Observed misconvergence in the constant modulus adaptive algorithm

Abstract

Practical application of the constant modulus algorithm (CMA) has demonstrated a number of circumstances in which CMA fails to converge, or, equally bad from a practical standpoint, converges to a solution which fails to equalize the input signal. The authors describe several situations in which misconvergence occurs, suggesting that a firmer analytical understanding is needed of the behavior of blind algorithms in the presence of cyclostationary and/or quasi-periodic, nonwhite inputs. While this analytical understanding is not yet established, the practical experience reported should be directly useful to those designing new digital communications systems. An example presented, is the use of CMA to equalize quadrature amplitude modulation (QAM) signals used to broadcast high-definition television signals.