LOCATION ESTIMATION IN PARTIALLY SYNCHRONIZED NETWORKS

• US 20050049821A1
• Filed: 08/26/2003
• Published: 03/03/2005
• Est. Priority Date: 08/26/2003
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Information Technology Center America, Inc. (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Electric Information Technology Center America, Inc. (Mitsubishi Electric Corporation)
• Inventors: Sahinoglu, Zafer
• Granted Patent: US 6,885,969 B2
• Time in Patent Office: Days
• US Class Current: 702/150
• CPC Class Codes: G01S 5/0289 of multiple transceivers, e.g. in ad hoc networks
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A method locates a mobile node in a partially synchronized wireless network comprised of nodes with heterogeneous communication ranges. The time intervals it takes for messages to travel from stationary nodes at known location to a mobile node at an unknown location are measured and used to determine a set of possible coordinates of the mobile node. This time-based set of coordinates is in the form of a hyperbolic function. The received signal strengths of a message received from the mobile node is measured in two additional stationary nodes at known location. These RSS-based measurements provide two more sets of possible coordinates of the mobile node. The three sets are then intersected to estimate the location of the mobile node.

Claims

1. A method for locating a mobile node in a partially synchronized wireless network, comprising:

measuring a first time interval to transmit a first message from a first stationary node at a first known location to a mobile node at an unknown location;

measuring a second time interval to transmit a second message from a second stationary node at a second known location to the mobile node, in which the first stationary node is time synchronized with the second stationary node;

broadcasting from the mobile node, a third message to a third stationary node at third known location and a fourth stationary node at fourth known location;

measuring a first received signal strength of a the third message at the third stationary node;

measuring a second received signal strength of the third message at the fourth stationary node;

determining a first set of possible coordinates of the mobile node from the first time interval and the second time interval;

determining a second set of possible coordinates of the mobile node from the first received signal strength;

determining a third set of possible coordinates of the mobile node from the second received signal strength; and

intersecting the first, second and third sets of possible coordinates of the mobile node to estimate a location of the mobile node.

2. The method of claim 1, in which each node includes a unique identification, and each message includes a unique serial number.

3. The method of claim 1, in which the mobile nodes are sensor nodes in an ad hoc wireless network.

4. The method of claim 1, in which the messages are transmitted in response to a locate request message identifying the mobile node.

5. The method of claim 1, in which the first set of possible coordinates is a solution set of a hyperbolic function.

6. The method of claim 1, in which the first and second set of possible coordinates are solution sets of circular functions.

7. The method of claim 1, in which a communication rage of the mobile node is substantially less than a transmit communication range of the stationary nodes.

8. A system for locating a mobile node in a partially synchronized wireless network, comprising:

a mobile node at an unknown location configured to obtain a first time interval to transmit a first message from a first stationary node at a first known location to the mobile node and a second time interval to transmit a second message from a second stationary node at a second known location to the mobile node, in which the first stationary node is time synchronized with the second stationary node, and further configured to broadcast a third message to a third stationary node at a third location and a fourth stationary node at a fourth known location;

a third stationary node at a third known location configured to measure a first received signal strength of a third message broadcast by the mobile node;

a fourth stationary node at a fourth known location configured to measure a second received signal strength of the third message broadcast by the mobile node;

means for determining a first set of possible coordinates of the mobile node from the first time interval and the second time interval, a second set of possible coordinates of the mobile node from the first received signal strength, and a third set of possible coordinates of the mobile node from the second received signal strength; and

means for intersecting the first, second and third sets of possible coordinates of the mobile node to estimate a location of the mobile node.