Patent Publication Number: US-8526943-B2

Title: Mobile radio terminal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation of U.S. patent application Ser. No. 11/950,205, filed Dec. 4, 2007, which claims priority to Japanese Application No. 2007-128767, filed May 5, 2007. The foregoing Patent applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mobile radio terminal capable of roaming domestically or overseas. 
     2. Description of the Related Art 
     In a cellular mobile radio terminal (for example, cf. 3GPP STANDARDS TS25.331, TS25.304, TS24.008), neighbor cells are searched at a standby time to maintain preferable receiving quality at any time. If, as a result of the search, a cell of preferable receiving quality is detected and it is discriminated on the basis of predetermined discrimination standards that a serving cell needs to be changed, the mobile radio terminal receives information from the cell and discriminates the necessity of location registration from a network number, location registration area number, and the like included in the received information. 
     If the mobile radio terminal discriminates that the location registration needs to be executed, the mobile radio terminal executes a location registration process. 
     At this time, in response to the location registration request transmitted to the network, a cause value indicating a location registration rejection such as roaming prohibition is often transmitted from the network to reject the location registration. In this case, the mobile radio terminal recognizes that the location registration area where the location registration request has been made is an area of roaming prohibition, from the notification, and stores the location registration area number as a roaming prohibition area. 
     After that, when the mobile radio terminal receives the information of the neighbor cell, the mobile radio terminal collates the location registration area number notified by the information with the location registration area number of the roaming prohibition area stored in the terminal. If the location registration area numbers match, the mobile radio terminal recognizes that the location registration area is the area of roaming prohibition, and operates not to execute the location registration. 
     In the mobile radio terminal of the cellular system, the cell is reselected in accordance with movement, in the above steps. However, if the condition that the receiving quality of the roaming prohibition cell is high is maintained as a result of search of the neighbor cell, the process of receiving the information from the roaming prohibition cell is repeated and the current consumption is therefore increased. 
     To discriminate whether the cell detected by the search prohibits roaming, it is necessary to receive the information and discriminate whether the network number and the location registration area number in the information match those of the roaming prohibition cell stored in the mobile radio terminal, as described above. For this reason, the process of receiving the information is required, which results in the above problem. 
     To solve this problem, a method of using the frequency of the prohibition cell as a prohibition frequency, excluding the prohibition frequency from the search and not executing the process of receiving the information of the prohibition cell has been proposed (cf., for example, Jpn. Pat. Appln. KOKAI Publication No. 2006-311329). 
     Since reception in a specified frequency is prohibited in this method, no problem occurs in a case of prohibiting roaming in unit of network. However, if roaming is prohibited in unit of location registration area, in the networks of the same frequency, the location registration area where roaming is not prohibited is regarded as the roaming prohibition area and roaming cannot be executed. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has been accomplished to solve the above-described problems. The object of the present invention is to provide a mobile radio terminal, capable of reducing a power consumed for the process of receiving the information from the base station and preventing delay in cell detection caused by an unnecessary information receiving process, even when roaming is prohibited in unit of location registration area. 
     To achieve this object, an aspect of the present invention is a mobile radio terminal, establishing radio communications with a base station which is accommodated in a mobile communications network and which forms a cell. The mobile radio terminal comprises: a storage unit which stores identification information of a cell where roaming is rejected; a detecting unit which detects cells by executing reception using a plurality of elements of the identification information if a receiving quality from the base station is deteriorated; and a receiving unit which receives notification information from cells other than cells having identification information stored in the storage unit, of the cells detected by the detecting unit. 
     In the present invention, the identification information of the cell where roaming is rejected is stored, the cell is detected in a case where the receiving quality of the reception from the base station is deteriorated, and notification information is received from the cell other than the cell having identification information stored. 
     Since the reception of the identification information from the cell where roaming is rejected is not executed, the present invention can provide a mobile radio terminal, capable of reducing a power consumed for the process of receiving the information from the base station and preventing delay in cell detection caused by an unnecessary information receiving process, even when roaming is prohibited in each cell. 
     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 embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a block diagram showing a configuration of a mobile radio terminal according to a first embodiment of the present invention; 
         FIG. 2  is an illustration describing information stored in a storage unit of the mobile radio terminal shown in  FIG. 1 ; 
         FIG. 3  is a flowchart describing a location registration process of the mobile radio terminal shown in  FIG. 1 ; 
         FIG. 4  is a flowchart describing a reselection process of the mobile radio terminal shown in  FIG. 1 ; 
         FIG. 5  is a block diagram showing a configuration of a mobile radio terminal according to a second embodiment of the present invention; 
         FIG. 6  is an illustration describing information stored in a storage unit of the mobile radio terminal shown in  FIG. 5 ; 
         FIG. 7  is a flowchart describing a location registration process of the mobile radio terminal shown in  FIG. 5 ; 
         FIG. 8  is a flowchart describing a reselection process of the mobile radio terminal shown in  FIG. 5 ; 
         FIG. 9  is a block diagram showing a configuration of a mobile radio terminal according to a third embodiment of the present invention; 
         FIG. 10  is an illustration describing information stored in a storage unit of the mobile radio terminal shown in  FIG. 9 ; 
         FIG. 11  is a flowchart describing a location registration process of the mobile radio terminal shown in  FIG. 9 ; and 
         FIG. 12  is a flowchart describing a reselection process of the mobile radio terminal shown in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described below with reference to the accompanying drawings. 
     (First Embodiment) 
       FIG. 1  shows a configuration of a mobile radio terminal according to a first embodiment of the present invention. 
     The mobile radio terminal comprises an antenna  10 , a transmitting-receiving unit  200 , a signal processing unit  300 , a storage unit  401 , and a control unit  101 . The mobile radio terminal is employed in, for example, a mobile radio communications system of W-CDMA (Wideband Code Division Multiple Access) to execute speech communications and data communications. 
     The transmitting-receiving unit  200  executes radio communications in W-CDMA with the base station BS accommodated in a mobile communications network via the antenna  10 . More specifically, a carrier frequency and PSC are directed to the transmitting-receiving unit  200  by the control unit  101 , on the basis of a modulation signal generated by the signal processing unit  300 , and the transmitting-receiving unit  200  generates a radio signal of the carrier frequency by using the PSC. 
     In addition, a carrier frequency and PSC are directed to the transmitting-receiving unit  200  by the control unit  101 , and the transmitting-receiving unit  200  receives a radio signal of the carrier frequency by using the PSC. The result of reception is output to the signal processing unit  300  and the control unit  101 . The transmitting-receiving unit  200  has a function of detecting quality of the received signal, and notifies the detected receiving quality to the control unit  101 . 
     The signal processing unit  300  encodes a transmission speech signal. The signal processing unit  300  also generates the modulation signal on the basis of the speech data and the other data obtained by encoding, and outputs the modulation signal to the transmitting-receiving unit  200 . In addition, the signal processing unit  300  demodulates the signal received by the transmitting-receiving unit  200  and decodes the result of modulation to obtain speech data and the like and detect the signal transmitted from the base station BS. 
