Narrowband interference cancellation method and circuit

Abstract

A narrowband interference (NBI) canceller is coupled to an A/D converter to receive an input signal and supply an NBI-canceled signal to an error correcting decoder. In the NBI canceller, a first arithmetic unit receives the input signal and a predicted- interference signal, and supplies a difference thereof as the interference-canceled signal. A slicer receives the interference-canceled signal and supplies a decision signal. A second arithmetic unit subtracts the decision signal from the input signal to generate a noise signal. A coarse frequency estimator receives the noise signal and analyzes the frequency spectrum to generate a coarse estimate of a fundamental frequency of the NBI. The coarse estimate is used by an adaptive narrowband interference predictor to generate the predicted-interference signal while adaptively tracking the narrowband interference. Use of the NBI canceller in a transceiver can eliminate link drop caused by operation of wireless devices that generate EMI in a cable.

1 - 16 . (canceled) 
     
     
         17 . A method for cancelling interference in a first signal, the method comprising:
 slicing the first signal to generate a decision signal;   subtracting the decision signal from the first signal to obtain a noise signal;   determining a coarse estimate of a fundamental frequency of an interference in the noise signal;   adaptively filtering the noise signal, based on the coarse estimate, to refine the coarse estimate of the fundamental frequency into a fine estimate of the fundamental frequency;   preparing a predicted-interference signal based on the fine estimate of the fundamental frequency; and   subtracting the predicted-interference signal from the first signal to generate an interference-cancelled signal.   
     
     
         18 . The method of  claim 17  further comprising:
 slicing the interference-cancelled signal to generate a second decision signal; and 
 subtracting the second decision signal from the first signal to obtain the noise signal. 
 
     
     
         19 . The method of  claim 17 , wherein the first signal is a digital signal comprising a plurality of samples, wherein each sample comprises at least one of:
 a received signal;   residual noise remaining after the received signal is processed to remove internally generated noise; and   externally-generated electromagnetic interference injected into the first signal.   
     
     
         20 . The method of  claim 17  further comprising recording the fine estimate into a computer memory at least once. 
     
     
         21 . The method of  claim 17  further comprising:
 evaluating the coarse estimate, and until the coarse estimate satisfies at least one predetermined criterion, repeatedly:
 slicing the first signal to generate the decision signal; 
 subtracting the decision signal from the first signal to obtain the noise signal; and 
 determining the coarse estimate of the fundamental frequency of the interference in the noise signal. 
 
 
     
     
         22 . The method of  claim 17  further comprising:
 accumulating in a storage element, for a period of time, power of a tone in the interference at least at the fine estimate of the fundamental frequency; and 
 if accumulated power in the storage element does not satisfy at least one predetermined criterion, repeatedly:
 slicing the first signal to generate the decision signal; 
 subtracting the decision signal from the first signal to obtain the noise signal; and 
 determining the coarse estimate of the fundamental frequency of the interference in the noise signal, and if the accumulated power in the storage element satisfies the at least one predetermined criterion:
 slicing the interference-cancelled signal to generate a second decision signal; and 
 subtracting the second decision signal from the first signal to obtain the noise signal. 
 
 
 
     
     
         23 . The method of  claim 20  further comprising:
 operating a digital quadrature oscillator (DQO) at a center frequency derived at least partially from the recorded fine estimate. 
 
     
     
         24 . The method of  claim 23 , wherein the center frequency is derived by average the recorded fine estimate. 
     
     
         25 . The method of  claim 24 , wherein the averaging is performed over multiple values of the recorded fine estimate during a predetermined period of time. 
     
     
         26 . The method of  claim 23  further comprising:
 subtracting from a second signal, the decision signal and a second predicted-interference signal, to generate a second noise signal, wherein the DQO generates the second predicted-interference signal based on the second noise signal; and 
 subtracting the second predicted-interference signal from the second signal to generate the first signal. 
 
     
     
         27 . The method of  claim 23  further comprising:
 storing an input signal in a memory; and 
 subtracting from a second signal output from said memory, the data signal and a second predicted-interference signal, to generate a second noise signal, wherein the DQO generates the second predicted-interference signal based on the second noise signal. 
 
     
     
         28 . A receiver operable to cancel interference in a first signal, the receiver comprising:
 means for slicing the first signal to generate a decision signal;   means for subtracting the decision signal from the first signal to obtain a noise signal;   means for determining a coarse estimate of a fundamental frequency of an interference in the noise signal;   means for adaptively filtering the noise signal, based on the coarse estimate, to refine the coarse estimate of the fundamental frequency into a fine estimate of the fundamental frequency;   means for preparing a predicted-interference signal based on the fine estimate of the fundamental frequency; and   means for subtracting the predicted-interference signal from the first signal to generate an interference-cancelled signal.   
     
     
         29 . The receiver of  claim 28  further comprising:
 means for accumulating in a storage element, for a period of time, power of a tone in the interference at least at the fine estimate of the fundamental frequency. 
 
     
     
         30 . The receiver of  claim 28  further comprising:
 means for operating a digital quadrature oscillator (DQO) at a center frequency derived at least partially from the fine estimate. 
 
     
     
         31 . The receiver of  claim 30  further comprising:
 means for averaging the fine estimate, wherein the means for averaging is coupled to the means for operating, to supply thereto the center frequency. 
 
     
     
         32 . A receiver comprising
 an interference canceller comprising:
 first and second arithmetic units, wherein the first and second arithmetic units receive a common input signal, wherein the first arithmetic unit is operable to receive a predicted-interference signal from an adaptive interference predictor, and wherein the first arithmetic unit is further operable to subtract the predicted-interference signal from the common input signal to generate an interference-cancelled signal; 
 a slicer operable to receive the interference-cancelled signal from the first arithmetic unit to generate a decision signal, wherein the second arithmetic unit is operable to receive the decision signal and subtract the decision signal from the common input signal to generate a noise signal; and 
 a coarse frequency estimator operable to receive the noise signal from the second arithmetic unit, wherein the coarse frequency estimator is operable to directly analyze a frequency spectrum of the noise signal to identify a candidate for interference, wherein the coarse frequency estimator estimates a frequency of the interference, wherein the coarse frequency estimate is input into the adaptive interference predictor to produce the predicted-interference signal. 
   
     
     
         33 . The receiver of  claim 32 , wherein the common input signal is a digital signal comprising a plurality of samples, wherein each sample comprises at least one of:
 a received signal;   residual noise remaining after the received signal is processed to remove internally generated noise; and   externally-generated electromagnetic interference injected into the first signal.   
     
     
         34 . The receiver of  claim 32  further comprising a memory element operable to record the fine estimate at least once. 
     
     
         35 . The receiver of  claim 32  further comprising an error correcting decoder operable to supply an interference-cancelled signal. 
     
     
         36 . The receiver of  claim 35 , wherein the error correcting decoder comprises a low density parity checking circuit.