Abstract:
A 3G wireless control unit, a WiFi wireless control unit, and a WiMAX wireless control unit each select one data communication method from data communication methods that each supports, and any one supporting the selected data communication method performs communication using the selected data communication method. A 3G non-coverage area search processing unit, a WiFi non-coverage area search processing unit, and a WiMAX non-coverage area search processing unit each detect a base station supporting a data communication method that each supports. A search control unit controls the frequency of execution of a base-station detecting process performed by the WiMAX non-coverage area search processing unit on the basis of respective communication states and predetermined priorities of data communication methods.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2011-227450, filed on Oct. 14, 2011, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are directed to a wireless communication terminal and a method for controlling the wireless communication terminal. 
       BACKGROUND 
       [0003]    In recent years, various data communication methods, such as the 3G (3rd Generation) cellular phone method, fixed wireless communication standards (WiMax™ (Worldwide Interoperability for Microwave Access)), and wireless LAN standards (WiFi™ (Wireless Fidelity)), have been proposed. The data communication methods provide a variety of transmission rates and communication ranges. In general, a transmission rate and a communication range are in a trade-off relationship; therefore, it is difficult to simultaneously achieve a high transmission rate and a wide communication range in a single wireless transmission system. 
         [0004]    Consequently, communication suitable for an operator&#39;s demand is established by switching among data communication methods depending on the situation. In such a case, respective cells of different data communication methods may adjoin or overlap with each other. In a wireless communication system having a plurality of data communication methods as just described, a wireless communication terminal performs a search to determine whether there is any base station or access point supporting a data communication method that the wireless communication terminal supports in order to perform communication using the data communication method. 
         [0005]    Conventional technologies for such a search of an access point include a technology of changing the interval to perform a search depending on the communication quality (for example, Japanese Laid-open Patent Publication No. 2008-061015). Furthermore, as a wireless communication system using a plurality of data communication methods, there is proposed a conventional technology to determine which data wireless communication method is used to acquire standby paging on the basis of the priority order or the signal strength (for example, Japanese Laid-open Patent Publication No. 2006-262178). Moreover, there is proposed a conventional technology to perform handover by determining a wireless base station as a destination of handover on the basis of respective priorities of data communication methods (for example, Japanese Laid-open Patent Publication No. 2008-131587). 
         [0006]    However, in the conventional search methods, problems arise when, in a state where a high-priority data communication method based on a communication rate and a communication range, etc. is being used, a data communication method of which the priority is lower than that of the high-priority data communication method is low is unlikely to be used. Namely, in such a case, in spite of the fact that the lower-priority data communication method is unlikely to be used, a search using the lower-priority data communication method is frequently performed. Furthermore, also when the radio quality of the high-priority data communication method is good, a search using the lower-priority data communication method is frequently performed. Moreover, when three or more data communication methods are used, a search using all the data communication methods is not requested to be frequently performed. In this manner, in spite of the fact that normally, there is little advantage of frequently performing a search using any of data communication methods, a search using the data communication method is frequently performed, resulting in wasteful power consumption, and therefore, it is difficult to reduce power consumption. 
         [0007]    Furthermore, even if the conventional technology of changing the interval to perform a search depending on the communication quality is used, a fruitless search using a data communication method by which a search does not actually have to be performed so often arises, so it is difficult to reduce power consumption. Moreover, even if any of the technology to determine a data wireless communication method for standby paging and the technology to determine a destination of handover on the basis of priorities is used, a fruitless search arises, so it is difficult to reduce power consumption. 
       SUMMARY 
       [0008]    According to an aspect of an embodiment, a wireless communication terminal includes, a wireless communication unit that selects one data communication method from a plurality of data communication methods, and performs communication using the selected data communication method, a search processing unit that detects a base station supporting a data communication method other than the data communication method selected by the wireless communication unit, and a search control unit that controls frequency of execution of a base-station detecting process performed by the search processing unit using the data communication method other than the data communication method being used in the communication on the basis of respective communication states and predetermined priorities of the plurality of data communication methods. 
         [0009]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0010]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is a diagram illustrating communication areas in a case where there is a plurality of different data communication methods; 
           [0012]      FIG. 2  is a block diagram of a wireless communication terminal according to embodiments; 
           [0013]      FIG. 3  is a diagram of an example of a search-frequency determining table according to a first embodiment; 
           [0014]      FIG. 4  is a flowchart of a WiMAX search control determining process in the first embodiment; 
           [0015]      FIG. 5  is a flowchart of a WiMAX communication non-coverage area search frequency determining process in the first embodiment; 
           [0016]      FIG. 6  is a diagram of an example of a search-frequency determining table according to a second embodiment; 
           [0017]      FIG. 7  is a flowchart of a WiMAX communication non-coverage area search frequency determining process in the second embodiment; 
           [0018]      FIG. 8  is a diagram of an example of a search-frequency determining table according to a third embodiment; 
           [0019]      FIG. 9  is a flowchart of a WiMAX communication non-coverage area search frequency determining process in the third embodiment; and 
           [0020]      FIG. 10  is a diagram illustrating a hardware configuration of the wireless communication terminal. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    Preferred embodiments of the present invention will be explained with reference to accompanying drawings. Incidentally, the wireless communication terminal and the method for controlling the wireless communication terminal according to the present invention are not limited by the embodiments. The wireless communication terminal includes, for example, a cell-phone unit, a smartphone, and the like; however, the wireless communication terminal is not limited to these, and can be any other units that establish wireless communication using a plurality of data communication methods. 
       [a] First Embodiment 
       [0022]      FIG. 1  is a diagram illustrating communication areas in a case where there is a plurality of different data communication methods.  FIG. 2  is a block diagram of a wireless communication terminal according to embodiments. 
         [0023]    A wireless communication terminal  1  according to a first embodiment establishes wireless communication using 3G communication, WiMAX communication, and WiFi communication as data communication methods. A base station  2  in  FIG. 1  is a WiFi access point. A communication area  5  is a communication area of the base station  2 . A base station  3  is a WiMAX access point. A communication area  6  is a communication area of the base station  3 . Base stations  4 A to  4 C are base stations of the 3G communication. A communication area  7 A is a communication area of the base station  4 A. A communication area  7 B is a communication area of the base station  4 B. A communication area  7 C is a communication area of the base station  4 C. In the description below, the WiFi and WiMAX access points are also referred to as the “base station”. 
         [0024]    As illustrated in  FIG. 1 , the 3G communication covers the widest communication area, followed by the WiMAX communication, and then the WiFi communication. On the contrary, the WiFi communication provides the highest transmission rate, followed by the WiMAX communication, and then the 3G communication. It is conceivable that a user of the wireless communication terminal  1  wants communication at a higher transmission rate; therefore, in the present embodiment, a higher priority is placed on a data communication method with a higher transmission rate. Namely, in the present embodiment, there is described a case where the WiFi communication is given the highest priority, followed by the WiMAX communication, and then the 3G communication. However, the priority order can be determined on the basis of another factor; for example, the priority order of the data communication methods can be determined on the basis of the size of communication area. 