     The storage unit  401  stores control programs and control data of the mobile radio terminal, inherent identification information assigned to the mobile radio terminal and the user, and a number of PSC (Primary Scrambling Code), besides telephone book data associating names with telephone numbers, data obtained from data communications, and downloaded data. The storage unit  401  comprises a prohibition cell list storage area  401   a , a prohibition count storage area  401   b , a candidate cell list storage area  401   c  and the like. 
     The prohibition cell list storage area  401   a  stores identification information PN of PSC used for communications in a cell where roaming is prohibited, as shown in  FIG. 2 . In this example, the prohibition cell list storage area  401   a  stores identification information of five PSC PN 1 -PN 5 , and older information is erased when new information is stored. 
     The prohibition count storage area  401   b  is an area where values obtained by counting by PSC the number of times of checking possibility in receiving the notified information in a roaming prohibition cell by a reselection process to be described later are stored as shown in  FIG. 2 . The candidate cell list storage area  401   c  is an area where a list of identification information of PSC of candidate cells arranged in the order of higher receiving quality is stored. 
     The control unit  101  controls all the units of the mobile radio terminal on the basis of the control programs and control data stored in the storage unit  401 , executes control on a staying cell, requests the base station BS to execute the location registration, manages radio resources of the mobile radio terminal, and controls setting and opening of a radio connection. 
     More specifically, the control unit  101  comprises a location registration control unit  101   a  configured to execute the location registration for the base station BS if necessary, a reselection control unit  101   b  configured to execute the reselection of cells if the receiving condition becomes worse, and the like. 
     The mobile radio terminal comprises a speaker configured to output a reception speech signal, a microphone configured to input a transmission speech signal, a unit configured to convert the speech data into the reception speech signal, a unit configured to convert the transmission speech signal into the speech data, a display unit configured to display images on the basis of the reception data, an operation unit configured to accept a request from the user, and the like, though they are not shown in  FIG. 1 . 
     Next, operations of the mobile radio terminal having the above-explained configuration will be described. In the following descriptions, steps of establishing a communications link with the base station BS, control to implement speech communications and data communications, and registration, calling and edition of telephone book data and the like are omitted, but operations relating to location registration and reselection are described. 
       FIG. 3  shows a flowchart of a location registration process, which is executed by the location registration control unit  101   a  of the control unit  101 . A control program for implementing a control represented by the flowchart is stored in the storage unit  401 . This process is implemented if a cell for location registration can be specified. 
     First, in step  3   a , the location registration control unit  101   a  controls the transmitting-receiving unit  200  to transmit a location registration request to a cell which is specified by the control unit  101  and is to be subjected to location registration (for example, a cell having preferable receiving quality detected by the transmitting-receiving unit  200 , as a result of the cell search). The location registration control unit  101   a  proceeds to step  3   b.    
     The transmitting-receiving unit  200  transmits the location registration request to the cell (base station BS). More specifically, the location registration control unit  101   a  notifies the transmitting-receiving unit  200  of PSC used in the cell which is to be subjected to location registration. The transmitting-receiving unit  200  makes the location registration request to the cell by transmitting the location registration request by using the notified PSC. 
     In step  3   b , the location registration control unit  101   a  controls the transmitting-receiving unit  200  to receive a response signal responding to the location registration request from the cell. More specifically, the location registration control unit  101   a  notifies the identification information of the PSC used in the cell to the transmitting-receiving unit  200 , and the transmitting-receiving unit  200  receives the response signal by using the PSC corresponding to the notified identification information. 
     The location registration control unit  101   a  refers to the response signal from the cell detected by the signal processing unit  300  and discriminates whether or not the cell accepts the location registration request made in step  3   a . If the response signal indicates the cell accepts (permits) the location registration request, the location registration control unit  101   a  proceeds to step  3   c . If the response signal indicates the cell does not accept (rejects) the location registration request, the location registration control unit  101   a  proceeds to step  3   .    
     In step  3   c , the location registration control unit  101   a  controls the transmitting-receiving unit  200  and the signal processing unit  300  to execute the location registration process and end this process. More specifically, in the location registration process, the location registration control unit  101   a  establishes communications with the base station BS belonging to the cell, transmits the identification information of the own terminal and the like, and executes registration in the position management database in the network. 
     In step  3   d , the location registration control unit  101   a  refers to a cause value included in the response signal received from the cell and detects the reason why the location registration request has not been accepted. The location registration control unit  101   a  proceeds to step  3   e  if the cause value represents prohibition of roaming or proceeds to step  3   f  if the cause value represents elements other than prohibition of roaming. 
     In step  3   e , the location registration control unit  101   a  stores identification information PN n  of the PSC corresponding to the cell where roaming is prohibited, in the prohibition cell list storage area  401   a , and proceeds to step  3   f.    
     In step  3   f , the location registration control unit  101   a  executes a location registration rejection process and ends this process. More specifically, in the location registration rejection process, the location registration control unit  101   a  erases the identification information of the area, and stores the identification information of the network and the area in the prohibition network list and the prohibition area list, in accordance with the cause value, and ends the location registration process. These processes are provided in 3GPP STANDARDS TS24.018, TS25.331, TS25.304, TS24.008. 
       FIG. 4  is a flowchart showing the reselection process, which is executed by the reselection control unit  101   b  of the control unit  101 . A control program for implementing a control shown in the flowchart is stored in the storage unit  401 . This process is executed when it is discriminated that the reselection of cells needs to be executed since the receiving quality of the currently serving cell is deteriorated, for example, when it is discriminated that the reselection of cells needs to be executed at every discrimination of the receiving quality of the currently serving cell at every discontinuous reception. 
     First, in step  4   a , the reselection control unit  101   b  notifies the transmitting-receiving unit  200  of the identification of a plurality of PSC to urge the transmitting-receiving unit  200  to execute neighbor cell search. Then, the reselection control unit  101   b  proceeds to step  4   b . The transmitting-receiving unit  200  receives pilot signals transmitted from the cell and detects their receiving qualities, by sequentially using PSC corresponding to the identification information notified by the reselection control unit  101   b , and notifies the control unit  101  of the detected receiving qualities together with the identification information of the PSC. 
     In step  4   b , the reselection control unit  101   b  detects the PSC by which receiving qualities higher than predetermined receiving qualities can be obtained, on the basis of the receiving qualities notified by the transmitting-receiving unit  200  in step  4   a , creates a candidate list in which elements of the identification information of the detected PSC are arranged in an order of higher receiving qualities, and stores the candidate list in the candidate cell list storage area  401   c . Then, the reselection control unit  101   b  proceeds to step  4   c . In other words, in step  4   b , the reselection control unit  101   b  creates a candidate list in which the PSC considered desirable as candidates of the reselection are arranged in an order of higher possibilities. 
     In step  4   c , the reselection control unit  101   b  discriminates whether or not the identification information of at least one PSC is included in the candidate list created in step  4   b . If the identification information of at least one PSC is included in the candidate list, the reselection control unit  101   b  proceeds to step  4   d . If the candidate list does not include the identification information of any PSC, the reselection control unit  101   b  ends the process. If it is discriminated that the reselection of cells needs to be executed again at a next discontinuous reception time, the reselection control unit  101   b  executes this flow from the first step. 
