Abstract:
According to an aspect of an embodiment, a communication system comprisies: a) a mobile communication terminal; b) a first apparatus comprising: and a controller for controlling communication with the mobile communication terminal and for receiving a local information from the mobile communication terminal, c) a second apparatus comprising: a controller for transmitting a request for starting the direct communication with the mobile communication terminal when selected by the first apparatus, and d) an exchange comprising: a communication unit capable of communicating with the mobile communication terminal via the second apparatus, and a controller for starting communication with the mobile communication terminal via the selected second apparatus upon receiving the request from the selected second apparatus, wherein the storage unit stores information relating to the second apparatus, and the controller of the first apparatus selects the second apparatus to start the direct communication with the mobile communication terminal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a communication control technology for mobile communication terminals. 
         [0003]    2. Description of the Related Art 
         [0004]    Portable phones, which are one type of mobile communication terminals, achieve calls based on a specific implemented communication system. Based on the communication system, a portable phone establishes a communication with a base station and then uses the base station or a base station therearound to maintain the call. When the radio waves between the portable phone and the base station are weak, the portable phone and the base station perform operations for strengthening the radio waves so as to prevent an influence on the communication. Thus, there are problems in that the power consumption of the portable phone increases and the maximum call time of the portable phone decreases. 
         [0005]    Japanese Laid-open Patent Publication No. 10-248078 discloses a technology in which a base-station control apparatus, which controls multiple base stations, changes a base station for controlling a portable phone based on the strength of radio waves received from the portable phone. Japanese Laid-open Patent Publication No. 11-187451 discloses a technology in which a portable phone detects available radio waves and notifies a base station about the detected radio waves. 
       SUMMARY 
       [0006]    According to an aspect of an embodiment, a communication system comprisies: a) a mobile communication terminal comprising: a communication unit for communication, and a controller for transmitting local information indicative of a location of the mobile communication terminal; b) a first apparatus comprising: a communication unit for communicating with the mobile communication terminal, a storage unit, and a controller for controlling communication with the mobile communication terminal and for receiving the local information transmitted from the mobile communication terminal, c) a second apparatus comprising: a communication unit for communicating with the mobile communication terminal, a controller for transmitting a request for starting the direct communication with the mobile communication terminal when selected by the first apparatus, and d) an exchange comprising: a communication unit capable of communicating with the mobile communication terminal via the first apparatus or the second apparatus, and a controller for starting communication with the mobile communication terminal via the selected second apparatus upon receiving the request from the selected second apparatus, wherein the storage unit stores information relating to the second apparatus, and the controller of the first apparatus selects the second apparatus to start the direct communication with the mobile communication terminal in accordance with the information and the local information. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic diagram of the present invention; 
           [0008]      FIG. 2  is a block diagram showing the hardware configuration of a portable phone; 
           [0009]      FIG. 3  shows the structure of communication data for the portable phone; 
           [0010]      FIG. 4  is a block diagram showing the hardware configuration of a low-power apparatus; 
           [0011]      FIG. 5  shows the structure of communication data for the low-power apparatus; 
           [0012]      FIG. 6  is a block diagram showing the hardware configuration of a wide-area base-station; 
           [0013]      FIG. 7  shows the structure of communication control data for the low-power apparatus; 
           [0014]      FIG. 8  shows the structure of communication data for the wide-area base-station; 
           [0015]      FIG. 9  is a block diagram showing the hardware configuration of an exchange; 
           [0016]      FIG. 10  shows the structure of communication data for the exchange; 
           [0017]      FIG. 11  is a flowchart of communication control information registration processing performed by the low-power apparatus; 
           [0018]      FIG. 12  is a flowchart of communication control information registration processing performed by the wide-area base-station; 
           [0019]      FIG. 13  is a flowchart of processing performed by the portable phone; 
           [0020]      FIG. 14  is a flowchart of processing performed by the wide-area base-station; 
           [0021]      FIG. 15  is a flowchart of processing performed by the low-power apparatus; and 
           [0022]      FIG. 16  is a flowchart of processing performed by the exchange. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    An embodiment relating to the present invention will be described below with reference to the accompanying drawings. 
       1. Overview of the Present Invention 
       [0024]      FIG. 1  is a schematic diagram of the present invention. A communication system achieves calls of portable phones according to the present invention. The communication system includes a portable phone  1 , a low-power apparatus  3 , a wide-area base-station  5 , and an exchange  7 . The portable phone  1  can transmit/receive radio waves over a frequency used for portable phones and a frequency used for a wireless LAN. The frequency used for the portable phones is typically several hundreds megahertz (MHz) to 3 gigahertz (GHz). The frequency used for the wireless LAN has, for example, a 2.4 GHz or 5 GHz band defined by IEEE (Institute of Electrical and Electronics Engineers) 802.11. The portable phone  1  can transmit radio waves at 1 W or less. The portable phone  1  is compliant with an SIP (session imitation protocol), which is one communication protocol for controlling internet phone calls. The portable phone  1  can serve as a mobile communication terminal. 
         [0025]    The low-power apparatus  3  serves as a relay apparatus that is located between the portable phone  1  and the exchange  7 . The low-power apparatus  3  converts information, wirelessly received from the portable phone  1 , into information that uses a cable/line and that can be processed by the exchange  7 , and transmits the cable/line-based information thereto. The low-power apparatus  3  also performs reverse processing of the processing. The low-power apparatus  3  registers, with the wide-area base-station  5 , communication control information for communication. The low-power apparatus  3  serves as a wireless LAN apparatus. The wireless LAN apparatus used in this case is wireless communication equipment that is compliant with IEEE802.11 and uses radio waves in a 2.4 GHz or 5 GHz band and that has a radio-wave output of 10 mW or less per frequency band of 1 MHz. The communication distance of the low-power apparatus  3  is up to about 100 m, but depends on the power of radio waves. The low-power apparatus  3  uses a wireless LAN to communicate with the portable phone  1  and uses the Internet or a dedicated line to communicate with the wide-area base-station  5  and the exchange  7 . For the communication, the user of the low-power apparatus  3  files an application to a telecommunications carrier that manages the wide-area base-station  5  and the exchange  7  to obtain permission for using the addresses thereof and the telecommunications carrier makes them available. The low-power apparatus  3  corresponds to a second apparatus. 
