Abstract:
A position information acquisition device includes, a first communication unit to communicate with at least another position information acquisition device; a detection unit to detect whether a number of other position information acquisition devices that are not communicable with the first communication unit reaches a threshold or higher based on history information that records position information of the other position information acquisition devices that were previously communicable with the first communication unit and information of the other position information acquisition devices that are currently communicable with the first communication unit; a position measuring unit to measure a position of the position information acquisition device when the detection unit performs a detection; and a second communication unit to transmit position information measured by the position information measuring unit to a server that manages position information of the position information acquisition device and the other position information acquisition devices.

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. 2010-19752, filed on Jan. 29, 2010, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein relate to a position information acquisition device, a position information acquisition program and a position information acquisition system. 
       BACKGROUND 
       [0003]    Technologies to acquire position information of devices etc. are conventionally known. As one example of technologies to acquire position information of devices etc., Japanese Laid-open Patent Publication No. 2004-179905 discusses a technology in which position information acquired by a devices etc. is transmitted to an external device and the external device manages the movement path of the device. 
         [0004]    As another example of technologies to acquire position information of devices etc., Japanese Laid-open Patent Publication No. 2008-85785 discusses a technology that groups devices etc. that are assumed to be carried together and issues an alarm when any of the devices does not exist in a certain distance, and notifying the user that the device is being left behind. 
         [0005]    Losing a position of a device may hinder work when maintaining, inspecting, and moving many devices, thus managing position information of devices etc. collectively by an external device etc. has been performed. 
       SUMMARY 
       [0006]    In accordance with an aspect of the embodiments, a position information acquisition device includes, a first communication unit to communicate with at least another position information acquisition device; a detection unit to detect whether a number of other position information acquisition devices that are not communicable with the first communication unit reaches a threshold or higher based on history information that records position information of the other position information acquisition devices that were previously communicable with the first communication unit and information of the other position information acquisition devices that are currently communicable with the first communication unit; a position measuring unit to measure a position of the position information acquisition device when the detection unit performs a detection; and a second communication unit to transmit position information measured by the position information measuring unit to a server that manages position information of the position information acquisition device and the other position information acquisition devices. 
         [0007]    The object and advantages of the invention will be realized and attained by at least the features, elements and combinations particularly pointed out in the claims. 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 various embodiments, as claimed. 
         [0008]    The above-described embodiments of the present invention are intended as examples, and all embodiments of the present invention are not limited to including the features described above. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]    These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0010]      FIG. 1  is a configuration of an example of a position information acquisition system according to an embodiment; 
           [0011]      FIG. 2  is a hardware configuration of an example of a position information DB server; 
           [0012]      FIG. 3  is a hardware configuration of an example of a position information acquisition device; 
           [0013]      FIG. 4  is a block diagram of an example of a position information DB server according to the embodiment; 
           [0014]      FIG. 5  is a block diagram of an example of a position information acquisition device according to the embodiment; 
           [0015]      FIG. 6  illustrates processing procedures of a position information acquisition system according to the embodiment (1 of 2); 
           [0016]      FIG. 7  illustrates processing procedures of the position information acquisition system according to the embodiment (2 of 2); 
           [0017]      FIG. 8  illustrates a data structure of an example of an own node position information history DB; 
           [0018]      FIG. 9  illustrates a data structure of an example of a node position information history DB; 
           [0019]      FIG. 10  illustrates a data structure of an example of an adjacent node acquisition method of each node DB; 
           [0020]      FIG. 11  illustrates a data structure of an example of an adjacent nodes position information history DB; 
           [0021]      FIG. 12  illustrates a data structure of an example of an own node movement determination method of each node DB; 
           [0022]      FIG. 13  is a flowchart illustrating a first method in which an own node movement determination function unit determines a movement of the own node; 
           [0023]      FIGS. 14A ,  14 B, and  14 C illustrate one example of the first method in which the own node movement determination function unit determines a movement of the own node; and 
           [0024]      FIGS. 15A ,  15 B, and  15 C illustrate one example of a second method in which the own node movement determination function unit determines a movement of the own node. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    The problems were discovered by inventor, as one example of methods to acquire accurate position information of a device, for example, a global positioning system (GPS) is often used. However, measuring position information by some GPSs are costly. For example, some devices seldom move. For devices that seldom move, reducing cost may be considered by measuring a position with a certain interval by a GPS to determine whether the device has been moved. However, the measurement with the certain interval incurs costs for communication and power every time measurement is performed with the certain interval. 
