JP7334538B2 - Position estimation device and position estimation method - Google Patents

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 arrival time, which is the time at which a radio wave transmitted by a terminal arrives at a fixed station. With TOA, highly accurate positioning is possible when both the terminal and the fixed station have highly accurate timers (clock sources). However, assuming that the terminal is a general-purpose device such as a smartphone, it is difficult to provide the terminal with a highly accurate timer.

Therefore, as another positioning method, TDOA (Time Difference Of Arrival), which utilizes the difference in arrival time of radio waves to each fixed station, is also under consideration. In TDOA, the terminal only needs to be able to transmit radio waves, and the terminal does not have to have a reception function for positioning. Therefore, there is no need to provide a high-precision timer in the terminal, and the terminal is easy to manufacture.

Techniques related to such positioning are also disclosed in Patent Documents 1 to 4, for example. Specifically, Patent Literature 1 discloses a device having a plurality of sensors. The device calculates the arrival time difference to each sensor for a signal transmitted from a mobile station, and Positioning of the mobile station is performed using the time difference. Patent documents 2 and 3 disclose a system having a plurality of fixed stations, reference stations, and mobile stations, each fixed station receiving a signal from the mobile station and a signal from the reference station, and using the signal from the reference station to calculate the time. A system for determining the position of a mobile station after synchronizing is disclosed. Patent Document 4 discloses a technique in which wireless LAN signals are received by a plurality of fixed stations, each fixed station transmits an "observed deviation value" to a server, and the server builds a database. When the fixed station receives the signals from the mobile stations, it calculates the position of the mobile station based on the database and the difference in arrival times of the signals of each fixed station.

JP 2007-198742 A WO2016/178381 WO2017/204087 Japanese translation of PCT publication No. 2013-513786

However, existing positioning methods have problems. For example, in order to implement TDOA, it is desirable for each fixed station to synchronize time with high precision, but this would result in a large-scale system configuration. Specifically, highly accurate time synchronization can be achieved by preparing a rubidium oscillator with high clock accuracy and supplying a synchronization signal from the oscillator to all fixed stations. However, in situations where TDOA is used for automated driving and traffic, each fixed station is generally installed several tens of meters or more apart, and all fixed stations are connected by cables. It is practically difficult to supply a sync signal through a cable. In summary, TDOA has some technical inadequacies regarding the feasibility of time synchronization.

Therefore, the present invention has been made in view of the above problems. An object of the present invention is to provide a new and improved position estimation device and position estimation method.

In order to solve the above problems, according to one aspect of the present invention, there is provided a position estimation device for estimating the position of a terminal using a time counter value calculated in each of three or more fixed stations, A 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. a counter value acquisition unit that acquires a second counter value calculated at each fixed station; a first difference that is a difference in the first counter value between the two fixed stations; a counter difference calculator for calculating a second difference that is the difference in the second counter value between stations; and a difference change amount that is a change amount from the first difference to the second difference. a plurality of difference change amounts calculated for each of a plurality of combinations of two fixed stations out of the three or more fixed stations, and the positions of the three or more fixed stations; and a position estimating unit that estimates the position of the terminal, the position estimating unit estimating, in addition to the plurality of difference change amounts and the positions of the three or more fixed stations, the terminal receiving the first radio wave. estimating a second position, which is the position of the terminal at the time when the terminal transmits the second radio wave, based on a first position, which is the position of the terminal at the time of transmission; setting a plurality of temporary positions as the first positions, evaluating the likelihood of each of a plurality of second positions obtained by estimation based on each of the plurality of temporary positions, and estimating each second position is weighted according to the likelihood of each second position, and based on the plurality of weighted temporary positions, the position of the terminal at the time when the terminal transmitted the first radio wave A position estimation device is provided that estimates a more probable position .

The position estimating unit calculates, for each of a plurality of combinations of the two fixed stations, a first distance difference that is a difference in distance from each of the two fixed stations to the first position, and and the sum of the distance obtained by multiplying the difference change amount calculated for the combination of and the distance obtained by multiplying the propagation speed of the radio wave, and the sum is the difference in the distance from each of the two fixed stations to the second position. An equation may be obtained that equates to a second distance difference, and the second position may be estimated by solving a plurality of said equations obtained for each of said plurality of combinations.

