JP2008122132A - Position estimation method and position estimation system - Google Patents

Abstract

An initial setting for starting position estimation of a wireless terminal is simplified.
A position estimation system includes a wireless node 1 that measures received radio wave intensity from a wireless terminal 10 and a position estimation device 2. The position estimation device 2 calculates a theoretical value of the received radio wave intensity for each radio node using a parameter depending on the radio wave environment and the provisional position of the radio terminal 10, and is based on a difference between the actually measured value and the theoretical value of the received radio wave intensity. Using a value as an evaluation function, parameter calculation means for obtaining a parameter that minimizes the evaluation function, and a provisional position calculation that calculates a theoretical value for each wireless node using the provisional parameter to obtain a provisional position that minimizes the evaluation function Means, repetitive means for alternately executing the processing of the parameter calculation means and the provisional position calculation means, and position determination means for setting the provisional position when the end condition is satisfied to be the estimated position of the wireless terminal 10.
[Selection] Figure 1

Description

  The present invention relates to a position estimation method and a position estimation system for estimating the position of a wireless terminal using a plurality of wireless nodes.

  Conventionally, as a method for detecting the position of a person or an object using radio, a cell-ID method for determining whether a radio terminal is within a radio wave coverage area and detecting the position of the radio terminal by a base station, A radio station arrival time difference method that detects the position of the wireless terminal by measuring the arrival time of the radio terminal from the wireless terminal at the base station and performing a three-sided survey, and measuring the radio field intensity from the wireless terminal at multiple base stations There is a radio wave reception intensity method for detecting the position of a wireless terminal by performing edge surveying (see, for example, Patent Document 1 and Non-Patent Document 1).

  However, these methods are greatly affected by multipath fading (fluctuation of electric field strength due to delayed waves), so that the position accuracy is lowered, and in order to prevent the position accuracy from being lowered, it takes time and cost for calibration. There was a problem.

Therefore, in the position detection method described in Non-Patent Document 1, first, while changing the distance between the wireless terminal and the wireless node, the wireless node receives the radio wave from the wireless terminal and measures the received radio wave intensity in advance. And the relationship between the distance between the wireless nodes and the received radio wave intensity. Next, the actual propagation environment is modeled in consideration of the radio propagation characteristics to obtain a probability model of the radio propagation environment. It is known that the received radio field intensity in the actual propagation environment can be modeled by exponential distribution. According to this probabilistic model, the received radio wave intensity P and the distance r from the wireless terminal to the wireless node are expressed by the following relationship.
P = C × r ^−α (1)
The constant C and the attenuation constant α are parameters determined when modeling the propagation environment. By performing statistical estimation by the maximum likelihood method using such a probability model, the position of the wireless terminal can be detected.

JP 2005-274364 A Ono Masayuki et al., “Position detection using wireless”, Oki Technical Review, October 2005, No. 204, Vol. 72, no. 4, p. 24-27

According to the position detection method described in Non-Patent Document 1, the wireless node can be reduced in cost, size, and high position estimation accuracy.
However, in the position detection method described in Non-Patent Document 1, in order to determine the parameter α in Equation (1), a large number of observation data is measured in advance in the actual propagation environment before the position estimation is performed, and this data It is necessary to model the propagation environment based on the above and determine the parameter α, and there is a problem that it takes time and effort to perform the initial setting until the position estimation is started.

  The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a position estimation method and a position estimation system that can simplify the initial setting for starting position estimation of a wireless terminal.

The present invention provides a position estimation method for estimating a position of a wireless terminal, a measurement procedure for measuring received radio wave intensity from a wireless terminal at a plurality of wireless nodes, a parameter depending on a radio wave environment, and a provisional position of the wireless terminal. Using the theoretical value of the received radio wave strength for each wireless node, and using the evaluation function as a value based on the difference between the actual value of the received radio wave strength measured in the measurement procedure and the theoretical value, Using the parameter calculation procedure for obtaining the minimum parameter and the parameter and the provisional position of the wireless terminal, the theoretical value of the received radio wave intensity is calculated for each wireless node, and the evaluation function is minimized. The provisional position calculation procedure for obtaining the provisional position of the terminal and the parameter calculation procedure or the provisional position calculation procedure as the first procedure are calculated in the parameter calculation procedure. The parameter calculation procedure and the provisional position calculation procedure are alternately repeated so that the parameter is used in the provisional position calculation procedure, and the provisional position of the wireless terminal calculated in the provisional position calculation procedure is used in the parameter calculation procedure. An iterative procedure to be executed, and a position determination procedure for determining the provisional position at the time when a predetermined end condition is satisfied as the estimated position of the wireless terminal.
In addition, one configuration example of the position estimation method of the present invention further includes an initial position setting unit that gives an initial value of the provisional position of the wireless terminal, and the parameter calculation procedure uses an initial value of the provisional position of the wireless terminal. Using a first parameter calculation procedure for obtaining the parameter, and a second parameter calculation procedure for obtaining the parameter using the provisional position of the wireless terminal calculated in the provisional position calculation procedure. The first parameter calculation procedure is the first procedure, and the temporary position calculation procedure and the second parameter calculation procedure are alternately and repeatedly executed.
In addition, one configuration example of the position estimation method of the present invention further includes initial parameter setting means for giving an initial value of the parameter, and the iterative procedure determines the provisional position of the wireless terminal using the initial value of the parameter. The provisional position calculation procedure to be obtained is an initial procedure, and the parameter calculation procedure and the provisional position calculation procedure are alternately and repeatedly executed.

