Method of determining position of wireless communication terminal

• US 6,329,948 B1
• Filed: 08/10/2000
• Issued: 12/11/2001
• Est. Priority Date: 08/12/1999
• Status: Expired due to Fees

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Ishikawa, Seiji
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US09/636,570
• Time in Patent Office: 488 Days
• Field of Search: 342/457, 342/463, 342/465, 342/357.06, 342/357.14, 701/213
• US Class Current: 342/457
• CPC Class Codes: G01S 19/46 the supplementary measurement being of a radio-wave signal type
• CPC Class Codes: G01S 19/48 by combining or switching between position solutions derived from the satellite radio beacon positioning system and position solutions derived from a further system
• CPC Class Codes: G01S 5/0063 of measured values, i.e. measurement on base station and position calculation on mobile
• CPC Class Codes: G01S 5/011 Identifying the radio environment
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

In order to determine a position of a mobile station in a wireless communication system including a plurality of mobile stations each having a wireless communication terminal installed therein, a plurality of base stations and a communication control station, times of receipt at which a radio wave emitted by a wireless communication terminal provided in a mobile station whose position is to be determined are received by at least three base stations substantially synchronized with a standard time are measured, a plurality of representative points are set on a position calculation area within an overlapped portions of cover areas of these base stations, communication delay times at respective representative points are calculated with [(x−xi)²+(y−yi)²]^½/C (C is a velocity of light), wave emitting times TMi are calculated as differences between the times of receipt Ti and the communication delay times, a sum D of squares of differences between two calculated wave emitting times in all combinations of two calculated wave emitting times is calculated, and a position of the mobile station is determined at one of said plurality of representative points which gives a minimum sum.

Claims

1. A method of determining a position of a wireless communication terminal in a wireless communication system including a plurality of mobile stations each having a wireless communication terminal installed therein, a plurality of base stations each being arranged at known positions on a plane and a communication control station controlling communication between said plurality of wireless communication terminals and said plurality of base stations, comprising the steps of:

measuring times of receipt at which a radio wave emitted by a wireless communication terminal provided in a mobile station whose position is to be determined are received by at least three base stations which are substantially synchronized with a standard time;

deriving calculated wave emitting times for each of said at least three base stations by replacing a position of the mobile station in equations by a plurality representative positions within a position calculation area set in a simultaneous communication area in which said at least three base stations can simultaneously communicate with the mobile station, said equations being obtained by modifying equations in which products of a velocity of light and differences between an actual wave emitting time at which the radio wave is emitted from the wireless communication terminal of the mobile station and said measured times of receipt become equal to distances between said mobile station and said at least three base stations;

deriving a sum of unsigned differences between two calculated wave emitting times in all combinations of two calculated wave emitting times obtained from at least three calculated wave emitting times for each of a plurality of representative points; and

determining a position of the mobile station at one of said plurality of representative points at which said sum becomes minimum.

2. A method according to claim 1, wherein said step of deriving the calculated wave emitting times is performed by initializing the position calculation area having a predetermined shape and a size, setting said representative points (xi, yi) within the position calculation area, calculating communication delay times at respective representative points from [(x−

xi)²+(y−

yi)²]^½

/C, wherein (x, y) denotes a position of the mobile station and C is a velocity of light, and calculating the calculated wave emitting times TMi as differences between the times of receipt Ti and the communication delay times.

3. A method according to claim 2, wherein said step of measuring the communication delay times from differences between the wave emitting time at the mobile station and the times of receipt at the base stations is performed at the communication control station or at the wireless communication terminal.

4. A method according to claim 2, wherein said step of determining a position of the mobile station is performed at the mobile station or at least one of said base stations while information is transmitted to the mobile station or at least one of said base stations through the communication control station.

5. A method according to claim 2, wherein said step of measuring the communication delay times from differences between the wave emitting time and the times of receipt and the step of determining a position of the mobile station are performed at both the base stations and the communication control station.

6. A method according to claim 2, wherein a function of the communication control station is performed by the base stations.

7. A method according to claim 2, wherein said sum of unsigned differences between two calculated wave emitting times in all combinations of two calculated wave emitting times obtained from at least three calculated wave emitting times is derived for all representative points which are distributed such that a required precision is satisfied.

8. A method according to claim 7, wherein said step of determining a position of the mobile station as a representative point at which the difference D becomes minimum is repeated each time a size of the position calculation area is reduced until a size of the position calculation area becomes not larger than the required precision.

9. A method according to claim 8, wherein said position calculation area is set to be a square shape, and a length of a side of the square position calculation area is reduced by 0.75 each time the position determining process is repeated.

