System and method for optimizing location estimate of mobile unit
View Patent ↗The location of a wireless mobile device may be estimated using, at least in part, one or more pre-existing Network Measurement Reports (“NMRs”) which include calibration data for a number of locations within a geographic region. The calibration data for these locations is gathered and analyzed so that particular grid points within the geographic region can be determined and associated with a particular set or sets of calibration data from, for example, one or more NMRs. Embodiments of the present subject matter also provide a method of improving a location estimate of a mobile device. Received signal level measurements reported by a mobile device for which a location estimate is to be determined may be evaluated and/or compared with the characteristics associated with the various grid points to estimate the location of the mobile device.
1. A method of locating a mobile device comprising the steps of:
(a) providing a plurality of grid points in a geographic region using a processor in a component of a communications network, each of said grid points including at least one characterizing parameter of calibration data;
(b) providing a plurality of network measurement reports for a mobile device in the geographic region;
(c) comparing data values associated with ones of said plurality of grid points to at least one parameter of ones of said plurality of network measurement reports;
(d) generating a first location estimate of the mobile device for each of said ones of said plurality of network measurement reports (“NMR”) based on the comparison performed in step (c);
(e) determining a second location estimate of the mobile device as a function of at least one of said generated first location estimates; and
(f) interpolating between ones of said plurality of grid points when more than one grid point corresponds to said at least one parameter of said plurality of network measurement reports,
wherein said interpolating is a function of the following relationship:
C _Ratio i =[C i −C min ]/[C N −C min ]
for a set of N grid points, N>1, where C i is a metric associated with an i th grid point, C N is a metric associated with the worst grid point, and C min is a metric associated with the best corresponding grid point.
2. The method of claim 1 further comprising the step of identifying and omitting outlier first location estimates by:
(i) determining a Mahalanobis distance from each first location estimate to the second location estimate;
(ii) determining a distance threshold from a median of the Mahalanobis distances multiplied by a predetermined factor; and
(iii) determining a third location estimate by averaging two or more of said first location estimates,
wherein first location estimates having a Mahalanobis distance to the second location estimate greater than the distance threshold are omitted from said determined third location estimate.
3. The method of claim 1 wherein determining a second location estimate further comprises averaging two or more first location estimates.
4. The method of claim 1 further comprising the step of omitting a first location estimate having an error estimate greater than a predetermined threshold.
5. The method of claim 1 wherein determining a second location estimate further comprises employing a weighted averaging of ones of said first location estimates.
6. The method of claim 1 wherein determining a second location estimate further comprises weighting a first location estimate by an inverse of a distance metric.
7. The method of claim 1 wherein determining a second location estimate further comprises normalizing a first location estimate by a sum of an inverse of a distance metric.
8. The method of claim 1 wherein determining a second location estimate further comprises weighting a first location estimate as a function of the number of reporting neighboring cells to a serving cell serving said mobile device.
9. The method of claim 1 wherein a grid point having a C_Ratio i less than a predetermined threshold is a candidate grid point for said interpolating.
10. The method of claim 1 wherein a grid point having a distance from the best corresponding grid point less than a predetermined threshold is a candidate grid point for said interpolating.
11. The method of claim 1 wherein comparing ones of said plurality of grid points further comprises generating a distortion measure which is a function of a combination of parameters of ones of said plurality of network measurement reports and corresponding parameters of ones of said plurality of grid points.
12. The method of claim 11 wherein said distortion measure is selected from the group consisting of: a Mahalanobis distance; a comparison of received signal strengths of a serving cell and a neighboring cell between ones of said plurality of NMRs and grid points; a comparison of received signal strengths of a neighboring cell between ones of said plurality of NMRs and grid points; a comparison of received signal strengths of a first common neighboring cell and another neighboring cell between ones of said plurality of NMRs and grid points; a comparison of average received signal strengths of reporting neighboring cells and received signal strengths of a neighboring cell between ones of said plurality of NMRs and grid points; a comparison of average received signal strengths of serving and reporting neighbor cells received signal strengths of a selected neighbor or serving cell between ones of said plurality of NMRs and grid points; and any combination thereof.
13. The method of claim 1 further comprising the step of providing a default location for said second location estimate when a second location estimate cannot be determined as a function of at least one of said generated first location estimates.
14. The method of claim 13 wherein said default location is a predetermined distance from a serving cell serving said mobile device at a heading along a serving sector azimuth.
15. The method of claim 13 wherein said default location is a function of timing advance or round trip time.
16. The method of claim 15 wherein said default location is an approximate range estimate from a serving cell serving said mobile device.
17. The method of claim 13 wherein said default location is a region determined as a function of a time difference of arrival (“TDOA”) measurement.
18. The method of claim 17 wherein said region is the intersection of a hyperbola defined by said TDOA with a timing advance region applicable to a serving cell serving said mobile device.
19. The method of claim 13 wherein said default location is determined as a function of a priori knowledge of sector coverage density.
20. A method of locating a mobile device comprising the steps of:
(a) providing a plurality of grid points in a geographic region using a processor in a component of a communications network, each of said grid points including at least one characterizing parameter of calibration data;
(b) providing a plurality of network measurement reports for a mobile device in the geographic region;
(c) comparing data values associated with ones of said plurality of grid points to at least one parameter of ones of said plurality of network measurement reports;
(d) generating a first location estimate of the mobile device for each of said ones of said plurality of network measurement reports (“NMR”) based on the comparison performed in step (c);
(e) determining a second location estimate of the mobile device as a function of at least one of said generated first location estimates; and
(f) interpolating between ones of said plurality of grid points when more than one grid point corresponds to said at least one parameter of said plurality of network measurement reports,
wherein said interpolating is a function of the following relationship:
C _Ratio i =[C i −C min ]/[C min ]
for a set of N grid points, N>1, where C i is a metric associated with an i th grid point and C min is a metric associated with the best corresponding grid point.
21. A method of locating a mobile device comprising the steps of:
(a) providing a plurality of grid points in a geographic region using a processor in a component of a communications network, each of said grid points including at least one characterizing parameter of calibration data;
(b) providing a plurality of network measurement reports for a mobile device in the geographic region;
(c) comparing data values associated with ones of said plurality of grid points to at least one parameter of ones of said plurality of network measurement reports;
(d) generating a first location estimate of the mobile device for each of said ones of said plurality of network measurement reports (“NMR”) based on the comparison performed in step (c);
(e) determining a second location estimate of the mobile device as a function of at least one of said generated first location estimates;
(f) interpolating between ones of said plurality of grid points when more than one grid point corresponds to said at least one parameter of said plurality of network measurement reports; and
(g) assigning weights to the i th grid point as a function of the following relationship:
Wi
=
1
Ci
∑
i
=
1
N
(
1
Ci
)
for a set of N grid points, N>1, where C i is a metric associated with an i th grid point.