Location Accuracy Improvement Using a priori Probabilities

• US 20120052835A1
• Filed: 08/27/2010
• Published: 03/01/2012
• Est. Priority Date: 08/27/2010
• Status: Active Grant

• Current Assignee: Skyhook Holding, Inc. (Liberty Broadband Corp.)
• Original Assignee: TruePosition Incorporated
• Inventors: Bull, Jeffrey F., Mia, Rashidus S., Anderson, Robert J.
• Granted Patent: US 8,478,291 B2
• Time in Patent Office: Days
• US Class Current: 455/404.2
• 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: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A large volume of high accuracy location data is determined in many commercial wireless networks from location based services (LBS) and, in the United States, for E911. Uplink-Time-Difference-of-Arrival (UTDOA) and Assisted GPS (AGPS) are the predominant geolocation technologies providing these high accuracy locations. In the US alone over 10 million wireless subscribers are located every month because they dial the national emergency number “911” on their mobile phones. This rich set of location data provides an a priori distribution of the location of subscribers in the wireless network. All digital wireless communications networks have a mechanism for the subscribers to time synchronize their handsets to the network. This mechanism provides a band of ranges from the serving cell site to the handset. An a posteriori location estimate can be determined very quickly by considering the a priori distribution of callers in the range band that the current subscriber is in.

Claims

1. A cell identification with ranging wireless location method for determining a subscriber handset location estimate, wherein the method is for use in association with a wireless communications network (WCN) including a mechanism to determine an initial, low accuracy location estimate based on a range estimate and a cell sector identifier, and wherein the location method employs a predetermined distribution of high accuracy subscriber handset location estimates together with an initial, low accuracy location estimate, comprising:

defining a grid overlaying the coverage area of the WCN, wherein the grid includes a plurality of grid boxes each of which corresponds to a respective geographic area;

associating with each box of the grid a number representing a count of high accuracy subscriber handset locations corresponding to the geographic area associated with that cell;

determining an expected location for each of a plurality of range bands in the WCN;

receiving an initial location estimate for a subscriber handset, wherein said initial location estimate includes a range value and a cell sector identifier; and

in response to receiving the initial location estimate for said subscriber handset, providing an improved accuracy location estimate based on the expected location and the range value of the initial location estimate.

2. A method as recited in claim 1, wherein said range value is based on a timing advance (TA) value.

3. A method as recited in claim 1, wherein said range value is based on a power measurement.

4. A method as recited in claim 2, wherein the WCN includes a mechanism for subscriber handsets to time synchronize to the network and to determine an initial, low accuracy location estimate based on a timing advance (TA) value and a cell global identifier (CGI), and wherein said initial location estimate is a low accuracy estimate based on a TA value and a CGI.

5. A method as recited in claim 1, wherein the initial location estimate is based on network-based timing or power measurements.

6. A method as recited in claim 1, wherein the initial location estimate is based on handset-based timing or power measurements.

7. A method as recited in claim 1, further comprising updating at least one number associated with a box of the grid as new high accuracy subscriber handset location data are provided.

8. A method as recited in claim 1, wherein determining an improved location for the plurality of range bands comprises utilizing configuration information about the configuration of the WCN.

9. A method as recited in claim 8, wherein said configuration information comprises at least one of the following:

cell site location information, sector type information, sector orientation information, sector antenna beamwidth information, and sector identification information.

10. A method as recited in claim 1, wherein said grid boxes have a resolution consistent with that of the high accuracy geolocation system.

11. A method as recited in claim 1, wherein the WCN includes a database populated with high accuracy location data from location based services (LBS) and emergency services.

12. A method as recited in claim 11, wherein the high accuracy location data is pre-determined using uplink-time-difference-of-arrival (UTDOA) and assisted GPS (AGPS) geolocation technologies.

13. A method as recited in claim 1, wherein a location node associated with the WCN contains means for location calculation using an improved Cell-ID engine for performing cell-ID with timing-based or and/or power-based ranging with historical, high accuracy location data.

14. A method as recited in claim 13, wherein the cell-ID with timing-based and/or power-based ranging includes at least one of:

Cell-Global-Identifier with Timing Advance (CGI+TA), Cell Identifier with Round Trip Time (CI+RTT), Cell-Global-Identifier with Received Signal Strength Indicator (CGI+RSSI), Cell Identity with Reference Signal Received Quality (RSRQ), Physical Cell ID with LTE Timing Advance (PCI+Tadv).