         [0026]    The wide-area base-station  5  serves as a relay apparatus located between the portable phone  1  and the exchange  7 . The wide-area base-station  5  converts information, wirelessly received from the portable phone  1 , into information that uses a cable/line and that can be processed by the exchange  7 , and transmits the cable/line based information to the exchange  7 . The wide-area base-station  5  also performs reverse processing of the processing. The wide-area base-station  5  stores the communication control information received from the low-power apparatus  3 , and transmits it to the portable phone  1  in response to a request issued from the portable phone  1 . The communication control information is required for the portable phone  1  and the exchange  7  to communicate with each other via the low-power apparatus  3 . For the communication, the wide-area base-station  5  uses a portable phone  1  address on an available channel assigned by the wide-area base-station  5 . For the communication, the wide-area base-station  5  uses an exchange  7  address that has been pre-exchanged with the exchange  7  connected through a dedicated line. For the communication, the wide-area base-station  5  uses a low-power apparatus  3  address that has been received together with the communication control information. The wide-area base-station  5  corresponds to a first apparatus. 
         [0027]    The exchange  7  is an apparatus that identifies a communication target of the portable phone  1  and that controls communication with the identified communication target. The exchange  7  receives information for communication from the wide-area base-station  5  and transmits the received information to an exchange that manages the communication equipment of the communication target. The exchange  7  also performs reverse processing of the processing. Also, the exchange  7  receives information for communication from the low-power apparatus  3  and transmits the received information to an exchange that manages the communication equipment of the communication target. The exchange  7  also performs reverse processing of the processing. For the communication, the exchange  7  uses a wide-area base-station  5  address that has been pre-exchanged with the wide-area base-station  5  connected through the dedicated line. For the communication, the exchange  7  uses a low-power apparatus  3  address that has been received together with the information for communication. 
         [0028]    An operation of a communication system according to the present invention will be briefly described below. 
       (1) Communication-Control-Information Registration 
       [0029]    The low-power apparatus  3  transmits, to the wide-area base-station  5 , communication control information for communicating with the portable phone  1 . The wide-area base-station  5  performs processing for storing the received communication control information and transmits a result of the processing to the low-power apparatus  3 . The communication control information serves as communication information. 
       (2) Low-Power-Apparatus Search 
       [0030]    The portable phone  1  transmits a low-power-apparatus search request to the wide-area base-station  5  that is in communication. The expression “being in communication” indicates a state in which a control channel and a call channel are established between the portable phone  1  and the exchange  7  for controlling a communication with a communication target. The term “channels” in this case represent paths for information for communication. The low-power-apparatus search request is aimed for searching for a low-power apparatus  3  located in close proximity to the portable phone  1 . The wide-area base-station  5  searches for information corresponding to the received search request based on the communication control information stored during the communication-control-information registration ( 1 ) described above, and transmits the result of the search to the portable phone  1 . 
       (3) New Channel Establishment 
       [0031]    The portable phone  1  establishes a communication with the exchange  7  via the low-power apparatus  3  based on the communication control information obtained as a result of the low-power-apparatus search ( 2 ) described above. In this communication establishment processing, a control channel is first established and a call channel is then established. A method for establishing the channels will be described below. 
         [0032]    Processing for establishing the control channel will now be described. The portable phone  1  transmits, to the low-power apparatus  3 , a control-channel establishment request for establishing the control channel. The low-power apparatus  3  assigns a control IP (internet protocol) address. In the control-channel establishment processing, the control IP address is used as information for identifying the portable phone  1 . The low-power apparatus  3  transmits the control IP address to the portable phone  1  and the exchange  7 . The portable phone  1  stores the received control IP address. The exchange  7  uses the received control IP address to generate control information for communicating with the portable phone  1  and transmits the generated control information to the portable phone  1  via the low-power apparatus  3 . When the portable phone  1  receives the control information, the control channel is established. 
         [0033]    Processing for establishing the call channel will now be described. The portable phone  1  transmits, to the low-power apparatus  3 , a call-channel establishment request for establishing the call channel. The low-power apparatus  3  assigns a call IP address. In the call-channel establishment processing, the call IP address is used as information for identifying the portable phone  1 . The low-power apparatus  3  transmits the call IP address to the portable phone  1  and the exchange  7 . The portable phone  1  stores the received call IP address. The exchange  7  uses the received call IP address to generate call information for communicating with the portable phone  1  and transmits the generated call information to the portable phone  1  via the low-power apparatus  3 . When the portable phone  1  receives the call information, the call channel is established. The control IP address and the call IP address serve as identification information. The control-channel establishment request and the call-channel establishment request serve as call start requests. 
       (4) Channel Switching 
       [0034]    Switching is performed between the call channel established in the previous communication and the call channel newly, established in the channel establishment ( 3 ) described above. The term “handover” herein refers to switching between a call channel established in a previous communication and the newly established call channel. The portable phone  1  transmits a release request to the exchange  7  via the wide-area base-station  5  to release a call channel established in a previous communication. The portable phone  1  transmits a continuation request to the exchange  7  via the low-power apparatus  3  to continuously use the call channel newly established in the new channel establishment ( 3 ). Upon receiving the release request and the continuation request, the exchange  7  puts the call channel used in the previous communication into an unused state and puts only the newly established channel into a use state. The exchange  7  transmits a channel release request to the portable phone  1  via the wide-area base-station  5 . The channel release request indicates that the call channel used in the previous communication is in the unused state. The portable phone  1  transmits a channel release response to the wide-area base-station  5 . Upon receiving the channel release response, the wide-area base-station  5  releases the call channel used in the previous communication. This processing is performed to increase the number of channels used for other portable phones covered by the wide-area base-station  5 . 
       2. Hardware Configuration of Portable Phone 
       [0035]      FIG. 2  is a block diagram showing one example of the hardware configuration of the portable phone  1 . The portable phone  1  includes a CPU (central processing unit)  11 , a RAM (random access memory)  12 , a ROM (read only memory)  13 , a storage unit  14 , a display  15 , keys  16 , a communication unit  17 , and a GPS (global positioning system)  18 . 
