Abstract:
An operating method, a base station, and terminal of a cell of a first communication system for a handover between the first communication system and a second communication system are provided. The method includes, receiving, by the base station, a measurement report including measured signal quality, from a terminal, determining, by the base station, a handover initiation to a target radio access network, based on the measured signal quality, transmitting, by the base station, a handover request message to the target radio access network via a core network, receiving, by the base station, radio-related information that is required if the terminal accesses the target radio access network, from the target radio access network via the core network, and transmitting, by the base station, the radio-related information of the target radio access network, to the terminal, wherein the handover between the source radio access network and the target radio access network comprises an inter radio access technology (RAT) handover.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of a prior application Ser. No. 13/591,805 that was filed on Aug. 22, 2012 and issued as U.S. Pat. No. 8,805,378 on Aug. 12, 2014, which is a continuation of U.S. patent application Ser. No. 12/029,809 that was filed on Feb. 12, 2008 and issued as U.S. Pat. No. 8,254,933 on Aug. 28, 2012, and claims the benefit under 35 U.S.C. §119(a) of a Korean patent application filed in the Korean Intellectual Property Office on Feb. 12, 2007 and assigned Serial No. 10-2007-0014280, the entire disclosure of each of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus and a method for handover between heterogeneous networks in a broadband wireless communication system. More particularly, the present invention relates to an apparatus and a method for seamless handover from a border cell of a broadband wireless communication system to a heterogeneous network. 
     2. Description of the Related Art 
     High speed Internet services allow a user to access the Internet at a high data rate (at 1 Mbps or so). The high speed Internet services originated with wired services for a stationary user. However, the high speed Internet services have been extended to be provided wirelessly at anytime and anywhere to a mobile user using a portable terminal. Currently, high speed Internet services are supported by broadband wireless communication systems based on Institute of Electronics and Electrical Engineers (IEEE) 802.16 or wireless communication systems based on Wideband Code Division Multiple Access (WCDMA)/High Speed Downlink Packet Access (HSDPA). 
     While broadband wireless communication systems are used to service dense urban areas, heterogeneous communication systems (WCDMA/HSDPA or EVolution Data Only (EV-DO)) are used to service any area. Accordingly, in the broadband wireless communication system, a region between dense urban areas would not be serviced unless a base station is installed in that region. By contrast, in the heterogeneous communication system, a terminal would be serviced in every area. Hence, when the terminal travels outside the coverage of the broadband wireless communication system in the region between the dense urban areas, a call drop occurs. After the call drop, the terminal is no longer serviced unless it re-enters the broadband wireless communication system. If the terminal is a dual-mode dual-band terminal which can be serviced by both the heterogeneous communication system and the broadband wireless communication system, the terminal attempts to reconnect the call through the heterogeneous communication system after the call drop occurred in the broadband wireless communication system. However, when the dual-mode dual-band terminal travels outside the service coverage area of the broadband wireless communication system and suffers the call drop, there are no apparatus and method for handover between the broadband wireless communication system and the heterogeneous networks without service interruption. 
     With advances in mobile communications, 2.5 th  generation, 3 rd  generation and 4 th  generation networks coexist and ability to provide a dual-mode dual-band function requires accessibility to various communication networks. Therefore, when a dual-mode dual-band terminal gets out of a service coverage area of a broadband wireless communication system, what is needed is an apparatus and a method for seamless handover to a heterogeneous communication system. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to address at least the above mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an apparatus and a method for handover between a broadband wireless communication system and a heterogeneous communication system. 
     Another aspect of the present invention is to provide an apparatus and a method for handover between a broadband wireless communication system and a heterogeneous communication system through a periodic signal strength report in a border cell in of the broadband wireless communication system. 
     Yet another aspect of the present invention is to provide an apparatus and a method for handover between a broadband wireless communication system and a heterogeneous communication system when a terminal is handed over to a dummy cell in a broadband wireless communication system. 
     Still another aspect of the present invention is to provide an apparatus and a method for handover between a broadband wireless communication system and a heterogeneous communication system using a state of an active set in a broadband wireless communication system. 
     The above aspects are addressed by providing an operating method of a base station for a handover between a broadband wireless communication system and a heterogeneous communication system. The operating method includes when a terminal enters a border cell, sending a message requesting to measure a signal level of a downlink, to the terminal, when a signal level measured by the terminal falls below a preset threshold, requesting a handover, to a corresponding heterogeneous communication system, over a core network, receiving a message, including channel allocation information for the handover, from the corresponding heterogeneous communication system, and forwarding the message, including the channel allocation information, to the terminal. 