         [0025]    In a state of  FIG. 1 , the wireless communication terminal  1  is within the communication area  5  of the WiFi communication and the communication area  7 A of the 3G communication. Furthermore, in the state of  FIG. 1 , the wireless communication terminal  1  is not within any communication area of the WiMAX communication including the communication area  6 . When the wireless communication terminal  1  is within a certain communication area, the wireless communication terminal  1  can establish communication with a base station having the communication area by using a data communication method corresponding to the base station. Namely, in the state of  FIG. 1 , the wireless communication terminal  1  can establish communication with the base station  2  using the WiFi communication. Furthermore, the wireless communication terminal  1  can establish communication with the base station  4 A using the 3G communication. However, in the state of  FIG. 1 , it is difficult that the wireless communication terminal  1  establishes communication using the WiMAX communication. Furthermore, for example, when the wireless communication terminal  1  has moved to a location where the communication area  6  has an overlap with only the communication area  7 A from the state of  FIG. 1 , the wireless communication terminal  1  can communicate with the base station  4 A using the 3G communication, and can communicate with the base station  3  using the WiMAX communication. However, in this case, it is difficult that the wireless communication terminal  1  establishes communication using the WiFi communication. 
         [0026]    In this manner, when the wireless communication terminal  1  has moved from the state of being in communication with a base station having a certain communication area and deviated from the communication area, the wireless communication terminal  1  performs handover to switch the connection to a base station of which the communication area contains a moving destination and continue the communication. Therefore, the wireless communication terminal  1  detects a base station which could be a destination of the handover in advance. Such detection of a base station is referred to as a “search”. 
         [0027]    Then, a search operation that the wireless communication terminal  1  periodically performs to detect the existence or non-existence of an electric field from a base station since a data communication unit has determined that the wireless communication terminal  1  is out of an electric field from a base station until the wireless communication terminal  1  comes within the electric field is referred to as a “non-coverage area search”. Here, being out of an electric field indicates that the wireless communication terminal  1  is out of a communication area of a base station having the electric field; on the other hand, being within an electric field indicates that the wireless communication terminal  1  is within a communication area having the electric field. Furthermore, a search operation that the wireless communication terminal  1  periodically performs to measure the strength of an electric field from a base station since an electric field from a base station in data communication has been detected and it has been determined that the wireless communication terminal  1  is within the electric field until it is detected that the wireless communication terminal  1  is out of the electric field is referred to as a “coverage area search”. 
         [0028]    The non-coverage area search and coverage area search are explained taking, for example, the 3G communication as a data communication method. In a non-coverage area search, a radio frequency and a diffusion code are unknown, so whether electric field strength equal to or higher than a predetermined threshold (a received signal strength indicator (RSSI)) is detected in any radio frequency is implemented as a search operation. The electric field strength may also be referred to as “received signal strength”. On the other hand, a coverage area search is implemented as a search operation to measure an energy value as a result of code demodulation using a known radio frequency and a known diffusion code. When the wireless communication terminal  1  in the state of periodically performing the coverage area search operation has moved, thereby becoming unable to detect the strength of an electric field from a base station and determines to be out of service, the wireless communication terminal  1  makes the transition to the state of periodically performing the non-coverage area search operation. Furthermore, when the wireless communication terminal  1  in the state of periodically performing the non-coverage area search operation has moved, thereby becoming able to detect the strength of an electric field from a base station and determines to be within a coverage area, a radio frequency and a diffusion code are identified, and the wireless communication terminal  1  makes the transition to the state of periodically performing the coverage area search operation. 
         [0029]    Subsequently, a detailed configuration of the wireless communication terminal  1  according to the present embodiment is explained. As illustrated in  FIG. 2 , the wireless communication terminal  1  according to the present embodiment includes a 3G wireless control unit  11 , a WiFi wireless control unit  12 , and a WiMAX wireless control unit  13 . Furthermore, the wireless communication terminal  1  according to the present embodiment includes a 3G baseband processing unit  21 , a WiFi baseband processing unit  22 , a WiMAX baseband processing unit  23 , and a control unit  30 . The control unit  30  includes a 3G coverage area search processing unit  31 , a WiFi coverage area search processing unit  32 , a WiMAX coverage area search processing unit  33 , a 3G non-coverage area search processing unit  34 , a WiFi non-coverage area search processing unit  35 , and a WiMAX non-coverage area search processing unit  36 . Furthermore, the control unit  30  includes a search control unit  37 , a usage-state managing unit  38 , and a communication control unit  39 . In the following description, various search processing and communication switching control based on a result of the search processing, which are primary objects of the present application, are explained, and description of the operation involved in transmission and reception of data to be communicated is omitted. 
         [0030]    The 3G wireless control unit  11  receives a radio signal transmitted from a base station through 3G communication (hereinafter, referred to as a “3G signal”) via an antenna. The 3G wireless control unit  11  performs a frequency conversion to a baseband on the received 3G signal, and generates a baseband signal. The 3G wireless control unit  11  outputs the 3G signal, which is the baseband signal, to the 3G baseband processing unit  21 . 
         [0031]    Furthermore, the 3G wireless control unit  11  outputs information for measurement of electric field strength based on a pilot signal contained in the received 3G signal to the 3G coverage area search processing unit  31  and the 3G non-coverage area search processing unit  34 . The information for measurement of electric field strength is, for example, a control amount of automatic gain control (AGC) for controlling gain of an attenuator for attenuating a radio signal. The pilot signal for 3G communication, which is the baseband signal, is subjected to a correlation operation with a diffusion code in the 3G baseband processing unit  21 , and an energy value obtained as a result of the correlation operation is output to the 3G coverage area search processing unit  31 . 
         [0032]    The WiFi wireless control unit  12  receives a radio signal transmitted from a base station through WiFi communication (hereinafter, referred to as a “WiFi signal”) via an antenna. The WiFi wireless control unit  12  performs a frequency conversion to a baseband on the received WiFi signal, and generates a baseband signal. The WiFi wireless control unit  12  outputs the WiFi signal, which is the baseband signal, to the WiFi baseband processing unit  22 . 
         [0033]    Furthermore, the WiFi wireless control unit  12  outputs information for measurement of electric field strength based on a pilot signal contained in the received WiFi signal to the WiFi coverage area search processing unit  32  and the WiFi non-coverage area search processing unit  35 . Moreover, for a coverage area search, the WiFi wireless control unit  12  outputs the pilot signal for WiFi communication, which is the baseband signal, to the WiFi baseband processing unit  22 . 
