A modified constant modulus algorithm for adaptive channel equalization for QAM signals

Abstract

A modified constant modulus algorithm (MCMA) for adaptive equalization of the wireless indoor channel for QAM signals is presented. The algorithm minimizes an error cost function that includes both the amplitude and phase of the equalizer output. In addition to the amplitude-dependent term that is provided by the conventional constant modulus algorithm (CMA), the cost function includes a signal constellation matched error (CME) term. This term speeds up convergence and allows the equalizer to switch to decision directed (DD), or any soft-decision mode, faster than the CMA applied alone. The constellation-matched error term is constructed using polynomials with desirable properties. The MCMA is applied to a decision feedback equalizer and shown to provide improved performance over dual mode techniques.