JP2012137296A - Mobile terminal positioning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mobile terminal positioning method capable of solving a conventional problem of decrease in positioning accuracy which occurs with a method of obtaining a terminal position through reading an IC tag installed at a fixed position.SOLUTION: In a mobile terminal positioning method, an IC tag is also installed in a body of a mobile terminal so as to enable mobile terminals to obtain a positional relation with each other. Through performing an analysis while taking into consideration the positional relation of respective mobile terminals which are moving, in addition to a positional relation with a fixed IC tag, a position of the mobile terminal can be determined with higher accuracy. Moreover, position-fix accuracy is further improved by considering states of the mobile terminal, such as "talking", "operating screen", "waiting", "silent mode", and "out-of-service".

Description

  The present invention relates to a technique for measuring the position of a device, particularly a mobile terminal.

  There are many ways to know the location of a terminal. GPS is widespread outdoors, but there is still no standard positioning means indoors. Even outdoors, there is a demand for improving the GPS position accuracy.

  In addition, it receives signals from a fixed wireless transmitter, calculates a plurality of provisional predicted positions using a plurality of calculation methods such as triangulation, and based on the predicted positions and reference information on the wireless communication environment. There is a method for calculating a predicted position with high accuracy.

JP 2004-215258 A

  One of the positioning means is an IC tag reading function. This is a method of knowing the position of the terminal by reading an IC tag installed at a predetermined position (for example, a fixed position). In this case, there is a problem that the communication distance and the position accuracy conflict. If an IC tag with a short communication distance is used, the IC tag cannot be read unless it is brought close to the IC tag. There is also a problem that a large number of IC tags must be installed. If an IC tag with a long communication distance is used, the position accuracy is reduced by the amount that can be read from a distance.

  An object of the present invention is to accurately acquire the position of a mobile terminal.

  An IC tag is also installed in the mobile terminal body so that the positional relationship between the mobile terminals can be acquired. In addition to the positional relationship with the IC tag installed at a predetermined position, the position of the mobile terminal can be specified with higher accuracy by analyzing the positional relationship between the mobile terminals that move. As the number of portable terminals increases, the position accuracy can be improved.

  In addition, the mobile terminal has states such as “busy”, “screen operation”, “waiting”, “silent mode”, and “out of service area”. The communication distance of the IC tag varies depending on each state. Considering this point, the positioning accuracy can be further improved.

  The positioning accuracy of the mobile terminal device can be improved by installing an IC tag on the mobile terminal body.

Overall system configuration Configuration of terminal positioning server Configuration of terminal reception table Configuration of terminal information table Structure of fixed IC tag table Structure of distance function table Examples of distance functions for each standby state Configuration of terminal location table Overview and calculation method of position calculation Configuration of terminal location calculation device Position calculation procedure

  FIG. 1 shows the overall configuration of the system. The terminal positioning server 101 receives the positioning data from the portable terminal 102, and calculates the terminal position with the highest probability that the terminal exists in consideration of the relationship between the terminals. The calculation result can be referred from the mobile terminal. The portable terminal includes its own IC tag 104 and IC tag reading device 105. The IC tag 104 of the mobile terminal 102 can be read from another mobile terminal. The IC tag reader 105 reads the IC tag and the fixed IC tag 103 of another terminal existing in the communication range. The fixed IC tag 103 is fixed as the name indicates, and the installation location is open to the public.

  FIG. 2 shows the configuration of the terminal positioning server 101. The terminal reception device 207 communicates with the mobile terminal 102, collects positioning data from the mobile terminal, and stores it in the terminal reception table 201. Based on the terminal positioning data in the terminal reception table 201, the terminal position calculation device 206 calculates an estimated value of the terminal position while referring to the data in the terminal information table 202, the fixed IC tag table 203, and the distance function table 204. The current position with the highest probability of each terminal is calculated, and the result is stored in the terminal position reference table 205. The mobile terminal 102 can communicate with the terminal location reference device 208 to obtain the location of the terminal.

  FIG. 3 shows the configuration of the terminal reception table 201. The terminal reception table 201 is an aggregate of a plurality of terminal reception records 301 each storing a state when each terminal receives a signal from a tag. The terminal reception record 301 stores the terminal ID of the terminal that has read the tag, the reading time, the standby state, the reading tag ID, and the reading reception intensity. The terminal ID is a unique identifier assigned to the mobile terminal. The reading time indicates the time when the portable terminal reads the IC tag. The standby state indicates the state of the terminal when the mobile terminal reads the IC tag. Normally, one of the five states of “busy”, “referencing screen”, “waiting”, “silent mode”, and “out of service area” is assumed. The read tag ID is the ID number of the IC tag read by the mobile terminal. There are IC tags attached to mobile phones (terminal IC tags) and IC tags attached to fixed objects on walls and desks (fixed IC tags). When a plurality of IC tags are read simultaneously, the terminal reception records 301 are stored for the number of readings. The read reception intensity indicates the reception intensity when the IC tag is read. In general, the closer the IC tag is, the stronger the reception intensity.

