SYSTEM AND METHOD FOR DETERMINING A LOCATION AREA OF A MOBILE USER

• US 20090156231A1
• Filed: 10/20/2008
• Published: 06/18/2009
• Est. Priority Date: 12/13/2007
• Status: Active Grant

• Current Assignee: InterDigital Patent Holdings, Inc. (InterDigital, Inc.)
• Original Assignee: Swisscom AG (Government of Switzerland)
• Inventors: TAILLARD, Eric, BAILLY, Patrick, LAURENT, Maxence, VERSTEEG, Ernst
• Granted Patent: US 8,532,608 B2
• Time in Patent Office: Days
• US Class Current: 455/456.100
• CPC Class Codes: G01S 5/02521 using a radio-map
• CPC Class Codes: G01S 5/0278 involving statistical or probabilistic considerations G01S5/0252, G01S5/0294 take precedence
• CPC Class Codes: H04B 7/026 Co-operative diversity, e.g. using fixed or mobile stations as relays
• CPC Class Codes: H04W 4/021 Services related to particular areas, e.g. point of interest [POI] services, venue services or geofences
• CPC Class Codes: H04W 64/003 locating network equipment

Abstract

A computer system determines location probabilities for defined sub-areas (41, 43) of a geographical area (4), e.g. for squares arranged in a grid (40), based on field strengths expected in the small sub-areas (41, 43) from the antennas (A1, A2 A3, A4), and based on the antenna used by the mobile communication terminal. The location probabilities indicate for a sub-area (41, 43) the probability that the mobile communication terminal is located in the respective sub-area (41, 43). The computer system determines at least one ellipse defining the location area, based on the location probabilities of the sub-areas (41, 43). The location probabilities make it possible to determine elliptical location areas of mobile users much smaller than the area each antenna does cover physically, but without the need for measuring at the mobile communication terminal signal properties such as signal strength or observed time differences.

Claims

1. A computer-implemented method of determining a location area of a user using a mobile communication terminal (1) in a geographical area (4) covered by a mobile radio network (2), the method comprising:

dividing (S3) the geographical area (4) into a plurality of sub-areas (41, 43);

determining (S4) for the sub-areas (41, 43) location probabilities, each location probability indicating the probability that the mobile communication terminal (1) is located in the respective sub-area (41, 43), based on field strengths expected in the sub-areas (41, 43) for antennas (A1, A2, A3, A4) located in the geographical area (4), and based on the antenna used by the mobile communication terminal (1); and

determining (S5) at least one ellipse (5) defining the location area, based on the location probabilities of the sub-areas (41, 43).

2. The method of claim 1, wherein determining (S5) the at least one ellipse (5) comprises:

defining (S51) a single ellipse (5) around a polygon (6) enveloping probable sub-areas having at least a defined minimum location probability;

assessing whether the single ellipse (5) defines the location area with a defined minimal density of probable sub-areas; and

determining more than one ellipse (5) for defining the location area, otherwise.

3. The method of claim 1, wherein determining (S5) the at least one ellipse (5) comprises:

defining (S51) a single ellipse (5) around a polygon (6) enveloping probable sub-areas having at least a defined minimum location probability; and

defining the location area by the single ellipse (5), if the number of the probable sub-areas is lower than a defined maximum number of sub-areas and a density of the probable sub-areas is higher than a defined minimum density, and determining more than one ellipse (5) for defining the location area, otherwise.

4. The method of one of claims 2 or 3, wherein determining more than one ellipse (5) comprises:

determining sub-areas to be considered by selecting from the sub-areas with descending location probability those sub-areas which together make up at least a defined target probability;

grouping the sub-areas to be considered into areas of connected sub-areas; and

determining an ellipse (5) around each of the areas of connected sub-areas to define the location area.

5. The method of claim 4, wherein grouping the sub-areas comprises:

determining an area of connected sub-areas by selecting with descending location probability, from the sub-areas to be considered, sub-areas which share a common border with a sub-area already included in the respective area of connected sub-areas;

removing selected sub-areas from the sub-areas to be considered; and

starting to determine an area of connected sub-areas with the sub-area of the remaining sub-areas to be considered having the highest location probability.

6. The method of one of claims 4 or 5, wherein determining more than one ellipse (5) further comprises:

determining whether the number of ellipses (5) obtained exceeds a defined maximum number of ellipses;

increasing the target probability, if the defined maximum number of ellipses (5) is exceeded; and

repeating the determining of more than one ellipse (5) using the increased target probability.

7. The method of one of claims 2 or 3, wherein determining more than one ellipse (E1, E2) comprises:

using for enlarging an ellipse (E2) those sub-areas closest to the ellipse (E2) which have an intermediate area (8) with at least a defined minimum mean location probability;

generating new ellipses at sub-areas where the mean location probability of the intermediate area (8) is below the minimum mean location probability, if a maximum number of ellipses has not been reached.