         [0036]    The CPU  11  controls the individual units and performs computation/processing on data. The CPU  11  is a device for executing a program loaded into the memory. The term “memory” in this case means a semiconductor storage device, such as the RAM  12  or the ROM  13 . The CPU  11  receives data from the keys  16 , the GPS  18 , and/or the storage unit  14 , performs computation/processing on the data, and outputs the resulting data on the display  15  an/or to the storage unit  14 . The RAM  12  is a storage device using a semiconductor and stores data required for executing a program and data temporarily required by the program. The ROM  13  is a storage device using a semiconductor and reads once-written data. The expression “once-written data” herein means data that does not have to be overwritten or data that should not be overwritten. 
         [0037]    The storage unit  14  stores a portable-phone communication program  141  and portable-phone communication data  142 . The portable-phone communication program  141  performs the following operation for switching between a previously established call channel and a newly established call channel. The portable-phone communication program  141  establishes a communication with an arbitrary communication target. The portable-phone communication program  141  obtains, from the wide-area base-station  5 , communication control information associated with the low-power apparatus  3  that is located in close proximity to the portable phone  1 . Based on the obtained communication control information, the portable phone  1  establishes a communication with the exchange  7  via the low-power apparatus  3 . In the communication establishment processing, a control channel is first established and a call channel is then established. The portable phone  1  issues, to the low-power apparatus  3  and the wide-area base-station  5 , an instruction for switching between a newly established call channel and a call channel established in a previous communication. The CPU  11  serves as control unit by controlling the portable-phone communication program  141 . 
         [0038]    The display  15  is a device for displaying operation-result information indicating a result of operation of the keys  16 . The keys  16  are devices for inputting information, including characters and numerals, to the portable phone  1 . The communication unit  17  is responsible for communication with the low-power apparatus  3  or the wide-area base-station  5 . The communication unit  17  can transmit/receive radio waves over a frequency used for the portable phone  1  and another frequency used for a wireless LAN. The frequency used for the portable phone  1  is typically several hundreds megahertz to 3 GHz. The frequency used for the wireless LAN has, for example, a 2.4 GHz or 5 GHz band defined by IEEE802.11. The communication unit  17  can transmit radio waves at about 1 W or less. The communication unit  17  is compliant with an SIP, which is one communication protocol for controlling internet phone calls. The GPS  18  is a device for obtaining local information. The term “local information” herein refers to latitude, longitude, and altitude. The communication unit  17  corresponds to a second communication unit that is capable of transmitting/receiving high-power electromagnetic waves for communication with the wide-area base-station  5  and also corresponds to a second communication unit that is capable of transmitting/receiving low-power electromagnetic waves for communication with the low-power apparatus  3 . 
       2.1. Structure of Portable-Phone Communication Data 
       [0039]      FIG. 3  shows the portable-phone communication data  142  containing data used when the portable phone  1  communicates with the low-power apparatus  3  or the wide-area base-station  5 . The data includes a phone number indicated by reference numeral  1421 , a channel (CH) number  1  indicated by  1422 , a control timeslot (TS) indicated by  1423 , a call timeslot indicated by  1424 , a channel number  2  indicated by  1425 , a control IP address indicated by  1426 , and a call IP address indicated by  1427 . The term “channels” in this case refers to frequency bands separated at regular intervals. A timeslot refers to the location of each of channels separated at regular periods of time and also serves as information for identifying an individual communication. The phone number  1421  represents a phone number assigned to the portable phone  1 . The channel number  1  indicated by  1422  represents a channel used in a previous communication. The control timeslot represents a timeslot used for control in the previous communication. The call timeslot  1424  represents a timeslot used for a call in the previous communication. The channel number  2  indicated by  1425  represents a channel used in a communication established via the low-power apparatus  3 . The control IP address  1426  represents an IP address used for control in the communication established via the low-power apparatus  3 . The call IP address  1427  represents an IP address used for a call in the communication established via the low-power apparatus  3 . 
       3. Hardware Configuration of Low-Power Apparatus 
       [0040]      FIG. 4  is a block diagram showing one example of the hardware configuration of the low-power apparatus  3 . The low-power apparatus  3  includes a CPU  31 , a RAM  32 , a ROM  33 , a storage unit  34 , a communication unit  37 , and a GPS  38 . 
         [0041]    The CPU  31  controls the individual units and performs computation/processing on data. The CPU  31  is a device for executing a program loaded into the memory. The term “memory” in this case means a semiconductor storage device, such as the RAM  32  or the ROM  33 . The CPU  31  receives data from the communication unit  37 , the GPS  38 , and/or the storage unit  34 , performs computation/processing on the received data, and outputs the resulting data to the communication unit  37  and/or the storage unit  34 . The RAM  32  is a storage device using a semiconductor and stores data required for executing a program and data temporarily required by the program. The ROM  33  is a storage device using a semiconductor and reads once-written data. The expression. “once-written data” herein means data that does not have to be overwritten or data that should not be overwritten. 
         [0042]    The storage unit  34  stores a low-power-apparatus communication-control-information registration request program  341 , a low-power-apparatus communication program  342 , and low-power-apparatus communication data  343 . The low-power-apparatus registration request program  341  registers, with the wide-area base-station  5 , communication control information associated with the low-power apparatus  3 . The low-power-apparatus communication program  342  establishes a communication between the portable phone  1  and the exchange  7 . In the communication establishment processing, a control channel is first established and a call channel is then established. The low-power-apparatus communication program  342  relays a communication-channel switching instruction, received from the portable phone  1 , to the exchange  7 . The communication unit  37  is responsible for communication with the portable phone  1  and the exchange  7 . The communication unit  37  can transmit/receive radio waves in a frequency used for a wireless LAN. The frequency used for a wireless LAN has, for example, a 2.4 GHz or 5 GHz band defined by IEEE802.11. The communication unit  37  can output radio waves at 10 mW or less per frequency band of 1 MHz. The GPS  38  is a device for obtaining local information. The term “local information” herein refers to latitude, longitude, and altitude. 