The position estimation unit sets a plurality of temporary positions as the first positions, evaluates the likelihood of each of a plurality of second positions obtained by estimation based on each of the plurality of temporary positions, The provisional positions used to estimate 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 provisional positions. A more probable position of the terminal at the time point of time may be estimated.

In order to solve the above problems, according to another aspect of the present invention, a position estimating apparatus for estimating the position of a terminal using a time counter value calculated in each of three or more fixed stations performs: A position estimation method comprising: a first counter value calculated at each fixed station indicating the time point when a first radio wave transmitted from a terminal arrives at each fixed station; acquiring a second counter value calculated at each fixed station that indicates the time point at which the second radio wave arrives; calculating a difference and a second difference that is the difference in the second counter values between the two fixed stations; and calculating a difference that is the amount of change from the first difference to the second difference. calculating a change amount; and based on a plurality of the difference change amounts calculated for each of a plurality of combinations of two fixed stations among the three or more fixed stations and the positions of the three or more fixed stations. , and estimating the position of the terminal, wherein in addition to the plurality of difference change amounts and the positions of the three or more fixed stations, the terminal detects the first estimating a second position, which is the position of the terminal when the terminal transmits the second radio wave, based on a first position, which is the position of the terminal when the radio wave is transmitted; Estimating the position of the terminal includes setting a plurality of temporary positions as the first position and evaluating the likelihood of each of a plurality of second positions obtained by estimation based on each of the plurality of temporary positions. and weighting the tentative positions used to estimate each second position according to the likelihood of each second position, and based on the plurality of weighted tentative positions, the terminal determines the first A position estimation method is provided , including estimating a more probable position of the terminal at the time of transmitting radio waves .

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.

1 is an explanatory diagram showing the configuration of a position estimation system according to one embodiment of the present invention; FIG. 1 is an explanatory diagram showing the configuration of a mobile terminal 20 according to one embodiment of the present invention; FIG. 1 is an explanatory diagram showing the configuration of a fixed station 10 according to one embodiment of the present invention; FIG. FIG. 3 is an explanatory diagram showing an example of arrangement of fixed stations 10 and mobile terminals 20 at time t; 3 is an explanatory diagram showing transmission of a first radio wave from a mobile terminal 20; FIG. 3 is an explanatory diagram showing transmission of a second radio wave from a mobile terminal 20; FIG. 10 is a flow chart showing the operation when the fixed station 10 executes the processing example A. FIG. FIG. 4 is an explanatory diagram showing an example of arrangement of particles; FIG. 10 is an explanatory diagram showing an example of distribution of error e; 10 is a flow chart showing the operation when the fixed station 10 executes processing example B; FIG. 4 is an explanatory diagram showing a displacement vector; 10 is a flow chart showing the operation when the fixed station 10 executes the processing example C. FIG. 2 is a block diagram showing the hardware configuration of fixed station 10. FIG.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

In addition, in this specification and drawings, a plurality of components having substantially the same functional configuration may be distinguished by attaching different alphabets after the same reference numerals. However, when there is no particular need to distinguish between a plurality of constituent elements having substantially the same functional configuration, only the same reference numerals are given to each of the plurality of constituent elements.

<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) that utilizes a further difference of the "difference of arrival time" in TDOA. First, with reference to FIG. 1, an outline of a position estimation system according to one embodiment of the present invention will be described.

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

A fixed station 10 is a communication device installed at a fixed location. The fixed station 10 receives radio waves transmitted from the mobile terminal 20 . Each fixed station 10 calculates a counter value of time, and each fixed station 10 specifies the counter value indicating the time when radio waves are received from the mobile terminal 20 . A fixed station 10 can also communicate with another fixed station 10 . Note that in one embodiment of the present invention, the counter values calculated at each of the fixed stations 10 need not be synchronized.

