Patent Publication Number: US-2023152802-A1

Title: Position estimation device, position estimation method, and autonomous driving system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a position estimation device, a position estimation method, and an autonomous driving system. 
     2. Description of the Background Art 
     In order to achieve autonomous driving for a mobile body, it is necessary to always recognize the own position of the mobile body accurately. As a method for estimating the own position of the mobile body, for example, there is a method using a satellite signal in a case where the mobile body travels outdoors. In addition, in an environment where a satellite signal is hardly received such as indoors, for example, there is a method using signals from a plurality of beacon signal transmitters provided at roadsides and the like. 
     Among locations where the mobile body travels as described above, communication methods with which position information of the mobile body can be acquired are different. Therefore, in order to always achieve accurate positioning, technology for switching communication methods to be used for positioning as necessary at each location is required. 
     In a position detection system described in Patent Document 1, in positioning the own position of a mobile body, positioning using a satellite signal is performed outdoors and positioning using a beacon signal is performed indoors, thus enabling the own position of the mobile body to be assuredly detected indoors and outdoors. 
     In a communication control system described in Patent Document 2, a communication method associated with a location where a mobile body is present is preferentially used, thus enabling switching to an appropriate communication method and achieving continuation of communication.
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2019-132627   Patent Document 2: Japanese Patent No. 5966291   

     The position detection system described in Patent Document 1 is set in advance such that, in a case where the own position can be positioned with both positioning systems of a satellite type and a beacon type, the beacon positioning system is used. Therefore, there is a problem that, in some cases, a positioning result of the satellite positioning system which is more accurate than the beacon positioning system cannot be used. That is, a problem is to make it possible to use a positioning result of the satellite positioning system when the positioning result of the satellite positioning system is more accurate than that of the beacon positioning system. 
     In the communication control system described in Patent Document 2, a communication method associated with a location where a mobile body is present is preferentially used. Therefore, there is a problem that, even if there is a communication method capable of more accurate positioning, a positioning result thereof cannot be used. That is, a problem is to make it possible to use a communication method having highest positioning accuracy at each location. 
     SUMMARY OF THE INVENTION 
     The present disclosure has been made to solve the above problem, and an object of the present disclosure is to provide a position estimation device and a position estimation method for estimating the own position of a mobile body with high accuracy, and an autonomous driving system having high stability with use of the position estimation device. 
     A position estimation device according to the present disclosure is a position estimation device which is provided to a mobile body and estimates position information of the mobile body, the position estimation device including: a communication-method-based reception unit which receives signals transmitted respectively in a plurality of communication methods, by a plurality of reception units corresponding to the respective communication methods; an own position calculation unit which calculates first position information of the mobile body per calculation cycle, using the signal transmitted in each of the plurality of communication methods; a movement amount calculation unit which calculates a movement amount of the mobile body per the calculation cycle; an autonomous navigation positioning unit which calculates, for each of the plurality of communication methods, second position information of the mobile body on the basis of the first position information calculated by the own position calculation unit and the movement amount of the mobile body calculated by the movement amount calculation unit; and an index value calculation unit which calculates, for each of the plurality of communication methods, a variance value of difference values between the first position information and the second position information, as an index value. 
     An autonomous driving system according to the present disclosure includes: the above position estimation device which calculates position information of an own vehicle on the basis of signals transmitted respectively in a plurality of communication methods; a traveling route generation device which generates a traveling route for the own vehicle to reach a target location from the own-vehicle position, using the position information of the own vehicle outputted from the position estimation device; and a vehicle control device which sets a target track and a target vehicle speed for executing autonomous driving control for the own vehicle on the generated traveling route. 
     A position estimation method according to the present disclosure is a position estimation method for estimating position information of a mobile body, the method including: a communication-method-based reception step of receiving signals transmitted respectively in a plurality of communication methods, by a plurality of reception units corresponding to the respective communication methods; an own position calculation step of calculating first position information of the mobile body per calculation cycle, using the signal transmitted in each of the plurality of communication methods; a movement amount calculation step of calculating a movement amount of the mobile body per the calculation cycle; an autonomous navigation positioning step of calculating, for each of the plurality of communication methods, second position information of the mobile body on the basis of the first position information calculated in the own position calculation step and the movement amount of the mobile body calculated in the movement amount calculation step; and an index value calculation step of calculating, for each of the plurality of communication methods, a variance value of difference values between the first position information and the second position information, as an index value. 
     In the position estimation device according to the present disclosure, position information by a communication method for which the output priority determined on the basis of the index value is highest is selected from position information of the mobile body calculated by a plurality of communication methods, whereby it becomes possible to calculate position information of the mobile body on the basis of an optimum communication method among the plurality of communication methods, thus providing an effect of obtaining a position estimation device capable of outputting position information with high accuracy. 
     In the position estimation method according to the present disclosure, position information by a communication method for which the output priority determined on the basis of the index value is highest is selected from position information of the mobile body calculated by a plurality of communication methods, whereby it becomes possible to calculate position information of the mobile body on the basis of an optimum communication method among the plurality of communication methods, thus providing an effect of obtaining a position estimation method capable of calculating position information with high accuracy. 
