JP2021032720A - Position estimating device and position estimating method - Google Patents

Abstract

To estimate a position with high accuracy even when a general-purpose oscillator is used.SOLUTION: Provided is a position estimating device for estimating the position of a terminal using a counter value at a time-of-day when calculation is made in each of three or more fixed stations. The position estimating device comprises: a counter value acquisition unit for acquiring a first counter value calculated at each fixed station that indicates a point of time at which a first radio wave transmitted from a terminal to each fixed station has arrived and a second counter value calculated at each fixed station that indicates a point of time at which a second radio wave transmitted from a terminal to each fixed station has arrived; a difference change amount calculation unit for calculating a difference change amount that represents a change amount from a first difference that is a difference in the first counter value between two fixed stations to a second difference that is a difference in the second counter value between the two fixed stations; and a position estimation unit for estimating the position of the terminal on the basis of a plurality of calculated difference change amounts, for each of a plurality of combinations of two fixed stations among the three or more fixed stations.SELECTED DRAWING: Figure 3

Description

The present invention relates to a position estimation device and a position estimation method.

In recent years, various positioning methods have been actively studied. As one of the positioning methods, TOA (Time Of Arrival) is known, which uses the arrival time, which is the time when the radio wave transmitted by the terminal arrives at the fixed station. In TOA, high-precision positioning is possible when both the terminal and the fixed station have a high-precision timer (clock source). However, assuming that the terminal is a general-purpose machine such as a smartphone, it is difficult to provide a highly accurate timer on the terminal.

Therefore, as another positioning method, TDOA (Time Difference Of Arrival), which utilizes the difference in the arrival time of radio waves to each fixed station, is also being studied. In TDOA, the terminal only needs to be able to transmit radio waves, and the terminal does not have to have a receiving function for positioning. Therefore, it is not necessary to provide the terminal with a highly accurate timer, and the terminal can be easily manufactured.

Techniques related to such positioning are also disclosed in, for example, Patent Documents 1 to 4. Specifically, Patent Document 1 discloses a device having a plurality of sensors, and the device calculates the arrival time difference to each sensor for a signal transmitted from a mobile station, and arrives at the plurality of signals. Positioning of mobile stations is performed using the time difference. Patent Document 2 and Patent Document 3 are systems having a plurality of fixed stations, reference stations, and mobile stations, in which each fixed station receives a signal from the mobile station and a signal from the reference station, and the time is determined by the signal from the reference station. A system for determining the position of a mobile station after synchronizing the above is disclosed. Patent Document 4 discloses a technique in which a plurality of fixed stations receive a wireless LAN signal, each fixed station transmits a "deviation observed value" to a server, and the server constructs a database. When the fixed station receives a signal from the mobile station, the fixed station calculates the position of the mobile station based on the database and the difference in the arrival time of the signal of each fixed station.

Japanese Unexamined Patent Publication No. 2007-1987742 International Publication No. 2016/178381 International Publication No. 2017/204087 Special Table 2013-513786

However, the existing positioning method has a problem. For example, in order to realize TDOA, it is desirable that each fixed station synchronizes the time with high accuracy, but the system configuration becomes large. Specifically, if a rubidium oscillator having high clock accuracy is prepared and a synchronization signal is supplied from the oscillator to all fixed stations, highly accurate time synchronization can be realized. However, when using TDOA for autonomous driving or traffic, it is common for each fixed station to be installed at a distance of several tens of meters or more, and all fixed stations are connected with a cable to all fixed stations. It is practically difficult to supply a synchronization signal via a cable. From the above, TDOA has a technically insufficient aspect regarding the feasibility of time synchronization.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is that the position can be estimated with sufficient accuracy even when a general-purpose oscillator is used. It is an object of the present invention to provide a new and improved position estimation device and a position estimation method.

In order to solve the above problems, according to a certain viewpoint of the present invention, it is a position estimation device that estimates the position of a terminal by using a counter value of time calculated in each of three or more fixed stations, and each fixed station. The first counter value calculated at each fixed station indicating the time when the first radio wave transmitted from the terminal arrives at the station, and the time when the second radio wave transmitted from the terminal arrives at each fixed station. The counter value acquisition unit that acquires the second counter value calculated at each fixed station shown, the first difference that is the difference between the first counter value between the two fixed stations, and the two fixed stations. A counter difference calculation unit that calculates the second difference, which is the difference between the second counter values between stations, and a difference change amount, which is the amount of change from the first difference to the second difference, are calculated. Based on the difference change amount calculation unit, the plurality of difference change amounts calculated for each of the plurality of combinations of the two fixed stations among the three or more fixed stations, and the positions of the three or more fixed stations. Provided is a position estimation device including a position estimation unit for estimating the position of the terminal.

The position estimation unit is based on the plurality of differential changes, the positions of the three or more fixed stations, and the first position, which is the position of the terminal at the time when the terminal transmits the first radio wave. , The second position, which is the position of the terminal at the time when the terminal transmits the second radio wave, may be estimated.

For each of the plurality of combinations of the two fixed stations, the position estimation unit includes a first distance difference, which is a difference in the distance from each of the two fixed stations to the first position, and the two fixed stations. The sum of the distances obtained by multiplying the difference change amount calculated for the combination of the above is multiplied by the propagation velocity of the radio wave, and the sum is the difference in the distances from each of the two fixed stations to the second position. The second position may be estimated by obtaining an equation equal to the second distance difference and solving the plurality of equations obtained for each of the plurality of combinations.

The first position may be known.

