from HeNB  930 . 
         [0104]    In step  905 , UE  900  transmits a sounding report to the macro eNB  920 , including the HeNB ID length indicator or the net HeNB ID length. And the message can also include CGI, TAI and the sounding result for the UE  900 . 
         [0105]    The macro eNB  920  determines whether to perform switching according to the sounding result for the UE  900 . If the macro eNB  920  determines to switch UE  900  to the HeNB cell, in step  906 , it transmits the “switching request” message to MME  940  (if the switching is implemented between different MMEs, the MME is a source MME). The macro eNB  920  includes the PLMN ID and the HeNB ID in the Target ID in the message. The container of transparent transmission from source eNB to target eNB in the “switching request” message includes the CGI or CI for the target cell. 
         [0106]    The length of HeNB GW is fixed, and the HeNB GW ID is included in the HeNB ID. 
         [0107]    When switching between different MMEs, the source MME transmits the “forwarding relocation request” message to the target MME after receiving the “switching request” message. In subsequent embodiments, the way of the source MME finding the target MME is given. When switching between different MMEs, the MME mentioned later in present embodiment refers to the target MME. 
         [0108]    In step  907 , MME  940  transmits the “switching request” message to HeNB GW  970 . According to the length of the target ID, MME  940  knows that the target eNB is not a macro eNB, and according to the length of the HeNB GW  970  (e.g., n bits), MME  940  obtains the HeNB GW ID by extracting corresponding length of bits (viz., the first n bits in HeNB) in the front of the HeNB ID. With the “S 1  establishment request” message, MME  940  obtains the HeNB GW IDs of all HeNB GWs to which it connects during the process of establishing S 1 . MME  940  finds the target HeNB GW  970  according to the HeNB GW ID and transmits the “switching request” message to HeNB GW  970 . 
         [0109]    In step  908 , HeNB GW  970  finds the HeNB  930  according to the CGI or CI in the container of transparent transmission from source eNB to target eNB. The ID for the HeNB serving cell can be allocated by HeNB GW  970 . Then, it is transmitted from HeNB GW  970  to HeNB  930  with the HeNB registration process or the S 1 -h establishing process, as described in regard to  FIG. 10 . The ID for the HeNB serving cell can also be allocated by the operation and maintenance center. It is transmitted from HeNB  930  to HeNB GW  970  with the S 1 -h establishing process. The method for HeNB GW  970  to obtain the ID for the HeNB cell from HeNB  930  is illustrated in  FIG. 9 . 
         [0110]    HeNB GW  970  can also find HeNB  930  with the HeNB ID in the Target ID. 
         [0111]    In step  909 , the subsequent operation flow of S 1  switch is the same as that in existing technique. 
         [0112]      FIG. 10  illustrates a method with which HeNB GW obtains the ID for the HeNB serving cell. 
         [0113]    In step  1001 , HeNB  1030  obtains the ID of the serving cell, i.e. an HeNB ID, from the operation and maintenance center. HeNB  1030  transmits the “S 1 -h establishment request” message to HeNB GW  1070 . The message includes the HeNB ID and the serving cell ID list. Here, the cell ID can be either CGI or the unique CI under PLMN. 
         [0114]    In step  1002 , after HeNB GW  1070  receives this message, HeNB GW  1070  saves relevant information and transmits the “S 1 -h establishment response” message to HeNB  1030 . 
         [0115]    In above embodiments, explanation is primarily made to how the target MME finds downstream access network nodes. In configuration for HeNB, the HeNB access system will attempt connection to the MME pool shared by the macro-cell where the macro-cell is located to avoid the UE switching between different MMEs and simplifying the switching process. However, at present the possibility of relocation between different MMEs when UE switches between a macro eNB and the HeNB can not be eliminated. If two MMEs belong to different MME pools, the following methods can be adopted to make the source MME find target MME. 
         [0116]    One method is based on TAI, and includes steps of the HeNB transmitting the ID of the TA where the HeNB cell is located; the UE obtaining the sounding gap from the macro eNB; the UE obtaining the ID of the TA where the HeNB cell is located by reading the broadcast information for the HeNB; the UE transmitting the ID of TA where the HeNB cell is located to the macro eNB when it transmits the sounding report to the macro eNB; and the macro eNB including the TAI in the Target ID in the “switching request” message, with the information elements in the Target ID for the target MME in finding the downstream nodes being described in above embodiments. The method based on TAI also includes the macro eNB determining whether to perform switching according to the sounding result for the UE. If the macro eNB determines to switch UE to HeNB cell, it transmits the “switching request” message to the source MME, and the macro eNB includes the ID of the TA where the target cell locates in the Target ID in the message. Also, the macro eNB includes the HeNB GW ID or HeNB ID in the Target ID in the message. 
         [0117]    The method based on TAI further includes the MME storing the corresponding relationship between TAI and the MME list and the source MME finding the target MME according to the TAI. The source MME transmits the “forwarding relocation request” message to the target MME. 
         [0118]    Solutions mentioned above can be adopted to solve the problem how target MME finds the target eNB, and subsequent operation flow of S 1  switching is the same that in existing technique. 
