Abstract:
A method of performing a handover from a Wideband Code Division Multiple Access (WCDMA) system to a Code Division Multiple Access (CDMA) system in a multi-mode terminal having a WCDMA module and a CDMA module is disclosed. The method includes determining whether a handover to the CDMA system is necessary during a call through a WCDMA system; acquiring a pilot signal from the CDMA system by activating the CDMA module if it is determined that the handover to the CDMA system is necessary; receiving a sync signal if the pilot signal from the CDMA system is acquired; transmitting information for handover to the WCDMA system through the WCDMA module; allowing the CDMA module to enter a CDMA traffic state using handover information if the handover information is received from the WCDMA system through WCDMA module; and releasing a traffic state of WCDMA module.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to a method of performing a handover from a wideband code division multiple access system to a code division multiple access system and, more particularly, to a method of performing a handover by receiving a sync signal through the acquisition of a pilot signal from a code division multiple access network if it is determined that a handover to a code division multiple access system is necessary, requesting the handover from a wideband code division multiple access system using related information, and causing a mobile communication terminal to enter into a code division multiple access traffic mode based on a handover message from the system if the handover message responding to the request is received by the terminal from the system.  
         [0003]     2. Description of the Related Art  
         [0004]     A mobile communication terminal capable of being used both in a Code Division Multiple Access (CDMA) network and in a Wideband CDMA (WCDMA) network is referred to as a “multi-mode mobile communication terminal.” Such a multi-mode mobile communication terminal is equipped with both a Radio Frequency (RF) circuit and modem for a CDMA network and an RF circuit and modem for a WCDMA network so that the terminal can be used in both networks.  
         [0005]     In case of switching from one base station to another base station during a call using a mobile communication terminal (i.e., a handover), it is preferable that the switching is performed without an interruption of the call. Conventionally, however, a handover from a WCDMA base station to a CDMA base station is performed by turning off the power of the WCDMA module and turning on the power of the CDMA module in the multi-mode mobile communication terminal. As a result, a call is disconnected when a mobile communication terminal moves from a WCDMA area to a CDMA area.  
       SUMMARY OF THE INVENTION  
       [0006]     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method of performing a handover, which can be applied to the case where a multi-mode mobile communication terminal enters into a CDMA network from a WCDMA network.  
         [0007]     Another object of the present invention is to provide a method of performing a handover, which can be applied to the case where a multi-mode mobile communication terminal, configured with a modular chip designed in such a way that a connection part for the CDMA RF transmission/reception circuits and the WCDMA RF transmission/reception circuits is shared, enters into a CDMA network from a WCDMA network.  
         [0008]     In the present invention, it is determined whether a handover to a CDMA system is necessary during a call using a WCDMA module. For example, when the intensity of a WCDMA signal from a base station of a cell to which a terminal pertains is equal to or lower than a predetermined level and there is no WCDMA signal from a neighboring cell, it may be determined that the handover to the CDMA system is necessary. If it is determined that the handover to the CDMA system is necessary, it is determined whether the terminal can be operated in a CDMA mode. For example, when the terminal is set to a WCDMA-only-mode or is currently situated in a location where the terminal cannot be operated in a CDMA mode, the process of handover to the CDMA system is stopped. Alternatively, whether the handover to the CDMA system is currently available may be inquired from the WCDMA system.  
         [0009]     In case where the terminal can be operated in a CDMA mode, the CDMA module is activated and the acquisition of a pilot signal from the CDMA network is attempted. When the pilot signal from the CDMA network is acquired, a sync signal is received. In this case, the pilot signal and the sync signal may be acquired with reference only to a primary frequency. Meanwhile, the activation of the CDMA module can be achieved by causing the CDMA module to exit from a low power mode.  
         [0010]     When the sync signal is received from the CDMA network, information for a handover is transmitted to the WCDMA system through the WCDMA module. In this case, the transmitted information may include frequency information, Pseudo Noise (PN) offset information and pilot intensity information. Meantime, during the process of the handover, it is possible to determine again whether a handover to the CDMA system is still necessary when the sync signal is received from the CDMA network and to perform the following handover procedure only if the handover to the CDMA system is still necessary.  