     In step  4   d , the reselection control unit  101   b  selects one PSC, in the candidate list stored in the candidate cell list storage area  401   c , and proceeds to step  4   e . When the reselection control unit  101   b  proceeds from step  4   c  to step  4   d , the reselection control unit  101   b  selects the PSC of the highest order in the candidate list. When the reselection control unit  101   b  proceeds from step  4   g  or step  4   l  to step  4   d , the reselection control unit  101   b  selects the PSC of the order next to the PSC selected in previous step  4   d.    
     In other words, for example, if the reselection control unit  101   b  selects the PSC of the highest order in previous step  4   d , the reselection control unit  101   b  selects the PSC of the second order in current step  4   d . If the reselection control unit  101   b  selects the PSC of the third order in previous step  4   d , the reselection control unit  101   b  selects the PSC of the fourth order in current step  4   d . If the reselection control unit  101   b  selects the PSC of the lowest (fifth) order in previous step  4   d , the reselection control unit  101   b  selects the PSC of the highest (first) order in current step  4   d.    
     In step  4   e , the reselection control unit  101   b  discriminates whether or not the identification information PN x  of the PSC selected in step  4   d  is stored in the prohibition cell list storage area  401   a . If the identification information PN x  matches any one of PN 1 -PN 5  stored in the prohibition cell list storage area  401   a , i.e. if the identification information PN x  is the PSC of the prohibition cell, the reselection control unit  101   b  proceeds to step  4   f . If the identification information PN x  does not match any one of PN 1 -PN 5 , i.e. if the identification information PN x  is not the PSC of the prohibition cell, the reselection control unit  101   b  proceeds to step  4   i.    
     In step  4   f , the reselection control unit  101   b  increments the count value of the prohibition count storage area  401   b  corresponding to the identification information PN x  of the PSC selected in step  4   d , by one. Then, the reselection control unit  101   b  proceeds to step  4   g.    
     In step  4   g , the reselection control unit  101   b  discriminates whether or not the count value of the prohibition count storage area  401   b  corresponding to the identification information PN x  of the PSC selected in step  4   d , is equal to or more than a preset threshold value “5”. If the count value of the prohibition count storage area  401   b  is equal to or more than the preset threshold value, i.e. if the loop process in steps  4   d  to  4   g  corresponding to the identification information PN x  the PSC selected in step  4   d  is repeated at the times equal to or more than a preset threshold value, the reselection control unit  101   b  proceeds to step  4   h . If the count value of the prohibition count storage area  401   b  is less than the preset threshold value, i.e. if the loop process in steps  4   d  to  4   g  is not repeated at the times equal to or more than a preset threshold value, the reselection control unit  101   b  proceeds to step  4   d.    
     In step  4   h , the reselection control unit  101   b  resets the count value of the prohibition count storage area  401   b  corresponding to the identification information PN x  of the PSC selected in step  4   d  to 0. The reselection control unit  101   b  proceeds to step  4   i.    
     In step  4   i , the reselection control unit  101   b  notifies of the identification information PN x  of the PSC selected in step  4   d  and controls the transmitting-receiving unit  200  to receive the notification information transmitted from the cell using the PSC. Then, the reselection control unit  101   b  proceeds to step  4   j . The transmitting-receiving unit  200  executes the reception using the PSC corresponding to the identification information notified by the reselection control unit  101   b , and the signal processing unit  300  thereby detects the notification information from the received signal. 
     The reselection control unit  101   b  executes the reselection process in step  4   j , and then proceeds to step  4   k . The reselection process includes processes of reading the location registration area number from the notification information received in step  4   i  and, if the location registration area number is different from the currently registered location registration area number, controlling the transmitting-receiving unit  200  and the signal processing unit  300  to transmit the location registration request to the base station BS that has transmitted the notification information received in step  4   i , under predetermined protocol. 
     In step  4   k , the reselection control unit  101   b  discriminates whether or not the location registration request made in step  4   j  has been accepted. If the location registration request has not been accepted, the reselection control unit  101   b  proceeds to step  4   l . If the location registration request has been accepted and if the location registration does not need to be executed, the reselection control unit  101   b  controls the transmitting-receiving unit  200  and the signal processing unit  300  to establish communications with the base station BS, start camping for an incoming call, and ends this process, according to a predetermined protocol. 
     In step  4   l , the reselection control unit  101   b  discriminates whether or not the notification information has been received in step  4   i  at, at least, one time in relation to all the PSC included in the candidate list created in step  4   b . If the notification information has been received in step  4   i  at, at least, one time, the reselection control unit  101   b  ends this process. Then, if it is discriminated that the reselection of the cells is required again at a next discontinuous reception, the reselection control unit  101   b  executes this flow from the first step. If the notification information has not been received in relation to all the PSC, the reselection control unit  101   b  proceeds to step  4   d.    
     In the mobile radio terminal having the above-described configuration, the PSC used in the roaming prohibition cell is prestored. After that, if the selection of the cells is required for the reason that the receiving conditions become worse or other reasons, the PSC of the neighbor cells are detected and listed as candidates, the notification information is received from the cell using the PSC other than the roaming prohibition cell in the list, and the reselection is executed. 
     Therefore, since the notification information is received by positively using the PSC other than the PSC of the cell which has been discriminated as the roaming prohibition cell, reception of the notification information from the roaming prohibition cell is restricted even if the roaming prohibition cell is detected as the neighbor cell (candidate for the reselection). 
     For this reason, even if roaming is prohibited in each cell, reception of the notification information from the roaming prohibition cell which cannot consequently carry out the reselection is restricted (limited) and unnecessary electric power to be wasted for this process can be reduced. In addition, delay in detecting the cell due to unnecessary reception of the notification information can be prevented. 
     In general, since the PSC is repeatedly used in the same network, the cell cannot be uniquely distinguished according to the PSC but, normally, the assignment of the PSC to the cell is executed such that the same PSC is not used in a plurality of cells in a comparatively small region. However, since the PSC is finite, the same PSC may be repeatedly used in the entire network. In other words, the PSC used in the roaming prohibition cell may be used in a remote cell where roaming can be executed. If it is used as the PSC of the roaming prohibition cell, it may cause any problems at the moving mobile radio terminal. 
     In the mobile radio terminal having the above-described configuration, however, if the PSC included in the candidate list of the neighbor cell is the PSC of the roaming prohibition cell, the counter is incremented until the count value reaches a predetermined count and then the notification information is received from the cell using the PSC. 
     For this reason, even if the mobile radio terminal moves to the cell where roaming can be executed and which uses the same PSC as the PSC of the roaming prohibition cell, the notification information can be received when the time elapses until the counter counts a predetermined value, and occurrence of the problem can be prevented. 
     In addition, after the counter is incremented until the count value reaches a predetermined count, the notification information is received from the cell using the PSC. If the used PSC is the PSC of the roaming prohibition cell, the count value is reset to 0, the counter is incremented until the count value reaches a predetermined count, and the notification information is received from the cell using the PSC. 