The fixed station 10 according to one embodiment of the present invention also includes a function as a position estimator for estimating the position of the mobile terminal 20. FIG. However, a position estimation device may be provided separately from the fixed station 10 . In this case, the position estimating device is connected to each fixed station 10 locally or via a network, collects counter values from each fixed station 10, and uses the counter values to determine the position of the mobile terminal 20 by a process described later. can 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 calculates the first counter value calculated in each fixed station 10 indicating the time when the first radio wave transmitted from the mobile terminal 20 arrived at each fixed station 10, and the counter value 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 waves arrived 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 . If only some of the fixed stations 10 estimate the position of the mobile terminal 20 , the fixed station 10 that has estimated the position may transmit the position estimation result to the other fixed stations 10 .

The position estimation system is used, for example, for automatic travel control of vehicles at intersections. Specifically, a pedestrian has a mobile terminal 20, a traffic signal functions as a fixed station 10 to estimate the position of the mobile terminal 20, the traffic signal transmits the estimation result of the position of the mobile terminal 20 to the vehicle, and the vehicle may control automatic travel based on the position of the mobile terminal 20 . The configurations of the mobile terminal 20 and the fixed station 10 will be described in more detail below.

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

(Displacement calculator)
The displacement calculator 210 calculates a displacement vector, which is the amount and direction of displacement of the mobile terminal 20 between two times. For example, the displacement calculator 210 has a motion sensor such as an acceleration sensor or a gyroscope, and calculates a displacement vector by performing predetermined processing on values obtained by the motion sensor.

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

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

<3. Fixed station configuration>
FIG. 3 is an explanatory diagram showing the configuration of the fixed station 10 according to one 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 .

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

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

(oscillator)
The oscillator 130 generates a clock signal and supplies the clock signal to the counter value calculator 140 . In one embodiment of the present invention, even if the oscillator 130 is a general-purpose oscillator, it is possible to estimate the position of the mobile terminal 20 with high accuracy for reasons described later.

(counter value calculator)
The counter value calculator 140 repeats the increment of the counter value based on the clock signal supplied from the oscillator 130 . Then, when the digital received signal is input from sampling section 120, counter value calculating section 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 identifies the counter value at the time when the leading position of the wireless packet is detected.

Here, the mobile terminal 20 according to an embodiment of the present invention repeats radio wave transmission a plurality of times, and the counter value calculator 140 calculates a first counter value, which is a counter value for the first radio wave, and A second counter value, which is the counter value for the second radio wave, is identified. That is, the counter value calculator 140 functions as a counter value acquirer that acquires the first counter value and the second counter value. Counter value calculation section 140 outputs the specified first counter value and second counter value to counter value communication section 150 and counter difference calculation section 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 performs counter value calculation. It has a function of transmitting the first counter value and the second counter value specified by the unit 140 to other fixed stations 10 . Note that the counter value communication unit 150 may communicate with another fixed station 10 by wire or wirelessly. Also, radio section 110 may include the function of counter value communication section 150 and radio section 110 may communicate with another fixed station 10 .

(Counter difference calculator)
Counter difference calculator 160 calculates a first difference that is the difference in the first counter values between the two fixed stations 10 and a second difference that is the difference in the second counter values between the two fixed stations 10 . Calculate the difference of 2. For example, the counter difference calculator 160 of the fixed station 10#1 calculates the difference between the first counter value specified in the fixed station 10#1 and the first counter value specified in the fixed station 10#2. A first difference and a second difference between the second counter value identified in fixed station 10#1 and the second counter value identified in fixed station 10#2 are calculated. Counter difference calculator 160 calculates a first difference and a second difference for each of a plurality of combinations of two fixed stations 10 .

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

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

<4. Processing example A>
First, a position estimation processing example A according to an embodiment of the present invention will be described. 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 is obtained, for example, by positioning using landmarks or positioning using a laser range finder corresponding to 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 mobile terminal 20 is estimated will be described, but the number of fixed stations 10 may be four or more. , the three-dimensional position of the mobile terminal 20 can be estimated. It is also assumed that the position of each fixed station 10 is known. In the following, the position of the mobile terminal 20 at time t is also known as described above, and an example of estimating the position of the mobile terminal 20 at 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 the following drawings, for the sake of clarity, fixed station 10#1 is indicated by a square mark (1), fixed station 10#2 is indicated by a square mark (2), and fixed station 10#3 is indicated by a square mark (2). 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 X coordinate values and Y coordinate values as shown in FIG.

