Patent Publication Number: US-11656360-B2

Title: Location information system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2020-095741 filed on Jun. 1, 2020, the contents of which are hereby incorporated by reference into the present application. 
     TECHNICAL FIELD 
     The technique disclosed herein relates to a location information system comprising a plurality of base stations and a mobile body. 
     Japanese Patent Application Publication No. 2000-346925 describes a location management system for identifying the location of a vehicle. The location management system includes a base station device and a mobile station device mounted on the vehicle. The base station device uses radio waves received from global positioning system (GPS) satellites to create correction information used to correct the location measured by the GIPS and transmits the information to the mobile station device. The mobile station device uses radio waves received from the GPS satellites to create location information indicating the location of the mobile station device. The mobile station device creates corrected location information by correcting the created location information with the received correction information. 
     SUMMARY 
     In the above-described system, a base station has to be located such that it can receive radio waves from the GPS satellites, and a GPS receiver has to be installed in the base station to receive radio waves. A location information system for estimating location of a mobile body may include a plurality of base stations for communication with a transferable mobile body. In this case, a device configured to receive radio waves from GPS satellites has to be installed in each one of the plurality of base stations. 
     The disclosure herein provides a technique that allows each of a plurality of base stations not to receive radio waves from GPS satellites. 
     A location information system disclosed herein may comprise a first mobile body; a plurality of base stations communicable with the first mobile body; and a location obtainer device mounted on a second mobile body and communicable with the plurality of base stations. The first mobile body may comprise a moving mechanism configured to move the first mobile body; and a first location obtainer configured to obtain first location information indicating a location of the first mobile body. Each of the plurality of base stations may comprise a base station location obtainer configured to obtain base station location information indicating a location of the base station, wherein the location of the base station is obtained by using the first location information and a distance between the first mobile body and the base station. The location obtainer device may comprise a second location obtainer configured to obtain second location information indicating a location of the second mobile body, wherein the location of the second mobile body is obtained by using one or more of the base station location information obtained by one or more of the base stations and a distance between the second mobile body and the one or more of the plurality of base stations. 
     In the above configuration, the first mobile body has the first location information indicating the location of the first mobile body. The location of each base station may be identified using the first location information and the distance between the first mobile body and the base station. Thus, the location of each base station may be identified without the base stations receiving radio waves from UPS satellites. In this configuration, the location of the second mobile body may be identified using the distance between the base station whose location has been identified and the second mobile body. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    shows a configuration of a location information system according to an embodiment; 
         FIG.  2    shows a configuration of a base station; 
         FIG.  3    shows a configuration of a first mobile body; 
         FIG.  4    shows a configuration of a second mobile body; 
         FIG.  5    shows a flowchart of a base station location estimating process; and 
         FIG.  6    shows a flowchart of a mobile body location estimating process. 
     
    
    