     In the autonomous driving system according to the present disclosure, position information of the own-vehicle position can be calculated with high accuracy using the above position estimation device, thus providing an effect of obtaining an autonomous driving system that can achieve autonomous driving control having high stability on the basis of accurate position information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    schematically shows a situation in which a position estimation device according to the first embodiment of the present disclosure is used; 
         FIG.  2    is a function block diagram showing the configuration of the position estimation device according to the first embodiment; 
         FIG.  3    is a schematic diagram of a processing circuit in the position estimation device according to the first embodiment; 
         FIG.  4    is a flowchart showing a position estimation method according to the first embodiment; 
         FIG.  5    is a flowchart showing a position estimation method according to the second embodiment of the present disclosure; 
         FIG.  6    is a function block diagram showing the configuration of a position estimation device according to the third embodiment of the present disclosure; 
         FIG.  7    is a flowchart showing a position estimation method according to the third embodiment; 
         FIG.  8    is a function block diagram showing the configuration of an autonomous driving system according to the seventh embodiment of the present disclosure; 
         FIG.  9    schematically shows a vehicle provided with the autonomous driving system according to the seventh embodiment; 
         FIG.  10    shows a hardware configuration for implementing the position estimation devices according to the first and third embodiments; and 
         FIG.  11    shows a hardware configuration for implementing the position estimation devices according to the first and third embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     First Embodiment 
       FIG.  1    schematically shows a situation in which a position estimation device  200  according to the first embodiment of the present disclosure is used. In  FIG.  1   , a vehicle  101   a  and a vehicle  101   b  which axe examples of mobile bodies are each provided with the position estimation device  200  according to the first embodiment. The vehicle  101   a  is inside a construction  103 , and the vehicle  101   b  is outside the construction  103 . A satellite signal transmitter  102  emits a radio signal toward the ground. A beacon signal transmitter  104  is provided in the construction  103 . The beacon signal transmitter  104  is fixed to a wall of the construction  103 . The vehicle  101   a  and the vehicle  101   b  each move indoors and outdoors while calculating own position information on the basis of a received satellite signal or beacon signal by using the position estimation device  200 . Hereinafter, the vehicle  101   a  and the vehicle  101   b  may be collectively referred to as mobile bodies. 
       FIG.  2    is a function block diagram showing the configuration of the position estimation device  200  according to the first embodiment. The position estimation device  200  is provided to a mobile body such as a vehicle, for example. The position estimation device  200  according to the first embodiment includes a communication-method-based reception unit  201 , an own position calculation unit  202 , a movement amount calculation unit  203 , an autonomous navigation positioning unit  204 , an index value calculation unit  205 , and a position information selection unit  206 . The communication-method-based reception unit  201  includes a plurality of radio signal reception units corresponding to different communication methods, i.e., n radio signal reception units; a first radio signal reception unit  201   a , a second radio signal reception unit  201   b , . . . , an nth radio signal reception unit  201   n.    
       FIG.  3    is a schematic diagram of a processing circuit in the position estimation device  200  according to the first embodiment. Each function of the position estimation device  200  according to the first embodiment is implemented by a processing circuit  300  provided to the position estimation device  200 . 
     The processing circuit  300  is composed of a processor  301 , a storage device  302 , and a clock  303 , for example. In the storage device  302 , software for implementing each function is written. Each function may be implemented by a plurality of processing circuits. In a case of having a plurality of processing circuits, the processing circuits communicate with each other using communication means such as a controller area network (CAN), to implement the functions of the position estimation device  200 . 
     Hereinafter, the details of the functions of the position estimation device  200  according to the first embodiment will be described. 
     As described above, the communication-method-based reception unit  201  includes a plurality of radio signal reception units respectively corresponding to a plurality of communication methods, i.e., the first radio signal reception unit  201   a , the second radio signal reception unit  201   b , . . . , the nth radio signal reception unit  201   n . In the function block diagram of the position estimation device  200  shown in  FIG.  2   , the number of the radio signal reception units is n. A radio signal emitted from a transmitter based on each communication method is received by the radio signal reception unit corresponding to that communication method. 
     Examples of the plurality of communication methods include code division multiple access (CDMA) and impulse-radio ultra wide band (IR-UWB). In the position estimation device  200  according to the first embodiment, COMA is used as satellite communication and IF-UWE is used as beacon communication. However, as long as the object of the present disclosure can be achieved, the communication methods are not limited to the above ones. 
     In order to calculate position information of a mobile body on the basis of a radio signal emitted from a transmitter using each communication method, the communication-method-based reception unit  201  performs distance measurement and angle measurement between the transmitter and the radio signal reception unit. Specific examples of a distance measurement method include a time of flight (ToF) method and a received signal strength indicator (RSSI) method. 
     Specific examples of an angle measurement method include an angle of arrival. (AoA) method and an angle of departure (AoD) method. In the position estimation device  200  according to the first embodiment, distance measurement by the ToF method is used. However, as long as the object of the present disclosure can be achieved, methods for distance measurement and angle measurement are not particularly limited. 
     The own position calculation unit  202  calculates position information of a mobile body, using signals respectively transmitted by a plurality of communication methods and received by the communication-method-based reception unit  201 . The position information of the mobile body calculated by the own position calculation unit  202  may be referred to as first position information of the mobile body. 
     In a case of satellite communication, the position estimation device  200  according to the first embodiment derives an equation shown by the following Expression (1) having, as unknowns, position information (x, y, z) of the vehicle  101   a  and the vehicle  101   b , and clock error t of the radio signal reception unit, using position information (x i , y i , z i ) of the satellite signal transmitter  102 , a distance r i  from the satellite signal transmitter  102  to the communication-method-based reception unit  201 , and the speed of light c, from the received signal. 
