A two-stage approach for improving the convergence of least-mean-square adaptive decision-feedback equalizers in the presence of severe narrowband interference

Authors:
Arun Batra;James R. Zeidler;A. A. Beex
Affiliations:
Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, CA;Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, CA;Wireless@VT and the DSP Research Laboratory, Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA
Venue:
EURASIP Journal on Advances in Signal Processing
Year:
2008

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Abstract

It has previously been shown that a least-mean-square (LMS) decision-feedback filter can mitigate the effect of narrowband interference (L.-M. Li and L. Milstein, 1983). An adaptive implementation of the filter was shown to converge relatively quickly for mild interference. It is shown here, however, that in the case of severe narrowband interference, the LMS decision-feedback equalizer (DFE) requires a very large number of training symbols for convergence, making it unsuitable for some types of communication systems. This paper investigates the introduction of an LMS prediction-error filter (PEF) as a prefilter to the equalizer and demonstrates that it reduces the convergence time of the two-stage system by asmuch as two orders of magnitude. It is also shown that the steady-state bit-error rate (BER) performance of the proposed system is still approximately equal to that attained in steady-state by the LMS DFE-only. Finally, it is shown that the two-stage system can be implemented without the use of training symbols. This two-stage structure lowers the complexity of the overall systemby reducing the number of filter taps that need to be adapted, while incurring a slight loss in the steady-state BER.