Optimal narrowband interference removal for signals separated in time

• US 8,588,724 B2
• Filed: 08/19/2010
• Issued: 11/19/2013
• Est. Priority Date: 08/20/2009
• Status: Active Grant

• Current Assignee: Alfred E. Mann Foundation For Scientific Research
• Original Assignee: Alfred E. Mann Foundation For Scientific Research
• Inventors: Hess, Phillip B., Nercessian, Patrick
• Primary Examiner(s): Urban, Edward
• Assistant Examiner(s): HU, RUI MENG
• Application Number:
  US12/859,730
• Publication Number:
  US 20110053546A1
• Time in Patent Office: 1,188 Days
• Field of Search: 455296-312, 455 631- 65, 455/67.13, 455/570, 455501-506, 375316-352
• US Class Current: 455/312
• CPC Class Codes: H03H 17/0213 Frequency domain filters using Fourier transforms
• 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 1/109 by improving strong signal performance of the receiver when strong unwanted signals are present at the receiver input
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H

Abstract

A system and method for improving the processing of communications signals received in the presence of narrowband interference signals. The received communications signals are time sampled and transformed into a series of spectral terms in the frequency domain that are then evaluated to identify narrowband interference signals. The identified narrowband interference terms can be calculated to a value that will optimize the corrupted spectral terms resulting from the communication, and an inverse transformation can be used to generate a time domain signal that is free from interference.

Claims

1. A method of removing narrowband interference signals from communication signals having both data and data free intervals comprising the steps of:

sampling the communication signals to generate time domain data samples thereof;

transforming the time domain samples into a first series of spectral terms in the frequency domain, said samples containing data and data free intervals;

generating a representation of an inverse transform of the first series of spectral terms related to respective time domain data samples;

identifying spectral terms corrupted by said narrowband interference signals;

reducing the representation of the inverse transform by removal of data containing entries of the representation, which are entries for time domain samples known to contain data;

decomposing the representation of the inverse transform into contributions from spectral terms corrupted by said narrowband interference signals and into contributions from spectral terms not corrupted by narrowband interference signals;

inserting, into non-corrupted entries of the decomposed representation, which are the entries for spectral terms not corrupted by narrowband interference signals, predetermined values for the time domain samples that are known to be data free;

subtracting the contribution of the non-corrupted spectral terms from the data free entries of the representation, which are entries for time domain samples known to be data free, to provide thereby a representation that defines the contribution of the corrupted spectral terms to a predetermined time domain signal at the data free entries;

estimating the value for the corrupted spectral terms that contribute to the predetermined time domain signal at the data free entries to provide a replacement value for the corrupted spectral terms;

replacing only those corrupted spectral terms in the first series of spectral terms with a corresponding respective replacement value of the corrupted spectral terms to provide thereby a second series of spectral terms; and

inverse transforming the second series of spectral terms to provide an essentially interference free signal.

2. The method of claim 1, wherein the step of estimating further comprises the step of utilizing a least means square fitting technique to calculate the value for the corrupted spectral terms to provide a replacement value for the corrupted spectral terms.

3. The method of claim 1, wherein the step of transforming to the frequency domain comprises the step of performing a Fast Fourier Transform on the time domain data samples.

4. The method of claim 1, wherein the step of inverse transforming the second series of spectral terms comprises the step of performing an inverse Fast Fourier Transform on the second series of spectral terms.

5. A method of removing narrowband interference signals from RF signal transmissions having both data and data free intervals comprising the steps of:

receiving the RF signals;

mixing the RF signals with a local oscillator to generate a frequency limited baseband signal;

sampling the baseband signal to generate time domain data samples;

storing the samples in a capture memory as time domain data samples;

transforming to the frequency domain the time domain data samples from the capture memory into a first series of spectral terms;

generating a representation of an inverse transform of the first series of spectral terms related to respective time domain data samples;

identifying spectral terms corrupted by said narrowband interference signals;

reducing the representation of the inverse transform by removal of selected data containing entries of the representation, which are entries for time domain samples known to contain data;

decomposing the representation of the inverse transform into contributions from spectral terms corrupted by said narrowband interference signals and into contributions from spectral terms not corrupted by narrowband interference signals;

inserting, into non-corrupted entries of the decomposed representation, which are the entries for spectral terms not corrupted by narrowband interference signals, predetermined values for the time domain samples that are known to be data free;

subtracting the contribution of the non-corrupted spectral terms from selected data free entries of the representation, which are entries for time domain samples known to be data free, to provide thereby a representation that defines the contribution of the corrupted spectral terms to a predetermined time domain signal at the selected data free entries;

estimating the value for the corrupted spectral terms that contribute to the predetermined time domain signal at the selected data free entries to provide a replacement value for the corrupted spectral terms;

replacing only those corrupted spectral terms in the first series of spectral terms with a corresponding respective replacement value of the corrupted spectral terms to provide thereby a second series of spectral terms; and

inverse transforming the second series of spectral terms to provide an essentially interference free signal.

6. A system for removing narrowband interference signals from communication signals having both data and data free intervals comprising:

a receiver that is arranged to sample the communication signals and to generate time domain samples thereof;

a capture memory that is arranged to store the time domain samples associated with the communication signals; and

a signal processor that is arranged to process the stored time domain samples, wherein the signal processor is arranged to;

transform into a first series of spectral terms in the frequency domain, the stored time domain samples, said samples containing data and data free intervals;

evaluate the series of spectral terms in the transformed domain to identify one or more corrupted spectral terms associated with the narrowband interference signals from the narrowband interference source, wherein the identified corrupted spectral terms are unrelated to the communication signals;

generate a representation of an inverse transform of the first series of spectral terms related to respective time domain samples;

reduce the representation of an inverse transform by removal of selected entries known to contain data;

decompose the representation of the inverse transform into contributions from spectral terms corrupted by said narrowband interference signals and into contributions from spectral terms not corrupted by narrowband interference signals;

insert, into non-corrupted entries of the decomposed representation, which are the entries for spectral terms not corrupted by narrowband interference signals, predetermined values for the time domain samples that are known to be data free;

subtract the contribution of the non-corrupted spectral terms from selected data free entries of the representation, which are entries for time domain samples known to be data free, to provide thereby a representation that defines the contribution of the corrupted spectral terms to a predetermined time domain signal at the selected data free entries;

estimate the value for the corrupted spectral terms associated with the narrowband interference source as a replacement value for said spectral terms;

replace those corrupted spectral terms with a corresponding respective replacement value to generate a second series of spectral terms which represents a series of spectral terms having the interference signal removed without removing the content of the communication signals, the second series of spectral terms being determined in consideration of the contribution of the corrupted spectral terms to a predetermined time domain signal at selected spectral terms related to the data free intervals; and

inverse transform the second series of spectral terms to provide an interference free signal.

7. The system of claim 6 wherein the predetermined values are a mathematical zero or a mathematical constant, other than zero.

8. The system of claim 6, wherein the signal processor is further arranged to store each spectral term in a respective bin from an array of bins after the transformation from the time domain into the transformed domain, wherein each bin from the array of bins represents a portion of a predetermined baseband frequency bandwidth.

9. The system of claim 6, wherein the signal processor is further arranged such that stored samples that are grouped together within a time domain interval are transformed together into the series of spectral terms.

10. The system of claim 6, wherein the signal processor is further arranged to evaluate the series of spectral terms by comparing the accumulated values in each bin to a threshold value.