         [0011]     The WCDMA system, which has received the information for a handover, consults with the CDMA system about the handover, sets various parameters for the handover of the terminal, and transmits handover information to the terminal. The handover information may include CDMA channel information, frame offset information, code information and early stage power control-related information.  
         [0012]     The terminal, which has received the handover information from the WCDMA system, causes the CDMA module to enter into a CDMA traffic state. Furthermore, the handover process is completed by setting the parameters of the resources necessary for a call suitable to the CDMA mode and releasing the traffic state of the WCDMA module. In this case, it is possible to notify the CDMA system of the successful completion of the handover and release the traffic state of the WCDMA module as a response confirming the successful completion of handover.  
         [0013]     In case where the handover information is not received within a predetermined period of time after the transmission of the information for handover to the WCDMA system, the handover process to the CDMA system may be cancelled. Meanwhile, even though an idle state is initiated after the initialization of the CDMA module during a WCDMA call to perform a handover to the CDMA system, the terminal does not register a location in the CDMA system. Furthermore, in case where the terminal acquires the sync signal and enters into an idle state, an idle handover may not be performed before an ongoing handover is completed.  
         [0014]     The present invention may be applied to a multi-mode terminal in which RF transmission and reception units are shared between the WCDMA and CDMA communications. In this case, if it is determined that a handover to a CDMA system is necessary, the RF transmission and reception units are set to a CDMA mode and the CDMA module is activated, so that the acquisition of a pilot signal from a CDMA network is attempted. When the pilot signal is acquired, the RF transmission and reception units are set back to a WCDMA mode and the acquired pilot information is transmitted to a WCDMA system through the WCDMA module. Thereafter, when handover information is received from the WCDMA system through the WCDMA module, the RF transmission and reception units are set to a CDMA mode again, and the CDMA module enters into a CDMA traffic state using the received information. Further, the handover process is completed by setting the parameters of the resources necessary for a call suitable to a CDMA mode and releasing the traffic state of the WCDMA module.  
         [0015]     Other and further aspect of the present invention will become apparent during the course of the following detailed description and by reference to the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a conceptual diagram illustrating a handover from a WCDMA system to a CDMA system;  
         [0017]      FIG. 2  is a schematic diagram illustrating parts related to the handover from the WCDMA system to the CDMA system in a multi-mode mobile communication terminal;  
         [0018]      FIG. 3  is a flowchart illustrating a method of performing the handover according to the present invention;  
         [0019]      FIG. 4  is a diagram showing the data transmission and reception between the terminal, the WCDMA system and the CDMA system during the handover process according to the present invention;  
         [0020]      FIG. 5  is a flowchart illustrating a method of performing a handover according to a second embodiment of the present invention;  
         [0021]      FIG. 6  is a schematic block diagram showing parts related to the handover from a WCDMA system to a CDMA system in a multi-mode mobile communication terminal in which RF transmission and reception units are shared for WCDMA and CDMA communications;  
         [0022]      FIG. 7  is a flowchart illustrating a method of performing a handover according to a third embodiment of the present invention; and  
         [0023]      FIG. 8  is a conceptual diagram illustrating the operation of a channel converter during the handover process.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.  
         [0025]      FIG. 1  is a conceptual diagram illustrating a handover procedure from a WCDMA system  400  to a CDMA system  500 . When a dual-mode or multi-mode mobile communication terminal  100  available both in the WCDMA and CDMA systems moves from a WCDMA or combined WCDMA and CDMA area A to a border area B which is again adjacent to a CDMA area C, the received pilot signal level of a WCDMA base station  200  decreases while the pilot signal level of a CDMA base station  300  increases. However, since the terminal  100  currently operates in a WCDMA mode, the terminal cannot detect the pilot signal from the CDMA base station  300 .  
         [0026]     Meanwhile, the terminal  100  continuously searches for a pilot signal from a neighboring WCDMA base station to prepare for a handover to the neighboring WCDMA base station. When the terminal  100  enters into the area B, a pilot signal from the neighboring WCDMA base station is not searched for because there is no WCDMA base station in the area B. Accordingly, if the pilot signal level of the current WCDMA base station decreases to or below a certain value and the pilot signal level from the neighboring base station is lower than a certain level, the terminal  100  determines that a handover to the CDMA system  500  is necessary.  