  FIG. 4 shows the configuration of the terminal information table 202. The terminal information table 202 is an aggregate of a plurality of terminal information records 401 in which information regarding each terminal is stored. The terminal information record 401 stores individual terminal information such as a terminal ID, a terminal tag ID, a reading device type, and user information. The terminal ID is a primary key and uniquely identifies the terminal. The terminal tag ID is the ID number of the IC tag 104 attached to the mobile terminal. The terminal tag ID is also unique. The reading device type indicates the type of the IC tag reading device 105 mounted on the portable terminal. Even if the distance between the IC tag and the portable terminal is the same, the reception intensity varies depending on the performance of the terminal reader 105.

  FIG. 5 shows the configuration of the fixed IC tag table 203. The fixed IC tag table 203 is an aggregate of a plurality of fixed IC tag records 501 in which information related to each fixed IC tag is stored. The fixed IC tag record 501 stores a tag ID, a tag installation position, and a tag type. The tag ID is stored in the fixed IC tag 103 and is unique. The tag installation position is information indicating the position where the fixed IC tag 103 is installed. In the case of outdoors, coordinates such as latitude and longitude are common. In the case of indoor, it is often expressed by relative coordinates in the building. Although any expression can calculate the position of the mobile terminal, the load of position calculation can be reduced by selecting an appropriate expression according to the application. The tag type literally indicates the type (model) of the tag. Depending on the type of tag, reception strength may be different even at the same distance from the tag. Use to correct calculations as needed.

FIG. 6 shows the configuration of the distance function table 204. The distance function table 204 is an aggregate of a plurality of distance function records 601 in which various distance functions according to the state of the terminal when receiving a signal from the tag are stored. The distance function record 601 includes a reading device type, a standby state, a reception intensity of a signal received from a tag, and a distance function P _i (X) corresponding to these parameters (i is an identifier of the distance function, X is an own terminal, and The distance between the partner terminal or the fixed tag) is stored. The terminal position calculation device 206 extracts the reading device type, the standby state, and the reading reception intensity from the terminal reception record 301, searches the distance function table 204, and performs position calculation using the distance function of the matching record. The distance function indicates the probability distribution of the distance between the mobile terminal and the IC tag under the specified conditions (reception strength, terminal reader type, standby state). If the reception intensity is strong, the probability that the terminal and the IC tag exist in the vicinity is high, and a function having a peak in the vicinity is obtained, and if the reception intensity is weak, a function having a peak in the distance is obtained. The type of reading device (signal reception performance from the tag according to the type of reading device) also affects. If the output of the reading device is strong, there is a high possibility of being far away even if the reception intensity is the same. The distance function is also affected by the standby state. Details of the influence will be described below with reference to FIG.

  FIG. 7 shows an example of the distance function for each standby state. A function 701 shows an example of a distance function when the terminal is in a call state. If the terminal is in a call, it is highly likely that the terminal is in the head position, and it is considered that the condition is good for the line of sight. If the reception strengths of the reception states and the positions of the other parties are the same, there is a high probability that the distance between the terminal and the IC tag is long. A function 702 shows an example of a distance function when the screen is being operated. Since the user is looking at the screen of the terminal, it is considered that the height of the terminal is lower and the reception intensity is weaker than the call state compared to the call state. Compared to the call state, the distance function has a peak at a close distance. A function 703 shows an example of a distance function when in a standby state. In the standby state, the terminal is likely to be in the user's pocket or the like. When the terminal is in close contact with the body, it is considered that the reception intensity of the radio wave decreases due to the influence of the body as a conductor. It is expected to be a function having a peak at a shorter distance than the screen operating state. A function 704 shows an example of a distance function in the manner mode. That the manner mode is set means that the user cannot use or intends to use the terminal. It is considered that the terminal is likely to be housed in a cage or the like, and it is considered that the reception condition is quite bad. The distance function is expected to have a peak nearby.

  The distance function can be created by logical calculation by simulation or the like, or may be created based on actually measured data. When the place to be used is limited to some extent, actual measurement is performed at that place, but it is the most reliable and accurate.

