Patent Publication Number: US-2005124343-A1

Title: Radio communication apparatus and common control channel reception method

Description:
TECHNICAL FIELD  
      The present invention relates to a mobile station in a CDMA communication system, and more particularly to a receiving method of a common control channel in a handover area.  
     BACKGROUND ART  
      A conventional mobile station (radio communication apparatus) receives a physical channel SCCPCH, a common control channel a base station transmits, via a single radio link (Radio Link, RL), as specified by Max no of S-CCPCH RL (=1) described in 3GPP (3rd Generation Partnership Project) TS25.331 10.3.3.27 Physical channel capability.  FIG. 9  is a block diagram showing a receiving section of such a mobile station.  
      In  FIG. 9 , the reference numeral  101  designates a radio stage for receiving a high frequency signal from a base station, and for converting it to a digital signal; and  102  designates a baseband demodulator for demodulating the digital signal from the radio stage  101 . The base band demodulator  102  includes finger sections  103  and  104  each for despreading the digital signal from the radio stage  101  with respect to each receiving path from the base station, and combiners  105  and  106  for rake combining the signal despread for each receiving path. The finger sections  103  and  104  have a plurality of fingers  1031 ,  1032 , . . . ,  103   m  and  1041 ,  1042 , . . . ,  104   n,  respectively, each provided for one of the receiving paths, where m and n are integers. The finger section  103  and the combiner  105  are used for demodulating a physical channel (PCCPCH) including broadcast information, and the finger section  104  and the combiner  106  are used for demodulating a common control channel (SCCPCH) or dedicated channel (DPCH) including control information or data. The combiners  105  and  106  each have parameters set in accordance with the frame structure of the channel to be demodulated. As for the dedicated channel, since a plurality of base stations that communicate with the mobile station transmit the same signal, the single combiner  106  can demodulate the dedicated channel from the plurality of base station. As for the common control channel, on the other hand, since the individual base stations transmit their own data which differ from each other, the mobile station can receive the common control channel only from the single cell. The reference numeral  107  designates a communication path encoder connected to the baseband demodulator  102 . The communication path encoder includes physical format converters  108   a  and  108   b  for converting the physical formats of the signals demodulated by the combiners  105  and  106 , respectively. The reference numeral  109  designates a radio communication controller for accepting the signals from the communication path encoder to receive the broadcast information, control information and data, and for controlling the baseband demodulator  102 .  
      Next, referring to  FIG. 10 , a control procedure will be described of the conventional mobile station when it carries out communication in a handover area via the common control channel.  FIG. 10  is a schematic diagram showing a configuration of a communication network including the conventional mobile station (UE). In  FIG. 10 , the reference numeral  111  designates the mobile station; reference numerals  112  and  113  each designate a base station (Node B) for making communication with the mobile station  111 ; the reference numeral  114  designates a radio network controller (RNC) for controlling the base stations  112  and  113 ; and  115  designates a core network (CN) for carrying out the call control, service control and the like of the entire communication system. The base station  112  manages the cell  1 A, and the base station  113  manages the cell  2 B. Reference numerals  116 ,  117  and  118  each designate a signal flow of the common control channel communicated between the mobile station  111  and the base stations  112  and  113 : the reference numeral  116  designates a signal from the mobile station  111  to the base station  112 ,  117  designates a signal from the mobile station  111  to the base station  113 , and  118  designates a signal from the base station  112  to the mobile station  111 .  
      First, the mobile station  111  sends a reconnection request message as the signal  116  to the cell  1 A (that is, the base station  112 ) during communication because of degradation in communication quality or the like. In this case, in the baseband demodulator  102 , the combiner  106  has the parameters set for the common control channel to be sent from the cell  1 A, and is activated in such a manner that the combiner  106  can demodulate the common control channel from the cell  1 A. Here, consider the case where the mobile station  111  carries out cell switching from the cell  1 A to the cell  2 B before the cell  1 A transmits a response message to the reconnection request message to the cell  1 A, which can occur when the receiving level of the mobile station varies or its physical movement between the cells takes place. In this case, the mobile station  111  transmits to the cell  2 B (the base station  113 ) the same reconnection request message as that transmitted to the cell  1 A as the signal  117 , and terminates the combiner  106  in the baseband demodulator  102  once. Then, having the parameters set for the common control channel from the cell  2 B, the combiner  106  is restarted in a state it can demodulate the common control channel from the cell  2 B.  
