Concurrent blind equalization suitable for 16-QAM signal

A new concurrent scheme for blind equalization suitable for 16-QAM signal is proposed. It combines modified modulus algorithm (MCMA) and modified decision directed (MDD) algorithm. By exploiting the inherent structural relationship between the 4-QAM signal´s coordinates and 16-QAM signals´ coordinates, another style of cost function for constant modulus algorithm (CMA) is defined, and we have proved that MCMA with such cost function outperforms the conventional CMA considerably. Unfortunately, MCMA has the same inherent defect as CMA which is that it is not sensitivity for phase offset of received signals. So when it occurs, the performance of MCMA will be impaired and even MCMA cannot work. Accordingly for overcoming the shortcomings of MCMA we introduce the decision directed (DD) algorithm, and modify it with the same method as MCMA. Consequently the new concurrent blind equalization with MCMA and MDD is proposed. Simulation results with underwater acoustic channel model show that the proposed algorithm achieves satisfactory performance.