US 6,868,114 B2Granted

Interference suppression in a spread spectrum communications system using non-linear frequency domain excision

AssigneeThe Titan Corporation

InventorsTheodore Bially, Paul F. McKenzie

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Abstract

In a frequency-domain excision system for a wide band receiver, a window function is applied to blocks of received signal samples and a transform function is applied to the windowed blocks. Each block of frequency-domain coefficients from the transform function is morphologically filtered to generate a threshold function representing an estimate of the spectrum of the desired wide band signal, and a non-linear gain function is applied to the coefficients. The gain function has a fixed-gain region for input values less than a threshold value from the threshold function, an excision region for input values greater than a multiple of the threshold value, and a soft limiting region between the fixed-gain region and the excision region. The inverse transform is performed on the excised blocks of coefficients, and an overlap-eliminating central portion of the inverse of the window function is applied to the resulting blocks of signal samples.

Claims20

Dependent claims

A method of performing frequency domain excision on a received signal including a desired wideband signal component, comprising:

applying a window function to each of overlapped blocks of samples of the received signal to generate windowed blocks of signal samples, the window function having a central maximum and tapering to zero at beginning and ending points;
performing a predetermined transform function on each of the windowed blocks of signal samples to generate corresponding blocks of frequency-domain coefficients;
for each block of frequency-domain coefficients:
(1) morphologically filtering the coefficients to generate a threshold function representing an estimate of the spectrum of the desired wideband signal component, the threshold function including a plurality of threshold values corresponding to the coefficients;
and
(ii) applying a gain function to each coefficient to generate an excised block of coefficients, the gain function for each coefficient having a fixed-gain region for input values less than the corresponding threshold value from the threshold function, an excision region for input values greater than a predetermined multiple of the corresponding threshold value, and a soft limiting region between the fixed-gain region and the excision region;
performing the inverse of the transform function on the excised blocks of coefficients to generate excised blocks of signal samples;
and
applying an overlap-eliminating central portion of the inverse of the window function to each excised block of signal samples.

6 more elements

An excision system for performing frequency domain excision on a received signal including a desired wideband signal component, comprising:

a window component operative to apply a window function to each of overlapped blocks of samples of the received signal to generate windowed blocks of signal samples, the window function having a central maximum and tapering to zero at beginning and ending points;
a transform component operative to perform a predetermined transform function on each of the windowed blocks of signal samples to generate corresponding blocks of frequency-domain coefficients;
an excision processing component operative for each block of frequency-domain coefficients to:
(1) morphologically filter the coefficients to generate a threshold function representing an estimate of the spectrum of the desired wideband signal component, the threshold function including a plurality of threshold values corresponding to the coefficients;
and
(ii) apply a gain function to each coefficient to generate an excised block of coefficients, the gain function for each coefficient having a fixed-gain region for input values less than the corresponding threshold value from the threshold function, an excision region for input values greater than a predetermined multiple of the corresponding threshold value, and a soft limiting region between the fixed-gain region and the excision region;
an inverse transform component operative to perform the inverse of the transform function on the excised blocks of coefficients to generate excised blocks of signal samples;
and
an inverse window component operative to apply an overlap-eliminating central portion of the inverse of the window function to each excised block of signal samples.

6 more elements

Dependencies are inferred from the claim text.