Robust Precoding for Rate-Splitting-Based Cell-Free MU-MIMO Networks
A. Flores, R. de Lamare
TL;DR
This work tackles robust downlink transmission in cell-free MU-MIMO under imperfect CSIT and multiuser interference. It develops a rate-splitting based framework with MMSE-designed robust common and private precoders, incorporating CSI statistics and an efficient alternating optimization for the private precoder, plus a power-allocation strategy. The authors derive closed-form ergodic sum-rate expressions and analyze computational cost, demonstrating that the proposed scheme outperforms conventional robust and non-robust approaches, with the robust common precoder delivering significant gains and fast convergence. The approach advances CF-MIMO practicality by improving reliability and throughput under realistic channel uncertainties and signaling constraints, aided by AP clustering/selection to control complexity.
Abstract
Cell-free (CF) multiuser multiple-input multiple-output (MU-MIMO) systems are an emerging technology that provides service simultaneously to multiple users but suffers from multiuser interference (MUI). In this work, we propose a robust transmit scheme based on rate-splitting (RS) for CF MU-MIMO systems in the presence of imperfect channel state information (CSI) and MUI. We also develop a robust linear precoder design for both private and common precoders based on the minimum mean square error (MMSE) criterion, which incorporates in its design statistical information about the imperfect CSI to provide extra robustness to RS-CF MU-MIMO systems. A statistical analysis is carried out to derive closed-form sum-rate expressions along with a study of the computational complexity of the proposed scheme. Simulation results show that the proposed scheme outperforms conventional robust and non-robust schemes.