Diamond contour-based phase recovery for (CROSS)-QAM constellations

Two new iterative methods for blind phase estimation of QAM signals are presented. The algorithms seek the maxima of certain cost functions derived from the dispersion of the derotated data with respect to a diamond-shaped contour, and their distinctive feature is the inclusion of a sign nonlinearity at every iteration. A connection between one of these methods and the standard fourth-power method is presented. Simulations with cross-QAM constellations show that, when properly initialized, the new schemes present lower variance than the fourth-power method, and may even outperform Cartwright´s eighth-order method