ESTIMATION OF GLOBAL POSITION OF A SENSOR NODE

• US 20080228437A1
• Filed: 02/04/2008
• Published: 09/18/2008
• Est. Priority Date: 03/31/2005
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Original Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Inventors: Damarla, Thyagaraju
• Granted Patent: US 8,060,338 B2
• Time in Patent Office: Days
• US Class Current: 702/151
• CPC Class Codes: G01S 5/02213 Receivers arranged in a network for determining the position of a transmitter
• CPC Class Codes: G01S 5/0289 of multiple transceivers, e.g. in ad hoc networks
• CPC Class Codes: G01S 5/18 using ultrasonic, sonic, or infrasonic waves

Abstract

Methods and apparatuses for locating a sensor node are disclosed. A representative apparatus, among others, includes a processing unit that receives sensor node data and object trajectory information data for an object. The sensor node data is related to the object'"'"'s trajectory, and a data point in the object trajectory information data comprises a time stamp and the coordinates of a position. The position corresponds the location of the object at the given time. The processing unit is adapted to correlate at least a portion of the sensor node data with at least a portion of the object trajectory information data to determine an absolute position of the sensor node.

Claims

1. A method of locating a sensor node, the method comprising:

collecting object trajectory information data for an object, wherein the object trajectory information data is collected over a first time span;

acquiring sensor node data at the sensor node, wherein the sensor node data is acquired over a second time span and is related to the object trajectory information data;

determining several direction indicators, each direction indicator providing an approximate sensor node bearing from the sensor node to the object at given instant of time during the second time span; and

determining coordinates of the sensor node using at least a portion of the collected trajectory information data and at least a portion of the acquired sensor node data.

2. The method of claim 1, wherein the trajectory information data includes multiple data points, each data point associates a specific instant of time with a position of the object at the specific instant of time.

3. The method of claim 2, wherein determining the coordinates further includes:

choosing a first data point from the trajectory information data; and

selectively choosing a second data point from the trajectory information data based upon a parameter and the first data point.

4. The method of claim 3, wherein the first data point is defined by a first position and a first time, the second data point is defined by a second position and a second time, the parameter corresponds to a specific distance, and the first and second positions are separated by a distance that is greater than the specific distance.

5. The method of claim 1, wherein the acquired sensor node data includes multiple data points, further including:

determining a first bearing angle for a first data point included in the trajectory information data;

determining a second bearing angle for a second data point included in the trajectory information data;

determining the difference between the first and second bearing angles;

determining whether the difference between the first and second bearing angles is greater than a predetermined amount; and

responsive to the difference being greater than the predetermined amount, determining not to use the second data point.

6. The method of claim 1, wherein determining coordinates of the sensor node further includes:

determining a first estimate of the sensor node coordinates;

determining an offset angle using the first estimate of the sensor node coordinates;

determining a second estimate of the sensor node coordinates using the offset angle and trajectory information data.

7. The method of claim 6, wherein determining a second estimate of the sensor node coordinates further includes:

selecting data points of the trajectory information data in sets of points;

for each set of data points of the trajectory information data, using a set of data points of the trajectory information data to determine a third estimate of the sensor node coordinates; and

averaging the set of third estimate of the sensor node coordinates, wherein the average of the set of third estimate of the sensor node coordinates is the second estimate of the sensor node coordinates.

8. The method of claim 1, wherein determining coordinates of the sensor node further includes the steps of:

determining a first estimate of the sensor node coordinates;

determining a set of sensor node bearing angles from the sensor node data;

determining a set of object bearing angles using the first estimate of the sensor node coordinates and the trajectory information data;

defining a grid about the first estimate of the sensor node coordinates;

determining for points on the grid the error between the set of sensor node bearing angles and the set of object bearing angles; and

determining a second estimate of the sensor node bearing angles based upon the determined errors.

9. The method of claim 1, wherein determining a second estimate of the sensor node coordinates further includes the step of:

synchronizing the sensor node data with the trajectory information data.

10. An apparatus for locating a sensor node, the apparatus comprising:

a processing unit that receives sensor node data and object trajectory information data for an object, wherein the sensor node data is related to the object trajectory information data, wherein a data point in the object trajectory information data comprises a time stamp, which corresponds to a given time, and coordinates of the object at the given time, wherein the processing unit is adapted to correlate at least a portion of the sensor node data with at least a portion of the object trajectory information data to determine an absolute position of the sensor node.