10. A method according to claim 2, wherein said sum of unsigned differences between two calculated wave emitting times in all combinations of two calculated wave emitting times obtained from at least three calculated wave emitting times for each of said plurality of representative points are performed by deriving a sum of squares of unsigned differences.

11. A method according to claim 2, wherein said sum of unsigned differences between two calculated wave emitting times in all combinations of two calculated wave emitting times obtained from at least three calculated wave emitting times for each of said plurality of representative points is derived by making a sum of absolute values of unsigned differences.

12. A method of determining a position of a wireless communication terminal in a wireless communication system including a plurality of mobile stations each having a wireless communication terminal installed therein, a plurality of base stations each being arranged at known positions on a plane and a communication control station controlling communication between said plurality of wireless communication terminals and said plurality of base stations, wherein

(a) when a position of a mobile station could not be determined by a GPS method owing to a fact that the relevant mobile station does not have a GPS receiver or although the relevant mobile station has a GPS receiver, GPS radio waves could not be received, a position of the mobile station is determined by a base station method;

(b) when a position of a mobile station could not be determined by the base station method due to a fact that at least three base stations are not existent around the relevant mobile station, a position of the mobile station is determined by the GPS method; and

(c) when a position of a mobile station could be determined by both the base station method and the GPS method, a position of the mobile station is determined by a hybrid method utilizing, information obtained by the GPS method and information obtained by the base station method.

13. A method according, to claim 12, wherein a step of determining a position of a mobile station by the base station method comprises the steps of:

measuring times of receipt at which a radio wave emitted by a wireless communication terminal provided in a mobile station whose position is to be determined are received by at least three base stations which are substantially synchronized with a standard time;

modifying equations in which products of a velocity of light and differences between an actual wave emitting time at which the radio wave is emitted from the wireless communication terminal of the mobile station and said measured times of receipt become equal to distances between said mobile station and said at least three base stations, into equations by means of which, calculated wave emitting times are derived for each of said at least three base stations by replacing a position of the mobile station by a plurality representative positions set in a simultaneous communication area in which said at least three base stations can simultaneously communicate with the mobile station;

deriving a sum of unsigned differences between two calculated wave emitting times in all combinations of two calculated wave emitting times obtained from at least three calculated wave emitting times for each of said plurality of representative points; and

determining a position of the mobile station at one of a plurality of representative points at which said sum becomes minimum.

14. A method according to claim 13, wherein said step of deriving the calculated wave emitting times is performed by initializing the position calculation area having a predetermined shape and a size, setting said representative points (xi, yi) within the position calculation area, calculating communication delay times at respective representative points from [(x−

xi)²+(y−

yi)²]^½

/C, wherein (x, y) denotes a position of the mobile station and C is a velocity of light, and calculating the calculated wave emitting times TMi as differences between the times of receipt Ti and the communication delay times.

15. A method according to claim 14, wherein said hybrid method is carried out such that said representative points in the base station method are set within an position estimation error range in the GPS method.

16. A method according to claim 14, wherein a step of measuring communication delay times from differences between the wave emitting time at the mobile station and the times of receipt at the base stations is performed at the communication control station or at the wireless communication terminal.

17. A method according to claim 14, wherein said step of determining a position of the mobile station is performed at the mobile station or at least one of said base stations while information is transmitted to the mobile station or at least one of said base stations through the communication control station.

18. A method according to claim 14, wherein a process of measuring communication delay times from differences between the wave emitting time and the times of receipt and a process of determining a position of the mobile station are performed at both the base stations and the communication control station.

19. A method according to claim 14, wherein a function of the communication control station is replaced by the base stations.

20. A method according to claim 14, wherein said sum of unsigned differences between two calculated wave emitting times in all combinations of two calculated wave emitting times obtained from at least three calculated wave emitting times is derived for all representative points which are distributed on the plane such that the required precision is satisfied.

21. A method according to claim 20, wherein said process of determining a position of the mobile station as a representative point at which the difference D becomes minimum is repeated each time a size of the position calculation area is reduced until a size of the position calculation area becomes not larger than the required precision.

22. A method according to claim 21, wherein said position calculation area is set to be a square shape, and a length of a side of the square position calculation area is reduced by 0.75 each time the position determining process is repeated.

23. A method according to claim 14, wherein said sum of unsigned differences between two calculated wave emitting times in all combinations of two calculated wave emitting times obtained from at least three calculated wave emitting times for each of said plurality of representative points is derived by making a sum of squares of unsigned differences.

24. A method according to claim 14, wherein said sum of unsigned differences between two calculated wave emitting times in all combinations of two calculated wave emitting times obtained from at least three calculated wave emitting times for each of said plurality of representative points is derived by making a sum of absolute values of unsigned differences.