Abstract:
A method includes: receiving beacon signals transmitted by each of a plurality of beacon devices around a positioning target terminal; first calculating, based on the received beacon signals, location information indicating locations of a plurality of mobile beacon devices included in the plurality of beacon devices; selecting a plurality of second mobile beacon devices from among the plurality of mobile beacon devices by excluding one or more first mobile beacon devices having similar azimuth directions from the positioning target terminal among the plurality of mobile beacon devices based on the calculated location information; and second calculating by circuitry, based on the selected plurality of second mobile beacon devices, a location of the positioning target terminal.

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. 2016-049858, filed on Mar. 14, 2016, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present embodiments are related to a method, a system, and storage medium. 
       BACKGROUND 
       [0003]    There is known a radio beacon technology for estimating location information of a device such as a user terminal (User Equipment; hereinafter, called a “UE”), which moves and is typified by a mobile phone or the like, by using received electric field strength information (Received Signal Strength Indicator; hereinafter, called “RSSI”) of a radio wave transmitted with a fixed output by an equipment serving as a transmission source and an installation location (location information) of the equipment. 
         [0004]    In this technology, by using a property that the RSSI is attenuated at a fixed rate in accordance with a distance from the transmission source, a distance between the UE and the equipment serving as the transmission source is calculated, thereby estimating a location of the UE at that point of time. 
         [0005]    In a case where, as illustrated in, for example,  FIG. 1 , a fixed radio beacon device FN is used as the equipment serving as the transmission source, the radio beacon device FN utilizes an advertisement signal of Bluetooth (registered trademark) Low Energy (hereinafter, called “BLE”) as a beacon signal and calculates a distance between the radio beacon device FN and the UE by using RSSI information of the beacon signal, identification information (hereinafter, called “ID information”) of the radio beacon device FN, and installation location information of the radio beacon device FN, the identification information being included in the beacon signal. It is possible to specify the location of the UE, based on the installation location information of the radio beacon device FN. Furthermore, in a case where the UE is able to receive beacon signals of radio beacon devices FN, it is possible to calculate location information of the UE with a higher degree of accuracy by using a trilateration method or the like. 
         [0006]    On the other hand, there is known a radio beacon technology for estimating a location of a UE by using a radio beacon device that moves. In this technology, as illustrated in, for example,  FIG. 2 , locations of radio beacon devices MN 1  to MN 5  that move are detected in another way, for example, in a way of using fixed radio beacon devices FN 1  and FN 2  that remain stationary and locations of which are known. For this reason, the radio beacon devices MN 1  to MN 5  that move are regarded as fixed radio beacon devices. By doing so, the UE is able to estimate the location information of the self-terminal by using pieces of RSSI information of respective beacon signals transmitted by the beacon device MN 1  to MN 5  that move and locations of which are known, 
         [0007]    For the sake of convenience, in the present specification, the fixed radio beacon devices used in the former configuration are called “fixed beacon devices” or “fixed nodes”, and the mobile radio beacon devices used in the latter configuration are called “mobile beacon devices” or “mobile nodes”. As for each of these, the UE that receives a corresponding one of the beacon signals calculates the location of the self-terminal. 
         [0008]    In order to estimate the location of the UE in the above-mentioned environment in which the fixed nodes and the mobile nodes are mixed, a distance between each of a large number of fixed nodes and the UE and a distance between each of fixed nodes and mobile nodes and the UE are calculated. Furthermore, by using distance information calculated in such a way, the location information of the UE is calculated. However, in such a method, in a case where the number of nodes (the number of beacons) becomes large, a calculation amount increases, a processing load turns out to become high, and power consumption becomes high, thereby exceeding a processing capacity of the UE. 
         [0009]    In contrast, there is proposed a method for calculating a location of a UE only by using beacon signals of nodes that are included in mobile nodes and that actually remain stationary at that point of time (in other words, nodes that are movable and that temporarily stop). 
         [0010]    According to the above-mentioned proposal, by reducing the number of beacon signals to be used, it is possible to decrease a processing period of time and to reduce power consumption. In addition, it is possible to use only fixed nodes and mobile nodes in stationary states. Furthermore, it is possible to detect whether or not a mobile node is in a stationary state, by observing a corresponding one of beacon signals and a change in information of a distance from a fixed node or a mobile node that remains stationary. 
         [0011]    As an example of related art, Higuchi et al., Information Processing Society of Japan (IPSJ) 72nd National Convention, 3ZD-2, 2010, Japanese Patent No. 5792412, Japanese Laid-open Patent Publication No. 2005-099018, and Japanese National Publication of International Patent Application No. 2014-502339. 
       SUMMARY 
       [0012]    According to an aspect of the invention, a method includes: receiving beacon signals transmitted by each of a plurality of beacon devices around a positioning target terminal; first calculating, based on the received beacon signals, location information indicating locations of a plurality of mobile beacon devices included in the plurality of beacon devices; selecting a plurality of second mobile beacon devices from among the plurality of mobile beacon devices by excluding one or more first mobile beacon devices having similar azimuth directions from the positioning target terminal among the plurality of mobile beacon devices based on the calculated location information; and second calculating by circuitry, based on the selected plurality of second mobile beacon devices, a location of the positioning target terminal. 