     For this reason, even if the count value of the counter reaches a predetermined count and then desirable receiving quality can be obtained as the candidates for the reselection, the notification information is not sequentially received. In addition, even if the used PSC is discriminated as the PSC of the roaming prohibition cell, the notification information is received again from the cell using the PSC when the count value of the counter reaches a predetermined count. In other words, even if the used PSC is the PSC of the roaming prohibition cell, the notification information is discontinuously received from the cell using the PSC and the above problem caused by a movement to be made later can be thereby prevented. 
     Incidentally, when the power consumption was measured under the condition that a single roaming prohibition cell is always detected at the highest quality, an effect of reducing the power consumption at 40% was confirmed under certain conditions, by executing the method of receiving the notification information at one time at every five times of detection, as compared with a case where the present invention is not employed. 
     (Second Embodiment) 
     Next, a mobile radio terminal according to the second embodiment of the present invention will be described. 
       FIG. 5  shows a configuration of a mobile radio terminal according to the second embodiment. 
     The mobile radio terminal comprises an antenna  10 , a transmitting-receiving unit  200 , a signal processing unit  300 , a storage unit  402 , and a control unit  102 . The mobile radio terminal is employed in, for example, a mobile radio communications system of W-CDMA (Wideband Code Division Multiple Access) to execute speech communications and data communications. 
     The transmitting-receiving unit  200  executes radio communications in W-CDMA with the base station BS accommodated in a mobile communications network via the antenna  10 . More specifically, a carrier frequency and PSC are directed to the transmitting-receiving unit  200  by the control unit  102 , on the basis of a modulation signal generated by the signal processing unit  300 , and the transmitting-receiving unit  200  generates a radio signal of the carrier frequency by using the PSC. 
     In addition, a carrier frequency and PSC are directed to the transmitting-receiving unit  200  by the control unit  102 , and the transmitting-receiving unit  200  receives a radio signal of the carrier frequency by using the PSC. The result of reception is output to the signal processing unit  300  and the control unit  102 . The transmitting-receiving unit  200  has a function of detecting quality of the received signal, and notifies the detected receiving quality to the control unit  102 . 
     The signal processing unit  300  encodes a transmission speech signal. The signal processing unit  300  also generates the modulation signal on the basis of the speech data and the other data obtained by encoding, and outputs the modulation signal to the transmitting-receiving unit  200 . In addition, the signal processing unit  300  demodulates the signal received by the transmitting-receiving unit  200  and decodes the result of modulation to obtain speech data and the like and detect the signal transmitted from the base station BS. 
     The storage unit  402  stores control programs and control data of the mobile radio terminal, inherent identification information assigned to the mobile radio terminal and the user, and a number of PSC (Primary Scrambling Code), besides telephone book data associating names with telephone numbers, data obtained from data communications, and downloaded data. The storage unit  402  comprises a prohibition cell list storage area  402   a , a prohibition time storage area  402   b , a candidate cell list storage area  402   c  and the like. 
     The prohibition cell list storage area  402   a  stores identification information PN of PSC used for communications in a cell where roaming is prohibited, as shown in  FIG. 6 . In this example, the prohibition cell list storage area  402   a  stores identification information of five PSC PN 1 -PN 5 , and older information is erased when new information is stored. 
     The prohibition time storage area  402   b  is an area where reselection prohibition end time Tm is stored by each PSC used for the communications in the cell in which roaming is prohibited, as shown in  FIG. 6 . The candidate cell list storage area  402   c  is an area where a list of identification information of PSC of candidate cells arranged in the order of higher receiving quality is stored. 
     The control unit  102  controls all the units of the mobile radio terminal on the basis of the control programs and control data stored in the storage unit  402 , executes control on a staying cell, requests the base station BS to execute the location registration, manages radio resources of the mobile radio terminal, and controls setting and opening of a radio connection. The control unit  102  has a function of measuring the time. 
     Here specifically, the control unit  102  comprises a location registration control unit  102   a  configured to execute the location registration for the base station BS if necessary, a reselection control unit  102   b  configured to execute the reselection of cells if the receiving condition becomes worse, and the like. 
     The mobile radio terminal comprises a speaker configured to output a reception speech signal, a microphone configured to input a transmission speech signal, a unit configured to convert the speech data into the reception speech signal, a unit configured to convert the transmission speech signal into the speech data, a display unit configured to display images on the basis of the reception data, an operation unit configured to accept a request from the user, and the like, though they are not shown in  FIG. 5 . 
     Next, operations of the mobile radio terminal having the above-explained configuration will be described. In the following descriptions, steps of establishing a communications link with the base station BS, control to implement speech communications and data communications, and registration, calling and edition of telephone book data and the like are omitted, but operations relating to location registration and reselection are described. 
       FIG. 7  shows a flowchart of a location registration process, which is executed by the location registration control unit  102   a  of the control unit  102 . A control program for implementing a control represented by the flowchart is stored in the storage unit  402 . This process is implemented if a cell for location registration can be specified. 
     First, in step  7   a , the location registration control unit  102   a  controls the transmitting-receiving unit  200  to transmit a location registration request to a cell which is specified by the control unit  102  and is to be subjected to location registration (for example, a cell having preferable receiving quality detected by the transmitting-receiving unit  200 , as a result of the cell search). The location registration control unit  102   a  proceeds to step  7   b.    
     The transmitting-receiving unit  200  transmits the location registration request to the cell (base station BS). More specifically, the location registration control unit  102   a  notifies the transmitting-receiving unit  200  of PSC used in the cell which is to be subjected to location registration. The transmitting-receiving unit  200  makes the location registration request to the cell by transmitting the location registration request by using the notified PSC. 
     In step  7   b , the location registration control unit  102   a  controls the transmitting-receiving unit  200  to receive a response signal responding to the location registration request from the cell. More specifically, the location registration control unit  102   a  notifies the identification information of the PSC used in the cell to the transmitting-receiving unit  200 , and the transmitting-receiving unit  200  receives the response signal by using the PSC corresponding to the notified identification information. 
     The location registration control unit  102   a  refers to the response signal from the cell detected by the signal processing unit  300  and discriminates whether or not the cell accepts the location registration request made in step  7   a . If the response signal indicates the cell accepts (permits) the location registration request, the location registration control unit  102   a  proceeds to step  7   c . If the response signal indicates the cell does not accept (rejects) the location registration request, the location registration control unit  102   a  proceeds to step  7   d.    
     In step  7   c , the location registration control unit  102   a  controls the transmitting-receiving unit  200  and the signal processing unit  300  to execute the location registration process and end this process. More specifically, in the location registration process, the location registration control unit  102   a  establishes communications with the base station BS belonging to the cell, transmits the identification information of the own terminal and the like, and executes registration in the position management database in the network. 
     In step  7   d , the location registration control unit  102   a  refers to a cause value included in the response signal received from the cell and defects the reason why the location registration request has not been accepted. The location registration control unit  102   a  proceeds to step  7   e  if the cause value represents prohibition of roaming or proceeds to step  7   g  if the cause value represents elements other than prohibition of roaming. 
