Adaptive narrowband interference prediction circuit and method
An input signal that includes narrowband interference is spectrally enhanced by an adaptive circuit that supplies as output signal(s), portion(s) of NBI at one or more frequencies that change adaptively. The output signal(s) are used in one or more tone predictor(s) to generate, based on prior values of the NBI portion, one or more predicted tone signals that are subtracted from a received signal containing the NBI, and the result is used in the normal manner, e.g. decoded. The adaptive circuit and the one or more tone predictor(s), form a feed-forward NBI predictor wherein the received signal is supplied as the input signal of the adaptive circuit. The result of subtraction may be supplied to a slicer that slices the result, yielding a sliced signal which is subtracted from the received signal to generate a signal can be used as the input signal, to implement a feedback NBI predictor.
1. A receiver to process a received signal, the receiver comprising:
an adaptive circuit operable to receive an input signal comprising a narrowband interference (NBI) signal, the adaptive circuit further operable to supply an output signal comprising at least a portion of the NBI signal filtered at a first, frequency changing adaptively over time, said portion of the NBI signal having a bandwidth narrower than the input signal, and wherein the adaptive circuit is operable to supply a second output signal comprising a second portion of the NBI signal having a second frequency;
a first tone predictor coupled to the adaptive circuit to receive the output signal, the first tone predictor having a first tone prediction line to supply thereon a first predicted tone signal derived by use of said portion of the NBI signal at a plurality of past times differing from one another by a predetermined duration of time;
a second tone predictor operable to receive the second output signal, the second tone predictor having a second tone prediction line to supply thereon a second predicted tone signal derived from another portion of the NBI signal;
a first arithmetic unit operable to receive said received signal, the first arithmetic unit subtracting from the received signal a sum of the first predicted tone signal and the second predicted tone signal, to generate a version of the received signal comprising a remote signal but lacking the first predicted tone signal and the second predicted tone signal;
a slicer coupled to the first arithmetic unit, the slicer operable to supply a modulated signal obtained by slicing said version of the remote signal, received from the first arithmetic unit;
a second arithmetic unit coupled to the adaptive circuit to supply thereto said input signal comprising the NBI signal, the second arithmetic unit being further coupled to the slicer to receive therefrom the modulated signal, and the second arithmetic unit operable to receive said received signal, the second arithmetic unit subtracting from the received signal, at least the modulated signal, thereby to generate said input signal comprising the NBI signal; and
a third arithmetic unit coupled to the first tone prediction line and the second tone prediction line, the third arithmetic unit coupled to the first arithmetic unit, the third arithmetic unit supplying to the first arithmetic unit the sum of the first predicted tone signal and the second predicted tone signal.
2. The receiver of claim 1 wherein: the adaptive circuit comprises a spectral enhancement circuit.
3. The receiver of claim 1 wherein the duration of time required for signal propagation, through a loop formed by the adaptive circuit, the first tone predictor, the first arithmetic unit, the slicer, and the second arithmetic unit, is hereinafter Δt, and wherein the first tone predictor comprises:
a sequence of delay elements and a plurality of taps to supply said portion of the NBI signal, at a corresponding plurality of past times; and
a Least Mean Squared (LMS) engine to supply a plurality of coefficients based on an actual sample φ(t) of the received signal at a current time t and an estimated sample φ′(t) at the current time t; and
a third arithmetic unit coupled to said taps in the delay line to receive the first portion of the NBI signal at said plurality of past times, the third arithmetic unit being further coupled to the LMS engine to receive the plurality of coefficients, wherein the third arithmetic unit supplies on the first tone prediction line, the estimated sample φ′(t) at the current time t.
4. The receiver of claim 1 wherein the duration of time required for signal propagation, through a loop formed by the adaptive circuit, the first tone predictor, the first arithmetic unit, the slicer, and the second arithmetic unit, is hereinafter Δt, and wherein the first tone predictor comprises:
a sequence of delay elements and a pair of taps to supply said portion of the NBI signal (1) at a first past time (t−Δt) and (2) at a second past time (t−2Δt); a Least Mean Squared (LMS) engine to supply a pair of coefficients a 11 and a 12 based on an actual sample φ(t) at a current time t and an estimated sample φ′(t) at the current time t; and
a third arithmetic unit coupled to said pair of taps in the delay line to receive the first portions φ(t−Δt) and φ(t−2Δt) of the NBI signals at said first past time and said second past time, the third arithmetic unit being further coupled to the LMS engine to receive the pair of coefficients a 11 and a 12 , wherein the third arithmetic unit supplies on the first tone prediction line: φ′(t)=a 11 *φ(t−Δt)+a 12 *φ(t−2Δt).