     According to one aspect of the present invention, an operating method of a base station of a cell of a first communication system for a handover between the first communication system and a second communication system is provided. The method includes, when a terminal initiates a handover between the first communication system and the second communication system, transmitting, by the base station, a message, requesting to measure a signal level of a downlink, to the terminal, when a signal level measured by the terminal falls below a preset threshold, requesting, by the base station, a handover to the second communication system over a core network, receiving, by the base station, a message, including radio channel parameters the that is required when the terminal accesses to the second communication system, from the second communication system, and forwarding, by the base station, the message, including the radio channel parameters of the second communication system, to the terminal. 
     According to another aspect of the present invention, an operating method of a terminal for a handover between a first communication system and a second communication system is provided. The method includes receiving, by the terminal, a message, requesting a measurement of a signal level of a downlink, from a base station of the first communication system, transmitting, by the terminal, a message, reporting of the signal level of the downlink, to the base station, receiving, by the terminal, a message, including radio channel parameters the that is required when the terminal accesses to the second communication system, from the base station, when the signal level of the downlink falls below a threshold, and attempting, by the terminal, the handover from the first communication system to the second communication system using the radio channel parameters of the second communication system received from the first communication system. 
     According to yet another aspect of the present invention, a base station of a cell of a first communication system for a handover between the first communication system and a second communication system is provided. The base station includes a controller for transmitting, to a terminal, a message requesting a measurement of a signal level of a downlink, when the terminal initiates a handover between the first communication system and the second communication system, a handover processor for requesting a handover to the second communication system over a core network, when a signal level measured by the terminal falls below a preset threshold, and an interface for receiving a message, including radio channel parameters that is required when the terminal accesses to the second communication system, from the second communication system. The controller forwards the message, including the radio channel parameters of the second communication system, to the terminal. 
     According to still another aspect of the present invention, a terminal for a handover between a first communication system a second communication system is provided. The terminal includes a controller for receiving a message requesting a measurement of a signal level of a downlink from a base station of the first communication system and for transmitting a message reporting of the signal level of the downlink to the base station, and a handover controller for receiving a message including radio channel parameters the that is required when the terminal accesses to the second communication system, from the base station, when the signal level of the downlink falls below a threshold and for attempting the handover from the first communication system to the second communication system using the radio channel parameters of the second communication system received from the first communication system. 
     Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of certain exemplary embodiments the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram of a handover between a heterogeneous communication system and a broadband wireless communication system, according to an exemplary embodiment of the present invention; 
         FIG. 2  is a diagram of a handover between a heterogeneous communication system and a broadband wireless communication system, according to another exemplary embodiment of the present invention; 
         FIG. 3  is a diagram of a handover between a heterogeneous communication system and a broadband wireless communication system, according to yet another exemplary embodiment of the present invention; 
         FIG. 4  is a signal flow diagram of a handover between a heterogeneous communication system and a broadband wireless communication system, according to an exemplary embodiment of the present invention; 
         FIG. 5  is a signal flow diagram of a handover between a heterogeneous communication system and a broadband wireless communication system, according to another exemplary embodiment of the present invention; 
         FIG. 6  is a signal flow diagram of a handover between a heterogeneous communication system and a broadband wireless communication system, according to yet another exemplary embodiment of the present invention; 
         FIG. 7  is a flowchart of operations of a base station for a handover between a heterogeneous communication system and a broadband wireless communication system, according to an exemplary embodiment of the present invention; 
         FIG. 8  is a flowchart of operations of a terminal for a handover between a heterogeneous communication system and a broadband wireless communication system, according to an exemplary embodiment of the present invention; 
         FIG. 9  is a flowchart of operations of a base station for a handover between a heterogeneous communication system and a broadband wireless communication system, according to another exemplary embodiment of the present invention; 
         FIG. 10  is a flowchart of operations of a terminal for a handover between a heterogeneous communication system and a broadband wireless communication system, according to another exemplary embodiment of the present invention; 
         FIG. 11  is a flowchart of operations of a base station for a handover between a heterogeneous communication system and a broadband wireless communication system, according to yet another exemplary embodiment of the present invention; 
         FIG. 12  is a flowchart of operations of a terminal for a handover between a heterogeneous communication system and a broadband wireless communication system, according to yet another exemplary embodiment of the present invention; 
         FIG. 13  is a block diagram of the base station of  FIG. 9  for the handover between the heterogeneous communication system and the broadband wireless communication system, according to an exemplary embodiment of the present invention; and 
         FIG. 14  is a block diagram of a terminal for a handover between a heterogeneous communication system and a broadband wireless communication system, in the broadband wireless communication system according to an exemplary embodiment of the present invention. 
     