         [0013]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0014]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  illustrates an example of positioning of a UE with use of a fixed beacon device. 
           [0016]      FIG. 2  illustrates an example of positioning of a UE with use of mobile beacon devices. 
           [0017]      FIG. 3  is a diagram for explaining positioning of a UE according to an embodiment. 
           [0018]      FIG. 4  illustrates an example of a functional configuration of a positioning server according to an embodiment. 
           [0019]      FIG. 5  illustrates an example of a fixed node information table according to an embodiment. 
           [0020]      FIG. 6  illustrates an example of a hardware configuration of the positioning server according to an embodiment. 
           [0021]      FIG. 7  is a flowchart illustrating an example of location estimation processing of a UE according to an embodiment. 
           [0022]      FIG. 8  is a flowchart illustrating an example of location calculation processing of mobile nodes according to an embodiment. 
           [0023]      FIG. 9  is a diagram for explaining location calculation of mobile nodes according to an embodiment. 
           [0024]      FIG. 10  is a flowchart illustrating an example of primary filter processing according to an embodiment. 
           [0025]    FIG,  11  is a flowchart illustrating an example of secondary filter processing according to an embodiment. 
           [0026]      FIG. 12  is a flowchart illustrating an example of tertiary filter processing according to an embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    In the above-mentioned conventional technologies, in, for example, a case where all beacons to move remain stationary, it is difficult to appropriately select beacons to be used for estimating a location of a UE. Therefore, power consumption of the UE may increase and exceed a processing capacity of the UE, and it may become difficult to estimate the location with accuracy. 
         [0028]    Therefore, in one aspect, an object of the present disclosure is to estimate a location of a terminal with accuracy while reducing power consumption. 
         [0029]    Hereinafter, an embodiment of the present disclosure will be described with reference to attached drawings. Note that, in the specification and the drawings, the same symbol is attached to a configuration element having practically the same functional configuration and the redundant description thereof will be omitted. 
         [0030]    [Outline of Location Estimation] 
         [0031]    First, an outline of location estimation according to an embodiment of the present disclosure will be described with reference to  FIG. 3 .  FIG. 3  is a diagram for explaining an outline of location estimation according to an embodiment. In  FIG. 3 , by using multi-stage filtering, mobile nodes to be used for location estimation of a UE are determined. In  FIG. 3 , a positioning server  10  aggregates pieces of information received by fixed nodes FN 1  to FN 4  serving as respective receiving stations and information received by the UE, thereby estimation a location of the UE. Hereinafter, the fixed nodes FN 1  to FN 4  are also collectively called “fixed nodes FN”. In addition, mobile nodes MN 1  to MN n  are also collectively called “mobile nodes MN”. Note that while four fixed nodes FN 1  to FN 4  are installed in the present embodiment, the number of fixed nodes is not limited to this and only has to be one or more. In the same way, as for the mobile nodes MN, “n” indicating the number of the mobile nodes MN 1  to MN n  only has to be an integer greater than or equal to one. 
         [0032]    Each of beacon signals observed by the UE has ID information of a node that transmits the relevant beacon signal, and an RSSI information. In a primary filter of the present embodiment, mobile nodes MN located within a given distance from the UE are selected. For the selection, RSSIs observed by the UE are used. By preliminarily investigating the strengths of RSSIs in a case where mobile nodes MN are located within the given distance, the selection becomes available. In  FIG. 3 , in a case where the UE receives a beacon signal of an RSSI having a strength greater than or equal to a predetermined level, a mobile node is selected as a corresponding one of the mobile nodes MN, located within the given distance from the UE. For this reason, mobile nodes MN located outside, for example, a circle C having the given distance from the UE in  FIG. 3  are mobile nodes MN that do not pass through the primary filter, and are not used for location estimation of the UE. 
         [0033]    Next, in a secondary filter, mobile nodes MN that pass through the primary filter are further narrowed down by other filtering. In the secondary filter, mobile nodes MN having near azimuth directions viewed from the UE are excluded, and mobile nodes MN (in this regard, however, three or more) that surround the UE in respective different directions are selected as far as possible. 
         [0034]    Mobile nodes MN (remaining stationary) that pass through the primary filter and the secondary filter in this way are used, and the location of the UE is estimated. Accordingly, it is possible to decrease a processing load at a time of location estimation of the UE and to reduce power consumption. Note that, based on filtering performed by the single secondary filter, the same advantage as the above-mentioned advantage may be expected without using the primary filter. 
         [0035]    Furthermore, in  FIG. 3 , the mobile nodes MN 1  to MN 7  that pass through the primary filter and the secondary filter are further narrowed down based on filtering performed by a tertiary filter. In the tertiary filter, three or more mobile nodes MN (in this regard, however, three or more) that are separate by approximately equal angles with respect to the UE are selected, for example. In, for example,  FIG. 3 , the mobile beacon devices MN 1  to MN 4  that are arranged at respective approximately equal angles (in other words, θ 1 , θ 2 , θ 3 , and θ 4  are the approximately equal angles) with respect to the UE are selected. 