Further, in one configuration example of the position estimation method of the present invention, the position determination procedure is performed when a minimum value of the evaluation function when the provisional position of the wireless terminal or the parameter is obtained is smaller than a predetermined threshold value. , It is assumed that the end condition is satisfied.
Further, in one configuration example of the position estimation method of the present invention, the position determination procedure considers that the end condition is satisfied when the number of repetitions reaches a predetermined threshold value. .
Further, in one configuration example of the position estimation method of the present invention, the position determination procedure includes a parameter calculated in the parameter calculation procedure and a temporary parameter used in the temporary position calculation procedure immediately before the parameter calculation procedure. When the absolute value of the difference between is smaller than a predetermined threshold value, it is considered that the termination condition is satisfied.
Further, in one configuration example of the position estimation method of the present invention, the evaluation function obtains, for each wireless node, a square of a difference between an actual measurement value of the received radio wave intensity measured by the measurement procedure and the theoretical value, The sum of the squares of the differences for all wireless nodes.

Further, the position estimation system of the present invention uses the plurality of wireless nodes that measure the received radio wave intensity from the radio terminal, the parameter depending on the radio wave environment, and the provisional position of the radio terminal, the theoretical value of the received radio wave intensity. For each wireless node, and using a value based on the difference between the measured actual value of the received radio wave intensity and the theoretical value as an evaluation function, parameter calculation means for obtaining the parameter that minimizes the evaluation function; Temporary position calculating means for calculating the theoretical value of the received radio field strength for each wireless node using the parameter and the temporary position of the wireless terminal, and obtaining the temporary position of the wireless terminal that minimizes the evaluation function; The parameter calculation unit or the provisional position calculation unit is used as a first unit, and the parameter calculated by the parameter calculation unit is used by the provisional position calculation unit. Repetitive means for alternately and repeatedly executing the processing of the parameter calculating means and the provisional position calculating means so that the temporary position of the wireless terminal calculated by the temporary position calculating means is used by the parameter calculating means, and a predetermined end Position determining means for determining the provisional position at the time when the condition is satisfied as the estimated position of the wireless terminal.
In addition, one configuration example of the position estimation system of the present invention further includes initial position setting means for giving an initial value of the provisional position of the wireless terminal, and the parameter calculation means calculates an initial value of the provisional position of the wireless terminal. A first parameter calculation unit that uses the provisional position of the wireless terminal calculated by the provisional position calculation unit, and a second parameter calculation unit that obtains the parameter using the provisional position of the wireless terminal. The first parameter calculation means is the first means, and the processes of the temporary position calculation means and the second parameter calculation means are alternately and repeatedly executed.
In addition, one configuration example of the position estimation system of the present invention further includes initial parameter setting means for giving an initial value of the parameter, and the repetition means determines the temporary position of the wireless terminal using the initial value of the parameter. The provisional position calculation means to be obtained is a first means, and the processing of the parameter calculation means and the provisional position calculation means is repeatedly executed alternately.

Further, in one configuration example of the position estimation system of the present invention, the position determination unit is configured such that the minimum value of the evaluation function when the provisional position of the wireless terminal or the parameter is obtained is smaller than a predetermined threshold value. , It is considered that the termination condition is satisfied.
Further, in one configuration example of the position estimation system of the present invention, the position determination means considers that the end condition is satisfied when the number of repetitions reaches a predetermined threshold value.
Further, in one configuration example of the position estimation system of the present invention, the position determination unit includes a parameter calculated by the parameter calculation unit and a temporary parameter used by the temporary position calculation unit immediately before the parameter calculation unit. When the absolute value of the difference between is smaller than a predetermined threshold value, it is considered that the termination condition is satisfied.