      As for the response to the request message such as the reconnection request message from the network side, it can sometimes be transmitted with a large delay because of the processing load of the network. The conventional mobile station is controlled as described above. Accordingly, even if the response from the cell  1 A is transmitted at last as the signal  118  after the cell switching from the cell  1 A to the cell  2 B, the mobile station cannot receive the response message because it can receive only the common control channel from the single cell (cell  2 B in this case) as described above. As is often the case in the handover area, if the mobile station carries out the cell switching further from the cell  2 B to another cell before the cell  2 B transmits a response message, the mobile station cannot receive the response message from the cell  2 B transmitted with a delay because the same control is carried out. Repetition of such operation will bring about a timeout because a predetermined time period has elapsed without receiving any response to the request message, thereby causing a communication problem such as call disconnection.  
      Thus, the conventional mobile station rather easily cause a communication problem such as a call disconnection if the response to the request message via the common control channel is delayed because of the processing delay on the network side, thereby offering a problem of bringing about unstable communication.  
     DISCLOSURE OF THE INVENTION  
      Therefore it is an object of the present invention to provide a radio communication apparatus and receiving method of a common control channel capable of receiving the response message through the common control channel regardless of the processing delay on the network side.  
      According to a first aspect of the present invention, there is provided a radio communication apparatus comprising: a transmitting section for transmitting a request message to a first cell and a second cell; a first combiner for demodulating a first common control channel transmitted from the first cell; a second combiner for demodulating a second common control channel transmitted from the second cell; a baseband controller for starting the first combiner and the second combiner, and for controlling the combiners into a state in which the combiners can demodulate the first common control channel and the second common control channel simultaneously; and a radio communication controller for receiving a response message to the request message contained in one of the first common control channel and the second common control channel. Here, the baseband controller may start both the first combiner and the second combiner, when the radio communication controller issues instructions to make cell switching before receiving the response message from the first cell.  
      This configuration makes it possible to receive the response message contained in the common control channel positively even in a handover area in which the cell switching can occur frequently, thereby enabling the improvement of the stability of the communication.  
      The request message may be a message that requests reconnection of a dedicated channel, and the response message may be a message that specifies a dedicated channel to be reconnected. Thus, it can increase the success rate of the reconnection of the dedicated channel, thereby implementing the stability of the communication.  
      The request message may be a message that requests switching from a dedicated channel to the common control channel, and the response message may be a message that permits the switching from the dedicated channel to the common control channel. Thus, it can improve the success rate of the switching from the dedicated channel to the common control channel, thereby implementing the stability of the communication.  
      The request message may be a message that requests cell reselection for making cell switching during communication via the common control channel, and the response message may be a message that enables the cell reselection. Thus, it can increase the success rate of the cell reselection, thereby implementing the stability of the communication.  
      According to a second aspect of the present invention, there is provided a radio communication apparatus comprising: a transmitting section for transmitting a request message to a first cell and a second cell; a first combiner that is set in a time shared manner that enables the first combiner to demodulate one of a first common control channel and a physical channel containing broadcast information, which channels are transmitted from the first cell; a second combiner that is set in a manner that enables the second combiner to demodulate a second common control channel transmitted from the second cell; a baseband controller for setting the first combiner and the second combiner, and for controlling the combiners into a state in which the combiners can demodulate the first common control channel and the second common control channel simultaneously; and a radio communication controller for receiving a response message to the request message, which response message is contained in one of the first common control channel and the second common control channel. Here, the baseband controller may control into the state in which the first common control channel and the second common control channel can be demodulated simultaneously, when the radio communication controller issues instructions to make cell switching before receiving the response message from the first cell. In addition, the baseband controller may set the first combiner in a state that the first combiner can demodulate the physical channel including the broadcast information, when receiving the physical channel containing the broadcast information and the first common control channel simultaneously.  
      This configuration makes it possible to receive the response message contained in the common control channel positively without increasing the number of combiners even in a handover area in which the cell switching can occur frequently, thereby preventing up sizing of the circuit and enabling the improvement of the stability of the communication.  
      The request message may be a message that requests reconnection of a dedicated channel, and the response message may be a message that specifies a dedicated channel to be reconnected. Thus, it can increase the success rate of the reconnection of the dedicated channel, thereby implementing the stability of the communication.  
