METHOD FOR AN IMPROVED LINEAR LEAST SQUARES ESTIMATION OF A MOBILE TERMINAL'S LOCATION UNDER LOS AND NLOS CONDITIONS AND USING MAP INFORMATION

• US 20090069029A1
• Filed: 09/02/2008
• Published: 03/12/2009
• Est. Priority Date: 09/12/2007
• Status: Active Grant

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Inventors: Inamura, Hiroshi, Watanabe, Fujio, Guvenc, Ismail
• Granted Patent: US 8,219,111 B2
• Time in Patent Office: Days
• US Class Current: 455/456.100
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A linear least squares (LLS) estimator provides a low complexity estimation of the location of a mobile terminal (MT), using one of the fixed terminals (FTs) as a reference FT to derive a linear model. A method for selecting a reference FT is disclosed, which improves the location accuracy relative to an arbitrary approach to selecting the reference FT. In addition, a covariance-matrix based LLS estimator is proposed in line-of-sight (LOS) and non-LOS (NLOS) environments to further provide accuracy, taking advantage of the correlation of the observations. Different techniques for selecting the reference FT under non-LOS (NLOS) conditions are disclosed. A map-based two-stage LLS estimator assists in selecting the reference FT under NLOS conditions.

Claims

1. A method for localization of a mobile terminal using the known positions of a plurality of fixed terminals, comprising:

selecting a reference terminal from the fixed terminals according to a predetermined selection criterion;

using the characteristics of the reference terminal, creating a linear model that relates the measured distances of the fixed terminals relative to the positions of the fixed terminals; and

based on the linear model, determining the position of the mobile terminal using a location estimator,

2. A method as in claim 1, wherein the selection criterion comprises selecting as the reference terminal the fixed terminal having the least measured distance from the mobile terminal.

3. A method as in claim 1, wherein the selection criterion excludes fixed terminals under non-line-of-sight (NLOS) conditions relative to the mobile terminal.

4. A method as in claim 3, wherein the selection criterion includes a fixed terminal under NLOS conditions provided the measured distance between the fixed terminal and the mobile terminal is less than a predetermined threshold.

5. A method as in claim 1, wherein the location estimator comprises a linear least squares (LLS) estimator.

6. A method as in claim 1, wherein the location estimator comprises a maximum likelihood (ML) estimator.

7. A method as in claim 6, further comprises computing a covariance matrix of the linear model.

8. A method as in claim 7, wherein the linear model includes noise and non-line-of-sight (NLOS) bias in the measured distance between each fixed terminal and the mobile terminal.

9. A method as in claim 8, wherein the covariance matrix is calculated using values of one or more of the NLOS biases.

10. A method as in claim 8, wherein the covariance matrix is calculated using variances of one or more of the NLOS biases.

11. A method as in claim 8, wherein the measured distances are corrected for measured values of the NLOS biases.

12. A method as in claim 8, wherein the measured distances are corrected for expected values of the NLOS biases.

13. A method as in claim 1, wherein the measured distances are calculated from time-of-arrival measurements.

14. A method as in claim 1, wherein the measured distances are calculated from received signal strength measurements.

15. A method as in claim 1, further comprising, prior to selecting the reference terminal:

providing an initial estimate of the location of the mobile terminal; and

based on the initial estimate and geographical map information, determining an existence of non-line-of-sight (NLOS) condition between each fixed terminal and the mobile terminal.

16. A method as in claim 15, wherein the selecting the reference terminal further takes into account the NLOS conditions determined.

17. A method as in claim 1, wherein the selection criterion comprises selecting as the reference terminal the fixed terminal having the least measured noise variance.

18. A method as in claim 1, wherein the selection criterion comprises selecting as the reference terminal the fixed terminal having the least noise standard deviation and distance product.