EURASIP Journal on Advances in Signal Processing 
Volume 2008 (2008), Article ID 390102, 13 pages
doi:10.1155/2008/390102
Research Article

A Two-Stage Approach for Improving the Convergence of Least-Mean-Square Adaptive Decision-Feedback Equalizers in the Presence of Severe Narrowband Interference

Arun Batra,1 James R. Zeidler,1 and A. A. (Louis) Beex2

 1Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, CA 92093-0407, USA
2Wireless@VT and the DSP Research Laboratory, Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA 24061-0111, USA
Received 3 January 2007; Revised 16 April 2007; Accepted 8 August 2007

Recommended by Peter Handel

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 as much 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 system by reducing the number of filter taps that need to be adapted, while incurring a slight loss in the steady-state BER.