Robust Constrained Constant Modulus Algorithm for Signal Steering Vector Mismatches

The constant modulus algorithm (CMA) has been known as blind adaptive beamforming because it requires no knowledge about the signal except that the transmitted signal waveform has a constant envelope. But in practical applications, the performance of the linearly constrained CMA is known to degrade severely in the presence of even slight signal steering vector mismatches. To account for the mismatches, a novel robust CMA algorithm is proposed via the oblique projection of signal steering vector. To improve robustness, the weight vector is optimized to involve minimization of a constant modulus algorithm objective function with penalty for the worst-case signal steering vector by the Lagrange multiplier method, in which the parameter can be precisely derived at each iterative step. Moreover, the performance analysis of the proposed algorithm is presented in this paper. The proposed robust constrained CMA provides a significantly improved robustness against the signal steering vector mismatches and improves the mean output array SINR as compared with the conventional constrained CMA. The simulation experiments have been carried out to demonstrate the superiority of the proposed algorithm on beampattern control and output SINR enhancement.