         [0119]    Another method is illustrated in  FIG. 11 , which shows an MME relocation process when the UE switches between a macro eNB and the HeNB. The manner of how target MME finds target eNB has been described in the above embodiments, and the above solutions can be adopted to solve this problem. In this example, with a focus on how source MME finds target MME. 
         [0120]    In this method, the HeNB access network (HeNB AN) can consist of only HeNB or HeNB and HeNB GW. 
         [0121]    In step  1101 , the eNB  1120  transmits the MME group ID (MMEGI) through the BCCH. 
         [0122]    In step  1102 , UE  1100  moves to the area close to its HeNB  1130  and requests a sounding gap from the macro eNB  1120 . UE  1100  transmits the “sounding gap requesting” message to the macro eNB  1120 . And according to the footprint information, UE  1100  knows that it arrives at the area close to its HeNB  1130 . For example, UE arrives at the macro cell where the HeNB  1130  is located, or UE arrives at the TA of the macro cell where the HeNB  1130  is located. In this case, it will be confirmed that UE  1100  arrives at the area close to its HeNB  1130 . 
         [0123]    In step  1103 , the macro eNB  1120  transmits the “sounding gap response” message to UE  1100 . This message includes the sounding gap allocated to UE  1100 . 
         [0124]    In step  1104 , UE  1100  receives the broadcast information from HeNB  1130 . 
         [0125]    In step  1105 , UE  1100  transmits the sounding report to the macro eNB  1120 , including the HeNB indicator or CSG indicator or the HeNB length indicator or the HeNB length, and CGI in the HeNB cell information. The message can also include the MMEGI of the MME that the HeNB  1130  connects to. 
         [0126]    The macro eNB  1120  determines whether to perform switching according to the sounding result for the UE  1100 . If the macro eNB  1120  determines to switch UE  1100  to the HeNB cell, in step  1106 , it transmits the “switching request” message to the source MME  1140 . The macro eNB  1120  includes the MMEGI of the target eNB in the message. MMEGI can also be included in the Target ID. And the macro eNB  1120  includes the PLMN ID and the HeNB GW ID or the HeNB ID in the Target ID in the message. With the “S 1  establishment request” message, MME obtains the HeNB GW IDs or HeNB IDs of all HeNB GWs to which it connects during the process of establishing S 1 . 
         [0127]    In step  1107 , the source MME  1140  selects some default MME or any MME in the target MME pool as the target MME  1150  according to the MMEGI. The source MME  1140  transmits the “forward relocation request” message to the target MME  1150 . After the target MME  1150  receives this message, it can forward this message to other MMEs in the MME pool. 
         [0128]    In step  1108 , the target MME  1150  finds the downstream node according to the PLMN ID and the HeNB ID or the HeNB GW ID in the Target ID, and then transmits the “switching request” message to its downstream node (e.g., the HeNB or the HeNB GW). 
         [0129]    In step  1109 , subsequent operation flow of S 1  switch is the same as that in existing technique. 
         [0130]    The MME relocation method performing S 1  switch mentioned above is still suitable for the scenario that UE moves from a macro eNB to another macro eNB, as shown in  FIG. 12 . 
         [0131]    In step  1201  of  FIG. 12 , the target eNB  1230  transmits the MME group ID (MMEGI) through BCCH. 
         [0132]    In step  1202 , UE  1200  transmits the “sounding report” message to the source eNB  1220  where it belongs and then reports the sounding result to the source eNB. 
         [0133]    In step  1203 , the source eNB  1220  detects that the information reported by UE  1200  contain none of adjacent cells, it transmits the “request to report information on some cell” message to UE  1200 , requesting it to report information (like CGI) on certain cell. 
         [0134]    In step  1204 , UE  1200  receives the broadcast information “requesting to report information on a cell”. 
         [0135]    In step  1205 , UE  1200  transmits the report to the source eNB  1220  it belongs to, including the CGI and the TA where the cell locates or the MMEGI of the source eNB  1220 . 
         [0136]    The source eNB  1220  determines whether to perform switching according to the sounding result for the UE  1200 . If yes, in step  1206 , the source eNB  1220  transmits the “switching request” message to the source MME  1240 . The source eNB  1220  includes the MMEGI of the target eNB  1230  in the message. MMEGI can also be included in the Target ID. The source eNB  1220  includes the PLMN ID and the target access network node ID like the eNB ID in the Target ID in the message. With the “S 1  establishment request” message, MME obtains the IDs of all access network nodes to which it connects during the process of establishing S 1 . 
         [0137]    In step  1207 , the source MME  1240  selects some default MME or any MME in the target MME pool as the target MME according to the MMEGI. The source MME  1240  transmits the “forwarding relocation request” message to the target MME  1250 . After the target  1250  MME receives this message, it can forward this message to other MMEs in the MME pool. 
         [0138]    In step  1208 , the target MME  1250  finds the downstream node according to the PLMN ID and the eNB ID in the Target ID, and then transmits the “switching request” message to its downstream node. 
         [0139]    In step  1209 , the subsequent operation flow of S 1  switching is the same as that in existing technique. 
         [0140]    While the invention has been shown and described with reference to certain exemplary embodiments of the present invention 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 present invention as defined by the appended claims and their equivalents.