Apparatus and method for two stage hybrid space-time adaptive processing in radar and communication systems

• US 6,252,540 B1
• Filed: 12/21/1999
• Issued: 06/26/2001
• Est. Priority Date: 12/21/1999
• Status: Expired due to Term

• Current Assignee: United States Air Force (Government of the United States of America)
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Hale, Todd B., Adve, Raviraj S., Wicks, Michael C.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US09/468,044
• Time in Patent Office: 553 Days
• Field of Search: 342/89, 342/90, 342/93, 342/159, 342/160, 342/161, 342/162, 342/163, 342/165, 342/173, 342/174, 342/192, 342/195, 342/196, 342/203
• US Class Current: 342/159
• CPC Class Codes: G01S 13/524 based upon the phase or frequency shift resulting from movement of objects, with reference to the transmitted signals, e.g. coherent MTi
• CPC Class Codes: G01S 7/2921 based on data belonging to one radar period

Abstract

A Two-Stage Hybrid algorithm offers significant improvement in the false alarm rate and detection performance of Space-Time Adaptive Processing in non-homogeneous environments for both radar and digital communications. The first stage analyzes data from a range cell of interest by direct data domain processing, suppressing discrete interferers within the range cell of interest. The second stage implements a purely statistical STAP algorithm, preferably an enhanced version of the Joint-Domain Localized (“JDL”) statistical algorithm. For radar this second stage estimates the interference within the range cell of interest from the surrounding range cells. For a communications system, the second stage estimates the covariance matrix of the interference from the entire data block. For both radar and communications, an adaptive filter that suppresses the interference is generated from the estimate by second-order statistics. The present invention is the first two-dimensional STAP technique; all prior-art is one-dimensional.

Claims

1. Apparatus for adaptive signal processing, which comprises:

a receiver effective for receiving a plurality of signals;

a signal processor effective for adaptively transforming said plurality of signals into a plurality of samples;

said plurality of samples comprising a cell under test and related secondary cells;

said signal processor being further effective for a first transformation of said cell under test and said related secondary cells from a spatial-temporal domain to a look-angle Doppler domain;

said look-angle Doppler domain comprising a plurality of points; and

said signal processor being further effective for a second transformation of said plurality of points to mitigate electromagnetic interference and clutter that masks desired returns.

2. Apparatus as in claim 1, wherein said first transformation applies a direct data domain least-squares algorithm.

3. Apparatus as in claim 2, wherein said first transformation suppresses discrete interferers.

4. Apparatus as in claim 2, wherein said first transformation maximizes a difference between desired signal power and interference power in a chosen look-angle Doppler direction.

5. Apparatus as in claim 1, wherein said second transformation applies a sample matrix inversion or its equivalent.

6. Apparatus as in claim 5, wherein said second transformation suppresses distributed interference.

7. Apparatus as in claim 5, wherein said second transformation employs a steering vector associated with a chosen look-angle Doppler direction.

8. Apparatus as in claim 1, wherein said receiver and said signal processor comprise a radar system.

9. Apparatus as in claim 8, wherein said radar system is mobile.

10. Apparatus in claim 9, wherein said system is a phased-array, pulsed-Doppler radar.

11. Apparatus as in claim 1, wherein said receiver and said signal processor comprise a digital communications system.

19. Apparatus as in claim 1, wherein said receiver and said signal processor comprise a sonar system.

20. Apparatus as in claim 1, wherein said receiver and said signal processor comprise a seismic wave detection system.

12. A method of adaptive signal processing comprising the steps of:

selecting at least one primary cell from a plurality of signals by spatially and temporally sampling from said plurality;

sequentially choosing a main angle-look direction and a main Doppler in relation to said at least one primary cell;

forming a steering vector based on said angle-look direction and said Doppler;

computing, for said at least one primary cell, a first set of adaptive weights based on said steering vector;

applying said first set of adaptive weights to signals in said at least one primary cell to form a primary localized processing region (“

LPR”

);

selecting from said plurality of signals a set of secondary cells associated with said at least one primary cell;

further applying said first set of adaptive weights to said set of secondary cells to form a plurality of secondary LPRs and to convert said steering vector to a LPR steering vector;

estimating, from first interference statistics of said plurality of secondary LPRs, second interference statistics for said primary LPR;

computing a second set of adaptive weights from said second interference statistics and said LPR steering vector;

still further applying said second set of adaptive weights to said primary LPR; and

comparing a result from said step of still further applying to a threshold value to determine presence or absence of a desired signal.

13. The method of claim 12, wherein said plurality of signals includes desired returns from targets and undesired interference.

14. The method of claim 13, wherein said interference further comprises at least one of

returns from said targets at non-chosen look directions and non-chosen Dopplers, clutter, and

any other electromagnetic energy capable of masking at least one of said targets.

15. Apparatus for adaptive signal processing, which comprises:

first selection means for selecting at least one primary cell from a plurality of signals by spatially and temporally sampling from said plurality;

means for sequentially choosing a main angle-look direction and a main Doppler in relation to said at least one primary cell;

means for forming a steering vector based on said angle-look direction and said Doppler;

first computing means for computing, for said at least one primary cell, a first set of adaptive weights based on said steering vector;

first application means for applying said first set of adaptive weights to signals in said at least one primary cell to form a primary localized processing region (“

LPR”

);

second selection means for selecting from said plurality of signals a set of secondary cells associated with said at least one primary cell;

second application means for applying said first set of adaptive weights to said set of secondary cells to form a plurality of secondary LPRs and to convert said steering vector to a LPR steering vector;

means for estimating, from first interference statistics of said plurality of secondary LPRs, second interference statistics for said primary LPR;

second computing means for computing a second set of adaptive weights from said second interference statistics and said LPR steering vector;

third application means for applying said second set of adaptive weights to said primary LPR; and

means for comparing a result from said third application means to a threshold value to determine presence or absence of a desired signal.

16. Apparatus as in claim 15, wherein said plurality of signals includes desired returns from targets and undesired interference.

17. Apparatus as in claim 16, wherein said interference further comprises at least one of

returns from said targets at non-chosen look directions and non-chosen Dopplers, clutter, and

any other electromagnetic energy capable of masking at least one of said targets.

18. Apparatus as in claim 15, wherein said steering vector can be measured, calculated, or theoretically constructed.