  FIG. 8 shows the configuration of the terminal location table 205. The terminal location table 205 is a collection of terminal location records 801 in which information regarding the location at the measurement time of each terminal is stored. The terminal location record 801 stores a terminal ID, a measurement time, and a terminal location. These are the results calculated by the terminal position calculation device 206. The mobile terminal 102 can refer to the terminal position record 205 via the terminal position reference device 208.

  FIG. 9 shows the concept and calculation method of position calculation. Fixed IC tags 901 and 902 exist in the environment. The portable terminal 903 reads the fixed tag 901 and is located somewhere in the communication range 906. The portable terminal 904 reads the fixed tag 902 and is located somewhere in the communication range 907. Only the information of the fixed IC tag does not reveal the detailed position. If the portable terminals 903 and 904 can read each other's IC tag, it can be seen that the relative distance is within the communication range 912. Considering this fact, it can be seen that the portable terminal cannot be located at a position such as 905, and can only be located at the position 904 in the figure. Since the mobile terminal moves, the position cannot be determined directly, but the position of the mobile terminal can still be narrowed using the distance relationship between the terminals. When this method is used, more terminals provide each other's position information, so that the position accuracy of the terminals can be improved.

  Expression 910 is a specific calculation formula of the probability P for obtaining the estimated value of the terminal position, which is expressed by the sum of the probability determined by the distance between terminals and the probability determined by the distance between the terminal and the fixed tag. The probability functions Pij and Pik are determined according to the reception strength and the standby state. The total probability can be obtained by summing the probability obtained from the positional relationship with other portable terminals and the probability obtained from the positional relationship with the fixed tag. Xi is a vector indicating the location of each terminal. Various values of Xi are changed, and Xi that maximizes the overall probability P is calculated. The calculation for obtaining the condition that the function takes the maximum value is a general one, and can be easily executed by a numerical calculation library if a high-speed computer is used. A specific calculation method of Xi that maximizes the overall probability P will be described later.

  FIG. 10 shows the configuration of the terminal position calculation device 206. The input / output circuit 1003 transfers data between each table and the work memory 1004. The arithmetic circuit 1002 executes calculation using data on the work memory 1004 in accordance with a numerical calculation algorithm. A control circuit 1001 controls the entire process. The work memory 1004 is literally a storage device for holding mid-calculation data. When all calculations are completed, all data is deleted. The terminal position array 1005 is an array that holds the position of the terminal being calculated. An estimated value of the terminal position obtained so that the probability P represented by Expression 910 in FIG. The terminal-terminal distance function array 1006 holds a distance function used when calculating the terminal-terminal probability. It is set as an input value at the beginning of the probability calculation and does not change during the calculation. The terminal-fixed tag distance function array 1007 holds a distance function used when calculating the probability between the terminal and the fixed tag. It is set as an input value at the beginning of the probability calculation and does not change during the calculation.

  FIG. 11 shows the procedure for calculating the position. As an overall procedure, in steps 1101 to 1111, information necessary for calculation is set in the working memory, and in step 1112, the actual calculation is performed. First, input data for calculation is set. Since the item of the terminal position in the terminal position array 1005 is an item to be obtained from now on, an item excluding it is set. The terminal ID is acquired from the terminal reception record. The position of the fixed IC tag is acquired from the fixed IC tag table. The distance function is selected from the distance function table based on the type of the reading device of the terminal and the reception intensity. Up to this point, all the information necessary for the calculation is available. In step 1112, the terminal position item of the terminal position array 1005 is actually calculated. There are various calculation algorithms. For example, in addition to the calculation based on the mathematical algorithm, there is also a method of obtaining a position where the probability becomes maximum while changing the terminal position little by little. When the calculation is completed, the calculation result is output to the terminal location table. Details of the procedure are described below.

  First, in processing 1101, the terminal reception table 201 is scanned, and only records having the latest reading time are extracted for each terminal ID. Since the mobile terminal moves, data with a reading time older than a certain time is removed because it is highly likely that the position has already changed. Next, in processing 1102, a terminal position array 1005 is created based on the extracted records. At this time, only the terminal ID is buried, and the terminal position is empty.

  In processing 1003, the following processing is repeated for each extracted terminal reception record 301. When all the records have been processed, the process proceeds to process 1112 to actually calculate the position.

  Processing differs depending on the read tag ID of the terminal reception record. In processing 1104, the terminal information table 202 is searched to search for a record in which the terminal ID and the read tag ID match. Since the terminal ID of the terminal and the terminal ID of the other party are known, the distance function corresponding to the condition is selected. The distance function table 204 is searched using the terminal type, standby state, and reception intensity as keys, and the corresponding distance function is acquired. The searched distance function is added to the terminal-terminal distance function array 1006, and the process returns to step 1103.