         [0027]     As illustrated in  FIG. 1 , a WCDMA base station  200  is connected to a WCDMA system  400 , and a CDMA base station  300  is connected to a CDMA system  500 . Furthermore, the WCDMA system  400  is connected to the CDMA system  500 , so that the WCDMA system  400  and the CDMA system  500  can exchange necessary information when a handover from the WCDMA system  400  to the CDMA system  500  is necessary.  
         [0028]      FIG. 2  is a schematic diagram illustrating parts related to the handover from the WCDMA system  400  to the CDMA system  500  in the multi-mode mobile communication terminal  100 . The multi-mode mobile communication terminal  100  capable of operating in two or more modes is equipped with circuits (i.e., modules) for supporting operations in respective modes.  
         [0029]     The present invention targets a mobile communication terminal that can be operated in at least WCDMA and CDMA modes. Accordingly, the multi-mode mobile communication terminal  100  of the present invention includes a WCDMA module  130  and a CDMA module  140 . The terminal  100  of the present invention further includes a main control unit  110  for controlling operations in both modes and memory  120  for storing program code and data required by the main control unit  110 . The modules  130  and  140  are connected to an antenna  151  through a duplexer  150 . In general, both modules  130  and  140  are not activated at the same time, and the duplexer  150  separates the transmission and reception signals of each module.  
         [0030]     Each of the modules  130  and  140  includes an RF transmission/reception module  137  or  147 , a modem  135  or  145 , a control unit  131  or  141 , and memory  133  and  143 . These elements may be separately implemented with a plurality of Integrated Circuit (IC) chips or Monolithic Microwave ICs (MMICs), or with a single chip or several chips.  
         [0031]     With reference to  FIGS. 3 and 4 , a handover process according to an embodiment of the present invention is described in detail below.  
         [0032]     A multi-mode mobile communication terminal  100  of the present invention running in a WCDMA mode determines whether a handover is necessary while monitoring various pilot signals during a call. In the present invention, the terminal  100  determines whether handover is necessary while monitoring pilot signals during a call at step S 301  in the WCDMA area A using the WCDMA module  130 . The terminal  100  of the present invention determines whether a handover to the CDMA system  500 , in addition to a general handover within the WCDMA system  400 , is necessary at step S 303 . When the intensity of a WCDMA signal from the WCDMA base station  200  of the cell to which the terminal  100  pertains is equal to or lower than a certain level and there is no WCDMA signal from a neighboring cell, it may be determined that a handover to the CDMA system  500  is necessary.  
         [0033]     If a handover to the CDMA system is necessary, the WCDMA control unit  131  fo the terminal  100  notifies the main control unit  110  of the necessity for a handover to the CDMA system  500 . Subsequently, the main control unit  110  determines whether the terminal  100  can be operated in a CDMA mode, although not illustrated in the drawing. If it is determined that the terminal  100  cannot be operated in a CDMA mode, the main control unit  110  terminates the ongoing handover procedure. For example, if it is determined that a mobile communication terminal is set to a WCDMA-only-mode or is situated in a location where the terminal cannot be operated in a CDMA mode, the handover process to a CDMA system may be stopped. Alternatively, whether a handover to the CDMA system is currently available may be inquired from the WCDMA system  400  through the WCDMA module  130 .  
         [0034]     The main control unit  110  of the terminal  100 , which is notified of the necessity for a handover to the CDMA system  500 , activates the CDMA module  140  at step S 331 . Then, the CDMA module  140  attempts to acquire a pilot signal from the CDMA system  500  at step S 361 , and receives a sync signal if the pilot signal has been acquired from the CDMA system  500 . In this case, the pilot signal and the sync signal may be acquired with reference only to a primary frequency so as to perform a quick handover operation. If the sync signal is received from the CDMA system  500 , information for handover, including frequency information, Pseudo Noise (PN) offset information and pilot intensity information, may be acquired based on the sync signal. The CDMA control unit  141  of the CDMA module  140  transmits the signal to the main control unit  110  at step S 363 .  
         [0035]     After transmitting the information for a handover to the main control unit  110  of the terminal  100 , the CDMA module  140  continues an initializing procedure and enters into an idle state. Even though the terminal enters into the idle state after the initialization of the CDMA module, the terminal does not perform location registering in the CDMA system  500 . Further, an idle handover may not be performed until the ongoing handover is completed.  
