Abstract:
A heterogeneous communication system of performing a handover from a WiMAX communication system to a LTE communication system includes a UE adapted to request a handover connection establishment to the LTE communication system while receiving a CS service from the WiMAX communication system, request an authentication to the first WiMAX system, preferentially perform the handover to the LTE communication system, and switch to the LTE communication system in response to a handover message; and a GANC adapted to deliver the request of the handover connection establishment to the LTE communication system, notify the procedure of the authentication to the LTE communication system and provide the handover command message to the UE to switch to the LTE communication system, thereby providing the CS service to the UE through the LTE communication system. A handover from an LTE communication system to a WiMAX communication system is also disclosed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a system and method for handover between heterogeneous networks, and more particularly, to a heterogeneous communication system of Long Term Evolution (LTE) communication system and Worldwide interoperability for Microwave Access (WiMAX) communication system for providing a circuit switched (CS) service therebetween and a method therefor. 
       BACKGROUND OF THE INVENTION 
       [0002]    A wireless communication technique, allowing users to communicate with each other without restrictions to locations or wires, started in the form of supporting voice services, but has been advanced to support high speed packet data. Research and development are being conducted to enable the Internet and various other techniques to interwork. 
         [0003]    One of the most typical communication schemes among the wireless communication techniques is a 3rd generation mobile communication system using a cellular system. As the 3rd generation mobile communication system, 3GPP2 (3rd generation partnership project 2) of a North American scheme, has been already commercialized, and 3GPP of a European scheme, has almost reached a commercialization phase. The standard proposed by the European scheme is called 3GPP-LTE (3GPP-Long Term Evolution), and currently, most parts of the 3GPP-LTE are under standardization. 
         [0004]    Another communication scheme may be Worldwide interoperability for Microwave Access (WiMAX), which proposes to perform communication by using orthogonal frequency division multiple access (OFDMA). The WiMAX has a wider bandwidth than that of the existing 3rd generation mobile communication system and utilizes more resources. As it is advantageous to high speed and large capacity data communication, commercialization of the WiMAX scheme has been accelerated. 
         [0005]    Meanwhile, when a 3GPP-LTE network and a WiMAX network are integrated, users can selectively use a network suitable for a current situation in an integrated network environment. For example, in case of integrated 3GPP-LTE/WiMAX networks, a user is currently served by a network, e.g., 3GPP-LTE network that offers the best performance, and when the user gets out of the service area of the currently served network according to his or her movement, the user may be served by another available network, e.g., a WiMAX network. The sequential operational process occurring during the network change is called handover. 
         [0006]      FIG. 1  is a flowchart illustrating the sequential process of receiving CS data in performing handover from a WiMAX access network  120  to an LTE access network  130  according to the prior art. 
         [0007]    Specifically, when a user equipment (UE)  101  accesses the WiMAX network  120  at an early stage, it receives a CS service through a generic access network controller (GANC)  103  from a serving mobile switching center (MSC)  105  in step S 11 . In this case, when the UE  101  determines that the WiMAX network  120  is currently in a poor condition not enough to smoothly provide the CS service, the UE  101  determines to perform handover in step S 12  and may attempt to access the LTE network  130 . 
         [0008]    While the UE  101  is accessing the LTE network  130 , a UE authentication is performed in step S 13 , location is updated and subscriber information is retrieved in step S 14 , and a default bearer is set up in step S 15  and a connection of a radio resource control (RRC) is established in step S 16 . And then, the process of accessing the LTE network  130  is completed in step S 17 . 
         [0009]    Thereafter, when the UE  101  updates a registration to the GANC  103  in step S 18 , an evolved packet system (EPS) bearer for the CS service is established and a real-time transport protocol (RTP) path is also established in step S 19 . Thus, after this process, the GANC  103  can provide the CS service to the UE  101  located in the LTE network  130  in step  1300 . 
         [0010]      FIG. 2  is a flowchart illustrating the sequential process of receiving CS data in performing handover from the LTE network  130  to the WiMAX network  120  according to the prior art. 