  If the terminal ID and the read tag ID in the terminal information table do not match, the fixed IC tag table 203 is searched in processing 1108 to search for a record in which the tag ID and the read tag ID match. If there is a matching record, the read tag is a fixed IC tag. Since the terminal ID and the position of the fixed IC tag are known, a distance function corresponding to the condition is selected. The distance function table 204 is searched using the reading device type, the standby state, and the received intensity as keys, and the corresponding distance function is acquired. The acquired distance function is added to the terminal-fixed IC tag distance function array 1107, and the processing proceeds to processing 1103.

  If neither the terminal information table 202 nor the fixed IC tag table 203 is included, it is determined that an IC tag unrelated to the present system has been read, skips reading, and returns to processing 1103.

  Up to this point, the terminal position array 1005, the terminal-terminal distance function array 1006, and the terminal-fixed tag distance function array 1007 are all buried except for the terminal position. All that remains is to perform a numerical calculation to find the terminal location.

  In step 1112, the terminal position is calculated. To do this simply, the probability calculation is repeated many times while changing the value of the terminal position little by little, and the terminal position with the maximum probability may be obtained. However, since this method is simple and simple, there is a problem that it is inefficient and takes a long processing time. It is good when the number of terminals is small, but the calculation time increases as the number of terminals increases. It is more efficient to calculate the condition under which the probability is extreme using an existing numerical calculation library. The operation for obtaining the extreme value of a function is a general process, and various algorithms have been developed. There is also a numerical library that has become a commercial product. In consideration of the number of terminals and the required response, an appropriate numerical calculation library may be adopted.

When the calculation is completed, the calculation result is written in the terminal position table 205 in processing 1113. This makes it possible to refer to the position of the terminal.
(Specific procedure for calculating the estimated value of the terminal position and approximation method for quick calculation)
Here, using the equation 910 in FIG. 9, that is, the probability determined by the distance between the terminals and the probability determined by the distance between the terminal and the fixed tag, and using the probability P for obtaining the estimated value of the terminal position. A specific procedure for obtaining an estimated value of the terminal position when there are n terminals and m fixed tags will be described below.

  Pij shown in FIG. 9 is a distance function when terminal i receives a signal from terminal j, Pji is a distance function when terminal j receives a signal from terminal i (generally different from Pij), and Pik is a terminal i is a distance function when a signal from the fixed tag k is received, and examples of distance functions corresponding to various conditions are shown in FIG. The distance functions Pij, Pji, and Pik are probability functions having the distance value as a variable. In any of the functions shown in FIG. 7, the area of the region surrounded by the function and the coordinate axis is 1.

From the condition that the total probability P expressed by Expression 910 is the maximum value, the estimated value of the position coordinate of the terminal i is obtained as Expressions 920 to 924. Considering the equations 920 and 921 as multi-dimensional linear simultaneous equations each having n X coordinate values and n Y coordinate values as variables, the coefficients of the diagonal elements of the coefficient matrix include a plurality of non-diagonal elements. Since it corresponds to the sum, each coefficient matrix is regarded as a diagonal dominant matrix. In consideration of such characteristics of the coefficient matrix, n X coordinate values and n Y coordinate values are obtained by the following successive approximation method.
(1) A distance function as shown in FIG. 7 is selected according to the condition of the terminal i.
(2) The number of steps N for successive approximation is set to N = 1.
(3) The coordinate value of terminal i in N steps is obtained by calculating the right side of equations 920 and 921 using the coordinate values obtained in N-1 step (previous step) for terminal j other than terminal i. . (This calculation is performed for all terminals (i = 1 to n).)
(4) For all terminals (i = 1 to n), the absolute value of the difference between the coordinate value obtained in N steps and the coordinate value obtained in N-1 steps is obtained. If the maximum value among these absolute values is smaller than a predetermined error ε (error of the estimated value of the terminal position), the calculation is terminated, and the coordinate value obtained in N steps is used as the estimated value of the terminal position. . If the maximum value among these absolute values is not smaller than the predetermined error ε, it is determined that the solution in the successive approximation has not converged, and 1 is added to N to make N = N + 1, and again, The process (3) is performed. As an initial value (coordinate value of 0 step) of the coordinate value in the successive approximation calculation, an estimated value of the terminal position obtained by the previous calculation or a terminal position obtained by another means is used.