         [0036]     The CDMA control unit  131  of the CDMA module  130  of the terminal  100  may activate a timer after transmitting the handover information to the main control unit  110 , and cancel the handover process to the CDMA system  500  if the CDMA control unit  131  does not receive the handover information from the WCDMA system  400  within a certain period of time. Alternatively, it is possible that the main control unit  110 , which has received information for handover from the CDMA control unit  131 , activates a timer, and cancels the handover process to the CDMA system  500  if the handover information from the WCDMA system  400  is not received within a certain period of time.  
         [0037]     The main control unit  110  of the terminal  100 , which has received the handover information from the CDMA control unit  141 , transmits the handover information to the WCDMA control unit  131  at step S 333 , and the WCDMA control unit  131  requests the handover to the CDMA system  500  from the WCDMA system  400  while transmitting the handover information to the WCDMA system  400  indicated as arrow “a” in  FIG. 4 .  
         [0038]     The WCDMA system  400  then negotiates with the CDMA system  500  about the handover, sets various parameters for the handover of the terminal  100  indicated as arrow “b” in  FIG. 4 , and transmits corresponding information to the terminal  100  indicated as arrow “c” in  FIG. 4 . The corresponding information may include CDMA channel information, frame offset information, code information and initial information for power control-related information.  
         [0039]     The WCDMA control unit  131  of the terminal  100 , which has received the handover information from the WCDMA system  400 , transmits the handover information to the main control unit  110  of the terminal  100  at step S 307 , and the main control unit  110  transmits the handover information to the CDMA control unit  141  at step S 335 . By setting the received information in CDMA modem  145  of the CDMA module  140  at step S 365 , the CDMA control unit  141  directly enters into a communication channel determined through the consultation between the WCDMA system  400  and the CDMA system  500  at step S 367 . When the CDMA module  140  enters into a communication state, the main control unit  110  commands the WCDMA control unit  131  to terminate the WCDMA call and sets necessary parameters of the resources suitable to a CDMA mode at step S 337  so that the WCDMA control unit  131  terminates the WCDMA call at step S 309 , and the main control unit  110  controls the terminal in a CDMA mode at step S 339 , thus performing a CDMA call through the CDMA module  140  at step S 369 . As a result, a call originated at the WCDMA sytem  400  continues to be maintained by the CDMA system  500  without being disconnected.  
         [0040]     In the above-described embodiment, when the intensity of a received WCDMA signal decreases to or below a certain level during a call through the WCDMA system  400 , the CDMA modem  141  acquires a sync signal, obtains information required for a handover, and then performs a handover procedure in conjunction with the WCDMA system  400 . In the meantime, since a period of time is required until the CDMA modem  145  acquires the sync signal, the case where the intensity of the WCDMA signal is recovered may occur during the acquisition of the CDMA sync signal.  
         [0041]     An embodiment, in which a WCDMA mode is maintained rather than being converted to a CDMA mode so as to prepare for the above-described case when the intensity of the WCDMA signal is recovered during switching from a WCDMA mode to a CDMA mode, is illustrated in  FIG. 5 .  
         [0042]     A multi-mode mobile communication terminal  100  of the present invention running in a WCDMA mode determines whether a handover is necessary while monitoring various pilot signals during a call. In the present invention, the terminal  100  determines whether a handover is necessary while monitoring pilot signals during a call at step S 501  in the WCDMA area A using the WCDMA module  130 . Meanwhile, in this case, the CDMA modem  145  may be in a low power mode at step S 560 .  
         [0043]     Moreover, the terminal  100  of the present invention determines whether a handover to the CDMA system  500 , in addition to a general handover within the WCDMA system  400 , is necessary at step S 503 . When the intensity of a WCDMA signal from the WCDMA base station  200  of the cell to which the terminal  100  pertains is equal to or lower than a certain level and there is no WCDMA signal from a neighboring cell, it can be determined that a handover to the CDMA system is necessary.  
         [0044]     If it is determined that handover to the CDMA system  500  is necessary, the WCDMA control unit  131  notifies the main control unit  110  of the necessity for a handover to the CDMA system  500 . Subsequently, the main control unit  110  determines whether the terminal  100  can be operated in a CDMA mode, although not illustrated in the drawing. If it is determined that the terminal  100  cannot be operated in a CDMA mode, the main control unit  110  terminates the ongoing handover procedure. For example, if a mobile communication terminal is set to a WCDMA-only-mode or is situated in a location where the terminal cannot be operated in a CDMA mode, the handover process to the CDMA system  500  may be stopped. Alternatively, whether a handover to the CDMA system  500  is currently available may be inquired from the WCDMA system  400  through the WCDMA module  130 .  