FIG. 5 is an explanatory diagram showing transmission of the first radio wave from the mobile terminal 20. As shown in FIG. Here, it is assumed that mobile terminal 20 transmits the first radio wave at absolute time t. Let c1 ^t be the counter value of fixed station 10#1 at absolute time t, and c2 ^t be the counter value of fixed station 10#2 at 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 fixed station 10#1 after arrival time f1 ^t has passed, and reaches fixed station 10#2 after arrival time f2 ^t has passed. Coming. Therefore, if the counter values obtained at the fixed stations 10#1 and 10#2 when the first radio wave arrives at the fixed stations 10#1 and 10#2 are cf1 ^t and cf2 ^t , cf1 ^t and cf2 ^t are expressed as the following equations (1) and (2). Note that cf1 ^t and cf2 ^t correspond to the first counter value described above.

Here, the arrival times f1 ^t and f2 ^t are geometrically represented by the following equations (3) and (4). Note that the parameter c is the speed of light.

As a premise of the 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 f1 ^t and f2 ^t can be calculated by substituting the positions of .

Next, suppose that time k has passed and mobile terminal 20 transmits a second radio wave at absolute time t+k. FIG. 6 is an explanatory diagram showing transmission of the second radio wave from the mobile terminal 20. As shown in FIG. If c1 t+k is the counter value of fixed station 10#1 at absolute time t ^+k and c2 ^t+k is the counter value of fixed station 10#2 at absolute time t+k, then counter values c1 ^t+k and c2 ^t+k are given by equations (5) and ( 6) is expressed as follows. However, like the counter values c1 ^t and c2 ^t , each fixed station 10 cannot directly recognize the counter values c1 ^t+k and c2 ^t+k at the 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 fixed station 10#1 after arrival time f1 ^t+k has passed, and reaches fixed station 10#2 after arrival time f2 ^t+k has passed. Coming. Therefore, if the counter values obtained at fixed stations 10#1 and 10#2 when the second radio waves arrive at fixed stations 10#1 and 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 equations (5) and (6). Note that cf1 ^t+k and cf2 ^t+k correspond to the above-described second counter value.

The arrival times f1 ^t+k and f2 ^t+k are geometrically expressed as Equations (9) and (10) below.

Here, the difference between cf1 ^t and cf2 ^t corresponds to the above-described first difference, and the difference between cf1 ^t+k and cf2 ^t+k corresponds to the second difference. Then, the amount of difference change, which is the amount of change from the first difference to the second difference, is expressed as the left side of the following equation (11), and the left side of the equation (11) is given by equations (1) and (2). ), (7) and (8) gives the right hand side of equation (11).

The difference change amount, that is, the terms constituting the left side of 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 by setting the difference change amount to α as shown in expression (12) and arranging expression (11), expression (13) is obtained.

Further, by rewriting equation (13) using equations (3), (4), (9) and (10), equation (14) is obtained. Note that α′ in equation (14) is the multiplication formula of the difference variation 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 10#2. is the sum of the first distance difference, which is the difference in the distance to . The α' is a value that can be specifically specified using the known position of each fixed station 10 or the like. On the other hand, the left side of equation (14) corresponds to the second distance difference, which is the difference in distance from each of fixed station 10#1 and fixed station 10#2 to the position of mobile terminal 20 at absolute time t+k.

Similarly, when calculation is performed for the combination of fixed station 10#1 and fixed station 10#3, Equation (15) is obtained.

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

However, in practice, there are cases where the position of mobile terminal 20 cannot be uniquely determined from equations (14) and (15) due to the influence of errors. Therefore, position estimating section 180 similarly creates equations for other combinations of two fixed stations 10, and finds the position that best fits all the equations, that is, the position with the highest likelihood of absolute time of mobile terminal 20. It may be estimated as the position at t+k.

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

FIG. 7 is a flow chart showing the operation when the fixed station 10 executes the processing example A. As shown in FIG. As shown in FIG. 7, first, when the radio unit 110 of the fixed station 10 receives radio waves from the mobile terminal 20 (S304), the counter value calculator 140 calculates a first counter value cf1 ^t (S308). Further, when the radio unit 110 receives radio waves from the mobile terminal 20 (S312), the counter value calculation unit 140 calculates a 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 other fixed stations 10 (S320).

