JP2001051042A - Method of specifying position of radio communication terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a position specification method in which the calculation amount is reduced and in which the installation cost of a base station is reduced by simplifying the calculation used to specify the position when the position of a mobile station with a radio communication terminal is specified by measuring the time in which radio waves radiated from the mobile station are received by three or more base stations. SOLUTION: In this specification method of position, radio waves are radiated from a mobile station 1 in order to specify the position of the mobile station 1 in a radio communication system wherein a communication control station 3 which controls communications to be performed between the mobile station 1 and three or more base stations 2 is contained. The time in which the radio waves are received by the three or more base stations 2 synchronized substantially with the reference time is measured. An equation in which an amount obtained by multiplying the difference between the reception time and the radiation time by a light velocity is equal to the distance between the mobile station and the base stations is deformed in such a way that the radio-wave radiation time as an unknown quantity is found with reference to the base stations. The position of a representative point in which the sum not taking into consideration the difference between radio-wave radiation times in all combinations of two radio-wave radiation times obtained from three of more radio-wave radiation times found by the deformed equation, e.g. the square sum, becomes minumum is found as the position of the mobile station.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of mobile stations each having a radio communication terminal attached thereto, and a plurality of base stations, each of which has a known position, for communicating with the mobile stations.
In a wireless communication system including a communication control station that controls communication performed between a plurality of mobile stations and a plurality of base stations, a method for specifying the position of each mobile station by communication with the base station. is there.

[0002]

2. Description of the Related Art It is expected that many applications will be developed in which a technology for specifying the position of a wireless communication terminal, particularly a communication position of a mobile phone called PHS, will be developed in the future. Has conventionally proposed a base station system, but recently a GPS system using a GPS receiver has been proposed.
A scheme has been proposed. Although each system has advantages and disadvantages, in particular, the base station system has problems in the capital investment scale of the base station required for position identification, the accuracy of position identification, and the like.

As a method of specifying the position of a wireless communication terminal by a base station system, for example, as described in Japanese Patent Application Laid-Open No. 7-154848, a radio wave transmitted from a wireless communication terminal as a mobile station is installed. There is disclosed a technique in which a base station whose position is known receives a signal, the distance from the mobile station to the base station is measured from the intensity of the received radio wave, and the position of the mobile station is specified from the measured distance.

[0004]

However, the method for measuring the distance from the intensity of the received radio wave does not provide sufficient accuracy to determine the position of the wireless communication terminal, and determines which base station is closest to at most. You can only know.
Therefore, in this case, the position of one base station is specified in the communicable zone unit. However, if the position cannot be specified in a sufficiently narrow zone, the value as the position information decreases. Therefore, there is a problem that a high-density base station distribution is required in order to obtain a desired position identification accuracy.

On the other hand, a method of using a propagation delay time to measure a distance between a mobile station with a wireless communication terminal and a base station is disclosed in, for example, JP-A-1-206279 and JP-A-3-206279.
Nos. 2,350,077 and 5,608,553. In this method, a signal transmitted from a certain mobile station is received by three or more base stations whose positions are known and whose measurement time is substantially synchronized, and the mobile station is determined based on a difference between the received times. And the distance between each base station and
From these distances, one point on the plane is specified as the position of the mobile station.

Here, as a method of specifying one point on a plane, hyperbolic navigation is generally used. In other words, this method utilizes the fact that a curve in which the difference between the distances measured by the two base stations is constant becomes a hyperbola with the focus on the two base stations. One station is shared, and three stations obtain two sets of hyperbolas, and it is determined that the intersection is the position of the mobile station. In this case, a diagram called Loran diagram for determining the position can be used, but this method cannot be adopted unless the base station is arranged so as to correspond to the diagram. In addition, this method has a problem that it is difficult to consider an error in distance measurement.

Further, there is a method of solving a simultaneous ternary quadratic equation analytically, but the calculation becomes extremely complicated. It is conceivable that the calculation can be simplified by approximating a simultaneous ternary linear equation by Taylor expansion, but such approximation can be made because the distance between the mobile station and the base station depends on the position update of the mobile station. However, there is a problem that it is limited to a case where the distance is very large compared to the required moving distance.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned various drawbacks of the prior art, and to reduce the distribution density of base stations to a feasible level when specifying the position of a mobile station by the base station method.
It is an object of the present invention to provide a method for specifying a position of a wireless communication terminal that can obtain a desired position specifying accuracy even if the calculation is significantly simplified.