         [0011]    Specifically, when a UE  201  accesses the LTE network  130  at an early stage, it receives a CS service through a GANC  203  from a serving MSC  205  in step S 21 . In this case, when the UE  201  determines that the LTE network  130  is in a poor condition insufficient to smoothly provide the CS service, it determines to perform handover in step S 23  and may attempt to access the WiMAX network  120 . 
         [0012]    While the UE  201  is accessing the WiMAX network  120 , a radio link initial access (synchronization and ranging) is performed in step S 25 , a basic capability negotiation is performed in step S 27 , an UE authentication and registration is performed in step S 29 , a traffic connection establishment is made in step S 31 , and the like. And then, the process of accessing the WiMAX network  120  is completed in step S 33 . 
         [0013]    Thereafter, when the UE  201  updates a registration to the GANC  203  in step S 35 , an EPS bearer for the CS service is established and an RTP path is also established in step S 37 . Thus, after this process, the GANC  203  can provide the CS service to the UE  201  present in the WiMAX network  120  in step S 39 . 
         [0014]    However, according to the prior arts discussed above, when the UE performs the handover from the WiMAX network  120  to the LTE network  130  or when the UE performs the handover from the LTE network  130  to the WiMAX network  120 , the required process, such as resource allocation, to perform registration and receive data in the new network needs to be performed, which causes a discontinuation of the CS service. That is, the discontinuation of the CS service occurs between a point when the UE attempts to access the LTE network or the WiMAX network in performing handover and a point when the RTP path is established between the UE and the GANC. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention provides a heterogeneous communication system of a LTE and a WiMAX communication system for providing a circuit switched (CS) service and a method therefor, which are capable of reducing a discontinuation of the CS service in performing the handover. 
         [0016]    In accordance with a first aspect of the present invention, there is provided a heterogeneous communication system of performing a handover from a first communication system to a second communication system integrated therein, the heterogeneous communication system including: 
         [0017]    a user equipment (UE) adapted to request a handover connection establishment to the second communication system while receiving a CS (Circuit Switch) service from the first communication system, request an authentication to the first communication system, preferentially perform the handover to the second communication system after the authentication, and disconnect a connection with the first communication system and switch to the second communication system in response to a handover message; and 
         [0018]    a generic access network controller (GANC) adapted to deliver the request of the handover connection establishment to the second communication system, notify the procedure of the authentication to the second communication system, and provide the handover command message to the UE to switch to the second communication system, thereby providing the CS service to the UE through the second communication system. 
         [0019]    In the apparatus, the first communication system is a worldwide interoperability for microwave access (WiMAX) communication system and the second communication system is a long term evolution (LTE) communication system. 
         [0020]    In accordance with a second aspect of the present invention, there is provided a heterogeneous communication system of performing a handover from a first communication system to a second communication system integrated therein, the heterogeneous communications system including: 
         [0021]    a user equipment (UE) adapted to form an authentication with the second communication system, perform a handover preparation to the second communication system to establish a traffic connection for the CS service, disconnect a connection with the first communication system and switch to the second communication system, and perform a radio link initial access and basic capability negotiation with the second communication system; and 
         [0022]    a generic access network controller (GANC) adapted to deliver a message related to the authentication to the second communication system, after the authentication is performed, transmit a context information for the UE to the second communication system to establish the traffic connection, perform a registration update and establish the RTP path with the UE to provide the CS service, thereby providing the CS service to the UE through the second communication system. 
         [0023]    In the apparatus, the first communication system is a long term evolution (LTE) communication system and the second communication system is a worldwide interoperability for microwave access (WiMAX) communication system. 
         [0024]    In accordance with a third aspect of the present invention, there is provided a method for performing a handover from a first communication system to a second communication system in a heterogeneous communication system having a generic access network controller (GANC), the method including: 
         [0025]    in the GANC, delivering a request of a handover connection establishment from a user equipment (UE), which receives a CS (Circuit Switched) service from the first communication system, to the second communication system; 
         [0026]    in the GANC, notifying an authentication between the UE and the first communication system to the second communication via the GANC; 
         [0027]    in the UE, preferentially performing the handover of the UE to the second communication system through the first communication system after a connection to the second communication system is completed; 
         [0028]    in the UE, in response to a handover command message, disconnecting a connection to the first communication system and switching to the second communication system; and 
         [0029]    in the UE, performing a resource reservation to the second communication system to receive the CS service from the first communication system through the second communication system via the GANC. 