The position estimation unit sets a plurality of temporary positions as the first position, evaluates the likelihood of each of the plurality of second positions obtained by estimation based on each of the plurality of temporary positions, and evaluates each of the likelihoods. The temporary positions used for estimating the second position are weighted according to the likelihood of each second position, and the terminal transmits the first radio wave based on the plurality of weighted temporary positions. The more probable position of the terminal at the time of this may be estimated.

The position estimation unit, in addition to the plurality of differential changes and the positions of the three or more fixed stations, from the time of transmission of the first radio wave to the time of transmission of the second radio wave calculated by the terminal. The position of the terminal may be estimated based on the displacement vector of the terminal.

The position estimation unit is the difference from each of the two fixed stations to the first position, which is the position of the terminal at the time of transmitting the first radio wave, for each of the plurality of combinations of the two fixed stations. After adding the displacement vector to the first position, the sum of the first distance difference and the distance obtained by multiplying the difference change amount calculated for the combination of the two fixed stations by the propagation speed of the radio wave is added to the first position. Obtaining an equation equal to the second distance difference, which is the difference in distance from the two fixed stations to the second position of, and solving the plurality of the equations obtained for each of the plurality of combinations. May estimate the first position.

Further, in order to solve the above problems, according to another viewpoint of the present invention, it is executed in a position estimation device that estimates the position of the terminal using the counter value of the time calculated in each of the three or more fixed stations. This is a position estimation method, in which the first counter value calculated at each fixed station indicating the time when the first radio wave transmitted from the terminal arrives at each fixed station, and the first counter value transmitted from the terminal to each fixed station. Acquiring the second counter value calculated at each fixed station indicating the time when the second radio wave arrives, and the first difference between the two fixed stations, which is the difference between the first counter values. Calculation of the difference and the second difference which is the difference of the second counter value between the two fixed stations and the difference which is the amount of change from the first difference to the second difference. Based on the calculation of the amount of change, the plurality of differential changes calculated for each of the plurality of combinations of the two fixed stations among the three or more fixed stations, and the positions of the three or more fixed stations. , A position estimation method including estimating the position of the terminal is provided.

According to the present invention described above, it is possible to estimate the position with sufficient accuracy even when a general-purpose oscillator is used.

It is explanatory drawing which shows the structure of the position estimation system by one Embodiment of this invention. It is explanatory drawing which shows the structure of the mobile terminal 20 by one Embodiment of this invention. It is explanatory drawing which shows the structure of the fixed station 10 by one Embodiment of this invention. It is explanatory drawing which shows the arrangement example at time t of a fixed station 10 and a mobile terminal 20. It is explanatory drawing which shows the transmission of the 1st radio wave from a mobile terminal 20. It is explanatory drawing which shows the transmission of the 2nd radio wave from the mobile terminal 20. It is a flowchart which shows the operation when the fixed station 10 executes a process example A. It is explanatory drawing which shows the arrangement example of the particle. It is explanatory drawing which shows the distribution example of an error e. It is a flowchart which shows the operation when the fixed station 10 executes a process example B. It is explanatory drawing which shows the displacement vector. It is a flowchart which shows the operation when the fixed station 10 executes the process example C. It is a block diagram which showed the hardware composition of the fixed station 10.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

Further, in the present specification and the drawings, a plurality of components having substantially the same functional configuration may be distinguished by adding different alphabets after the same reference numerals. However, when it is not necessary to particularly distinguish each of the plurality of components having substantially the same functional configuration, only the same reference numerals are given to each of the plurality of components.

<1. Overview of position estimation system>
One embodiment of the present invention relates to a position estimation system for estimating the position of a mobile terminal by DTDOA (Difference of TDOA) utilizing a further difference in "difference in arrival time" in TDOA. First, the outline of the position estimation system according to the embodiment of the present invention will be described with reference to FIG.

FIG. 1 is an explanatory diagram showing a configuration of a position estimation system according to an embodiment of the present invention. As shown in FIG. 1, the position estimation system according to the embodiment of the present invention has three or more fixed stations 10 # 1 to 10 # 3, and a mobile terminal 20.

The fixed station 10 is a communication device installed at a fixed position. The fixed station 10 receives the radio wave transmitted from the mobile terminal 20. Each of the fixed stations 10 calculates a counter value of time, and each fixed station 10 specifies a counter value indicating a time when a radio wave is received from the mobile terminal 20. The fixed station 10 can also communicate with another fixed station 10. In one embodiment of the present invention, the counter values calculated by each of the fixed stations 10 may not be synchronized.

The fixed station 10 according to the embodiment of the present invention also includes a function as a position estimation device for estimating the position of the mobile terminal 20. However, a position estimation device may be provided separately from the fixed station 10. In this case, the position estimation device is connected to each fixed station 10 locally or via a network, collects a counter value from each fixed station 10, and uses the counter value to perform a process described later to position the mobile terminal 20. May be estimated.

The mobile terminal 20 is an example of a terminal carried by a user. The mobile terminal 20 has a wireless communication function and communicates with each fixed station 10. The wireless communication function of the mobile terminal 20 may be a wireless LAN (Local Area Network) communication function or a Bluetooth (registered trademark) communication function.

In such a position estimation system, the mobile terminal 20 periodically transmits radio waves, and each fixed station 10 receives the radio waves transmitted by the mobile terminal 20. The fixed station 10 has a first counter value calculated at each fixed station 10 indicating the time when the first radio wave transmitted from the mobile terminal 20 arrives at each fixed station 10, and is transmitted from the mobile terminal 20. The position of the mobile terminal 20 is estimated based on the second counter value calculated at each fixed station 10 indicating the time when the second radio wave arrives at each fixed station 10. Of the three or more fixed stations 10, only the representative fixed station 10 may estimate the position of the mobile terminal 20, or a plurality of fixed stations 10 may estimate the position of the mobile terminal 20. When only a part of the fixed stations 10 estimate the position of the mobile terminal 20, the fixed station 10 that estimates the position may transmit the position estimation result to the other fixed stations 10.