       3.1. Structure of Low-Power-Apparatus Communication Data 
       [0043]      FIG. 5  shows the low-power-apparatus communication data  343  containing data used when the low-power apparatus  3  communicates with the portable phone  1  or the exchange  7 . The data includes a channel (CH) indicated by  3431 , a control IP address indicated by  3432 , and a call IP address indicated by  3433 . The channel  3431  represents a channel used for a communication established via the low-power apparatus  3 . The control IP address  3432 , represents an IP address used for control in the communication established via the low-power apparatus  3 . The call IP address  3433  represents an IP address used for a call in the communication established via the low-power apparatus  3 . 
       4. Hardware Configuration of Wide-Area Base-Station 
       [0044]      FIG. 6  is a block diagram showing one example of the hardware configuration of the wide-area base-station  5 . The wide-area base-station  5  includes a CPU  51 , a RAM  52 , a ROM  53 , a storage unit  54 , and a communication unit  57 . 
         [0045]    The CPU  51  controls the individual units and performs computation/processing on data. The CPU  51  is a device for executing a program loaded into the memory. The term “memory” in this case means a semiconductor storage device, such as the RAM  52  or the ROM  53 . The CPU  51  receives data from the communication unit  57  and/or the storage unit  54 , performs computation/processing on the received data, and outputs the resulting data to the communication unit  57  and/or the storage unit  54 . The RAM  52  is a storage device using a semiconductor and stores data required for executing programs and data temporarily required by the programs. The ROM  53  is a storage device using a semiconductor and reads once-written data. The expression “once-written data” herein means data that does not have to be overwritten or data that should not be overwritten. 
         [0046]    The storage unit  54  stores a wide-area-base-station communication-control-information registration program  541 , low-power-apparatus communication control data  542 , a wide-area-base-station communication program  543 , and wide-area-base-station communication data  544 . The wide-area-base-station communication-control-information registration program  541  registers information related to communication of the low-power apparatus  3 , the information being received from the low-power apparatus  3 . In response to an instruction received from the portable phone  1 , the wide-area-base-station communication program  543  releases a call channel used in a previous communication. 
       4.1. Structure of Low-Power-Apparatus Communication Control Data 
       [0047]      FIG. 7  shows the low-power-apparatus communication control data  542  containing data used when the wide-area base-station  5  searches for the low-power apparatus  3  located in close proximity to the portable phone  1 . The data includes low-power apparatus identification information indicated by  5421 , a low-power-apparatus installation location indicated by  5422 , a frequency indicated by  5423 , a channel indicated by  5424 , a radio-wave output indicated by  5425 , a maximum communication area indicated by  5426 , a communication protocol indicated by  5427 , and a communication program indicated by  5428 . The low-power-apparatus identification information  5421  is information for identifying the low-power apparatus  3  and is, for example, a MAC (media access control) address. The low-power-apparatus installation address is information indicating the location at which the low-power apparatus  3  is installed. The information includes, for example, latitude, longitude, and altitude. The frequency  5423  represents the type of radio waves used in communication between the portable phone  1  and the low-power apparatus  3 . The channel  5424  represents a path for information for communication. The radio-wave output  5425  represents the strength of radio waves used in the communication between the portable phone  1  and the low-power apparatus  3 . The radio-wave output  5425  indicates radio-wave intensity. The maximum communication area  5426  represents an approximate maximum distance of communication that can be performed between the portable phone  1  and the low-power apparatus  3 . The communication protocol  5427  represents a procedure used in the communication between the portable phone  1  and the low-power apparatus  3 . The communication program  5428  represents a program that runs on the portable phone  1  to implement the procedure used in the communication between the portable phone  1  and the low-power apparatus  3 . 
       4.2. Structure of Wide-Area-Station Communication Data 
       [0048]      FIG. 8  shows the wide-area-base-station communication data  544  containing data used when the wide-area base-station  5  communicates with the portable phone  1  or the exchange  7 . The data includes a channel (CH) indicated by  5442 , a control timeslot (TS) indicated by  5443 , and a call timeslot indicated by  5444 . The channel  5442  represents a channel used for a communication established via the wide-area base-station  5 . The control timeslot  5443  represents a timeslot used for control in the communication established via the wide-area base-station  5 . The call timeslot  5444  represents a timeslot used for a call in the communication established via the wide-area base-station  5 . 
       5. Hardware Configuration of Exchange 
       [0049]      FIG. 9  is a block diagram showing one example of the hardware configuration of the exchange  7 . The exchange  7  includes a CPU  71 , a RAM  72 , a ROM  73 , a storage unit  74 , and a communication unit  77 . 
         [0050]    The CPU  71  controls the individual units and performs computation/processing on data. The CPU  71  is a device for executing a program loaded into the memory. The term “memory” in this case means a semiconductor storage device, such as the RAM  72  or the ROM  73 . The CPU  71  receives data from the communication unit  77  and/or the storage unit  74 , performs computation/processing on the received data, and outputs the resulting data to the communication unit  77  and/or the storage unit  74 . The RAM  72  is a storage device using a semiconductor and stores data required for executing a program and data temporarily required by the program. The ROM  73  is a storage device using a semiconductor and reads once-written data. The expression “once-written data” herein means data that does not have to be overwritten or data that should not be overwritten. The storage unit  74  stores an exchange communication program  741  and exchange communication data  742 . The exchange communication program  741  switches between a call communication path used in a previous call and a call communication path established via the low-power apparatus  3 . The communication unit  77  is a device that is responsible for communication with the low-power apparatus  3  or the wide-area base-station  5 . 
       5.1 Structure of Exchange Communication Data 
       [0051]      FIG. 10  shows the exchange communication data  742  containing data used when the exchange  7  communicates with the low-power apparatus  3  or the wide-area base-station  5 . The data includes a transmitting-end phone number indicated by  7421 , a receiving-end phone number  7422 , a control timeslot (TS) indicated by  7423 , a call timeslot indicated by  7424 , a call timeslot state indicated by  7425 , a control IP address indicated by  7426 , a call IP address indicated by  7427 , and a call IP state  7428 . 