     In step  7   e , the location registration control unit  102   a  stores identification information PN n  of the PSC corresponding to the cell where roaming is prohibited, in the prohibition cell list storage area  402   a . Then, the location registration control unit  102   a  proceeds to step  7   f.    
     In step  7   f , the location registration control unit  102   a  stores the time which has elapsed by a preset time (for example, 25 seconds) from the current time, as a prohibition end time, in association with the PSC stored in step  7   e , in the prohibition time storage area  402   b . The location registration control unit  102   a  proceeds to step  7   g.    
     In step  7   g , the location registration control unit  102   a  executes a location registration rejection process and ends this process. More specifically, in the location registration rejection process, the location registration control unit  102   a  erases the identification information of the area, and stores the identification information of the network and the area in the prohibition network list and the prohibition area list, in accordance with the cause value, and ends the location registration process. These processes are provided in 3GPP STANDARDS TS24.018, TS25.331, TS25.304, TS24.008. 
       FIG. 8  is a flowchart showing the reselection process, which is executed by the reselection control unit  102   b  of the control unit  102 . A control program for implementing a control shown in the flowchart is stored in the storage unit  402 . This process is executed when it is discriminated that the reselection of cells needs to be executed since the receiving quality of the currently serving cell is deteriorated, for example, when it is discriminated that the reselection of cells needs to be executed at every discrimination of the receiving quality of the currently serving cell at every discontinuous reception. 
     First, in step  8   a , the reselection control unit  102   b  notifies the transmitting-receiving unit  200  of the identification of a plurality of PSC to urge the transmitting-receiving unit  200  to execute neighbor cell search. Then, the reselection control unit  102   b  proceeds to step  8   b . The transmitting-receiving unit  200  receives pilot signals transmitted from the cell and detects their receiving qualities, by sequentially using PSC corresponding to the identification information notified by the reselection control unit  102   b , and notifies the control unit  102  of the detected receiving qualities together with the identification information of the PSC. 
     In step  8   b , the reselection control unit  102   b  detects the PSC by which receiving qualities higher than predetermined receiving qualities can be obtained, on the basis of the receiving qualities notified by the transmitting-receiving unit  200  in step  8   a , creates a candidate list in which elements of the identification information of the detected PSC are arranged in an order of higher receiving qualities, and stores the candidate list in the candidate cell list storage area  402   c . Then, the reselection control unit  102   b  proceeds to step  8   c . In other words, in step  8   b , the reselection control unit  102   b  creates a candidate list in which the PSC considered desirable as candidates of the reselection are arranged in an order of higher possibilities. 
     In step  8   c , the reselection control unit  102   b  discriminates whether or not the identification information of at least one PSC is included in the candidate list created in step  8   b . If the identification information of at least one PSC is included in the candidate list, the reselection control unit  102   b  proceeds to step  8   d . If the candidate list does not include the identification information of any PSC, the reselection control unit  102   b  ends the process. If it is discriminated that the reselection of cells needs to be executed again at a next wait and discontinuous reception time, the reselection control unit  102   b  executes this flow from the first step. 
     In step  8   d , the reselection control unit  102   b  selects one PSC, in the candidate list stored in the candidate cell list storage area  402   c , and proceeds to step  8   e . When the reselection control unit  102   b  proceeds from step  8   c  to step  8   d , the reselection control unit  102   b  selects the PSC of the highest order in the candidate list. When the reselection control unit  102   b  proceeds from step  8   f  or step  8   j  to step  8   d , the reselection control unit  102   b  selects the PSC of the order next to the PSC selected in previous step  8   d.    
     In other words, for example, if the reselection control unit  102   b  selects the PSC of the highest order in previous step  8   d , the reselection control unit  102   b  selects the PSC of the second order in current step  8   d . If the reselection control unit  102   b  selects the PSC of the third order in previous step  8   d , the reselection control unit  102   b  selects the PSC of the fourth order in current step  8   d . If the reselection control unit  102   b  selects the PSC of the lowest (fifth) order in previous step  8   d , the reselection control unit  102   b  selects the PSC of the highest (first) order in current step  8   d.    
     In step  8   e , the reselection control unit  102   b  discriminates whether or not the identification information PN x  of the PSC selected in step  8   d  is stored in the prohibition cell list storage area  402   a . If the identification information PN x  matches any one of PN 1 -PN 5  stored in the prohibition cell list storage area  402   a , i.e. if the identification information PN x  is the PSC of the prohibition cell, the reselection control unit  102   b  proceeds to step  8   f . If the identification information PN x  does not match any one of PN 1 -PN 5 , i.e. if the identification information PN x  is not the PSC of the prohibition cell, the reselection control unit  102   b  proceeds to step  8   g.    
     In step  8   f , the reselection control unit  102   b  refers to prohibition end time Tx of the prohibition time storage area  402   b  corresponding to the identification information PN x  of the PSC selected in step  8   d , and discriminates whether or not the current time has passed the prohibition end time Tx. If the current time has passed the prohibition end time Tx, the reselection control unit  102   b  proceeds to step  4   g . If the current time has not passed the prohibition end time Tx, the reselection control unit  102   b  proceeds to step  4   d.    
     In step  8   g , the reselection control unit  102   b  notifies the transmitting-receiving unit  200  of the identification information PN x  of the PSC selected in step  8   d , and controls the transmitting-receiving unit  200  to receive the identification information transmitted from the cell using the PSC. Then, the reselection control unit  102   b  proceeds to step  8   h . The transmitting-receiving unit  200  executes the reception using the PSC corresponding to the identification information notified by the reselection control unit  102   b , and the signal processing unit  300  thereby detects the notification information from the received signal. 
     The reselection control unit  102   b  executes the reselection process in step  8   h , and then proceeds to step  8   i . The reselection process includes processes of reading the location registration area number from the notification information received in step  8   g  and, if the location registration area number is different from the currently registered location registration area number, controlling the transmitting-receiving unit  200  and the signal processing unit  300  to transmit the location registration request to the base station BS that has transmitted the notification information received in step  8   g , under a predetermined protocol. 
     In step  8   i , the reselection control unit  102   b  discriminates whether or not the location registration request made in step  8   h  has been accepted. If the location registration request has not been accepted, the reselection control unit  102   b  proceeds to step  8   j . If the location registration request has been accepted and if the location registration does not need to be executed, the reselection control unit  102   b  controls the transmitting-receiving unit  200  and the signal processing unit  300  to establish communications with the base station BS, start camping for an incoming call, and ends this process, according to a predetermined protocol. 
     In step  8   j , the reselection control unit  102   b  discriminates whether or not the notification information has been received in step  8   g  at, at least, one time in relation to all the PSC included in the candidate list created In step  8   b . If the notification information has been received at, at least, one time, the reselection control unit  102   b  ends this process. Then, if it is discriminated that the reselection of the cells is required again at a next discontinuous reception, the reselection control unit  102   b  executes this flow from the first step. If the notification information has not been received in relation to all the PSC, the reselection control unit  102   b  proceeds to step  8   d.    