     DETAILED DESCRIPTION 
     Some of the features characteristic to the location information system disclosed herein will be listed. It should be noted that the respective technical elements are independent of one another, and are useful solely or in combinations. 
     The first mobile body may further comprise a distance obtainer configured to obtain plural pieces of distance information, wherein the plural pieces of distance information indicate respective distances between the first mobile body and the plurality of base stations; a base station location estimator configured to estimate locations of the plurality of base stations by using the obtained plural pieces of distance information; and a base station location transmitter configured to transmit, to each of the plurality of base stations, base station location information indicating the estimated location of the base station. Each base station location obtainer may be configured to obtain the base station location information by receiving the base station location information. 
     With this configuration, the first mobile body may estimate the locations of the base stations. The base stations may obtain their locations estimated by the first mobile body. 
     At each of a plurality of timings while the first mobile body is moving, the first location obtainer may be configured to obtain the first location information; for the respective base stations, the distance obtainer may be configured to obtain the plural pieces of distance information between the first mobile body and the base stations; and for the respective base stations, the base station location estimator may be configured to estimate locations of the base stations by using the obtained plural pieces of first location information and the plural pieces of distance information. 
     With this configuration, it is possible to identify, from a positional relationship between the first mobile body and one base station among the plurality of base stations, the location of the base station. Thus, the location of the one base station for which location estimation is to be executed may be estimated without using locations of the other base stations other than that base station. 
     The first mobile body may further comprise a storage controller configured to cause a storage to cumulatively store the obtained plural pieces of distance information and the obtained plural pieces of first location information. For each of the plurality of base stations, the base station location estimator may be configured to estimate the location of the base station by using corresponding one of the plural pieces of first location information and corresponding one of the plural pieces of distance information which are cumulatively stored in the storage. 
     With this configuration, the first mobile body may estimate the locations of the base stations using the plural pieces of distance information and the plural pieces of first location information that are cumulatively stored in the storage. 
     The first location obtainer may be configured to obtain the first location information from an external server. The base station location obtainer may be configured to obtain the base station location information from the external server. The second location obtainer may be configured to obtain the second location information from the external server. 
     With this configuration, the first mobile body does not have to be provided with a device configured to calculate the location of the first mobile body because the information is obtained from the external server different from the location information system. 
     The plurality of base stations may be immobile. 
     With this configuration, the base station location information does not have to be updated every time the location of the second mobile body is to be identified using the base station location information. 
     The first mobile body may further comprise a plurality of distance obtainers disposed at different height levels, wherein each of the plurality of distance obtainers is configured to obtain distance information indicating a distance between the distance obtainer and a specific base station of the plurality of the base stations; and a base station location estimator configured to estimate locations of the base stations. The first location information may comprise plural pieces of first location information indicating locations of the plurality of distance obtainers. The first location obtainer may be configured to obtain the plural pieces of first location information. The base station location estimator may be configured to estimate a location of the specific base station by using the plural pieces of first location information indicating the locations of the plurality of distance obtainers at each of a plurality of points while the first mobile body is moving and the plural pieces of distance information indicating distances between the specific base station and the plurality of distance obtainers. 
     In obtaining the location of the specific base station by using the location of the first mobile body and the distance between the first mobile body and the specific base station, when the height-wise position of the first mobile body is unchanged throughout the plurality of points, an actual location where the specific base station is actually located and a wrong location, which is symmetric to the actual location of the specific base station with respect to a plane including the plurality of points, may be estimated. With the above-described configuration, the location of the specific base station is identified by using the plural pieces of first location information indicating the locations of the plurality of distance obtainers disposed at different height levels. This configuration may avoid erroneous estimation for the location of the specific base station. 
     EMBODIMENTS 
     First Embodiment 
     A location information system  10  according to an embodiment shown in  FIG.  1    is configured to estimate the location of a second mobile body  80  with a user on board. The location information system  10  includes a plurality of base stations  20 ,  22 ,  24 , and  26 , a first mobile body  50 , and a controller  90  mounted on the second mobile body  80 . A server  100  depicted by a broken line in  FIG.  1    is used in a third embodiment, but is not used in the first embodiment. 
     (Configurations of Base Stations  20 ,  22 ,  24 , and  26 ) 
     The plurality of base stations  20 ,  22 ,  24 , and  26  is stationary on the ground. The base stations  20 ,  22 ,  24 , and  26  are spaced from each other. The base stations  20 ,  22 ,  24 , and  26  are installed by a provider of the location information system  10 . 
