Method, system and computer program product for positioning and synchronizing wireless communications nodes

• US 20050020275A1
• Filed: 08/15/2001
• Published: 01/27/2005
• Est. Priority Date: 08/15/2000
• Status: Active Grant

• Current Assignee: University of Maryland, College Park
• Original Assignee: University of Maryland, College Park
• Inventors: Szajda, Douglas C., Larsen, Ronald L., Shankar, A. Udaya, Agrawala, Ashok Kumar
• Granted Patent: US 7,224,984 B2
• Time in Patent Office: Days
• US Class Current: 455/456.100
• CPC Class Codes: G01S 11/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0244 Accuracy or reliability of position solution or of measurements contributing thereto
• CPC Class Codes: G01S 5/0289 of multiple transceivers, e.g. in ad hoc networks
• 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 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

An asset positioning method and system (700) rapidly and accurately determine the special location of wireless nodes distributed in three-dimensional space. Furthermore, as a by-product, every node also determines the relative offset and drift of every other node'"'"'s clock, so that it is possible for all nodes to carry out a precise synchronized action (708). The positioning and synchronization protocol has significant implications for a broad range of wireless networking infrastructure and applications. For instance, the rapid availability of accurate location information greatly simplifies and optimises the implementation of ad-hoc networks and sensor-based applications (716). Additionally, the synchronized node operations facilitate the development of new applications, such as phase-locked arrays, in which several low power transmitters coordinate to form a powerful group transmitter. Since the positioning protocol yields rapid responses and positional accuracy in the range of a few centimeters, the positioning protocol permits mobile nodes to be tracked while they are moving.

Claims

1. A method of determining the location of communications nodes in a distributed network, comprising the steps of:

creating, at a first node, a transmit timestamp for a message as said message is transmitted by said first node to a second node;

creating, at said second node, a receive timestamp as said message is received by said second node;

storing, at said second node, a measurement tuple corresponding to said message, wherein said storing includes recording an identifier for said first node, said transmit timestamp from said first node and said receive timestamp from said second node;

exchanging, by said second node, said measurement tuple with said first node, so that said first node and said second node each have a record of all measurement tuples stored therein; and

analyzing said record of measurement tuples to determine the location of said first node and said second node with respect to each other.

2. A method of claim 1, wherein said storing step is repeated at least once prior to said exchanging step.

3. A method of claim 1, wherein said analyzing step comprises determining a distance between said first node and said second node.

4. A method of claim 1, wherein said analyzing step comprises determining spatial coordinates for said first node and said second node.

5. A method of claim 1, wherein said exchanging step comprises exchanging, by said second node, said measurement tuple with multiple nodes, so that said second node and said multiple nodes each have a record of all measurement tuples stored therein;

whereby said analyzing step determines the location of said second node and said multiple nodes with respect to each other.

6. A method of claim 1, further comprising the step of determining clock attributes for at least one of said first node and said second node.

7. A method of claim 6, further comprising the step of determining clock attributes as a measure of relative offset and/or drift for at least one of said first node and said second node.

8. A method of claim 6, further comprising the step of synchronizing said first node and said second node with respect to each other based on one of said clock attributes.

9. A method of claim 1, further comprising the step of determining the location of a mobile sensor node while said mobile sensor node is in motion, wherein said mobile sensor node is one of said first node and said second node.

10. A method of claim 1, further comprising the step of determining the location of a sensor node in a wireless network, wherein said sensor node is one of said first node and said second node.

11. A method of claim 1, further comprising the step of transmitting said message and/or exchanging said measurement tuple at a UHF frequency.

12. A method of claim 1, wherein at least one of said first node and said second node is selected from a group consisting of an automobile, aircraft, submarine, and ship.

13. A method of claim 1, further comprising the step of determining the location of an object that is not a sensor node.

14. A method of claim 1, further comprising the steps of:

creating, at said second node, a transmit timestamp for a second message as said second message is transmitted by said second node to said first node;

creating, at said first node, a receive timestamp as said second message is received by said first node;

storing, at said first node, a second measurement tuple corresponding to said second message, wherein said storing includes recording an identifier for said second node, said transmit timestamp from said second node and said receive timestamp from said first node; and

exchanging, by said first node, said second measurement tuple with said second node, so that said second node and said first node each have a record of all second measurement tuples stored therein, wherein said analyzing step processes both sets of measurement tuples to determine the location of said first node and said second node with respect to each other.