      The request message may be a message that requests switching from a dedicated channel to the common control channel, and the response message may be a message that permits the switching from the dedicated channel to the common control channel. Thus, it can improve the success rate of the switching from the dedicated channel to the common control channel, thereby implementing the stability of the communication.  
      The request message may be a message that requests cell reselection for making cell switching during communication via the common control channel, and the response message may be a message that enables the cell reselection. Thus, it can increase the success rate of the cell reselection, thereby implementing the stability of the communication.  
      According to a third aspect of the present invention, there is provided a receiving method of a common control channel comprising: a first step of setting a first combiner such that the first combiner can demodulate a first common control channel transmitted from a first cell; a second step of transmitting a request message to the first cell; a third step of switching a cell that carries out communication from the first cell to a second cell; a fourth step of setting a second combiner such that the second combiner can demodulate a second common control channel transmitted from the second cell; a fifth step of transmitting a request message to the second cell; and a sixth step of activating the first combiner and the second combiner to receive the response message contained in one of the first and second common control channels, when the third step is carried out before the response message to the request message is received from the first cell after the second step.  
      This makes it possible to receive the response message contained in the common control channel positively even in a handover area in which the cell switching can occur frequently, thereby enabling the improvement of the stability of the communication. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a functional block diagram showing a radio communication apparatus of an embodiment in accordance with the present invention;  
       FIG. 2  is a block diagram showing a detailed configuration of a receiving section of an embodiment 1 in accordance with the present invention;  
       FIG. 3  is a block diagram showing a configuration of a communication network including the radio communication apparatus in accordance with the present invention;  
       FIG. 4  is a flowchart illustrating the control of the radio communication controller of the embodiment 1 in accordance with the present invention;  
       FIG. 5  is a flowchart illustrating the control of the radio communication controller of the embodiment 1 in accordance with the present invention;  
       FIG. 6  is a flowchart illustrating the control of the baseband controller of the embodiment 1 in accordance with the present invention;  
       FIG. 7  is a flowchart illustrating the control of the baseband controller of the embodiment 1 in accordance with the present invention;  
       FIG. 8  is a block diagram showing a detailed configuration of a receiving section of an embodiment 2 in accordance with the present invention;  
       FIG. 9  is a block diagram showing a detailed configuration of a receiving section of a conventional radio communication apparatus; and  
       FIG. 10  is a diagram showing a communication network including the conventional radio communication apparatus. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      The best mode for carrying out the invention will now be described with reference to the accompanying drawings to explain the present invention in more detail.  
     EMBODIMENT 1  
      The embodiment  1  in accordance with the present invention will be described.  FIG. 1  is a functional block diagram showing a radio communication apparatus (mobile station) of the embodiment 1 in accordance with the present invention. In  FIG. 1 , the reference numeral  1  designates an antenna for transmitting and receiving a high frequency signal to and from the base station; and  2  designates a radio stage including a down-converter  21  and an up-converter  22 . The down-converter  21  down-converts the high frequency signal received from the base station, and outputs a digital signal. The up-converter  22  up-converts a modulated digital signal to a high frequency band.  
      The reference numeral  3  designates a baseband modulator-demodulator including a baseband demodulator  31  for carrying out baseband demodulation, a baseband modulator  32  for carrying out baseband modulation, and a baseband controller  33  for controlling them in accordance with the control from a radio communication controller  5 . The baseband controller  33  has a memory for storing the finally used combiner, which will be described later. The baseband demodulator  31  has a configuration for implementing the characteristics of the present invention, the details of which will be described with reference to  FIG. 2 .  
      The reference numeral  4  designates a communication path encoder including a decoder  41  and an encoder  42 . A radio communication controller  5  carries out protocol control for radio communication, controls the radio stage  2 , baseband modulator-demodulator  3  and communication path encoder  4 , and communicates with a terminal interface  6 . The terminal interface  6  has interface functions with user interface modules  7  such as a camera, video recorder, LCD and operating panel, and includes a data format converter  61 , terminal interface controller  62 , speech encoder/decoder  63 , and individual module interface  64 .  