    
    
     Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features and structures. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the present invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
     Exemplary embodiments of the present invention provide an apparatus and a method for handover to a heterogeneous communication system from a broadband wireless communication system. Hereafter, several conditions are assumed for the understanding of the exemplary embodiments of the present invention. First, a cell of the broadband wireless communication system supports a Fast Base Station BS Switching (FBSS). Secondly, a terminal is a dual-mode dual-band terminal which supports a modem for the broadband wireless communication system and a modem for the heterogeneous communication system (e.g., EV-DO and WCDMA/HSDPA). Thirdly, a service coverage area of the heterogeneous communication system is larger than a service coverage area of the broadband wireless communication system. Fourthly, terminal information and channel allocation messages can be transmitted between the broadband wireless communication system and the heterogeneous communication system over a core network. Fifthly, the terminal is not aware of a border cell. Sixthly, since interference from the border cell of the broadband wireless communication system to the heterogeneous network is much less than that of an overlay network, relatively good Carrier to Interference and Noise Ratio (CINR) is presented even with a low Received Signal Strength Indication (RSSI). 
       FIGS. 1 ,  2  and  3  are diagrams of handover between a heterogeneous communication system and a broadband wireless communication system, according to exemplary embodiments of the present invention.  FIGS. 4 ,  5  and  6  illustrate three exemplary embodiments of the present invention in detail. 
       FIG. 1  is a diagram of a handover between a heterogeneous communication system and a broadband wireless communication system, according to an exemplary embodiment of the present invention. 
     Broadband cells  102   a ,  102   b ,  102   c  and  102   d  of the broadband wireless communication system define a service coverage area of the broadband wireless communication system. Broadband cell  102   d  is a border cell of the broadband wireless communication system. As a border cell, broadband cell  102   d  is positioned on the border of the cells of the service coverage area of the broadband wireless communication system. Heterogeneous cells  100   a ,  100   b ,  100   c  and  100   d  of the heterogeneous communication system define a service coverage area of the heterogeneous communication system. The service coverage area of the heterogeneous communication system is larger than that of the broadband wireless communication system. The service coverage area is divided to an overlay area  106  overlapped by the service coverage area of the broadband wireless communication system and the service coverage area of the heterogeneous communication system, and a heterogeneous cell only area  108 . Herein, if a dual-mode dual-band terminal, serviced in border cell  102   d  of the broadband wireless communication system, enters the heterogeneous cell only area  108 , the terminal will not receive service unless handover is performed between the broadband wireless communication system and the heterogeneous communication system. 
     According to an exemplary embodiment of the present invention, to avoid the out-of-service scenario described above, when the terminal enters the border cell  102   d  of the broadband wireless communication system, the terminal periodically measures a signal level of a downlink and sends the measured signal level to its base station, which is a base station in charge of the border cell. Under the control of the base station, when the signal level of the border cell  102   d  falls below a certain level, the terminal receives channel allocation information from an upper network entity and attempts the handover  104  to the heterogeneous cell  100   d , which will be described in more detail below by referring to  FIG. 4 . 
       FIG. 2  is a diagram of a handover between a heterogeneous communication system and a broadband wireless communication system, according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , broadband cells  202   a ,  202   b ,  202   c  and  202   d  of the broadband wireless communication system define a service coverage area of the broadband wireless communication system. Heterogeneous cells  200   a ,  200   b ,  200   c  and  200   d  of the heterogeneous communication system define a service coverage area of the heterogeneous communication system. The service coverage area of the heterogeneous communication system is larger than that of the broadband wireless communication system. The service coverage area is divided to an overlay area  206  overlapped by the service coverage area of the broadband wireless communication system and the service coverage area of the heterogeneous communication system, and a heterogeneous cell only area  208 . Broadband cell  202   c  is a border cell of the broadband wireless communication system and Broadband cell  202   d  is a dummy cell of the broadband wireless communication system. 