         [0026]    Moreover, as one example of transmission methods to transmit position information acquired by a device to an external device, a mobile phone network is often used because of the wide communication area. However, using the mobile phone network has drawbacks in that communication cost is caused and power consumption is large. 
         [0027]    In the embodiment, an example in which a position information acquisition device is installed on a machine tool will be described. However, the position information acquisition device may be installed on devices and apparatuses other than machine tools. 
         [0028]      FIG. 1  is a configuration of an example of a position information acquisition system according to an embodiment. A position information acquisition system  1  includes a position information DB server  11 , a client PC 12 , position information acquisition devices  13 A to  13 D, and machine tools  14 A to  14 D. Hereinafter, if a position information acquisition device may be any of the position information acquisition devices  13 A to  13 D, the device is simply called a position information acquisition device  13 . If a machine tool may be any of the machine tools  14 A to  14 D, the machine tool is simply called a machine tool  14 . 
         [0029]    The position information DB server  11  manages position information of a plurality of position information acquisition devices that includes the position information acquisition devices  13 A to  13 D. The client PC 12  is communicably connected to a position information DB server  11  through a network  15  such as the Internet. The client PC 12  may refer to position information managed by the position information DB server  11 . 
         [0030]    The machine tools  14 A to  14 D are installed in a factory illustrated in  FIG. 1 . The machine tool  14 A is equipped with the position information acquisition device  13 A, and connected with the position information acquisition device  13 A through a wired LAN, and supplies power to the position information acquisition device  13 A. The machine tools  14 B to  14 D are also equipped with the position information acquisition device  13 B to  13 D and connected to the position information acquisition devices  13 B to  13 D with a wired LAN and supply power to the position information acquisition devices  13 B to  13 D. The position information acquisition devices  13 A to  13 D include batteries and may be operated without power supplied from the machine tools  14 A to  14 D. The position information acquisition devices  13 A to  13 D may be operated with batteries when the devices are stored in a warehouse as stocks prior to be installed in the factory. 
         [0031]    The position information acquisition devices  13 A to  13 D perform short distance communication, for example, through a wired LAN, a wireless LAN, and a Bluetooth (registered trademark) with an adjacent position information acquisition device  13 . The position information acquisition devices  13 A to  13 D acquire a position of the own device respectively, which will be described later. Position information acquired by the position information acquisition devices  13 A to  13 D includes at least one of latitude and longitude information measured by a GPS, a mobile phone station or an access point of a wireless LAN used for communication, an IP address of a gateway device used for communication, and an IP address of the own device. 
         [0032]    The position information acquisition device  13 A illustrated in  FIG. 1  may acquire position information of the position information acquisition devices  13 B to  13 D by performing short distance communication with the position information acquisition devices  13 B to  13 D. The position information acquisition device  13 A determines whether the own device is moved or not based on the number of the position information acquisition devices  13 B to  13 D to which short distance communication is possible or the number of the position information acquisition devices  13 B to  13 D the position information of which is changed. 
         [0033]    The position information acquisition device  13 A acquires position information when the position information acquisition device  13 A determines the own device is moved. The position information acquisition device  13 A may measure more accurate position information, for example, by using a GPS, which is costly. The position information acquisition device  13 A transmits the acquired position information to the position information DB server  11  through a carrier (mobile phone) network  16  and the network  15 . 
         [0034]      FIG. 2  is a hardware configuration of an example of a position information DB server. The position information DB server  11  includes an input device  21 , an output device  22 , a drive device  23 , an auxiliary storage device  24 , a main storage device  25 , an arithmetic processing unit  26  and an interface device  27  that are interconnected through a bus  29 . 
         [0035]    The input device  21  is, for example, a keyboard and a mouse. The input device  21  is used for inputting various signals. The output device  22  is, for example, a display device. The output device  22  is used for displaying various windows and data etc. The interface device  27  is, for example, a modem or a LAN card. The interface device  27  is used to connect to the network  15 . 
         [0036]    A program that controls the position information DB server  11  is provided through distribution of a storage medium  28  or a download from the network  15 . The program is installed in the auxiliary storage device  24 . The auxiliary storage device  24  stores desired files and data etc. other than the installed program. 