      Next, referring to  FIG. 2 , a detailed configuration of the baseband demodulator  31  having a major function for implementing the present invention will be described. In  FIG. 2 , the same reference numerals designate the same components as those of  FIG. 1 . In  FIG. 2 , the baseband demodulator  31  includes finger sections  34  and  35  each for despreading the digital signal fed from the radio stage  2  for each receiving path from the base station, and combiners  36 ,  37  and  38  for rake combining the signals despread for respective receiving paths. The finger sections  34  and  35  include a plurality of fingers  341 ,  342 , . . . ,  34   m  and  351 ,  352 , . . . ,  35   n  provided for the individual receiving paths, where m and n are integers. The finger section  34  and combiner  36  are used for demodulating a physical channel (PCCPCH) including broadcast information. Among the finger section  35 , the fingers  351  and  352  are connected to the combiner  37 , and the fingers  353 ,  354 , . . . ,  35   n  are connected to the combiner  38 . The assignment of the fingers, however, is not fixed, but is variable in accordance with the number of the receiving paths and the levels of the individual cells so that the fingers connected to the individual combiners  37  and  38  are dynamically changed. This control is carried out by the baseband controller. Both the combiners  37  and  38  are used for demodulating the common control channel (SCCPCH) or dedicated channel (DPCH). In addition, the baseband controller  33  sets the parameters of the combiners  36 ,  37  and  38  in accordance with the frame structure of the channels to be demodulated. The communication path encoder  4  includes physical format converters  41   a  and  41   b  for converting the physical format of the signals demodulated by the combiners  36 ,  37  and  38 .  
      For the primary common control channel, which is a physical channel transmitted from the base station to users in common, is used for transmitting broadcast information, the combiner  36  operates dedicatedly to enable reception of the system information, cell information and the like. The secondary common control channel (SCCPCH), which is a physical channel transmitted from the base station to users in common, is used for transmitting control information and short packets. The dedicated channel (DPCH), which is a physical channel assigned to each user, is used for transmitting data such as speech, packets and the like. The common control channel and the dedicated channel are not received simultaneously. As for the dedicated channel (DPCH), the same signal is transmitted through it from a plurality of base stations with which the mobile station can communicate. On the other hand, the secondary common control channel (SCCPCH) differs from cell to cell, and the parameters to be set to the combiners also differ from cell to cell. According to the present configuration, since the two combiners  37  and  38  can simultaneously demodulate two common control channels containing the data proper to the individual cells, the mobile station can wait for receiving common control channels simultaneously from the two cells.  
      An example of the operation of the mobile station with the foregoing configuration will now be described.  FIG. 3  is a block diagram showing a configuration of a communication network, which illustrates a signal flow when the mobile station in communication makes a reconnection request. In  FIG. 3 , the reference numeral  301  designates the mobile station (UE), reference numerals  302  and  303  each designate a base station (Node B) that communicates with the mobile station  301 , the reference numeral  304  designates a radio network controller (RNC) for controlling the base stations  302  and  303 ; and the reference numeral  305  designates a core network (CN) for carrying out the call control, service control and the like of the entire communication system. The base station  302  manages the cell  1 A, and the base station  303  manages the cell  2 B. Reference numerals  306 ,  307 ,  308  and  309  designate signal flows of the common control channel communicated between the mobile station  301  and the base stations  302  and  303 : the reference numeral  306  designates the signal from the mobile station  301  to the base station  302 ;  307  designates the signal from the mobile station  301  to the base station  303 ;  308  designates the signal from the base station  302  to the mobile station  301 ; and  309  designates the signal from the base station  303  to the mobile station  301 .  
       FIGS. 4-7  are flowcharts illustrating a control procedure carried out when the mobile station  301  makes a reconnection request in the communication network of  FIG. 3 .  FIGS. 4 and 5  mainly illustrate the control procedure of the radio communication controller  5  of the mobile station  301 , and  FIGS. 6 and 7  illustrate the control procedure of the baseband controller  33  corresponding to the control of the radio communication controller  5 .  
      In  FIG. 4 , the mobile station  301  is in a communication state with the cell  1 A of the base station  302  via the dedicated channel (step S 401 ). At step S 402 , if the communication quality deteriorates, the radio communication controller  5  of the mobile station  301  instructs the baseband controller  33  to complete the dedicated channel, that is, to stop the combiners  37  and  38  operating for the dedicated channel (step S 403 ), and to capture the broadcast information of the cell  1 A (step S 404 ). In this case, the communication falls into an instantaneous interruption.  