         [0036]    Mobile nodes MN that pass through the primary filter to the tertiary filter in this way are used, and the location of the UE is estimated. Accordingly, it is possible to decrease a processing load at a time of location estimation of the UE and to reduce power consumption. 
         [0037]    Note that while, in the present embodiment, filtering of the mobile nodes MN is performed based on the RSSIs of the beacon signals, arrival times of the respective beacon signals or signal radio wave arrival angles may be used for relative locations between the fixed nodes and the mobile nodes without limitation to RSSIs, in the location estimation of the UE according to the present embodiment. 
         [0038]    The location calculation processing and the filtering processing of the mobile nodes, described above, are performed by the positioning server  10 . The positioning server  10  is coupled to the fixed nodes FN 1  to FN 4  and aggregates pieces of RSSI information detected by the respective fixed nodes FN 1  to FN 4  and pieces of RSSI information detected by the UE, thereby performing filtering of the mobile nodes MN, based on the RSSI information. In what follows, an example of a functional configuration of the positioning server  10  will be described with reference to  FIG. 4 . The positioning server  10  is an example of an information processing device for radio positioning. The positioning server  10  may be a server on a cloud. 
         [0039]    [Functional Configuration] 
         [0040]      FIG. 4  illustrates an example of a functional configuration of a positioning server according to an embodiment. The positioning server  10  includes a communication unit  11 , a recording unit  12 , a mobile node location calculation unit  13 , a primary filter processing unit  14 , a secondary filter processing unit  15 , a tertiary filter processing unit  16 , and a location notification unit  17 . 
         [0041]    The communication unit  11  detects pieces of RSSI information of respective beacon signals received from the mobile nodes MN and the UE by the fixed nodes FN and pieces of RSSI information of respective beacon signals received from the mobile nodes MN by the UE. 
         [0042]    The recording unit  12  records therein a fixed node information table  121 . The recording unit  12  records therein various kinds of data and various kinds of programs. The fixed node information table  121  records therein locations of the fixed beacon devices FN (hereinafter, also called “fixed nodes”).  FIG. 5  illustrates an example of the fixed node information table  121  according to an embodiment. The fixed node information table  121  includes coordinate information  121   b  for each fixed node  12   a  (each fixed beacon device FN). 
         [0043]    From pieces of RSSI information received from the respective fixed nodes FN and the pieces of coordinate information  121   b  of the respective fixed nodes  121   a  recorded in the fixed node information table  121 , the mobile node location calculation unit  13  calculates the location of the respective mobile nodes MN. 
         [0044]    From among calculated mobile nodes MN the primary filter processing unit  14  removes mobile nodes MN other than mobile nodes MN for which distances thereof from the UE serving as a positioning target fall within a predetermined distance. Mobile nodes for each of which RSSI (S 1 ) observed by the UE≧S th  [dBm] is satisfied are left as outputs of the primary filter, for example. The threshold value S th  is determined in advance by a preliminary experiment or the like. As a result, in the example of  FIG. 3 , mobile nodes located within the predetermined circle C centered at the UE are left, and mobile nodes located outside the circle C are removed by the filtering. In other words, the mobile nodes MN located outside the predetermined distance are subjected to the filtering and are not used for the location estimation of the UE. 
         [0045]    By using the secondary filter, the secondary filter processing unit  15  further narrows down the mobile nodes MN that pass through the primary filter. In other words, the secondary filter processing unit  15  removes mobile nodes MN having near azimuth directions viewed from the UE and selects mobile nodes MN (in this regard, however, three or more) that surround the UE in respective different directions as far as possible. In the example illustrated in  FIG. 3 , as a result of the secondary filter processing, the mobile nodes MN 1  to MN 7  that are separated by about a given distance C from the UE are selected, for example. 
         [0046]    In other words, based on pieces of RSSI information of respective beacon signals observed by the fixed nodes, the secondary filter processing unit  15  only causes pieces of RSSI information of respective predetermined mobile nodes MN to pass therethrough. First, four fixed nodes FN i  (1≦i≦4) in an adjacent location relationship are determined. The RSSIs of respective mobile nodes MN j  (1≦j≦m) are observed by each of the fixed nodes FN j . Indexes j of mobile nodes MN j  each having a maximum or minimum RSSI observed by a corresponding one of the fixed nodes FN i  are recorded. “j” corresponds to eight types at a maximum and corresponds to one type at a minimum. The secondary filter processing unit  15  leaves, as outputs of the secondary filter, mobile nodes each having the index j recorded as above and removes mobile nodes other than those, based on the filtering. 