       FIG. 2  depicts the handover when a dummy cell  202   d  is present next to a border cell  202   c  in the broadband wireless communication system. Herein, the dummy cell  202   d  extends the service coverage area to a virtual service coverage area. When a terminal serviced by the broadband wireless communication system enters the border cell  202   c  and needs to handover to the dummy cell  202   d , the terminal attempts the handover  204  to the heterogeneous cell  200   c  under the control of a network entity, which will be explained in more detail below by referring to  FIG. 5 . 
       FIG. 3  is a diagram of a handover between a heterogeneous communication system and a broadband wireless communication system, according to yet another exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , broadband cells  302   a ,  302   b ,  302   c  and  302   d  of the broadband wireless communication system define a service coverage area of the broadband wireless communication system. Heterogeneous cells  300   a ,  300   b ,  300   c  and  300   d  of the heterogeneous communication system define a service coverage area of the heterogeneous communication system. The service coverage area of the heterogeneous communication system is larger than that of the broadband wireless communication system. The service coverage area is divided to an overlay area  306  overlapped by the service coverage area of the broadband wireless communication system and the service coverage area of the heterogeneous communication system, and a heterogeneous cell only area  308 . Broadband cell  302   d  is a border cell of the broadband wireless communication system. 
     When a terminal serviced by the broadband wireless communication system enters border cell  302   d  at point A, it can acquire a plurality of active set information that is updated for the handover. Herein, the active set is a set of base stations currently in communications. There may be several base stations in the set according to the handover. When the terminal moves to a heterogeneous cell only area  308 , the active set includes only the base station of the border cell  302   d . When the active set includes only the base station of the border cell  302   d , the terminal attempts the handover  304  to heterogeneous cell  300   d  at point B, which will be explained in more detail below by referring to  FIG. 6 . 
     In  FIGS. 4 ,  5  and  6 , the terminal, which includes a first modem and a second modem, can access to both the broadband wireless communication system and the heterogeneous communication system. The modem for the broadband wireless communication system is referred to as a first modem and the modem for the heterogeneous communication system is referred to as a second modem. It is assumed that the terminal operates using the first modem in the overlay areas  106 ,  206  and  306  overlapped by the service coverage areas of the broadband wireless communication system and the heterogeneous communication system, and that the second modem can transition from a low power mode into an active mode when the first modem is interrupted. 
       FIG. 4  is a signal flow diagram of the handover between a heterogeneous communication system and a broadband wireless communication system, according to an exemplary embodiment of the present invention.  FIG. 4  is described below with reference to  FIG. 1  which was described above. 
     When a terminal enters border cell  102   d , a base station in the broadband wireless communication system  404  periodically sends a message Report_Request (REP_REQ) requesting a Received Signal Strength Indication (RSSI) of the downlink to the first modem  402  of terminal in step  410 . 
     In step  412 , the first modem  402  of terminal sends a response message Report_ReSPonse (REP_RSP) including the measured RSSI to the base station in the broadband wireless communication system  404 . 
     When the RSSI measured by the terminal falls below a threshold, the base station in the broadband wireless communication system  404  requests handover to the heterogeneous communication system  406  over a core network (N/W) in step  414 . Herein, when the threshold is too high, the terminal, which enters the border cell and immediately attempts the handover to the heterogeneous communication system, may waste the border cell area. By contrast, when the threshold is too low, call drop is likely to occur because the handover is carried out far away from the base station. 
     In step  416 , the heterogeneous communication system  406  allocates a channel to a target heterogeneous cell  100   d  to which the terminal moves, in response to the handover request and sends a message including the allocated channel information to the base station of broadband wireless communication system  404  over the core N/W. For example, the channel allocation message of the heterogeneous communication system may be a Universal Handoff Direction Message (UHDM) in CDMA 1x, a Traffic Channel Assignment (TCA) message in the EV-DO, or an Active Set Update (ASU) message in the WCDMA. 
     In step  418 , the base station of broadband wireless communication system  404  forwards the channel allocation information received from the heterogeneous communication system  406  to the first modem  402  in the terminal using an RNG_RSP message. The channel allocation information may be TLV-coded and added to TLV encoded information of the RNG_RSP message. Table 1 shows the RNG_RSP message format and Table 2 shows channel allocation information parameters of the heterogeneous communication system, which are added to the RNG_RSP message. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
             