[0009]

According to the present invention, there is provided a method for specifying the position of a wireless communication terminal, comprising the steps of: communicating with a plurality of mobile stations each having a wireless communication terminal attached thereto; The position of each mobile station in a wireless communication system including a plurality of known base stations and a communication control station that controls communication performed between a plurality of wireless communication terminals and a plurality of base stations, the base station and In specifying based on the communication of, the radio wave emitted from the radio communication terminal of a certain mobile station,
The times received by three or more base stations substantially synchronized with the reference time are measured, and the difference between these received times and the time fired by the mobile station is multiplied by the speed of light to determine the amount of the mobile station. An equation, which is assumed to be equal to the distance between a station and the three or more base stations, is calculated for a plurality of representative points in the area where simultaneous communication is possible by the three or more base stations. For each of the three or more base stations, and 3
The sum without considering the sign of the difference between the radio wave emission times in all combinations of two radio emission times obtained from two or more radio emission times is the position of the representative point that is the smallest of the plurality of representative points, It is characterized in that it is obtained as the position of a mobile station.

In the method for specifying the position of a wireless communication terminal according to the present invention, the time at which a radio wave is emitted from the wireless communication terminal of the mobile station and the time at which the radio wave is received by three or more base stations are determined. The process of measuring the communication delay time from the difference can be performed by the communication control station or the wireless communication terminal. For example, in the case of performing at a mobile station, reception time data measured at each base station is received from a base station or a communication control station, and the data and the emission time data of radio waves stored in the mobile station are used. The communication delay time can be measured.

Further, the process of specifying the position of the mobile station from the reception time of the radio wave emitted from the radio communication terminal of the mobile station is performed by the mobile station or the base station by relaying information by the communication control station. be able to. For example, in the case of performing at a mobile station, the radio control apparatus collects radio wave reception time data measured at each base station and transmits the data to the mobile station, whereby the mobile station can specify its own position. it can. Such processing can be performed by each base station.

Further, in the present invention, a communication delay time is measured from a difference between a time when a radio wave is emitted from the radio communication terminal of the mobile station and a time when the radio wave is received by three or more base stations. It is preferable that the process and the process of specifying the position of the mobile station based on the radio wave reception time at the base station be distributed between the base station and the communication control station. With this configuration, the load on the arithmetic processing at the base station and the communication control station is reduced as compared with the case where these processes are performed at the base station or the communication control station, so that the balance as a whole system is improved. Is done. Further, the function of the communication control station can be performed by the base station.

In the present invention, a sum that does not take into account the sign of the difference between the radio wave emission times is obtained for all representative points selected so as to satisfy a desired position identification accuracy in the simultaneous call possible area, The position of the representative point giving the minimum sum among them can be obtained as the position of the mobile station. Even in this case, the calculation is simplified and the amount of calculation is extremely small as compared with a case where a complete analytical solution is taken into account in the mobile station and the base station in consideration of a reference time error.
However, as in an embodiment to be described later, the process of obtaining the position of the representative point where the sum of squares of the difference between the radio wave emission times is the smallest among the plurality of representative points as the position of the mobile station is performed by a plurality of representative points. Is repeated until the desired position accuracy is obtained while gradually reducing the size of the position calculation area including the, the calculation amount can be further reduced. In this case, if the position calculation area is a square, and the length of one side is reduced by 0.75 times each time, the accuracy of position specification can be further improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an entire configuration of a wireless communication system implementing a method for specifying a position of a wireless communication terminal according to the present invention. A plurality of base stations 2 are arranged around a mobile station 1 with a wireless communication terminal. The positions of these base stations 2 are known. Each base station 2 has a function of measuring a time at which a specific radio wave emitted from the mobile station 1 is received. In the present invention, these base stations 2
In order to determine the position of the mobile station 1 by comparing the radio wave reception times in the above, a time synchronization device synchronized with the reference time is required for measuring the radio wave reception time. However, even if there is a difference in the reference time between these base stations 3, the difference is known as long as the difference is within the correction range. That is, in the present invention, the plurality of base stations 3 only need to be substantially synchronized with the reference time.

As shown in FIG. 1, a plurality of base stations 2 are connected to a communication control station 3. In this example, the communication control station 3 has a function of performing arithmetic processing for specifying the position of the mobile station 1 in addition to a function of controlling communication with the base station 2. In the present invention, the base station 2 can have an arithmetic function for specifying the position of the mobile station 1 as described above. In this case, the function of the communication control station 3 is performed by the base station 2.

Next, a method for specifying the position of a mobile station according to the present invention will be described. Now, it is assumed that a specific radio wave is emitted from the mobile station 1 at time TM, and this radio wave is received at three or more base stations 2 at time Ti (i is the number of the base station). Here, the distance Ri from each base station i to the mobile station 1 is given by Ri = C (Ti-TM) (1) where C is the speed of light. Further, the known position of the base station i is represented by (x
i, yi), the position (x, y) of the mobile station 1 whose position is unknown can be expressed as (x-xi) ² + (y-yi) ² = Ri ² --- (2) .