         [0030]    In the method, the first communication system is a worldwide interoperability for microwave access (WiMAX) communication system and the second communication system is a long term evolution (LTE) communication system. 
         [0031]    In accordance with a fourth aspect of the present invention, there is provided a method for performing a handover from a first communication system to a second communication system in a heterogeneous communication system having a generic access network controller (GANC), the method including: 
         [0032]    in the GANC, delivering an authentication-related message between the second communication system and a user equipment (UE), which receives a CS (Circuit Switched) service from the first communication system; 
         [0033]    in the UE, delivering a handover preparation message to the second communication system via the GANC to establish a traffic connection for the CS service after the authentication; 
         [0034]    in the UE, switching to the second communication system; 
         [0035]    in the UE, performing a radio link initial access and basic capability negotiation with the second communication system; 
         [0036]    in the second communication system, providing an unsolicited registration response message to the UE via the GANC in response to the radio link initial access and basic capability negotiation; and 
         [0037]    in the UE, in response to the unsolicited registration response message, performing a registration update to the GANC and establishing the RTP path to receive the CS service from the GANC. 
         [0038]    In the method, the first communication system is a long term evolution (LTE) communication system and the second communication system is a worldwide interoperability for microwave access (WiMAX) communication system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    The above and other objects and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which: 
           [0040]      FIG. 1  is a flowchart illustrating the sequential process of receiving CS data in performing a handover from a WiMAX access network to an LTE access network according to the prior art; 
           [0041]      FIG. 2  is a flowchart illustrating the sequential process of receiving CS data in performing a handover from the LTE communication system to the WiMAX communication system according to the prior art; 
           [0042]      FIG. 3  illustrates a block diagram of a heterogeneous communication system for providing a CS service in accordance with an embodiment of the present invention; and 
           [0043]      FIG. 4A  and  FIG. 4B , which is a continuation of  FIG. 4A , are a detailed flowchart illustrating a handover method in a heterogeneous communication system in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0044]    Hereinafter, embodiments of the present invention will be described in detail with the accompanying drawings, which forms a part thereof. 
         [0045]      FIG. 3  illustrates a block diagram of a heterogeneous communication system for providing a CS service in accordance with an embodiment of the present invention. The heterogeneous communication system includes a WiMAX communication system, an LTR communication system and a generic access network controller (GANC)  313 . The WiMAX communication system includes a base station (BS)  303 , an abstract syntax notation (ASN)  305 , a mobile switching center (MSC)  315 , and a home subscriber server (HSS)  317 . 
         [0046]    The LTE communication system includes an eNodeB  307 , a mobility management entity (MME)  309 , and a gateway (GW)  311 . Communication may be performed between the BS  303  and a user equipment (UE)  301  through a WiMAX access network  320 , or communication may be performed between the eNodeB  307  and the UE  301  through an LTE access network  330 . 
         [0047]    The UE  301  may receive a CS service from the MSC  315  through the GANC  313 , the ASN  305  and the BS  303  in a state that it is connected to the WiMAX access network  320  at an early stage. On the contrary, the UE  301  may receive a CS service from the MSC  315  through the GANC  313 , the GW  311  and the eNodeB  307  in a state that is connected to the LTE communication system at an early stage. 
         [0048]    The UE  301  checks whether to perform a handover to the LTE access network  330  while receiving the CS service through the WiMAX access network  320 , or whether to perform handover to the WiMAX access network  320  while receiving a CS service through the LTE access network  330 . 
         [0049]    In case where the UE  301  performs the handover to the LTE access network  330  based on the check result in which the condition of the WiMAX access network  320  is currently not so good as to provide the CS service, the UE  301  performs a process of accessing the LTE access network  330  by transmitting an uplink direct transmission message including attach request message to the GANC  313  through the BS  303  and the ASN  305  in order to establish a handover connection. That is, the UE  301  transmits the uplink direct transmission message including the handover request information to the GANC  313  through the BS  303  and the ASN  305  to perform the handover to the LTE access network  330  in advance. 