The position estimation system is used, for example, for automatic driving control of a vehicle at an intersection. Specifically, a pedestrian has a mobile terminal 20, a traffic light functions as a fixed station 10 to estimate the position of the mobile terminal 20, and the traffic light transmits the estimation result of the position of the mobile terminal 20 to the vehicle. May control automatic travel based on the position of the mobile terminal 20. Hereinafter, the configurations of the mobile terminal 20 and the fixed station 10 will be described more specifically.

<2. Mobile terminal configuration>
FIG. 2 is an explanatory diagram showing a configuration of a mobile terminal 20 according to an embodiment of the present invention. As shown in FIG. 2, the mobile terminal 20 has a displacement calculation unit 210, a transmission instruction unit 220, and a radio unit 230.

(Displacement calculation unit)
The displacement calculation unit 210 calculates a displacement vector which is the amount and direction in which the mobile terminal 20 is displaced between the two times. For example, the displacement calculation unit 210 has a motion sensor such as an acceleration sensor or a gyroscope, and calculates a displacement vector by performing a predetermined process on a value obtained by the motion sensor.

(Transmission instruction unit)
The transmission instruction unit 220 instructs the radio unit 230 to transmit radio waves. In one embodiment of the present invention, the transmission instruction unit 220 instructs the radio unit 230 to transmit a predetermined radio wave such as a beacon at regular intervals, for example.

(Wireless section)
The wireless unit 230 has a wireless communication function for transmitting radio waves. For example, the radio unit 230 has a digital signal processing unit, an analog signal processing unit, an antenna, and the like, and transmits radio waves from the antenna at a timing instructed by the transmission instruction unit 220. Further, the wireless unit 230 may have a wireless communication function for receiving radio waves, and in this case, the wireless unit 230 can receive the estimation result of the position of the mobile terminal 20 from the fixed station 10.

<3. Fixed station configuration>
FIG. 3 is an explanatory diagram showing a configuration of a fixed station 10 according to an embodiment of the present invention. As shown in FIG. 3, the fixed station 10 includes a radio unit 110, a sampling unit 120, an oscillator 130, a counter value calculation unit 140, a counter value communication unit 150, a counter difference calculation unit 160, a difference change amount calculation unit 170, and a position. It has an estimation unit 180.

(Wireless section)
The wireless unit 110 functions as a receiving unit that receives radio waves transmitted from the mobile terminal 20. The radio unit 110 may include, for example, an antenna and a digital signal processing unit. The radio unit 110 converts the radio wave received from the mobile terminal 20 into an electrical reception signal, and outputs the reception signal to the sampling unit 120.

(Sampling section)
The sampling unit 120 is an AD converter that converts a received signal input from the wireless unit 110 from an analog format to a digital format. The sampling unit 120 outputs the received signal in the digital format obtained by the conversion to the counter value calculation unit 140.

(Oscillator)
The oscillator 130 generates a clock signal and supplies the clock signal to the counter value calculation unit 140. In one embodiment of the present invention, the position of the mobile terminal 20 can be estimated with high accuracy even if the oscillator 130 is a general-purpose oscillator for the reason described later.

(Counter value calculation unit)
The counter value calculation unit 140 repeatedly increments the counter value based on the clock signal supplied from the oscillator 130. Then, when the reception signal in the digital format is input from the sampling unit 120, the counter value calculation unit 140 specifies the counter value at that time. For example, when the radio wave transmitted from the mobile terminal 20 is a packet, the counter value calculation unit 140 specifies the counter value at the time when the head position of the wireless packet is detected.

Here, the mobile terminal 20 according to the embodiment of the present invention repeats the transmission of radio waves a plurality of times, and the counter value calculation unit 140 has a first counter value, which is a counter value for the first radio wave, and a first counter value. The second counter value, which is the counter value for the second radio wave, is specified. That is, the counter value calculation unit 140 has a function as a counter value acquisition unit that acquires the first counter value and the second counter value. The counter value calculation unit 140 outputs the specified first counter value and the second counter value to the counter value communication unit 150 and the counter difference calculation unit 160.

(Counter value communication unit)
The counter value communication unit 150 functions as a counter value acquisition unit that receives the first counter value and the second counter value specified in the other fixed station 10 from the other fixed station 10, and counter value calculation. It has a function of transmitting the first counter value and the second counter value specified by the unit 140 to another fixed station 10. The counter value communication unit 150 may communicate with another fixed station 10 by wire or wirelessly. Further, the radio unit 110 may include the function of the counter value communication unit 150, and the radio unit 110 may communicate with another fixed station 10.

(Counter difference calculation unit)
The counter difference calculation unit 160 is a first difference which is a difference of the first counter value between the two fixed stations 10 and a second difference which is a difference of the second counter value between the two fixed stations 10. Calculate the difference between 2. For example, the counter difference calculation unit 160 of the fixed station 10 # 1 is a difference between the first counter value specified by the fixed station 10 # 1 and the first counter value specified by the fixed station 10 # 2. The first difference and the second difference, which is the difference between the second counter value specified in the fixed station 10 # 1 and the second counter value specified in the fixed station 10 # 2, are calculated. The counter difference calculation unit 160 calculates the first difference and the second difference for each of the plurality of combinations of the two fixed stations 10.