         [0052]    The transmitting-end phone number  7421  represents a phone number assigned to the communication equipment of the transmitting end. The receiving-end phone number  7422  represents a phone number assigned to the communication equipment of the receiving end. The communication equipment in this case includes, for example, portable phones and fixed-line phones. The control timeslot  7423  represents a timeslot used for control in a communication between the transmitting-end phone number  7421  and the receiving-end phone number  7422 . The call timeslot  7424  represents a timeslot used for a call in the communication between the transmitting-end phone number  7421  and the receiving-end phone number  7422 . The control timeslot  7423  is equivalent to the control channel the portable phone  1  uses for the communication with the wide-area base-station  5 . The call timeslot  7424  is equivalent to the call channel that the portable phone  1  uses for communication with the wide-area base-station  5 . The call timeslot state  7425  represents whether the call time slot  7424  is in use or not in use. The control IP address  7426  represents an IP address used for control in the communication between the transmitting-end phone number  7421  and the receiving-end phone number  7422 . The call IP address  7427  represents an IP address used for a call between the transmitting-end phone number  7421  and the receiving-end phone number  7422 . The control IP address  7426  is equivalent to the control channel address that the portable phone  1  uses for communication with the low-power apparatus  3 . The call IP address  7427  is equivalent to the call channel address that the portable phone  1  uses for communication with the low-power apparatus  3 . The call IP state  7428  represents whether the call IP address  7427  is in use or not in use. 
         [0053]    The operations of the apparatuses will be described below in detail in conjunction with the operations illustrated in  FIG. 1 . First, a description will be given of the operations of the low-power apparatus  3  and the wide-area base-station  5  when the communication control information registration ( 1 ) shown in  FIG. 1  is performed. 
       6. Operation of Low-Power Apparatus 
       [0054]      FIG. 11  is a flowchart showing a procedure of the processing of the low-power apparatus  3  when the communication control information registration ( 1 ) shown in  FIG. 1  is performed. The CPU  31  of the low-power apparatus  3  achieves processing for registering the communication control information with the wide-area base-station  5  by controlling the low-power-device communication-control-information registration request program  342 . 
         [0055]    In step S 3411 , by using the GPS  38 , the CPU  31  obtains local information regarding the low-power apparatus  3 . The local information includes latitude, longitude, and altitude, and indicates a low-power-apparatus installation location. 
         [0056]    In step S 3412 , the CPU  31  generates communication control information. The communication control information is information that the portable phone  1  uses for communication with the low-power apparatus  3 . The communication control information includes low-power-apparatus identification information, a low-power-device installation location, a frequency, a channel, a radio-wave output, a maximum communication area, a communication protocol, and a communication program. The low-power-apparatus identification information is information for identifying a low-power apparatus, and includes, for example, a MAC address. The low-power-apparatus installation location represents the location at which the low-power apparatus  3  is installed. This information is obtained in step S 3411  described above. The frequency represents the frequency band of radio waves of the wireless LAN used for communication between the portable phone  1  and the low-power apparatus  3 . The channel in this case refers to a wireless LAN frequency band separated at regular intervals. The portable phone  1  and the low-power apparatus  3  uses the channel for performing communication with each other. The radio-wave output represents the strength of the radio waves used in the communication between the portable phone  1  and the low-power apparatus  3 . The maximum communication area represents an approximate maximum distance of communication that can be performed between the portable phone  1  and the low-power apparatus  3 . The communication protocol represents a procedure used in the communication between the portable phone  1  and the low-power apparatus  3 . This procedure indicates, for example, a LAN (WLAN), AM, or FM. The communication protocol  5427  represents a program that runs on the portable phone  1  to implement the procedure used in the communication between the portable phone  1  and the low-power apparatus  3 . The communication control information is contained in the low-power-apparatus communication-control-information registration request program  342  or is stored in the storage unit  34 . 
         [0057]    In step S 3413 , the CPU  31  generates a packet containing the communication control information and transmits the packet to the wide-area base-station  5 . 
         [0058]    In step S 3414 , the CPU  31  receives, from the wide-area base-station  5 , a response packet corresponding to the packet transmitted in step S 3413 . The response packet contains information indicating whether the communication-control-information registration processing performed by the wide-area base-station  5  succeeded or failed. 
       7. Operation of Wide-Area Base Station 
       [0059]      FIG. 12  is a flowchart showing a procedure of processing of the wide-area base-station  5  when the communication control information registration ( 1 ) shown in  FIG. 1  is performed. By controlling the wide-area-base-station communication-control-information registration program  541 , the CPU  51  of the wide-area base station  5  achieves processing for registering the communication control information received from the low-power apparatus  3 . 
         [0060]    In step S 5411 , the CPU  51  receives the packet containing the communication control information from the low-power apparatus  3 . 
         [0061]    In step S 5412 , the CPU  51  retrieves the communication control information from the received packet and stores the retrieved communication control information in the low-power-apparatus communication control data  542 . 
         [0062]    In step S 5413 , the CPU  51  generates a response packet that contains information indicating whether the processing performed in step S 5412  succeeded or failed, and transmits the generated response packet to the low-power apparatus  3 . 
         [0063]    Next, a description will be given of the processing of the portable phone  1  and the wide-area base-station  5  when the low-power-apparatus search ( 2 ) shown in  FIG. 1  is performed. 
       8. Operation of Portable Phone 
       [0064]    Steps S 1411  and S 1412  shown in  FIG. 13  (which correspond to the low-power-apparatus search ( 2 ) in  FIG. 1 ) show a procedure for processing when the portable phone  1  transmits a low-power-apparatus search request to the wide-area base-station  5 . By controlling the portable-phone communication program  141 , the CPU  11  of the portable phone  1  achieves processing related to the low-power-apparatus search request that the portable phone  1  transmits to the wide-area base-station  5 . 