From the above equations (1) and (2), (x-xi) ² + (y-yi) ² = C ² (Ti-TM) ^2- (3) is obtained. In reality, the time on the mobile station 1 side and the base station 2
Since the time is not synchronized with the time on the side, the radio wave reception time TM actually measured includes a synchronization deviation, and the synchronization deviation is an unknown number. Therefore, the radio wave emission time TM to be measured in the mobile station 1 may be handled as an unknown number. However, it is assumed that time synchronization between the plurality of base stations 2 has been established using, for example, a known time synchronization device.

Taking the square root of both sides of the above equation (3),
When all unknowns are put together on the left side, the following equation (4) is obtained. [(X-xi) ² + (y-yi) ² ] ^1/2 + CTM = CTi (4) When both sides are divided by C, the following equation (5) is obtained. [(X-xi) ² + (y-yi) ² ] ^1/2 / C + TM = Ti (5) In this equation (5), since the unknowns are three of x, y, and TM, at least 3 Reception time Ti at one base station 3
Is measured, the position (x, y) of the mobile station 1 can be specified.

In the GPS, since the distance to a satellite serving as a base station is very long, that is, 20,000 km or more, it can be converted to a linear expression by Taylor expansion and the position can be obtained by convergence calculation. In the case of a mobile phone, the range in which the mobile station moves within the time required to update the position cannot be ignored compared to the distance to the base station, and therefore, the three-dimensional simultaneous two-way system without tailoring is used. The following equation needs to be solved. Here, considering that the time synchronization accuracy between the base stations 2 is about 100 ns, the measurement accuracy converted into the distance is about 30 m. That is, it can be said that it is sufficient to divide the coverage area of the base station 2 into meshes of about 10 to 20 m and to specify a discontinuous position to find which grid point is closest to the representative point of the position.

The unknown value TM in the above equation (5) is
Naturally, the values should be the same in the equations for all base stations 2. That is, TMi = TM (i is the number of the base station) (6) where TMi = Ti − [(x−xi) ² + (y−yi) ² ] ^1/2 / C— (7) Since this formula (6) holds when there is no measurement error of the radio wave reception time, it is determined whether the lattice point is appropriate as the specified position when the discrepancy of the unknown number TMi for each base station is minimized. Can be determined as That is, in the present invention, the sum not considering the sign of the difference between the radio emission times in all combinations of the two radio emission times obtained from the radio emission times obtained for the respective base stations is the plurality of representative points. Is determined as the position of the mobile station. In this example, the discrepancy amount D of the unknown number TMi for each base station is
As expressed by the following equation (8), the difference is obtained as the sum of squares of the difference between the two radio wave emission times. D = (((dij) ² , i (j --- (8) where dij = TMi-TMj

As described above, for all the grid points in the communication area, the value of D in equation (8) is calculated, and the grid point that gives the minimum value is specified as the position of the mobile station 1, which is described above. As shown in equation (5), the amount of calculation is considerably smaller than when a complete analytical solution in which the occurrence of an error is taken into account is obtained. As described above, when the value of D is calculated for all the grid points in the coverage area of the base station and the grid point where D is minimized is obtained, for example, the 1000 m square coverage area is set to 1
If it is divided by grid points every 0 m, the value of D should be calculated for 10,000 grid points.

A preferred embodiment of the present invention capable of further reducing the above-mentioned calculation amount will be further described.
That is, by using the property that the only minimum value of the change with respect to the position (x, y) of the mobile station 1 coincides with the minimum value to be obtained, the value of D can be calculated with far fewer grid points. Can be obtained, and this grid point can be specified as the position of the mobile station 1.

FIG. 2 is a flowchart showing the sequential operation in the preferred embodiment according to the present invention, and FIGS.
It is a diagram for explaining these operations. In the following description, the coverage area of the base station is a square for convenience of description, but a representative point other than four points may be used. First, in step S1, an initial value of the position calculation area is set based on the shape of the base station cover area. Here, the base station cover area and the position calculation area are square. Therefore, the length L of one side of the position calculation area and the coordinates (0, 0) of the origin (the lower left corner of the square) are set. In the next step S2, as shown in FIG. 3, a plurality of representative points are set in the position calculation area A1 thus set.
In the example shown in FIG. 3, four points (i), (ii), (iii),
(Iv) is determined. The position of this representative point is a square 4
It is assumed that the point is inside by 1/4 of the length of one side from the corner.
Therefore, the coordinates of the representative point (i) are (0.25L, 0.
25L).