(Difference change amount calculation unit)
The difference change amount calculation unit 170 calculates the difference change amount, which is the change amount from the first difference to the second difference, for each of the plurality of combinations of the two fixed stations 10. For example, the difference change amount calculation unit 170 of the fixed station 10 # 1 subtracts the first difference from the second difference calculated for the combination of the fixed station 10 # 1 and the fixed station 10 # 2, and the fixed station 10 Obtain the difference change amount for the combination of # 1 and fixed station 10 # 2. Further, the difference change amount calculation unit 170 of the fixed station 10 # 1 subtracts the first difference from the second difference calculated for the combination of the fixed station 10 # 1 and the fixed station 10 # 3, and the fixed station 10 The difference change amount for the combination of # 1 and the fixed station 10 # 3 is obtained.

(Position estimation unit)
The position estimation unit 180 estimates the position of the mobile terminal 20 based on the plurality of difference change amounts calculated by the difference change amount calculation unit 170, the positions of three or more fixed stations, and the like. The position estimation unit 180 can estimate the position of the mobile terminal 20 by processing various methods using a plurality of differential changes. Hereinafter, some processes will be specifically described.

<4. Processing example A>
First, a processing example A of position estimation according to an embodiment of the present invention will be described. The processing example A is a processing example applicable when the position of the mobile terminal 20 is obtained at a certain time t. The position (first position) of the mobile terminal 20 at time t can be obtained by, for example, positioning using a landmark or positioning using a laser range finder corresponding to a part of a narrow range.

For convenience of explanation, an example in which the number of fixed stations 10 is three and the two-dimensional position of the mobile terminal 20 is estimated will be described. However, the number of fixed stations 10 may be four or more, in which case. , The three-dimensional position of the mobile terminal 20 can be estimated. Further, it is assumed that the position of each fixed station 10 is known. Hereinafter, as described above, the position of the mobile terminal 20 at the time t is also known, and an example of estimating the position of the mobile terminal 20 at a time (time t + k) after that will be described.

(theory)
FIG. 4 is an explanatory diagram showing an arrangement example of the fixed station 10 and the mobile terminal 20 at time t. In FIG. 4 and subsequent drawings, the fixed station 10 # 1 is indicated by a square mark (1), the fixed station 10 # 2 is indicated by a square mark (2), and the fixed station 10 # 3 is indicated from the viewpoint of clarity of the drawing. Is indicated by a square mark (3), and the mobile terminal 20 is indicated by a circle mark. The positions of the fixed station 10 and the mobile terminal 20 at time t are represented by the X coordinate value and the Y coordinate value as shown in FIG.

FIG. 5 is an explanatory diagram showing transmission of a first radio wave from the mobile terminal 20. Here, it is considered that the mobile terminal 20 transmits the first radio wave at the absolute time t. ^{Let c1 t be} the counter value of the fixed station 10 # 1 at the ^{absolute time t, and c2 t be} the counter value of the fixed station 10 # 2 at the absolute time t. However, each fixed station 10 cannot directly recognize the ^{counter values c1 t} and c2 ^{t at the absolute time t.} This is because the first radio wave arrives at each fixed station 10 after the arrival time has elapsed from the absolute time t. Specifically, as shown in FIG. 5, the first radio wave arrives at the fixed station 10 # 1 after ^{the arrival time f1 t} has elapsed, and reaches the fixed station 10 # 2 after the ^{arrival time f2 t has elapsed.} Coming. Therefore, if the counter values acquired by the fixed stations 10 # 1 and the fixed stations 10 # 2 when the first radio wave arrives at the fixed stations 10 # 1 and the fixed stations 10 # 2 are cf1 ^t and cf2 ^t, cf1 ^t and cf2 ^t are expressed by the following equations (1) and (2). In addition, cf1 ^t and cf2 ^t correspond to the above-mentioned first counter value.

Here, the arrival times f1 ^t and f2 ^t are geometrically expressed as the following equations (3) and (4). The parameter c is the speed of light.

As a premise of processing example A, since the position (x _t, y _{t ) of the mobile terminal 20 at the absolute time t is known, (x t,} y _t ) and each fixed station 10 are shown in equations (3) and (4). By substituting the position of, f1 ^t and f2 ^t can be calculated.

Next, it is considered that the time k elapses and the mobile terminal 20 transmits the second radio wave at the absolute time t + k. FIG. 6 is an explanatory diagram showing transmission of a second radio wave from the mobile terminal 20. Assuming that the counter value of the fixed station 10 # 1 at the absolute time t + k is c1 ^{t + k} and the counter value of the fixed station 10 # 2 at the absolute time t + k is c2 ^{t + k , the counter values c1 t + k} and c2 ^{t + k} are the equations (5) and ( It is expressed as 6). However, the fixed station 10, similarly to the counter value c1 ^t and c2 ^t, can not be directly recognize the counter value ^{c1 t + k} and ^{c2 t + k} in absolute time t + k.

The second radio wave arrives at each fixed station 10 after the arrival time has elapsed. Specifically, as shown in FIG. 6, the second radio wave arrives at the fixed station 10 # 1 after the ^{arrival time f1 t + k} elapses, and arrives at the fixed station 10 # 2 after the ^{arrival time f2 t + k elapses.} Coming. Therefore, if the counter values acquired by the fixed stations 10 # 1 and the fixed stations 10 # 2 when the second radio wave arrives at the fixed stations 10 # 1 and the fixed stations 10 # 2 are cf1 ^{t + k} and cf2 ^{t + k.} , Cf1 ^{t + k} and cf2 ^{t + k} are expressed as the following equations (7) and (8) using the equations (5) and (6). In addition, cf1 ^{t + k} and cf2 ^{t + k} correspond to the above-mentioned second counter value.

