Closed-loop multistage beamformer

• US 6,598,014 B1
• Filed: 10/20/2000
• Issued: 07/22/2003
• Est. Priority Date: 10/21/1999
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Zatman, Michael, Rabideau, Daniel
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): Cherry, Stephen J.
• Application Number:
  US09/692,871
• Time in Patent Office: 1,005 Days
• Field of Search: 342/378, 342/379, 342/382, 342/383, 375/148, 600/443, 702/189, 702/190, 702/191, 702/194
• US Class Current: 702/194
• CPC Class Codes: G01S 3/023 Monitoring or calibrating
• CPC Class Codes: G01S 3/74 Multi-channel systems specially adapted for direction-finding, i.e. having a single antenna system capable of giving simultaneous indications of the directions of different signals systems in which the directions of different signals are determined sequentially and displayed simultaneously G01S3/04, G01S3/14
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00
• CPC Class Codes: G01S 7/36 Means for anti-jamming , e.g. ECCM, i.e. electronic counter-counter measures

Abstract

A system and method of tracking ambient signals, detecting or receiving desired signals, and suppressing undesired signals. An array of sensors receives ambient signals and generates N channels of data. A transformation device accepts the data from the array and generates N′ channels of data. An adaptive processor accepts the N′ channels of data from the output of the transformation device and processes the N′ channels of data to update the settings of the transformation device, such that only N′ degrees of freedom are adaptively manipulated by the adaptive processor at an instant, the manipulation being done in a manner that instantaneously senses changes in signal environment and adjusts the settings of the transformation device in a closed-loop. The adaptive processor optionally combines these N′ channels to produce system output beam(s) that remove residual interference present out the output of the transformation device. Over time, the adaptive processor controls all N degrees of freedom adaptively, thus nulling and tracking performance is then limited by the N degrees of freedom and not the N′ degrees of freedom that are actually used adaptively at any instant.

Claims

1. A system for tracking ambient signals, detecting or receiving desired signals, and suppressing undesired signals, comprising:

an array of sensors through which ambient signals are received, said array generating N channels of data, wherein N is an integer greater than zero;

a transformation device that accepts the data from said array and generates N′

channels of data, wherein N′

is an integer greater than zero;

an adaptive processor that accepts the N′

channels of data from the output of the transformation device, said adaptive processor processes the N′

channels of data to update the settings of said transformation device, such that only N′

degrees of freedom are adaptively manipulated by said adaptive processor at any instant, the manipulation being done in a manner that instantaneously senses changes in signal environment and adjusts the settings of said transformation device in a closed-loop, wherein

said adaptive processor controls all N degrees of freedom adaptively over time, thus nulling and tracking performance is then limited by the N degrees of freedom and not the N′

degrees of freedom that are actually used adaptively at any instant.

2. The system of claim 1, wherein said transformation device utilizes control information supplied by said adaptive processor to generate said N′

channels of data.

3. The system of claim 1, wherein the number of channels N′

is fixed.

4. The system of claim 1, wherein the number of sources of ambient signals can exceed the number of channels N′

.

5. The system of claim 1, wherein said adaptive processor combines the number of channels N′

to produce at least one system output beam that removes residual interference passing through said transformation device.

6. The system of claim 1, wherein the nulling and/or tracking adjusts to calibration errors.

7. The system of claim 1, wherein the transformation device is digital.

8. The system of claim 1, wherein the N′

outputs of the transformation device span the space of n′

main beams, and m′

related beams, wherein n′ and

m′

are integers greater than zero.

9. The system of claim 8, wherein the main beams are chosen to enhance target detection and estimation or signal reception, and the related beams are chosen to detect and estimate jammers, and to enhance the nulling of jammers.

10. The system of claim 9, wherein the main and related beams have nulls steered toward acquired jammers.

11. The system of claim 1, wherein the m′

related beams comprise r refinement beams and a auxiliary beams, wherein m′

, r and a are integers greater than zero.

12. The system of claim 11, wherein both r and α

can be adjusted by the adaptive processor, the sum r+α

being equal to m′

.

13. The system of claim 11, wherein the auxiliary beams cover the region corresponding to all possible jammers.

14. The system of claim 11, wherein the refinement beams are chosen to have responses that span certain estimated jammer subspaces so to improve subsequent estimates of the jammer parameter vector.

15. The system of claim 1, wherein the adaptive processor estimates jammers in a closed-loop fashion and sends control information to the transformation device which is used to steer beams at some sources and directions, while steering nulls at other sources.

16. The system of claim 1, wherein said adaptive processor comprises a detection subsystem, an estimation subsystem, a beam selection subsystem, and a beamforming subsystem.

17. The system of claim 16, wherein said beam selection subsystem is operable for testing for convergence of estimates, and association with other estimates.

18. The system of claim 17, wherein prior to convergence, the estimation subsystem outputs are used to steer refinement beams, and after convergence, the estimation subsystem outputs are used to steer nulls at estimated jammers.

19. The system of claim 1, wherein said adaptive processor automatically senses when nulls are steered badly, and initiates updates.

20. The system of claim 1, wherein said adaptive processor performs pre-scheduled updates.

21. The system of claim 1, wherein said adaptive processor lowers update rates by artificially widening jammer nulls.

22. The system of claim 1, wherein said adaptive processor uses jammer track history and array platform motion data to adjust nulls steered toward acquired jammers, thereby lowering the required update rate.

23. The system of claim 16, wherein said beam selection subsystem utilizes tracked jammer information to select whether or nor to use the transformation device to steer nulls at the jammer.

24. A method of tracking ambient signals, detecting or receiving desired signals, and suppressing undesired signals, comprising:

receiving ambient signals with an array of sensors, said array generating N channels of data, wherein N is an integer greater than zero;

receiving the data from said array with a transformation device and generating N′

channels of data, wherein N′

is an integer greater than zero;

receiving the N′

channels of data from the output of the transformation device with an adaptive processor, said adaptive processor processing the N′

channels of data to update the settings of said transformation device, such that only N′

degrees of freedom are adaptively manipulated by said adaptive processor at any instant, the manipulation being done in a manner that instantaneously senses changes in signal environment and adjusts the settings of said transformation device in a closed-loop, wherein

said adaptive processor controls all N degrees of freedom adaptively over time, thus nulling and tracking performance is then limited by the N degrees of freedom and not the N′

degrees of freedom that are actually used adaptively at any instant.