         [0065]    In step S 1411 , the CPU  11  generates a packet for a low-power-apparatus search request and transmits the generated packet to the wide-area base-station  5 . The transmission of the packet uses a channel and a control timeslot used in a previously established communication. In this case, it is assumed that CH2 and TS8 are used. CH2 includes call timeslot “TS16”, but TS16 is not used in this case. The packet contains local information regarding the portable phone  1 . The local information includes latitude, longitude, and altitude. The local information is obtained through the use of the GPS  18 . 
         [0066]    In step S 1412 , the CPU  11  receives, from the wide-area base-station  5 , a response packet corresponding to the packet transmitted in step S 1411 . The response packet contains communication control information of the low-power apparatus  3  located in close proximity to the portable phone  1 . The communication control information is similar to the low-power-apparatus communication control data shown in  FIG. 7 . The CPU  11  stores the communication control information in the RAM  12  or the storage unit  14 . 
       9. Operation of Wide-Area Base Station 
       [0067]    Steps S 5431  to S 5433  in  FIG. 14  (which correspond to the low-power-apparatus search ( 2 ) in  FIG. 1 ) show a procedure when the wide-area base-station  5  processes the low-power-apparatus search request received from the portable phone  1 . By controlling the wide-area-base-station communication program  543 , the CPU  51  of the wide-area base-station  5  achieves processing related to a low-power-apparatus search request received from the portable phone  1 . 
         [0068]    In step S 5431 , the CPU  51  receives a packet for the low-power-apparatus search from the portable phone  1 . 
         [0069]    In step S 5432 , the CPU  51  retrieves local information from the received packet. Based on the local information, the CPU  51  searches for the low-power-apparatus communication control data  542 . This search is aimed to search for information related to low-power-apparatus installation locations in close proximity to the local information. When the number of pieces of communication control information obtained by the search is one, the CPU  51  determines, as the communication target of the portable phone  1 , the low-power apparatus  3  indicated by the obtained communication control information. When the number of pieces of communication control information obtained by the search is two or more, the CPU  51  determines the communication target of the portable phone  1  by using one of two methods described below. In a first method, the CPU  51  first calculates the distances between the portable phone  1  and low-power apparatuses  3  based on the local information of the portable phone  1  and the low-power-apparatus installation locations contained in the communication control information. Of the distances relative to the low-power apparatuses  3 , the CPU  51  determines the low-power apparatus  3  having the shortest distance as the communication target of the portable phone  1 . In a second method, the CPU  51  first calculates the distances between the portable phone  1  and the low-power apparatuses  3  based on the local information of the portable phone  1  and the low-power-apparatus installation locations contained in the communication control information. The CPU  51  then calculates decay rates from the distances. The decay rate calculation utilizes the property of a radio wave strength that decays in inverse proportion to the square of the distance. The CPU  51  multiplies the decay rate by a radio-wave intensity in the communication control information to calculate the radio-wave intensity of the low-power apparatus  3 . Lastly, the CPU  51  determines the low-power apparatus  3  having the strongest radio-wave intensity as the communication target of the portable phone  1 . 
         [0070]    In step S 5433 , the CPU  51  generates a packet containing the communication control information obtained in step S 5432  described above and transmits the generated packet to the portable phone  1 . 
         [0071]    Next, a description will be given of processing of the portable phone  1 , the low-power apparatus  3 , the wide-area base-station  5 , and the exchange  7  when the new channel establishment ( 3 ) shown in  FIG. 1  is performed. 
       10. Operation of Portable Phone 
       [0072]    Steps S 1413  to S 1421  in  FIG. 13  (which correspond to the new channel establishment ( 3 ) in  FIG. 1 ) show a procedure when the portable phone  1  establishes a communication with the exchange  7  via the low-power apparatus  3  based on the communication control information obtained in step S 1412 . By controlling the portable-phone communication program  141 , the CPU  11  of the portable phone  1  achieves processing for establishing communication with the exchange  7  via the low-power apparatus  3 . 
         [0073]    In step S 1413 , based on the communication control information received in step S 1412 , the CPU  11  selects a low-power apparatus  3  that becomes a communication target. When the number of pieces of communication control information obtained by the search is one, the CPU  11  determines, as the communication target of the portable phone  1 , the low-power apparatus  3  indicated by the obtained communication control information. When the number of pieces of communication control information obtained by the search is two or more, the CPU  11  determines the communication target of the portable phone  1  by using one of two methods described below. In a first method, the CPU  11  first calculates the distances between the portable phone  1  and low-power apparatuses  3  based on the local information of the portable phone  1  and the low-power-apparatus installation locations contained in the communication control information. The CPU  11  determines, as the communication target of the portable phone  1 , the low-power apparatus  3  having the shortest distance of the calculated distances. In a second method, the CPU  11  first calculates the distances between the portable phone  1  and low-power apparatuses  3  based on the local information of the portable phone  1  and the low-power-apparatus installation locations contained in the communication control information. The CPU  11  then calculates decay rates from the distances. The decay-rate calculation utilizes the property of a radio wave strength that decays in inverse proportion to the square of the distance. Next, the CPU  11  multiplies the decay rates by radio-wave intensities in the communication control information to calculate the radio-wave intensities of the low-power apparatuses  3 , respectively. Lastly, the CPU  11  determines the low-power apparatus  3  having the strongest radio-wave intensity as the communication target of the portable phone  1 . When the portable phone  1  does not store a program for realizing the procedure used for communication with the low-power apparatus  3 , the portable phone  1  uses a communication program in the communication control information to communicate with the low-power apparatus  3 . 
         [0074]    In step S 1414 , the CPU  11  generates a packet for a control-channel establishment request and transmits the generated packet to the low-power apparatus  3 . The packet contains a control IP address assignment command. The packet transmission uses an available channel included in the frequency band of the low-power apparatus  3  determined in step S 1413 . It is assumed in this case that channel “CH6” is used. The packet transmission/reception processing in steps S 1414  to S 1421  uses “CH6”. 
         [0075]    In step S 1415 , the CPU  11  receives a packet containing a control IP address from the low-power apparatus  3 . This reception uses “CH6”. The CPU  11  retrieves the control IP address from the received packet and stores the control IP address as the control IP address  1426  in the portable-phone communication data  142 . This control IP address serves as information used when the portable phone  1  establishes a control channel with the exchange  7  via the low-power apparatus  3 . 