         [0037]    The main storage device  25  reads the program from the auxiliary storage device  24  when the position information DB server  11  is started. The arithmetic processing device  26  achieves various types of unit processing and functions, which will be described later, according to the program stored in the main storage device  25 . 
         [0038]      FIG. 3  is a hardware configuration of an example of a position information acquisition device. The position information acquisition device  13  includes an input device  31 , an output device  32 , a drive device  33 , an auxiliary storage device  34 , a main storage device  35 , an arithmetic processing unit  36  and an interface device  37  that are interconnected through a bus  39 . 
         [0039]    The input device  31  is, for example, a keyboard and a mouse. The input device  31  is used for inputting various signals. The output device  32  is, for example, a display device. The output device  32  is used for displaying various windows and data etc. The interface device  37  includes interfaces for a short distance communication and for a carrier network, and a GPS receiver. 
         [0040]    The interface for short distance communication is, for example, a wired LAN, a wireless LAN, and Bluetooth (registered trade mark). The interface for the carrier network is, for example, a communication card that supports the carrier (mobile phone) network  16 . The GPS receiver receives a radio wave from a GPS satellite and measures a position. The interface for the carrier network and the GPS receiver are implemented, for example, by a communication card with a GPS function. 
         [0041]    The position information acquisition program according to the embodiment is at least a part of various programs that control the position information acquisition device  13 . The position information acquisition program is provided through distribution of a storage medium  38  and a download from the network. As the storage medium  38  that stores the position information acquisition program, various types of storage media may be used such as a storage medium that stores information optically or magnetically such as a Compact Disc-Read Only Memory (CD-ROM), a flexible disk, and a magneto-optical disk, or a semiconductor memory that stores information electronically such as a Read Only Memory (ROM) and a flash memory. 
         [0042]    The position information acquisition program is installed in the auxiliary storage device  34  from the storage medium  38  through the drive device  33 . The position information acquisition program downloaded from the network is installed in the auxiliary storage device  34  through the interface device  37 . The auxiliary storage device  34  stores desired files and data etc. other than the position information acquisition program. 
         [0043]    The main storage device  35  reads the position information acquisition program from the auxiliary storage device  34  when the position information acquisition device  13  is started. The arithmetic processing device  36  achieves various types of unit processing and functions, which will be described later, according to the position information acquisition program stored in the main storage device  35 . In order to save power consumption and reduce the size, the input device  31 , the output device  32 , the drive device  33 , and the storage medium  38  may be omitted when the position information acquisition device  13  is installed on the machine tool  14 . 
         [0044]      FIG. 4  is a block configuration of an example of a position information DB server according to the embodiment. The position information DB server  11  in  FIG. 4  includes a node position information acquisition function unit  41 , a server request instruction function unit  42 , a node transmission/reception function unit  43 , a node position information history DB 44 , an adjacent node acquisition method of each node DB 45 , and an own node movement determination method of each node DB 46 . 
         [0045]    The node position information acquisition function unit  41  acquires position information from the position information acquisition device  13  (hereinafter called a node). The server request instruction function unit  42  instructs an adjacent node acquisition method or an own node movement determination method to a node as a server request. The node transmission/reception function unit  43  performs communication with a node. 
         [0046]    The node position information history DB 44  stores history of position information acquired from a node. The adjacent node acquisition method of each node DB 45  stores an adjacent node acquisition method that is instructed to a node as a server request. The own node movement determination method of each node DB 46  stores an own node movement determination method instructed to a node as a server request. 
         [0047]      FIG. 5  is a block diagram of an example of a position information acquisition device according to the embodiment. The position information acquisition device  13  in  FIG. 5  includes a server transmission/reception function unit  51 , a node transmission/reception function unit  52 , an own node movement determination function unit  53 , a server request acquisition function unit  54 , an own node position information acquisition function unit  55 , an adjacent node position information acquisition function unit  56 , an own node position information history DB 57 , an adjacent node position information history DB 58 , an adjacent node acquisition method DB 59 , and an own node movement determination method DB 60 . 
         [0048]    The server transmission/reception function unit  51  communicates with the position information DB server  11 . The node transmission/reception function unit  52  communicates with adjacent nodes of each node (an adjacent node). The own node movement determination function unit  53  determines whether an own node is moved or not, which will be described later. The server request acquisition function unit  54  acquires an adjacent node acquisition method or an own node movement determination method instructed from the position information DB server  11  as a server request. 