Next, in step S3, for each of the four representative points determined as described above, the value of D is calculated based on the above equation (8). The representative point that gives the minimum value among the four values of D calculated as described above is determined. Subsequently, in step S5, the length L of one side of the current position calculation area is compared with the required position identification accuracy. If the determination is "Yes", the process further proceeds to step S7, and the representative point giving the minimum D is specified as the position of the mobile station as described above.

On the other hand, the determination in step S5 is "N
In the case of "o", the process proceeds to step S6. This step S
At 6, a new position calculation area is set based on the representative point giving the minimum value of D. FIG. 4 shows how the new position calculation area A2 is set. That is, the origin is updated as necessary, and the length of one side of the first position calculation area A1 is reduced to 0.75 times the length 0.75.
The position is updated to a position calculation area A2 having L as one side. For example, when the representative point giving the minimum value of D is the point (i) shown in FIG. 3, the origin does not move as shown on the left end of FIG. 4, but the length of one side becomes 0.75L. A new reduced position calculation area A2 is set. When the representative point giving the minimum value of D is point (ii) shown in FIG. 3, the origin moves rightward by 0.25 L and the length of one side is 0.75 L
A new position calculation area A2 reduced to
Is the point (iii) that gives the minimum value of, the origin moves upward by 0.25 L and the length of one side is 0.7
When a new position calculation area A2 reduced to 5L is set and the representative point giving the minimum value of D is point (iv), the origin is 0.25L rightward as shown in the right end of FIG. Then, a new position calculation area A2 in which the length of one side is reduced to 0.75L is set.

After updating the position calculation area A2 as described above in step S6, the process returns to step S2 to determine four representative points in this position calculation area.
For example, when the representative point that gives the minimum value of D in the first position calculation area A1 is the point (i) shown in FIG. 2, the coordinates of the lower left representative point set in the updated position calculation area A2 are: (0.75L / 4, 0.75L / 4). Subsequently, in step S3, the value of D is calculated for each of the four representative points determined in this way, and further, in step S4, the representative point that gives the minimum D is determined. Here, in step S5, it is determined whether or not the length 0.75L of one side of the newly updated position calculation area A2 is smaller than a desired position accuracy.

As described above, while the position calculation area is gradually reduced, the operation of determining the representative point giving the minimum D is repeated until the desired position accuracy is obtained. The location of the station can be specified. In this example, as described above, the process of determining the representative point giving the minimum D while reducing the length of one side of the position calculation area to 0.75 times is repeated. The reason will be described below. .

FIG. 5 shows the change of D from the representative point (i) to the representative point (ii). Since there is only one point where the minimum value = minimum value in the base station cover area, when the value of D at the representative point (i) is smaller than the value of D at the representative point (ii), the point from the origin is obtained. Although there is no minimum value of D in the base station cover area farther than the representative point (ii), the representative point (ii) is located between the representative point (i) and the representative point (ii). ) May exist in the vicinity. The representative point (iii) and the representative point (i
Since the same applies to v), even if the representative point (i) gives the minimum D among the four points, as shown in FIG. 4, the position calculation area includes the remaining three points on the boundary. Is a safe way to reduce the position calculation area while including the minimum value of D.

As described above, each time D is calculated for four points in the position calculation area, the length of one side of the square position calculation area is reduced to 0.75 times.
In the case of a base station service area of 00 m square, it is only necessary to repeat D at most 20 times, that is, calculate D for 80 points, in order to specify a position with an accuracy equivalent to a grid point of 10 m. Compared to a simple method that requires calculation of D for 10,000 points and minimum value search, there is an advantage that processing only for a hundredth or less representative points is required.

As described above, in the present invention, each base station is provided with a time synchronizing device for measuring the radio wave reception time, and this device is a highly accurate time standard such as an atomic clock. Devices, devices that can use an external high-precision time standard such as GPS receivers, devices that correct unsynchronized time using communication delay time measured in advance by communication between base stations, and the like can be considered. .

Next, restrictions on the arrangement of base stations will be described. In the present invention, it is a requirement that three or more base stations measure the radio wave reception time. However, when these three base stations are arranged in a straight line, the position of the mobile station on the arranged straight line is determined. Cannot be specified. In this case, the position of the mobile station cannot be specified unless the radio wave emission time TM itself is specified in the mobile station. Of course, there is no problem if a base station located out of the straight line in which the base stations are arranged is added as a base station used for position identification. Therefore, as the location of the base station,
It is preferable to arrange so as to surround the base station cover area. Further, as the mobile station moves away from the base station outside the polygon formed by connecting three or more base stations used for specifying the position, the influence of the reception time measurement error on the position specifying accuracy increases. Therefore, even if it is easy to secure a base station cover area in which three or more stations have overlapping communicable areas, it is necessary to avoid arranging base stations close to each other.