15. A method as recited in claim 13, wherein the location node is coupled to or includes a coverage area sectional database (CASD) comprising data concerning the WCN'"'"'s service area, mapping data, and radio access network (RAN) settings and parameters.

16. A method as recited in claim 13, wherein the location node is coupled to or includes an improved cell-id with ranging database (ICRD) comprising a model of at least one sub-sectioned coverage area with associated call details.

17. A method as recited in claim 16, wherein the model of the sub-sectioned the coverage area includes a plurality of ranging bands and separately addressable geographic grid boxes.

18. A method as recited in claim 1, comprising a process for obtaining data concerning WCN settings and parameters and merging that data with geographical data, said process comprising:

obtaining WCN information and geographic information via electronic transfer from an Operational Support System (OSS) that manages provisioning and inventory databases for WCN, and obtaining geographic information from a Geographic Information System (GIS), wherein the collected WCN information includes at least one of the following;

location of cell sites, identifier for each cell site, number of sectors at each cell site, identifier for each sector, orientation of each sector, angular range of each sector, maximum range of each sector, radial width of each range band, WCN identifier of each range band;

determining nominal geographic coverage areas of the range band;

sectioning the coverage areas and forming separately addressable, geographical grid boxes corresponding to the service area, wherein the size of the grid boxes is selected to be consistent with the accuracy of the highest accuracy location technique providing a priori location estimates, and wherein coordinates of the center of each grid box are recorded such that each grid box possesses an identifying number and location; and

using the coverage areas and range bands, creating an initial association of grid boxes with coverage areas and range bands.

19. A method as recited in claim 18, further comprising constructing and numbering power level contours to form range bands for power-based range measurements.

20. A method as recited in claim 16, comprising a process for populating the improved cell-ID with ranging database, said process comprising:

obtaining high accuracy location estimates for calls placed within one or more coverage areas; and

associating each a priori high accuracy location estimate with a grid box, wherein a location counter is associated with each grid box and is updated and one or more range bands associated with the updated grid box is identified and an a posteriori, improved location estimate for the range band(s) is updated.

21. A method as recited in claim 20, wherein the improved location estimate for each range band is calculated by multiplying the latitude and longitude of each grid box by the number of location estimates associated with each grid box in the range band, summing the results for all grid boxes in the range band, and then dividing the results by the summation of the number of location estimates in all grid boxes in the range band.

22. A method as recited in claim 16, comprising populating the ICRD at start-up with recorded high accuracy extended location records without need for prior range band mapping

23. A method as recited in claim 16, comprising populating the ICRD over time using high accuracy extended location records without need for prior range band mapping.

24. A method as recited in claim 21, further comprising using extended high accuracy location records to adjust one or more range bands.

25. A method as recited in claim 20, further comprising using time and date information associated with high accuracy location records to improve the accuracy of a cell-id with ranging location estimate.

26. A method as recited in claim 20, further comprising indexing of the ICRD with calling/called number information or services identifier information.

27. A computer readable medium comprising instructions that, when executed by a processor, cause the processor to carry out a cell identification with ranging wireless location method, wherein the method comprises:

defining a grid overlaying the coverage area of the WCN, wherein the grid includes a plurality of grid boxes each of which corresponds to a respective geographic area;

associating with each box of the grid a number representing a count of high accuracy subscriber handset locations corresponding to the geographic area associated with that grid box;

determining an expected location for each of a plurality of range bands in the WCN;

receiving an initial location estimate for a subscriber handset, wherein said initial location estimate includes a range value and a cell sector identifier; and

in response to receiving the initial location estimate for said subscriber handset, providing an improved accuracy location estimate based on the range value of the initial location estimate and the expected location.

28. A cell identification with ranging wireless location system for determining a subscriber handset location estimate, wherein the system is for use in association with a wireless communications network (WCN) including a mechanism to determine an initial, low accuracy location estimate based on a range estimate and a cell sector identifier, comprising:

means for defining a grid overlaying the coverage area of the WCN, wherein the grid includes a plurality of grid boxes each of which corresponds to a respective geographic area;

means for associating with each box of the grid a number representing a count of high accuracy subscriber handset locations corresponding to the geographic area associated with that cell;

means for determining an expected location for each of a plurality of range bands in the WCN;

means for receiving an initial low accuracy subscriber handset location estimate based on a range value and a cell sector identifier; and

means for providing an improved accuracy location estimate based on the initial location estimate and the expected location.