     The base station  20  includes a controller  30 , a storage  32 , a wireless communication interface  34  (hereinbelow, “interface” will be denoted as “I/F”), and a ranging signal processor  36 . The storage  32  includes a memory device such as a hard disk and/or the like. The storage  32  has a storage area that is used to store location information indicating the location of the base station  20 . The wireless communication I/F  34  includes an interface configured to be wirelessly communicable with a mobile communications network  4  such as Long Term Evolution (LTE). Owing to the wireless communication IF  34 , the base station  20  is wirelessly communicable with external devices via the mobile communications network  4 . The wireless communication I/F  34  is wirelessly communicable with the first mobile body  50 . 
     The ranging signal processor  36  includes a transmitter configured to transmit ranging signals such as ultrasound, radio waves, etc., and a receiver configured to receive ranging signals transmitted by other devices. The controller  30  is communicably connected to the storage  32 , the wireless communication I/F  34 , and the ranging signal processor  36  by wiring (not shown). The controller  30  includes a CPU and a memory. The controller  30  controls the storage  32 , the wireless communication I/F  34 , and the ranging signal processor  36  in accordance with a computer program stored in the memory. 
     The base stations  22 ,  24 , and  26  each have the same configuration as the base station  20 . 
     (Configuration of First Mobile Body  50 ) 
     The first mobile body  50  is a vehicle such as an automobile or the like. As shown in  FIG.  3   , the first mobile body  50  includes a controller  60 , a storage  62 , a wireless communication I/F  64 , a location identifier  66 , a ranging signal processor  68 , and a traction mechanism  69 . The traction mechanism  69  includes devices used for the first mobile body  50  to travel, such as a drive unit such as an engine, a motor, and/or the like, wheels, a transmission, and the like. 
     The wireless communication OF  64  has the same configuration as the wireless communication I/F  34 . Owing to the wireless communication I/F  64 , the first mobile body  50  is wirelessly communicable with external devices via the mobile communications network  4 . The wireless communication I/F  64  is wirelessly communicable with the base stations  20 ,  22 ,  24 , and  26 . 
     The location identifier  66  includes an antenna configured to receive locating signals from a plurality of GPS satellites. The location identifier  66  receives locating signals that it is capable of receiving, among locating signals transmitted from the GPS satellites. 
     As with the ranging signal processor  36 , the ranging signal processor  68  includes two ranging sensors  68   a  and  68   b  each including a transmitter configured to transmit ranging signals such as ultrasound, radio waves, etc., and a receiver configured to receive ranging signals transmitted by other devices. The controller  60  is communicably connected to the storage  62 , the wireless communication I/F  64 , the location identifier  66 , and the ranging signal processor  68  by wiring (not shown). The controller  60  includes a CPU and a memory. The controller  60  controls the storage  62 , the wireless communication L/F  64 , the location identifier  66 , and the ranging signal processor  68  in accordance with a computer program stored in the memory. 
     (Configuration of Second Mobile Body  80 ) 
     The second mobile body  80  is a vehicle such as an automobile or the like, as with the first mobile body  50 . The location information system  10  estimates the location of the second mobile body  80 . This allows a passenger in the second mobile body  80  to know his/her present location. As shown in  FIG.  4   , the second mobile body  80  includes a controller  90 , a storage  92 , a wireless communication I/F  94 , a ranging signal processor  98 , and a traction mechanism  99 . The traction mechanism  99  is the same as the traction mechanism  69 . The storage  92  is the same as the storage  62 . 
     The wireless communication T/F  94  has the same configuration as those of the wireless communication I/Fs  34  and  64 . Owing to the wireless communication I/F  94 , the second mobile body  80  is wirelessly communicable with external devices via the mobile communications network  4 . The wireless communication I/F  94  is wirelessly communicable with the base stations  20 ,  22 ,  24 , and  26 . The ranging signal processor  98  has the same configuration as that of the ranging signal processor  36 . 
     The controller  90  is connected communicably with the storage  92 , the wireless communication I/F  94 , and the ranging signal processor  98  by wiring (not shown). The controller  90  includes a CPU and a memory. The controller  90  controls the storage  92 , the wireless communication I/F  94 , and the ranging signal processor  98  in accordance with a computer program stored in the memory. The controller  90  is included, for example, in a navigation system that displays the present location of the second mobile body  80 , a route to a destination, and/or the like. 
     (Base Station Location Estimating Process) 
     The base stations  20 ,  22 ,  24 , and  26  are immobile. A location P 20  of the base station  20  is represented as (x 0 , y 0 , z 0 ) relative to a preset reference point ( 0 ,  0 ,  0 ). Similarly, a location P 22  of the base station  22  is represented as (x 2 , y 2 , z 2 ), a location P 24  of the base station  24  is represented as (x 4 , y 4 , z 4 ), and a location P 26  of the base station  26  is represented as (x 6 , y 6 , z 6 ). At the time when the base stations  20 ,  22 ,  24 , and  26  were installed, the locations of the base stations  20 ,  22 ,  24 , and  26  were not identified. The locations of the base stations  20 ,  22 ,  24 , and  26  are estimated through a base station location estimating process. 
     The base station location estimating process is executed by the controller  60  of the first mobile body  50 . The controller  60  executes the base station location estimating process while moving the first mobile body  50 . In the base station location estimating process, the controller  60  first identifies a location P 50  (x 50 , y 50 , z 50 ) of the first mobile body  50 . In S 12 , the controller  60  obtains locating signals received by the location identifier  66  from UPS satellites. Then, in S 14 , the controller  60  identifies the location P 50  of the first mobile body  50 . Using the locating signals received by the location identifier  66  from the plurality of GPS satellites, the controller  60  identifies the locations of the GPS satellites and time periods from the emission of the locating signals to the receipt of them at the location identifier  66 . Next, using the time periods until the receipt of the locating signals, the controller  60  calculates distances from the first mobile body  50  to the GPS satellites. The controller  60  identifies the location P 50  of the first mobile body  50  using the locations of the GPS satellites and the distances from the first mobile body  50  to the GPS satellites. The controller  60  causes the storage  62  to store location information indicating the identified location P 50  of the first mobile body  50 . In the base station location estimating process, steps from S 12  to S 22  are executed repeatedly. In S 14 , the controller  60  cumulatively stores location information without deleting one or more pieces of location information indicating the location P 50  of the first mobile body  50  that have been already stored in the storage  62  as a result of the step S 14  having been executed before. 