     In the mobile radio terminal having the above-described configuration, the PSC used in the roaming prohibition cell is prestored. After that, if the selection of the cells is required for the reason that the receiving conditions become worse or other reasons, the PSC of the neighbor cells are detected and listed as candidates, the notification information is received from the cell using the PSC other than the roaming prohibition cell in the list, and the reselection is executed. 
     Therefore, since the notification information is received by positively using the PSC other than the PSC of the cell which has been discriminated as the roaming prohibition cell, reception of the notification information from the roaming prohibition cell is restricted even if the roaming prohibition cell is detected as the neighbor cell (candidate for the reselection). 
     For this reason, even if roaming is prohibited in each cell, reception of the notification information from the roaming prohibition cell which cannot consequently carry out the reselection is restricted (limited) and unnecessary electric power to be wasted for this process can be reduced. In addition, delay in detecting the cell due to unnecessary reception of the notification information can be prevented. 
     In general, since the PSC is repeatedly used in the same network, the cell cannot be uniquely distinguished according to the PSC but, normally, the assignment of the PSC to the cell is executed such that the same PSC is not used in a plurality of cells in a comparatively small region. However, since the PSC is finite, the same PSC may be repeatedly used in the entire network. In other words, the PSC used in the roaming prohibition cell may be used in a remote cell where roaming can be executed. If it is used as the PSC of the roaming prohibition cell, inconvenience may be caused at the moving mobile radio terminal. 
     In the mobile radio terminal having the above-described configuration, however, if the PSC included in the candidate list of the neighbor cell is the PSC of the roaming prohibition cell, the notification information is received from the cell using the PSC after the time to prohibit the reselection has elapsed. 
     For this reason, even if the mobile radio terminal moves to the cell where roaming can be executed and which uses the same PSC as the PSC of the roaming prohibition cell, the notification information can be received when the prohibition time has elapsed. The above inconvenience can be thereby prevented. 
     In the second embodiment, the notification information is not received definitely until the end time of reselection prohibition has elapsed, but the invention is not limited to this. For example, if counting is executed for each candidate and the count value reaches a predetermined value, as described in the first embodiment, the notification information may be received irrespective of the end time of reselection prohibition. 
     In addition, in the second embodiment, the time to prohibit the reselection is set for each cell where roaming is prohibited, in step  7   f , and it is discriminated in step  8   f  whether the prohibition time has elapsed. Instead of this, however, the timer to prohibit the reselection may be started for each cell where roaming is prohibited, in step  7   f , and it may be discriminated in step  8   f  whether the timer counts a predetermined time or the timer stops after counting a predetermined time. 
     (Third Embodiment) 
     Next, a mobile radio terminal according to the third embodiment of the present invention will be described. 
       FIG. 9  shows a configuration of a mobile radio terminal according to the second embodiment. 
     The mobile radio terminal comprises an antenna  10 , a transmitting-receiving unit  200 , a signal processing unit  300 , a storage unit  403 , a control unit  103  and a GPS (Global Positioning System) receiving unit  500 . The mobile radio terminal is employed in, for example, a mobile radio communications system of W-CDMA (Wideband Code Division Multiple Access) to execute speech communications and data communications. 
     The transmitting-receiving unit  200  executes radio communications in W-CDMA with the base station BS accommodated in a mobile communications network via the antenna  10 . More specifically, a carrier frequency and PSC are directed to the transmitting-receiving unit  200  by the control unit  103 , on the basis of a modulation signal generated by the signal processing unit  300 , and the transmitting-receiving unit  200  generates a radio signal of the carrier frequency by using the PSC. 
     In addition, a carrier frequency and PSC are directed to the transmitting-receiving unit  200  by the control unit  103 , and the transmitting-receiving unit  200  receives a radio signal of the carrier frequency by using the PSC. The result of reception is output to the signal processing unit  300  and the control unit  103 . The transmitting-receiving unit  200  has a function of detecting quality of the received signal, and notifies the detected receiving quality to the control unit  103 . 
     The signal processing unit  300  encodes a transmission speech signal. The signal processing unit  300  also generates the modulation signal on the basis of the speech data and the other data obtained by encoding, and outputs the modulation signal to the transmitting-receiving unit  200 . In addition, the signal processing unit  300  demodulates the signal received by the transmitting-receiving unit  200  and decodes the result of modulation to obtain speech data and the like and detect the signal transmitted from the base station BS. 
     The storage unit  403  stores control programs and control data of the mobile radio terminal, inherent identification information assigned to the mobile radio terminal and the user, and a number of PSC (Primary Scrambling Code), besides telephone book data associating names with telephone numbers, data obtained from data communications, and downloaded data. The storage unit  403  comprises a prohibition cell list storage area  403   a , a prohibition position storage area  403   b , a candidate cell list storage area  403   c  and the like. 
     The prohibition cell list storage area  403   a  stores identification information PN of PSC used for communications in a cell where roaming is prohibited, as shown in  FIG. 10 . In this example, the prohibition cell list storage area  403   a  stores identification information of five PSC PN 1 -PN 5 , and older information is erased when new information is stored. 
     The prohibition position storage area  403   b  is an area where cell position data Pm is stored by each PSC used for the communications in the cell in which roaming is prohibited, as shown in  FIG. 10 . The candidate cell list storage area  403   c  is an area where a list of identification information of PSC of candidate cells arranged in the order of higher receiving quality is stored. 
     The GPS receiving unit  500  receives GPS signals transmitted from at least three GPS satellites and measures a position of the mobile radio terminal, in each preset cycle (for example, 1 second), and outputs position information (latitude, longitude and height) representing the measured position to the control unit  103 . Instead of the GPS receiving unit  500 , a receiving unit using service of measuring the position of the mobile radio terminal by the mobile communications network and the base station BS and obtaining the position information provided by the service from the base station BS may be provided. 
     The control unit  303  controls all the units of the mobile radio terminal on the basis of the control programs and control data stored in the storage unit  403 , executes control on a staying cell, requests the base station BS to execute the location registration, manages radio resources of the mobile radio terminal, and controls setting and opening of a radio connection. The control unit  103  has a function of measuring the time. 
     More specifically, the control unit  103  comprises a location registration control unit  103   a  configured to execute the location registration for the base station BS if necessary, a reselection control unit  103   b  configured to execute the reselection of cells if the receiving condition becomes worse, and the like. 
     The mobile radio terminal comprises a speaker configured to output a reception speech signal, a microphone configured to input a transmission speech signal, a unit configured to convert the speech data into the reception speech signal, a unit configured to convert the transmission speech signal into the speech data, a display unit configured to display images on the basis of the reception data, an operation unit configured to accept a request from the user, and the like, though they are not shown in  FIG. 9 . 
     Next, operations of the mobile radio terminal having the above-explained configuration will be described. In the following descriptions, steps of establishing a communications link with the base station BS, control to implement speech communications and data communications, and registration, calling and edition of telephone book data and the like are omitted, but operations relating to location registration and reselection are described. 