         [0045]     The main control unit  110  of the terminal  100  of the present invention, which is notified of the necessity for a handover to the CDMA system  500 , transmits a channel activation signal to the CDMA module  140  at step S 531 . Then, the CDMA module  140  exits from the low power mode at step S 561 , attempts to acquire a pilot signal from the CDMA system at step S 562 , and receives a sync signal if the pilot signal has been acquired from the CDMA system  500 . In this case, the pilot signal and the sync signal may be acquired with reference only to a primary frequency, so as to perform a quick handover operation. If the sync signal is received from the CDMA system  500 , the handover information, including a frequency, PN offset information and pilot intensity information, may be acquired based on the sync signal. The CDMA control unit  141  transmits the signal to the main control unit  110  at step S 563 .  
         [0046]     Meanwhile, after transmitting the handover information to the main control unit  110  of the terminal  100 , the CDMA module  140  continues an initializing procedure and enters into an idle state. Even though the terminal enters into the idle state after the initialization of the CDMA module  140 , the terminal does not register a location in the CDMA system  500 . Further, an idle handover is not performed until the ongoing handover is completed.  
         [0047]     The CDMA control unit  131  of the terminal  100  of the present invention activates a timer after transmitting the handover information to the main control unit  110 , and cancels the handover process to the CDMA system  500  if the CDMA control unit  131  does not receive the handover information from the WCDMA system  400  within a certain period of time. Alternatively, it is possible that the main control unit  110 , which has received the handover information, activates a timer, and cancels the handover process to the CDMA system  500  if the CDMA control unit  131  does not receive the handover information from the WCDMA system  400  within a certain period of time.  
         [0048]     The main control unit  110  of the terminal  100  of the present invention, which has received the handover information from the CDMA control unit  141 , transmits the handover information to the WCDMA control unit  131  at step S 533 , and the WCDMA control unit  131  determines again whether the handover to the CDMA system is still necessary at step S 505 .  
         [0049]     If it is determined that the handover to the CDMA system  500  is still necessary, the terminal  100  requests the handover to the CDMA system  500  from the WCDMA system  400  while transmitting the handover information to the WCDMA system  400  at step S 507  indicated as arrow “a” in  FIG. 4 .  
         [0050]     Then, the WCDMA system  400  negotiates with the CDMA system  500  about the handover, sets various parameters for the handover of the terminal  100  indicated as arrow “b” in  FIG. 4 , and transmits corresponding information to the terminal  100  indicated as arrow “c” in  FIG. 4 . The corresponding information may include CDMA channel information, frame offset information, code information and initial information for power control-related information.  
         [0051]     The WCDMA control unit  131 , which has received the handover information from the WCDMA system  400 , transmits the handover information to the main control unit  110  at step S 509 , and the main control unit  110  transmits the handover information to the CDMA control unit  141  at step S 535 . By setting the received information in the CDMA modem  145  at step S 565 , the CDMA control unit  141  directly enters into a communication channel determined through the consultation between the WCDMA system  400  and the CDMA system  500  at step S 567 . The CDMA control unit  141  notifies the CDMA system  500  of the successful completion of the handover, and waits for a response confirming the completion of the handover.  
         [0052]     If the response confirming the completion of the handover is received from the CDMA system  500 , the main control unit  110  commands the WCDMA control unit  131  to terminate the WCDMA call and sets necessary parameter of the resources suitable to a CDMA mode at step S 511  so that the WCDMA control unit  131  terminates the WCDMA call at step S 537 , and the main control unit  110  controls the terminal in a CDMA mode at step S 539 , thus performing a CDMA call through the CDMA module  140  at step S 569 . As a result, a call originated in the WCDMA system  400  continues to be maintained in the CDMA system  500  without being disconnected.  