         [0034]    The WiMAX wireless control unit  13  receives a radio signal transmitted from a base station through WiMAX communication (hereinafter, referred to as a “WiMAX signal”) via an antenna. The WiMAX wireless control unit  13  performs a frequency conversion to a baseband on the received WiMAX signal, and generates a baseband signal. The WiMAX wireless control unit  13  outputs the WiMAX signal, which is the baseband signal, to the WiMAX baseband processing unit  23 . 
         [0035]    Furthermore, the WiMAX wireless control unit  13  outputs information for measurement of electric field strength based on a pilot signal contained in the received WiMAX signal to the WiMAX coverage area search processing unit  33  and the WiMAX non-coverage area search processing unit  36 . Moreover, for a coverage area search, the WiMAX wireless control unit  13  outputs the pilot signal for WiFi communication, which is the baseband signal, to the WiMAX baseband processing unit  23 . 
         [0036]    The 3G baseband processing unit  21  receives input of a 3G signal, which is a baseband signal, from the 3G wireless control unit  11 . Then, the 3G baseband processing unit  21  demodulates the received 3G signal at a baseband frequency. And then, the 3G baseband processing unit  21  outputs the demodulated 3G signal to the 3G coverage area search processing unit  31 . 
         [0037]    The WiFi baseband processing unit  22  receives input of a WiFi signal, which is a baseband signal, from the WiFi wireless control unit  12 . Then, the WiFi baseband processing unit  22  demodulates the received WiFi signal at a baseband frequency. And then, the WiFi baseband processing unit  22  outputs the demodulated WiFi signal to the WiFi coverage area search processing unit  32 . 
         [0038]    The WiMAX baseband processing unit  23  receives input of a WiMAX signal, which is a baseband signal, from the WiMAX wireless control unit  13 . Then, the WiMAX baseband processing unit  23  demodulates the received WiMAX signal at a baseband frequency. And then, the WiMAX baseband processing unit  23  outputs the demodulated WiMAX signal to the WiMAX coverage area search processing unit  33 . 
         [0039]    The 3G coverage area search processing unit  31  receives an instruction to perform a coverage area search from the search control unit  37 . Then, the 3G coverage area search processing unit  31  measures electric field strength of a received 3G signal using information for measurement of electric field strength input from the 3G wireless control unit  11  at a predetermined frequency, and determines whether the wireless communication terminal  1  is within a 3G coverage area by comparing the measured electric field strength with a 3G coverage area threshold. Here, the 3G coverage area threshold is a predetermined threshold for determining whether the wireless communication terminal  1  is within a communication area of a base station for 3G communication. In the present embodiment, for example, the 3G coverage area search processing unit  31  measures electric field strength of a received 3G signal at a search frequency of once every 5 to 10 seconds. In what follows, the search frequency of once every 5 to 10 seconds is referred to as a regular frequency. When determined to be within the 3G coverage area, the 3G coverage area search processing unit  31  further performs identification of a radio frequency and a diffusion code on a 3G signal input from the 3G baseband processing unit  21  to identify a source base station that transmitted the received 3G signal. At this time, the 3G coverage area search processing unit  31  measures strength of an electric field received from each base station on the basis of an energy value obtained from the 3G baseband processing unit  21 . Then, the 3G coverage area search processing unit  31  outputs identification information of the base station and the measured electric field strength to the communication control unit  39 . 
         [0040]    Furthermore, when electric field strength of a 3G signal from a base station is below the 3G coverage area threshold, the 3G coverage area search processing unit  31  determines that the wireless communication terminal  1  is outside of a communication area of the base station. Then, when the wireless communication terminal  1  is outside of any communication area for 3G communication (hereinafter, referred to as “out of 3G communication service”), the 3G coverage area search processing unit  31  notifies the search control unit  37  of information about the wireless communication terminal  1  being out of 3G communication service. When the wireless communication terminal  1  is out of 3G communication service, the 3G coverage area search processing unit  31  stops the search operation. 
         [0041]    The WiFi coverage area search processing unit  32  receives an instruction to perform a coverage area search from the search control unit  37 . Then, the WiFi coverage area search processing unit  32  measures electric field strength of a received WiFi signal using information for measurement of electric field strength input from the WiFi wireless control unit  12 , for example, at the regular frequency. Furthermore, the WiFi coverage area search processing unit  32  identifies a source base station from the WiFi signal input from the WiFi baseband processing unit  22 . Then, the WiFi coverage area search processing unit  32  outputs identification information of the base station and the measured electric field strength to the communication control unit  39 . 
         [0042]    Furthermore, when electric field strength of a WiFi signal from a base station is below a WiFi coverage area threshold, the WiFi coverage area search processing unit  32  determines that the wireless communication terminal  1  is outside of a communication area of the base station. Here, the WiFi coverage area threshold is a predetermined threshold for determining whether the wireless communication terminal  1  is within a communication area of a base station for WiFi communication. Then, when the wireless communication terminal  1  is outside of any communication area for WiFi communication (hereinafter, referred to as “out of WiFi communication service”), the WiFi coverage area search processing unit  32  notifies the search control unit  37  of information about the wireless communication terminal  1  being out of WiFi communication service. When the wireless communication terminal  1  is out of WiFi communication service, the WiFi coverage area search processing unit  32  stops the search operation. 
         [0043]    The WiMAX coverage area search processing unit  33  receives an instruction to perform a coverage area search from the search control unit  37 . Then, the WiMAX coverage area search processing unit  33  measures electric field strength of a received WiMAX signal using information for measurement of electric field strength input from the WiMAX wireless control unit  13 , for example, at the regular frequency. Furthermore, the WiMAX coverage area search processing unit  33  identifies a source base station from the WiMAX signal input from the WiMAX baseband processing unit  23 . Then, the WiMAX coverage area search processing unit  33  outputs identification information of the base station and the measured electric field strength to the communication control unit  39 . 
         [0044]    Furthermore, when electric field strength of a WiMAX signal from a base station is below a WiMAX coverage area threshold, the WiMAX coverage area search processing unit  33  determines that the wireless communication terminal  1  is outside of a communication area of the base station. Here, the WiMAX coverage area threshold is a predetermined threshold for determining whether the wireless communication terminal  1  is within a communication area of a base station for WiMAX communication. Then, when the wireless communication terminal  1  is outside of any communication area for WiMAX communication (hereinafter, referred to as “out of WiMAX communication service”), the WiMAX coverage area search processing unit  33  notifies the search control unit  37  of information about the wireless communication terminal  1  being out of WiMAX communication service. When the wireless communication terminal  1  is out of WiMAX communication service, the WiMAX coverage area search processing unit  33  stops the search operation. 