               
                 RNG_RSP_Message_Format( ) { 
                   
                   
               
               
                 Management Message Type = 5 
                 8 bits 
               
               
                 reserved 
                 8 bits 
                 Shall be set to zero 
               
               
                 TLV Encoded Information 
                 variable 
                 TLV specific 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
             
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Name 
                 Type (1 byte) 
                 Length 
                 Value (variable-length) 
               
             
          
           
               
                 . . . existing parameters defined . . . 
               
               
                   
               
             
          
           
               
                 Heterogeneous 
                 34 
                 variable 
                 message contents of 
               
               
                 message 
                   
                   
                 heterogeneous 
               
               
                 encoding 
                   
                   
                 communication system 
               
               
                   
               
             
          
         
       
     
     Next, the first modem  402  of the terminal provides the received channel allocation information to the second modem  400  to access to the heterogeneous communication system in step  420 . 
     The terminal operating using the second modem  400  acquires an uplink of the heterogeneous communication system  406  using the channel allocation information through the second modem in step  422 , and transmits a handover complete report message to the heterogeneous communication system  406  in step  424 . Herein, the handover complete report message of the heterogeneous communication system may be a Handoff Complete Message (HCM) in the CDMA 1x, a Traffic Channel Complete (TCC) message in the EV-DO, or an Active Set Update Complete (ASUC) message in the WCDMA. 
     Next, the handover between the broadband wireless communication system and the heterogeneous communication system is finished. 
       FIG. 5  is a signal flow diagram of the handover between the heterogeneous communication system and the broadband wireless communication system, according to another exemplary embodiment of the present invention.  FIG. 5  is described below with reference to  FIG. 2  which was described above. 
     When the RSSI falls below a handover threshold and the handover to the dummy cell  202   c  is needed, a first modem  502  in a terminal in the border cell  202   c  of the broadband wireless communication system sends a handover request message MOB_MSHO_REQ to a base station of the broadband wireless communication system  504  in step  510 . 
     When the handover requested by the first modem  502  of the terminal is a request for handover to the dummy cell, the base station of the broadband wireless communication system  504  requests handover to the heterogeneous communication system  506  in step  518 . In response, the base station of the broadband wireless communication system  504  sends a handover response message MOB_BSHO_RSP to the first modem  502  in the terminal in step  512 . 
     In step  520 , the heterogeneous communication system  506  allocates a channel to a target cell heterogeneous  200   d  in response to the handover request and sends a message including the allocated channel information to the base station of the broadband wireless communication system  504  over a core N/W. 
     In step  514 , the base station  504  forwards the channel allocation information received from the heterogeneous communication system  506  to the first modem  502  of the terminal using an RNG_RSP message. The RNG_RSP message format is shown in Table 1 and Table 2. 
     In step  522 , to access the heterogeneous communication system, the first modem  502  of the terminal provides the received channel allocation information to the second modem  500  of the terminal. 
     The terminal operating using the second modem  500  acquires an uplink of the heterogeneous communication system  506 , using the channel allocation information, through the second modem  500  in step  524 , and sends a handover complete report message to the heterogeneous communication system  506  in step  526 . 
     Next, the handover between the broadband wireless communication system and the heterogeneous communication system is finished. 
       FIG. 6  is a signal flow diagram of the handover between the heterogeneous communication system and the broadband wireless communication system, according to yet another exemplary embodiment of the present invention.  FIG. 6  is described below with reference to  FIG. 3  which was described above. 
     When the RSSI falls below a preset handover threshold, a first modem  602  in a terminal sends a handover request message to a base station of a broadband wireless communication system  604  in step  610 . 