When calculating the expressions 920 and 921 in FIG. 9 in the process of (3) in the above-described successive approximation calculation, as shown in the expressions 922 and 923, the distance functions Pij, Pji, and Pik themselves are not differentiated. The coefficient needs to be calculated. On the other hand, as can be seen from the change in the distance function shown in FIG. 7, the differential coefficient of the distance function is substantially constant except near the local maximum of the distance function. That is, the differential coefficient is a positive value a (a> 0) in a region smaller than the distance u at which the distance function is maximized, and in a region smaller than the upper limit v of the distance function definition region. The differential coefficient is a negative value −b (b> 0). Therefore, the differential coefficient of the distance function included in the expressions 922 and 923 necessary for the calculation of the expressions 920 and 921 in FIG. 9 in the process of (3) is a step expressed by four parameters a, b, u, and v. It can be approximated by a function (a if 0 <r <u, -b if u <r <v). However, distance function, since it is also a probability function, from the condition in which the area of a region surrounded by the function and the coordinate axis becomes 1, while the ^{parameter, b (v 2 -u 2)} / 2-au 2/2 = 1 holds. Further, when the above step function is expressed as a function of the distance r using a Gaussian symbol [] ([X] is the maximum integer not exceeding X), a− (a + b) [r / u] + b [r / v] It becomes.

  Usually, since the position of each mobile terminal changes frequently, in order to reduce the discrepancy between the actual terminal position and the estimated value, it is necessary to quickly execute the calculation using the formula shown in FIG. There is. Therefore, as described above, the terminal position can be estimated quickly by approximating the differential coefficient of the distance function necessary for the calculation of the terminal position estimation with a step function that is easy to calculate. Further, when registering the distance function in the distance function table 204 shown in FIG. 6, rather than holding the distance function for each coordinate value or the value of the differential coefficient (a set of about several tens of data) as described above. In addition, the amount of data to be held can be reduced by holding the four parameters a, b, u, v of the step function approximating the differential coefficient of the distance function necessary for the calculation of the estimation of the terminal position.

101 Terminal positioning server 102 Mobile terminal 103 Terminal IC tag 104 IC tag reader 105 Fixed IC tag

Claims (4)

A positioning method in a terminal positioning server that exchanges information with a plurality of mobile terminals,
Receiving radio waves from an IC tag installed in each of the plurality of mobile terminals,
Select a first distance function according to the type of reading device of the mobile terminal, the standby state and the reception intensity of radio waves from the IC tag,
Each of the plurality of mobile terminals receives radio waves from a fixed IC tag installed in at least one predetermined place,
Select a second distance function according to the type of the reading device of the mobile terminal, the standby state and the reception intensity of the radio wave from the fixed IC tag,
Obtaining a terminal position where the sum of the first distance function and the second distance function for the plurality of mobile terminals is maximized;
Obtaining a positional relationship between the plurality of mobile terminals based on the terminal position;
The positioning method of a mobile terminal, wherein the positional relationship is notified to each of the plurality of mobile terminals. A terminal positioning server for exchanging information with a plurality of mobile terminals,
Means for receiving radio waves from an IC tag installed in each of the plurality of portable terminals;
Means for selecting a first distance function according to the type of the reading device of the portable terminal, the standby state, and the reception intensity of radio waves from the IC tag;
Means for each of the plurality of portable terminals to receive radio waves from a fixed IC tag installed in at least one predetermined location;
Means for selecting a second distance function according to the type of the reading device of the portable terminal, the standby state, and the reception intensity of the radio wave from the fixed IC tag;
Means for obtaining a terminal position at which a sum of the first distance function and the second distance function for the plurality of portable terminals is maximized;
Means for acquiring a positional relationship between the plurality of portable terminals based on the terminal positions;
A terminal positioning server comprising means for notifying each of the plurality of portable terminals of the positional relationship. When determining the terminal position where the sum of the first distance function and the second distance function is maximum,
From the condition that the value of the sum takes a maximum value, a relational expression between the position of each terminal and the position of the other terminal other than each terminal and the position of the fixed IC tag is obtained,
Using the position of the other terminal other than each terminal obtained last time, performing the sequential calculation to obtain the position of each terminal this time by the relational expression,
Of the absolute values of the difference between the current position of each terminal and the last determined position of each terminal, the calculation is terminated if the maximum value is smaller than a predetermined value, and the current position of each terminal is determined. Output as an estimated value of the position of each terminal; otherwise, execute the sequential calculation again with the position of the terminal of the current time as the position of other terminals other than the terminal determined previously. The positioning method of the portable terminal according to claim 1, wherein   4. The mobile terminal according to claim 3, wherein, in the sequential calculation, an expression that approximates a change in a differential coefficient of each of the first distance function and the second distance function with a step function is used. Positioning method.

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