The arrival times f1 ^{t + k} and f2 ^{t + k} are geometrically expressed by the following equations (9) and (10).

Here, ^{the difference between cf1 t} and cf2 ^t corresponds to the first difference described above, and the difference between cf1 ^{t + k} and cf2 ^{t + k} corresponds to the second difference. Then, the difference change amount, which is the change amount from the first difference to the second difference, is expressed as the left side of the following equation (11), and the equations (1) and (2) are on the left side of the equation (11). ), (7) and (8) are substituted to obtain the right side of the equation (11).

The difference change amount, that is, the terms constituting the left side of the equation (11) are all counter values acquired by the counter value calculation unit 140 or the counter value communication unit 150. Therefore, the difference change amount is a value that can be specifically specified, and if the difference change amount is set to α as shown in the equation (12) and the equation (11) is rearranged, the equation (13) can be obtained.

Further, by rewriting the equation (13) using the equations (3), (4), (9) and (10), the equation (14) is obtained. In addition, α'in the equation (14) is a multiplication equation of the difference change amount α and the propagation speed c of the radio wave, and the position of the mobile terminal 20 at the absolute time t from each of the fixed stations 10 # 1 and the fixed stations 10 # 2. It is the sum of the first distance difference, which is the difference of the distances to. The α'is a value that can be specifically specified by using a known position of each fixed station 10. On the other hand, the left side of the equation (14) corresponds to the second distance difference, which is the difference in the distances from each of the fixed stations 10 # 1 and the fixed stations 10 # 2 to the position of the mobile terminal 20 at the absolute time t + k.

Similarly, when the calculation is performed with respect to the combination with the fixed station 10 # 1 and the fixed station 10 # 3, the equation (15) is obtained.

There are two unknowns in equations (14) and (15). Therefore, the position estimation unit 180 can obtain the estimation result of the position (second position) of the mobile terminal 20 at the absolute time t + k by solving the simultaneous equations composed of the equations (14) and (15).

However, in reality, the position of the mobile terminal 20 may not be uniquely determined from the equations (14) and (15) due to the influence of the error. Therefore, the position estimation unit 180 similarly creates equations for other combinations of the two fixed stations 10, and sets the position that best fits all the equations, that is, the position with the highest likelihood, as the absolute time of the mobile terminal 20. It may be estimated as a position at t + k.

(motion)
The theory of processing example A has been described above. Subsequently, with reference to FIG. 7, the operation when the fixed station 10 executes the processing example A will be arranged.

FIG. 7 is a flowchart showing an operation when the fixed station 10 executes the processing example A. As shown in FIG. 7, first, when the radio unit 110 of the fixed station 10 receives a radio wave from the mobile terminal 20 (S304), the counter value calculation unit 140 calculates the first counter value cf1 ^t (S308). Further, when the radio unit 110 receives the radio wave from the mobile terminal 20 (S312), the counter value calculation unit 140 calculates the second counter value cf1 ^{t + k} (S316). Then, the counter value communication unit 150 collects the first counter value and the second counter value from the other fixed station 10 (S320).

After that, the fixed station 10 executes the operations of S324 to S332 for a plurality of combinations of the two fixed stations 10. That is, the counter difference calculation unit 160 of the fixed station 10 has a first difference (for example, cf1 ^{t −} cf2 ^t ) which is a difference of the first counter values of the two fixed stations 10, and a second of the two fixed stations 10. ^{The second difference (for example, cf1 t + k} −cf2 ^{t + k} ), which is the difference between the counter values of 2, is calculated (S324, S328). The operation corresponds to the operation in each term on the left side of the equation (12). Then, the difference change amount calculation unit 170 calculates the difference change amount α, which is the change amount from the first difference to the second difference (S332). The operation corresponds to the operation of the entire left side of the equation (12).

When the operations S324 to S332 are executed for the plurality of combinations of the two fixed stations 10 and the difference change amount is calculated for each of the plurality of combinations of the two fixed stations 10, the position estimation unit 180 performs the plurality of difference changes. Based on the quantity and the position of each fixed station 10, the position of the fixed station 10 at the absolute time t + k is estimated (S336). Specifically, the position estimation unit 180 obtains the estimation result of the position of the mobile terminal 20 at the absolute time t + k by solving the series equation including the equations (14) and (15).

(Action effect)
Since the counter values obtained at each fixed station 10 normally operate continuously, errors are accumulated in the counter values. Therefore, when trying to estimate the position of the mobile terminal 20 using the counter value itself, the accuracy deteriorates due to the error accumulated in the counter value. On the other hand, in the above-mentioned processing example A, the position of the mobile terminal 20 is estimated using the difference change amount α represented by the equation (12) instead of the counter value itself obtained by each fixed station 10. The difference change amount α is also affected by the error accumulated in the counter value between the absolute time t and the absolute time t + k, but if the time k is sufficiently small, the counter is between the absolute time t and the absolute time t + k. The error accumulated in the value is very small. Therefore, in the processing example A, the position of the mobile terminal 20 can be estimated with high accuracy even if a general-purpose oscillator is used instead of the highly accurate oscillator whose counter value is hard to shift.

<5. Processing example B>
Next, a processing example B of position estimation will be described. The processing example B is a processing example that can be applied even when the position of the mobile terminal 20 at a certain time t is unknown by using a statistical method. Here, a method using a particle filter as a statistical method will be described.

(theory)
FIG. 8 is an explanatory diagram showing an example of particle arrangement. FIG. 8 shows three fixed stations 10 and five particles that are temporary positions of the mobile terminal 20. Although the accuracy of position estimation improves as the number of particles increases, the number of particles is set to 5 for convenience of explanation.