         [0049]    The own node position information acquisition function unit  55  acquires position information of the own node. The adjacent node position information acquisition function unit  56  acquires position information of an adjacent node. The own node position information history DB 57  stores a history of position information of the own node. The adjacent node position information history DB 58  stores a history of position information acquired from an adjacent node. The adjacent node acquisition method  59  stores an adjacent node acquisition method instructed from the position information DB server  11 . The own node movement determination method DB 60  stores an own node movement determination method instructed from the position information DB server  11 . 
         [0050]    Hereinafter, processing procedures of the position information acquisition system according to the embodiment will be described.  FIG. 6  and  FIG. 7  illustrate processing procedures of a position information acquisition system according to the embodiment. Note that  FIG. 6  and  FIG. 7  illustrate a node A and a node B among a plurality of nodes included in the position information acquisition system according to the embodiment. 
         [0051]    In operation S 1  of  FIG. 6 , the position information DB server  11  performs a position information acquisition request to the node A. The node position information acquisition function unit  41  of the position information DB server  11  performs a position information acquisition request to the node A by using the node transmission/reception function unit  43 . The own node position information acquisition function unit  55 A of the node A receives the position information acquisition request from the position information DB server  11  by using a server transmission/reception function unit  51 A. The own node position information acquisition function unit  55 A of the node A that receives the position information acquisition request from the position information DB server  11  acquires position information of the own node (the node A itself). The own node position information acquisition function unit  55 A stores the acquired own node position information in an own node position information history DB 57 A. 
         [0052]      FIG. 8  illustrates a data structure of an example of an own node position information history DB. The own node position information history DB 57 A stores a history of the acquired own node position information. The own node position information history DB 57 A illustrated in  FIG. 8  includes a node name, a position acquisition time, a GPS (latitude), a GPS (longitude), an IP address, a GWIP address, a wireless LAN-AP, and a transmission destination as data item. 
         [0053]    The position information acquisition time is when the position information is acquired. The GPS (latitude) and the GPS (longitude) indicate latitude and longitude information measured by a GPS. The IP address indicates an IP address of the own node. The GWIP address indicates an IP address of a gateway device used for communication. The wireless LAN-AP indicates a wireless LAN access point used for communication. The transmission destination indicates a transmission destination of position information. 
         [0054]    In Operation S 2 , the node A acquires position information from the adjacent nodes. The adjacent node position information acquisition function unit  56 A of the node A checks adjacent nodes that exist near the own node. A method to check adjacent nodes is defined in the node A. For example, one example of methods to check adjacent nodes is to receive, from the position information DB server  11 , a list of adjacent nodes that are likely to exist near the own node based on position information of each node stored in the node position information history DB 44 . 
         [0055]      FIG. 9  illustrates a data structure of an example of the node position information history DB. The node position information history DB 44  stores a history of position information acquired from a node. The node position information history DB 44  illustrated in  FIG. 9  includes a node name, a position acquisition time, a GPS (latitude), a GPS (longitude), an IP address, a GWIP address, a wireless LAN-AP, and a transmission destination as data item. 
         [0056]    The position acquisition time is when a node acquires the position information. The GPS (latitude) and the GPS (longitude) are latitude and longitude information measured by the node using a GPS. The IP address indicates an IP address of the node for which the position information is acquired. The GWIP address indicates an IP address of a gateway device used for communication by the node for which the position information is acquired. The wireless LAN-AP indicates a wireless LAN access point used for communication by the node for which the position information is acquired. The transmission destination is that the node for which the position information is acquired transmits the position information. 
         [0057]    A method to receive the list of adjacent nodes that are likely to exist near the own node from the position information DB server  11  is, for example, transmitting position information of the own node (for example, latitude and longitude information measured by a GPS) to the position information DB server  11  and searching for adjacent nodes of the node A in the node position information history DB 44  by the position information DB server  11 . Moreover, another example to confirm adjacent nodes is, for example, the node A autonomously searches for and detects adjacent nodes, for example, by using ad hoc communication. 