     [Mathematical 1] 
       √{square root over (( x−x   i ) 2 +( y−y   i ) 2 +( z−z   i ) 2 )}+ t×c=r   i   (1)
 
     Expression (1) is derived for each received signal, and from four or more Expressions (1), the position information of the vehicle  101   a  and the vehicle  101   b , i.e., the first position information of the vehicle  101   a  and the vehicle  101   b , is calculated. 
     In the beacon communication method, the first position information of the vehicle  101   a  and the vehicle  101   b  is calculated on the basis of a trilateration principle, using distance information obtained from three or more received signals. 
     However, as long as the object of the present disclosure can be achieved, the calculation method for the position information of the mobile body is not particularly limited. For calculating the position information of the mobile body, different methods may be used depending on respective communication methods. 
     The movement amount calculation unit  203  acquires information from a sensor that can detect position information of a mobile body, and calculates a relative movement amount of the mobile body from a given location, on the basis of the information from the sensor. In the position estimation device  200  according to the first embodiment, the movement amount of the mobile body is calculated using time integral values of the acceleration and the angular velocity of the vehicle obtained from an inertia measurement device (not shown) provided to each of the vehicle  101   a  and the vehicle  101   b . However, as long as the object of the present disclosure can be achieved, the sensor type and the calculation method for the movement amount of the mobile body are not particularly limited. 
     The movement amount of the mobile body calculated by the movement amount calculation unit  203  is stored in the storage device  302 . Meanwhile, when a reset signal is transmitted from the autonomous navigation positioning unit  204  to the storage device  302 , the movement amount of the mobile body stored in the storage device  302  is deleted. 
     The autonomous navigation positioning unit  204  calculates the absolute position of the mobile body at present, using the absolute position of the mobile body at a given location and the relative movement amount from the absolute position. The position information of the mobile body calculated by the autonomous navigation positioning unit  204  may be referred to as second position information of the mobile body. The absolute position of the mobile body is regularly acquired from the own position calculation unit  202 . Here, regular acquisition means such a case of performing acquisition per calculation cycle, for example. The movement amount of the mobile body is acquired from the movement amount calculation unit  203 . 
     The autonomous navigation positioning unit  204  acquires the position information of the mobile body from the own position calculation unit  202 , i.e., the first position information, and at the same time, transmits a reset signal to the movement amount calculation unit  203 . Thus, the movement amount of the mobile body calculated by the movement amount calculation unit  203  is treated as a movement amount from the absolute position acquired from the own position calculation unit  202 . 
     The index value calculation unit  205  calculates an index value representing reliability of the position information of the mobile body calculated in each of the plurality of communication methods, using the first position information of the mobile body calculated by the own position calculation unit  202  and the second position information of the mobile body calculated by the autonomous navigation positioning unit  204 . 
     The calculation method for the index value by the index value calculation unit  205  will be described. First, at the same time as a signal is received by the communication-method-based reception unit  201 , the index value calculation unit  205  acquires the second position information of the mobile body calculated by the autonomous navigation positioning unit  204 . After acquiring the second position information, the index value calculation unit  205  calculates a difference value between the first position information f rom the own position calculation unit  202  and the second position information from the autonomous navigation positioning unit  204 . The calculated difference values for a certain number of times of sampling are stored in the storage device  302  in time series. The index value calculation unit  205  calculates a variance value from the stored difference values for the certain number of times of sampling, and uses the variance value as the index value. Here, the certain number of times of sampling means such a case of calculating the first position information and the second position information per calculation cycle through a predetermined number of consecutive calculation cycles. 
     On the basis of the index value, the position information selection unit.  206  imparts, to the first position information of the mobile body calculated in each communication method, an output priority for the position estimation device  200  to output the first position information, selects the first position information of the mobile body that is based on the communication method for which the output priority is highest, and outputs the selected first position information. That is, the position information selection unit  206  compares the index values for all the communication methods, and imparts a higher output priority in the ascending order of the index value. 
     The output of the position information selection unit  206  is transmitted to a vehicle control device of the mobile body described later, and the like, using communication means such as CAN. The position information selection unit  206  can perform output at a certain cycle in synchronization with the clock  303  of the processing circuit  300 . 
     Position Estimation Method According to the First Embodiment 
     A position estimation method according to the first embodiment will be described with reference to a flowchart in  FIG.  4   . First, in step S 101 , the communication-method-based reception unit  201  receives radio signals from a plurality of transmitters for respective communication methods. 
     In the position estimation method according to the first embodiment, from the satellite signal transmitter  102 , the following are received: distance information of the satellite signal transmitter  102 , the position information of the satellite signal transmitter  102 , clock error information between the satellite signal transmitter  102  and the communication-method-based reception unit  201 , individual identification information of the satellite signal transmitter  102 , and the like. From the beacon signal transmitter  104 , the following are received: distance information of the beacon signal transmitter  104 , individual identification information of the beacon signal transmitter  104 , and the like. 
     In step S 102 , the communication-method-based reception unit  201  confirms whether or not a necessary number of radio signals for calculating the first position information of the mobile body have been received, for each of the plurality of communication methods. In the position estimation method according to the first embodiment, whether or not four or more signals have been received in a case of a satellite signal, or whether or not three or more signals have been received in a case of a beacon signal, is confirmed on the basis of identification information of each radio transmitter. In a case where the transmission frequencies of the satellite signal transmitter  102  and the beacon signal transmitter  104  are different from each other, reception confirmation is performed in accordance with each transmission frequency. 
     In step S 102 , if it is determined that a necessary number of radio signals for calculating the first position information of the mobile body have not been received for a given communication method, i.e., in the case of NO in step S 102 , in step S 103 , the own position calculation unit  202  does not perform calculation of the first position information of the mobile body for that communication method. 