  According to the present invention, the theoretical value of the received radio wave intensity is calculated for each radio node using the provisional position of the radio terminal, and the value based on the difference between the actual value of the received radio wave intensity measured in the measurement procedure and the theoretical value is calculated. As an evaluation function, a parameter calculation procedure for obtaining a parameter that minimizes the evaluation function, a theoretical value of the received radio wave intensity is calculated for each wireless node using the temporary parameter, and the provisional of the wireless terminal that minimizes the evaluation function The provisional position calculation procedure for obtaining the position is repeatedly executed alternately until a predetermined end condition is satisfied, and the provisional position at the time when the end condition is satisfied is determined as the estimated position of the wireless terminal. In this way, it is not necessary to preliminarily collect a large number of observation data in the actual propagation environment and determine the parameters. It can be easy. Further, in the present invention, the position of the wireless terminal can be accurately estimated using the radio wave intensity that is said to be inaccurate when used for position estimation.

  Further, in the present invention, when the minimum value of the evaluation function when the provisional position or parameter of the wireless terminal is obtained is smaller than a predetermined threshold, the minimum value of the evaluation function is determined by assuming that the end condition is satisfied. Since the parameter calculation procedure and the provisional position calculation procedure are alternately executed until the value becomes smaller than the threshold value, the error can be reduced as much as possible and the position can be determined with high reliability.

  Further, in the present invention, when the number of repetitions reaches a predetermined threshold value, the parameter calculation procedure and the temporary position calculation procedure are repeatedly executed a predetermined number of times by assuming that the end condition is satisfied. Therefore, the error can be reduced as much as possible, and the position can be determined with high reliability.

  In the present invention, the absolute value of the difference between the parameter calculated in the parameter calculation procedure and the temporary parameter used in the temporary position calculation procedure immediately before the parameter calculation procedure is smaller than a predetermined threshold value. Assuming that the end condition is satisfied, the parameter calculation procedure and the provisional position calculation procedure are alternately executed until the absolute value of the difference becomes smaller than the threshold value. And position determination with high reliability can be performed.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the position estimation system according to the first embodiment of the present invention.
The position estimation system according to the present embodiment includes a plurality of wireless nodes 1 that measure the received radio wave intensity from the radio terminal 10 and a position estimate that estimates the position of the radio terminal 10 based on the received radio wave intensity measured by the radio node 1. The apparatus 2 is comprised. As a wireless communication used between the wireless node 1 and the wireless terminal 10, for example, there is ZigBee. Note that the wireless node 1 is a fixed wireless node, and the wireless terminal 10 is a mobile wireless node, both of which are wireless nodes. Here, in order to easily distinguish the two, the mobile wireless node is referred to as a wireless terminal. Called.

  FIG. 2 is a block diagram illustrating a configuration example of the position estimation apparatus 2. The position estimation device 2 uses reception means 20 that receives data of received radio wave intensity from the wireless terminal 10, initial position setting means 21 that gives an initial value of the temporary position of the wireless terminal 10, and the temporary position of the wireless terminal 10. Calculates the theoretical value of the received radio wave strength for each wireless node 1, and uses the value based on the difference between the actually measured value and the theoretical value of the received radio wave strength as an evaluation function to calculate the attenuation constant α that minimizes the evaluation function. Means 22, provisional position calculation means 23 for calculating a theoretical value of received radio wave intensity for each wireless node 1 using a provisional attenuation constant α, and obtaining a provisional position of the wireless terminal 10 having the smallest evaluation function; Using the provisional position of the wireless terminal 10 calculated by the position calculating means 23, the theoretical value of the received radio wave intensity is calculated for each wireless node 1, and the attenuation constant recalculating means for recalculating the attenuation constant α that minimizes the evaluation function. 2 When, and a position determining means 25 for determining the provisional position of the radio terminal 10 at the time the predetermined termination condition is satisfied as the estimated position of the wireless terminal 10.

The attenuation constant calculating means 22 constitutes a first parameter calculating means for calculating an attenuation constant α that is a parameter depending on the radio wave environment, and the attenuation constant recalculating means 24 is also a second parameter for calculating the attenuation constant α. It constitutes a calculation means. Further, the position determining means 25 constitutes an iterative means for causing the attenuation constant calculating means 22, the temporary position calculating means 23, and the attenuation constant recalculating means 24 to repeatedly execute processing until a predetermined end condition is satisfied.
Note that α is a parameter that depends on the radio wave environment, but is generally called an attenuation constant, so it is also called an attenuation constant α in the present invention.

Next, the operation of the position estimation system according to the present embodiment will be described. FIG. 3 is a flowchart showing the operation of the position estimation apparatus 2.
First, each wireless node 1 receives a radio wave from the radio terminal 10 and measures the received radio wave intensity. Each wireless node 1 wirelessly transmits the measured received radio wave intensity data to the position estimation device 2.

The receiving means 20 of the position estimation device 2 receives the received radio wave intensity data from each wireless node 1 (step S1 in FIG. 3).
The initial position setting means 21 sets the predetermined position in the space for which position estimation is to be performed (the space where the wireless terminal 10 is supposed to exist) as the initial position of the wireless terminal 10 and outputs data of the initial position (step S2). ).

