Method for correcting NLOS error in wireless positioning system

• US 20040127228A1
• Filed: 12/30/2002
• Published: 07/01/2004
• Est. Priority Date: 12/30/2002
• Status: Active Grant

• Current Assignee: KT Corporation, University of Cincinnati
• Original Assignee: KT Corporation, University of Cincinnati
• Inventors: Venkatraman, Saipradeep, Caffery, James J. Jr., You, Heung Ryeol, Al-Jazzar, Saleh
• Granted Patent: US 7,065,368 B2
• Time in Patent Office: Days
• US Class Current: 455/456.1
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• 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

Provided is a method for correcting a non-line-of-sight (NLOS) error in a wireless positioning system that enhances the location accuracy of a mobile station by correcting location error caused by NLOS propagation when the mobile station is positioned in a wireless mobile communication environment, and a computer-readable recording medium for recording a program that implements the method. The method checks out the location of the MS in the above environment and provides diverse services by correcting the location error caused by NLOS propagation included in a received signal. That is, a user can enjoy a high-quality location service by receiving the location information only within the radius which user wants, such as traveler'"'"'s information, vehicle tracking, location service, and location-based advertisements, because the location of the user'"'"'s MS is detected precisely.

Claims

1. A method for correcting a non-line-of-sight (NLOS) error in a wireless positioning system, comprising the steps of:

a) determining whether the number of received signals from a mobile station (MS) is larger than a predetermined number;

b) if the number of the received signals from the mobile station is equal to or less than the predetermined number, determining a location of the MS based on a weighting factors obtained through an optimization process with respect to each of the received signals which are assumed to include an error caused by NLOS propagation; and

c) if the number of the received signals from the mobile station is larger than the predetermined number, determining a location of the MS based on second moments of the received signals.

2. The method as recited in claim 1, wherein the step b) includes the steps of:

b1) making constraints and obtaining a weighting factors through an optimization process with respect to each received signal which is assumed to include an error caused by NLOS propagation; and

b2) based on the weighting factors, correcting the NLOS error and determining the location of the MS.

3. The method as recited in claim 2, wherein a cost function of the location of the MS is expressed by an equation as:

f(x,y)=(x−

U_x)²+(y−

U_y)²+(x−

V_x)²+(y−

V_y)²+(x−

W_x)²+(y+W_y)²

where U, V and W denote coordinates of points in which three circles are overlapped, x and y denote coordinates of the location of the MS.

4. The method as recited in claim 2, wherein the NLOS error is corrected by obtaining a NLOS distance using a linear line of position (LLOP) algorithm.

5. The method as recited in claim 4, wherein the location of the MS is expressed by an equation as:

Minimize F(v) Subject to g(v)=0, LB≦

v≦

UB

wherein the LB and UB are as follows;

$v=\left[\begin{array}{c}\mathrm{\alpha <br><br>}\\ \mathrm{\beta <br><br>}\\ \mathrm{\gamma <br><br>}\end{array}\right],L<br><br>\text{\hspace{1em}<br><br>}<br><br>B=\left[\begin{array}{c}{\mathrm{\alpha <br><br>}}_{\min }\\ {\mathrm{\beta <br><br>}}_{\min }\\ {\mathrm{\gamma <br><br>}}_{\min }\end{array}\right],U<br><br>\text{\hspace{1em}<br><br>}<br><br>B=\left[\begin{array}{c}1\\ 1\\ 1\end{array}\right].$

6. The method as recited in claim 1, wherein the step c) includes the steps of:

c1) obtaining second moments of a signal which is assumed to include an error caused by NLOS propagation, and comparing the second moments with theoretical values of scattering models;

c2) based on the comparison result, obtaining LOS distance and parameters of the scattering models; and

c3) based on the LOS distance and the parameters, correcting the NLOS error and determining the location of the MS.

7. The method as recited in claim 6, wherein the NLOS error is corrected through one of a ring of scatterers (ROS) model, disk of scatterers (DOS) model and Gaussian distributed scattering model.

8. The method as recited in claim 6, wherein the NLOS error is corrected by matching the mean and variance obtained from the ROS/DOS/Gaussian scattering model using the second moments with the mean and variance obtained from the received signal.