     The base station of the broadband wireless communication system  604  sends a handover response message to the first modem  602  of the terminal in step  612  and receives a message MOB_HO_IND informing of the handover in step  614 . Also, the base station of the broadband wireless communication system  604  determines whether the active set includes only a border cell. When the active set includes only the border cell in step  616 , the base station of the broadband wireless communication system  604  sends a handover request message to the heterogeneous communication system  606  in step  618  and receives a channel allocation information message in step  620 . Herein, the active set is a set of currently connectable base stations. There may be multiple base stations, according to the handover. Since the active set changes according to the movement of the terminal, the base station can determine based on the active set information whether the terminal needs to handover to the heterogeneous communication system. 
     In step  622 , the base station of the broadband wireless communication system  604  forwards the channel allocation information received from the heterogeneous communication system  606  to the first modem  602  of the terminal using an RNG_RSP message. The RNG_RSP message format is shown in Table 1 and Table 2. 
     In step  624 , the first modem  602  of the terminal provides the received channel allocation information to the second modem  600  of the terminal to access to the heterogeneous communication system. 
     The terminal operating using the second modem  600  acquires an uplink of the heterogeneous communication system  606 , using the channel allocation information, through the second modem  600  in step  626  and sends a handover complete report message to the heterogeneous communication system  606  in step  628 . 
     Next, the handover between the broadband wireless communication system and the heterogeneous communication system is finished. 
       FIG. 7  is a flowchart of operations of a base station for the handover between the heterogeneous communication system and the broadband wireless communication system, according to an exemplary embodiment of the present invention. 
     In step  700 , the base station determines whether the terminal is present in the border cell. When the terminal is in the border cell, the base station sends a downlink RSSI measure request message to the terminal in step  702 . When the terminal is not in the border cell, the base station performs a corresponding function. 
     In step  704 , the base station receives a downlink RSSI report message from the terminal as requested. 
     When the RSSI reported by the terminal falls below the threshold in step  706 , the base station requests the handover to the heterogeneous communication system in step  708 . 
     In step  710 , the base station receives information relating to a channel allocated by the heterogeneous communication system to a corresponding cell. The corresponding cell is a cell to which the terminal is handed over. 
     In step  712 , the base station sends a message RNG_RSP including the received channel allocation information to the terminal. 
     Next, the base station finishes the process. 
       FIG. 8  is a flowchart of operations of the terminal for the handover between the heterogeneous communication system and the broadband wireless communication system, according to an exemplary embodiment of the present invention. 
     In step  800 , the terminal receives the downlink RSSI measure request message for the border cell from the base station. 
     In step  802 , the terminal measures the downlink RSSI for the border cell and periodically reports the measured RSSI to the base station. 
     In step  804 , the terminal receives the message including the channel allocation information of the heterogeneous communication system from the base station. 
     In step  806 , the terminal transitions to the heterogeneous communication system connection mode. For example, the terminal interrupts the first modem in use and activates the second modem to connect to the heterogeneous communication system. 
     In step  808 , the terminal acquires the uplink of the heterogeneous communication system using the channel allocation information. 
     In step  810 , the terminal sends the handover complete report message to the heterogeneous communication system. 
     Next, the terminal finishes this process. 
       FIG. 9  is a flowchart of operations of the base station for the handover between the heterogeneous communication system and the broadband wireless communication system, according to another exemplary embodiment of the present invention. 
     In step  900 , the base station receives the handover request message MOB_MSHO_REQ from the terminal and sends the handover response message MOB_BSHO_RSP. 
     Next, the base station determines whether the handover requested by the terminal is the request to handover to the dummy cell. In case of the request to handover to the dummy cell, the base station requests the handover to the heterogeneous communication system in step  904 . When the request to handover is not to the dummy cell, the base station operates in the corresponding mode. 