     On the other hand, in step S 102 , if it is determined that a necessary number of radio signals for calculating the first position information of the mobile body have been received for a given communication method, i.e., in the case of YES in step S 102 , processing in step S 104  is executed. 
     In step S 104 , the own position calculation unit  202  calculates the first position information of the mobile body using the radio signals. In the position estimation device  200  according to the first embodiment, for each of the vehicle  101   a  and the vehicle  101   b  which are mobile bodies, the first position information of the vehicle  101   a  and the vehicle  101   b  is calculated using satellite signals and beacon signals. 
     In a case of using satellite signals, four or more Expressions (1) are derived from four or more received signals, and then are solved as simultaneous equations, to calculate the first position information of the mobile body. On the other hand, in a case of using beacon signals, the first position information of the mobile body is calculated on the basis of a trilateration principle, using distance information obtained from three or more received signals. Calculation of the first position information of the mobile body may be repeatedly executed per calculation cycle. 
     In step S 105 , the autonomous navigation positioning unit  204  calculates the second position information of the mobile body. 
     In the position estimation method according to the first embodiment, the second position information of the vehicle  101   a  and the vehicle  101   b  is calculated using the absolute position (first position information) calculated from the satellite signals acquired in the past and the movement amount from the absolute position. The movement amount of the mobile body is calculated using time integral values of the acceleration and the angular velocity obtained from the inertia measurement device (not shown). In a case where the transmission frequencies of the satellite signal transmitter  102  and the beacon signal transmitter  104  are different from each other, at the same time as each sampling timing, the autonomous navigation positioning unit  204  executes calculation of the second position information of the mobile body. 
     In step S 106 , the index value calculation unit  205  determines whether or not the first position information and the second position information of the mobile body can be calculated by both of the own position calculation unit  202  and the autonomous navigation positioning unit  204 . If one of the first position information and the second position information of the mobile body cannot be calculated, i.e., in the case of NO in step S 106 , the process proceeds to step S 107 . On the other hand, if the first position information and the second position information of the mobile body can be both calculated, i.e., in the case of YES in step S 106 , the process proceeds to step S 108 . 
     In step S 107 , the index value calculation unit  205  does not perform calculation of the index value for the corresponding communication method. After the processing in step S 107 , the process is ended. 
     In step S 109 , the index value calculation unit  205  calculates the index value, using the first position information of the mobile body from the own position calculation unit  202  and the second position information of the mobile body from the autonomous navigation positioning unit  204 . 
     For the vehicle  101   a  which is an example of a mobile body in the first embodiment, as shown in  FIG.  1   , the construction  103  acts as a shielding object against satellite signals and thus the line-of-sight condition for the satellite signals is poor, so that noise mixing or multipath propagation is highly likely to occur. As a result, the first position information of the vehicle  101   a  calculated from the satellite signals is unstable and thus the index value calculated from the first position information becomes great. 
     On the other hand, for beacon signals transmitted from the beacon signal transmitter  104  provided in the construction  103 , the line-of-sight condition to the vehicle  101   a  present in the same construction  103  is good. Therefore, the first position information of the vehicle  101   a  calculated from the beacon signals is stable and thus the index value calculated from the first position information becomes small. 
     Here, the line-of-sight condition means whether or not there is an obstacle between a transmitter and a receiver in radio communication. A good line-of-sight condition means that there are no obstacles between a transmitter and a receiver. On the other hand, a poor line-of-sight condition means that there is an obstacle between a transmitter and a receiver. 
     For the vehicle  101   b  which is an example of a mobile body in the first embodiment, such shielding objects against satellite signals are not present around the vehicle  101   b . Therefore, the line-of-sight condition for satellite signals is good. As a result, the first position information of the vehicle  101   b  calculated from the satellite signals is stable and thus the index value calculated from the first position information of the vehicle  101   b  becomes small. 
     On the other hand, for the beacon signal transmitter  104  provided in the construction  103 , the construction  103  acts as a shielding object against beacon signals. Therefore, the line-of-sight condition for beacon signals is poor for the vehicle  101   b  present outside the construction  103 . In addition, the more distant the vehicle  101   b  is from the construction  103 , the poorer the line-of-sight condition for beacon signals is. As a result, the first position information of the vehicle  101   b  calculated from the beacon signals is unstable and thus the index value calculated from the first position information of the vehicle  101   b  becomes great. 
     In step S 109 , the position information selection unit  206  imparts an output priority to the communication method for which the index value has been obtained. For the vehicle  101   a  which is an example of a mobile body in the first embodiment and is present inside the construction  103 , the index value based on beacon signals is smaller than the index value based on satellite signals, and therefore the output priority for the first position information of the vehicle  101   a  calculated on the basis of beacon signals becomes higher. 
     On the other hand, for the vehicle  101   b  present outside the construction  103 , the index value based on satellite signals is smaller than the index value based on beacon signals, and therefore the output priority for the first position information of the vehicle  101   b  calculated on the basis of satellite signals becomes higher. 
     In step S 110 , the position information selection unit  206  selects the first position information of the mobile body that is based on the communication method for which the output priority is highest, and outputs the selected first position information. For the vehicle  101   a  in the first embodiment, the output priority of the beacon communication is highest, and therefore the first position information of the vehicle  101   a  calculated on the basis of the beacon signals is outputted. On the other hand, for the vehicle  101   b , the output priority of the satellite communication is highest, and therefore the first position information of the vehicle  101   b  calculated on the basis of the satellite signals is outputted. 
