Location finding system, using reflected radio frequency or acoustic signals in a crowded reflector environment

• US 20060198244A1
• Filed: 01/13/2006
• Published: 09/07/2006
• Est. Priority Date: 01/14/2005
• Status: Active Grant

• Current Assignee: Southwest Research Institute
• Original Assignee: Southwest Research Institute
• Inventors: Koets, Michael A.
• Granted Patent: US 7,130,243 B2
• Time in Patent Office: Days
• US Class Current: 367/37
• CPC Class Codes: G01V 1/001 Acoustic presence detection

Abstract

A method of locating one or more reflectors in an environment crowded with reflectors. A transmitter and multiple receivers are used to obtain reflected signals. Each path of a reflected signal is defined by an ellipse having the transmitter at one focus and a receiver at the other. A reflector is assumed to lie on the ellipse, and an intersection of ellipses is assumed to be a reflector location. The region is iteratively divided into smaller and smaller cells, and a search algorithm is performed to determine whether a given point in each cell lies on an ellipse. A “solution” is a point that lies on the same number of ellipses as the number of receivers.

Claims

1. A method of locating one or more reflectors in a region of interest, comprising:

using a transmitter to transmit a radio frequency or acoustic wave to a reflector;

using a set of receivers to receive a set of reflected signals;

calculating the path distance of each reflected signal;

defining an ellipse contour associated with each reflected signal, with the transmitter at one focus and the receiver of that signal at the other;

representing the region of interest as a first cell;

representing the cell as a point in the cell;

calculating the fit of the point to each ellipse contour;

if the point fits a sufficient number of ellipse contours, dividing the cell into smaller cells, each cell represented by a point in the cell;

repeating the calculating step for each new cell; and

determining the location of a reflector from the location of any cell containing a point that fits a sufficient number of ellipse contours.

2. The method of claim 1, wherein the dividing step is performed by dividing the cell into four cells.

3. The method of claim 1, wherein the calculating step is performed by transforming rectilinear coordinates of the region to a new coordinate space consisting of ellipsoids.

4. The method of claim 1, wherein the calculating step is performed by using a scoring function to determine the fit of the selected point to reflector criterion.

5. The method of claim 1, wherein the scoring function is based on the smallest region that contains the smallest circular region containing the cell.

6. The method of claim 1, wherein the sufficient number of ellipses is the same as the number of receivers.

7. The method of claim 1, wherein the cells are square and each cell is represented by a point in the center of that cell.

8. The method of claim 1, wherein the method is performed in two dimensions, such that the cells and ellipses are two dimensional.

9. The method of claim 1, wherein the method is performed in three dimensions, such that the cells and ellipses are three dimensional.