         [0047]    The tertiary filter processing unit  16  further narrows down the mobile beacon devices MN that pass through the primary filter and the secondary filter, by using the tertiary filter. In other words, the tertiary filter processing unit  16  removes mobile beacon devices MN having near azimuth directions viewed from the UE and selects mobile beacon devices MN (in this regard, however, three or more) that surround the UE in respective different directions as far as possible. In, for example,  FIG. 3 , the mobile nodes MN 5  and MN 6  having near azimuth directions viewed from the UE with respect to the mobile node MN 3  are removed, and the mobile node MN 7  having a near azimuth direction viewed from the UE with respect to the mobile node MN 1  is excluded. 
         [0048]    As a result, in the tertiary filter, mobile nodes other than mobile nodes arranged at respective approximately equal angles with respect to the UE are removed from among the mobile nodes MN 1  to MN 7 . In, for example,  FIG. 3 , the mobile nodes MN 1  to MN 4  that are arranged at respective approximately equal angles (in other words, θ 1 , θ 2 , θ 3 , and θ 4  are the approximately equal angles) with respect to the UE and that are arranged at respective approximately equal distances on the circumference of the circle C are selected. 
         [0049]    The location notification unit  17  notifies the terminal UE of the pieces of RSSI information received from the respective selected mobile nodes MN 1  to MN 4  and pieces of location information of the respective mobile nodes MN 1  to MN 4 . Based on the pieces of RSSI information and pieces of location information of the respective mobile nodes MN 1  to MN 4 , given notice of, the UE estimates distances between the UE and the respective mobile nodes MN 1  to MN 4  and performs location estimation of the UE by using trilateration or the like. A low of distance attenuation in a free space is used for a method for estimating distances between nodes, based on pieces of RSSI information. 
         [0050]    [Hardware Configuration] 
         [0051]    Next, a hardware configuration of the positioning server  10  according to the present embodiment will be described with reference to  FIG. 6 .  FIG. 6  illustrates an example of a hardware configuration of the positioning server according to an embodiment. The positioning server  10  includes an input device  101 , a display device  102 , an external I/F  103 , a random access memory (RAM)  104 , a read only memory (ROM)  105 , a central processing unit (CPU)  106 , a communication I/F  107 , a hard disk drive (HDD)  108 , and so forth, and these are coupled to one another via a bus B. 
         [0052]    The input device  101  includes a keyboard, a mouse, and so forth and is used for inputting information to the positioning server  10 . The display device  102  includes a display and so forth and displays various kinds of processing results. The communication I/F  107  is an interface that couples the positioning server  10  to a network. For this reason, the positioning server  10  is able to transmit and receive signals to and from the fixed nodes FN and the UE via the communication I/F  107 . 
         [0053]    The HDD  108  is a non-volatile storage device that stores therein programs and data. Examples of the stored programs and data include a basic software to control the entire positioning server  10  and application software. Various kinds of databases, programs, and so forth may be stored in the HDD  108 , for example. 
         [0054]    The external I/F  103  is an interface with an external device. Examples of the external device includes a recording medium  103   a.  For this reason, the positioning server  10  is able to perform reading and/or writing of the recording medium  103   a  via the external I/F  103 . Examples of the recording medium  103   a  includes a compact disc (CD), a digital versatile disc (DVD), an SD memory card, and a Universal Serial Bus memory (USB memory). 
         [0055]    The ROM  105  is a non-volatile semiconductor memory (storage device) able to hold internal data even in a case of turning off a power source. In the ROM  105 , a program and data such as a network configuration are stored. The RAM  104  is a volatile semiconductor memory (storage device) that temporarily holds a program and data. The CPU  106  is an arithmetic circuit that loads programs and data onto the RAM  104  from the above-mentioned storage devices (for example, the HDD  108 , the ROM  105 , and so forth) and that performs processing, thereby realizing control of an entire device and mounted functions. 
         [0056]    In the positioning server  10  according to the present embodiment, based on such a configuration, by using data and an information processing program stored within the ROM  105  or the HDD  108 , the CPU  106  performs information processing that is related to filtering of the mobile nodes MN and that is used for location estimation of the UE. The information processing used for the location estimation of the UE includes the location calculation processing of the mobile nodes, the primary filter processing, the secondary filter processing, and the tertiary filter processing. 
         [0057]    Note that information stored in the fixed node information table  121  may be stored in the RAM  104 , the HDD  108 , or a server or the like on a cloud coupled to the positioning server  10  via the network. 
         [0058]    In addition,  FIG. 4  illustrates a block diagram focused on functions, and individual units indicated by these functional blocks may be realized only by hardware, only by software, or by a combination of hardware and software. 
         [0059]    [Entire Processing] 
         [0060]    Next, entire processing of location estimation of a UE according to the present embodiment will be described with reference to  FIG. 7 .  FIG. 7  is a flowchart illustrating an example of the location estimation processing of a UE according to an embodiment.  FIG. 7  illustrates processing operations to be performed by the individual mobile nodes MN 1 , MN 2 , . . . , and MN n , fixed nodes FN 1 , FN 2 , FN 3 , and FN 4 , positioning server  10 , and UE, in order from the left side of the plane of paper. 