         [0050]    The UE  301  disconnects the connection to the WiMAX access network  320  through a handover command message included in a downlink direct transmission message received from the GANC  313  through the ASN  305  and the BS  303 , switches to connect to the LTE access network  330 , and then transmits a handover complete notification message to the MME  309  through the eNodeB  307  to inform that handover has been completed. 
         [0051]    The UE  301  updates a registration to the GANC  313 , establishes an RTP path between the UE  301  and the GANC  313 , and then receives the CS service from the MSC  315  through the GANC, the GW  311  and the eNodeB  307 . Here, the establishment of the RTP path is generated at the same time when the UE  301  transmits the handover complete notification message to the MME  309 . 
         [0052]    Meanwhile, in case where the UE  301  performs handover to the WiMAX access network  320  based on the check result in which the condition of the LTE access network  330  is currently not so good as to provide the CS service, the UE  301  exchanges an authentication message required for UE authenticating in the eNodeB  307  and the GW  311  with the GANC  313  through the current serving LTE access network  330 . 
         [0053]    When the UE  301  delivers a handover preparation message to the eNodeB  307  through the LTE access network  330 , context information regarding the UE  301  is delivered from the eNodeB  307  to the BS  303  of the WiMAX access network  320  through the GANC  313 , so that a traffic connection for the CS service is established in advance between the BS  303  and the GW  311 . In the state that the traffic connection is established, the UE  301  transmits a handover preparation message to the BS  303  through the WiMAX access network  320 , and after a certain time lapses or immediately when the handover preparation message is transmitted, the UE  301  disconnects a connection to the LTE access network  330  and is switched to the WiMAX access network  320  to perform a synchronization and ranging for a radio link initial connection to the BS  303  and a basic capability negotiation with the BS. Thereafter, the UE  301  receives an unsolicited registration response message in response, updates a registration to the GANC  313  through the BS  303  and the ASN  305 , establishes an RTP path, and then receives the CS service from the MSC  315  through the GANC  313 , the ASN  305 , and the BS  303 . 
         [0054]    When the BS  303  performs the synchronization and ranging and the basic capability negotiation with the UE  301  through the WiMAX access network  320 , the BS  303  transmits the unsolicited registration response message to the UE  301  through the WiMAX access network  320 . 
         [0055]    The MME  309  recognizes that the handover is performed to the LTE access network  330  in response to the attach request message input from the GANC  313 , and provides an authentication request message to the GANC  313 . 
         [0056]    In addition, the MME  309  performs a location updating and a subscriber data retrieval to the HSS  317  through the GANC  313  and the MSC  315 , performs a default bearer setup through the GW  311 , and establishes an RRC connection through the GANC  313  in establishing the RRC between the UE  301  and the LTE access network  330 . 
         [0057]    Also, the MME  309  performs a resource reservation operation (e.g., an EPS bearer setup operation, etc.) for the CS service in response to a relocation request message provided from the GANC  313  and then provides a relocation command message to the GANC  313 . 
         [0058]    The GANC  313  provides the attach request message included in the uplink direct transmission message received from the UE  301  through the BS  303  and the ASN  305  to the MME  309 . 
         [0059]    Further, the GANC  313  may provide a control to perform an authentication process between the UE  301  and the GANC  313  in response to an authentication request message input from the MME  309 . In this case, the GANC  313  provides controls to transmit and receive the authentication process between the UE  301  and the HSS  317  through the MME  309 . 
         [0060]    Also, the GANC  313  generates a relocation request message based on the handover request information included in the uplink direct transmission message received from the UE  301  through the BS  303  and the ASN  305 , and provides the relocation request message to the MME  309 . 
         [0061]    The GANC  313  generates the handover command message based on the relocation command message from the MME  309 , incorporates the handover command message into a downlink direct transmission message, and then transmits the downlink direct transmission message to the UE  301  through the ASN  305  and the BS  303 . 
         [0062]    Thus, the GANC  313  provides a control to transmit and receive an authentication message between the UE  301  and the HSS  317  through the eNodeB  307 , the GW  311  and the MSC  315 , and when the authentication process is successfully completed, the GANC  313  delivers context information regarding the UE  301  to the BS  303  of the WiMAX access network  320 . 