         [0058]    Here, the description continues under the assumption that nodes B, C, D and E are confirmed as adjacent nodes of the node A. The adjacent node position information acquisition function unit  56 A of the node A performs position information acquisition requests to the nodes B, C, D and E by using the node transmission/reception function unit  52 A. Processing of the nodes B, C, D and E that receive the position information acquisition request is substantially the same. Thus, as one example, the processing of the node B will be described. 
         [0059]    The adjacent node acquisition method DB 59 A stores what kind of position information the node A acquires from the adjacent nodes B, C, D, and E as an adjacent node acquisition method. The adjacent node acquisition method stored in the adjacent node acquisition method DB 59 A of the node A is instructed by the position information DB server  11  based on the adjacent node acquisition method of the node A stored in the adjacent node acquisition method of each node DB 45 . 
         [0060]      FIG. 10  illustrates a data structure of an example of adjacent node acquisition method of each node DB. The adjacent node acquisition method of each node DB 45  stores the adjacent node acquisition method that is instructed to a node as a server request. 
         [0061]    The adjacent node acquisition method of each node DB 45  in  FIG. 10  includes, as data item, a node name, an update date and time, and items to be acquired as position information. For example, in  FIG. 10 , an item that the node A acquires from adjacent node as position information is an IP address, and items that the node B acquires from adjacent nodes are an IP address and a GWIP address. 
         [0062]    An own node position information acquisition function unit  55 B of the node B receives a position information acquisition request from the node A by using the node transmission/reception function unit  52 B. The own node position information acquisition function unit  55 B that receives the position information acquisition request from the node A acquires position information of the own node (the node B itself). The own node position information acquisition function unit  55 B stores the acquired own node position information in an own node position information history DB 57 B. The own node position information acquisition function unit  55 B of the node B transmits position information of the own node to the node A by using the node transmission/reception function unit  52 B. 
         [0063]    The adjacent node position information acquisition function unit  56 A of the node A receives position information of the node B from the node B by using the node transmission/reception function unit  52 A. The adjacent node position information acquisition function unit  56 A stores the received position information of the node B in an adjacent node position information history DB 58 A. 
         [0064]      FIG. 11  illustrates a data structure of an example of an adjacent nodes position information history DB. The adjacent node position information history DB 58 A stores a history of the acquired adjacent node position information. The adjacent node position information history DB 58 A includes a node name, a position acquisition time, a GPS (latitude), a GPS (longitude), an IP address, a GWIP address, and a wireless LAN-AP as data item. 
         [0065]    The position information acquisition time indicates when the adjacent node acquires the position information. The GPS (latitude) and the GPS (longitude) indicate latitude and longitude information measured by the adjacent node by using a GPS. The IP address indicates an IP address of an adjacent node for which position information is acquired. The GWIP address indicates an IP address of a gateway device used for communication by the adjacent node for which position information is acquired. Moreover, the wireless LAN-AP indicates a wireless LAN access point used for communication by the adjacent node for which position information is acquired. 
         [0066]    When the adjacent node position information acquisition function unit  56 A acquires position information from the nodes B, C, D and E, the adjacent node position information acquisition function unit  56 A notifies the own node position information acquisition function unit  55 A of the acquisition. The adjacent node position information acquisition function unit  56 A may transmit position information of the own node (the node A itself) when the adjacent node position information acquisition function unit  56 A performs a position information acquisition request to the adjacent nodes. 
         [0067]    In Operation S 3 , the node A transmits the own node position information to the position information DB server  11 . Note that the node A may transmit position information of the adjacent node together with the position information of the own node to the position information DB server  11 . The own node position information acquisition function unit  55 A of the node A may transmit position information of the own node to the position information DB server  11  by using the server transmission/reception function unit  51 A. 
         [0068]    The node position information acquisition function unit  41  of the position information DB server  11  receives position information from the node A by using the node transmission/reception function unit  43 . The node position information acquisition function unit  41  stores position information received from the node A in the node position information history DB 44  illustrated in  FIG. 9 . 
         [0069]    In operation S 4  of  FIG. 7 , the own node position information acquisition function unit  55 A of the node A periodically requests position information of the nodes B, C, D, and E to the adjacent node position information acquisition function unit  56 A. In operation S 5 , as in operation S 2  of  FIG. 6 , the adjacent node position information acquisition function unit  56 A of the node A performs position information requests to the nodes B, C, D, and E. 