         [0061]    Upon initiating the present processing, beacon signals are transmitted by the respective mobile nodes MN by using broadcasting (step S 1 ). The beacon signals are received by the fixed nodes FN 1  to FN 4  and the UE (steps S 2  and S 3 ). The communication unit  11  in the positioning server  10  receives pieces of RSSI information of the respective beacon signals received by each of the fixed nodes FN 1  to FN 4  and pieces of ID information of the respective mobile nodes MN (step S 5 ). 
         [0062]    The UE transmits, to the positioning server  10 , the pieces of RSSI information of the respective received beacon signals and the pieces of ID information of the respective mobile nodes MN (step S 4 ). The positioning server  10  receives the pieces of RSSI information and the pieces of ID information, transmitted by the UE (step S 5 ). 
         [0063]    Next, the positioning server  10  performs location calculation processing of all the mobile nodes MN (step S 10 ). The location calculation processing of the mobile nodes MN will be described later by using  FIG. 8  and  FIG. 9 . Next, the positioning server  10  performs the primary filter processing (step S 20 ). For this reason, mobile nodes MN located within a predetermined distance from the UE are selected, and remaining mobile nodes MN are removed. The primary filter processing will be described by using  FIG. 10  after the location calculation processing of the mobile nodes MN. 
         [0064]    Next, the positioning server  10  performs the secondary filter processing (step S 30 ). For this reason, from among the mobile nodes MN selected by the primary filter, one to eight mobile nodes MN for which distances thereof from the UE are roughly equal to one another are selected. The secondary filter processing will be described by using  FIG. 11  after the primary filter processing. 
         [0065]    Next, the positioning server  10  performs the tertiary filter processing (step S 40 ). For this reason, from among the mobile nodes MN selected by the secondary filter, three or more mobile nodes MN for which angles between directions of adjacent mobile nodes MN are approximately equal to each other around the UE are selected. The tertiary filter processing, will be described by using  FIG. 12  after the secondary filter processing. 
         [0066]    Next, the positioning server  10  transmits, to the UE, pieces of location information of the respective mobile nodes MN that pass through the primary to tertiary filters (step S 6 ). The UE receives the pieces of location information of the respective mobile nodes MN, transmitted by the positioning server  10  (step S 7 ). Based on the received pieces of location information of the respective mobile nodes MN, the UE performs location estimation processing of the UE itself by using trilateration or the like (step S 50 ) and terminates the present processing once. The present processing is repeated at predetermined intervals. 
         [0067]    [Location Calculation Processing of Mobile Nodes] 
         [0068]    Next, the location calculation processing of mobile nodes according to the present embodiment, called in S 10  in  FIG. 7 , will be described with reference to  FIG. 8  and  FIG. 9 .  FIG. 8  is a flowchart illustrating an example of location calculation processing of mobile nodes according to the present embodiment.  FIG. 9  is a diagram for explaining location calculation of mobile nodes according to the present embodiment. 
         [0069]    In the location calculation processing of mobile nodes MN in  FIG. 8 , first the mobile node location calculation unit  13  acquires pieces of coordinate information that indicate the installation locations of the respective fixed nodes FN 1  to FN 4  and that are recorded in the fixed node information table  121  (step S 11 ). In the present embodiment, the coordinates of the fixed nodes FN 1  to FN 4  are two-dimensional absolute coordinates (x i , y i ) and i=1 to 4 is satisfied. The unit of each element of the “x” and “y” of the coordinates is m (meter). 
         [0070]    Next, the mobile node location calculation unit  13  acquires an RSSI vector of all the mobile nodes MN 1  to MN n , received by each of the fixed nodes FN 1  to FN 4  (step S 12 ). Components of the RSSI vector are RSSIs (S 1 , to S n ) of the respective mobile nodes MN 1  to MN n . 
         [0071]    Next, for each of the fixed nodes FN 1  to FR 4 , the mobile node location calculation unit  13  converts acquired RSSI information into a radius (radius) vector (step S 13 ). Elements of the radius vector in each of the fixed nodes FN 1  to FN 4  are (r i1 , r i2 , r i3 , . . . m and r in ), for example, and the number of the elements is equal to the number “n” of the mobile nodes MN. The unit of each of the elements of the radius vector is meter (m). 
         [0072]    Next, for each of the mobile nodes MN j , the mobile node location calculation unit  13  draws a circle that has a radius r ij  and that is centered at a corresponding one of the fixed nodes FN 1  to FN 4  (i=1 to 4, j=1 to n) (j=1 to n) (step S 14 ). The mobile node location calculation unit  13  defines, as coordinate information of the mobile node MN j , an intersection point of as many circles as the number of the fixed nodes FN 1  to FN 4  (step S 15 ). 
