Patent Publication Number: US-2007111751-A1

Title: Communication terminal apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      The present application is a Divisional Application of U.S. application Ser. No. 10/793,262, filed Mar. 4, 2004, which is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-197856, filed Jul. 16, 2003, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a communication terminal apparatus in a radio communication system such as a mobile telephone system.  
      2. Description of the Related Art  
      In a wideband code division multiple access (W-CDMA) system which is one of mobile telephone systems, generation of an incoming call is monitored in the intermittent reception scheme.  
      At the monitoring time, the intermittent reception scheme operates the communication function during a period when a paging signal notify presence or absence of an incoming call is transmitted intermittently from a base station (ready state), and operates an operating section, a display section and their related portions during other periods (sleep state).  
      If an incoming call is detected from the paging signal in the ready state, the intermittent reception is stopped, the communication function is continuously operated to make communication. If the incoming call is not detected, a timer is reset, a power supply of each section is turned off, and the sleep state is maintained again until the paging signal is transmitted.  
      Thus, the consumed power can be reduced at the incoming call standby time by employing the intermittent reception scheme.  
      Incidentally, when the ready state is set again from the sleep state, synchronization is to be made with a base station which has received signals in the previous ready state. However, if the receiving level from the base station is low, cell search or what is called reselection is executed to search for the other base station suitable for the communication.  
      For example, in the W-CDMA system based on the 3rd Generation Partnership Project (3GPP), inherent system information transmitted over a BCCH (referred to hereinafter as BCCH) notified from a newly detected base station is acquired when the reselection is executed. After that, intermittent reception is executed on the basis of the BCCH.  
      However, the BCCH provides the newly detected base station with a large amount of information and the reception of the information requires a receiving speed of about 1000 to 2000 milliseconds. For this reason, much power is consumed for the reception of the BCCH. If the reselection is frequently executed, battery power may be wasted.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention has been accomplished to solve the above-described problem. The object of the present invention is to provide a communication terminal apparatus capable of reducing power consumption during intermittent reception.  
      According to an aspect of the present invention, there is provided a communication terminal apparatus for making communication with a base station connectable with a communication network. The apparatus comprises receiving means for receiving a signal transmitted from the base station, storing means for storing first information and second information which are received from the base station by the receiving means, while making the first information and second information correspond to identification information of the base station, first control means for controlling the receiving means in accordance with the first information to receive a signal transmitted from a serving base station configured to transmit a paging signal to the apparatus, if a preset time has passed, level detecting means for detecting a level of the signal received by the receiving means under control of the first control means, second control means for controlling the receiving means to stop the operation of the receiving means if the level detected by the level detecting means is equal to or higher than a threshold value, base station detecting means for detecting an alternate base station suitable for the reception other than the serving base station by controlling the receiving means if the level detected by the level detecting means is lower than a threshold value, third control means for controlling the receiving means to receive second information from the alternate base station if information received from the alternate base station stored in the storing means, fourth control means for controlling the receiving means to receive the first information from the alternate base station if the second information received by the receiving means under control of the third control means does not correspond to the second information stored in the storing means, first storing controlling means for controlling storing of the first information received by the receiving means under control of the fourth control means, in the storing means, while making the first information correspond to identification information of the alternate base station, base station switching means for switching the alternate base station to the serving base station if the second information received by the receiving means under control of the third control means corresponds to the second information stored in the storing information, fifth control means for controlling the receiving means to receive the first information from the serving base station if there is a necessity to make communication with the serving base station, and second storing controlling means for controlling storing of the first information received by the receiving means under control of the fifth control means, in the storing means, while making the first information correspond to identification information of the serving base station.  
      Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
      The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.  