Each particle has an x-coordinate, a y-coordinate and a weight w as parameters. The position estimation unit 180 randomly sets the initial values of the x-coordinate and the y-coordinate of each particle, and divides the initial value of the weight w by 1 by the total number of particles (here, 1/5). Set to. Further, the position estimation unit 180 normalizes the weights of each particle so that the total weight of all particles becomes 1 at each time.

The coordinates of the terminal of the mobile terminal 20 at the absolute time t when the mobile terminal 20 transmits the first radio wave are shown by the equations (16) and (17) using the coordinates of each particle.

Focusing on the fixed station 10 # 1 and the fixed station 10 # 2 with respect to the particle 1 as in the processing example A, the equation (18) can be obtained.

Further, paying attention to the fixed stations 10 # 1 and the fixed stations 10 # 3, the equation (19) is obtained.

Further, paying attention to the fixed stations 10 # 2 and the fixed stations 10 # 3, the equation (20) is obtained.

Consider finding _{(x1 t + k} , y1 _{t + k} ) that satisfies equations (18), (19) and (20) based on equations (18), (19) and (20). Since there are two unknowns and three equations, it is uniquely determined _{that the three equations are satisfied (x1 t + k} , y1 _{t + k) if there is no error.} However, since there is actually an error, the position estimation unit 180 _{calculates (x1 t + k} , y1 _{t + k} ) that best fits the three equations as the second position, and calculates (x1 _{t + k} , y1 _{t + k} ). The likelihood is evaluated, and the evaluation value indicating the likelihood is reflected in the weight of the particles.

For example, the position estimation unit 180 solves a simultaneous equation consisting of the two equations (18) and (19) to obtain _{(x1't + k} , y1't _{+ k).} Here, as shown in the equation (21), the left side of the equation (20) is set to m.

Considering that an error e occurs, the equation (20) is expressed as the equation (22) using the equation (21).

Note that m in the equation (22) _{can be obtained by substituting (x1't + k} , y1't _{+ k} ) into the equation (21). γ'is specified as a specific value like α and α'described in the processing example A. Here, assuming that the error e is an error that follows a normal distribution, m, γ'and e can be represented by the relationship shown in FIG.

FIG. 9 is an explanatory diagram showing an example of distribution of the error e. The vertical axis of FIG. 9 is an evaluation value indicating the likelihood of particles. When the error e is 0, that is, when m and γ'match, the reliability of the particle 1 of interest is high, and the evaluation value is 1. When there is an error e, the evaluation value is z shown in FIG. The position estimation unit 180 updates the weight w of the particle 1 as shown in the equation (23) by using the evaluation value z thus specified.

The position estimation unit 180 also updates the weight w for the other particles 2 to 5 by the procedure described above. After the weights w of all particles are updated, the position estimation unit 180 normalizes the weights of each particle so that the sum of the weights w of all particles becomes 1. For example, the position estimation unit 180 normalizes the weight w of the particles 1 as shown in the equation (24).

Then, the position estimation unit 180 estimates the more probable position of the mobile terminal 20 at the absolute time t by calculating the equations (16) and (17) after the normalization of the weight w of each particle is completed. It is possible.

The position estimation unit 180 may resample the particles whose weight w has become sufficiently small, following the calculation procedure of a general particle filter. That is, the position estimation unit 180 may delete the corresponding particles and rearrange the particles at new coordinates obtained by adding a disturbance according to a normal distribution or the like to _{(x t} , y _t).

(motion)
The theory of processing example B has been described above. Subsequently, with reference to FIG. 10, the operation when the fixed station 10 executes the processing example B is arranged.

FIG. 10 is a flowchart showing an operation when the fixed station 10 executes the processing example B. As shown in FIG. 10, the fixed station 10 first performs the processes of S304 to S332 described with reference to FIG. 7 to calculate a plurality of difference changes (S300). Then, the position estimation unit 180 arranges a plurality of particles as described with reference to FIG. 8 (S404).

After that, the position estimation unit 180 executes the processes shown in S408 to S416 for each particle. That is, the position estimation unit 180 sets the position that best fits the equations (equations (18) and (19)) regarding the amount of difference change calculated by the two combinations of the two fixed stations 10 as the second position of the mobile terminal 20. Is calculated as (S408). Then, the position estimation unit 180 evaluates the likelihood of the calculated position by the method described with reference to, for example, FIG. 9 (S412), and updates the weight of the particles using the obtained evaluation value (S416). ..

After the weights of all the particles are updated, the position estimation unit 180 normalizes the weights of each particle so that the sum of the weights of all the particles becomes 1. (S420). After that, the position estimation unit 180 estimates a more probable position of the mobile terminal 20 at the absolute time t by calculating, for example, equations (16) and (17) based on the position and weight of each particle (S424). ). The position estimation unit 180 can further estimate the position of the mobile terminal 20 at the absolute time t + k by executing the processing example A using the more probable position of the mobile terminal 20 at the absolute time t. is there.

(Action effect)
Also in the processing example B described above, the position of the mobile terminal 20 is estimated based on the difference change amount, not the counter value itself obtained by each fixed station 10, as in the processing example A. Therefore, according to the processing example B, it is possible to estimate the position of the mobile terminal 20 with high accuracy by using a general-purpose oscillator even if there is no known position of the mobile terminal 20. In the above, the method using the particle filter as an example of the difference change amount and the statistical method has been described, but it is also possible to estimate the position of the mobile terminal 20 by using the difference change amount and other statistical methods. Is.