After that, the fixed station 10 performs the operations of S324 to S332 for multiple combinations of two fixed stations 10. FIG. That is, the counter difference calculator 160 of the fixed station 10 calculates a first difference (for example, cf1 ^t −cf2 ^t ) that is the difference between the first counter values of the two fixed stations 10 and the first counter value of the two fixed stations 10 A second difference (for example, cf1 ^t+k −cf2 ^t+k ), which is the difference between the two counter values, is calculated (S324, S328). This operation corresponds to the operation in each term on the left side of Equation (12). Then, the difference change amount calculator 170 calculates the difference change amount α, which is the amount of change from the first difference to the second difference (S332). This calculation corresponds to the calculation of the entire left side of Equation (12).

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

(Effect)
Since the counter value obtained by each fixed station 10 normally operates continuously, errors accumulate in the counter value. Therefore, if the position of the mobile terminal 20 is estimated using the counter value itself, the accuracy is degraded due to the error accumulated in the counter value. On the other hand, in the processing example A described above, the position of the mobile terminal 20 is estimated using the difference change amount α shown in Equation (12) instead of the counter value itself obtained at each fixed station 10 . The difference change amount α is also affected by the error accumulated in the counter value between absolute time t and absolute time t+k. The error that accumulates in the values is minute. Therefore, in the processing example A, it is possible to estimate the position of the mobile terminal 20 with high accuracy even if a general-purpose oscillator is used instead of a high-precision oscillator in which the counter value is unlikely to shift.

<5. Processing example B>
Next, the position estimation processing example B will be described. 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 arrangement of particles. FIG. 8 shows three fixed stations 10 and five particles that are tentative positions of the mobile terminal 20 . As the number of particles increases, the position estimation accuracy improves, but for convenience of explanation, the number of particles is set to five.

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 y-coordinate of each particle, and sets the initial value of the weight w to a value obtained by dividing 1 by the total number of particles (here, 1/5). set to In addition, the position estimation unit 180 normalizes the weight of each particle so that the sum of the weights 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 transmitted the first radio wave are expressed by equations (16) and (17) using the coordinates of each particle.

Regarding the particle 1, focusing on the fixed station 10#1 and the fixed station 10#2 in the same way as in the processing example A, Equation (18) is obtained.

Also, focusing on the fixed station 10#1 and the fixed station 10#3, Equation (19) is obtained.

Furthermore, focusing on fixed station 10#2 and fixed station 10#3, Equation (20) is obtained.

Based on equations (18), (19) and (20), consider finding (x1 _t+k , y1 _t+k ) that satisfy equations (18), (19) and (20). Since there are two unknowns and three equations, (x1 _t+k , y1 _t+k ) that satisfies the three equations is uniquely determined if there is no error. However, since there is actually an error, the position estimator 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 ) as the second position. The likelihood is evaluated, and the evaluation value indicating the likelihood is reflected in the weight of the particles.

For example, the position estimator 180 solves simultaneous equations consisting of two equations (18) and (19) to obtain (x1' _t+k , y1' _t+k ). Here, as shown in Equation (21), the left side of Equation (20) is m.

Considering the occurrence of error e, equation (20) is expressed as equation (22) using equation (21).

Note that m in Equation (22) is obtained by substituting (x1' _t+k , y1' _t+k ) into Equation (21). γ' is specified as a specific value in the same manner as α and α' described in Processing Example A. Here, assuming that the error e follows a normal distribution, m, γ' and e can be represented by the relationships shown in FIG.

FIG. 9 is an explanatory diagram showing a distribution example of the error e. The vertical axis in 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 focused particle 1 is high and the evaluation value is 1. If there is an error e, the evaluation value will be z shown in FIG. The position estimation unit 180 updates the weight w of the particle 1 using the evaluation value z specified in this way, as shown in Equation (23).

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

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

Note that the position estimating unit 180 may follow a general particle filter calculation procedure and resample particles whose weight w has become sufficiently small. That is, the position estimation unit 180 may delete the relevant particles and rearrange the particles at new coordinates obtained by adding disturbance according to a normal distribution or the like to (x _t , y _t ).