       FIG. 1  is a block diagram of a communication terminal apparatus according to an embodiment of the present invention;  
       FIG. 2  is a flowchart of operations at intermittent reception in the communication terminal apparatus shown in  FIG. 1 ;  
       FIG. 3  is a flowchart of reselection in the intermittent reception shown in  FIG. 2 ;  
       FIG. 4  is a flowchart of communication control in the intermittent reception shown in  FIG. 2 ;  
       FIG. 5  is an illustration of executing the intermittent reception by the communication terminal apparatus shown in  FIG. 1  while moving;  
       FIG. 6  is an illustration of executing the intermittent reception by the communication terminal apparatus shown in  FIG. 1  while moving;  
       FIG. 7  is an illustration of executing the intermittent reception by the communication terminal apparatus shown in  FIG. 1  while moving;  
       FIG. 8  is a block diagram of a communication terminal apparatus according to an embodiment of the present invention;  
       FIG. 9  is a flowchart showing an operation of a discontinuous reception processing unit according to the present invention; and  
       FIG. 10  is a chart of a system information table according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  is a block diagram of a communication terminal apparatus according to an embodiment of the present invention. A W-CDMA mobile communication terminal is explained in the following descriptions.  
      A radio unit  20  makes radio communication in the W-CDMA scheme with a base station (not shown) via an antenna  10 . The radio unit  20  down-converts a radio signal received from the base station to obtain a spread baseband signal.  
      A signal processing unit  30  despreads the baseband signal to obtain information indispensable for the communication with the base station and data to be transmitted to the mobile communication terminal. The signal processing unit  30  also has a function of detecting a receiving signal level for each base station on the basis of the baseband signal and notifies the detected level to a control unit  100 .  
      A speech processing unit  40  decodes the data obtained by the signal processing unit  30  to reproduce a speech signal. The speech signal is output from a speaker  50 . The speech processing unit  40  also encodes speech input from a microphone  60  as speech data, which is output to the signal processing unit  30 .  
      The signal processing unit  30  executes a spreading operation by using the speech data to generate a modulation signal. The radio unit  20  up-converts the modulation signal into a radio signal, which is transmitted to the base station via the antenna  10 .  
      An input unit  70  is composed of a plurality of keys and accepts various instructions from a user. The accepted information is output to the control unit  100 . A display unit  80  is a liquid crystal display (LCD) or the like which visually display the information. The display unit  80  is controlled by the control unit  100 .  
      A memory unit  90  is a unit using a semiconductor such as a RAM or ROM. The memory unit  90  stores the control program and control data of the control unit  100 , and user data such as telephone directory data and mail data.  
      The memory unit  90  has a cache area in which system information (BCCH) received from the base station is stored in association with identification information of the base station and the receiving level. The information about number m of base stations is also stored in the cache area.  
      The control unit  100  configured to wholly control the units of the mobile communication terminal controls the radio unit  20  and the signal processing unit  30  to implement the W-CDMA radio communication. In addition, the control unit  100  controls incoming and outgoing calls in accordance with the instructions from the input unit  70 , and controls the display unit  80  to display generation of incoming and outgoing calls, conditions of the mobile communication terminal, information stored in the memory unit  90  and the like.  
      The control unit  100  comprises an intermittent reception control unit  100   a.  The control unit  100   a  controls the radio unit  20 , the signal processing unit  30  and the like to make them execute intermittent operations at the standby time. Power consumption of a battery (not shown) can be thereby reduced.  
      Next, operations of the mobile communication terminal having the above-described structure will be explained. FIGS.  2  to  4  are flowcharts of the operations of the mobile communication terminal, which are controlled by the control unit  100   a.  The processing of  FIG. 2  is started when a sleep state of the mobile communication terminal is switched to a ready state.  
      First, in step  2   a,  the control unit  100   a  starts a timer Tr. The operation proceeds to step  2   b.    
      In step  2   b,  the control unit  100   a  starts the radio unit  20  and the signal processing unit  30  to execute the serving cell search and receive a radio signal from a base station in a serving cell (hereinafter referred to as a serving base station). The operation proceeds to step  2   c.  The serving cell indicates a cell including the base station which has made communication in the previous ready state.  