     In step  906 , the base station receives the channel allocation information message from the heterogeneous communication system and forwards the message RNG_RSP including the received channel allocation information to the terminal. 
     In step  908 , the base station receives the message MOB_HO_IND informing of the handover from the terminal. 
     Next, the base station finishes this process. 
       FIG. 10  is a flowchart of operations of the terminal for the handover between the heterogeneous communication system and the broadband wireless communication system, according to another exemplary embodiment of the present invention. 
     In step  1000 , when the RSSI falls below the preset handover threshold, the terminal sends the handover request message to the base station. 
     In step  1002 , the terminal receives the handover response message from the base station. 
     Upon receiving the message RNG_RSP including the channel allocation information of the heterogeneous communication system in step  1004 , the terminal sends the message MOB_HO_IND informing of the handover to the base station and transitions to the heterogeneous communication system connection mode in step  1006 . For example, the terminal interrupts the first modem in use and activates the second modem to connect to the heterogeneous communication system. 
     In step  1008 , the terminal acquires the uplink of the heterogeneous communication system using the channel allocation information. 
     In step  1010 , the terminal sends the handover complete report message to the heterogeneous communication system. 
     Next, the terminal finishes this process. 
       FIG. 11  is a flowchart of operations of the base station for the handover between the heterogeneous communication system and the broadband wireless communication system, according to yet another exemplary embodiment of the present invention. 
     In step  1100 , the base station receives the handover request message from the terminal. 
     In step  1102 , the base station sends the handover response message to the terminal. 
     In step  1104 , the base station sends the message MOB_HO_IND informing of the handover to target cell. 
     In step  1106 , the base station determines whether the active set includes only the border cell. When the active set includes only the border cell, the base station sends the handover request message to the heterogeneous communication system and then receives the channel allocation information message in step  1108 . When the active set does not only include the border cell, the base station operates in the corresponding mode. 
     In step  1110 , the base station forwards the message RNG_RSP including the received channel allocation information to the terminal. 
     Next, the base station finishes this process. 
       FIG. 12  is a flowchart of operations of the terminal for the handover between the heterogeneous communication system and the broadband wireless communication system, according to yet another exemplary embodiment of the present invention. 
     In step  1200 , the terminal sends the handover request message to the base station when the RSSI falls below the preset handover threshold. 
     In step  1202 , the terminal receives the handover response message from the base station. 
     In step  1204 , the terminal sends the message MOB_HO_IND informing of the handover to the target cell. 
     When the active set includes only the border cell in step  1206 , the terminal receives the channel allocation information message of the heterogeneous communication system from the base station in step  1208 . When the active set does not only include the border cell, the terminal operates in the corresponding mode. 
     In step  1210 , the terminal transitions to the heterogeneous communication system connection mode. For instance, the terminal interrupts the first modem and activates the second modem to connect to the heterogeneous communication system. 
     In step  1212 , the terminal acquires the uplink of the heterogeneous communication system using the channel allocation information. 
     In step  1214 , the terminal sends the handover complete report message to the heterogeneous communication system. 
     Next, the terminal finishes this process. 
       FIG. 13  is a block diagram of the base station for the handover between the heterogeneous communication system and the broadband wireless communication system, according to an exemplary embodiment of the present invention. 
     The base station of  FIG. 13  includes a receiver  1300 , a message processor  1302 , a controller  1304 , a handover processor  1306 , an interface  1308 , a message generator  1310 , and a transmitter  1312 . The receiver  1300  and the transmitter  1312  may be an OFDM receiver and the transmitter may be an OFDM transmitter. 
     The receiver  1300  receives a Radio Frequency (RF) signal from the terminal, demodulates and decodes the RF signal, and outputs the decoded data to the message processor  1302 . 