      In addition, the radio communication controller  5  instructs the baseband controller  33  to activate the common control channel, that is, to activate the combiner for the common control channel from the cell A (step S 405 ).  
      When a start request of the common control channel at step S 405  takes place at step S 601  of  FIG. 6 , the baseband controller  20   33  decides at step S 602  the latest combiner used as the common control channel among the combiners  37  and  38 . Since the finally used combiner has not yet been memorized here, the baseband controller  33  proceeds to step S 603  and activates the combiner  37  as the combiner for the common control channel of the cell  25   1 A, and memorizes the combiner  37  as the finally used combiner (step S 604 ). Thus, the common control channel of the cell  1 A enters into a communication state (receivable state) (step S 611 ).  
      Returning to  FIG. 4 , the mobile station  301  is now in the receivable state of the common control channel from the cell  1 A by the foregoing control (step S 406 ). At step S 407 , the mobile station  301  transmits to the cell  1 A a request message for requesting the reconnection of the dedicated channel as the signal  306 . In this case, the radio communication controller  5  starts a reconnection request retransmission timer and a reconnection instruction waiting timer. In addition, it measures levels of signals from neighboring cells at step S 408 . As a result, when the radio communication controller  5  detects a level change in which the signal from another cell (cell  2 B) exceeds the level of the signal from the serving cell  1 A, it advances the step to the cell switching at step S 501  ( FIG. 5 ). At step S 410 , when the retransmission timer expires, the radio communication controller  5  returns to step S 406 , and transmits the reconnection request message again at step S 407 . At step S 411 , if the waiting timer expires before receiving the response message (signal  308 ) instructing the reconnection, the radio communication controller  5  makes a decision that a reconnection failure occurs, and carries out abnormal processing (step S 413 ). If the radio communication controller  5  does not detect the level change at step S 409 , and receives at step S 412  the response message (signal  308 ) instructing the reconnection from the cell  1 A before the two timers expire at steps S 410  and S 411 , it proceeds to step S 512  ( FIG. 5 ), and carries out connection processing to the dedicated channel through a processing procedure which will be described later, thereby restarting the communication. If the radio communication controller  5  does not receive the reconnection instruction at step S 412 , it returns the processing to step S 408 .  
      In  FIG. 5 , the control procedure will be described which is carried out for making cell switching when the level change is detected at step S 409 . When the cell switching is started at step S 501 , the radio communication controller  5  instructs the baseband controller  33  to complete the common control channel, that is, to stop the combiner operating for the common control channel of the cell  1 A (step S 502 ), and to acquire the broadcast information of the cell  2 B (step S 503 ). In addition, the radio communication controller  5  instructs to activate the combiner for the common control channel from the cell B (step S 504 ).  
      If the completion request of the common control channel (cell  1 A) at step S 502  takes place at step S 701  of  FIG. 7 , the baseband controller  33  sets a timer for protecting rather than completing the combiner  37  operating for the cell  1 A step S 702 .  
      The time period to be set to the timer is made longer than the maximum delay time of an expected response message. Then, the combiner  37  maintains the current state, that is, the receivable state of the common control channel from the cell  1 A until the timer expires (step S 703 ).  
      If the start request of the common control channel (cell  2 B) at the foregoing step S 504  takes place at step S 601  of  FIG. 6 , the baseband controller  33  decides the finally used combiner at step S 602 . Since the combiner  37  is memorized as the finally used combiner as described above, the baseband controller  33  proceeds to step S 605 , at which it halts the combiner  38  if it is operating, and activates the combiner  38  anew as the common control channel for the cell  2 B (step S 606 ). Then, the baseband controller  33  memorizes the combiner  38  as the finally used combiner (step S 607 ), and both the cells  1 A and  2 B become a common control channel communication state (step S 611 ).  