  Subsequently, the attenuation constant calculating means 22 calculates the theoretical value of the received radio wave intensity for each wireless node 1 using the initial position of the wireless terminal 10 set in step S2, and receives the theoretical value and the reception received in step S1. An evaluation function is calculated from the actually measured value of the radio wave intensity, and an attenuation constant α that minimizes the evaluation function is obtained (step S3).

The theoretical value Pti [dBm] of the received radio wave intensity at the i-th wireless node 1 (where i is an integer in the range of 1 to n, where n is the number of wireless nodes 1) is given by the following equation from Equation (1): Can be sought.
Pti = 10 × log ₁₀ (C × r ^−α )
= 10 × log ₁₀ C−10 × α × log ₁₀ r
= 10 × log ₁₀ C
−10 × α × log ₁₀ (((x0−xb) ² + (y0−yb) ² ) ^1/2 )
... (2)
In Expression (2), r is the distance from the wireless terminal 10 to the wireless node 1, x0, y0 are the x coordinate and y coordinate of the initial position of the wireless terminal 10, xb, yb are the x coordinate of the wireless node 1, and y Coordinates.

  The attenuation constant calculating unit 22 calculates the theoretical value Pti of the received radio wave intensity for each wireless node 1 using Expression (2). At this time, a value common to each wireless node 1 is used as the attenuation constant α, and a preset value common to each wireless node 1 is used as the constant C. Then, the attenuation constant calculating means 22 calculates the evaluation function V from the measured value Pmi [dBm] and the theoretical value Pti [dBm] of the received radio wave intensity at the i-th wireless node 1 by the following equation.

  In other words, the attenuation constant calculating means 22 calculates the square of the difference between the actually measured value Pmi and the theoretical value Pti of the received radio wave intensity for each wireless node 1 and evaluates the sum of squared errors obtained by adding these for all the wireless nodes 1. Calculate as function V. In this way, the attenuation constant calculating means 22 calculates the attenuation constant α that minimizes the evaluation function V by repeating the calculations of the equations (2) and (3) while changing the attenuation constant α. The attenuation constant calculating unit 22 outputs the calculated attenuation constant α to the temporary position calculating unit 23. This completes the process of step S3.

  Next, the temporary position calculation means 23 calculates the theoretical value of the received radio wave intensity for each wireless node 1 using the attenuation constant α calculated in step S3, and the received radio wave intensity received in step S1. The evaluation function V is calculated from the actually measured values, and the provisional position (xp, yp) of the wireless terminal 10 at which the evaluation function V is minimized is calculated (step S4).

Here, the theoretical value Pti [dBm] of the received radio wave intensity at the i-th wireless node 1 is represented by the following equation from Equation (2).
Pti = 10 × log ₁₀ C
−10 × α × log ₁₀ (((xp−xb) ² + (yp−yb) ² ) ^1/2 )
... (4)
Expression (4) uses the x-coordinate xp and y-coordinate yp of the temporary position of the wireless terminal 10 instead of the initial position (x0, y0) of the wireless terminal 10 in Expression (2).

  The temporary position calculation means 23 calculates the theoretical value Pti of the received radio wave intensity for each wireless node 1 using Expression (4). As in the case of Equation (2), a value common to each wireless node 1 is used as the attenuation constant α, and a preset value common to each wireless node 1 is used as the constant C. The evaluation function V can be calculated by the equation (3) in the same manner as described above using the actual measurement value Pmi of the received radio wave strength and the theoretical value Pti of the received radio wave strength calculated by the equation (4). The provisional position calculation means 23 repeats the calculation of Expression (4) and Expression (3) while changing the provisional position (xp, yp) of the wireless terminal 10, so that the evaluation function V is minimized. The provisional position (xp, yp) is obtained.

  When a two-dimensional area in which the wireless terminal 10 is considered to exist is divided by an equally spaced grid, if k grid intersections are formed, the positions of the k intersections are defined as the provisional positions (xp, As yp), the provisional position (xp, yp) of the wireless terminal 10 at which the evaluation function V is minimized can be obtained by repeating the calculation of the expressions (4) and (3) for each position. The temporary position calculation unit 23 outputs the calculated data of the temporary position (xp, yp) of the wireless terminal 10 to the attenuation constant recalculation unit 24 and the position determination unit 25. This completes the process of step S4.

  Next, the attenuation constant recalculating unit 24 calculates the theoretical value of the received radio wave intensity for each wireless node 1 using the provisional position of the wireless terminal 10 calculated in step S4, and receives the theoretical value and the received value in step S1. The evaluation function V is calculated from the actually measured value of the received radio wave intensity, and the attenuation constant α that minimizes the evaluation function V is recalculated (step S5). The theoretical value Pti of the received radio wave intensity at the wireless node 1 can be calculated by equation (4). The attenuation constant recalculation unit 24 calculates the attenuation constant α that minimizes the evaluation function V by repeating the calculations of the equations (4) and (3) while changing the attenuation constant α. The attenuation constant recalculation unit 24 outputs the calculated attenuation constant α and the minimum value of the evaluation function V when the attenuation constant α is obtained to the position determination unit 25. This completes the process of step S5.