         [0073]    As above, locations of the respective mobile nodes MN j  (j=1 to n) are calculated. In  FIG. 9 , circles of the radii r 1j , r 2j , r 3j , and r 4j  are drawn with the fixed nodes FN 1  to FN 4  as respective center points. Coordinates (x j , y j ) of an intersection point of the four circles correspond to an example of a location of the mobile node MN j  calculated by the mobile node location calculation unit  13 . The unit of each of elements of the coordinates (x j , y j ) indicating the example of a location of the mobile node MN j  is meter (m), 
         [0074]    [Primary Filter Processing] 
         [0075]    Next, the primary filter processing according to the present embodiment will be described with reference to  FIG. 10 .  FIG. 10  is a flowchart illustrating an example of primary filter processing according to an embodiment. If the present processing is called in S 20  in  FIG. 7 , the primary filter processing unit  14  sets a threshold value S th  (step S 21 ). The threshold value S th  may be set to, for example, −60 dBm. −60 dBm corresponds to the strength of an RSSI of a node located about 5 m away from the UE. Note that the threshold value S th  may be set every time the primary filter processing in  FIG. 10  is performed or may be set only once at the beginning of the primary filter processing. 
         [0076]    Next, the primary filter processing unit  14  resets a counter i of the fixed nodes FN to “0” (step S 22 ). Next, the primary filter processing unit  14  acquires the number “n” of all mobile nodes observed by the UE and an RSSI vector of the individual mobile nodes (MN 1  to MN n ) (step S 23 ). Components of the RSSI vector are RSSIs (S 1  to S n ) of the respective mobile nodes (MN 1  to MN n ). 
         [0077]    Next, the primary filter processing unit  14  increments the counter i of the fixed nodes FN by “1” (step S 24 ). Next, the primary filter processing unit  14  determines whether or not the RSSI (S i ) is greater than or equal to the threshold value S th  (step S 25 ). In a case of determining that the RSSI (S i ) is greater than or equal to the threshold value S th , the primary filter processing unit  14  substitutes “1” into a flag F i  (step S 26 ), and in a case of determining that the RSSI (S i ) is less than the threshold value S th , the primary filter processing unit  14  substitutes “0” into the flag F i  (step S 27 ). The flag F i  is set to “0” in a case where the RSSI (S i ) is removed by the primary filter, the flag F i  is set to “1” in a case where the RSSI (S i ) is caused to pass through the primary filter, and the flag F i  is set to “0” in a case where the RSSI (S i ) is caused not to pass through the primary filter. For this reason, mobile nodes MN located outside the circle C that is illustrated in.  FIG. 3  and that corresponds to the threshold value S th  become mobile nodes MN that do not pass through the primary filter because the flags F i  thereof are set to “0”. In addition, mobile nodes MN located within the circle C become mobile beacon devices MN that pass through the primary filter because the flags F i  thereof are set to “1”. 
         [0078]    Returning to  FIG. 10 , next the primary filter processing unit  14  determines whether or not the counter i is less than the number “n” of all mobile nodes (step S 28 ). In a case of determining that the counter i is less than the number “n” of all mobile nodes, the primary filter processing unit  14  returns to step S 24  and adds “1” to the counter i (step S 24 ), thereby repeating the processing operations in steps S 25  to S 28 . In a case where it is determined, in step S 28 , that the counter i is not less than the number “n” of all mobile nodes, the recording unit  12  records all RSSIs (S i ) of the mobile nodes MN i  each having the flag F i  of “1” (step S 29 ) and terminates the present processing. 
         [0079]    Based on the primary filter processing described above, only pieces of RSSI information of respective mobile nodes located within the predetermined distance from the UE are recorded in the positioning server  10 , as information used for positioning of the UE. For this reason, it is possible to reduce the number of mobile nodes used for estimation of the location of the UE. For this reason, as for the estimation of the location of the UE, a load on processing is decreased, and power consumption is reduced. 
         [0080]    [Secondary Filter Processing] 
         [0081]    Next, the secondary filter processing according to the present embodiment will be described with reference to  FIG. 11 .  FIG. 11  is a flowchart illustrating an example of secondary filter processing according to an embodiment. The present processing is performed after the primary filter processing in  FIG. 10  finishes. If the present processing is called in S 30  in  FIG. 7 , the secondary filter processing unit  15  resets, to “0”, the counter i of the fixed nodes FN and a counter j of the mobile nodes MN (step S 31 ). Next, the secondary filter processing unit  15  acquires an RSSI vector of the mobile nodes MN 1  to MN n  observed by each of the fixed nodes FN 1  to FN 4  (step S 32 ). Components of the RSSI vector are S i1 , S i2 , S i3 , . . . , S ij , . . . , S in , and the unit thereof is dBm. 
         [0082]    Next, the secondary filter processing unit  15  increments the counter i of the fixed nodes FN by “1” (step S 33 ) and increments the counter j of the mobile nodes MN by “1” (step S 34 ). 
         [0083]    Next, the secondary filter processing unit  15  determines whether or not the RSSI (S ij ) is greater than or equal to the RSSI (S i, j-1 ) (step S 35 ). In a case of determining that the RSSI (S ij ) is greater than or equal to the RSSI (S i, j-1 ), the secondary filter processing unit  15  resets all flags recorded in the maximum-value-storage variable HS ij  (step S 36 ). Next, the secondary filter processing unit  15  stores a maximum value flag of “1” in the maximum-value-storage variable HS ij  (step S 37 ). In a case of determining that the RSSI (S ij ) is less than the RSSI (S i, j-1 ) the secondary filter processing unit  15  proceeds to step S 38  without change. 
