Digital interference suppression system for radio frequency interference cancellation

• US 5,872,540 A
• Filed: 06/26/1997
• Issued: 02/16/1999
• Est. Priority Date: 06/26/1997
• Status: Expired due to Term

• Current Assignee: Honeywell International Inc.
• Original Assignee: Electro-Radiation Incorporated (Honeywell International Inc.)
• Inventors: Rosen, Murray W., Casabona, Mario M., Hurley, Bernard W.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/883,077
• Time in Patent Office: 600 Days
• Field of Search: 342/378, 342/362, 342/361, 375/346, 375/349, 455/296, 455/283
• US Class Current: 342/362
• CPC Class Codes: G01S 1/045 Receivers
• 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: H01Q 3/2611 Means for null steering; Adaptive interference nulling
• CPC Class Codes: H04B 1/7097 Interference-related aspects
• CPC Class Codes: H04K 2203/32 including a particular configuration of antennas
• 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 digital signal processing system that produces an adaptive cancellation arrangement which nulls out all types of concurrent interference and/or jamming signals received by a Global Positioning System (GPS) or spread spectrum receiver from diverse antennas. The present invention uses a unique adaptive interference suppression technique to convert and digitize the analog input signals, and numerically modulate the data to produce effective cancellation of interference signals by nulling while preserving the multiple underlying spread spectrum signals. The invention generates digital and analog output signals which contain a reduced amount of interference. In the present arrangement, orthogonal components of the composite received signal are separated by the receive antenna arrangement and adjusted in the digital network between the antenna and receiver in phase and amplitude to optimally cancel components. The arrangement can be synergistically combined with digital adaptive transversal filter technology which is primarily used to supplement suppression performance by reducing narrowband interferences in the band. The orthogonal received signal components from the GPS satellite constellation and from interference sources are combined in the present arrangement to adaptively create a null that attenuates interference sources while slightly modifying the GPS received signals.

Claims

1. A digital adaptive suppression system for suppressing interference and jamming signals from a spread spectrum signal, the system comprising,

an antenna system for receiving the spread spectrum signal and any inband interference and jamming signals and dividing the received signals into two orthogonally polarized analog antenna output signal components;

analog-to-digital conversion means for converting each of said two orthogonally polarized analog output signal components to digital inputs;

a digital polarimeter for receiving the digital inputs and for receiving digital phase shifting coefficients from a coefficient generator to provide a digital polarimeter output representing the spread spectrum signal with the interference and jamming signals suppressed;

a coefficient generator connected with said digital polarimeter for generating the phase shifting coefficients and repetitively updating the phase shifting coefficients until the digital polarimeter output is at a minimum representing the spread spectrum signal with interference and jamming suppressed.

2. The digital adaptive suppression system of claim 1 wherein said antenna system receives global positioning satellite (GPS) signals in frequency bands L1 and L2 and divides at least one of the GPS L1 and L2 signals into two orthogonally polarized antenna output signal components.

3. The digital adaptive suppression system of claim 2 wherein said analog-to-digital conversion means comprises a balanced converter means for converting each of the two orthogonally polarized analog output signal components to a baseband frequency range, an automatic gain control means for receiving the output of said balanced converter means and for generating a pair of power-regulated analog signals from said output, and an analog-to-digital converter for converting each of said pair of power-regulated analog signals to said digital inputs.

4. The digital adaptive suppression system of claim 3 wherein said balanced converter means further includes means for converting each of said two orthogonally polarized analog output signals into quadrature components at a baseband frequency.

5. The digital adaptive suppression system of claim 4 wherein said automatic gain control means comprises means to control the gain of the quadrature components of the two orthogonally polarized analog output signals in a coordinated manner based on the largest of the output signals, means for amplifying the output signals by ganged variable gain to prevent signal clipping between an intermediate output signal level and a maximum signal level, and means for providing a maximum fixed gain for linear signal operation between an intermediate signal level and the lowest operating signal output level.

6. The digital adaptive suppression system of claim 4 wherein said analog-to-digital converter comprises means for sampling said pair of power-regulated analog signals in quadrature and for digitizing the samples to generate said digital inputs, said digital inputs represented as digital input signal vectors.

7. The digital adaptive suppression system of claim 6 wherein said digital polarimeter numerically processes the digital input signal vectors with the digital phase shifting coefficients to obtain a numeric output signal.

8. The digital adaptive suppression system of claim 7 wherein said numeric output signal is provided to said coefficient generator to update the digital phase shifting coefficients.

9. The digital adaptive suppression system of claim 8 wherein said coefficient generator includes means for continuously updating the digital phase shifting coefficients until said numeric output signal is minimized.

10. The digital adaptive suppression system of claim 7 further comprising a digital adaptive transversal filter connected with said digital polarimeter for receiving the numeric output signal, for processing the numeric output signal in accordance with a finite impulse response (FIR) filtering algorithm, and for coupling the filtered numeric output signal to said coefficient generator.

11. The digital adaptive suppression system of claim 10 wherein said coefficient generator processes the filtered numeric output signal to generate and repetitively update the phase shifting coefficients.

12. The digital adaptive suppression system of claim 11 wherein said digital adaptive transversal filter minimizes narrow-band interference signals.

13. The digital adaptive suppression system of claim 7 wherein said numerical processing of the digital input signal vectors with the digital phase shifting coefficients is in accordance with the following:

##EQU7## where Δ

is the numeric output signal, the vectors ##EQU8## are the digital input signal vectors, and ##EQU9## are the digital phase shifting coefficients, in vector form, from said coefficient generator.

14. The digital adaptive suppression system of claim 13 wherein said vector form digital phase shifting coefficients are generated by said coefficient generator in accordance with the following:

space="preserve" listing-type="equation">a.sub.11 =-sin γ

space="preserve" listing-type="equation">a.sub.12 =-cos γ

-1

space="preserve" listing-type="equation">a.sub.21 =cos γ

+1

space="preserve" listing-type="equation">a.sub.22 =-sin γ

space="preserve" listing-type="equation">b.sub.11 =cos γ

cos φ

-sin γ

sin φ

-cos φ

space="preserve" listing-type="equation">b.sub.12 =-cos γ

sin φ

-sin γ

cos φ

+sin φ

space="preserve" listing-type="equation">b.sub.21 =sin γ

cos φ

+cos γ

sin φ

-sin φ

space="preserve" listing-type="equation">b.sub.22 =-sin γ

sin φ

+cos γ

cos φ

where γ and

φ

values are continuously updated by said coefficient generator until the numeric output signal is minimized.