Improved Constant Envelope Multiuser Precoding for Massive MIMO Systems

This letter considers the constant envelope precoding method, proposed by Mohammed and Larsson, to minimize the multiuser interference (MUI) in a massive multiple-input multiple-output (MIMO) antenna system. To achieve promising performance for suppressing MUI, nevertheless, constant envelope precoding requires solving the intractable nonlinear least squares (NLS) problem of the transmit phase angles, which is non-convex and has multiple local minima. To tackle this, our approach is to use cross-entropy optimization (CEO) for solving the NLS problem of constant envelope precoding. Simulation results reveal that the CEO-optimized constant envelope precoding significantly outperforms the conventional gradient descent (GD) based constant envelope precoding and zero-forcing.