     The position estimation method according to the first embodiment is as described above. 
     Effects of First Embodiment 
     As described above, in the position estimation device and the position estimation method according to the first embodiment, output priorities are determined using index values, whereby it becomes possible to calculate position information of a mobile body at each location on the basis of an optimum communication method among a plurality of communication methods, thus providing an effect of obtaining a position estimation device and a position estimation method capable of outputting position information with high accuracy. 
     Second Embodiment 
     A position estimation method according to the second embodiment of the present disclosure will be described with reference to a flowchart in  FIG.  5   . Description of the same components as those in the above first embodiment is omitted. 
     In the position estimation method according to the first embodiment, first position information of a mobile body based on signals transmitted with a communication method for which the output priority is highest at each timing of sampling radio signals is selected. However, in such a situation that the output priorities frequently charge among communication methods, the communication method to be used for calculating the first position information of the mobile body is repeatedly switched. Under the situation in which the output priorities frequently change, if an offset occurs between respective first positions of the mobile body calculated on the basis of different communication methods, there is a possibility that the position information of the mobile body eventually outputted becomes unstable. 
     In the position estimation method according to the second embodiment, if the communication method for which the output priority is highest is identical over a predetermined number of consecutive calculation cycles, the first position information calculated by the communication method for which the output priority is highest is selected as position information of the mobile body. Therefore, by applying the position estimation method according to the second embodiment, the communication method to be used for calculating the position information of the mobile body can be prevented from being switched frequently, thus providing an effect of stabilizing the position information of the mobile body eventually outputted. 
     Position Estimation Method According to Second Embodiment 
     Hereinafter, the position estimation method according to the second embodiment will be described. The flowchart shown in  FIG.  5    is configured such that processing steps shown in  FIG.  5    are added subsequent to the processing in step S 109  in the flowchart shown in  FIG.  4   . 
     In step S 201 , the position information selection unit  206  stores the communication method for which the output priority is highest, in time series over a predetermined number of consecutive calculation cycles, in a specific storage area of the storage device  302 . Here, the specific storage area is defined as a storage area A. The predetermined number of consecutive calculation cycles means consecutive periods through a certain number of times of sampling. 
     In step s 202 , the position information selection unit  206  confirms whether or not the communication method stored in the storage area A is identical over the predetermined number of consecutive calculation cycles. 
     If the communication method stored in the storage area A is identical, i.e., in the case of YES in step S 202 , the process proceeds to step s 203 . On the other hand, if the communication methods stored in the storage area A include communication methods that are not identical, i.e., in the case of NO in step S 202 , the process proceeds to step S 204 . 
     In step S 203 , the position information selection unit  206  stores the identical communication method stored in the storage area A, into another specific storage area of the storage device  302 . Here, the other specific storage area is defined as a storage area B. 
     In step S 204 , the position information selection unit  206  determines whether or not the first position information of the mobile body can be calculated in the present calculation cycle using signals transmitted by the communication method stored in storage area B. If the first position information of the mobile body can be calculated, i.e., in the case of YES in step S 204 , the process proceeds to step S 205 . On the other hand, if the first position information of the mobile body cannot be calculated, i.e., in the case of NO in step S 204 , the process proceeds to step S 206 . 
     In step S 205 , the own position calculation unit  202  calculates the first position information of the mobile body from signals transmitted by the communication method stored in the storage area B. 
     In step S 206  which is executed in the case where the first position information of the mobile body cannot be calculated in step S 204 , the communication method for which the output priority is highest is selected from the communication methods for which whether or not the first position information of the mobile body can be calculated has not been confirmed yet, and then the process proceeds to step S 207 . 
     In step S 207 , the position information selection unit  206  determines whether or not the first position information of the mobile body in the present calculation cycle can be calculated from signals transmitted by the selected communication method. If the first position information of the mobile body can be calculated, i.e., in the case of YES in step S 207 , the process proceeds to step S 208 . On the other hand, if the first position information of the mobile body cannot be calculated, i.e., in the case of NO in step S 207 , the process proceeds to step S 209 . 
     In step S 208  which is executed in the case where the first position information of the mobile body can be calculated in step S 207 , the position information selection unit  206  outputs the first position information of the mobile body calculated from the signals transmitted by the selected communication method. 
     In step S 209  which is executed in the case where the first position information of the mobile body cannot be calculated in step S 207 , the position information selection unit  206  determines whether or not all the communication methods have been confirmed regarding whether or not the first position information of the mobile body can be calculated. If confirmation has not been done for all the communication methods, i.e., in the case of NO in step S 209 , the position information selection unit  206  performs processing from step S 206  again. On the other hand, if whether or not the first position information of the mobile body has been confirmed for all the communication methods, i.e., in the case of YES in step S 209 , the process proceeds to step S 210 . 
     In step S 210 , the position information selection unit  206  outputs the second position information of the mobile body acquired by the autonomous navigation positioning unit  204 . 
     The position estimation method according to the second embodiment is as described above. 
     Regarding the position estimation method according to the second embodiment, a specific processing content will be described in a case where the vehicle  101   a  moves from the position in  FIG.  1    to the position of the vehicle  101   b , as art example. 
     At the initial stage when the vehicle  101   a  starts to move from the position in  FIG.  1   , the vehicle  101   a  is present inside the construction  103 . Therefore, the line-of-sight condition for the satellite signal transmitter  102  is poor, whereas the line-of-sight condition is good for beacon signals transmitted from the beacon signal transmitter  104  provided in the construction  103 . Thus, the output priority for beacon communication is high consecutively over a certain period, so that, in step S 201 , beacon communication is stored in time series in the storage area A. 