(motion)
The theory of the processing example B has been described above. Next, with reference to FIG. 10, the operation when the fixed station 10 executes the processing example B will be organized.

FIG. 10 is a flowchart showing the operation when the fixed station 10 executes the processing example B. FIG. As shown in FIG. 10, the fixed station 10 first performs the processes of S304 to S332 described with reference to FIG. 7, and calculates a plurality of difference change amounts (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, position estimating section 180 selects the position that best fits the equations (formulas (18) and (19)) regarding the amount of change in difference calculated by two combinations of two fixed stations 10 as the second position of mobile terminal 20. (S408). Then, the position estimation unit 180 evaluates the calculated likelihood of the position, for example, by the method described with reference to FIG. 9 (S412), and uses the obtained evaluation value to update the weight of the particle (S416). .

After the weights of all particles have been updated, the position estimator 180 normalizes the weight of each particle so that the sum of the weights of all particles becomes 1 (S420). After that, the position estimator 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 estimating unit 180 can also estimate the position of the mobile terminal 20 at the absolute time t+k by subsequently executing the processing example A using the more probable position of the mobile terminal 20 at the absolute time t. be.

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

<6. Processing example C>
Next, the position estimation processing example C will be described. 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 a first radio wave at absolute time t, and transmits a second radio wave at absolute time t+k, which is k hours after absolute time t. At this time, the x-coordinate and y-coordinate of mobile terminal 20 at absolute time t+k are the x-coordinate and y-coordinate of mobile terminal 20 at absolute time t, and the displacement vector (vx _t , vy _t ) are expressed as the following equations (25) and (26) as shown in FIG.

Focusing on the combination of fixed station 10#1 and fixed station 10#2, substituting equations (25) and (26) into equation (9) yields equation (27), and equations (25) and (26) is substituted into equation (10), equation (28) is obtained.

Substituting equations (9), (10), (27) and (28) into equation (13) yields equation (29).

Next, by focusing on the combination of fixed station 10#1 and fixed station 10#3 and performing similar calculations, Equation (30) is obtained.

In equations (29) and (30), the unknowns are the x-coordinate and y-coordinate of mobile terminal 20 at absolute time t. It is possible to estimate the x- and y-coordinates of mobile terminal 20 at time t.

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

FIG. 12 is a flow chart showing the operation when the fixed station 10 executes the processing example C. As shown in FIG. As shown in FIG. 12, the fixed station 10 first performs the processes of S304 to S332 described with reference to FIG. 7, and calculates a plurality of difference change amounts (S300).

After that, position estimating section 180 uses the position of each fixed station 10, the plurality of difference change amounts, and the displacement vector of mobile terminal 20 to solve the simultaneous equations of, for example, Equations (29) and (30) to obtain the absolute time The position (x and y coordinates) 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 this case, the radio section 110 of the fixed station 10 receives the second radio wave including the displacement vector. Position estimating section 180 can then estimate the position of mobile terminal 20 at absolute time t+k by adding a displacement vector to the position of mobile terminal 20 at absolute time t.

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

<7. Hardware configuration>
The embodiments of the present invention have been described above. Information processing such as calculation of the difference change amount and position estimation described above is realized by cooperation between 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. As shown in FIG. 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 . The fixed station 10 also 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, a drive 312, and a network interface. 315.

The CPU 301 functions as an arithmetic processing device and a control device, and controls general operations within the fixed station 10 according to various programs. Alternatively, 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 programs used in the execution of the CPU 301, parameters that change as appropriate during the execution, and the like. These are interconnected by a host bus 304 comprising a CPU bus or the like. Functions of the above-described counter difference calculation unit 160, difference change amount calculation unit 170, position estimation unit 180, and the like can be realized by cooperation of the CPU 301, ROM 302, RAM 303, and software.

The host bus 304 is connected via a bridge 305 to an external bus 306 such as a PCI (Peripheral Component Interconnect/Interface) bus. It should be noted that the host bus 304, bridge 305 and external bus 306 do not necessarily have to be configured separately, 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, button, microphone, sensor, switch, and lever, and an input signal that generates an input signal based on the user's input and outputs it to the CPU 301. It consists 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 processing operations.