     Next, in S 16 , the controller  60  causes each of the ranging sensors  68   a  and  68   b  to transmit a ranging signal. Each of the ranging sensors  68   a  and  68   b  transmits the signal such that the signal is distinguishable from the ranging signal transmitted from the other ranging sensor. The controller  60  stores the time when each of the ranging signals was transmitted. When the ranging signal processor  36  receives the ranging signals, the controller  30  of the base station  20  causes the ranging signal processor  36  to transmit a ranging signal. When receiving the ranging signal from one of the ranging sensors  68   a  and  68   b , the ranging signal processor  36  transmits a ranging signal that includes the same signal as the received ranging signal. In S 18 , the controller  60  causes the ranging sensors  68   a  and  68   b  to receive the ranging signal transmitted from the base station  20 . The controller  60  determines which of the ranging signal transmitted from the ranging sensor  68   a  and the ranging signal transmitted from the ranging sensor  68   b  is included in the ranging signal received by the ranging sensors  68   a  and  68   b . The controller  60  causes the storage  62  to store the time when the ranging signal was received as the time when the ranging signal was received by the determined ranging sensor among the ranging sensors  68   a  and  68   b.    
     Then, in S 20 , the controller  60  calculates distances between the ranging sensors  68   a ,  68   b  and the base station  20 . Specifically, for the ranging sensor  68   a , the controller  60  first calculates a difference between the time when the ranging signal was transmitted in S 16  and the time when the ranging signal from the ranging sensor  68   a  was received in S 18 . Then, the controller  60  calculates, as a distance between the ranging sensor  68   a  and the base station  20 , a half of a distance calculated by multiplying the traveling speed of the ranging signal by the time difference. The controller  60  causes the storage  62  to store a combination of distance information indicating the calculated distance between the ranging sensor  68   a  and the base station  20  and location information indicating the location of the ranging sensor  68   a . The location information indicating the location of the ranging sensor  68   a  is the same as the location information already stored in the storage  62  in immediately precedent step S 14 , that is, the location information indicating the location of the first mobile body  50 . In the same way, the controller  60  calculates a distance between the ranging sensor  68   b  and the base station  20 . The controller  60  causes the storage  62  to store a combination of distance information indicating the calculated distance between the ranging sensor  68   b  and the base station  20  and location information indicating the location of the ranging sensor  68   b . The location of the ranging sensor  68   b  is obtained by subtracting a height difference between the ranging sensors  68   a  and  68   b  from the location of the ranging sensor  68   a , that is, the location of the first mobile body  50 . Hereinbelow, the location of the ranging sensor  68   a  and the location of the ranging sensor  68   b  will be collectively termed the location of the first mobile body  50 . 
     The above has described about communication of ranging signals with the base station  20  and calculation of distances from the base station  20 . However, as with the base station  20 , one or more of the base stations  22 ,  24 , and  26  that received the ranging signals transmitted from the first mobile body  50  in S 16  each transmits a ranging signal to the first mobile body  50 . As a result, in S 18 , one or more ranging signals are received from the one or more of the base stations  22 ,  24 , and  26 . In S 20 , for each of the one or more base stations, the controller  60  calculates distances from the base station, which is the transmitter of the ranging signal, by executing the same as the calculation of distances from the base station  20 , and causes the storage  62  to store combinations of the calculated distances and the location information indicating the location of the first mobile body  50 . 
     Then, in S 22 , the controller  60  determines whether distances have been calculated for a predetermined number of times. The predetermined number of times is equal to or more than the number of combinations of location information and distance information that is required to identify the location of the base station  20 , specifically combinations of the location information indicating the location of the first mobile body  50 , that is, the locations of the ranging sensors  68   a  and  68   b , and the distance information indicating the distance between the first mobile body  50  and the base station  20 . For example, the predetermined number of times may be four times or may be five times or more. 
     If the distances have not been calculated for the predetermined number of times (NO in S 22 ), the process returns to S 12  and steps S 12  to S 20  are executed again. The first mobile body  50  executes the base station location estimating process while moving. Therefore, each time the series of steps S 12  to S 20  is executed, a different combination of the location of the first mobile body  50  and distance from the base station  20  is calculated. 
     If the distances have been calculated for the predetermined number of times (YES in S 22 ), the controller  60  estimates, in S 24 , the location of the base station  20  using the predetermined number of combinations of plural pieces of distance information each indicating distance from the base station  20  and plural pieces of location information each indicating the location of the first mobile body  50 . 
     With the location P 20  of the base station  20 =(x 20 , y 20 , z 20 ) and a location P 50   k  of the first mobile body  50  at a specific timing=(x 50   k , y 50   k , z 50   k ), a distance D 20   k  between the first mobile body  50  and the base station  20  at the specific timing can be represented in the formula below.
 
