System and method for adaptive interference cancelling

• US 6,483,923 B1
• Filed: 08/06/1998
• Issued: 11/19/2002
• Est. Priority Date: 06/27/1996
• Status: Expired due to Term

• Current Assignee: Andrea Electronics Corporation
• Original Assignee: Andrea Electronics Corporation
• Inventors: Marash, Joseph
• Primary Examiner(s): Isen, Forester W.
• Assistant Examiner(s): MCCHESNEY, ELIZABETH A
• Application Number:
  US09/130,923
• Time in Patent Office: 1,566 Days
• Field of Search: 381/92
• US Class Current: 381/92
• 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 7/2883 using FFT processing
• CPC Class Codes: G01S 7/292 Extracting wanted echo-signals
• CPC Class Codes: G01S 7/36 Means for anti-jamming , e.g. ECCM, i.e. electronic counter-counter measures
• CPC Class Codes: G10K 11/341 Circuits therefor
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling
• CPC Class Codes: H04B 1/126 having multiple inputs, e.g. auxiliary antenna for receiving interfering signal aerials in general H01Q

Abstract

An adaptive system and method for reducing interference in a signal received from an array of sensors. Adaptive filters are used to generate cancelling signals that closely approximate the interference present in the received signal. The adaptive filter weights are converted into the frequency domain where the frequency representation values in a selected frequency range are truncated to avoid signal leakage involving narrow band signals. Deodorizing filters are used to produce the cancelling signals having a flat frequency spectrum. Normalized power difference is used limit the operation of the adaptive filters to the case where there is some directional interference to be eliminated.

Claims

1. A method for processing digital input data representing signals containing a source signal from a signal source on-axis from an array of sensors as well as interference signals from interference sources located off-axis from the signal source and for producing digital output data representing the source signal with reduced interference signals relative to the source signal, comprising the steps of:

generating a main channel from the digital input data, the main channel representing signals received in the direction of the signal source and having a source signal component and an interference signal component;

generating at least one reference channel from the digital input data, each reference channel representing signals received in directions other than that of the signal source;

adaptively filtering said at least one reference channel using filter weight values to generate a cancelling signal approximating the interference signal component in the main channel;

generating the digital output data by subtracting the cancelling signal from the main channel;

deriving new filter weight values so that the difference between the main channel and the cancelling signal is minimized; and

truncating the new filter weight values to predetermined threshold values when each of the new filter weight values exceeds the corresponding threshold value.

2. The method of claim 1, further comprising the step of filtering said at least one reference channel so that it has a substantially flat frequency spectrum.

3. The method of claim 1, further comprising the step of inhibiting the generation of the cancelling signal when a normalized power difference between the main channel and said at least one reference channel is positive.

4. A method for processing digital input data representing signals containing a source signal from a signal source on-axis from an array of sensors as well as interference signals from interference sources located off-axis from the signal source and for producing digital output data representing the source signal with reduced interference signals relative to the source signal, comprising the steps of:

generating a main channel from the digital input data, the main channel representing signals received in the direction of the signal source and having a source signal component and an interference signal component;

generating at least one reference channel from the digital input data, each reference channel representing signals received in directions other than that of the signal source;

filtering said at least one reference channel using filter weight values to generate a cancelling signal approximating the interference signal component in the main channel;

generating the digital output data by subtracting the cancelling signal from the main channel;

deriving new filter weight values so that the difference between the main channel and the cancelling signal is minimized; and

constraining the new filter weight values by converting the new filter weight values to frequency representation values, truncating the frequency representation values to predetermined threshold values, and converting them back to filter weight values.

5. The method of claim 4 wherein constraining the new filter weight values comprises:

generating frequency representation values of the new filter weight values;

divide the frequency representation values into a plurality of frequency bins;

truncating the frequency representation values in each frequency bin if they exceed a predetermined threshold value associated with each frequency bin; and

converting the frequency representation values back to filter weight values.

6. The method of claim 5 wherein generating the frequency representation is done by using the Fast Fourier Transform, and converting back is done by using the Inverse Fast Fourier Transform.

7. The method of claim 4, further comprising the step of filtering said at least one reference channel so that it has a substantially flat frequency spectrum.

8. The method of claim 4, further comprising the step of inhibiting the generation of the cancelling signal when a normalized power difference between the main channel and said at least one reference channel is positive.

9. A method for receiving a source signal from a signal source as well as interference signals from interference sources and for producing an output signal with reduced interference signals relative to the source signal, comprising the steps of:

receiving analog signals from a sensor array of spatially distributed sensors;

sampling the analog signals to convert them to digital form;

generating a main channel representing signals received in the direction of the signal source, the main channel having a source signal component and an interference signal component;

generating at least one reference channel, each reference channel representing signals received in directions other than that of the signal source;

,

filtering said at least one reference channel using filter weight values to generate a cancelling signal approximating the interference signal component in the main channel;

generating a digital output signal by subtracting the cancelling signal from the main channel;

converting the digital output signal to analog form;

deriving new filter weight values so that the difference between the main channel and the cancelling signal is minimized; and

truncating the new filter weight values to predetermined threshold values when each of the new filter weight values exceeds the corresponding threshold value.

10. The method of claim 9, further comprising the step of filtering said at least one reference channel so that it has a substantially flat frequency spectrum.

11. The method of claim 9, further comprising the step of inhibiting the generation of the cancelling signal when a normalized power difference between the main channel and said at least one reference channel is positive.

12. A method for receiving a source signal from a signal source as well as interference signals from interference sources and for producing an output signal with reduced interference signals relative to the source signal, comprising the steps of:

receiving analog signals from a sensor array of spatially distributed sensors;

sampling the analog signals to convert them to digital form;

generating a main channel representing signals received in the direction of the signal source, the main channel having a source signal component and an interference signal component;

generating at least one reference channel, each reference channel representing signals received in directions other than that of the signal source;

filtering said at least one reference channel using filter weight values to generate a cancelling signal approximating the interference signal component in the main channel;

generating a digital output signal by subtracting the cancelling signal from the main channel;

converting the digital output signal to analog form;

deriving new filter weight values so that the difference between the main channel and the cancelling signal is minimized; and

constraining the new filter weight values by converting the new filter weight values to frequency representation values, truncating the frequency representation values to predetermined threshold values, and converting them back to filter weight values.

13. The method of claim 12 wherein constraining the new filter weight values comprises:

generating frequency representation values of the new filter weight values;

divide the frequency representation values into a plurality of frequency bins;

truncating the frequency representation values in each frequency bin if they exceed a predetermined threshold value associated with each frequency bin; and

converting the frequency representation values back to filter weight values.

14. The method of claim 13 wherein generating frequency representation values is done by using the Fast Fourier Transform, and converting them back to filter weight values is done by using the Inverse Fast Fourier Transform.

15. The method of claim 12, further comprising the step of filtering said least one reference channel so that it has a substantially flat frequency spectrum.

16. The method of claim 12, further comprising the step of inhibiting the generation of the cancelling signal when a normalized power difference between the main channel and said at least one reference channel is positive.