     Since beacon communication is stored in the storage area A consecutively over a certain period, i.e., a certain number of consecutive calculation cycles, in step S 203 , beacon communication is stored in the storage area B. 
     In step S 204 , the position information selection unit  206  refers to the communication method in the storage area B, to confirm whether or not the first position information of the vehicle  101   a  at present, i.e., in the present calculation cycle, can be calculated using beacon signals. If the first position information can be calculated, in step S 205 , the position information selection unit  206  outputs the first position information of the vehicle  101   a  calculated using the beacon signals. 
     As the vehicle  101   a  moves from the position in  FIG.  1    frontward (rightward in  FIG.  1   ), the line-of-sight condition for satellite signals transmitted from the satellite signal transmitter  102  is gradually improved. In this case, in such a transient period, while the first position information of the vehicle  101   a  can be calculated using beacon signals, the output priority frequently changes between satellite communication and beacon communication. 
     However, if the position estimation method according to the second embodiment is applied, by the processing in step S 205 , it becomes possible to continue outputting the first position information of the vehicle  101   a  calculated using beacon signals, even in such a situation that the output priority frequently changes between satellite signals and beacon signals. Thus, it becomes possible to prevent such a phenomenon that the position information of the vehicle  101   a  becomes unstable, i.e., the position accuracy is reduced, due to an offset of the first position information of the vehicle  101   a  caused in a case of performing calculation using both satellite signals and beacon signals. 
     If the first position information of the vehicle  101   a  at present, i.e., in the present calculation cycle, cannot be calculated using beacon signals, in step S 207 , whether or not the first position information of the vehicle  101   a  can be calculated using satellite signals is confirmed. If the first position information of the vehicle  101   a  can be calculated using satellite signals, in step S 208 , the position information selection unit  206  outputs the first position information of the vehicle  101   a  calculated using satellite signals. 
     By the above processing steps in the position estimation method according to the second embodiment, even in a case where a timing when the first position information of the vehicle  101   a  cannot be calculated using the communication method stored in storage area B, i.e., a calculation cycle in which the first position information of the vehicle  101   a  cannot be calculated, arises, the position estimation device  200  can always output either the first position information or the second position information, which is the position information of the vehicle  101   a.    
     If the first position information of the vehicle  101   a  cannot be calculated using satellite signals, in step S 210 , using the past first position information of the vehicle  101   a  calculated from the past beacon signals and the movement amount of the mobile body obtained from the inertia measurement device, the second position information of the vehicle  101   a  at present, i.e., in the present calculation cycle, is calculated and outputted. The aforementioned past means the calculation cycle preceding the present calculation cycle by one cycle in the consecutive calculation cycles. However, the past may mean the calculation cycle more than one cycle ago. 
     Effects of Second Embodiment 
     As described above, in the position estimation method according to the second embodiment, even in a case where a timing when the first position information of the mobile body cannot be calculated even by using any of the radio communication methods arises, the first position information or the second position information, which is the position information of the mobile body can be always outputted, thus providing an effect that the position information of the mobile body can be stably outputted with high accuracy. 
     Third Embodiment 
       FIG.  6    is a function block diagram showing the configuration of a position estimation device  400  according to the third embodiment of the present disclosure. The position estimation device  400  according to the third embodiment is characterized by predicting position information of the mobile body. Description of the same components as those in the position estimation device  200  according to the above first embodiment is omitted. 
     The position estimation device  400  according to the third embodiment is configured by further providing an own position prediction unit  401  to the configuration of the position estimation device  200  according to the first embodiment. 
     The own position prediction unit  401  calculates a prediction value fox position information of a mobile body, using the first position information calculated by the own position calculation unit  202 . In a position estimation method according to the third embodiment, an approximate function is calculated by linear approximation using the first position information for the past several times of sampling, and a prediction value is obtained from a value on the approximate function. However, as long as the object of the present disclosure can be achieved, the calculation method for the prediction value is not particularly limited. The calculation method for the prediction value may be different among communication methods. Calculation of the prediction value is performed for each communication method. In the processing after the index value calculation unit  205 , the position information of the mobile body predicted by the own position prediction unit  401  is treated as the first position information calculated by the own position calculation unit  202 . 
     The position estimation method according to the third embodiment will be described with reference to a flowchart in  FIG.  7   . The flowchart in  FIG.  7    corresponds to processing between step S 101  and step S 105  in the flowchart in  FIG.  4    showing the position estimation method according to the first embodiment, and step S 103  in the flowchart in  FIG.  4    is replaced with step S 301  in the flowchart in  FIG.  7   . 
     In step S 102 , if the communication-method-based reception unit  201  cannot receive a necessary number of radio signals for calculating the position information of the mobile body in a given calculation cycle, in step S 301 , the own position prediction unit  401  calculates a prediction value for the first position information of the mobile body, which is needed for the next calculation cycle. 
     In  FIG.  1    showing a situation in which the position estimation device  400  and the position estimation method according to the third embodiment are used, if the first position information of the vehicle  101   a  cannot be calculated even by using satellite signals, a linear approximation function is calculated using the past first position information of the vehicle  101   a  calculated using satellite signals. The present time is substituted into the calculated linear approximation function, to obtain a prediction value for the present position information of the vehicle  101   a . The past position information of the vehicle  101   a  calculated using satellite signals is read from the storage device  302 . In the above description, the present means the present calculation cycle. The past means, for example, the calculation cycle preceding the present, i.e., the present calculation cycle, by one cycle, in the consecutive calculation cycles. However, the past may mean the calculation cycle more than one cycle ago. 