       FIG. 11  shows a flowchart of a location registration process, which is executed by the location registration control unit  103   a  of the control unit  103 . A control program for implementing a control represented by the flowchart is stored in the storage unit  403 . This process is implemented if a cell for location registration can be specified. 
     First, in step  11   a , the location registration control unit  103   a  controls the transmitting-receiving unit  200  to transmit a location registration request to a cell which is specified by the control unit  103  and is to be subjected to location registration (for example, a cell having preferable receiving quality detected by the transmitting-receiving unit  200 , as a result of the cell search). The location registration control unit  103   a  proceeds to step  11   b.    
     The transmitting-receiving unit  200  transmits the location registration request to the cell (base station BS). More specifically, the location registration control unit  103   a  notifies the transmitting-receiving unit  200  of PSC used in the cell which is to be subjected to location registration. The transmitting-receiving unit  200  makes the location registration request to the cell by transmitting the location registration request by using the notified PSC. 
     In step  11   b , the location registration control unit  103   a  controls the transmitting-receiving unit  200  to receive a response signal responding to the location registration request from the cell. More specifically, the location registration control unit  103   a  notifies the identification information of the PSC used in the cell to the transmitting-receiving unit  200 , and the transmitting-receiving unit  200  receives the response signal by using the PSC corresponding to the notified identification information. 
     The location registration control unit  103   a  refers to the response signal from the cell detected by the signal processing unit  300  and discriminates whether or not the cell accepts the location registration request made in step  11   a . If the response signal indicates the cell accepts (permits) the location registration request, the location registration control unit  103   a  proceeds to step  11   c . If the response signal, indicates the cell does not accept (rejects) the location registration request, the location registration control unit  103   a  proceeds to step  11   d.    
     In step  11   c , the location registration control unit  103   a  controls the transmitting-receiving unit  200  and the signal processing unit  300  to execute the location registration process and end this process. More specifically, in the location registration process, the location registration control unit  103   a  establishes communications with the base station BS belonging to the cell, transmits the identification information of the own terminal and the like, and executes registration in the position management database in the network. 
     In step  11   d , the location registration control unit  103   a  refers to a cause value included in the response signal received from the cell and detects the reason why the location registration request has not been accepted. The location registration control unit  103   a  proceeds to step  11   e  if the cause value represents prohibition of roaming or proceeds to step  11   g  if the cause value represents elements other than prohibition of roaming. 
     In step  11   e , the location registration control unit  103   a  stores identification information PN n  of the PSC corresponding to the cell where roaming is prohibited, in the prohibition cell list storage area  403   a . Then, the location registration control unit  103   a  proceeds to step  11   f.    
     In step  11   f , the location registration control unit  103   a  detects the position information of the cell where roaming is prohibited, on the basis of the position information measured by the GPS receiving unit  500 , and stores the detected position information as prohibited position data in association with the PSC stored in step  11   e , in the prohibition position storage area  403   b . The location registration control unit  103   a  proceeds to step  11   g.    
     In step  11   g , the location registration control unit  103   a  executes a location registration refection process and ends this process. More specifically, in the location registration rejection process, the location registration control unit  103   a  erases the identification information of the area, and stores the identification informatics of the network and the area in the prohibition network list and the prohibition area list, in accordance with the cause value, and ends the location registration process. These processes are provided in 3GPP STANDARDS TS24.018, TS25.331, TS25.304, TS24.008. 
       FIG. 12  is a flowchart showing the reselection process, which is executed by the reselection control unit  103   b  of the control unit  103 . A control program for implementing a control shown in the flowchart is stored in the storage unit  403 . This process is executes when it is discriminated that the reselection of cells needs to be executed since the receiving quality of the currently serving cell is deteriorated, for example, when it is discriminated that the reselection of cells needs to be executed at every discrimination of the receiving quality of the currently serving cell at every discontinuous reception. 
     First, in step  12   a , the reselection control unit  103   b  notifies the transmitting-receiving unit  200  of the identification of a plurality of PSC to urge the transmitting-receiving unit  200  to execute neighbor cell search. Then, the reselection control unit  103   b  proceeds to step  12   b . The transmitting-receiving unit  200  receives pilot signals transmitted from the cell and detects their receiving qualities, by sequentially using PSC corresponding to the identification information notified by the reselection control unit  103   b , and notifies the control unit  103  of the detected receiving qualities together with the identification information of the PSC. 
     In step  12   b , the reselection control unit  103   b  detects the PSC by which receiving qualities higher than predetermined receiving qualities can be obtained, on the basis of the receiving qualifies notified by the transmitting-receiving unit  200  in step  12   a , creates a candidate list in which elements of the identification information of the detected PSC are arranged in an order of higher receiving qualities, and stores the candidate list in the candidate cell list storage area  403   c . Then, the reselection control unit  103   b  proceeds to step  12   c . In other words, in step  12   b , the reselection control unit  103   b  creates a candidate list in which the PSC considered desirable as candidates of the reselection are arranged in an order of higher possibilities. 
     In step  12   c , the reselection control unit  103   b  discriminates whether or not the identification information of at least one PSC is included in the candidate list created in step  12   b . If the identification information of at least one PSC is included in the candidate list, the reselection control unit  103   b  proceeds to step  12   d . If the candidate list does not include the identification information of any PSC, the reselection control unit  103   b  ends the process. If it is discriminated that the reselection of cells needs to be executed again at a next discontinuous reception time, the reselection control unit  103   b  executes this flow from the first step. 
     In step  12   d , the reselection control unit  103   b  selects one PSC, in the candidate list stored in the candidate cell list storage area  403   c , and proceeds to step  12   e . When the reselection control unit  103   b  proceeds from step  12   c  to step  12   d , the reselection control unit  103   b  selects the PSC of the highest order in the candidate list. When the reselection control unit  103   b  proceeds from step  12   f  or step  12   j  to step  12   d , the reselection control unit  103   b  selects the PSC of the order next to the PSC selected in previous step  12   d.    
     In other words, for example, if the reselection control unit  103   b  selects the PSC of the highest order in previous step  12   d , the reselection control unit  103   b  selects the PSC of the second order in current step  12   d . If the reselection control unit  103   b  selects the PSC of the third order in previous step  12   d , the reselection control unit  103   b  selects the PSC of the fourth order in current step  12   d . If the reselection control unit  103   b  selects the PSC of the lowest (fifth) order in previous step  12   d , the reselection control unit  103   b  selects the PSC of the highest (first) order in current step  12   d.    
     In step  12   e , the reselection control unit  103   b  discriminates whether or not the identification information PN x  of the PSC selected in step  12   d  is stored in the prohibition cell list storage area  403   a . If the identification information PN x  matches any one of PN 1 -PN 5  stored in the prohibition cell list storage area  403   a , i.e. if the identification information PN x  is the PSC of the prohibition cell, the reselection control unit  103   b  proceeds to step  12   f . If the identification information PN x  does not match any one of PN 1 -PN 5 , i.e. if the identification information PN x  is not the PSC of the prohibition cell, the reselection control unit  103   b  proceeds to step  12   g.    