  After the end of step S5, the position determination means 25 determines whether or not a condition for ending the position estimation of the wireless terminal 10 is satisfied (step S6). If the end condition is not satisfied, the process returns to step S4. At this time, the position determining means 25 sets the attenuation constant α obtained in step S5 for the temporary position calculating means 23. As a result, in step S4, the temporary position calculation means 23 calculates equation (4) using the newly set attenuation constant α instead of the attenuation constant α calculated in step S3. Thus, the processes of steps S4 to S6 are repeated until the end condition is satisfied.

  As the threshold value for the end condition, a threshold value for the evaluation function V and a threshold value for the number of repetitions of the processes in steps S4 and S5 are set. When the minimum value of the evaluation function V calculated in step S5 is smaller than the threshold value of the evaluation function V or when the number of repetitions of steps S4 and S5 reaches the number of times threshold, It is assumed that the end condition is satisfied (YES in step S6), and the provisional position (xp, yp) of the wireless terminal 10 at the time when the end condition is satisfied is determined as the final estimated position of the wireless terminal 10 (step S7). If the minimum value of the evaluation function V is greater than or equal to the threshold value and the number of repetitions of steps S4 and S5 has not reached the threshold value, it is determined that the end condition is not satisfied, and the process returns to step S4 as described above.

  As described above, in the present embodiment, the theoretical value of the received radio wave intensity is calculated for each wireless node 1 using the provisional position of the wireless terminal 10, and the procedure for obtaining the attenuation constant α that minimizes the evaluation function V, And calculating a provisional position of the wireless terminal 10 at which the evaluation function V is minimized until a predetermined end condition is satisfied. By repeatedly executing alternately and determining the provisional position when the end condition is satisfied as the estimated position of the wireless terminal 10, a large number of observation data is preliminarily collected in the actual propagation environment as in the past. Therefore, it is not necessary to determine the attenuation constant α, so that the initial setting for starting the position estimation of the wireless terminal 10 can be made quickly and easily. Moreover, in this Embodiment, the position of the radio | wireless terminal 10 can be estimated with sufficient precision using the radio wave intensity | strength said that it is not good to use for position estimation.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. Also in the present embodiment, the configuration of the position estimation system is the same as that of the first embodiment, and therefore, description will be made using the reference numerals in FIG.
FIG. 4 is a block diagram illustrating a configuration example of the position estimation apparatus 2 according to the present embodiment. The position estimation apparatus 2 according to the present embodiment uses the reception means 20, the initial attenuation constant setting means (initial parameter setting means) 26 for giving an initial value of the attenuation constant α, and the received radio wave intensity using the provisional attenuation constant α. Is calculated for each wireless node 1, the provisional position calculating means 27 for obtaining the provisional position of the wireless terminal 10 having the smallest evaluation function, and the theoretical value of the received radio wave intensity is wirelessly obtained using the provisional position of the wireless terminal 10. An attenuation constant calculation means (parameter calculation means) 28 that calculates the attenuation constant α that minimizes the evaluation function, calculated for each node 1, and the provisional position of the wireless terminal 10 when a predetermined end condition is satisfied Position determining means 29 for determining the estimated position. The position determining means 29 constitutes a repeating means for causing the temporary position calculating means 27 and the attenuation constant calculating means 28 to repeatedly execute the processing until a predetermined end condition is satisfied.

Next, the operation of the position estimation system according to the present embodiment will be described. FIG. 5 is a flowchart showing the operation of the position estimation apparatus 2.
Similarly to the first embodiment, each wireless node 1 receives a radio wave from the radio terminal 10, measures the received radio wave intensity, and wirelessly transmits the received radio wave intensity data to the position estimation device 2. . The receiving means 20 of the position estimation device 2 receives the received radio wave intensity data from each wireless node 1 (step S11 in FIG. 5).

Next, the initial attenuation constant setting means 26 outputs an initial value α0 of a preset attenuation constant α (step S12). For example, a value in the range of 2 to 4 is used as the initial value α0.
The temporary position calculating means 27 calculates the theoretical value of the received radio wave intensity for each wireless node 1 using the initial value α0 of the attenuation constant α set in step S12, and the received radio wave intensity received in step S11. The evaluation function V is calculated from the actual measurement value of, and the provisional position (xp, yp) of the wireless terminal 10 at which the evaluation function V is minimized is calculated (step S13).