         [0084]    Next, the secondary filter processing unit  15  determines whether or not the RSSI (S ij ) is less than or equal to the RSSI (S i, j-1 ) (step S 35 ). In a case of determining that the RSSI (S ij ) is less than or equal to the RSSI (S i, j-1 ), the secondary filter processing unit  15  resets all flags recorded in a minimum-value-storage variable LS j  (step S 39 ) and stores a minimum value flag of “1” in the minimum-value-storage variable. LS ij  (step S 40 ). In a case of determining that the RSSI (S ij ) is greater than the RSSI (S i, j-1 ), the secondary filter processing unit  15  proceeds to step S 41  without change. 
         [0085]    Next, the secondary filter processing unit  15  determines whether or not the counter j of the mobile nodes is less than “n” (step S 41 ). In a case of determining that the counter j of the mobile nodes is less than “n”, the secondary filter processing unit  15  returns to step S 34  and increments the counter j of the mobile nodes by “1”, thereby repeating the processing operations in steps S 35  to S 41  (a loop of the mobile nodes). 
         [0086]    In a case of determining, in step S 41 , that the counter j of the mobile nodes is not less than “n”, the secondary filter processing unit  15  determines whether or not the counter i of the fixed nodes is less than four (step S 42 ). In a case of determining that the counter i of the fixed nodes is less than four, the secondary filter processing unit  15  returns to step S 33 . 
         [0087]    The secondary filter processing unit  15  increments, in step S 33 , the counter i of the fixed nodes by “1” and repeats the processing operations in steps S 34  to S 42 . The secondary filter processing unit  15  repeats the processing operations in steps S 33  to S 42  until it is determined, in step S 42 , that the counter i of the fixed nodes is not less than four (a loop of the fixed nodes). In a case of determining that the counter i of the fixed nodes is not less than four, the secondary filter processing unit  15  proceeds to step S 44 , and the recording unit  12  records the maximum-value-storage variables HS ij  and the minimum-value-storage variables LS ij  of each of the fixed nodes FN 1  to FN 4 , and terminates the present processing. 
         [0088]    In the secondary filter processing described above, the indexes j of the mobile nodes MN j  each having a maximum or minimum RSSI observed by a corresponding one of the fixed nodes FN i  are recorded. “j” corresponds to eight types at a maximum and corresponds to one type at a minimum. The secondary filter processing unit  15  leaves, as outputs of the secondary filter, mobile nodes each having the index j recorded as above and removes mobile nodes other than those, based on the filtering. 
         [0089]    In, for example, the example of  FIG. 3 , from among mobile nodes MN located within the circle C, mobile nodes MN located at approximately equal distances from the UE pass through the secondary filter, and mobile nodes MN other than those do not pass through the secondary filter. In other words, the mobile nodes MN j  each having the index j of the maximum-value-storage variable HS ij  or minimum-value-storage variable LS ij  in which “1” is set turn out to be mobile node that pass through the primary filter and the secondary filter. 
         [0090]    [Tertiary Filter Processing] 
         [0091]    Next, the tertiary filter processing according to the present embodiment will be described with reference to  FIG. 12 .  FIG. 12  is a flowchart illustrating an example of tertiary filter processing according to an embodiment. The present processing is performed after the secondary filter processing in  FIG. 10  finishes. If the present processing is called in  540  in  FIG. 7 , the tertiary filter processing unit  16  acquires the number of RSSI vectors (i, j) of mobile nodes MN ij  each corresponding to one of all the maximum-value-storage variables HS ij  and minimum-value-storage variables LS ij  that pass through the primary filter and the secondary filter (step S 51 ). 
         [0092]    Next, from among the RSSI vectors (i, j) of the mobile nodes MN ij  each corresponding to one of the maximum-value-storage variables HS ij  and the minimum-value-storage variables LS ij , the tertiary filter processing unit  16  extracts the number of unique RSSI vectors (i, j) (step S 52 ). 
         [0093]    Here, as examples of the unique RSSI vectors (i, j), the mobile beacon devices MN 1  to MN 7  located on the circumference of the circle C illustrated in  FIG. 3  may be cited. As other examples of the unique RSSI vectors (i, j), RSSI vectors of mobile nodes nearest to the respective fixed nodes FN 1  to FN 4  may be cited. 
         [0094]    Next, the tertiary filter processing unit  16  determines whether or not the total number of the extracted RSSI vectors (i, j) is greater than or equal to five (step S 53 ). In a case of determining that the total number of the RSSI vectors (i, j) is less than or equal to four, the tertiary filter processing unit  16  terminates the present processing. 
         [0095]    In a case of determining, in step S 53 , that the total number of the RSSI vectors (i, j) is greater than or equal to five, the tertiary filter processing unit  16  acquires coordinates (x ij , y ij ) of mobile beacon devices MN ij  for which all remaining maximum-value-storage variables HS ij  and all remaining minimum-value-storage variables LS ij  are recorded and that pass through the primary filter and the secondary filter (step S 54 ). 
