Efficient space-time adaptive processing (STAP) filter for global positioning system (GPS) receivers

• US 7,292,663 B1
• Filed: 12/01/2004
• Issued: 11/06/2007
• Est. Priority Date: 09/26/2001
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Van Wechel, Robert J., Johnston, Ivan L.
• Primary Examiner(s): ODOM, CURTIS B
• Application Number:
  US11/000,827
• Time in Patent Office: 1,070 Days
• Field of Search: 375/350, 375/346, 708/514, 708/520, 701213-215
• US Class Current: 375/350
• CPC Class Codes: G01S 1/024 of beacon transmitters
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/36 relating to the receiver frond end
• CPC Class Codes: H04K 3/228 Elimination in the received signal of jamming or of data corrupted by jamming interference suppression in receivers H04B1/10
• CPC Class Codes: H04K 3/90 related to allowing or preventing navigation or positioning, e.g. GPS

Abstract

A system for efficiently filtering interfering signals in a front end of a GPS receiver is disclosed. Such interfering signals can emanate from friendly, as well as unfriendly, sources. One embodiment includes a GPS receiver with a space-time adaptive processing (STAP) filter. At least a portion of the interfering signals are removed by applying weights to the inputs. One embodiment adaptively calculates and applies the weights by Fourier Transform convolution and Fourier Transform correlation. The Fourier Transform can be computed via a Fast Fourier Transform (FFT). This approach advantageously reduces computational complexity to practical levels. Another embodiment utilizes redundancy in the covariance matrix to further reduce computational complexity. In another embodiment, an improved FFT and an improved Inverse FFT further reduce computational complexity and improve speed. Advantageously, embodiments can efficiently null a relatively large number of jammers at a relatively low cost and with relatively low operating power.

Claims

1. A method of filtering interference using a GPS space-time adaptive processing (STAP) filter, the method comprising:

calculating at least one row of a sub-matrix of a covariance matrix for the GPS STAP filter, wherein the sub-matrix corresponds to a variance of an antenna element of a GPS receiver or to a covariance of two antenna elements of the GPS receiver;

copying at least one value from the calculated row, wherein the copied value is loaded to a position in the sub-matrix that is displaced in time from the calculated value; and

using the sub-matrix for computation of the covariance matrix of the STAP filter for filtering of interference received by the GPS receiver.

2. The method as defined in claim 1, wherein the time displacement is one tap.

3. The method as defined in claim 1, wherein the sub-matrix corresponds to a variance of an antenna element, further comprising copying a complex conjugate of a second value from the calculated row, wherein the second copied value is loaded to a position in the sub-matrix that is reflected across a diagonal of the sub-matrix.

4. The method as defined in claim 1, wherein the sub-matrix corresponds to covariance of two antenna elements, further comprising:

calculating at least one column of the sub-matrix; and

copying at least a second calculated value from the calculated column, wherein the second copied value is loaded to a position in the sub-matrix that is displaced in time from the second calculated value.

5. The method as defined in claim 1, wherein copying comprises copying from a memory circuit.

6. A GPS space-time adaptive processing (STAP) filter adapted to filter interference, the GPS STAP filter comprising:

means for calculating at least one row of a sub-matrix of a covariance matrix for the GPS STAP filter, wherein the sub-matrix corresponds to a variance of an antenna element of a GPS receiver or to a covariance of two antenna elements of the GPS receiver;

means for copying at least one value from the calculated row, wherein the copied value is loaded to a position in the sub-matrix that is displaced in time from the calculated value; and

means for using the sub-matrix for computation of the covariance matrix of the STAP filter for filtering of interference received by the GPS receiver.

7. The signal processor as defined in claim 6, wherein the time displacement is one tap.

8. The signal processor as defined in claim 6, wherein the sub-matrix corresponds to a variance of an antenna element, further comprising means for copying a complex conjugate of a second value from the calculated row, wherein the second copied value is loaded to a position in the sub-matrix that is reflected across a diagonal of the sub-matrix.

9. The signal processor as defined in claim 6, wherein the sub-matrix corresponds to covariance of two antenna elements, further comprising:

means for calculating at least one column of the sub-matrix; and

means for copying at least a second calculated value from the calculated column, wherein the second copied value is loaded to a position in the sub-matrix that is displaced in time from the second calculated value.

10. A method of filtering interference using a space-time adaptive processing (STAP) filter for a GPS receiver, the method comprising:

determining if negative eigenvalues are present in a covariance matrix to be inverted, wherein the covariance matrix comprises sub-matrices of variances and covariances of antenna elements of the GPS receiver;

selecting a factorization technique in response to the determination, wherein the factorization technique selected is compatible with negative eigenvalues when negative eigenvalues are detected;

performing triangular factorization on the covariance matrix;

performing substitution to invert the covariance matrix; and

using the inverted factorized covariance matrix in the STAP filter for filtering of interference received by the GPS receiver.

11. The method as defined in claim 10, wherein the triangular factorization comprises Bunch-Kaufman decomposition.

12. The method as defined in claim 10, wherein the triangular factorization is selected from the group consisting of Bunch-Kaufman decomposition, Cholesky decomposition, and Gauss elimination.

13. The method as defined in claim 10, wherein the substitution comprises backwards substitution.

14. The method as defined in claim 10, wherein the substitution comprises forwards substitution.

15. The method as defined in claim 10, wherein the substitution comprises backwards or forwards substitution.

16. The method as defined in claim 10, further comprising:

using Bunch-Kaufman decomposition for factorization if negative eigenvalues are present; and

using Cholesky decomposition if negative eigenvalues are not present.

17. The method as defined in claim 10, further comprising selecting the factorization technique during production of a GPS receiver embodying the method.

18. The method as defined in claim 10, wherein the covariance matrix holds variance-covariance information for a multiple-element GPS antenna array.

19. The method as defined in claim 10, further comprising maintaining the covariance matrix in a memory circuit for the GPS STAP filter.

20. A method of filtering interference using a GPS space-time adaptive processing (STAP) filter of a GPS receiver, the method comprising:

calculating at least one value of a first position of a sub-matrix of a covariance matrix for the GPS STAP filter, wherein the sub-matrix corresponds to a variance of an antenna element of the GPS receiver or to a covariance of two antenna elements of the GPS receiver;

storing the calculated value in a memory circuit; and

copying the value for use as a value for a second position in the sub-matrix, wherein the copied value is loaded to a position in the sub-matrix that is displaced in time from the calculated value for computation of the covariance matrix of the STAP filter for filtering of interference received by the GPS receiver.

21. The method as defined in claim 20, wherein the value is copied such that at least two values of the sub-matrix that are diagonally adjacent by row and column are the same.