         [0063]    Meanwhile, when the UE  301  does not perform the handover due to failure of a handover prediction, the GANC  313  requests the HSS  317  to release resources previously reserved for a network predicted to perform handover thereto and delete relevant UE location information if a register update message is not received from the UE  301  within a preset time. The HSS  317  may release the previously reserved resources and delete the relevant UE location information in response to the request from the GANC  313 . 
         [0064]    Thus, in the present invention, because the duration of discontinuation of the CS service can be reduced in performing handover in the IP-based 3GPP-LTE and an IEEE-WiMAX convergence network in which two or more heterogeneous wireless communication techniques coexist by performing the authentication and registration process in advance through the GANC, a high quality service can be provided to the UE. 
         [0065]    Now, the handover process between the heterogeneous network of the LTE and the WiMAX communication system in accordance with the embodiment of the present invention having the configuration as described above will be explained with reference to  FIG. 4 . 
         [0066]      FIG. 4  illustrates a flowchart illustrating a handover method in a heterogeneous communication system of an LTE and a WiMAX communication system in accordance with an embodiment of the present invention. 
         [0067]    The UE  301  is in a state that is connected to the WiMAX access network  320  at the early stage, and the UE  301  receives a CS service from the serving MSC  315  through the GANC  313 , the ASN  305  and the BS  303 . 
         [0068]    The UE  301  determines whether to perform a handover to the LTE access network  330  while receiving the CS service through the WiMAX access network  320  by checking whether the condition of the WiMAX access network  320  is currently not so good as to provide the CS service. 
         [0069]    In case where the UE  301  performs the handover to the LTE access network  330  in step S 403  based on the check result in step S 401 , the UE  301  then transmits an uplink direct transmission message including attach request message to the GANC  313  through the BS  303  and the ASN  305  in order to establish a handover connection in step S 405 . 
         [0070]    The GANC  313  provides the attach request message included in the uplink direct transmission message received from the UE  301  through the BS  303  and the ASN  305  to the MME  309  in step S 407 . 
         [0071]    The MME  309  recognizes that the handover is performed to the LTE access network  330  based on the attach request message from the GANC  313 , and provides an authentication request message to the GANC  313  in step S 409 . 
         [0072]    The GANC  313  provides a control to perform an authentication process between the UE  301  and the GANC  313  in response to the authentication request message from the MME  309  in step S 411 . In this case, the GANC  313  controls to execute the authentication process between the UE  301  and the HSS  317  through the MME  309 . 
         [0073]    Then, the MME  309  performs location updating and subscriber data retrieval to the HSS  317  through the GANC  313  and the MSC  315  in step S 413 , performs a default bearer setup through the GW  311  in step S 415 , and then establishes an RRC connection between the UE  301  and the LTE access network  330  through the GANC  313  in step S 417 . 
         [0074]    Thereafter, the UE  301  transmits the uplink direct transmission message including the handover request information to the GANC  313  through the BS  303  and the ASN  305  to perform the handover to the LTE access network  330  in advance in step S 421 . 
         [0075]    The GANC  313  generates a relocation request message based on handover request information included in the uplink direct transmission message received from the UE  301  through the BS  303  and the ASN  305  in step S 423 , and provides the relocation request message to the MME  309  in step S 425 . 
         [0076]    The MME  309  performs a resource reservation operation, e.g., an EPS bearer setup procedure, for the CS service in response to the relocation request message from the GANC  313  in step S 427  and then provides a relocation command message to the GANC  313  in step S 429 . 
         [0077]    The GANC  313  generates a handover command message based on the relocation command message from the MME  309  in step S 431 , incorporates the generated handover command message into a downlink direct transmission message, and then transmits the same to the UE  301  through the ASN  305  and the BS  303  in step S 433 . 
         [0078]    The UE  301  cuts off the connection to the WiMAX access network  320  depending on the handover command message included in the downlink direct transmission message received from the GANC  313 , switches to connect to the LTE access network  330  in step S 435 , and then transmits a handover complete notification message to the MME  309  through the eNodeB  307  to inform that handover has been completed in step S 437 . 