         [0076]    In step S 1416 , the CPU  11  receives a packet for a control-channel establishment request from the low-power apparatus  3 . This packet contains an SIP “invite” request. 
         [0077]    In step S 1417 , the CPU  11  generates a response packet in response to the packet received in step S 1416  and transmits the generated response packet to the low-power apparatus  3 . This response contains an SIP  200  (OK) response. 
         [0078]    In step S 1418 , the CPU  11  generates a packet for a communication channel-establishment request and transmits the generated packet to the low-power apparatus  3 . 
         [0079]    In step S 1419 , the CPU  11  receives a packet containing a call IP address from the low-power apparatus  3 . The CPU  11  retrieves the call IP address from the received packet and stores the call IP address as the call IP address  1427  in the portable-phone communication data  142 . The call IP address serves as information used when the portable phone  1  establishes a call channel with the exchange  7  via the low-power apparatus  3 . 
         [0080]    In step S 1420 , the CPU  11  receives a packet for a call-channel establishment request from the low-power apparatus  3 . This packet contains an SIP “invite” request. 
         [0081]    In step S 1421 , the CPU  11  generates a response packet in response to the packet received in step S 1416  and transmits the generated response packet to the low-power apparatus  3 . This packet contains an SIP  200  (OK) response. 
         [0000]    11. Operation of Low-Power Apparatus Steps S 3422  to S 3433  in  FIG. 15  (which are included in the new channel establishment ( 3 ) in  FIG. 1 ) show a procedure for processing when the low-power apparatus  3  establishes a communication between the portable phone  1  and the exchange  7  based on the request received from the portable phone  1 . By controlling the low-power-apparatus communication program  342 , the CPU  31  of the low-power apparatus  3  achieves processing for establishing a communication between the low-power apparatus  3  and the exchange  7 . 
         [0082]    In step S 3421 , the CPU  31  receives a packet containing a control-channel establishment request from the portable phone  1 . This reception uses “CH6”. 
         [0083]    In step S 3422 , the CPU  31  assigns a control IP address that is unused one of IP addresses stored in the storage unit  34  of the low-power apparatus  3 . In this case, it is assumed that “10.10.10.8” is assigned as the control IP address. 
         [0084]    In step S 3423 , the CPU  31  generates a packet containing the control IP address assigned in step S 3423  and transmits the generated packet to the portable phone  1 . This transmission uses “CH6”. 
         [0085]    In step S 3424 , the CPU  31  generates a packet containing the control IP address assigned in step S 3423  and transmits the generated packet to the exchange  7 . This transmission uses an address that the administrator of the exchange  7  makes available to the user of the low-power apparatus  3  in advance. 
         [0086]    In step S 3425 , the CPU  31  relays the control-channel establishment request packet, received from the exchange  7 , to the portable phone  1 . This packet contains an SIP “invite” request. This relay uses “CH6”. 
         [0087]    In step S 3426 , the CPU  31  relays the control-cannel-establishment response packet, received from the portable phone  1 , to the exchange  7 . This packet contains the SIP  200  (OK) response. This relay uses “CH6”. 
         [0088]    In step S 3427 , the CPU  31  receives a packet for a call-channel establishment request from the portable phone  1 . This reception uses “CH6”. 
         [0089]    In step S 3428 , the CPU  31  assigns a call IP address that is unused one of IP addresses stored in the storage unit  34  of the low-power apparatus  3 . In this case, it is assumed that “10.10.10.16” is assigned as the call IP address. 
         [0090]    In step S 3429 , the CPU  31  generates a packet containing the call IP address assigned in step S 3429  and transmits the generated packet to the portable phone  1 . This transmission uses “CH6”. 
         [0091]    In step S 3430 , the CPU  31  generates a packet containing the call IP address assigned in step S 3423  and transmits the generated packet to the exchange  7 . This transmission uses the address that the administrator of the exchange  7  makes available to the user of the low-power apparatus  3  in advance. 
         [0092]    In step S 3431 , the CPU  31  relays the call-channel establishment request packet, received from the exchange  7 , to the portable phone  1 . This packet contains an SIP “invite” request. This relay uses “CH6”. 
         [0093]    In step S 3432 , the CPU  31  relays the call-cannel-establishment response packet, received from the portable phone  1 , to the exchange  7 . This packet contains the SIP  200  (OK) response. This relay uses “CH6”. 
       12. Operation of Exchange 
       [0094]    S 7411  to S 7418  in  FIG. 16  (which are included in the new channel establishment ( 3 ) in  FIG. 1 ) show a procedure for processing when the exchange  7  establishes a new communication between the portable phone  1  and the exchange  7  based on the request received from the low-power apparatus  3 . By controlling the exchange communication program  742 , the CPU  71  of the exchange  7  achieves processing for establishing a new communication between the portable phone  1  and the exchange  7 . 
         [0095]    In step S 7411 , the CPU  71  receives the packet containing the control IP address from the low-power apparatus  3 . This reception uses the address that the administrator of the exchange  7  makes available to the user of the low-power apparatus  3  in advance. The CPU  71  retrieves the control IP address from the received packet and stores the control IP address as the control IP address  7426  in the exchange communication data  742 . 
         [0096]    In step S 7412 , the CPU  71  generates a packet for a control-channel-establishment request. This packet contains an SIP “invite” request that indicates, as a transmission destination (To Header), the control IP address contained in the packet received in step S 7411 . 
         [0097]    In step S 7413 , the CPU  71  transmits the packet generated in step S 7412  to the low-power apparatus  3 . This transmission uses the address of the low-power apparatus  3 , the address being contained in the packet received in step S 7411 . 
         [0098]    In step S 7414 , the CPU  71  receives the control-channel establishment response packet from the low-power apparatus  3 . This reception uses the address that the administrator of the exchange  7  makes available to the user of the low-power apparatus  3  in advance. This packet contains the SIP  200  (OK) response. 