         [0070]    When there is no response from any of the adjacent nodes for which position information is periodically acquired, or when the acquired position information is different from the one stored in the adjacent node position information history DB 58 A, the adjacent node position information acquisition function unit  56 A notifies the own node position information acquisition function unit  55 A accordingly. 
         [0071]    In operation S 6 , in response to the notification from the adjacent node position information acquisition function unit  56 A, the own node position information acquisition function unit  55 A requests an own node movement determination function unit  53 A to determine whether the own node is moved or not. The own node movement determination function unit  53 A determines whether the own node is moved or not, which will be described later, according to the own node movement determination method stored in an own node movement determination method DB 60 A. 
         [0072]    The own node movement determination method stored in the own node movement determination method DB 60 A is instructed by the position information DB server  11  based on the own node movement determination method stored in the own node movement determination method of each node DB 46 . 
         [0073]      FIG. 12  illustrates a data structure of an example of an own node movement determination method of each node DB. The own node movement determination method of each node DB 46  stores the own node movement determination method instructed to the node as a server request. The own node movement determination method of each node DB 46  in  FIG. 12  includes a node name, an update date and time, items of position information to check whether the node position is changed or not, the number of no-response nodes, and the number of no-responses. 
         [0074]    The update date and time indicates when the own node movement determination method of each node is updated. The items of position information to check whether the node position is changed is, for example, the IP address for the node A, the IP address and the GWIP address for the node B, the IP address, the GWIP address, and the wireless LAN-AP for the node C. In the items of position information to check whether the node position is changed or not, the double circle indicates AND operation, while the circle indicates OR operation. Moreover, the number of no-response nodes provides a threshold to determine whether the own node is moved or not based on the number of adjacent nodes that do not respond. The number of no-responses provides a threshold to determine whether the node is an adjacent node that does not respond. 
         [0075]    When the own node is determined to be moved, the own node movement determination function unit  53 A notifies the own node position information acquisition function unit  55 A of the determination result that indicates the own node is moved. When the node A is notified of the determination result that indicates the own node is moved, the node A proceeds to operation S 7 , and transmits the position information of the own node to the position information DB server  11  according to substantially the same procedures as those of operation S 3 . 
         [0076]    When the own node is determined not to be moved, the own node movement determination function unit  53 A notifies the own node position information acquisition function unit  55 A of the determination result that indicates the own node is not moved. When the own node position information acquisition function unit  55 A is notified of the determination result that indicates the own node is not moved, the processing ends without proceeding to operation S 7 . 
         [0077]    Hereinafter, how the own node movement determination function unit  53 A of the node A determines a movement of the own node will be described. The first method that the own node movement determination function unit  53 A determines whether the own node is moved or not is based on the number of adjacent nodes that do not respond to position information acquisition requests. 
         [0078]      FIG. 13  is a flowchart illustrating the first method in which the own node movement determination function unit determines a movement of the own node. Descriptions of a part of the flowchart in  FIG. 13  will be simplified because the part of the flowchart overlaps with those illustrated in  FIG. 6  and  FIG. 7 . 
         [0079]    In operations S 11  to S 14 , the node A periodically performs position information acquisition requests to the adjacent nodes and receives position information from the adjacent nodes. In operation S 15 , the node A stores position information received from the adjacent nodes in the adjacent node position information history DB 58 A. In operation S 16 , the node A determines whether the number of adjacent nodes that do not respond to the position information acquisition requests is 3 or more. The number “3,” for example, used in operation S 16  is acquired from data item of the own node movement determination method DB 60 A, “the number of no-response nodes.” The number “3” used in operation S 16  may be determined according to the number of the adjacent nodes the position information (for example, a half of the number of adjacent nodes) of which is stored in the adjacent node position information history DB 58 A. 
         [0080]    The node A returns to operation S 11  and continue the processing if the number of the adjacent nodes that do not respond to the position information acquisition requests is not 3 or more. Meanwhile, the node A reacquires the position information if the number of the adjacent nodes that do not respond to the position information acquisition requests is 3 or more. Processing proceeds to operation S 18  and the server A notifies the position information DB server  11  about the position information of the own node. 
         [0081]      FIGS. 14A ,  14 B, and  14 C illustrate one example of a first method in which the own node movement determination function unit determines a movement of the own node. Here, an example will be described in which the data item of the number of non-response nodes in the own node movement determination method DB 60 A is “3.” 
