Robust Precoding Design for Coarsely Quantized MU-MIMO Under Channel Uncertainties

TL;DR

This paper develops a robust precoding method for coarsely quantized MU-MIMO systems that accounts for channel uncertainties, enabling reliable high-order modulation support while reducing hardware costs.

Contribution

It introduces a novel robust precoding design that handles channel uncertainties in low-resolution DAC MU-MIMO systems using a convex reformulation and SDR approach.

Findings

The proposed precoder is robust to channel uncertainties.

Supports higher-order modulations like 16QAM.

Outperforms existing methods in robustness and modulation support.

Abstract

Recently, multi-user multiple input multiple output (MU-MIMO) systems with low-resolution digital-to-analog converters (DACs) has received considerable attention, owing to the capability of dramatically reducing the hardware cost. Besides, it has been shown that the use of low-resolution DACs enable great reduction in power consumption while maintain the performance loss within acceptable margin, under the assumption of perfect knowledge of channel state information (CSI). In this paper, we investigate the precoding problem for the coarsely quantized MU-MIMO system without such an assumption. The channel uncertainties are modeled to be a random matrix with finite second-order statistics. By leveraging a favorable relation between the multi-bit DACs outputs and the single-bit ones, we first reformulate the original complex precoding problem into a nonconvex binary optimization problem. Then, using the S-procedure lemma, the nonconvex problem is recast into a tractable formulation with convex constraints and finally solved by the semidefinite relaxation (SDR) method. Compared with existing representative methods, the proposed precoder is robust to various channel uncertainties and is able to support a MUMIMO system with higher-order modulations, e.g., 16QAM.