     The message processor  1302  decomposes a control message input from the receiver  1300  and provides the result to the controller  1304  and the handover processor  1306 . For example, the message processor  1302  processes the handover request message or the handover indication message from the terminal in relation with the handover, provides the processed message to the handover processor  1306 , and provides the other control messages to the controller  1302 . 
     The controller  1304  processes the information output from the message processor  1302  and provides the processed result to the message generator  1310 . The controller  1304  requests the handover to the heterogeneous communication system through the interface  1308  by referring to the handover information from the handover processor  1306  or receives the channel allocation information from the heterogeneous communication system. Herein, the channel allocation information is channel information relating to the cell, to which the terminal moves, of the heterogeneous communication system. 
     Receiving the handover related information from the message processor  1302  and determining the terminal to be in the border, the heterogeneous network handover processor  1306  requests the terminal to report of the RSSI of the downlink. When the RSSI falls below the threshold, the handover processor  1306  requests the handover to the heterogeneous communication system through the interface  1308 . When the terminal is handed over to the dummy cell, the handover processor  1306  requests the handover to the heterogeneous communication system through the interface  1308 . When the active set of the terminal includes only the border cell, the handover processor  1306  requests the handover to the heterogeneous communication system through the interface  1308 . 
     The message generator  1310  generates a message with the various information provided from the controller  1304  and outputs the generated message to the transmitter  1312 . According to an exemplary embodiment of the present invention, the message generator  1310  receives the channel allocation information from the controller  1304  and generates the RNG_RSP message with the received channel allocation information. 
     The sender  1312  receives data from the message generator  1310 , encodes and modulates the received data, converts the modulated data to an RF signal, and outputs the RF signal via an antenna. 
       FIG. 14  is a block diagram of the terminal for the handover between the heterogeneous communication system and the broadband wireless communication system, according to an exemplary embodiment of the present invention. 
     The terminal of  FIG. 14  includes a first transceiver  1400 , a first message processor  1402 , a controller  1404 , a handover controller  1406 , a second message processor  1408 , and a second transceiver  1410 . 
     The first transceiver  1400 , which may support the OFDM based physical layer, modulates/demodulates and encodes/decodes signals and exchanges the signals with the first message processor  1402 . 
     The first message processor  1402  decomposes a control message input from the first transceiver  1400  and provides the result to the controller  1404  and the handover controller  1406 . For instance, the first message processor  1402  processes the handover response message from the base station in relation to the handover or the message RNG_RSP including the channel allocation information for the handover between the heterogeneous network, provides the processed message to the handover controller  1406 , and provides the other control messages to the controller  1404 . The first message processor  1402  generates a message with the various information provided from the controller  1404  and outputs the message to the first transceiver  1400 . 
     The controller  1404  processes the information provided from the message processor  1402  and provides the processed result to the first message processor  1402 . 
     The handover controller  1406  receives the handover related information from the first message processor  1402 , measures the RSSI of the downlink, and reports the measured RSSI to the base station. Also, the handover controller  1406  receives the channel allocation information for the handover and attempts the handover to the heterogeneous communication system. 
     The second message processor  1408  decomposes a control message input from the second transceiver  1410  and provides the result to the controller  1404 . In the handover, the second message processor  1408  generates a message for the channel connection to the heterogeneous communication system. 
     The second transceiver  1410 , which may support the CDMA physical layer, modulates/demodulates and encodes/decodes signals and exchanges the signals with the second message processor  1408 . 
     As set forth above, the periodic RSSI report, the handover information to the dummy cell, and the active set information are used in the border cell of the broadband wireless communication system. Therefore, when the dual-mode dual-band terminal gets out of the service coverage area of the broadband wireless communication system, it can be handed over to the heterogeneous communication system seamlessly. 
     While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.