Wireless Based Positioning Method and Apparatus

• US 20090280835A1
• Filed: 05/01/2009
• Published: 11/12/2009
• Est. Priority Date: 05/06/2008
• Status: Active Grant

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Worrell, Gary C., Males, Jared R.
• Granted Patent: US 8,081,991 B2
• Time in Patent Office: Days
• US Class Current: 455/456.500
• 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
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A system and method is described herein to determine the physical location of a user within an edifice. At least three wireless access points, for example, 802.11 nodes, receives and transmits information to a handheld device in order to determine the location information.

Claims

1. A method for determining a users position employing a wireless network, said method comprising:

providing an edifice containing the wireless network comprised of a plurality of wireless access points throughout the edifice;

providing a handheld device operable to transmit and receive transmissions from the plurality of wireless access points;

transmitting location information from the at least three wireless access points to the handheld device;

receiving said transmitted location information at the handheld device;

processing said transmitted location information to determine location of handheld device within the edifice.

2. The method as claimed in claim 1, wherein said processing further comprises:

measuring radio signal power of the at least three wireless access points;

receiving spatial coordinates of the at least three wireless access points;

estimating the distance from the handheld device to the at least three wireless access points by processing the measured radio signal power and the received spatial coordinates;

determining the location of the handheld device within the edifice by comparing the estimated distance to the predetermined locations of the at least three access points within the edifice.

3. The method of claim 1, wherein said transmitted location information includes determining the three dimensional spatial coordinates of each network access point by using a floor plan of the edifice, determining the radio signal power of each network access point at a fixed predetermined distance, encoding said spatial coordinate information and radio signal power, transmitting said encoded spatial coordinate information and radio signal power at a fixed predetermined distance, receiving said encoded information, and decoding and comparing said information for each access point with measured radio signal power of that access point at the location of the handheld device.

4. The method of claim 3, wherein GPS information is used to determine the three dimensional spatial coordinate of one or more of the access points.

5. The method of claim 4, wherein said encoding and comparing further comprising:

providing the measured radio signal power of two of the at least three access points and the predetermined radio power of each at a fixed predetermined distance to calculate a squared ratio of the estimated distances to two of the at least three access points being compared by the following, where

$Q_{\mathrm{ij}}=\left(\frac{k_i}{k_j}\right)<br><br>\left(\frac{P_{\mathrm{rj}}}{P_{\mathrm{ri}}}\right).$

providing the squared ratio of the estimated distances to the two of the at least three access points being compared and the three dimensional spatial coordinates of the two of the at least three access points being compared to calculate the three dimensional coordinates of the center and the radius of a sphere forming the locus of all points where the ratio of the estimated distances is constant;

$x_{\mathrm{cij}}=\frac{x_i-Q_{\mathrm{ij}}<br><br>x_j}{1-Q_{\mathrm{ij}}}$ $y_{\mathrm{cij}}=\frac{y_i-Q_{\mathrm{ij}}<br><br>y_j}{1-Q_{\mathrm{ij}}}$ $z_{\mathrm{cij}}=\frac{z_i-Q_{\mathrm{ij}}<br><br>z_j}{1-Q_{\mathrm{ij}}}$ $d_{\mathrm{cij}}^2=\frac{Q_{\mathrm{ij}}<br><br>d_{\mathrm{ij}}^2}{{\left(1-Q_{\mathrm{ij}}\right)}^2}$

providing these parameters to calculate the distance between a three dimensional spatial coordinate and the surface of the sphere defined by these parameters;

Δ

d_ij=√

{square root over ((x_cij−

x)²+(y_cij−

y)²+(z_cij−

z)²)}{square root over ((x_cij−

x)²+(y_cij−

y)²+(z_cij−

z)²)}{square root over ((x_cij−

x)²+(y_cij−

y)²+(z_cij−

z)²)}−

√

{square root over (d_cij²)}.

determining the three dimensional spatial coordinates by minimizing the distance between a three dimensional spatial coordinate and the surface of the sphere and using the three dimensional coordinates as the estimate of the three dimensional spatial coordinates of the handheld device.

6. A system for determining a users position employing a wireless network, said method comprising:

an edifice containing the wireless network comprised of a

plurality of wireless access points throughout the edifice operable to transmit and receive location information from the at least three wireless access points;

a handheld device operable to transmit and receive transmissions from the plurality of wireless access points and process said transmissions from the wireless access points to determine location information of the users within said edifice.

7. A computer readable medium operable to determine a users position employing a wireless network, said method comprising:

a first set of instructions to provide an edifice containing the wireless network comprised of a plurality of wireless access points throughout the edifice;

a second set of instructions to provide a handheld device operable to transmit and receive transmissions from the plurality of wireless access points;

a third set of instructions transmitting location information from the at least three wireless access points to the handheld device;

a fourth set of instructions receiving said transmitted location information at the handheld device;

a fifth set of instructions processing said transmitted location information to determine location of handheld device within the edifice.