         [0045]    The 3G non-coverage area search processing unit  34  receives an instruction to perform a non-coverage area search from the search control unit  37 . Then, the 3G non-coverage area search processing unit  34  measures electric field strength of a received 3G signal using information for measurement of electric field strength input from the 3G wireless control unit  11 , for example, at the regular frequency, and detects a base station of which the electric field strength exceeds the 3G coverage area threshold. Such detection of a base station capable of 3G communication by the 3G non-coverage area search processing unit  34  is a 3G communication non-coverage area search. Then, when detected a base station for 3G communication, the 3G non-coverage area search processing unit  34  determines that the wireless communication terminal  1  is within a 3G communication coverage area. Then, when the wireless communication terminal  1  is within the 3G communication coverage area, the 3G non-coverage area search processing unit  34  notifies the search control unit  37  of information about the wireless communication terminal  1  being within the 3G communication coverage area. When determined that the wireless communication terminal  1  is within the 3G communication coverage area, the 3G non-coverage area search processing unit  34  stops the search operation. 
         [0046]    The WiFi non-coverage area search processing unit  35  receives an instruction to perform a non-coverage area search from the search control unit  37 . Then, the WiFi non-coverage area search processing unit  35  measures electric field strength of a received WiFi signal using information for measurement of electric field strength input from the WiFi wireless control unit  12 , for example, at the regular frequency, and detects a base station of which the electric field strength exceeds the WiFi coverage area threshold. Such detection of a base station capable of WiFi communication by the WiFi non-coverage area search processing unit  35  is a WiFi communication non-coverage area search. Then, when detected a base station for WiFi communication, the WiFi non-coverage area search processing unit  35  determines that the wireless communication terminal  1  is within a WiFi communication coverage area. Then, when the wireless communication terminal  1  is within the WiFi communication coverage area, the WiFi non-coverage area search processing unit  35  notifies the search control unit  37  of information about the wireless communication terminal  1  being within the WiFi communication coverage area. When determined that the wireless communication terminal  1  is within the WiFi communication coverage area, the WiFi non-coverage area search processing unit  35  stops the search operation. 
         [0047]    The WiMAX non-coverage area search processing unit  36  receives a specification of a search frequency and an instruction to perform a non-coverage area search from the search control unit  37 . Here, the specification of a search frequency includes a specification not to perform a search. Then, the WiMAX non-coverage area search processing unit  36  measures electric field strength of a received WiMAX signal using information for measurement of electric field strength input from the WiMAX wireless control unit  13  at the specified search frequency, and detects a base station of which the electric field strength exceeds the WiMAX coverage area threshold. Such detection of a base station capable of WiMAX communication by the WiMAX non-coverage area search processing unit  36  is a WiMAX communication non-coverage area search. Furthermore, when received a specification of a search frequency from the search control unit  37  during execution of a non-coverage area search, the WiMAX non-coverage area search processing unit  36  changes the frequency of non-coverage area search to the specified search frequency, and continues the non-coverage area search. Then, when detected a base station for WiMAX communication, the WiMAX non-coverage area search processing unit  36  determines that the wireless communication terminal  1  is within a WiMAX communication coverage area. Then, when the wireless communication terminal  1  is within the WiMAX communication coverage area, the WiMAX non-coverage area search processing unit  36  notifies the search control unit  37  of information about the wireless communication terminal  1  being within the WiMAX communication coverage area. When determined that the wireless communication terminal  1  is within the WiMAX communication coverage area, the WiMAX non-coverage area search processing unit  36  stops the search operation. 
         [0048]    Here, even if not to perform a search is specified as the search frequency, when the wireless communication terminal  1  fails to establish WiFi communication, the wireless communication terminal  1  switches the data communication method to 3G communication, and the WiMAX non-coverage area search processing unit  36  performs a WiMAX communication non-coverage area search. Then, the WiMAX non-coverage area search processing unit  36  detects a base station for WiMAX communication. Accordingly, the wireless communication terminal  1  can switch the data communication method to WiMAX communication. In this manner, by controlling not to perform a WiMAX non-coverage area search while the wireless communication terminal  1  is using WiFi, a time to perform 3G communication is shortened, and therefore, it is possible to suppress a decrease in transmission rate. 
         [0049]    The usage-state managing unit  38  receives a notification of information on a data communication method being used in communication from the communication control unit  39 . Then, when received the notification of information on the data communication method from the communication control unit  39 , the usage-state managing unit  38  notifies the search control unit  37  of the information on the data communication method being used in communication. Furthermore, the usage-state managing unit  38  stores therein the information on the data communication method being used in communication. 
         [0050]    When received information about the wireless communication terminal  1  being within the 3G coverage area from the 3G non-coverage area search processing unit  34 , the search control unit  37  notifies the 3G coverage area search processing unit  31  of an instruction to perform a coverage area search. Furthermore, when received information about the wireless communication terminal  1  being within the WiFi coverage area from the WiFi non-coverage area search processing unit  35 , the search control unit  37  notifies the WiFi coverage area search processing unit  32  of an instruction to perform a coverage area search. Moreover, when received information about the wireless communication terminal  1  being within the WiMAX coverage area from the WiMAX non-coverage area search processing unit  36 , the search control unit  37  notifies the WiMAX coverage area search processing unit  33  of an instruction to perform a coverage area search. 
         [0051]    Furthermore, the search control unit  37  stores therein a search-frequency determining table  51  as illustrated in  FIG. 3 . Then, when received information about the wireless communication terminal  1  being out of the 3G coverage area from the 3G coverage area search processing unit  31 , the search control unit  37  notifies the 3G non-coverage area search processing unit  34  of an instruction to perform a non-coverage area search. Furthermore, when received information about the wireless communication terminal  1  being out of the WiFi coverage area from the WiFi coverage area search processing unit  32 , the search control unit  37  notifies the WiFi non-coverage area search processing unit  35  of an instruction to perform a non-coverage area search. 
         [0052]    Moreover, when received information about the wireless communication terminal  1  being out of the WiMAX coverage area from the WiMAX coverage area search processing unit  33 , the search control unit  37  acquires information on a data communication method being used in communication at the time from the usage-state managing unit  38 . The search control unit  37  acquires a search frequency of WiMAX communication non-coverage area search corresponding to the acquired data communication method being used in communication from the search-frequency determining table  51 . Specifically, when the wireless communication terminal  1  is communicating using WiFi communication, the search control unit  37  acquires a low search frequency as a search frequency of WiMAX non-coverage area search. Furthermore, when the wireless communication terminal  1  is not communicating using WiFi communication, the search control unit  37  acquires a high search frequency as a search frequency of WiMAX non-coverage area search. The high and low search frequencies here just represent a difference in frequency when the search frequencies are compared each other. For example, in the present embodiment, the high search frequency shall denote a regular search frequency, and the low search frequency shall denote no search to be made. Then, the search control unit  37  notifies the WiMAX non-coverage area search processing unit  36  of a specification of the acquired search frequency and an instruction to perform a non-coverage area search. 