 D   2 20 k=∥P 50 k−P 20∥ 2   [Formula I]
 
     As with D 20   k , where the locations of the base stations  22 ,  24 , and  26  are respectively represented as P 22 , P 24 , and P 26 , each of distances D 22   k , D 24   k , and D 26   k  between the first mobile body  50  and the base stations  22 ,  24 , and  26  at the specific timing can be represented in the above formula. However, using GPS signals and ranging signals to estimate locations and measure distances may have errors due to signal transmission noise, time clocked by the first mobile body  50  being different from the actual time, and/or the like. The controller  60  estimates the locations of the base stations  20 ,  22 ,  24 , and  26  such that an evaluation value J calculated from the formula below becomes minimum. 
     
       
         
           
             
               
                 
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     Here, M is the predetermined number of times. P 50   k  is the location P 50  of the first mobile body  50  at k th  time, where it is distinguished between the ranging sensors  68   a  and  68   b . Pi is the locations of a plurality of base stations i, where i includes 20, 22, 24, and 26. Dki is a distance between the base station i and the first mobile body  50  at k th  time, where it is distinguished between the ranging sensors  68   a  and  68   b.    
     (Mobile Body Location Estimating Process) 
     Next, a mobile body location estimating process executed by the controller  90  will be described with reference to  FIG.  6   . The mobile body location estimating process estimates the location of the second mobile body  80 . In the mobile body location estimating process, the controller  90  first causes the ranging signal processor  98  to transmit a ranging signal in S 32 . When the ranging signal processor  36  receives the ranging signal, the controller  30  of the base station  20  causes the ranging signal processor  36  to transmit a ranging signal. When receiving the ranging signal from the ranging signal processor  98 , the ranging signal processor  36  transmits a ranging signal that includes the same signal as the received ranging signal. Similarly, when the ranging signal processors of the base stations  22 ,  24 , and  26  receive the ranging signal, the controllers of the base stations  22 ,  24 , and  26  cause the ranging signal processors to transmit ranging signals. 
     In S 34 , the controller  90  causes the ranging signal processor  98  to receive the ranging signals transmitted from the base stations  20 ,  22 ,  24 , and  26 . In S 36 , the controller  90  obtains plural pieces of location information respectively indicating the locations of the base stations  20 ,  22 ,  24 , and  26  from the base stations  20 ,  22 ,  24 , and  26  via the wireless communication I/F  94 . Then, in S 38 , the controller  90  estimates the location of the second mobile body  80 . Specifically, the controller  90  first calculates a distance between the second mobile body  80  and the base station  20  using the time when the ranging signal was transmitted in S 32 , the time when the ranging signal from the base station  20  was received in S 34 , and the traveling speeds of the ranging signals. Similarly, the controller  90  calculates distances between the second mobile body  80  and each of the base stations  22 ,  24 , and  26 . 
     Then, the controller  90  calculates the location of the second mobile body  80  using a relational expression between the location P 80  of the second mobile body  80 , the location P 20  of the base station  20 , and the distance D 80  between the second mobile body  80  and the base station  20 , namely D 2 80=∥P80−P20∥ 2 , and using the location of the second mobile body  80 , the locations of the base stations  22 ,  24 , and  26 , and the distances between the second mobile body  80  and each of the base stations  22 ,  24 , and  26 . 
     When estimating the location of the second mobile body  80  from positional relationship with four or more base stations  20 ,  22 ,  24 , and  26 , the controller  90  estimates, as in the base station location estimating process, the location of the second mobile body  80  such that evaluation values J are minimized, where the evaluation values J are differences between distances between each of the base stations  20 ,  22 ,  24 , and  26  and the location of the second mobile body  80  calculated from the location of the second mobile body  80  and the locations of the base stations  20 ,  22 ,  24 , and  26  and distances between each of the base stations  20 ,  22 ,  24 , and  26  and the location of the second mobile body  80  obtained by the transmission and receipt of the ranging signals. 
     (Effects) 
     In the location information system  10 , the first mobile body  50  includes the location identifier  66  to identify the location of the first mobile body  50 , while none of the base stations  20 ,  22 ,  24 , and  26  includes a device configured to receive signals from GPS satellites. This simplifies configuration of the plurality of base stations  20 ,  22 ,  24 , and  26  included in the location information system  10 . Further, in the location information system  10 , the base stations  20 ,  22 ,  24 , and  26  do not have to receive signals from GPS satellites, and therefore the base stations  20 ,  22 ,  24 , and  26  can be installed at places where signals from GPS satellites are hard to reach (e.g., indoors). 
