Method and system for providing a GPS-based position

• US 8,165,728 B2
• Filed: 08/19/2008
• Issued: 04/24/2012
• Est. Priority Date: 08/19/2008
• Status: Expired due to Fees

• Current Assignee: Navy The USA As Represented By The Secretary of The
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Schultz, Abraham
• Primary Examiner(s): Dager, Jonathan M
• Application Number:
  US12/193,985
• Publication Number:
  US 20100049376A1
• Time in Patent Office: 1,344 Days
• Field of Search: 701 1- 14, 701/23, 701200-225, 701300-302, 342350-35752, 340988-996
• US Class Current: 701/2
• CPC Class Codes: G01S 19/40 Correcting position, velocity or attitude
• CPC Class Codes: G01S 19/51 Relative positioning
• CPC Class Codes: G01S 5/0027 of actual mobile position, i.e. position determined on mobile
• CPC Class Codes: G01S 5/0072 Transmission between mobile stations, e.g. anti-collision systems
• CPC Class Codes: G01S 5/0284 Relative positioning

Abstract

A cooperative engagement group-position determining system employs a group of at least three cooperative units, for example a group of unmanned aerial vehicles (UAV'"'"'s), with each unit including a GPS system for determining a GPS-based position, an inter-distance measurement module for measuring a distance of the unit relative to at least one other unit, and a computer having a computer-readable storage medium encoded with a program algorithm for correcting the GPS-based position based on at least one relative distance between two units, providing an improved GPS-based position for the unit and for the group. The system can also include a ground controller, for example, for providing flight control for UAV'"'"'s.

Claims

1. A cooperative engagement group-position determining system, comprising:

a group of at least three cooperative units, wherein each said unit comprises;

i) a GPS system for determining a GPS-based position;

ii) an inter-distance measurement module for measuring a distance of the unit relative to at least one other unit; and

iii) a computer including a computer-readable storage medium encoded with a program algorithm that includes instructions for correcting the GPS-based position based on at least one relative distance between two units to thereby provide an improved GPS-based position for the unit and for the group; and

wherein the algorithm comprises an iterative process for i) generating a set of position vectors for each unit to thereby obtain a set of computed positional data and inter-distances for each unit and ii) minimizing a mean square error between the inter-distances and the GPS-based position, thereby correcting the GPS-based position and providing the improved GPS-based position, and repeating steps i) and ii) until a desired degree of convergence and a final converged estimate of positions of units is obtained, and wherein the GPS errors over all units in the cluster are averaged by applying a rigid body transformation of space to the final converged estimate of positions of units to thereby minimize an objective function of the type given by E=D(A⁽ⁿ⁾, A)+D(B⁽ⁿ⁾, B)+D(C⁽ⁿ⁾, C), where A⁽ⁿ⁾, B⁽ⁿ⁾ and C⁽ⁿ⁾ are the final converged estimate of positions of units.

2. A group-position determining system as in claim 1, wherein the group has at least four cooperative units.

3. A group-position determining system as in claim 2, wherein the units are unmanned aerial vehicles (UAV'"'"'s).

4. A group-position determining system as in claim 3, further comprising a ground controller for flight-controlling the UAV'"'"'s.

5. A radar system, comprising:

a plurality of at least four unmanned airborne platforms, each comprising;

i) a synthetic aperture radar system configured to exchange radar data with at least one of the other unmanned airborne platforms;

ii) an on-board GPS system for linking with a satellite-based GPS system to compute an individual GPS-based position;

iii) an inter-distance computing module for measuring an inter-distance to at least one other platform; and

iv) a computer including a computer-readable storage medium encoded with a program algorithm that includes instructions for a) applying the inter-distance measurement to at least one individual GPS-based position to thereby provide an improved GPS-based group position, and b) constructing an improved SAR radar image based on the improved GPS-based group position; and

wherein the algorithm comprises an iterative process for i) generating a set of position vectors for each unit to thereby obtain a set of computed positional data and inter-distances for each unit and ii) minimizing a mean square error between the inter-distances and the GPS-based position, thereby correcting the GPS-based position and providing the improved GPS-based position, and repeating steps and ii) until a desired degree of convergence and a final converged estimate of positions of units is obtained, and wherein the GPS errors over all units in the cluster are averaged by applying a rigid body transformation of space to the final converged estimate of positions of units to thereby minimize an objective function of the type given by E=D(A⁽ⁿ⁾, A)+D(B⁽ⁿ⁾, B)+D(C⁽ⁿ⁾, C), where A⁽ⁿ⁾, B⁽ⁿ⁾ and C⁽ⁿ⁾ are the final converged estimate of positions of units.

6. A radar system as in claim 5, wherein the unmanned airborne platforms are UAV'"'"'s.

7. A radar system as in claim 6, further comprising a ground controller for flight-controlling the UAV'"'"'s.

8. A method of correcting a GPS-based position for a cooperative engagement group, comprising:

deploying a group of at least three cooperative units, wherein each said unit comprises;

i) a GPS system for determining a GPS-based position;

ii) an inter-distance measurement module for measuring a distance of the unit relative to at least one other unit; and

iii) a computer including a computer-readable storage medium encoded with a program algorithm that includes instructions for correcting the GPS-based position based on at least one relative distance between two units; and

wherein the algorithm comprises an iterative process for i) generating a set of position vectors for each unit to thereby obtain a set of computed positional data and inter-distances for each unit and ii) minimizing a mean square error between the inter-distances and the GPS-based position, thereby correcting the GPS-based position and providing the improved GPS-based position, and repeating steps i) and ii) until a desired degree of convergence and a final converged estimate of positions of units is obtained, and wherein the GPS errors over all units in the cluster are averaged by applying a rigid body transformation of space to the final converged estimate of positions of units to thereby minimize an objective function of the type given by E=D(A⁽ⁿ⁾, A)+D(B⁽ⁿ⁾, B)+D(C⁽ⁿ⁾, C), where A⁽ⁿ⁾, B⁽ⁿ⁾ and C⁽ⁿ⁾ are the final converged estimate of positions of units;

obtaining an initial GPS-based position for each of the units;

measuring an inter-distance between at least two of the units; and

correcting the initial GPS-based position for each unit based on at least one relative distance between two units to thereby provide an improved GPS-based position for the unit and for the group.

9. A method as in claim 8, wherein the inter-distance is measured between each unit and each remaining unit and the GPS-based position is corrected based on all inter-distance measurements thus obtained.

10. A method as in claim 9, wherein each of the units is a UAV having an onboard SAR for obtaining an SAR radar image, and further comprising the step of constructing an improved SAR radar image based on the improved GPS-based group position.

11. A method as in claim 10, further comprising flight-controlling the UAV'"'"'s using a ground control system.