      In step  2   c,  the control unit  100   a  compares a level of the signal received in step  2   b  with a threshold value and determines whether a reselection processing is needed. If the level of the signal received in step  2   b  is lower than the threshold value and the reselection is needed, the operation proceeds to step  2   d.  If the reselection is not needed, the operation proceeds to step  2   e.    
      In step  2   d,  the control unit  100   a  executes the reselection. The operation proceeds to step  2   e.  Details of the reselection will be described later.  
      In step  2   e,  the control unit  100   a  receives, of the signal transmitted from the serving base station, a paging signal inserted into a slot assigned to the mobile communication terminal. The operation proceeds to step  2   f.    
      In step  2   f,  the control unit  100   a  determines whether an incoming call is generated, on the basis of the paging signal received in step  2   e.  The control unit  100   a  also determines whether an outgoing call request is made via the input unit  70  by a user and whether a position registration processing (registration) needs to be executed via the serving base station. If a result of either of the determinations is “positive”, the operation proceeds to step  2   g.  If the results of both the determinations are “negative”, the operation proceeds to step  2   h.    
      In step  2   g,  the control unit  100   a  executes any of the communication controls such as the control of notifying the generated incoming call, the outgoing call control and the position registration. The operation proceeds to step  2   h.  Details of the processing in this step will be described later.  
      In step  2   h,  the control unit  100   a  determines whether the count value of the timer Tr started in step  2   a  exceeds a threshold value t 0 . If the count value of the timer Tr exceeds the threshold value t 0 , the operation proceeds to step  2   i.  If the count value of the timer Tr does not exceed the threshold value t 0 , the operation returns to step  2   e.    
      In step  2   i,  the control unit  100   a  stops the timer Tr and starts a timer Ts to stop power supply to the radio unit  20  and the signal processing unit  30 . The apparatus thereby becomes in the sleep state.  
      After that, if the timer Ts reaches a threshold value T 1 , the processing of  FIG. 2  is started again. The threshold value T 1  is set by the control unit  100   a  on the basis of the timing at which the paging signal is transmitted from the base station to the apparatus.  
      Next, the reselection in step  2   d  will be explained with reference to  FIG. 3 . This processing is also executed by the control unit  100   a.    
      In step  3   a,  the control unit  100   a  sets “0” at parameter i. The operation proceeds to step  3   b.    
      In step  3   b,  the control unit  100   a  executes peripheral cell search. The peripheral cell search is to receive signals transmitted from base stations in cells near the serving cell, detect the cell from which the signals can be received preferably, detect identification information of the cell and detect the power level and the quality level of the received signals. The operation proceeds to step  3   c.    
      In step  3   c,  the control unit  100   a  determines whether the identification information detected in step  3   b  corresponds to i-th information item stored in the cache area of the memory unit  90 . If the identification information corresponds to the i-th information item, the operation proceeds to step  3   f.  If the identification information does not correspond to the i-th information item, the operation proceeds to step  3   d.    
      In step  3   d,  the control unit  100   a  determines whether number i is smaller than number m. If number i is smaller than number m, the operation proceeds to step  3   e.  If number i is equal to or greater than number m, the operation proceeds to step  3   i.    
      In step  3   e,  the control unit  100   a  adds “1” to number i. The operation returns to step  3   c.    
      In step  3   f,  the control unit  100   a  controls the signal processing unit  30  and receives MIB. The operation returns to step  3   g.  MIB indicates one of information items included in the BCCH. The BCCH is composed of MIB and SIB.  
      In step  3   g,  the control unit  100   a  determines whether the MIB received in step  3   f  corresponds to the MIB included in the i-th information item stored in the cache area of the memory unit  90 . If both of MIB correspond to each other, the operation returns to step  3   h.  If they do not correspond to each other, the operation returns to step  3   i.  The correspondence of MIB is determined by comparing tags added to them.  
      In step  3   h,  the control unit  100   a  switches the cell to be handed as the serving cell to the cell corresponding to the i-th information item stored in the cache area of the memory unit  90  and ends the processing. The operation returns to step  2   e.    