[0032]

As described above, according to the method for specifying the position of a radio communication terminal according to the present invention, the time of the mobile station whose position is to be specified is not synchronized with the time of the base station. The radio wave departure time obtained from the radio wave reception time measured at each base station is defined as an unknown number, and a sum that does not consider the sign of the difference of the unknown number for each base station, for example, a square point or a representative point at which the sum of the absolute value of the difference is minimized Is obtained, and this is specified as the position of the mobile station. Therefore, compared with the case of obtaining a complete analysis solution in consideration of the time error, the calculation amount is significantly reduced and the procedure becomes simple. is there.

As in the above-described embodiment, the operation of obtaining a representative point that minimizes the sum of squares D of the unknown difference for each base station while gradually reducing the position calculation area can be performed with a desired position accuracy. By repeating this process, there is an advantage that the position of the mobile station can be efficiently specified with a smaller amount of calculation.

Further, the base station installation density can be reduced in a range where the coverage area of three or more base stations overlaps, and the base station installation cost can be reduced.

Further, even if there is an error in the distance measurement, since the position of the mobile station is always found in the base station cover area, there is an advantage that the position can be stably specified.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a wireless telephone system to which a method for specifying a position of a wireless communication terminal according to the present invention is applied.

FIG. 2 is a flowchart showing a sequential operation for determining a position of a mobile station in the method according to the present invention;

FIG. 3 is a diagram for explaining the operation.

FIG. 4 is a diagram for explaining the operation thereof.

FIG. 5 is a diagram for explaining the operation.

[Explanation of symbols]

1 mobile station, 2 base station, 3 communication control station, A1,
A2 position calculation area, (i), (ii), (ii)
i), (iv) Representative points

Claims (8)

[Claims] 1. A plurality of mobile stations each having a radio communication terminal attached thereto, and a plurality of base stations, each of which has a known position, for performing communication between these mobile stations, and a plurality of radio communication terminals. When specifying the position of each mobile station in a wireless communication system including a communication control station that controls communication performed with a base station based on communication with the base station, The radio waves emitted from the terminal are measured at three or more base stations substantially synchronized with the reference time, and the times at which the signals are received and the times at which the mobile stations emit the radio waves are measured. An equation that the quantity multiplied by the speed of light is equal to the distance between the mobile station and the three or more base stations is calculated for a plurality of representative points in the area where simultaneous communication by the three or more base stations is possible. , The radio wave emission time, which is an unknown number, For each base station, and does not consider the sign of the difference between the radio emission times for all combinations of two radio emission times obtained from three or more radio emission times obtained from this modified equation A position specifying method for a wireless communication terminal, wherein a position of a representative point having a minimum sum among the plurality of representative points is obtained as a position of the mobile station. 2. A process for measuring a communication delay time from a difference between a time at which a radio wave is emitted from a radio communication terminal of the mobile station and a time at which the radio wave is received by three or more base stations. The method according to claim 1, wherein the method is performed by a control station or a wireless communication terminal. 3. A process for specifying a position of a mobile station from a reception time of a radio wave emitted from a wireless communication terminal of the mobile station,
3. The method according to claim 1, wherein the information is relayed by the communication control station to the mobile station or the base station. 4. 4. A process of measuring a communication delay time from a difference between a time at which a radio wave is emitted from a radio communication terminal of the mobile station and a time at which the radio wave is received by three or more base stations; The method according to claim 1, wherein the process of specifying the position of the mobile station from the reception time at the base station is distributed between the base station and the communication control station. 5. The method according to claim 1, wherein the function of the communication control station is performed by the base station. 6. A sum that does not consider the sign of the difference between the radio wave emission times is obtained for all representative points selected so as to satisfy a desired position identification accuracy within the simultaneous call possible area,
6. The method according to claim 1, wherein a position of a representative point that gives a minimum sum among them is determined as a position of the mobile station.
The method for specifying a position of a wireless communication terminal according to any one of the above. 7. A process for obtaining, as a mobile station position, a position of a representative point at which the sum of the differences of the radio wave emission times without considering the sign of the difference is a minimum among the plurality of representative points. The method according to any one of claims 1 to 5, wherein the process is repeated until a desired position accuracy is obtained while gradually reducing the size of the position calculation area to be obtained. 8. The method according to claim 7, wherein the position calculation area is a square, and the length of one side is reduced by 0.75 times each time.