5. The receiver of claim 1 wherein: the second frequency is a harmonic of the first frequency.
6. The receiver of claim 5 wherein:
the adaptive circuit comprises a first infinite impulse response (IIR) filter centered at the first frequency and the adaptive circuit further comprises a second IIR filter centered at the second frequency.
7. The receiver of claim 1 wherein the adaptive circuit further comprises:
a fourth arithmetic unit coupled to each of the first tone prediction line and the second tone prediction line;
a coefficient update circuit coupled to the fourth arithmetic unit, the coefficient update circuit generating a coefficient signal indicative of said frequency; and
a gradient filter coupled to the coefficient update circuit, the gradient filter receiving said portion of the NBI signal.
8. A method for processing a received signal comprising a narrowband interference (NBI) signal and a remote signal, the method comprising:
filtering at a first frequency changing adaptively over time, an input signal comprising the NBI signal, to obtain an output signal comprising at least a first portion of the NBI signal, said first portion of the NBI signal having a bandwidth narrower than the input signal;
supplying a second output signal comprising a second portion of the NBI signal comprising a second frequency;
generating a first predicted tone signal derived by use of said first portion of the NBI signal at a plurality of past times differing from one another by a predetermined duration of time;
generating a second predicted tone signal derived from said second portion of the NBI signal;
subtracting the first predicted tone signal and the second predicted tone signal from the received signal, to generate a version of the received signal comprising the remote signal but lacking the first and second predicted tone signals;
slicing said version of the remote signal to supply a modulated signal; and
subtracting from the received signal, at least the modulated signal, thereby to generate said input signal comprising the NBI signal.
9. The method of claim 8 wherein the second frequency is a harmonic of the first frequency.
10. The method of claim 8 further comprising:
generating a plurality of predicted tone signals derived from a plurality of respective portions of the NBI signal, wherein a quantity of predicted tone signals will be generated depending on a quantity of frequencies of NBI.
11. The method of claim 8 , wherein said filtering is performed with an infinite impulse response (IIR) filter centered at the first frequency, and wherein said filtering performs spectral enhancement and tone separation to generate the first portion of the NBI signal.
12. The method of claim 8 , wherein the method for processing the received signal comprising the NBI signal and the remote signal is performed by one of hardware, firmware, software, or a combination thereof.
13. A receiver to process a received signal comprising a narrowband interference (NBI) signal and a remote signal, the receiver comprising:
means for filtering at a frequency changing adaptively over time, an input signal comprising the NBI signal, to obtain an output signal comprising at least a portion of the NBI signal, said portion of the NBI signal having a bandwidth narrower than the input signal;
a means for supplying a second output signal comprising a second portion of the NBI signal comprising a second frequency;
means for generating a first predicted tone signal derived by use of said portion of the NBI signal at a plurality of past times differing from one another by a predetermined duration of time;
a means for generating a second predicted tone signal derived from said second portion of the NBI signal;
means for subtracting the first and second predicted tone signals from the received signal, to generate a version of the received signal comprising the remote signal but lacking the first and second predicted tone signals;
means for slicing said version of the remote signal to supply a modulated signal; and
means for subtracting from the received signal, at least the modulated signal, thereby to generate said input signal comprising the NBI signal.
14. The receiver of claim 13 , wherein the second frequency is a harmonic of the first frequency.
15. The receiver of claim 13 further comprising:
a means for generating a plurality of predicted tone signals derived from a plurality of respective portions of the NBI signal, wherein a quantity of predicted tone signals will be generated depending on a quantity of frequencies of NBI.
16. The receiver of claim 13 , wherein said means for filtering comprises an infinite impulse response (IIR) filter centered at the first frequency, and wherein said means for filtering comprises a means for spectral enhancement and tone separation to generate the first portion of the NBI signal.