      In step  3   i,  the control unit  100   a  controls the signal processing unit  30  to receive the SIB. The operation proceeds to step  3   j.    
      In step  3   j,  the control unit  100   a  determines whether the cache area of the memory unit  90  is full. If the cache area is full, the operation proceeds to step  3   k.  If the cache area includes free space, the operation proceeds to step  3   l.    
      In step  3   k,  the control unit  100   a  detects higher-order number m of information of the reception level, on the basis of the reception level detected in step  3   b  and the reception level corresponding to the information which has already been stored in the cache area of the memory unit  90 . The control unit  100   a  also stores the detected information in the cache area of the memory unit  90 . Then the operation proceeds to step  3   m.  If the reception level detected in step  3   b  is included in higher-order number m of information, the identification information of the cell detected in step  3   b,  and the power level and quality level of the received signal are made to correspond to the reception level and stored in the cache.  
      In step  31 , the control unit  100   a  makes the identification information of the cell detected in step  3   b,  and the power level and quality level of the received signal correspond to the reception level and stores them in the cache. The operation proceeds to step  3   m.    
      In step  3   m,  the control unit  100   a  switches the cell to be handled as the serving cell to the cell detected in step  3   b  and ends the processing. The operation returns to step  2   e.    
      Next, the communication control of step  2   g  will be explained with reference to  FIG. 4 . This processing is executed by the control unit  100   a.    
      In step  4   a,  the control unit  100   a  controls the signal processing unit  30  to receive BCCH, i.e. MIB and SIB. The operation proceeds to step  4   b.    
      In step  4   b,  the control unit  100   a  controls the radio unit  20  and the signal processing unit  30  to transmit RACH of the power level based on the SIB received in step  4   a.  The operation proceeds to step  4   c.  RACH includes the information about the mobile communication terminal which is indispensable for the communication to be made in step  4   c.    
      In step  4   c,  the control unit  100   a  executes any of communication controls such as control of notifying a generated incoming call, control of an outgoing call, and the position registration processing. The operation proceeds to step  2   h.    
      Next, the intermittent reception of the control unit  100   a  in a case where the mobile communication terminal moves across radio zones of base stations A, B and C which belong to different cells, will be explained. The control unit  100   a  moves through the radio zones of the base stations in order of base stations A, B, C, B, C, B, and A. An incoming call is generated in the radio zone of the base station A. FIGS.  5  to  7  show the intermittent reception operations of the radio unit  20  and the signal processing unit  30  in this case.  
      First, the mobile communication terminal, in the radio zone of base station A, detects base station A as the serving base station and receives BCCH from base station A as represented by R 1  of  FIG. 5 . As the BCCH received from base station A is not stored in the cache area of the memory unit  90 , the BCCH is stored therein (R 1 ). After that, the intermittent reception is executed while base station A having preferable reception quality serves as the serving base station, as represented by R 2  and R 3 .  
      The terminal moves from the radio zone of base station A to the radio zone of base station B. As the signal level received from base station A is lowered, the reselection is executed as represented by R 4 . On the basis of the reselection, the terminal receives the BCCH from base station B and switches base station A to base station B as the serving base station.  
      As the BCCH received from base station B is not stored in the cache area of the memory unit  90 , the BCCH is stored therein. After that, the intermittent reception is executed while base station B having preferable reception quality serves as the serving base station, as represented by R 5 .  
      The terminal moves from the radio zone of base station B to the radio zone of base station C. As the signal level received from base station B is lowered, the reselection is executed as represented by R 6 . On the basis of the reselection, the terminal receives the BCCH from base station C and switches base station B to base station C as the serving base station.  
      As the BCCH received from base station C is not stored in the cache area of the memory unit  90 , the BCCH is stored therein. After that, the intermittent reception is executed while base station C having preferable reception quality serves as the serving base station, as represented by R 7  and R 8 .  