         [0099]    In step S 7415 , the CPU  71  receives the packet containing the call IP address from the low-power apparatus  3 . This reception uses the address that the administrator of the exchange  7  makes available to the user of the low-power apparatus  3  in advance. This CPU  71  retrieves the call IP address from the received packet and stores the call IP address as the call IP address  7427  in the exchange communication data  742 . 
         [0100]    In step S 7416 , the CPU  71  generates a packet for a call-channel establishment request. This packet contains an SIP “invite” request that indicates, as a transmission destination (To Header), the call IP address contained in the packet received in step S 7415 . 
         [0101]    In step S 7417 , the CPU  71  transmits the packet generated in step S 7416  to the low-power apparatus  3 . This transmission uses the address of the low-power apparatus  3 , the address being contained in the packet received in step S 7411 . 
         [0102]    In step S 7418 , the CPU  71  receives the call-channel establishment response packet from the low-power apparatus  3 . This packet contains the SIP  200  (OK) response. This reception uses the address that the administrator of the exchange  7  makes available to the user of the low-power apparatus  3  in advance. 
         [0103]    Lastly, a description will now be given of processing of the portable phone  1 , the low-power apparatus  3 , the wide-area base-station  5 , and the exchange  7  when the channel switching ( 4 ) shown in  FIG. 4  is performed. 
       13. Operation of Portable Phone 
       [0104]    S 1422  to S 1425  in  FIG. 13  (which are included in the channel switching ( 4 ) in  FIG. 1 ) show a procedure for processing when the portable phone  1  performs processing for switching between the communication used in the previous call and the communication newly established in the new channel establishment ( 3 ). By controlling the portable-phone communication program  141 , the CPU  11  of the portable phone  1  achieves processing for switching between the communication used in the previous call by the portable phone  1  and the communication newly established in the new channel establishment ( 3 ). 
         [0105]    In step S 1422 , the CPU  11  generates a packet for handover and transmits the generated packet to the wide-area base-station  5 . This packet contains a command for releasing a call channel that has been previously used. This transmission uses “CH2”. 
         [0106]    In step S 1423 , the CPU  11  generates a packet for handover and transmits the generated packet to the low-power apparatus  3 . The packet contains a command for continuously using the newly established call channel. This transmission uses “CH6”. 
         [0107]    In step S 1424 , the CPU  11  receives a packet for a channel releasing request from the wide-area base-station  5 . The CPU  11  generates a packet for a channel release response. The channel to be released in this case is the call channel “CH2” used in the previous communication. 
         [0108]    In step S 1425 , the CPU  11  transmits the channel-release response packet generated in step S 1424  to the wide-area base-station  5 . 
       14. Operation of Low-Power Apparatus 
       [0109]    Step S 3433  in  FIG. 15  shows a procedure for handover processing of the low-power apparatus  3 . By controlling the low-power-apparatus communication program  341 , the CPU  31  of the low-power apparatus  3  achieves processing performed in step S 3433 . 
         [0110]    In step S 3433 , the CPU  31  performs processing for relaying the handover request packet, received from the portable phone  1 , to the exchange  7 . This packet is the packet that the portable phone  1  received in step S 1423  shown in  FIG. 13 . 
         [0000]    15. Operation of Wide-Area Base Station Steps S 5334  to S 5436  in  FIG. 14  show a procedure for the handover processing of the wide-area base-station  5 . By controlling the wide-area-base-station communication program  541 , the CPU  51  of the wide-area base-station  5  achieves the handover processing of the wide-area base-station  5 . 
         [0111]    In step S 5434 , the CPU  51  relays the channel-release request packet, received from the portable phone  1 , to the exchange  7 . This packet is the packet that the portable phone  1  received in step S 1422  shown in  FIG. 13 . 
         [0112]    In step S 5435 , the CPU  51  relays a handover response packet, received from the exchange  7 , to the portable phone  1 . This packet is a packet transmitted from the exchange  7  in step S 7422  described below and shown in  FIG. 16 . 
         [0113]    In step S 5436 , the CPU  51  receives the channel-release response packet from the portable phone  1 . The CPU  51  releases the call channel used in the previous communication. Specifically, the CPU  51  deletes the call timeslot  5444  in the wide-area-base-station communication data  544 . This processing is performed in order to increases the number of channels used by other portable phones converted by the wide-area base-station  5 . 
       16. Operation of Exchange 
       [0114]    Steps S 7419  to S 7422  in  FIG. 16  (which are included in the channel switching ( 4 ) in  FIG. 1 ) show a procedure for the handover processing of the exchange  7 . By controlling the exchange communication program  741 , the CPU  71  of the exchange  7  achieves processing for the handover processing of the exchange  7 . 
         [0115]    In step S 7419 , the CPU  71  receives a handover request packet from the wide-area base-station  5 . This packet contains a command for releasing the previously used call channel. 
         [0116]    In step S 7420 , the CPU  71  receives the handover request packet from the low-power apparatus  3 . This packet contains a command for continuously using the newly established call channel. 
         [0117]    In step S 7421 , the CPU  71  changes the call timeslot state  7425  in the exchange communication data  742  from a “used state” to an “unused state”. This processing is performed when the release command received in step S 7414  and the continuation command received in step S 7420  agree with each other. This processing is aimed to release the call channel of four channels that the exchange  7  used in the previous communication with the portable phone  1 . The released call channel corresponds to “TS16” in the call timeslot  7424  in the exchange communication data  742 . The other three channels correspond to the control timeslot “TS8” indicated by  7423 , the control IP address “10.10.10.8” indicated by  7426 , and the call IP address “10.10.10.16” indicated by  7427 , the control timeslot and the IP addresses being contained in the exchange communication data  742 . 
         [0118]    In step S 7422 , the CPU  71  generates a packet for a channel release request and transmits the generated packet to the wide-area base-station  5 . This packet contains a command for releasing a channel. The channel in this case refers to the call channel used in the previous communication by the wide-area base-station  5 . This channel corresponds to call time slot “TS16” (indicated by  5444 ) in the wide-area base-station communication data  544 . 
         [0119]    Although the present invention has been described above in conjunction with the embodiment thereof, the present invention is not limited thereto. Thus, the present invention can be carried out in various modifications and variations without departing from the spirit and scope of the present invention.