Optimal and Suboptimal MMSE Precoding for Multiuser MIMO Systems Using Constant Envelope Signals with Phase Quantization at the Transmitter and PSK Modulation

Abstract:
We propose an optimal MMSE precoding technique using quantized signals with constant envelope and PSK modulation. Unlike the existing MMSE design for 1-bit resolution, the proposed method employs uniform phase quantization and the bounding step in the branch-and-bound method is different in terms of considering the most restrictive relaxation of the nonconvex problem, which is then utilized for a suboptimal design also. Numerical simulations show that using the MMSE criterion instead of the established maximum distance to decision threshold yields a lower BER in many scenarios and a smaller average number of bound evaluations for low and medium SNR.