      After that, the terminal moves again from the radio zone of base station C to the radio zone of base station B. As the signal level received from base station C is lowered, the reselection is executed as represented by R 9 . On the basis of the reselection, the terminal receives the MIB only from base station B as the BCCH of base station B has been stored in the cache area of the memory unit  90 .  
      If the terminal confirms that the MIB received from base station B is not different from the MIB stored in the cache, the terminal switches base station C to base station B as the serving base station without receiving the SIB. After that, the terminal executes the intermittent reception while base station B having preferable reception quality serves as the serving base station, as represented by R 10  and R 11 .  
      The terminal moves again from the radio zone of base station B to the radio zone of base station C. As the signal level received from base station B is lowered, the reselection is executed as represented by R 12 . On the basis of the reselection, the terminal receives the MIB only from base station C as the BCCH of base station C has been stored in the cache area of the memory unit  90 .  
      If the terminal confirms that the MIB received from base station C is not different from the MIB stored in the cache, the terminal switches base station B to base station C as the serving base station without receiving the SIB. After that, the terminal executes the intermittent reception while base station C having preferable reception quality serves as the serving base station, as represented by R 13 .  
      After passing time T in the radio zone of base station C, the terminal moves from the radio zone of base station C to the radio zone of base station B. As the signal level received from base station C is lowered, the reselection is executed as represented by R 14 . On the basis of the reselection, the terminal receives the MIB only from base station B as the BCCH of base station B has been stored in the cache area of the memory unit  90 .  
      If the terminal confirms that the MIB received from base station B is not different from the MIB stored in the cache, the terminal switches base station C to base station B as the serving base station without receiving the SIB. After that, the terminal executes the intermittent reception while base station B having preferable reception quality serves as the serving base station, as represented by R 15 .  
      The terminal moves again from the radio zone of base station B to the radio zone of base station A. As the signal level received from base station B is lowered, the reselection is executed as represented by R 16 . On the basis of the reselection, the terminal receives the MIB only from base station B as the BCCH of base station A has been stored in the cache area of the memory unit  90  though much time has passed.  
      If the terminal confirms that the MIB received from base station A is not different from the MIB stored in the cache, the terminal switches base station B to base station A as the serving base station without receiving the SIB. After that, the terminal executes the intermittent reception while base station B having preferable reception quality serves as the serving base station, as represented by R 17 .  
      After that, if the terminal receives notification of the incoming call from the paging signal received from base station A, the terminal receives the BCCH from base station A, as represented by R 18 . In addition, the terminal transmits the RACH at the power level based on the BCCH and executes the incoming call processing.  
      In the reselection, as described above, the terminal having the above-described structure determines whether the BCCH stored in the cache area is new information or old information on the basis of the received MIB. If the MIB is the latest information, the terminal switches the serving base station on the basis of the BCCH stored in the cache area as represented by R 9  and R 12  in  FIG. 6 .  
      Even if a certain time has passed since storing the BCCH in the cache area, the terminal executes the reselection. The terminal determines whether the BCCH stored in the cache area is new information or old information on the basis of the received MIB. If the MIB is the latest information, the terminal switches the serving base station on the basis of the BCCH stored in the cache area as represented by R 14  and R 16  in  FIG. 7 .  
      In addition, the terminal receives the BCCH from the serving base station and executes any of communication controls such as control of notifying the generated incoming call, the outgoing call control and position registration, on the basis of the BCCH, as represented by R 18  of  FIG. 7 .  
      Thus, in the terminal having the above-described structure, the serving base station is switched on the basis of the BCCH stored in the cache area unless the MIB received from the serving base station is changed. For this reason, the BCCH does not need to be frequently received in the reselection and the consumption of the battery power can be thereby reduced.  
      Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.  