Here, the propagation loss PL [dBm] between the wireless terminal 10 and the wireless node 1 can be expressed as the following equation.
PL = 40 + 10 × α × log ₁₀ r (5)
Then, the theoretical value Pti [dBm] of the received radio wave intensity at the i-th wireless node 1 can be obtained from the equation (5) as follows.
Pti = Ps + Gs + Gr-PL
= Ps + Gs + Gr− (40 + 10 × α0
× log ₁₀ (((xp−xb) ² + (yp−yb) ² ) ^1/2 )) (6)
In Expression (6), Ps [dBm] is the transmission power of the radio terminal 10, Gs [dBm] is the gain of the transmission antenna of the radio terminal 10, and Gr [dBm] is the gain of the reception antenna of the radio node 1.

  The provisional position calculation means 27 calculates the theoretical value Pti of the received radio wave intensity for each wireless node 1 using the equation (6). The initial value α0 of the attenuation constant α, the transmission power Ps, the gain Gs of the transmission antenna, and the gain Gr of the reception antenna use values common to the wireless nodes 1. The evaluation function V can be calculated by Expression (3) in the same manner as in the first embodiment, using the measured value Pmi of the received radio wave intensity and the theoretical value Pti of the received radio wave intensity calculated by Expression (6). The provisional position calculation unit 27 repeats the calculations of Expression (6) and Expression (3) while changing the provisional position (xp, yp) of the wireless terminal 10, so that the evaluation function V is minimized. The provisional position (xp, yp) is obtained.

  When a two-dimensional area in which the wireless terminal 10 is considered to exist is divided by an equally spaced grid, if k grid intersections are formed, the positions of the k intersections are defined as the provisional positions (xp, As yp), the provisional position (xp, yp) of the wireless terminal 10 at which the evaluation function V is minimized can be obtained by repeating the calculations of the expressions (6) and (3) for each position. The temporary position calculating unit 27 outputs the calculated data of the temporary position (xp, yp) of the wireless terminal 10 to the attenuation constant calculating unit 28 and the position determining unit 29, and at the same time, the temporary attenuation constant used in Expression (6). α0 is output to the position determining means 29. This completes the process of step S13.

  Next, the attenuation constant calculating means 28 calculates the theoretical value of the received radio wave intensity for each wireless node 1 using the provisional position of the wireless terminal 10 calculated in step S13, and the reception value received in step S11. An evaluation function V is calculated from the actually measured value of the radio wave intensity, and an attenuation constant α that minimizes the evaluation function V is obtained (step S14).

The theoretical value Pti [dBm] of the received radio wave intensity at the i-th wireless node 1 can be obtained from Equation (6) as follows:
Pti = Ps + Gs + Gr− (40 + 10 × α
Xlog ₁₀ (((xp-xb) ² + (yp-yb) ² ) ^1/2 )) (7)

  The evaluation function V can be calculated by the equation (3) using the measured value Pmi of the received radio wave intensity and the theoretical value Pti of the received radio wave intensity calculated by the equation (7). The attenuation constant calculating means 28 obtains an attenuation constant α that minimizes the evaluation function V by repeating the calculations of the equations (7) and (3) while changing the attenuation constant α. The attenuation constant calculating unit 28 outputs the calculated attenuation constant α to the position determining unit 29. This completes the process of step S14.

  After the end of step S14, the position determination means 29 determines whether or not the condition for ending the position estimation of the wireless terminal 10 is satisfied (step S15). If the end condition is not satisfied, the process returns to step S13. At this time, the position determining means 29 sets the attenuation constant α obtained in step S14 for the temporary position calculating means 27. Thereby, in step S13, the provisional position calculation means 27 calculates Formula (6) using the newly set attenuation constant α instead of the initial value α0. In this way, the processes in steps S13 to S15 are repeated until the end condition is satisfied.

  As a threshold value for the termination condition, a threshold value for the difference in the attenuation constant α is set. The position determination means 29 has an absolute value of the difference between the attenuation constant α calculated in step S14 and the temporary attenuation constant α (α0) used in step S13 by the temporary position calculation means 27 immediately before step S14. If it is smaller than the threshold value, it is regarded that the end condition is satisfied (determination YES in step S15), and the temporary position (xp, yp) of the wireless terminal 10 at the time when the end condition is satisfied is determined as the final position of the wireless terminal 10. The estimated position is determined (step S16). If the absolute value of the difference in the attenuation constant α is greater than or equal to the threshold value, it is assumed that the end condition is not satisfied, and the process returns to step S13 as described above.