8. The method of claim 7, wherein the intermediate area (8) is a geometric object, placed between the sub-area in question (9) and the closest ellipse (E2) to the sub-area in question (9).

9. The method of one of claims 7 or 8, wherein determining more than one ellipse (E1, E2) further comprises:

lowering the defined minimum mean location probability of the intermediate area (8), if a defined target probability has not been reached; and

repeating the determining of more than one ellipse (E1, E2) using the lowered minimum mean location probability.

10. A computer system (3) for determining a location area of a user using a mobile communication terminal (1) in a geographical area (4) covered by a mobile radio network (2), the system (3) comprising:

a sub-area definition module (31) configured to divide the geographical area (4) into a plurality of sub-areas (41, 43);

an antenna determination module (34) configured to determine the antenna used by the mobile communication terminal (1);

means for determining for the sub-areas (41, 43) location probabilities, each location probability indicating the probability that the mobile communication terminal (1) is located in the respective sub-area (41, 43), based on field strengths expected in the sub-areas (41, 43) for antennas (A1, A2, A3, A4) located in the geographical area (4), and based on the antenna used by the mobile communication terminal (1); and

a location area determination module (37) configured to determine at least one ellipse (5) defining the location area, based on the location probabilities of the sub-areas (41, 43).

11. The system (3) of claim 10, wherein the location area determination module (37) is configured to determine the at least one ellipse (5) by defining a single ellipse (5) around a polygon (6) enveloping probable sub-areas having at least a defined minimum location probability;

assessing whether the number of the probable sub-areas is lower than a defined maximum of sub-areas and the single ellipse (5) defines the location area with a defined minimal density of probable sub-areas; and

determining more than one ellipse (5) for defining the location area, otherwise.

12. The system (3) of one of claims 10 or 11, wherein the location area determination module (37) is configured to determine more than one ellipse (5) by determining sub-areas to be considered by selecting from the sub-areas with descending location probability those sub-areas which together make up at least a defined target probability;

grouping the sub-areas to be considered into areas of connected sub-areas; and

determining an ellipse (5) around each of the areas of connected sub-areas to define the location area.

13. The system (3) of claim 12, wherein the location area determination module (37) is configured to group the sub-areas by determining an area of connected sub-areas by selecting with descending location probability, from the sub-areas to be considered, sub-areas which share a common border with a sub-area already included in the respective area of connected sub-areas;

removing selected sub-areas from the sub-areas to be considered; and

starting to determine an area of connected sub-areas with the sub-area of the remaining sub-areas to be considered having the highest location probability.

14. The system (3) of one of claims 12 or 13, wherein the location area determination module (37) is further configured to determine whether the number of ellipses (5) obtained exceeds a defined maximum number of ellipses;

increase the target probability, if the defined maximum number of ellipses is exceeded; and

repeat the determining of more than one ellipse (5) using the increased target probability.

15. The system (3) of one of claims 10 or 11, wherein the location area determination module (37) is configured to determine more than one ellipse (E1, E2) by enlarging an ellipse (E2) using those sub-areas closest to the ellipse (E2) which have an intermediate area (8) with at least a defined minimum mean location probability;

and generating new ellipses at sub-areas where the mean location probability of the intermediate area (8) is below the minimum mean location probability, if a maximum number of ellipses has not been reached.

16. The system (3) of claim 15, wherein the intermediate area (8) is a geometric object placed between the sub-area in question (9) and the closest ellipse (E2) to the sub-area in question (9).

17. The system (3) of one of claims 15 or 16, wherein the location area determination module (37) is further configured to lower the defined minimum mean location probability of the intermediate area (8), if a defined target probability has not been reached;

and repeat the determining of more than one ellipse (E1, E2) using the lowered minimum mean location probability.

18. A computer program product comprising computer program code means for controlling one or more processors of a computer system (3), such that the computer system (3)

stores a plurality of sub-areas (41, 43) for the geographical area (4);

determines the antenna used (S21) by the mobile communication terminal (1);

determines location probabilities for the sub-areas (41, 43), each location probability indicating the probability that the mobile communication terminal (1) is located in the respective sub-area (41, 43), based on field strengths expected in the sub-areas (41, 43) for antennas (A1, A2, A3, A4) located in the geographical area (4), and based on the antenna used by the mobile communication terminal (1); and

determines at least one ellipse (5) defining the location area, based on the location probabilities of the sub-areas (41, 43).

19. The computer program product of claim 18, comprising further computer program code means for controlling the processors of the computer system (3), such that the computer system (3) executes the method of one of the claims 1 to 9.