A dual-mode algorithm for blind equalization of QAM signals: CADAMA

The misadjustment exhibited by the constant modulus algorithm (CMA) can be excessive when it is used for blind equalization of QAM signals, thus degrading the performance of decision-directed carrier recovery algorithms. This paper introduces a hybrid blind equalization algorithm, the CMA-assisted decision adjusted modulus algorithm (CADAMA), that exhibits reductions in misadjustment on the order of 18 to 25 dB for higher order QAM constellations. CADAMA employs CMA to perform initial adjustment of the equalizer, and switches to decision adjusted modulus algorithm (DAMA) mode when the amplitude equalization has been sufficiently accomplished. DAMA is based on a phase-blind cost function that goes to zero at each ring of the QAM constellation.