         [0096]    Next, the tertiary filter processing unit  16  calculates cross-correlation values of coordinates between one of the mobile beacon devices MN ij  and all the other mobile beacon devices MN ij  (step S 55 ). Next, the tertiary filter processing unit  16  deletes coordinates of the mobile beacon device MN ij  having the highest cross-correlation value (step S 56 ). Next, the tertiary filter processing unit  16  determines whether or not the total number of RSSI vectors (i, j) after the deletion is greater than or equal to five (step S 57 ). In a case of determining that the total number of the RSSI vectors (i, j) is greater than or equal to five, the tertiary filter processing unit  16  returns to step S 54  and repeats the processing operations in steps S 54  to S 57  until the total number of the RSSI vectors (i, j) becomes less than or equal to four. In a case of determining, in step S 57 , that the total number of the RSSI vectors (i, j) is less than or equal to four, the tertiary filter processing unit  16  terminates the present processing. 
         [0097]    Based on the tertiary filter processing described above, in, for example, the example of  FIG. 3 , the mobile beacon devices MN 1  to MN 7  located on the circumference of the circle C illustrated in  FIG. 3  may be cited as examples of the unique RSSI vectors (i, j). From among those, the tertiary filter processing unit  16  excludes mobile beacon devices MN having near azimuth directions viewed from the UE and selects mobile nodes MN (in this regard, however, three or more) that surround the UE in respective different directions as far as possible. In, for example,  FIG. 3 , the mobile nodes MN 5  and MN 6  each having the highest cross-correlation value with respect to the mobile node MN 3  are removed, and the mobile node MN 7  having the highest cross-correlation value with respect to the mobile node MN 1  is excluded. 
         [0098]    For this reason, the mobile nodes MN 1 , MN 2 , MN 3 , and MN 4  arranged at respective approximately equal angles for which θ 1 , θ 2 , θ 3 , and θ 4  between adjacent mobile nodes MN and the UE are approximately 90 degrees pass through the tertiary filter, and the mobile nodes MN 5 , MN 6 , and MN 7  other than those do not pass through the tertiary filter. 
         [0099]    The UE is notified of the pieces of RSSI information of the respective mobile nodes MN 1 , MN 2 , MN 3 , and MN 4  selected in such a way as described above. Based on the pieces of RSSI information of the respective mobile nodes MN 1 , MN 2 , MN 3 , and MN 4 , given notice of, the UE performs location estimation of the UE by using trilateration or the like. A low of distance attenuation in a free space may be used for a method for estimating distances between nodes, based on pieces of RSSI information. 
         [0100]    As above, based on the primary to tertiary filter processing operations according to the present embodiment, in an environment in which a large number of mobile beacon devices MN exist around the UE serving as a positioning target, it is possible to decrease the number of mobile beacon devices MN used for calculating the location of the UE. For this reason, by decreasing, in the UE, a load on processing for estimating a location, a processing period of time is shortened, and power consumption is reduced. 
         [0101]    While, as above, the information processing device, the information processing method, and the information processing program, used for radio positioning, are explained based on the above-mentioned embodiment, the information processing device, the information processing method, and the information processing program, used for radio positioning and related to the present disclosure, are not limited to the above-mentioned embodiment and may be variously altered or modified within the scope of the present disclosure. In addition, in a case where examples of the above-mentioned embodiment and examples of a modification exist, these may be combined to the extent that these do not contradict each other. 
         [0102]    Without performing, for example, the first filter processing ( FIG. 8 ) called in step S 20  in  FIG. 7 , the second filter processing ( FIG. 11 ) called in step S 30  in  FIG. 7  may be performed. In other words, while it is desirable that the first filter processing is performed, the first filter processing does not have to be performed. 
         [0103]    In addition, the third filter processing ( FIG. 12 ) called in step S 40  in  FIG. 7  does not have to be performed after the second filter processing is performed. In other words, while it is desirable that the third filter processing is performed, the third filter processing does not have to be performed. 
         [0104]    By performing the second filter processing, N (N≧3) mobile nodes for which adjacent mobile nodes viewed from the UE have location relationships each forming an angle of 360 degrees/N or each drawing nigh to the angle are selected based on pieces of location information of respective mobile nodes. For this reason, it is possible to exclude mobile nodes having near azimuth directions viewed from the UE and to perform calculation for positioning of the UE by using a small number of mobile nodes MN surrounding the UE as far as possible. For this reason, it is possible to accurately estimate the location of the UE. In addition, by removing mobile nodes other than mobile nodes that are selected by the second filter processing and that surround the UE, a load on processing for estimating a location is decreased in the UE, thereby achieving a reduction in a processing period of time and a decrease in power consumption. 
         [0105]    Furthermore, based on the first filter processing and the third filter processing, the number of mobile nodes used at a time of estimation of a location, performed by the UE, is further decreased. Accordingly, a load on processing is decreased, thereby achieving a reduction in a processing period of time and a decrease in power consumption. 
         [0106]    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, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment of the present invention has 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.