     Each of the locations of the base stations  20 ,  22 ,  24 , and  26  is estimated from the location of the first mobile body  50  and the distance between the base station and the first mobile body  50 . The base stations  20 ,  22 ,  24 , and  26  can identify the locations of the base stations  20 ,  22 ,  24 , and  26  without receiving any signals from GPS satellites. Thus, the locations of the base stations  20 ,  22 ,  24 , and  26  do not have to be precisely identified in advance. 
     The first mobile body  50  identifies distances between itself and each of the base stations  20 ,  22 ,  24 , and  26  by transmitting ranging signals, and estimates the locations of the base stations  20 ,  22 ,  24 , and  26 . Thus, there is no need to separately provide a device to estimate the locations of the base stations  20 ,  22 ,  24 , and  26 . 
     To estimate the locations of the base stations  20 ,  22 ,  24 , and  26 , the first mobile body  50  identifies distances between itself and each of the base stations  20 ,  22 ,  24 , and  26  at a plurality of points. According to this configuration, the first mobile body  50  can estimate the location of the single base station  20  by identifying the locations of the first mobile body  50  and distances between the first mobile body  50  and the base station  20  at the plurality of points. Thus, when estimating the location of the single base station  20 , the first mobile body  50  does not have to estimate the locations of the other base stations  22 ,  24 , and  26 . The present embodiment improves the accuracy for estimation of the location of the base station  20  by identifying the locations of the first mobile body  50  and distances between the first mobile body  50  and the base station  20  at the plurality of points to estimate the location of the single base station  20 . 
     In the base station location estimating process, the first mobile body  50  cumulatively store, in the storage  62 , the location of the first mobile body  50  identified in S 14  and the distances between the first mobile body  50  and each of the base stations  20 ,  22 ,  24 , and  26  calculated in S 20 . According to this configuration, the first mobile body  50  can estimate the locations of the base stations  20 ,  22 ,  24 , and  26  using the location of the first mobile body  50  identified in S 14  and the distances between the first mobile body  50  and each of the base stations  20 ,  22 ,  24 , and  26  calculated in S 20  that are cumulatively stored in the storage  62 . Thus, according to this configuration, the first mobile body  50  can estimate the locations of the base stations  20 ,  22 ,  24 , and  26  anytime, as long as it stores in advance the location of the first mobile body  50  identified in S 14  and distances between the first mobile body  50  and each of the base stations  20 ,  22 ,  24 , and  26  calculated in S 20 . 
     The first mobile body  50  causes the ranging sensors  68   a  and  68   b , which are disposed at different height levels, to transmit ranging signals to identify distances between the ranging sensors  68   a ,  68   b  and the base stations  20 ,  22 ,  24 , and  26 . This can avoid erroneous estimation for height-wise locations of the base stations  20 ,  22 ,  24 , and  26  when the height-wise position of the first mobile body  50  is unchanged in the base station location estimating process. 
     As is apparent from the forgoing description, the controller  90  is an example of the “location obtainer device”. 
     Second Embodiment 
     In this embodiment, the configuration of the location identifier  66  of the first mobile body  50  is different from that of the first embodiment. Further, the steps for identifying the location of the first mobile body  50  in S 12  and S 14  in the base station location estimating process are different from those of the first embodiment. In the present embodiment, the location identifier  66  includes, instead of the GPS antenna, an emitter configured to emit laser light and a photoreceiver configured to receive laser light reflected by hitting surrounding objects. Further, the storage  62  stores in advance an environment map that shows arrangements of buildings and objects around the first mobile body  50 . 
     In S 12  and S 14  of the base station location estimating process, the location of the first mobile body  50  is identified using Light Detection and Ranging (LiDAR). Specifically, in S 12 , the controller  60  causes the location identifier  66  to emit laser light and receive reflected laser light from surrounding buildings and the like. In S 14 , the controller  60  then detects shapes of the buildings and the like around the first mobile body  50  from the timing when the laser light was received. Then, the controller  60  identifies the location of the first mobile body  50  by comparing the detected shapes and the environment map stored in the storage  62 . 
     With the above configuration, the first mobile body  50  does not have to receive signals from the GPS satellites. Therefore, the location of the first mobile body  50  can be identified even while the first mobile body  50  is traveling through places where signals from the GPS satellites are hard to reach. In a variant, the location identifier  66  of the first mobile body  50  may include a GPS antenna, an emitter configured to emit laser light, and a photoreceiver configured to receive laser light reflected by hitting surrounding objects. In this case, the controller  60  may identify the location of the first mobile body  50  using either of location identification using ranging signals from the GPS satellites or location identification using the LiDAR. 
