Discrete MMSE Precoding for Multiuser MIMO Systems with PSK Modulation

TL;DR

This paper introduces an optimal MMSE precoding method for multiuser MIMO systems with PSK modulation, employing quantized signals and novel detection schemes to improve bit-error-rate performance and computational efficiency.

Contribution

It presents a new MMSE precoding approach with uniform phase quantization, three soft detection methods, and an iterative decoding scheme that enhances low-resolution precoding with channel coding.

Findings

Lower bit-error-rate with MMSE over max-min distance criterion.

Reduced computational complexity at low/medium SNR.

Improved performance with LDPC coding.

Abstract

We propose an optimal MMSE precoding technique using quantized signals with constant envelope. Unlike the existing MMSE design that relies on 1-bit resolution, the proposed approach 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. Moreover, unlike prior studies, we propose three different soft detection methods and an iterative detection and decoding scheme that allow the utilization of channel coding in conjunction with low-resolution precoding. Besides an exact approach for computing the extrinsic information, we propose two approximations with reduced computational complexity. Numerical simulations show that utilizing the MMSE criterion instead of the established maximum-minimum distance to the decision threshold yields a lower bit-error-rate in many scenarios. Furthermore, when using the MMSE criterion, a smaller number of bound evaluations in the branch-and-bound method is required for low and medium SNR. Finally, results based on an LDPC block code indicate that the receive processing schemes yield a lower bit-error-rate compared to the conventional design.