      A mobile communication terminal apparatus according to an embodiment of the present invention will be described below with reference to the drawings, as will be a discontinuous receiving method of the mobile communication terminal apparatus.  FIG. 8  is a block diagram showing a configuration of the mobile communication terminal apparatus (mobile cell). The apparatus includes a control unit  11  for controlling the whole of the apparatus, an antenna  12   a  for transmitting/receiving a wave to/from a serving cell (not shown), a communication unit  12   b,  a transmission/reception unit  13 , a speaker  14   a,  a microphone  14   b,  a call unit  14   c,  an output unit  15 , an input unit  16 , a discontinuous reception processing unit  17 , a system information storage unit  18 , and a rechargeable battery (not shown) for supplying power to these units. The system information storage unit  18  stores a system information table  21 .  
      The operation of each of the units of the mobile communication terminal apparatus with the above configuration will be described with reference to  FIG. 8 .  
      The communication unit  12   b  transmits a radio-frequency signal from the antenna  12   a  to the transmission/reception unit  13 , and vice versa.  
      The transmission/reception unit  13  amplifies the radio frequency signal transmitted from the communication unit  12   b  and converts the frequency of the amplified signal. Then, the unit  13  demodulates the signal into a digital speech signal and sends the digital speech signal to the call unit  14   c.  The unit  13  also sends a control signal to the control unit  11 . Furthermore, the unit  13  modulates the digital speech signal output from the call unit  14   c  and the control signal output from the control unit  11 , and converts the frequencies of these modulated signals. Then, the unit  13  amplifies the signals to generate radio frequency signals, and sends them to the communication unit  12   b.    
      The call unit  14   c  converts the digital speech signal output from the transmission/reception unit  13  into an analog speech signal, amplifies the signal, and sends the amplified signal to the speaker  14   a.  The call unit  14   c  also amplifies the analog speech signal output from the microphone  14   b,  converts the amplified signal into a digital speech signal, and sends the digital speech signal to the transmission/reception unit  13 .  
      The output unit  15  is a display device such as an LCD. The output unit  15  is started by the control unit  11  to perform its display operation. The output unit  15  continues to display the same contents until it is started by the control unit  11  in response to an input operation of the input unit  16 .  
      The input unit  16  includes a plurality of keys. As the control unit  11  starts, the input unit  16  starts to operate. In response to a key input by a user, the input unit  16  notifies the control unit  11  of a code for identifying the key, thus completing its operation.  
      The operation of the discontinuous reception processing unit  17  will now be described. The unit  17  manages system information of an idle serving cell and detects the presence or absence of an incoming call. The unit  17  also determines whether to reselect a cell.  
       FIG. 9  is a flowchart of the operation of the discontinuous reception processing unit  17 . The unit  17  is started by the control unit  11  at every discontinuous reception cycle to perform its operation (step  17   a ). First, the unit  17  receives a common pilot signal from the idle serving cell through a common pilot channel and searches the idle serving cell (step  17   b ). At the same time, the unit  17  measures the quality of the wave of the common pilot signal that is transmitted through the common pilot channel. The quality of the wave is good as the intensity of the wave and as the signal-to-noise ratio of the wave.  
      The discontinuous reception processing unit  17  detects the presence or absence of a call coming to the unit  17  and causes its operation to branch according to the result of the detection (step  17   c ). In other words, the unit  17  receives a paging indicator signal through a paging indicator channel, and determines that no call is coming to the unit  17  if the signal indicates the absence of an incoming call.  
      If the paging indicator signal indicates the presence of an incoming call, the discontinuous reception processing unit  17  receives paging information through the paging channel and analyzes the information to determine the presence or absence of a call coming to the unit  17 .  
      If there is no call coming to the unit  17  (No in step  17   c ), the discontinuous reception processing unit  17  receives a common pilot signal from a serving cell neighboring to the idle serving cell through the common pilot channel, and searches the neighboring serving cell (step  17   d ). At the same time, the unit  17  measures the quality of the wave of the common pilot signal that is transmitted from the neighboring serving cell through the common pilot channel.  
      After that, the discontinuous reception processing unit  17  determines whether to reselect a cell (step  17   e ). In other words, the unit  17  determines that a cell is not reselected at once if the quality of the wave of the common pilot signal, which is measured in step  17   b,  is not less than a given threshold value.  