     Third Embodiment 
     As shown in  FIG.  1   , in this embodiment, a server  100  is installed. The server  100  is communicable, via the mobile communications network  4 , with the first mobile body  50 , the base stations  20 ,  22 ,  24 , and  26 , and the second mobile body  80 . The server  100  is disposed outside the location information system  10 . In the present embodiment, the server  100  is configured to execute a process for identifying the location of the first mobile body  50 , a process for estimating the locations of the base stations  20 ,  22 ,  24 , and  26 , and a process for identifying the location of the second mobile body  80 . Specifically, the controller  60  transmits ranging signals from the GPS satellites to the server  100 , as in S 12 . The server  100  identifies the location of the first mobile body  50  by executing the same step as S 14  using the received ranging signals from the GPS satellites. The server  100  transmits location information indicating the location of the first mobile body  50  to the first mobile body  50 . As a result, the controller  60  obtains the location information indicating the location of the first mobile body  50 . 
     The controller  60  then calculates distances from the base stations  20 ,  22 ,  24 , and  26  by executing steps S 16  to S 20 . Next, the controller  60  transmits plural pieces of distance information respectively indicating the calculated distances to the server  100 . In the server  100 , the locations of the base stations  20 ,  22 ,  24 , and  26  are estimated using the received plural pieces of distance information and the location information indicating the location of the first mobile body  50 . The server  100  transmits plural pieces of location information respectively indicating the estimated locations of the base stations  20 ,  22 ,  24 , and  26  to corresponding base stations  20 ,  22 ,  24 , and  26 . The controller  30  of the base station  20  obtains the location information by receiving the location information from the server  100 . The same applies to the controllers of the base stations  22 ,  24 , and  26 . 
     Further, the controller  90  of the second mobile body  80  transmits, to the server  100 , plural pieces of distance information respectively indicating distances between the second mobile body  80  and the base stations  20 ,  22 ,  24 , and  26  that are obtained by executing steps S 32  and S 34 . The server  100  estimates, as in S 38 , the location of the second mobile body  80  using the received plural pieces of distance information and the plural pieces of location information indicating the locations of the base stations  20 ,  22 ,  24 , and  26 . The server  100  transmits location information indicating the estimated location of the second mobile body  80  to the second mobile body  80 . The controller  90  of the second mobile body  80  obtains the location information by receiving the location information from the server  100 . 
     In the present embodiment, the location information system  10  does not have to include a device configured to execute a process for identifying the location of the first mobile body  50 , a process for estimating the locations of the base stations  20 ,  22 ,  24 , and  26 , and a process for identifying the location of the second mobile body  80 . This simplifies the location information system  10 . In a variant, the server  100  may execute one or more of the process for identifying the location of the first mobile body  50 , the process for estimating the locations of the base stations  20 ,  22 ,  24 , and  26 , and the process for identifying the location of the second mobile body  80 . 
     While specific examples of the present disclosure have been described above in detail, these examples are merely illustrative and place no limitation on the scope of the patent claims. The technology described in the patent claims also encompasses various changes and modifications to the specific examples described above. 
     (Variants) 
     (1) In the base station location estimating process, the locations of the base stations  20 ,  22 ,  24 , and  26  may be estimated using plural pieces of distance information each indicating a distance between a pair of two base stations among the plurality of base stations  20 ,  22 ,  24 , and  26 , in addition to the location of the first mobile body  50  and the distances between the first mobile body  50  and the base stations  20 ,  22 ,  24 , and  26 . The distances between the base stations may be identified by the base stations  20 ,  22 ,  24 , and  26  communicating ranging signals with each other, or may be stored in advance in the base stations  20 ,  22 ,  24 , and  26  or in the first mobile body  50 . In this case, estimated locations of the base stations  20  and  22  may be identified such that a difference between a distance between the base stations  20  and  22  calculated from estimated locations of the base stations  20  and  22  and a known distance between the base stations  20  and  22  is minimized. The same applies to the other base stations  24  and  26 .
 