<6. Processing example C>
Next, a processing example C of position estimation will be described. The processing example C is a processing example that can be applied even when the position of the mobile terminal 20 at a certain time t is unknown by using the displacement vector calculated by the mobile terminal 20 in the fixed station 10.

(theory)
The mobile terminal 20 transmits the first radio wave at the absolute time t, and transmits the second radio wave at the absolute time t + k, which is k hours after the absolute time t. At this time, the x-coordinate and y-coordinate of the mobile terminal 20 at the absolute time t + k are the x-coordinate and y-coordinate of the mobile terminal 20 at the absolute time t, and the displacement vector (vx) of the mobile terminal 20 from the absolute time t to the absolute time t + k. _{Using t} , by _t ), it is expressed as the following equations (25) and (26) as shown in FIG.

Focusing on the combination of fixed stations 10 # 1 and fixed stations 10 # 2, substituting equations (25) and (26) into equation (9) gives equation (27), equations (25) and (26). Is substituted into equation (10) to obtain equation (28).

By substituting the equations (9), (10), (27) and (28) into the equation (13), the equation (29) is obtained.

Next, the equation (30) can be obtained by performing the same calculation focusing on the combination of the fixed stations 10 # 1 and the fixed stations 10 # 3.

In equations (29) and (30), there are two unknowns, the x-coordinate and the y-coordinate of the mobile terminal 20 at absolute time t. Therefore, by solving the simultaneous equations consisting of equations (29) and (30), it is absolute. It is possible to estimate the x-coordinate and the y-coordinate of the mobile terminal 20 at time t.

(motion)
The theory of processing example C has been described above. Subsequently, with reference to FIG. 12, the operation when the fixed station 10 executes the processing example C will be arranged.

FIG. 12 is a flowchart showing an operation when the fixed station 10 executes the processing example C. As shown in FIG. 12, the fixed station 10 first performs the processes of S304 to S332 described with reference to FIG. 7 to calculate a plurality of difference changes (S300).

After that, the position estimation unit 180 solves a simultaneous equation consisting of, for example, equations (29) and (30) using the positions of each fixed station 10, a plurality of difference changes, and the displacement vectors of the mobile terminal 20, and determines the absolute time. The position (x-coordinate and y-coordinate) of the mobile terminal 20 at t is estimated (S500). The displacement vector may be included in the second radio wave transmitted from the mobile terminal 20, in which case the radio unit 110 of the fixed station 10 receives the second radio wave including the displacement vector. After that, the position estimation unit 180 can estimate the position of the mobile terminal 20 at the absolute time t + k by adding the displacement vector to the position of the mobile terminal 20 at the absolute time t.

(Action effect)
Also in the processing example C described above, the position of the mobile terminal 20 is estimated based on the difference change amount, not the counter value itself obtained by each fixed station 10, as in the processing example A. Therefore, according to the processing example C, it is possible to estimate the position of the mobile terminal 20 with high accuracy by using a general-purpose oscillator even if there is no known position of the mobile terminal 20.

<7. Hardware configuration>
The embodiments of the present invention have been described above. Information processing such as the calculation of the difference change amount and the position estimation described above is realized by the cooperation between the software and the hardware of the fixed station 10 described below.

FIG. 13 is a block diagram showing the hardware configuration of the fixed station 10. The fixed station 10 includes a CPU (Central Processing Unit) 301, a ROM (Read Only Memory) 302, a RAM (Random Access Memory) 303, and a host bus 304. Further, the fixed station 10 includes a bridge 305, an external bus 306, an interface 307, an input device 308, a display device 309, an audio output device 310, a storage device (HDD) 311 and a drive 312, and a network interface. It is equipped with 315.

The CPU 301 functions as an arithmetic processing unit and a control device, and controls the overall operation in the fixed station 10 according to various programs. Further, the CPU 301 may be a microprocessor. The ROM 302 stores programs, calculation parameters, and the like used by the CPU 301. The RAM 303 temporarily stores a program used in the execution of the CPU 301, parameters that change appropriately in the execution, and the like. These are connected to each other by a host bus 304 composed of a CPU bus or the like. By collaborating with the CPU 301, the ROM 302, the RAM 303, and the software, the above-mentioned functions such as the counter difference calculation unit 160, the difference change amount calculation unit 170, and the position estimation unit 180 can be realized.

The host bus 304 is connected to an external bus 306 such as a PCI (Peripheral Component Interconnect / Interface) bus via a bridge 305. It is not always necessary to separately configure the host bus 304, the bridge 305, and the external bus 306, and these functions may be implemented in one bus.

The input device 308 includes input means for the user to input information such as a mouse, keyboard, touch panel, buttons, microphone, sensor, switch and lever, and an input that generates an input signal based on the input by the user and outputs the input signal to the CPU 301. It is composed of a control circuit and the like. By operating the input device 308, the user of the fixed station 10 can input various data to the fixed station 10 and instruct the fixed station 10 to perform a processing operation.

The display device 309 includes, for example, a display device such as a CRT (Cathode Ray Tube) display device, a liquid crystal display (LCD) device, a projector device, an OLED (Organic Light Emitting Mode) device, and a lamp. Further, the audio output device 310 includes an audio output device such as a speaker and headphones.

The storage device 311 is a data storage device configured as an example of the storage unit of the fixed station 10 according to the present embodiment. The storage device 311 may include a storage medium, a recording device for recording data on the storage medium, a reading device for reading data from the storage medium, a deleting device for deleting the data recorded on the storage medium, and the like. The storage device 311 is composed of, for example, an HDD (Hard Disk Drive) or SSD (Solid Stage Drive), or a memory having an equivalent function. The storage device 311 drives the storage and stores programs and various data executed by the CPU 301.

