Blind Adaptive Array by Constant Modulus with Variable Step Size for Multi-beam Massive MIMO

A multibeam massive multiple-input multiple-output (MIMO) configuration has previously been proposed that utilizes beam selection to select high-power beams in an analog part and a blind algorithm such as the constant-modulus algorithm (CMA), which does not need channel state information (CSI), in a digital part. However, when least-squares CMA (LS-CMA) is applied to a quadrature amplitude modulation (QAM) signal whose amplitude changes, the interference cancellation effect decreases as the modulation order number increases. In this paper, variable-step-size-based CMA (VS-CMA), which modifies the step size of steepest-descent CMA (SD-CMA) as the blind adaptive algorithm instead of LS-CMA, is proposed. The basic performance of VS-CMA, its success in accomplishing interference cancellation, and its effectiveness with multibeam massive MIMO transmission are verified via computer simulation.