         [0053]    Furthermore, if there is a change in the data communication method, the search control unit  37  receives a notification of the change in the data communication method being used in communication from the usage-state managing unit  38 . Then, the search control unit  37  determines whether the wireless communication terminal  1  is within the WiMAX coverage area. When the wireless communication terminal  1  is out of the WiMAX coverage area, the search control unit  37  acquires a search frequency of WiMAX communication non-coverage area search corresponding to the data communication method being used in communication from the search-frequency determining table  51 . Then, the search control unit  37  notifies the WiMAX non-coverage area search processing unit  36  of a specification of the acquired search frequency. 
         [0054]    Here, in the present embodiment, there is described the configuration that the search control unit  37  stores therein the search-frequency determining table illustrated in  FIG. 3 ; however, it is not limited to this configuration. Namely, the search control unit  37  can set a search frequency of WiMAX communication non-coverage area search to low when WiFi communication is used and high when WiFi communication is not used. 
         [0055]    The communication control unit  39  performs switching of the data communication method and handover processing. Specifically, when high-priority data communication methods can be used, the communication control unit  39  switches to use a higher-priority data communication method. For example, when the wireless communication terminal  1  has moved from a place including only the communication area  7 A illustrated in  FIG. 1  to a place where the communication area  7 A has an overlap with the communication area  5 , the communication control unit  39  switches the access point from the base station  4 A to the base station  2 , and switches the data communication method from 3G communication to WiFi communication. Furthermore, for example, when the wireless communication terminal  1  has moved from the communication area  7 A illustrated in  FIG. 1  to the communication area  7 B, the communication control unit  39  switches the access point from the base station  4 A to the base station  4 B and performs handover. 
         [0056]    Subsequently, WiMAX search control performed by the wireless communication terminal according to the present embodiment is explained with reference to  FIG. 4 .  FIG. 4  is a flowchart of a WiMAX search control determining process in the first embodiment. 
         [0057]    The search control unit  37  implements a process of determining a frequency of WiMAX communication non-coverage area search (Step S 1 ). 
         [0058]    Then, the search control unit  37  instructs the WiMAX non-coverage area search processing unit  36  to perform a non-coverage area search at the determined frequency (Step S 2 ). 
         [0059]    The WiMAX non-coverage area search processing unit  36  performs periodic measurement of electric field strength at the specified search frequency. Then, the WiMAX non-coverage area search processing unit  36  determines whether the wireless communication terminal  1  is within a WiMAX coverage area from a result of the measurement (Step S 3 ). When the wireless communication terminal  1  is out of the WiMAX coverage area (NO at Step S 3 ), the WiMAX non-coverage area search processing unit  36  repeatedly performs the periodic measurement of electric field strength at the specified search frequency. 
         [0060]    On the other hand, when the wireless communication terminal  1  is within the WiMAX coverage area (YES at Step S 3 ), the WiMAX non-coverage area search processing unit  36  notifies the search control unit  37  of the wireless communication terminal  1  being within the WiMAX coverage area. Then, the search control unit  37  instructs the WiMAX coverage area search processing unit  33  to perform a coverage area search (Step S 4 ). 
         [0061]    The WiMAX coverage area search processing unit  33  performs periodic measurement of electric field strength in response to the instruction from the search control unit  37 . Then, the WiMAX coverage area search processing unit  33  determines whether the wireless communication terminal  1  is out of the WiMAX coverage area from a result of the measurement (Step S 5 ). When the wireless communication terminal  1  is within the WiMAX coverage area (NO at Step S 5 ), the WiMAX non-coverage area search processing unit  36  repeatedly performs the periodic measurement of electric field strength. 
         [0062]    On the other hand, when the wireless communication terminal  1  is out of the WiMAX coverage area (YES at Step S 5 ), the process control returns to Step S 1 . The wireless communication terminal  1  repeatedly performs Steps S 1  to S 5  until the operation ends. 
         [0063]    Subsequently, the WiMAX non-coverage area search frequency determining process performed by the wireless communication terminal according to the present embodiment is explained with reference to  FIG. 5 .  FIG. 5  is a flowchart of the WiMAX non-coverage area search frequency determining process in the first embodiment. The flow of  FIG. 5  is the process performed at Step S 1  in  FIG. 4 . Here, there is described a case where the data communication method is changed. 
         [0064]    Upon receipt of a notification of the change in the data communication method from the usage-state managing unit  38 , the search control unit  37  determines whether the wireless communication terminal  1  is out of a WiMAX coverage area (Step S 101 ). When the wireless communication terminal  1  is within the WiMAX coverage area (NO at Step S 101 ), the search control unit  37  does not issue an instruction to perform a non-coverage area search, and ends the non-coverage area search frequency determining process. 
         [0065]    On the other hand, when the wireless communication terminal  1  is out of the WiMAX coverage area (YES at Step S 101 ), the search control unit  37  determines whether the wireless communication terminal  1  is using WiFi communication (Step S 102 ). When the wireless communication terminal  1  is using WiFi communication (YES at Step S 102 ), the search control unit  37  determines to set the frequency of WiMAX communication non-coverage area search to a low frequency (Step S 103 ). 
         [0066]    On the other hand, when the wireless communication terminal  1  is not using WiFi communication (NO at Step S 102 ), the search control unit  37  determines to set the frequency of WiMAX communication non-coverage area search to a high frequency (Step S 104 ). 
         [0067]    In the flow of  FIG. 5 , there is described the case where the data communication method is changed; furthermore, when the wireless communication terminal  1  has moved from inside of the WiMAX coverage area to outside of the WiMAX coverage area, the search control unit  37  performs the processes at Steps S 102  to S 104  and determines the frequency of non-coverage area search in WiMAX communication. 
         [0068]    Here, there is explained the reason why the frequency of WiMAX communication non-coverage area search can be lowered. When the wireless communication terminal  1  is using WiFi communication, it is unlikely that an operator who is moving uses the wireless communication terminal  1 . Therefore, when the wireless communication terminal  1  is using WiFi communication, the probability of switching to the WiMAX communication is low; thus, it doesn&#39;t matter if the frequency of non-coverage area search in WiMAX communication having a lower priority than that of WiFi communication is lowered. Furthermore, also when the wireless communication terminal  1  is out of a communication area of WiFi communication, the communication continuity is ensured by 3G communication covering the widest communication area. Therefore, even if the wireless communication terminal  1  is out of the communication area for WiFi communication in a state where the wireless communication terminal  1  has not detected a base station for WiMAX communication because the search frequency in WiMAX communication is lowered, communication is continued by 3G communication. Moreover, when the data communication method is switched from WiFi communication to 3G communication, the frequency of WiMAX communication non-coverage area search is increased; thus, the wireless communication terminal  1  immediately detects a base station for WiMAX communication and switches from 3G communication to WiMAX communication, so a high transmission rate can be immediately ensured. 
         [0069]    As described above, when using WiFi communication, the wireless communication terminal according to the present embodiment lowers the frequency of non-coverage area search in low-priority WiMAX communication. This makes it possible to reduce electric power consumed in a non-coverage area search in WiMAX communication when the wireless communication terminal is in WiFi communication. Furthermore, the communication continuity can be maintained due to the low possibility of movement in WiFi communication and the backup by 3G communication. 