11. The apparatus of claim 10, wherein the sensor node data includes a sensor node bearing angle, which is measured from a local reference axis to a ray extending from the sensor node towards a given point, wherein the local reference axis is offset from a global reference axis by an offset angle, wherein the processing unit is adapted to synchronize the sensor node data with the object trajectory information data to eliminate the offset angle.

12. The apparatus of claim 11, wherein the processing unit is adapted to determine an estimate of the absolute position of the sensor node using at feast the difference in a pair of sensor node bearing angles and at least two data points included in the object trajectory information data.

13. The apparatus of claim 10, wherein the processing unit is adapted to selectively exclude data points in the trajectory information data such that the portion of the trajectory information data that is correlated with the sensor node data is a subset of the entire trajectory information data.

14. The apparatus of claim 13, wherein the processing unit excludes a data point of the trajectory information responsive to the data point corresponding to a first position that is less than a specific distance from a second position.

15. The apparatus of claim 10, wherein the processor unit is adapted to determine a first estimate of sensor node coordinates, determine an offset angle using the first estimate of the sensor node coordinates, and determine a second estimate of the sensor node coordinates using the offset angle and at least a portion of the trajectory information data.

16. The apparatus of claim 10, wherein the processor unit is adapted to synchronize at least a second portion of sensor node data with at least a second portion of the trajectory information data.

17. The apparatus of claim 10, further including:

a sensor node that acquires data regarding the object, wherein the sensor node is adapted to provide the sensor node data to the processing unit.

18. A program embodied in a computer readable medium, the program comprising:

logic configured to receive object trajectory information data for an object, wherein the object trajectory information data is collected over a first time span;

logic configured to receive sensor node data, wherein the sensor node data is acquired over a second time span and is related to the object trajectory information data;

logic configured to determine several direction indicators, each direction indicator providing an approximate sensor node bearing from the sensor node to the object at given instant of time during the second time span; and

logic configured to determine coordinates of the sensor node using at least a portion of the collected trajectory information data and at least a portion of the acquired sensor node data.

19. The program of claim 18, wherein the trajectory information data includes multiple data points, each data point associates a specific instant of time with a position of the object at the specific instant of time.

20. The program of claim 19, wherein the logic configured to determine the coordinates further includes logic configured to:

choose a first data point from the trajectory information data; and

selectively choose a second data point from the trajectory information data based upon a parameter and the first data point.

21. The program of claim 20, wherein the first data point is defined by a first position and a first time, the second data point is defined by a second position and a second time, the parameter corresponds to a specific distance, and the first and second positions are separated by a distance that is greater than the specific distance.

22. The program of claim 18, wherein the sensor node data includes multiple data points, further including logic configured to:

determine a first bearing angle for a first data point included in the trajectory information data;

determine a second bearing angle for a second data point included in the trajectory information data;

determine the difference between the first and second bearing angles;

determine whether the difference between the first and second bearing angles is greater than a predetermined amount; and

responsive to the difference being greater than the predetermined amount, determine not to use the second data point.

23. The program of claim 18, wherein the logic configured to determine coordinates of the sensor node further includes logic configured to:

determine a first estimate of the sensor node coordinates;

determine an offset angle using the first estimate of the sensor node coordinates;

determine a second estimate of the sensor node coordinates using the offset angle and trajectory information data.

24. The program of claim 23, wherein the logic configured to determine a second estimate of the sensor node coordinates further includes logic configured to:

select data points of the trajectory information data in sets of points;

for each set of data points of the trajectory information data, use a set of data points of the trajectory information data to determine a third estimate of the sensor node coordinates; and

average the set of third estimates of the sensor node coordinates, wherein the average of the set of third estimates of the sensor node coordinates is the second estimate of the sensor node coordinates.

25. The program of claim 18, wherein the logic configured to determine coordinates of the sensor node further includes logic configured to:

determine a first estimate of the sensor node coordinates;

determine a set of sensor node bearing angles from the sensor node data;

determine a set of object bearing angles using the first estimate of the sensor node coordinates and the trajectory information data;

define a grid about the first estimate of the sensor node coordinates;

determine for points on the grid the error between the set of sensor node bearing angles and the set of object bearing angles; and

determine a second estimate of the sensor node bearing angles based upon the determined errors.

26. The program of claim 25, wherein the logic configured to determine a second estimate of the sensor node coordinates further includes logic configured to:

synchronize the sensor node data with the trajectory information data.