9. The method as recited in claim 8, wherein in case of the ROS scattering model, the mean and the variance are expressed by equations as:

${\widehat{\mathrm{\mu <br><br>}}}_{\mathrm{ROS},j}=R_j+2<br><br>r_{\mathrm{ROS}}-\left(r_{\mathrm{ROS}}+\frac{1}{\mathrm{\pi <br><br>}}<br><br>\frac{317<br><br>r_{\mathrm{ROS}}^2}{420<br><br>\text{\hspace{1em}<br><br>}<br><br>R_j}+\frac{1}{\mathrm{\pi <br><br>}}<br><br>\frac{r_{\mathrm{ROS}}^4}{35<br><br>\text{\hspace{1em}<br><br>}<br><br>R_j^3}+\frac{1}{\mathrm{\pi <br><br>}}<br><br>\frac{2<br><br>r_{\mathrm{ROS}}^6}{1155<br><br>\text{\hspace{1em}<br><br>}<br><br>r_j^5}\right)${circumflex over (σ

)}_ROS,j²=R_j²+4R_jr_ROS4r_ROS²$-\frac{2}{\mathrm{\pi <br><br>}}<br><br>\left(\mathrm{\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>R_j<br><br>r_{\mathrm{ROS}}+\mathrm{\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>r_{\mathrm{ROS}}^2+\frac{317<br><br>r_{\mathrm{ROS}}^3}{420<br><br>\text{\hspace{1em}<br><br>}<br><br>R_j}+\frac{r_{\mathrm{ROS}}^5}{35<br><br>\text{\hspace{1em}<br><br>}<br><br>R_j^3}+\frac{2<br><br>r_{\mathrm{ROS}}^7}{1155<br><br>\text{\hspace{1em}<br><br>}<br><br>R_j}-{\widehat{\mathrm{\mu <br><br>}}}_{\mathrm{ROS},j}^2\right)$

where {circumflex over (μ

)}_ROS,j and {circumflex over (σ

)}_ROS,j² are a mean and a variance of the ROS scattering model, and R_j is a distance between the BS and the MS.

10. The method as recited in claim 8, wherein in case of the DOS scattering model, the mean and the variance are expressed by equations as:

11. The method as recited in claim 8, wherein in case of the Gaussian distributed scattering model, the mean and the variance are expressed by equations as:

12. The method as recited in claim 8, wherein the NLOS error is corrected by using a gradient algorithm, such as the Newton-Raphson method, to obtain a solution, in case of the ROS model.

13. The method as recited in claim 8, wherein the NLOS error is corrected by forming an error domain and matching the means and variances numerically, in case where a closed form of a solution cannot be obtained.

14. The method as recited in claim 13, wherein the size of the error domain is balanced by using a determinant of a standard deviation, instead of the variance.

15. The method as recited in claim 14, wherein the minimum value of the error domain is obtained by using a Nedler-Mead algorithm.

16. The method as recited in claim 6, wherein the NLOS error is corrected by obtaining a LOS distance using a LLOP algorithm.

17. A computer-readable recording medium for recording a program for executing a method for correcting a non-line-of-sight (NLOS) error in a wireless positioning system, comprising the steps of:

a) determining whether the number of received signals from a mobile station (MS) is larger than a predetermined number;

b) if the number of the received signals from the mobile station is equal to or less than the predetermined number, determining a location of the MS based on a weighting factors obtained through an optimization process with respect to each of the received signals which is assumed to include an error caused by NLOS propagation; and

c) if the number of the received signals from the mobile station is larger than the predetermined number, determining a location of the MS based on second moments of the received signals.

18. The computer-readable recording medium as recited in claim 17, wherein the step b) includes the steps of:

b1) making constraints and obtaining a weighting factors through an optimization process with respect to each received signal which is assumed to include an error caused by NLOS propagation; and

b2) based on the weighting factors, correcting the NLOS error and determining the location of the MS.

19. The computer-readable recording medium as recited in claim 17, wherein the step c) includes the steps of:

c1) obtaining second moments of a signal which is assumed to include an error caused by NLOS propagation, and comparing the second moments with theoretical values of scattering models;

c2) based on the comparison result, obtaining LOS distance and parameters of the scattering models; and

c3) based on the LOS distance and the parameters, correcting the NLOS error and determining the location of the MS.