       [b] Second Embodiment 
       [0070]    Subsequently, a second embodiment is explained. A wireless communication terminal according to the present embodiment differs in conditions for determination of the search frequency in WiMAX communication from the wireless communication terminal according to the first embodiment. So, a search-frequency determining process is mainly explained below. The wireless communication terminal according to the present embodiment is also expressed in the block diagram illustrated in  FIG. 2 . In the description below, a unit having the same reference numeral as in the first embodiment shall have the same function unless otherwise stated. 
         [0071]    The WiFi coverage area search processing unit  32  outputs identification information of a base station and measured electric field strength to the communication control unit  39  and the search control unit  37 . 
         [0072]    The communication control unit  39  notifies the usage-state managing unit  38  of a data communication method being used in communication and identification information of a base station to connect to. 
         [0073]    When received the data communication method and the identification information of the base station to connect to from the communication control unit  39 , the usage-state managing unit  38  notifies the search control unit  37  of these. Furthermore, the usage-state managing unit  38  stores therein the received data communication method being used in communication and identification information of the other end of the communication, i.e., the base station to connect to. 
         [0074]    The search control unit  37  stores therein a search-frequency determining table  52  as illustrated in  FIG. 6 .  FIG. 6  is a diagram of an example of the search-frequency determining table according to the second embodiment. In  FIG. 6 , electric field strength is denoted by RSSI. 
         [0075]    When received a notification of the wireless communication terminal  1  being out of a WiMAX coverage area from the WiMAX coverage area search processing unit  33 , the search control unit  37  acquires a data communication method being used in communication from the usage-state managing unit  38 . When the wireless communication terminal  1  is in communication using WiFi communication as the data communication method, the search control unit  37  acquires identification information of a destination base station in the WiFi communication. Then, the search control unit  37  acquires electric field strength of the destination base station from the electric field strength received from the WiFi coverage area search processing unit  32 . The search control unit  37  determines whether the acquired electric field strength is higher than a threshold (Th). 
         [0076]    Then, when the electric field strength is higher than the threshold (Th), the search control unit  37  determines the search frequency to be a low search frequency with reference to the search-frequency determining table  52 . Furthermore, when the electric field strength is equal to or lower than the threshold (Th), the search control unit  37  determines the search frequency to be a high search frequency with reference to the search-frequency determining table  52 . On the other hand, when the wireless communication terminal  1  is not in communication using WiFi communication as the data communication method, the search control unit  37  determines the search frequency to be a high search frequency regardless of electric field strength in 3G communication. Then, the search control unit  37  instructs the WiMAX non-coverage area search processing unit  36  to perform a non-coverage area search at the determined frequency. 
         [0077]    Furthermore, when received a notification of a change in the data communication method from the usage-state managing unit  38 , the search control unit  37  determines whether the wireless communication terminal  1  is out of WiMAX communication service. When the wireless communication terminal  1  is out of WiMAX communication service, the search control unit  37  performs the non-coverage area search frequency determining process in the same manner as when received the notification of the wireless communication terminal  1  being out of a WiMAX coverage area from the WiMAX coverage area search processing unit  33 . 
         [0078]    Here, it is preferable to set the threshold (Th) so as to meet the communication system operation. For example, to avoid a decrease in the transmission rate as much as possible, it is preferable to set the threshold (Th) to a high threshold, thereby making it easy to ensure the switching to WiMAX communication. Furthermore, to suppress power consumption as low as possible, it is preferable to set the threshold (Th) to a low threshold, thereby reducing execution of a non-coverage area search in WiMAX communication. Moreover, it is preferable to set the threshold (Th) appropriately taking into account a WiMAX communication environment and communication environments of the other data communications, etc. 
         [0079]    Subsequently, a WiMAX communication non-coverage area search frequency determining process performed by the wireless communication terminal according to the present embodiment is explained with reference to  FIG. 7 .  FIG. 7  is a flowchart of the WiMAX communication non-coverage area search frequency determining process in the second embodiment. Here, there is described a case where the data communication method is changed. 
         [0080]    Upon receipt of a notification of the change in the data communication method from the usage-state managing unit  38 , the search control unit  37  determines whether the wireless communication terminal  1  is out of a WiMAX coverage area (Step S 201 ). When the wireless communication terminal  1  is within the WiMAX coverage area (NO at Step S 201 ), the search control unit  37  does not issue an instruction to perform a non-coverage area search, and ends the non-coverage area search frequency determining process. 
         [0081]    On the other hand, when the wireless communication terminal  1  is out of the WiMAX coverage area (YES at Step S 201 ), the search control unit  37  determines whether the wireless communication terminal  1  is using WiFi communication (Step S 202 ). When the wireless communication terminal  1  is using WiFi communication (YES at Step S 202 ), the search control unit  37  determines whether electric field strength (RSSI) in the WiFi communication is higher than the threshold (Th) (Step S 203 ). When the electric field strength in the WiFi communication is higher than the threshold (YES at Step S 203 ), the search control unit  37  determines to set the frequency of WiMAX communication non-coverage area search to a low frequency (Step S 204 ). 
         [0082]    On the other hand, when the wireless communication terminal  1  is not using WiFi communication (NO at Step S 202 ) or when the electric field strength in the WiFi communication is equal to or lower than the threshold (NO at Step S 203 ), the search control unit  37  determines to set the frequency of WiMAX communication non-coverage area search to a high frequency (Step S 205 ). 
         [0083]    In the flow of  FIG. 7 , there is described the case where the data communication method is changed; furthermore, when the wireless communication terminal  1  has moved from inside to outside of the WiMAX coverage area, the search control unit  37  performs the processes at Steps S 202  to S 205  and determines the frequency of non-coverage area search in WiMAX communication. 
         [0084]    Here, there is explained the reason why the frequency of WiMAX communication non-coverage area search can be lowered. When the wireless communication terminal is using WiFi communication and also the radio quality is good, the wireless communication terminal is unlikely to switch the data communication method to another data communication method. Therefore, when the wireless communication terminal is using WiFi communication in the condition of the good radio quality, it doesn&#39;t matter if the frequency of non-coverage area search in WiMAX communication having a lower priority than that of WiFi communication is lowered. Furthermore, also when the wireless communication terminal  1  is out of a communication area of WiFi communication, the communication continuity is ensured by 3G communication covering the widest communication area. Therefore, even if the wireless communication terminal  1  is out of the communication area for WiFi communication in a state where the wireless communication terminal  1  has not detected a base station for WiMAX communication because the search frequency in WiMAX communication is lowered, communication is continued by 3G communication. Moreover, when the data communication method is switched from WiFi communication to 3G communication, the frequency of WiMAX communication non-coverage area search is increased; thus, the wireless communication terminal  1  immediately detects a base station for WiMAX communication and switches from 3G communication to WiMAX communication, so a high transmission rate can be immediately ensured. 