(2) At least one of the base stations  20 ,  22 ,  24 , and  26  may be mobile. In this case, the at least one mobile base station may include a moving mechanism such as a traction mechanism, a flying mechanism, or the like. Alternatively, the at least one mobile base station may float on the surface of an ocean, a lake, or the like, and may be mobile along with up-and-down motions of the water surface.
 
(3) The first mobile body  50  and the second mobile body  80  may move by flying, such as a drone or the like.
 
(4) The first mobile body  50  includes the ranging sensors  68   a  and  68   b , however, the configuration of the ranging signal processor  68  is not limited thereto. For example, the first mobile body  50  may include another ranging sensor in addition to the ranging sensors  68   a  and  68   b . In this case, the additional ranging sensor may be disposed at the same height level as at least one of the ranging sensors  68   a  and  68   b  and at a different position. Similarly, each of the second mobile body  80 , the base stations  20 ,  22 ,  24 , and  26  may include a plurality of ranging sensors. Further, for example, the first mobile body  50  may include only one ranging sensor  68   a . In this case, the ranging sensor  68   a  may be mobile in the first mobile body  50 . For example, the ranging sensor  68   a  may be mobile at least in up-down direction or may be rotatable.
 
(5) The location information system  10  may include a plurality of first mobile bodies  50 . In this case, each of the first mobile bodies  50  may include either one of the ranging sensors  68   a  and  68   b.  
 
(6) The base station location estimating process may be executed by a controller other than the controller  60 , for example, by the controller  30  or any one of the controllers of the base stations  22 ,  24 , and  26 . Similarly, the mobile body location estimating process may be executed by a controller other than the controller  90 , for example, by the controller  30  or the controller  60 .
 
     The technical elements explained in the present description or drawings provide technical utility either independently or through various combinations. The present disclosure is not limited to the combinations described at the time the claims are filed. Further, the purpose of the examples illustrated by the present description or drawings is to satisfy multiple objectives simultaneously, and satisfying any one of those objectives gives technical utility to the present disclosure.