      Returning to  FIG. 5 , the mobile station  301  is in the receivable state of both the common control channels from the cells  1 A and  2 B by the foregoing control (step S 505 ). At step S 506 , the mobile station  301  transmits a request message requesting the reconnection of the dedicated channel to the target cell  2 B for the cell switching as the signal  307 . In this case, the radio communication controller  5  starts the reconnection request retransmission timer and the reconnection instruction waiting timer. At step S 507 , the radio communication controller measures the levels of the signals from neighboring cells. If it detects the level change at which the signal level from another cell exceeds the level of the signal from the serving cell  2 B as a result of detection, it further proceeds to the cell switching (step S 501 ) and repeats the same control. If the retransmission timer expires at step S 509 , the radio communication controller  5  returns the processing to step S 505 , and transmits the reconnection request message at step S 506  again. If the waiting timer expires before receiving the response message instructing the reconnection at step S 510 , the radio communication controller  5  makes a decision that a reconnection failure occurs, and carries out abnormal processing (step S 515 ). If the radio communication controller  5  does not detect the level change at step S 508 , and receives at step S 511  the delayed response message (reconnection instruction, signal  308 ) from the cell  1 A or the response message (reconnection instruction, signal  309 ) from the cell  1 B before the two timers expire at steps S 509  and S 510 , the radio communication controller  5  instructs the baseband controller  33  to complete the common control channel (step S 512 ) and to start the dedicated channel (step S 513 ). Thus, the radio communication controller  5  completes the reconnection processing to the dedicated channel and restarts the communication (step S 514 ). If the radio communication controller  5  does not receive the reconnection instruction at step S 511 , it returns the processing to step S 507 .  
      If the start request of the common control channel at step S 504  takes place at step S 601  of  FIG. 6  in the case where the radio communication controller  5  detects the level change at step S 508  and carries out the cell switching after returning to step S 501 , the baseband controller  33  decides the finally used combiner (step S 602 ). Since the combiner  38  is memorized as the finally used combiner here, the baseband controller  33  proceeds to step S 608 , at which it halts the combiner  37  if it is operating, and activates the combiner  37  anew as the common control channel for the target cell (step S 609 ). Then, the baseband controller  33  memorizes the combiner  37  as the finally used combiner (step S 610 ), and both the cells  2 B and target cell become a common control channel communication state (step S 611 ).  
      If the completion request of the common control channels (of both the cells  1 A and  2 B) at step S 512  takes place at step S 701  of  FIG. 7 , the baseband controller  33  sets the timer for protecting rather than completing the serving combiners  37  and  38  at step S 702  as in the foregoing step S 502 , and maintains the current state of the combiners  37  and  38  (step S 703 ). On the other hand, if a start request of the dedicated channel at the foregoing step S 513  occurs (step S 704 ), the baseband controller  33  halts the serving combiners  37  and  38  (step S 705 ), and activates the combiner  37  or  38  (or both of them) for the dedicated channel (step S 706 ), thereby entering into the dedicated channel communication state (step S 707 ).  
      In addition, when the common control channel protective timer expires in  FIG. 7  (step S 708 ), the baseband controller  33  halts the combiner that has set the timer, and enters into a channel-closed state at which the common control channel is not received (step S 710 ). The time period to be set to the protective timer is made longer than the maximum delay time of the expected response message as described above. Accordingly, the channel-closed state in the control procedure is brought about when the communication is completed in a state other than the response message waiting state concerning the common control channel.  
      According to the foregoing control procedure, the mobile station can receive the common control channels from the two cells before and after the cell switching, even if the cell switching takes place before receiving the response message after transmitting the reconnection request. Thus, the mobile station can circumvent the problem of the communication interruption by receiving the response message from the cell that transmits the response first, even if the response message delays because of some cause on the network side. Consequently, the mobile station can continue stable communication even in a handover area in which the cell switching can easily occur.  
      In addition, such control is also possible in which the radio communication controller  5  starts the combiner  38  for the common control channel of the cell  2 B with maintaining the combiner  37  in the receivable state of the common control channel of the cell  1 A in the foregoing steps S 502  and S 504 . The present embodiment 1 can be implemented by merely modifying the physical layer without changing from the conventional control the control of the radio communication controller  5 , which is carried out in accordance with the higher level protocol. This makes it possible to facilitate the design of the mobile station.  
      Although the embodiment 1 is described by way of example of the control procedure during the reconnection request, a similar advantage can also be achieved in other control that needs the response message via the common control channel in the state in which the cell switching is easy to occur. For example, consider a case where the transmission volume decreases during the packet communication via the dedicated channel, and the switching of the communication is made to the common control channel. In this case, the mobile station must transmit a cell update signal to the cell in communication, and receive its response message via the common control channel. Thus, carrying out the same control as that of the embodiment 1 enables the mobile station to receive the delayed response message even in the handover area in which the cell switching is easy to occur, thereby being able to increase the success rate of the switching from the dedicated channel to the common control channel.  