      If the quality of the wave of the common pilot signal is less than the given threshold value and the unit  17  receives a wave whose quality is higher than the quality of the above wave from the neighboring serving cell, the unit  17  determines that a cell is reselected setting the serving cell, which transmits the wave of higher quality, as a new idle serving cell. In the other cases, the unit  17  determines that a cell is not reselected.  
      If the discontinuous reception processing unit  17  determines that a cell is not reselected (NO in step  17   e ), it completes its discontinuous reception processing (step  17   f ).  
      On the other hand, if the discontinuous reception processing unit  17  determines that a cell is reselected (YES in step  17   e ), it receives the update number of system information of a new idle serving cell, which is selected in step  17   e,  from the new idle serving cell through a broadcast common control channel (step  17   g ). After that, the unit  17  determines whether the system information of the new idle serving cell is stored in the system information table  21 , using an identifier of the new idle serving cell (step  17   h ).  
       FIG. 10  shows an example of the system information table  21 . The system information table  21  includes data of a serving cell identifier  21   a,  an update number  21   b,  a channel number  21   c,  a discontinuous reception cycle  21   d,  neighboring serving cell information  21   e,  an RACH transmission power initial value  21   f,  and a preamble interval  21   g.  The system information table  21  can include other data.  
      The serving cell identifier  21   a  is information for identifying a serving cell uniquely and a scrambling code of the serving cell. The update number  21   b,  channel number  21   c,  discontinuous reception cycle  21   d,  neighboring serving cell information  21   e,  RACH transmission power initial value  21   f,  and preamble interval  21   g  are system information of the serving cell that is identified by the serving cell identifier  21   a.    
      More specifically, the update number  21   b  is information that indicates the update statuses of the channel number  21   c,  discontinuous reception cycle  21   d  and neighboring serving cell information  21   e.  The channel number  21   c  is a channel number of a control channel used by a serving cell that is identified by the serving cell identifier  21   a.  The discontinuous reception cycle  21   d  is a time interval during which information about the presence or absence of an incoming call is transmitted from the serving cell that is identified by the serving cell identifier  21   a.    
      The neighboring serving cell information  21   e  is information of a serving cell neighboring to the serving cell identified by the serving cell identifier  21   a.  Specifically, the information  21   e  includes a channel number of the pilot channel common to the neighboring serving cells.  
      The channel number  21   c,  discontinuous reception cycle  21   d,  and neighboring serving cell information  21   e  are reception parameters necessary for performing a discontinuous receiving operation setting the serving cell identified by the serving cell identifier  21   a  as an idle serving cell.  
      The RACH transmission power initial value  21   f  is the initial value of power for transmitting a given preamble from a mobile communication terminal apparatus when call communication is started. The preamble interval  21   g  is a time interval during which the preamble is transmitted.  
      The RACH transmission power initial value  21   f  and preamble interval  21   g  are transmission parameters necessary for an RACH transmission process that is performed when call communication with the serving cell identified by the serving cell identifier  21   a  is started.  
      The transmission parameters, which depend upon the number of mobile cells with which a serving cell communicates and the power of transmission used for the communication, are determined by the serving cell. The RACH transmission power initial value  21   f  and preamble interval  21   g  transmitted by the serving cell are therefore updated at all times.  
      In step  17   h,  the discontinuous reception processing unit  17  searches the serving cell identifier  21   a  of the system information table  21  for data that is equal to the identifier of the new idle serving cell described above. When the unit  17  searches for the data (YES in step  17   h ), it compares the update number  21   b  of the searched data with the update number of system information of the new idle serving cell received in step  17   g  (step S 17   i ).  
      If the above two update numbers are equal to each other, the discontinuous reception processing unit  17  determines that the system information of the new idle serving cell stored in the system information table  21  is the latest (LATEST in step  17   i ). Then, the unit  17  reads the system information of the new idle serving cell from the system information table  21  (step  17   j ) and stores it in a given storage area (not shown) of the control unit  11 .  