     In step  12   f , the reselection control unit  103   b  compares the position data P x  of the prohibition position storage area  403   b  corresponding to the identification information PN x  of the PSC selected in step  12   d , with the current position information obtained from the GPS receiving unit  500 , and discriminates whether or not the current position is separated from the position represented by the position data P x  in a preset distance Z meters or more. If the current position is separated from the position represented by the position data P x  in a preset distance Z meters or more, the reselection control unit  103   b  proceeds to step  12   g . If the current position is separated from the position represented by the position data P x  in less than Z meters, the reselection control unit  103   b  proceeds to step  12   d.    
     In step  12   g , the reselection control unit  103   b  notifies the transmitting-receiving unit  200  of the identification information PN x  of the PSC selected in step  12   d , and controls the transmitting-receiving unit  200  to receive the identification information transmitted from the cell using the PSC. Then, the reselection control unit  103   b  proceeds to step  12   h . The transmitting-receiving unit  200  executes the reception using the PSC corresponding to the identification information notified by the reselection control unit  103   b , and the signal processing unit  300  thereby detects the notification information from the received signal. 
     The reselection control unit  103   b  executes the reselection process in step  12   h , and then proceeds to step  12   i . The reselection process includes processes of reading the location registration area number from the notification information received in step  12   g  and, if the location registration area number is different from the currently registered location registration area number, controlling the transmitting-receiving unit  200  and the signal processing unit  300  to transmit the location registration request to the base station BS that has transmitted the notification information received in step  12   g , under a predetermined protocol. 
     In step  12   i , the reselection control unit  103   b  discriminates whether or not the location registration request made in step  12   h  has been accepted. If the location registration request has not been accepted, the reselection control unit  103   b  proceeds to step  12   j . If the location registration request has been accepted and if the location registration does not need to be executed, the reselection control unit  103   b  controls the transmitting-receiving unit  200  and the signal processing unit  300  to establish communications with the base station BS, start camping for an incoming call, and ends this process, according to a predetermined protocol. 
     In step  12   j , the reselection control unit  103   b  discriminates whether or not the notification information has been received in step  12   g  at, at least, one time in relation to all the PSC included in the candidate list created in step  12   b . If the notification information has been received at, at least, one time, the reselection control unit  103   b  ends this process. Then, if it is discriminated that the reselection of the cells is required again at a next discontinuous reception, the reselection control unit  103   b  executes this flow from the first step. If the notification information has not been received in relation to all the PSC, the reselection control unit  103   b  proceeds to step  12   d.    
     In the mobile radio terminal having the above-described configuration, the PSC used in the roaming prohibition cell is prestored. After that, if the selection of the cells is required for the reason that the receiving conditions become worse or other reasons, the PSC of the neighbor cells are detected and listed as candidates, the notification information is received from the cell using the PSC other than the roaming prohibition cell in the list, and the reselection is executed. 
     Therefore, since the notification information is received by positively using the PSC other than the PSC of the cell which has been discriminated as the roaming prohibition cell, reception of the notification information from the roaming prohibition cell is restricted even if the roaming prohibition cell is detected as the neighbor cell (candidate for the reselection). 
     For this reason, even if roaming is prohibited in each cell, reception of the notification information from the roaming prohibition cell which cannot consequently carry out the reselection is restricted (limited) and unnecessary electric power to be wasted for this process can be reduced. In addition, delay in detecting the cell due to unnecessary reception of the notification information can be prevented. 
     In general, since the PSC is repeatedly used in the same network, the cell cannot be uniquely distinguished according to the PSC but, normally, the assignment of the PSC to the cell is executed such that the same PSC is not used in a plurality of cells in a comparatively small region. However, since the PSC is finite, the same PSC may be repeatedly used in the entire network. In other words, the PSC used in the roaming prohibition cell may be used in a remote cell where roaming can be executed. If it is used as the PSC of the roaming prohibition cell, inconvenience may be caused at the moving mobile radio terminal. 
     In the mobile radio terminal having the above-described configuration, however, if the current position is remote from the position where the roaming prohibition cell is detected, in a preset distance Z or more, the notification information is received from the cell using the PSC. 
     For this reason, even if the mobile radio terminal moves to the cell where roaming can be executed and which uses the same PSC as the PSC of the roaming prohibition cell, the notification information can be received when mobile radio terminal moves in a preset distance, Z meters or more. The above inconvenience can be thereby prevented. 
     In the third embodiment, the notification information is not received definitely unless the mobile radio terminal is remote from the roaming prohibition cell in a predetermined distance Z or more, but the invention is not limited to this. For example, when counting is executed for each candidate and the count value reaches a predetermined value, as described in the first embodiment, the notification information may be received even if the mobile radio terminal is not remote from the roaming prohibition cell in a predetermined distance Z or more. In other words, the third embodiment can also be applied to the first embodiment or the second embodiment. 
     The present invention is not limited to the embodiments described above but the constituent elements of the invention can be modified in various manners without departing from the spirit and scope of the invention. Various aspects of the invention can also be extracted from any appropriate combination of a plurality of constituent elements disclosed in the embodiments. Some constituent elements may be deleted in all of the constituent elements disclosed in the embodiments. The constituent elements described in different embodiments may be combined arbitrarily. 
     For example, in the above-described embodiments, the PSC used in the cell where roaming is prohibited is stored and the cell where roaming is prohibited is discriminated on the basis of the stored PSC. In addition to this, the frequency used in the cell where roaming is prohibited is also stored, and the roaming prohibition cell is discriminated in terms of both the PSC and the frequency, to restrict (limit) reception of the notification information. 
     In other words, if the roaming request is not accepted by the cell, the frequency used for the roaming request is stored as the prohibited frequency in association with the PSC used in the cell where roaming is prohibited (steps  3   e ,  7   e ,  11   e ). In the reselection process, sets of the PSC of the candidate cells end the used frequencies are listed (steps  4   b ,  8   b ,  12   b ), one of the sets is selected (steps  4   d ,  8   d ,  12   d ), and it is discriminated whether the selected set is stored as the PSC used in the cell where roaming is prohibited, and the prohibited frequency (steps  4   e ,  8   e ,  12   e ). 
     Even by this control, reception of the notification information from the roaming prohibition cell where the reselection cannon be consequently carried out is restricted (limited), and unnecessary electric power to be wasted for this process can be reduced. In addition, delay on the cell detection caused by unnecessary reception of the notification information can be prevented. 
     Moreover, in the above-described embodiments, reception of the notification information is limited irrespective of the outgoing request from the user. However, when the user makes an emergency outgoing call to a police station or a fire station, the notification information may be sequentially received from the PSC having the higher receiving qualities, without limiting the cells (PSC) receiving the notification information. Special numbers for emergency outgoing calls are prestored in storing units  401  to  403 , for the discrimination of the emergency outgoing calls. If the special number is input via the operating unit, the control units  101  to  103  discriminate the input as the emergency outgoing call. 
     Needless to say, the present invention can also be variously modified within a scope which does not depart from the gist of the present invention. 
     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.