Enhanced wireless node location using differential signal strength metric

• US 7,966,021 B2
• Filed: 09/12/2007
• Issued: 06/21/2011
• Est. Priority Date: 09/10/2004
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Systems, Inc.
• Inventors: Davi, Gregg Scott, Dietrich, Paul F.
• Primary Examiner(s): SANTIAGO CORDERO, MARIVELISSE
• Application Number:
  US11/854,499
• Publication Number:
  US 20080004042A1
• Time in Patent Office: 1,378 Days
• Field of Search: 455/456.1, 455/456.5, 455/456.6
• US Class Current: 455/456.1
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A wireless node location mechanism that employs a differential signal strength metric to reduce the errors caused by variations in wireless node transmit power, errors in signal strength detection, and/or direction-dependent path loss. As opposed to using the absolute signal strength or power of an RF signal transmitted by a wireless node, implementations of the location mechanism compare the differences between signal strength values detected at various pairs of radio receivers to corresponding differences characterized in a model of the RF environment. One implementation searches for the locations in the model between each pair of radio receivers where their signal strength is different by an observed amount.

Claims

1. A method for estimating the location of a wireless node relative to a plurality of radio receivers operative to detect the strength of radio frequency (RF) signals, wherein a plurality of RF coverage maps are associated with the plurality of radio receivers, wherein each RF coverage map corresponds to one of the radio receivers, and characterizes the signal strength values for locations in a physical region for the corresponding radio receiver, comprising:

collecting signal strength values, detected at a plurality of radio receivers, corresponding to signals transmitted by a wireless node;

determining a differential error surface comprising, for all unique pairs of three or more radio receivers of the plurality of radio receivers, the sum of the squares of the difference between the signal strength values detected by each pair of radio receivers less the difference between the signal strength values in the RF coverage maps associated with the pair of radio receivers; and

estimating the location of the wireless node using the differential error surface,

wherein the wireless node comprises an RF ID tag.