Urban terrain geolocation system

• US 20040070534A1
• Filed: 10/12/2002
• Published: 04/15/2004
• Est. Priority Date: 10/12/2002
• Status: Active Grant

• Current Assignee: Information Systems Laboratories, Inc.
• Original Assignee: Information Systems Laboratories, Inc.
• Inventors: Wolff, Douglas J., Halsey, J. Doss
• Granted Patent: US 6,762,721 B2
• Time in Patent Office: Days
• US Class Current: 342/442
• CPC Class Codes: G01S 5/0027 of actual mobile position, i.e. position determined on mobile
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308

Abstract

A system for tracking a moveable object such as a soldier in an urban environment includes a receiver that is positioned on the movable object and a plurality of signal transmitters. The transmitters are mutually dispersed at known locations within the urban environment and each transmitter is configured to generate a low frequency electromagnetic signal capable of penetrating into buildings in the urban environment. At the receiver, phase related information and the receiver location information are extracted from received signals and used to determine the location of the receiver. Phase related ambiguities can be eliminated by a processor to find the real receiver position using an algorithm such as the maximum likelihood method (MLM) algorithm. Once the real receiver position is calculated, it can be transmitted to a central location using a low probability of intercept (LPI) waveform to prevent hostile parties from intercepting the location of the soldier.

Claims

1. A system for locating a moveable target in an urban area, wherein the area is characterized by a feature size, said system comprising:

at least one transmitter for transmitting an electromagnetic signal into the urban area from a predetermined location, with said signal having a wavelength longer than said feature size;

a receiver positioned on said moveable target in the urban area for receiving said electromagnetic signal from said transmitter, wherein said received electromagnetic signal includes phase information indicative of the location of the target relative to said base transmitter; and

means for using said phase information in said electromagnetic signal to calculate the location of the target.

2. A system as recited in claim 1 wherein said electromagnetic signal has a Low Probability of Intercept (LPI) waveform.

3. A system as recited in claim 1 wherein said system comprises a plurality of transmitters and said system uses a GPS signal to self-synchronize said plurality of transmitters.

4. A system as recited in claim 1 wherein said means for using said phase information comprises:

an oscillator mounted on said target for measuring a phase for said low frequency signal; and

a processor for using said phase to calculate the location of the target.

5. A system as recited in claim 4 wherein said processor is positioned on the target.

6. A system as recited in claim 4 wherein said processor is positioned at a distance from the target, and said system further comprises a transmitter positioned at the target for transmitting said phase information to said computer via a signal having a Low Probability of Intercept (LPI) waveform.

7. A system as recited in claim 6 wherein said Low Probability of Intercept (LPI) waveform is a burst using a wide bandwidth spread spectrum.

8. A system for locating a moveable target in a structure within an urban area, said system comprising:

a plurality of transmitters dispersed at predetermined locations, with each said transmitter configured to transmit an electromagnetic signal having a wavelength, λ

, into the urban area wherein said wavelength λ

, is longer than 150 meters to allow each said signal to penetrate the structure;

a receiver positioned on said target for receiving each said signal from said transmitters, wherein each said received signal includes phase information indicative of the location of the target relative to each respective said transmitter; and

means for using said phase information in said signals to calculate the location of the target.

9. A system as recited in claim 8 further comprising a plurality of GPS receivers, with one said GPS receiver mounted on each said transmitter to synchronize each said transmitter with respect to at least one other said transmitter.

10. A system as recited in claim 8 further comprising a plurality of GPS receivers, with one said GPS receiver mounted on each said transmitter to determine the location of each said transmitter.

11. A system as recited in claim 10 wherein each transmitter further comprises a means for modulating the respective transmitter'"'"'s location onto said signal transmitted by said respective transmitter for receipt by said receiver.

12. A system as recited in claim 11 wherein said receiver further comprises a means for demodulating each transmitter'"'"'s location from said received signals.

13. A system as recited in claim 8 wherein said system further comprises a base site and wherein said receiver further comprises a means for generating a Low Probability of Intercept (LPI) waveform containing said phase information from said signals and transmitting said LPI waveform for receipt by said base site.

14. A system as recited in claim 8 wherein said means for using said phase information in said signals to calculate the location of the target is a processor mounted on said receiver and wherein said system further comprises a base site and wherein said receiver further comprises a means for generating a Low Probability of Intercept (LPI) waveform containing said calculated target location and transmitting said LPI waveform for receipt by said base site.

15. A system as recited in claim 8 wherein said means for using said phase information in said signals to calculate the location of the target is a processor mounted on said receiver and wherein said receiver further comprises a display for displaying said calculated target location.

16. A system as recited in claim 8 wherein said means for using said phase information in said signals to calculate the location of the target is a processor configured to process a Maximum Likelihood Method (MLM) algorithm to eliminate phase-related location ambiguities.

17. A method for locating a moveable target in a structure within an urban area, said method comprising the steps of:

transmitting signals into the urban area from a plurality of dispersed, predetermined locations, with each said signal having a wavelength, λ

, wherein said wavelength λ

is longer than 150 meters to allow each said signal to penetrate the structure;

receiving said signals at said target, said received signal including phase information indicative of the location of the target relative to each said predetermined transmitting location; and

using said phase information in said signals to calculate the location of the target.

18. A method as recited in claim 17 further comprising the step of using a plurality of GPS receivers to determine the location of each said predetermined transmitting location.

19. A method as recited in claim 17 further comprising the step of transmitting a Low Probability of Intercept (LPI) waveform containing said phase information from said target location for receipt by a base site.

20. A method as recited in claim 17 wherein said step of using said phase information in said signals to calculate the location of the target is performed at said target location and wherein said method further comprising the step of transmitting a Low Probability of Intercept (LPI) waveform containing said calculated location of the target from said target location for receipt by a base site.

21. A method as recited in claim 17 wherein said step of using said phase information in said signals to calculate the location of the target includes the step of processing a Maximum Likelihood Method (MLM) algorithm to eliminate phase-related location ambiguities.