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

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

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

The network interface 315 is, for example, a communication interface configured with a communication device or the like for connection. Also, the network interface 315 may be a wireless LAN (Local Area Network) compatible communication device or a wired communication device that performs wired communication.

Since the hardware configuration of the mobile terminal 20 described above is also applicable to the fixed station 10, detailed description of the hardware configuration of the fixed station 10 is omitted.

<8. Supplement>
Although the 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 obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

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

It is also possible to create a computer program for causing hardware such as a CPU, ROM, and RAM built into the fixed station 10 to exhibit functions equivalent to those of the components of the fixed station 10 described above. A storage medium 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 (3)

A position estimation device for estimating the position of a terminal using a time counter value calculated in each of three or more fixed stations,
A 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 arrival of the second radio wave transmitted from the terminal at each fixed station a counter value acquisition unit that acquires a second counter value calculated in each fixed station that indicates a point in time;
calculating a first difference, which is the difference in the first counter values between the two fixed stations, and a second difference, which is the difference in the second counter values between the two fixed stations; a counter difference calculator;
a difference change amount calculator that calculates a difference change amount that is a change amount from the first difference to the second difference;
estimating the position of the terminal based on a plurality of the difference change amounts calculated for each of a plurality of combinations of two fixed stations among the three or more fixed stations and the positions of the three or more fixed stations; a position estimator;
with
The position estimating unit is configured based on a first position, which is the position of the terminal when the terminal transmits the first radio wave, in addition to the plurality of difference change amounts and the positions of the three or more fixed stations. , estimating a second position, which is the position of the terminal at the time when the terminal transmitted the second radio wave,
The position estimation unit
setting a plurality of temporary positions as the first position;
evaluating the likelihood of each of a plurality of second positions obtained by estimation based on each of the plurality of tentative positions;
weighting the tentative positions used to estimate each second position according to the likelihood of each second position;
A position estimation device that estimates a more probable position of the terminal at the time when the terminal transmitted the first radio wave based on the plurality of weighted temporary positions. The position estimation unit
For each of the plurality of combinations of the two fixed stations, a first distance difference, which is the difference in distance from each of the two fixed stations to the first position, and the combination of the two fixed stations. calculating the sum of the difference change amount and the distance obtained by multiplying the propagation speed of the radio wave, and calculating the sum as the second distance difference, which is the difference in the distance from each of the two fixed stations to the second position Obtaining the equality equation,
The position estimation device according to claim 1 , wherein the second position is estimated by solving a plurality of said equations obtained for each of said plurality of combinations. A position estimation method executed in a position estimation device for estimating the position of a terminal using time counter values calculated in each of three or more fixed stations,
A first counter value calculated at each fixed station that indicates the point in time when the first radio wave transmitted from the terminal arrives at each fixed station, and a second radio wave transmitted from the terminal arrives at each fixed station obtaining a second counter value calculated at each fixed station indicative of a time point;
calculating a first difference, which is the difference in the first counter values between the two fixed stations, and a second difference, which is the difference in the second counter values between the two fixed stations; and
calculating a difference change amount that is a change amount from the first difference to the second difference;
estimating the position of the terminal based on a plurality of the difference change amounts calculated for each of a plurality of combinations of two fixed stations out of the three or more fixed stations and the positions of the three or more fixed stations; and
including
Estimating the position of the terminal includes the position of the terminal at the time when the terminal transmitted the first radio wave, in addition to the plurality of difference change amounts and the positions of the three or more fixed stations. estimating a second position, which is the position of the terminal at the time when the terminal transmitted the second radio wave, based on the position of
estimating the position of the terminal comprises:
setting a plurality of temporary positions as the first position;
evaluating the likelihood of each of a plurality of second positions obtained by estimation based on each of the plurality of tentative positions;
weighting the tentative positions used to estimate each second position according to the likelihood of each second position;
A position estimation method, comprising estimating a more probable position of the terminal at the time when the terminal transmitted the first radio wave based on the plurality of weighted temporary positions.

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