     In step S 302 , the own position calculation unit  202  or the own position prediction unit  401  stores the calculated first position information of the mobile body in the storage device  302 . In the steps subsequent to step S 105 , the prediction value from the own position prediction unit  401  is treated as the first position information of the mobile body calculated by the own position calculation unit  202 . 
     Effects of Third Embodiment 
     As described above, in the position estimation device and the position estimation method according to the third embodiment, even in such a situation that the first position information of the mobile body cannot be calculated at present, i.e., in the present calculation cycle, a prediction value for the first position information of the mobile body, calculated by the own position prediction unit, is used in the next calculation cycle, thus providing an effect that the position information of the mobile body can be stably outputted with high accuracy. 
     Fourth Embodiment 
     A position estimation method according to the fourth embodiment of the present disclosure is characterized as follows. It is noted that the configuration of the position estimation device is the same as the configuration of the position estimation device  200  according to the first embodiment shown in  FIG.  2   . 
     In the position estimation method according to the fourth embodiment, the index value calculation unit  205  shown in  FIG.  2    calculates a position accuracy reduction ratio on the basis of the location of the transmitter for each of a plurality of communication methods, such as the location of the satellite signal transmitter  102  or the beacon signal transmitter  104 , which transmits signals to the communication-method-based reception unit  201 . As a calculation method for the position accuracy reduction ratio, a known method is used. 
     If there is a communication method for which the calculated position accuracy reduction ratio is equal to or greater than a position accuracy threshold among the plurality of communication methods, the index value calculation unit  205  gives information about the position accuracy reduction ratio for that communication method to the position information selection unit  206 . The position information selection unit  206  excludes, from selection, such a communication method for which the position accuracy reduction ratio is equal to or greater than the position accuracy threshold, on the basis of the given information about the position accuracy reduction ratio for that communication method. 
     Effects of Fourth Embodiment 
     As described above, in the position estimation method according to the fourth embodiment, the position accuracy reduction ratio is calculated on the basis of the location of the transmitter for each of a plurality of communication methods, and if the position accuracy reduction ratio is equal to or greater than the position accuracy threshold, the corresponding communication method is excluded from selection, thus providing an effect that the position information of the mobile body is obtained with higher accuracy. 
     Fifth Embodiment 
     A position estimation method according to the fifth embodiment of the present disclosure is characterized as follows. It is noted that the configuration of the position estimation device is the same as the configuration of the position estimation device  200  according to the first embodiment shown in  FIG.  2   . 
     In the position estimation method according to the fifth embodiment, the number of mismatch bits in a preamble part of a signal received by the communication-method-based reception unit  201  is calculated for each of a plurality of communication methods, and if there is a communication method for which the calculated number of mismatch bits is equal to or greater than a bit threshold, the index value calculation unit  205  gives information about the number of mismatch bits for that communication method to the position information selection unit  206 . The position information selection unit  206  excludes, from selection, such a communication method fox which the number of mismatch bits is equal to or greater than the bit threshold, on the basis of the given information about the number of mismatch bits for that communication method. 
     Effects of Fifth Embodiment 
     As described above, in the position estimation method according to the fifth embodiment, the number of mismatch bits in a preamble part of a received signal is calculated for each of a plurality of communication methods, and if there is a communication method for which the calculated number of mismatch bits is equal to or greater than the bit threshold, that communication method is excluded from communication method selection, thus providing an effect that the position information of the mobile body is obtained with higher accuracy. 
     Sixth Embodiment 
     A position estimation method according to the sixth embodiment of the present disclosure is characterized as follows. It is noted that the configuration of the position estimation device is the same as the configuration of the position estimation device  200  according to the first embodiment shown in  FIG.  2   . 
     In the position estimation method according to the sixth embodiment, in the communication-method-based reception unit  201 , if a reception angle with respect to a radio signal transmitter can be calculated from a transmitted radio signal, a reception angle with respect to a radio signal transmitter is calculated for each communication method for which the calculation is possible. 
     If there is a communication method for which the reception angle with respect to the radio signal transmitter is equal to or smaller than the reception angle threshold, the index value calculation unit  205  gives information about the reception angle for that communication method to the position information selection unit  206 . The position information selection unit  206  excludes, from selection, such a communication method for which the reception angle is equal to or smaller than the reception angle threshold, on the basis of the information about the reception angle for that communication method. 
     Effects of Sixth Embodiment 
     As described above, in the position estimation method according to the sixth embodiment, a reception angle with respect to the radio signal transmitter is calculated for each of a plurality of communication methods, and if there is a communication method for which the calculated reception angle is equal to or smaller than the reception angle threshold, that communication method is excluded from communication method selection, thus providing an effect that the position information is obtained with higher accuracy. 
     Seventh Embodiment 
       FIG.  8    is a function block diagram showing the configuration of an autonomous driving system  500  according to the seventh embodiment of the present disclosure.  FIG.  9    schematically shows a vehicle  101   c  provided with the autonomous driving system  500  according to the seventh embodiment. The autonomous driving system  500  includes the position estimation device  200  according to the first embodiment, a traveling route generation device  510 , and a vehicle control device  520 . 