         [0053]     In case where the intensity of a WCDMA signal recovers to or above a certain level and, thus, it is determined that a handover to the CDMA system  500  is not necessary, the WCDMA module  130  notifies the main control unit  110  of the fact, and the main control unit  110  transmits a CDMA inactivation signal to the CDMA module  140  at step S 541 . Then, the CDMA module  140  enters into a low power mode again at step S 571 , thus terminating the switching process to a CDMA mode.  
         [0054]     Although in the above description, the case where two RF transmission/reception units are provided for the WCDMA and CDMA communications, respectively, has been described, it is possible to design the terminal  100  so that RF transmission and reception units are shared for the WCDMA and CDMA communications.  FIG. 6  is a schematic block diagram showing parts of a multi-mode mobile communication terminal  600  related to a handover from a WCDMA system  400  to a CDMA system  500  in which RF transmission and reception units are shared for the WCDMA and CDMA communications.  
         [0055]     According to a third embodiment of the present invention, a part of the terminal  100  in which an RF transmission/reception unit for WCDMA communication and an RF transmission/reception unit for CDMA communication are connected to a modem chip is formed in a single body. Furthermore, each of an RF reception unit  650  and an RF transmission unit  660  may be used for both the WCDMA and CDMA communications. A channel converter  670  controls whether the RF reception and transmission units  650  and  660  are used for the WCDMA or CDMA communications. A duplexer  680  allows an RF transmission signal to be transmitted to an antenna  681  and an RF reception signal to be transmitted to the RF reception unit  650 .  
         [0056]     An Intermediate Frequency (IF) signal from the RF reception unit  650  is converted into a base band frequency signal through a CDMA reception IF  641  in a CDMA mode or through a WCDMA reception IF  642  in a WCDMA mode and transmitted to a CDMA/WCDMA module  630 , while a base band frequency signal from the CDMA/WCDMA module  630  is converted into an IF frequency band signal through a CDMA transmission IF  643  in a CDMA mode or through a WCDMA transmission IF  644  in WCDMA mode and transmitted to the RF transmission unit  660 . Meanwhile, in case where a base band signal is converted into an RF band signal without passing through an IF stage, the CDMA reception IF  641 , the WCDMA reception IF  642 , the CDMA transmission IF  643 , and the WCDMA transmission IF  644  can be omitted. Furthermore, the CDMA reception IF  641 , the WCDMA reception IF  643 , the CDMA transmission IF  643  and the WCDMA transmission IF  644  may be shared, like the RF transmission and reception units. In this case, if IF frequencies are different, the IF stage requires a channel converter.  
         [0057]     The CDMA/WCDMA module  630  performs the processing of CDMA and WCDMA signals according to CDMA and WCDMA protocols. The multi-mode mobile communication terminal  100  of the present invention includes a control unit  610  for controlling operation in both modes and memory  620  for storing program code and data required by the control unit  610 .  
         [0058]     With reference to  FIG. 7 , a handover process according to the third embodiment of the present invention is described in detail below.  
         [0059]     When power is applied to the multi-mode mobile communication terminal  600  of the present invention in the case where a WCDMA mode has a higher priority than a CDMA mode, the WCDMA/CDMA module  630  is initialized and enters into an idle state after performing the system setting at step S 760 . After passing through the initialization procedure after the application of power, the WCDMA/CDMA module  630  acquires the pilot signal of a CDMA channel and then maintains synchronization with the system using sync channel information. Thereafter, the WCDMA/CDMA module  630  may conduct a resynchronization procedure at regular intervals while switching to a WCDMA mode.  
         [0060]     In the meantime, the terminal  600  operated in a WCDMA mode determines whether a handover is necessary while monitoring various pilot signals during a call through the WCDMA system  400  at step S 701 . In the present invention, the terminal  600  determines whether a handover is necessary while monitoring pilot signals during a call in the WCDMA area A using the WCDMA/CDMA module  630 . The terminal  600  of the present invention determines whether a handover to the CDMA system  500 , in addition to a general handover within in the WCDMA system  400 , is necessary at step S 703 . When the intensity of a WCDMA signal from the WCDMA base station  200  of the cell to which the terminal  600  pertains is equal to or lower than a certain level and there is no WCDMA signal from a neighboring cell, it can be determined that a handover to the CDMA system  500  is necessary.  
