Strategy to transition from the constant modulus algorithm to a decision feedback blind equalizer

The constant modulus algorithm (CMA) is commonly used for first stage blind equalization applications. CMA´s main advantage is that it will open the eye based on the received signal only. Decision directed (DD) equalization is often used as it provides a lower mean square error (MSE) in the equalized signal. Obvious from its name, DD equalization requires estimates of the transmitted symbols in order to adapt the equalizer - the eye must be open. This paper considers an elegant method to transition between CMA and DD equalization (in a decision feedback equalizer structure). A conventional “brute force” approach to perform the transition is to determine the filter coefficients for the DD equalizer through a MMSE design criterion based on the inverse CMA filter coefficients. This may cause a large procession delay at the point of transition between filter types and requires significant computations. The algorithm in this paper is low complexity and does not require a large processing delay when transitioning from CMA to DD LMS.