         [0082]      FIG. 14A  illustrates that the node A periodically acquires position information from the nodes B to E at normal operation.  FIG. 14B  illustrates that the node E does not respond to the position information acquisition request. The node A determines that the own node is not moved because the number of the adjacent nodes that does not respond to the position information acquisition requests is not 3 or more. 
         [0083]    In other words, the node A determines that the own node is not moved because the nodes B to D respond in substantially the same manner as before to the position information acquisition requests. Stated differently, the node A determines the node E is moved. 
         [0084]      FIG. 14C  illustrates that the nodes B to E do not respond to the position information acquisition requests. The node A determines that the own node is moved because the number of the adjacent nodes that do not respond to the position information acquisition requests is 3 or more. 
         [0085]    In other words, the node A determines that the own node is moved because the nodes B to E do not respond in substantially the same manner as before to the position information acquisition requests. Stated differently, the node A determines that the own node is moved. 
         [0086]    When the nodes D and E do not respond to the position information acquisition requests, the node A determines that the own node is not moved because the number of the adjacent nodes that do not respond to the position information acquisition requests is not 3 or more. In other words, the node A determines that the own node is not moved because the nodes B to C respond in substantially the same manner as before to the position information acquisition requests. Stated differently, the node A determines that both the nodes D and E are moved. 
         [0087]    When the nodes C to E do not respond to the position information acquisition requests, the node A determines that the own node is moved because the number of the adjacent nodes that do not respond to the position information acquisition requests is 3 or more. In other words, the node A determines that the own node is moved because the nodes C to E do not respond to the position information acquisition requests although the node B responds in substantially the same manner as before to the position information acquisition request. Stated differently, the node A determines that both the own node and the node B are moved. 
         [0088]    A second method in which the own node movement determination function unit  53 A determines whether the own node is moved or not is based on the number of the adjacent nodes the position information (for example, an IP address, a GWIP address, and a wireless LAN-AP) of which is changed. A flowchart of the second method in which the own node movement determination function unit  53 A determines a movement of the own node is substantially the same as the flowchart in  FIG. 13  other than the operation S 16 . 
         [0089]    In the second method to determine a movement of the own node, whether the number of the adjacent nodes the position information of which is changed is, for example, 3 or more is determined in the operation S 16 . The number, 3 used in the operation S 16  is acquired, for example, from the own node movement determination method DB 60 A. 
         [0090]    If the number of the adjacent nodes the position information of which is changed is not 3 or more, the node A returns to the operation S 11  and continues the processing. Meanwhile, the node A reacquires the position information if the number of the adjacent nodes the position information of which is changed is 3 or more. Processing proceeds to operation S 18  and the server A notifies the position information DB server  11  about position information of the own node. 
         [0091]      FIGS. 15A ,  15 B, and  15 C illustrate one example of a second method in which the own node movement determination function unit determines a movement of the own node.  FIG. 15A  illustrates that the node A periodically acquires position information from the nodes B to E at normal operation.  FIG. 15B  illustrates that the position information acquired from the node E is changed. The node A determines that the own node is not moved because the number of the adjacent nodes the position information of which are changed is not 3 or more. In other words, the node A determines that the own node is not moved because the position information acquired from the nodes B to D is not changed. Stated differently, the node A determines that the node E is moved. 
         [0092]      FIG. 15C  illustrates that the position information acquired from the nodes B to E is changed. The node A determines that the own node is moved because the number of the adjacent nodes the position information of which are changed is 3 or more. In other words, the node A determines that the own node is moved because the position information acquired from the nodes B to D is changed. Stated differently, the node A determines that the own node is moved. 
         [0093]    According to the embodiment, the node A reacquires the position information of the own node when the own node is determined to be moved, and notifies the position information DB server  11  of the position information. Therefore, the node A may reduce frequency to acquire position information of the own node and to notify the position information DB server  11  of the position information, and thereby power consumption and communication cost may be suppressed. 
         [0094]    Moreover, according to the embodiment, position information of the own node is reacquired and notified to the position information DB server  11  when the own node is determined to be moved. Accordingly, the position information DB server  11  may acquire accurate position information. Furthermore, according to the embodiment, the cost may further be reduced by making a node with lower cost in transmitting position information to the position information DB server  11  as a representative node and transmitting position information of each node from the representative node. 
         [0000]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. 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.