         [0061]     If a handover to the CDMA system  500  is necessary, the WCDMA/CDMA module  630  notifies the control unit  610  of the necessity for a handover to the CDMA system  500 . Then, the control unit  610  determines whether the terminal  600  can be operated in a CDMA mode, although not illustrated in the drawing. If, for example, a mobile communication terminal is set to a WCDMA-only-mode or is not situated in a location where the terminal can be operated in a CDMA mode, the handover process to the CDMA system  500  may be stopped. Alternatively, whether a handover to the CDMA system is currently available may be inquired from the WCDMA system  400  through the WCDMA/CDMA modem  630 .  
         [0062]     The control unit  610 , which is notified of the necessity for a handover to the CDMA system  500 , issues a system search command to the WCDMA/CDMA module  630  and switches the channel converter  670  to a CDMA mode at step S 731 . Then, the WCDMA/CDMA module  630  attempts to acquire a pilot signal from the CDMA system at step S 761 , and acquires the pilot information and intensity information of the CDMA system  500  at step S 763 . In this period of time, communication through the WCDMA system  400  may be stopped a little while. The CDMA module, which has acquired the pilot information, transmits the pilot information to the control unit  610  at step S 733 , and the control unit  610  transmits the pilot information to the WCDMA/CDMA module  630  and returns the channel converter  670  to a WCDMA mode. Then, the WCDMA/CDMA module  630  returns to the CDMA initialization state.  
         [0063]     The WCDMA/CDMA module  630  requests a handover to the CDMA system  500  while transmitting the received CDMA pilot information to the WCDMA system  400  indicated as arrow “a” of  FIG. 4 . Since the procedure of handover information transmission between the systems is similar to that set forth in the description related to  FIG. 4 , a detailed description thereof is omitted.  
         [0064]     By setting the handover information received from the control unit  610  at step S 765 , the WCDMA/CDMA module  630  directly enters into a communication channel determined through the consultation between the WCDMA system  400  and the CDMA system  500  at step S 767 . When the WCDMA/CDMA module  630  enters into a communication state, the control unit  610  commands the WCDMA/CDMA module  630  to terminate the WCDMA call and sets necessary parameters of the resources suitable to a CDMA mode at step S 737  so that the control unit  610  terminates the WCDMA call at step S 709 , and the control unit  610  controls the terminal  600  in a CDMA mode at step S 739 , thus performing a CDMA call through the WCDMA/CDMA module  630  at step S 769 . As a result, a call originated in the WCDMA system  400  continues to be maintained in the CDMA system  500  without being disconnected.  
         [0065]     With reference to  FIG. 8 , the operation of the channel converter  670  of the terminal  600  during the handover process is described below. Since the RF reception and transmission units  650 ,  660  are shared for the WCDMA and CDMA communications in the terminal  600  of the present embodiment, the frequency of the RF reception and transmission units  650 ,  660  must be converted to that for the CDMA communication to acquire a CDMA signal during the WCDMA communication.  
         [0066]     That is, during a WCDMA call, the channel converter  670  controls the RF reception and transmission units  650  and  660  in a WCDMA mode ( 51 ), and in the case of acquiring a CDMA pilot signal, the channel converter  670  converts the RF reception and transmission units  650  and  660  into a WCDMA mode ( 52 ). After the pilot signal has been acquired, the channel converter  670  converts the RF reception and transmission units  650  and  660  into a WCDMA mode ( 53 ) to allow the acquired CDMA pilot signal to be transmitted to the WCDMA system  400 . When handover-related information is received from the WCDMA system  400 , the channel converter converts the RF transmission and reception units  650  and  660  into CDMA mode and, thus, allows the RF transmission and reception units  650  and  660  to enter a CDMA traffic state.  
         [0067]     In the meantime, when a WCDMA mode is temporarily converted to a CDMA mode to acquire a CDMA pilot signal, an operation may be performed the same way as in a WCDMA compressed mode.  
         [0068]     As described above, the present invention provides a handover method that can be applied to the case where a multi-mode mobile communication terminal enters into a CDMA network from a WCDMA network. Furthermore, since a CDMA module performs the procedure necessary for a handover in conjunction with a WCDMA system after acquiring a sync signal and information required for the handover therefrom, the handover process can be performed rapidly.  
         [0069]     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. For example, while a method for switching a WCDMA call into a CDMA call is described, a method where a CDMA call is switched into a WCDMA call is easily configured.