The drive 312 is a reader / writer for a storage medium, and is built in or externally attached to the fixed station 10. The drive 312 reads the information recorded in the removable storage medium 24 such as the mounted magnetic disk, optical disk, magneto-optical disk, or semiconductor memory, and outputs the information to the RAM 303 or the storage device 311. The drive 312 can also write information to the removable storage medium 24.

The network interface 315 is, for example, a communication interface composed of a communication device or the like for connecting to. Further, the network interface 315 may be a wireless LAN (Local Area Network) compatible communication device or a wire communication device that performs wired communication.

Since the hardware configuration of the mobile terminal 20 described above can be applied to the fixed station 10, a detailed description of the hardware configuration of the fixed station 10 will be omitted.

<8. Supplement>
Although preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical idea described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

For example, each step in the processing of the fixed station 10 of the present specification does not necessarily have to be processed in chronological order in the order described as a flowchart. For example, each step in the processing of the fixed station 10 may be processed in an order different from the order described in the flowchart, or may be processed in parallel.

Further, it is possible to create a computer program for causing the hardware such as the CPU, ROM, and RAM built in the fixed station 10 to exhibit the same functions as each configuration of the fixed station 10 described above. A storage medium for storing the computer program is also provided.

10 Fixed station 110 Radio unit 120 Sampling unit 130 Oscillator 140 Counter value calculation unit 150 Counter value communication unit 160 Counter difference calculation unit 170 Difference change amount calculation unit 180 Position estimation unit 20 Mobile terminal 210 Displacement calculation unit 220 Transmission instruction unit 230 Radio unit

Claims (8)

It is a position estimation device that estimates the position of a terminal using the counter value of the time calculated in each of three or more fixed stations.
The first counter value calculated at each fixed station indicating the time when the first radio wave transmitted from the terminal arrived at each fixed station, and the second radio wave transmitted from the terminal arrived at each fixed station. A counter value acquisition unit that acquires a second counter value calculated at each fixed station indicating a time point, and a counter value acquisition unit.
Calculate the first difference, which is the difference between the first counter values between the two fixed stations, and the second difference, which is the difference between the second counter values between the two fixed stations. Counter difference calculation unit and
A difference change amount calculation unit that calculates a difference change amount that is a change amount from the first difference to the second difference, and a difference change amount calculation unit.
The position of the terminal is estimated based on the plurality of differential changes calculated for each of the plurality of combinations of the two fixed stations among the three or more fixed stations and the positions of the three or more fixed stations. Position estimation unit and
A position estimation device. The position estimation unit is based on the plurality of differential changes, the positions of the three or more fixed stations, and the first position, which is the position of the terminal at the time when the terminal transmits the first radio wave. The position estimation device according to claim 1, wherein the second position, which is the position of the terminal at the time when the terminal transmits the second radio wave, is estimated. The position estimation unit
For each of the plurality of combinations of the two fixed stations, the first distance difference, which is the difference in the distance from each of the two fixed stations to the first position, and the combination of the two fixed stations were calculated. The sum of the difference change amount and the distance obtained by multiplying the propagation speed of the radio wave is calculated, and the sum is the second distance difference, which is the difference in the distance from each of the two fixed stations to the second position. Get the equation to be equal,
The position estimation device according to claim 2, wherein the second position is estimated by solving a plurality of the equations obtained for each of the plurality of combinations. The position estimation device according to claim 2 or 3, wherein the first position is known. The position estimation unit
A plurality of temporary positions are set as the first position, and
The likelihood of each of the plurality of second positions obtained by the estimation based on each of the plurality of temporary positions is evaluated.
The temporary positions used to estimate each second position are weighted according to the likelihood of each second position.
The position estimation device according to claim 3, wherein a more probable position of the terminal at the time when the terminal transmits the first radio wave is estimated based on the weighted plurality of temporary positions. The position estimation unit, in addition to the plurality of differential changes and the positions of the three or more fixed stations, from the time of transmission of the first radio wave to the time of transmission of the second radio wave calculated by the terminal. The position estimation device according to claim 1, wherein the position of the terminal is estimated based on the displacement vector of the terminal. The position estimation unit
For each of the plurality of combinations of the two fixed stations, the first distance difference, which is the difference from each of the two fixed stations to the first position, which is the position of the terminal at the time of transmitting the first radio wave, and the first distance difference. , The sum of the distance obtained by multiplying the difference change amount calculated for the combination of the two fixed stations by the propagation speed of the radio wave is up to the second position after adding the displacement vector to the first position. Obtain an equation that is equal to the second distance difference, which is the difference between the distances from the two fixed stations.
The position estimation device according to claim 6, wherein the first position is estimated by solving a plurality of the equations obtained for each of the plurality of combinations. It is a position estimation method executed in a position estimation device that estimates the position of a terminal using a counter value of time calculated in each of three or more fixed stations.
The first counter value calculated at each fixed station indicating the time when the first radio wave transmitted from the terminal arrived at each fixed station, and the second radio wave transmitted from the terminal arrived at each fixed station. Acquiring the second counter value calculated at each fixed station indicating the time point,
Calculate the first difference, which is the difference between the first counter values between the two fixed stations, and the second difference, which is the difference between the second counter values between the two fixed stations. That and
To calculate the difference change amount, which is the change amount from the first difference to the second difference,
The position of the terminal is estimated based on the plurality of differential changes calculated for each of the plurality of combinations of the two fixed stations among the three or more fixed stations and the positions of the three or more fixed stations. That and
Position estimation methods, including.

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