      The discontinuous reception processing unit  17  notifies the idle serving cell prior to the reselection of a cell and the new idle serving cell of the reselection of a cell (step  17   k ), and completes its discontinuous reception processing (step  17   f ).  
      If the system information of the new idle serving cell is not stored in the system information table  21  (NO in step  17   h ), and the two update numbers are not equal to each other, or the system information of the new idle serving cell stored in the system information table  21  is not the latest (NOT LATEST in step  17   i ), the discontinuous reception processing unit  17  receives reception and transmission parameters of the system information from the new idle serving cell through the broadcast common control channel (step  17   m ).  
      The discontinuous reception processing unit  17  stores the received reception and transmission parameters, or the channel number  21   c,  discontinuous reception cycle  21   d,  neighboring serving cell information  21   e,  RACH transmission power initial value  21   f,  preamble interval  21   g,  and the update number  21   b  received in step  17   g  as well as the serving cell identifier  21   a  of the new idle serving cell in the system information table  21  (step  17   n ).  
      The discontinuous reception processing unit  17  stores the system information of the system information table  21  in a given storage area of the control unit  11  as system information of the idle serving cell. The unit  17  notifies the old and new idle serving cells of the reselection of a cell (step  17   k ) and completes its processing (step  17   f ).  
      If the discontinuous reception processing unit  17  detects the presence of an incoming call (YES in step  17   c ), it receives the system information of a serving cell through the broadcast common control channel (step  17   o ) and stores it in the system information table  21  (step  17   p ). Furthermore, the unit  17  stores the system information in a given storage area of the control unit  11  as the system information of the idle serving cell, and transfers its operation to an incoming call processing unit (not shown) (step  17   q ).  
      The system information of the idle serving cell, which is stored in a given storage area of the control unit  11 , is used when the incoming call processing unit makes an RACH transmission. In other words, the incoming call processing unit can make an RACH transmission by adequate transmission power, using the latest RACH transmission power initial value  21   f  and preamble interval  21   g.    
      The RACH transmission is made by an outgoing call processing unit (not shown) as well as the incoming call processing unit. The outgoing call processing unit performs a process of receiving the system information of the idle serving cell in step  17   o  and a process of storing the received system information in step  17   p  prior to its outgoing call processing.  
      Furthermore, the system information includes an identifier for a location registration area (general incoming call area) to which the serving cell belongs. Though not shown, the identifier is stored in the system information table  21 .  
      When an identifier for a location registration area of an idle serving cell prior to the reselection of a cell and an identifier for a location registration area of a new idle serving cell are different from each other, the discontinuous reception processing unit  17  not only notifies these serving cells of the reselection of a cell but also communicates with the new idle serving cell for the location registration in step  17   k.    
      Since the RACH transmission is used for communication for the location registration, the discontinuous reception processing unit  17  performs a process of receiving the system information of the idle serving cell in step  17   o  and a process of storing the received system information in step  17   p  before its RACH transmission and during the execution of step  17   k  after step  17   j  but not through step  17   m  or step  17   n.    
      When the system information table  21  has no storage capacity enough to store the system information of the new idle serving cell in step  17   n,  the system information of another serving cell is deleted to increase the storage capacity.  
      The discontinuous reception processing unit  17  stores the quality of the wave of a common pilot signal, which is transmitted through a common pilot channel from each serving cell, in the system information table  21 , and updates the stored quality when it makes the search for an idle serving cell in step  17   b  and the search for a serving cell neighboring to the idle serving cell in step  17   d.  In order to increase the storage capacity, the system information of a serving cell in which the lowest quality is stored is deleted. The present invention is not limited to the above configuration, but various modifications can be made.  
      As has been described above, according to the present invention, the system information of an old idle serving cell is stored and used. Thus, the amount of system information received from a new idle serving cell can be prevented from increasing and the idle serving cell can be prevented from being lost. Moreover, the power consumption of the mobile communication terminal apparatus in idle mode can be reduced.