      In addition, when the cell switching takes place during transmission of a short packet via the common control channel, the mobile station must transmit the cell update signal to the target cell of the switching, and receive the response message via the common control channel. In this case, if the cell switching occurs before receiving the response message, such a procedure will be repeated as the mobile station transmits the cell update signal to the next cell, and waits for the response message via the common control channel. In this case also, the success rate of reselecting the cell without any communication interruption is increased by receiving the response message from both the cells before and after the cell switching as in the embodiment 1.  
     EMBODIMENT 2  
      Next, an embodiment 2 in accordance with the present invention will be described. The functional block diagram of the radio communication apparatus (mobile station) of the present embodiment 2 is the same as that of  FIG. 1 . Referring to  FIG. 8 , a detailed arrangement of the baseband demodulator  31  with a characteristic configuration will be described. In  FIG. 8 , the same reference numerals designate the same components as those of  FIG. 2 . The baseband demodulator  31  includes the finger sections  34  and  35  each for despreading the digital signal fed from the radio stage  2  for each receiving path from the base station, and combiners  36  and  39  for rake combining the signals despread for respective receiving paths. The finger sections  34  and  35  include a plurality of fingers  341 ,  342 , . . . ,  34   m  and  351 ,  352 , . . . ,  35   n  provided for the individual receiving paths, where m and n are integers. The finger section  34  and combiner  36  are used for demodulating the physical channel (PCCPCH) including broadcast information or for demodulating the secondary common control channel (SCCPCH). The finger section  35  and combiner  39  are used for demodulating the secondary common control channel (SCCPCH) or dedicated channel (DPCH). In addition, the baseband controller  33  sets the parameters of the combiners  36  and  39  in accordance with the frame structure of the channels to be demodulated. The communication path encoder  4  includes the physical format converter  41   a  for converting the physical format of the signal including broadcast information demodulated by the combiner  36 , the physical format converter  41   b  for converting the physical format of the common control channel demodulated by the combiner  36  and for converting the physical format of the common control channel or dedicated channel demodulated by the combiner  39 .  
      The physical channel (PCCPCH) including the broadcast information transmits the system information, cell information and the like at a fixed rate. Although the broadcast information must always be placed in a receivable state, the information is not transmitted uninterruptedly. In view of this, as in the embodiment 1, when the cell switching occurs while waiting the response message via the common control channel, the baseband demodulator  31  halts the combiner  36  operating for the broadcast information, and restarts it as the combiner for the common control channel before the cell switching. In this case, the combiner  39  is activated as the combiner for the common control channel after the cell switching. Alternatively, it is possible to restart the combiner  36  as the combiner for the common control channel after the cell switching, and to start the combiner  39  as the combiner for the common control channel before the cell switching. Then, after receiving the response message with one of the combiners  36  and  39 , the baseband demodulator  31  halts the two combiners immediately, and restarts the combiner  36  as the combiner for the broadcast information, and restarts the combiner  39  in accordance with the contents of the response message.  
      As for the system having an occasion of receiving the physical channel including the broadcast information and the common control channel simultaneously (for example, 20 msec overlap at a period of every three seconds), it is necessary to control the combiner  36  in such a manner that the priority is assigned to receiving the broadcast information.  
      The foregoing control enables the combiners  36  and  39  to demodulate the two common control channels, which provide the data proper to the individual cells, simultaneously. Thus, the mobile station can receive the common control channels from the two cells before and after the cell switching. Accordingly, even if the response message is delayed because of some cause on the network side, the problem of the communication interruption can be avoided by receiving the response message from the cell that provides the response first. As a result, the mobile station can continue stable communication in a handover area in which the cell switching is likely to occur frequently.  
      Furthermore, using one of the combiners for both the broadcast information and common control channel by switching on a time sharing basis, the foregoing advantage can be achieved without increasing the number of the combiners. Even though the control is carried out in such a manner that the broadcast information is received first in the overlap section of the broadcast information and the common control channel, the foregoing advantage can be expected because the likeliness of receiving the response message at the overlap is low.