  As described above, in the present embodiment, the theoretical value of the received radio wave intensity is calculated for each wireless node 1 using the provisional attenuation constant α, and the provisional position of the wireless terminal 10 that minimizes the evaluation function V is obtained. A predetermined termination condition is established between the procedure and the procedure for calculating the theoretical value of the received radio wave intensity for each wireless node 1 using the provisional position of the wireless terminal 10 and obtaining the attenuation constant α that minimizes the evaluation function V. By repeating the process repeatedly until the end condition is satisfied, the provisional position at the time when the end condition is satisfied is determined as the estimated position of the wireless terminal 10, so that the same effect as in the first embodiment can be obtained.

An experimental result of actually measuring the received radio wave intensity of the radio terminal 10 using the position estimation system of the present embodiment and estimating the position of the radio terminal 10 based on the received radio wave intensity is shown below.
FIG. 6 is a plan view showing measurement conditions of the position estimation system in this measurement experiment. In the example of FIG. 6, eight wireless nodes 1 are two-dimensionally arranged to estimate the positions of the wireless terminals 10-1 to 10-3. The arrangement interval of the wireless nodes 1 is 7.5 m, the z coordinate of the wireless nodes 1 (the coordinate in the direction perpendicular to the paper surface of FIG. 6) is 1.3 m, and the z coordinates of the wireless terminals 10-1 to 10-3 are also 1. .3m.

  Further, the transmission power Ps of the radio terminals 10-1 to 10-3 is 1 mW, the gain Gs of the transmission antenna of the radio terminal 10 is 0 dBi, the gain Gr of the reception antenna of the radio node 1 is 2 dBi, and the radio node 1 in FIG. The width of the grid that divides the enclosed region was 0.5 m, and the threshold value of the difference in the attenuation constant α was 0.001. The experimental results at this time are shown in Table 1.

  The attenuation constant α obtained as a result of this experiment was 2.331691. According to Table 1, it can be seen that the error between the actual position and the estimated position of the wireless terminals 10-1 to 10-3 is about 2 m or less.

  In the present embodiment, the termination condition is established when the absolute value of the difference in the attenuation constant α is smaller than the threshold value. However, the present invention is not limited to this, and is the same as in the first embodiment. The end condition may be satisfied when the minimum value of the evaluation function V calculated in step S14 is smaller than the threshold value of the evaluation function V, and the number of repetitions of the processing in steps S13 and S14 is a threshold value. The end condition may be satisfied when the value is reached.

  In addition, the configuration excluding the receiving unit 20 in the position estimation device 2 of the first and second embodiments is realized by a computer having a CPU, a storage device, and an interface, and a program for controlling these hardware resources. be able to. The CPU executes the processing described in the first and second embodiments in accordance with a program stored in the storage device.

  The present invention can be applied to a technique for estimating the position of a wireless terminal.

FIG. 1 is a block diagram showing the configuration of the position estimation system according to the first embodiment of the present invention. It is a block diagram which shows the structural example of the position estimation apparatus in the position estimation system of FIG. It is a flowchart which shows operation | movement of the position estimation apparatus in the position estimation system of FIG. It is a block diagram which shows the structural example of the position estimation apparatus in the position estimation system of the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the position estimation apparatus in the position estimation system of the 2nd Embodiment of this invention. It is a top view which shows the measurement conditions of the position estimation system in a measurement experiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Wireless node, 2 ... Position estimation apparatus, 10 ... Wireless terminal, 20 ... Reception means, 21 ... Initial position setting means, 22, 28 ... Attenuation constant calculation means, 23, 27 ... Temporary position calculation means, 24 ... Attenuation constant Re-calculating means, 25, 29 ... position determining means, 26 ... initial damping constant setting means.

Claims (14)