         [0085]    As described above, when the wireless communication terminal according to the present embodiment performs WiFi communication and also electric field strength in the WiFi communication is higher than the threshold, the wireless communication terminal lowers the frequency of non-coverage area search in WiMAX communication. Consequently, when WiFi communication is in a good communication state, i.e., when WiFi communication is considered to be continued, it is possible to reduce electric power consumed in WiMAX communication non-coverage area search. 
       [c] Third Embodiment 
       [0086]    Subsequently, a third embodiment is explained. A wireless communication terminal according to the present embodiment differs from the wireless communication terminal according to the second embodiment in that a 3G communication state is further added in the conditions for determination of the search frequency in WiMAX communication. So, a search-frequency determining process taking into account a 3G communication state is mainly explained below. The wireless communication terminal according to the present embodiment is also expressed in the block diagram illustrated in  FIG. 2 . In the description below, a unit having the same reference numeral as in the first embodiment shall have the same function unless otherwise stated. 
         [0087]    The WiFi coverage area search processing unit  32  outputs identification information of a base station and measured electric field strength to the communication control unit  39  and the search control unit  37 . 
         [0088]    When the wireless communication terminal is within a 3G coverage area, the 3G coverage area search processing unit  31  outputs identification information of a base station and measured electric field strength to the communication control unit  39  and the search control unit  37 . When the wireless communication terminal is out of the 3G coverage area, the 3G non-coverage area search processing unit  34  outputs identification information of a base station and measured electric field strength to the communication control unit  39  and the search control unit  37 . 
         [0089]    The communication control unit  39  notifies the usage-state managing unit  38  of a data communication method being used in communication and identification information of a base station to connect to. 
         [0090]    When received the data communication method and the identification information of the base station to connect to from the communication control unit  39 , the usage-state managing unit  38  notifies the search control unit  37  of these. Furthermore, the usage-state managing unit  38  stores therein the received data communication method being used in communication and identification information of the other end of the communication, i.e., the base station to connect to. 
         [0091]    The search control unit  37  stores therein a search-frequency determining table  53  as illustrated in  FIG. 8 .  FIG. 8  is a diagram of an example of the search-frequency determining table according to the third embodiment. In  FIG. 8 , electric field strength is denoted by RSSI. 
         [0092]    When received a notification of the wireless communication terminal  1  being out of a WiMAX coverage area from the WiMAX coverage area search processing unit  33 , the search control unit  37  acquires a data communication method being used in communication from the usage-state managing unit  38 . When the wireless communication terminal  1  is in communication using WiFi communication as the data communication method, the search control unit  37  acquires identification information of a destination base station in the WiFi communication. Then, the search control unit  37  acquires electric field strength of the destination base station in the WiFi communication from the electric field strength received from the WiFi coverage area search processing unit  32 . Furthermore, when the wireless communication terminal  1  is within a 3G coverage area, the search control unit  37  acquires electric field strength in 3G communication from the 3G coverage area search processing unit  31 . When the wireless communication terminal  1  is out of the 3G coverage area, the search control unit  37  acquires electric field strength in 3G communication from the 3G non-coverage area search processing unit  34 . The search control unit  37  determines whether the acquired electric field strength in the WiFi communication is higher than a threshold (Th 1 ). Furthermore, the search control unit  37  determines whether the acquired electric field strength in the 3G communication is higher than a threshold (Th 2 ). 
         [0093]    Then, when the electric field strength in the WiFi communication is higher than the threshold (Th 1 ), regardless of the electric field strength in the 3G communication, the search control unit  37  determines the search frequency to be a low search frequency with reference to the search-frequency determining table  53 . Furthermore, when the electric field strength in the WiFi communication is equal to or lower than the threshold (Th 1 ) and the electric field strength in the 3G communication is higher than the threshold (Th 2 ), the search control unit  37  determines the search frequency to be a medium search frequency with reference to the search-frequency determining table  53 . Moreover, when the electric field strength in the WiFi communication is equal to or lower than the threshold (Th 1 ) and the electric field strength in the 3G communication is equal to or lower than the threshold (Th 2 ), the search control unit  37  determines the search frequency to be a high search frequency with reference to the search-frequency determining table  53 . On the other hand, when the wireless communication terminal  1  is not in communication using WiFi communication as the data communication method, the search control unit  37  determines the search frequency to be a high search frequency regardless of electric field strength in 3G communication. Then, the search control unit  37  instructs the WiMAX non-coverage area search processing unit  36  to perform a non-coverage area search at the determined frequency. 
         [0094]    For example, in the present embodiment, the high search frequency shall be a frequency of once every 5 to 10 seconds, the low search frequency shall be no non-coverage area search to be made, and the medium search frequency shall be a frequency in between the high search frequency and the low search frequency (for example, once every minute). 
         [0095]    Furthermore, when received a notification of a change in the data communication method from the usage-state managing unit  38 , the search control unit  37  determines whether the wireless communication terminal  1  is out of WiMAX communication service. When the wireless communication terminal  1  is out of WiMAX communication service, the search control unit  37  performs the non-coverage area search frequency determining process in the same manner as when received the notification of the wireless communication terminal  1  being out of a WiMAX coverage area from the WiMAX coverage area search processing unit  33 . 
         [0096]    Here, it is preferable to set the threshold (Th 1 ) and the threshold (Th 2 ) so as to meet the communication system operation. For example, to increase the communication continuity higher, it is preferable to set the threshold (Th 2 ) to a higher threshold, thereby making it possible to perform WiMAX communication certainly in case 3G communication is not performed. Furthermore, to suppress power consumption as low as possible, it is preferable to set the threshold (Th 2 ) to a lower threshold, thereby reducing execution of a non-coverage area search in WiMAX communication. Moreover, it is preferable to set the respective thresholds appropriately taking into account a WiMAX communication environment and a 3G communication environment, etc. 
         [0097]    Subsequently, a WiMAX non-coverage area search frequency determining process performed by the wireless communication terminal according to the present embodiment is explained with reference to  FIG. 9 .  FIG. 9  is a flowchart of the WiMAX non-coverage area search frequency determining process in the third embodiment. Here, there is described a case where the data communication method is changed. 
         [0098]    Upon receipt of a notification of the change in the data communication method from the usage-state managing unit  38 , the search control unit  37  determines whether the wireless communication terminal  1  is out of a WiMAX coverage area (Step S 301 ). When the wireless communication terminal  1  is within the WiMAX coverage area (NO at Step S 301 ), the search control unit  37  does not issue an instruction to perform a non-coverage area search, and ends the non-coverage area search frequency determining process. 