         [0079]    Finally, the UE  301  updates a registration to the GANC  313 , establishes an RTP path between the UE  301  and the GANC  313  in step S 439 , and then receives the CS service from the MSC  315  through the GANC  313 , the GW  311  and the eNodeB  307  in step S 441 . 
         [0080]    Meanwhile, in a state that the UE  301  is connected to the LTE access network  330  at an early stage while receiving the CS service from the registered MSC  315  through the GANC  313 , the GW  311  and the eNodeB  307 , in case where the UE  301  performs a handover to the WiMAX access network  320  in step S 443  based on the check result in step S 401  in which the condition of the LTE access network  330  is currently not so good as to provide the CS service, the UE  301  exchanges a authentication message required for authenticating thereof by the eNodeB  307  and the GW  311  with the GANC  313  through the LTE network  330 , the eNodeB  307  and the GW  311  in step S 445 . 
         [0081]    The GANC  313  provides a control to transmit and receive an authentication message between the UE  301  and the HSS  317  through the eNodeB  307  and the GW  311 , and in turn the MSC  315  to perform an UE authentication. Thereafter, when the UE authentication is successfully completed in step S 447 , the GANC  313  transmits context information regarding the UE  301  to the BS  303  of the WiMAX access network  320  in step S 449 . 
         [0082]    Next, the context information is transmitted by the GANC  313  to the BS  303  of the WiMAX access network  320 , and a traffic connection for the CS service can be established in advance between the BS  303  and the GW  311  in step S 451 . However, when the UE  301  does not perform the handover due to failure of a handover prediction, the GANC  313  requests the HSS  317  to release resources previously reserved for a network expected to perform handover thereto and delete relevant UE location information if a register update message is not received from the UE  301  within a preset time. 
         [0083]    Also, as the context information is transmitted to the BS  303  through the WiMAX access network  320  by the GANC  313 , a traffic connection for the CS service is established in advance between the BS  303  and the GW  311 . In the state that the traffic connection is established, the UE  301  transmits a handover preparation message to the BS  303  through the WiMAX access network  320 , and after a certain time lapses or immediately when the handover preparation message is transmitted, the UE  301  disconnects the connection to the LTE network  330  and is switched to the WiMAX access network  320  in step S 453  to perform a radio link initial connection to the BS  303  and a basic capability negotiation with the BS  303  in step S 455 . 
         [0084]    When the BS  303  performs the radio link initial connection and basic capability negotiation with the UE  301  through the WiMAX access network  320 , it transmits an unsolicited registration response message to the UE  301  through the WiMAX access network  320  in step S 457 . The UE  301  receives the unsolicited registration response message in response to the performing of the radio link initial connection and basic capability negotiation from the BS  303 , updates a registration to the GANC  313  through the BS  303  and the ASN  305  in step S 459 , establishes an RTP path in step S 461 , and then receives the CS service from the MSC  315  through the GANC  313 , the ASN  305 , and the BS  303  in step S 463 . 
         [0085]    The handover method between heterogeneous networks in accordance with various embodiments of the present invention may be implemented with software codes in a computer-readable storage medium that can be executed by a computer system. The computer-readable storage medium may include various types of storage devices including a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, carrier waves (e.g., transmission via the Internet), and the like. Further, the software codes or programs may be distributed in computer systems connected over a communication network and executed in order to perform the functions of the present invention. 
         [0086]    As described above, in accordance with the present invention, the authentication and registration process is performed in advance by the GANC, thereby reducing the discontinuation duration of the CS service in performing handover in a heterogeneous communication system of the IP-based 3GPP-LTE and an IEEE-WiMAX communication system, and a high quality service may be provided to users through a UE such as a mobile terminal, a personal digital assistance (PDA), a notebook computer, a modem, and the like. 
         [0087]    In addition, in accordance with the present invention, the UE performs switching to the LTE access network or the WiMAX access network, immediately updates a registration to the GANC and establishes an RTP path between the UE and the GANC, rather than performing a registration process, resource reservation, authentication, and the like. Accordingly, the discontinuation duration of the CS service can be drastically reduced to enhance user satisfaction about quality of service. 
         [0088]    While the invention has been shown and described with respect to the particular embodiments, it will be understood by those skilled in the art that various changes and modification may be made without departing the scope of the present invention as defined in the following claims.