Interference suppressor for a radio receiver

• US 5,410,750 A
• Filed: 02/24/1992
• Issued: 04/25/1995
• Est. Priority Date: 02/24/1992
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Cantwell, Robert H., Matthews, James B.
• Primary Examiner(s): Urban, Edward F.
• Application Number:
  US07/840,252
• Time in Patent Office: 1,156 Days
• Field of Search: 455/295, 455/296, 455/303, 455/304, 455/306, 455/307, 455/311, 455/308, 375/99, 375/102, 375/103, 375/1, 380/34
• US Class Current: 455/306
• 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 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: H04B 1/1036 with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters H04B1/123 takes precedence; filter circuits H03H
• CPC Class Codes: H04B 1/7102 with transform to frequency domain

Abstract

The RF input of a radio receiver is converted to IF including received signal, noise and interference and fed to an interference detector and to an interference canceler of an interference suppressor. A fast Fourier transform (FFT) at the front end of the interference detector detects samples of all the interferences in the frequency domain. The frequency domain samples are scaled for gain control and detection of interferences above a predetermined threshold. The interference detector suppresses interferences to the predetermined threshold level. The scaled frequency domain interference samples are phase rotated and fed to an inverse fast Fourier transform to obtain a time domain replica of the interferences which are phase shifted replicas of the detected interferences. Such digital time domain replicas are converted to a continuous analog replica of the interferences, converted back to IF and summed with the original IF which included received signals, noise and interferences in order to cancel the interferences at the output of the interference suppressor.

Claims

1. A radio receiver comprising:

means for generating an IF signal from a received spread spectrum signal including interference signals;

means coupled to said IF signal generating means for suppressing said interference signals coupled to said IF signal;

said suppressing means comprises means for down converting said IF signal including interference signals to baseband sampled signals;

means coupled to said down converting means for converting said baseband sampled signals from a time domain to a frequency domain;

means coupled to said time domain to frequency domain converting means for excising said interference signals in said frequency domain;

said excising means comprises a filter controller means coupled to said time domain to frequency domain converting means for generating delays for said frequency domain interference sampled signals to allow for continuous inputs and outputs of said suppressing means;

a cell magnitude detector means coupled to said delayed interference sampled signals from said filter controller means for detecting an adjacent and main cell magnitude of said interference sampled signals at a sampling frequency rate;

phase selector means coupled to said cell magnitude detector means for determining a phase rotation angle (φ

_K) of each of said frequency domain interference sampled signals;

phase rotator means coupled to said phase selector means and said filter controller means for providing said phase rotation angle (φ

_K) to each of said frequency domain interference sampled signals;

a frequency domain amplitude selector means coupled to said phase rotator means for denormalizing said phase rotated frequency domain interference sampled signals to generate frequency domain interference amplitude estimates in accordance with a frequency domain scale factor signal;

means coupled to said excising means for converting said excised interference signals from said frequency domain to said time domain;

means coupled to said frequency to time domain converting means for up-converting said interference signals from baseband sampled signals to intermediate frequency;

means coupled to said up-converting means and said means for generating an IF signal for summing said interference signals from said up-converting means with said IF signal including interference signals from said means for generating an IF signal to cancel out said interference signals coupled to said IF signal;

means coupled to said suppressing means for generating in-phase (I) and quadrature-phase (Q) samples of said IF output; and

means coupled to said I and Q samples generating means for processing said I and Q samples.

2. The radio receiver as recited in claim 1 wherein said interference signal suppressing means comprises means for discarding said IF signal including noise.

3. The radio receiver as recited in claim 1 wherein:

said interference signal suppressing means provides at least 25 dB of interference signal rejection.

4. The radio receiver as recited in claim 1 wherein said scale factor signal is produced by said time to frequency converter means and provides an estimate of the maximum received interference signals.

5. The radio receiver as recited in claim 1 wherein:

said means for generating in-phase and quadrature-phase samples comprises signal processor means for removing a doppler frequency and PN-code modulation from said IF signal.

6. The radio receiver as recited in claim 5 wherein:

said signal processor means comprises automatic gain control (AGC) means for holding the power approximately constant at the output of said I and Q samples generating means.

7. The radio receiver as recited in claim 6 wherein:

said AGC provides an estimate of interference cancellation.

8. An interference suppressor comprising:

means coupled to an IF signal which comprises interference signals for suppressing said interference signals, said suppressing means comprises

means for down converting said IF signal including interference signals to baseband sampled signals;

means coupled to said down converting means for converting said baseband sampled signals from a time domain to a frequency domain;

means coupled to said time domain to frequency domain converting means for excising said interference signals in said frequency domain;

said excising means comprises a filter controller means coupled to said time domain to frequency domain converting means for generating delays for said frequency domain interference sampled signals to allow for continuous inputs and outputs of said suppressing means;

a cell magnitude detector means coupled to said delayed interference sampled signals from said filter controller means for detecting an adjacent and main cell magnitude of said interference sampled signals at a sampling frequency rate;

phase selector means coupled to said cell magnitude detector means for determining a phase rotation angle (φ

_K) of each of said frequency domain interference sampled signals;

phase rotator means coupled to said phase selector means and said filter controller means for providing said phase rotation angle (φ

_K) to each of said frequency domain interference sampled signals; and

a frequency domain amplitude selector means coupled to said phase rotator means for denormalizing said phase rotated frequency domain interference sampled signals to generate frequency domain interference amplitude estimates in accordance with a frequency domain scale factor signal;

means coupled to said excising means for converting said excised interference signals from said frequency domain to said time domain;

means coupled to said frequency to time domain converting means for up converting said excised interference signals from baseband sampled signals to intermediate frequency; and

means for combining said interference signals with said IF signal which comprises interference signals to cancel said interference signals.

9. A method of suppressing interference signals comprising the steps of:

estimating said interference signals in a frequency domain by down converting IF signals including interference signals to baseband sampled signals;

converting said baseband sampled signals from a time domain to a frequency domain;

generating delays for said frequency domain interference sampled signals to allow for continuous inputs and outputs of said suppressing means with a filter controller means coupled to said time domain to frequency domain converting means;

detecting an adjacent and main cell magnitude of said interference sampled signals at a sampling frequency rate with a cell magnitude detector means coupled to said delayed interference sampled signals from said filter controller means;

determining a phase rotation angle (φ

_K) of each of said frequency domain interference sampled signals using a phase selector means coupled to said cell magnitude detector means;

providing said phase rotation angle (φ

_K) to each of said frequency domain interference sampled signals using a phase rotator means coupled to said phase selector means and said filter controller means;

denormalizing said phase rotated frequency domain interference sampled signals to generate frequency domain interference amplitude estimates in accordance with a frequency domain scale factor signal using a frequency domain amplitude selector means coupled to said phase rotator means;

converting said estimated interference signals from said frequency domain to said time domain;

up converting said estimated interference signals from baseband sampled signals to intermediate frequency; and

combining said estimated interference signals with said IF signals which comprise interference signals to cancel said interference signals.