         [0099]    On the other hand, when the wireless communication terminal  1  is out of the WiMAX coverage area (YES at Step S 301 ), the search control unit  37  determines whether the wireless communication terminal  1  is using WiFi communication (Step S 302 ). When the wireless communication terminal  1  is using WiFi communication (YES at Step S 302 ), the search control unit  37  determines whether electric field strength (RSSI) in the WiFi communication is higher than the threshold (Th 1 ) (Step S 303 ). When the electric field strength in the WiFi communication is higher than the threshold (YES at Step S 303 ), the search control unit  37  determines to set the frequency of WiMAX communication non-coverage area search to a low frequency (Step S 304 ). 
         [0100]    On the other hand, when the electric field strength in the WiFi communication is equal to or lower than the threshold (NO at Step S 303 ), the search control unit  37  determines whether electric field strength (RSSI) in 3G communication is higher than the threshold (Th 2 ) (Step S 305 ). When the electric field strength in the WiFi communication is higher than the threshold (YES at Step S 305 ), the search control unit  37  determines to set the frequency of WiMAX communication non-coverage area search to a medium frequency (Step S 306 ). 
         [0101]    On the other hand, when the wireless communication terminal  1  is not using WiFi communication (NO at Step S 302 ) or when the electric field strength in the 3G communication is equal to or lower than the threshold (NO at Step S 305 ), the search control unit  37  determines to set the frequency of WiMAX communication non-coverage area search to a high frequency (Step S 307 ). 
         [0102]    In the flow of  FIG. 9 , there is described the case where the data communication method is changed; furthermore, when the wireless communication terminal  1  has moved from inside to outside of the WiMAX coverage area, the search control unit  37  performs the processes at Steps S 302  to S 307  and determines the frequency of non-coverage area search in WiMAX communication. 
         [0103]    Here, there is explained the reason why the frequency of WiMAX communication non-coverage area search is determined as described above depending on the radio quality in 3G communication and WiFi communication. Even when, although the wireless communication terminal  1  is using WiFi communication, the radio quality has deteriorated, if the radio quality in 3G communication covering the widest communication area is high, the communication continuity is ensured by the 3G communication even if WiFi communication is out of service. Therefore, for example, when the wireless communication terminal  1  performing WiFi communication is out of a WiFi communication area in a state where the wireless communication terminal  1  has not detected a base station for WiMAX communication because the search frequency in WiMAX communication is lowered, communication is continued by 3G communication. On the other hand, in a condition where the radio quality in both WiFi communication and 3G communication has deteriorated, there is a case that the communication continuity is not maintained by only the WiFi communication and 3G communication; therefore, it is preferable to perform a WiMAX communication non-coverage area search. For such a reason, the frequency of WiMAX communication non-coverage area search is determined depending on the radio quality in 3G communication and WiFi communication as described above. 
         [0104]    As described above, the wireless communication terminal according to the present embodiment changes the frequency of WiMAX communication non-coverage area search depending on respective electric field strengths in WiFi communication and 3G communication. Consequently, when WiFi communication is in a good communication state, i.e., when WiFi communication is considered to be continued, it is possible to reduce electric power consumed in WiMAX communication non-coverage area search. Furthermore, even when WiFi communication is in a bad communication state, if 3G communication is in a good communication state and the communication continuity is ensured, it is possible to reduce a certain amount of electric power consumed in WiMAX communication non-coverage area search. 
         [0105]    [Hardware Configuration] 
         [0106]    Subsequently, a hardware configuration of the wireless communication terminal according to the embodiments is explained with reference to  FIG. 10 .  FIG. 10  is a diagram illustrating the hardware configuration of the wireless communication terminal. 
         [0107]    The wireless communication terminal  1  according to the above-described embodiments includes antennas  102 ,  112 , and  122 , a 3G wireless unit  104 , a WiFi wireless unit  114 , a WiMAX wireless unit  124 , a 3G baseband unit  106 , a WiFi baseband unit  116 , and a WiMAX baseband unit  126 . Furthermore, the wireless communication terminal  1  includes a processor  130 , a display unit  140 , an operation unit  150 , a microphone  160 , a speaker  170 , and a memory  180 . 
         [0108]    The 3G wireless unit  104 , the WiFi wireless unit  114 , and the WiMAX wireless unit  124  each include an oscillator, a multiplier, an amplifier, an attenuator, and an AGC, etc. The 3G wireless unit  104  is connected to the antenna  102 , and implements, for example, the function of the 3G wireless control unit  11  illustrated in  FIG. 2 . The WiFi wireless unit  114  is connected to the antenna  112 , and implements, for example, the function of the WiFi wireless control unit  12  illustrated in  FIG. 2 . The WiMAX wireless unit  124  is connected to the antenna  122 , and implements, for example, the function of the WiMAX wireless control unit  13  illustrated in  FIG. 2 . 
         [0109]    The 3G baseband unit  106 , the WiFi baseband unit  116 , and the WiMAX baseband unit  126  each include a modulator and a demodulator, etc. The 3G baseband unit  106  is connected to the 3G wireless unit  104  and the processor  130 , and implements, for example, the function of the 3G baseband processing unit  21  illustrated in  FIG. 2 . The WiFi baseband unit  116  is connected to the WiFi wireless unit  114  and the processor  130 , and implements, for example, the function of the WiFi baseband processing unit  22  illustrated in  FIG. 2 . The WiMAX baseband unit  126  is connected to the WiMAX wireless unit  124  and the processor  130 , and implements, for example, the function of the WiMAX baseband processing unit  23  illustrated in  FIG. 2 . 
         [0110]    The memory  180 , the display unit  140 , the operation unit  150 , the microphone  160 , and the speaker  170  are connected to the processor  130 . 
         [0111]    The display unit  140  includes, for example, a liquid crystal display or the like, and displays thereon respective electric field strengths of 3G, WiMAX, and WiFi, a service state or an out-of-service state, and a communication state, etc. in the form of an increase or decrease of antennas and the form of icons, etc. The display unit  140  operates under the control of the processor  130 . 
         [0112]    The operation unit  150  is a user interface for the control of start/end of a communication application, and includes, for example, buttons or a touch screen, etc. The operation unit  150  inputs information input through the touch screen or the like to the processor  130 . 
         [0113]    The microphone  160  receives a voice signal. The speaker  170  outputs an audio signal. The microphone  160  and the speaker  170  each include a coding unit and a decoding unit. 
         [0114]    The processor  130  and the memory  180  implement, for example, the function of the control unit  30  illustrated in  FIG. 2 . Specifically, the memory  180  stores therein various programs, such as a program for implementing the process performed by the communication control unit  39 , the usage-state managing unit  38 , and the search control unit  37 , etc. illustrated in  FIG. 2 . The processor  130  reads out these programs from the memory  180  and executes the programs, thereby generating processes for implementing the above-described functions. 
         [0115]    Accordingly, it is an object in one aspect of an embodiment of the invention to reduce power consumption. 
         [0116]    All examples and conditional language recited herein are intended for pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.