In a position estimation method for estimating a position of a wireless terminal,
A measurement procedure for measuring the received radio wave intensity from a wireless terminal at a plurality of wireless nodes;
A theoretical value of the received radio wave intensity is calculated for each radio node using a parameter depending on a radio wave environment and a provisional position of the radio terminal, and an actual value and the theoretical value of the received radio wave intensity measured in the measurement procedure are calculated. A parameter calculation procedure for obtaining the parameter that minimizes the evaluation function, using a value based on the difference between
Using the parameter and the provisional position of the wireless terminal to calculate a theoretical value of the received radio field strength for each wireless node, and to obtain a provisional position of the wireless terminal that minimizes the evaluation function;
The parameter calculation procedure or the provisional position calculation procedure is used as an initial procedure, the parameter calculated in the parameter calculation procedure is used in the provisional position calculation procedure, and the provisional position of the wireless terminal calculated in the provisional position calculation procedure is An iterative procedure for alternately executing the parameter calculating procedure and the provisional position calculating procedure, as used in a parameter calculating procedure;
A position estimation method comprising: a position determination procedure for determining the provisional position at the time when a predetermined end condition is satisfied as an estimated position of the wireless terminal. The position estimation method according to claim 1,
Furthermore, it comprises an initial position setting means for giving an initial value of the provisional position of the wireless terminal,
The parameter calculation procedure includes: a first parameter calculation procedure for obtaining the parameter using an initial value of the temporary position of the wireless terminal; and the parameter using the temporary position of the wireless terminal calculated in the temporary position calculation procedure. A second parameter calculation procedure to be obtained,
In the iterative procedure, the first parameter calculation procedure is the first procedure, and the provisional position calculation procedure and the second parameter calculation procedure are alternately executed repeatedly. The position estimation method according to claim 1,
Furthermore, an initial parameter setting means for giving an initial value of the parameter is provided,
In the iterative procedure, the provisional position calculation procedure for obtaining the provisional position of the wireless terminal using the initial value of the parameter is the first procedure, and the parameter calculation procedure and the provisional position calculation procedure are alternately executed repeatedly. A position estimation method characterized by the above. The position estimation method according to any one of claims 1 to 3,
The position determination procedure is characterized in that the end condition is considered to be satisfied when a minimum value of the evaluation function when the provisional position of the wireless terminal or the parameter is obtained is smaller than a predetermined threshold value. Position estimation method. The position estimation method according to any one of claims 1 to 3,
The position determination method, wherein the position determination procedure considers that the end condition is satisfied when the number of repetitions reaches a predetermined threshold value. The position estimation method according to claim 3,
In the position determination procedure, the absolute value of the difference between the parameter calculated in the parameter calculation procedure and the temporary parameter used in the temporary position calculation procedure immediately before the parameter calculation procedure is smaller than a predetermined threshold value. Sometimes, the position estimation method is characterized in that the termination condition is satisfied. The position estimation method according to any one of claims 1 to 6,
The evaluation function is a sum obtained by obtaining the square of the difference between the measured value of the received radio wave intensity measured in the measurement procedure and the theoretical value for each wireless node, and adding the square of the difference for all the wireless nodes. A position estimation method characterized by being. In a position estimation system for estimating the position of a wireless terminal,
A plurality of wireless nodes that measure received radio field strength from wireless terminals;
Using the parameter depending on the radio wave environment and the provisional position of the radio terminal, the theoretical value of the received radio wave intensity is calculated for each radio node, and the difference between the measured actual value of the received radio wave intensity and the theoretical value A parameter calculation means for obtaining the parameter that minimizes the evaluation function, with a value based on
Temporary position calculating means for calculating the theoretical value of the received radio field strength for each wireless node using the parameter and the temporary position of the wireless terminal, and obtaining the temporary position of the wireless terminal that minimizes the evaluation function;
The parameter calculation means or the provisional position calculation means is used as an initial means, the parameter calculated by the parameter calculation means is used by the provisional position calculation means, and the provisional position of the wireless terminal calculated by the provisional position calculation means is Repeating means for alternately executing the processing of the parameter calculating means and the provisional position calculating means, as used in the parameter calculating means,
A position estimation system comprising: position determination means for determining the provisional position when a predetermined end condition is satisfied as an estimated position of the wireless terminal. The position estimation system according to claim 8,
Furthermore, it comprises an initial position setting means for giving an initial value of the provisional position of the wireless terminal,
The parameter calculation means includes first parameter calculation means for obtaining the parameter using an initial value of the temporary position of the wireless terminal, and the parameter using the temporary position of the wireless terminal calculated by the temporary position calculation means. Second parameter calculation means to be obtained,
The position estimation system characterized in that the repetitive means uses the first parameter calculation means as the first means, and repeatedly executes the processes of the temporary position calculation means and the second parameter calculation means. The position estimation system according to claim 8,
Furthermore, an initial parameter setting means for giving an initial value of the parameter is provided,
The repetitive means uses the temporary position calculating means for obtaining the temporary position of the wireless terminal using the initial value of the parameter as the first means, and repeatedly executes the processing of the parameter calculating means and the temporary position calculating means. A position estimation system characterized by that. The position estimation system according to any one of claims 8 to 10,
The position determining means considers that the termination condition is satisfied when the minimum value of the evaluation function when the provisional position of the wireless terminal or the parameter is obtained is smaller than a predetermined threshold value. Position estimation system. The position estimation system according to any one of claims 8 to 10,
The position determination system, wherein the position determination unit considers that the end condition is satisfied when the number of repetitions reaches a predetermined threshold value. The position estimation system according to claim 10, wherein
The position determination means has an absolute value of a difference between the parameter calculated by the parameter calculation means and the temporary parameter used by the temporary position calculation means immediately before the parameter calculation means smaller than a predetermined threshold value. Sometimes, the position estimation system is characterized in that the end condition is satisfied. The position estimation system according to any one of claims 8 to 13,
The evaluation function is a sum obtained by calculating the square of the difference between the measured actual value of the received radio wave intensity and the theoretical value for each wireless node, and adding the square of the difference for all the wireless nodes. Feature location estimation system.

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