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

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.