     As described above, the position estimation device  200  outputs either the first position information or the second position information, which is own-vehicle position information of the vehicle  101   c , on the basis of signals transmitted by each of a plurality of communication methods. Instead of the position estimation device  200  according to the first embodiment, the position estimation device  400  according to the third embodiment may be used. The position estimation device  200  outputs the own-vehicle position information of the vehicle  101   c  to the traveling route generation device  510 . 
     The traveling route generation device  510  generates a traveling route for the vehicle  101   c  to reach a target location from the own-vehicle position, using the own-vehicle position information of the vehicle  101   c  outputted from the position estimation device  200 . For generation of the traveling route, a known method is applicable. 
     The vehicle control device  520  sets a target track and a target vehicle speed which are target control amounts needed for the vehicle  101   c  to travel on the traveling route generated by the traveling route generation device  510 , and calculates a target steering amount and a target acceleration/deceleration needed for following the target track and the target vehicle speed. For calculation of the target steering amount and the target acceleration/deceleration, a known calculation method is applicable. 
     The configuration of the autonomous driving system  500  is as described above. 
     Hereinafter, vehicle control for the vehicle  101   c  by the autonomous driving system  500  will be described. 
     The target steering amount and the target acceleration/deceleration which are target control amounts, calculated in the vehicle control device  520  of the autonomous driving system  500 , are outputted to an actuator  530 , whereby autonomous driving control for the vehicle  101   c  is executed. 
     The actuator  530  includes an electronic power steering (EPS) controller  531 , a powertrain controller  532 , a brake controller  533 , an EPS unit  535 , a powertrain unit  536 , and a brake unit  537 . 
     The actuator  530  controls EPS, a brake, and an accelerator so as to cause the vehicle  101   c  to follow the target steering amount and the target acceleration/deceleration. 
     The EPS controller  531  controls the EPS unit  535  on the basis of the target steering amount outputted from the autonomous driving system  500 . By the EPS controller  531 , for example, a steering angle for the vehicle  101   c  to travel along the target track can be controlled. 
     The powertrain controller  532  controls the powertrain unit  536  so as to achieve the target acceleration/deceleration outputted from the autonomous driving system  500 . In a case where a driver instead of autonomous driving control performs speed control, the powertrain unit  536  is controlled on the basis of the amount of tread on an accelerator pedal. 
     The brake controller  5 : 33  controls the brake unit  537  so as to achieve the target acceleration/deceleration outputted from the autonomous driving system  500 . In a case where the driver instead of autonomous driving control performs speed control, the brake unit  537  is controlled on the basis of the amount of tread on a brake pedal. 
     Effects of Seventh Embodiment 
     As described above, in the autonomous driving system according to the seventh embodiment, own-vehicle position information is calculated with high accuracy by the position estimation device  200 ,  400  according to the first or third embodiment, thus providing an effect that autonomous driving control having high stability can be achieved on the basis of accurate position information. 
     In the above description, the functions of the components of the position estimation devices  200 ,  400  according to the first and third embodiments and the autonomous driving system  500  according to the seventh embodiment are implemented by one of hardware and software, etc. However, without limitation thereto, some of the components of the position estimation devices  200 ,  400  according to the first and third embodiments and the autonomous driving system  500  according to the seventh embodiment may be implemented by dedicated hardware and the other components may be implemented by software, etc. 
     For example, as shown in  FIG.  10    and  FIG.  11   , for some of the components, the functions thereof may be implemented by the processing circuit  300  as dedicated hardware, and for the other components, the processing circuit  300  as the processor  301  may read and execute a program for causing a computer or the like to execute the position estimation method according to any of the first to sixth embodiments stored in the storage device  302 , thereby implementing the functions of the other components. 
     As shown in  FIG.  11   , setting data to be used in the function units and the like of the position estimation devices  200 ,  400  according to the first and third embodiments and the autonomous driving system  500  according to the seventh embodiment may be installed as a part of software to the storage device  302  from a storage medium  304  storing a program  305  for causing a computer or the like to execute the position estimation method according to any of the first to sixth embodiments. 
     As described above, the position estimation devices  200 ,  400  according to the first and third embodiments and the autonomous driving system  500  according to the seventh embodiment can implement the above-described functions by hardware, software, etc., or a combination thereof. 
     Although the disclosure is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects, and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations to one or more of the embodiments of the disclosure. 
     It is therefore understood that numerous modifications which have not been exemplified can be devised without departing from the scope of the present disclosure. For example, at least ore of the constituent components may be modified, added, or eliminated. At least one of the constituent components mentioned in at least one of the preferred embodiments may be selected and combined with the constituent components mentioned in another preferred embodiment. 
     DESCRIPTION OF THE REFERENCE CHARACTERS 
     
         
         
           
               101   a ,  101   b ,  101   c  vehicle 
               102  satellite signal transmitter 
               103  construction 
               104  beacon signal transmitter 
               200 ,  400  position estimation device 
               201  communication-method-based reception unit 
               201   a  first radio signal reception unit 
               201   b  second radio signal reception unit 
               201   n  nth radio signal reception unit 
               202  own position calculation unit 
               203  movement amount calculation unit 
               204  autonomous navigation positioning unit 
               205  index value calculation unit 
               206  position information selection unit 
               300  processing circuit 
               301  processor 
               302  storage device 
               303  clock 
               304  storage medium 
               305  program 
               401  own position prediction unit 
               500  autonomous driving system 
               510  traveling route generation device 
               520  vehicle control device 
               530  actuator 
               531  EPS controller 
               532  powertrain controller 
               533  brake controller 
               535  EPS unit 
               536  powertrain unit 
               537  brake unit