Rate-Splitting Multiple Access to Mitigate the Curse of Mobility in (Massive) MIMO Networks

TL;DR

This paper demonstrates that Rate-Splitting Multiple Access (RSMA) provides a robust and high-performing solution for downlink multi-antenna wireless networks, especially under user mobility and imperfect channel information, outperforming traditional MIMO strategies.

Contribution

The paper derives a lower bound on RSMA's ergodic sum-rate under mobility, proposes an optimal power allocation scheme, and shows RSMA's robustness and superior performance through simulations.

Findings

RSMA maintains high sum-rate under user mobility.

Proposed power allocation simplifies precoder design.

RSMA outperforms conventional MIMO in mobile scenarios.

Abstract

Rate-Splitting Multiple Access (RSMA) is a flexible and robust multiple access scheme for downlink multi-antenna wireless networks. RSMA relies on multi-antenna Rate-Splitting (RS) at the transmitter and Successive Interference Cancellation (SIC) at the receivers. In this work, we study the performance of RSMA under the practical important setup of imperfect Channel State Information at Transmitter (CSIT) originating from user mobility and latency in the network. First, we derive a lower bound on the ergodic sum-rate of RSMA for an arbitrary number of transmit antennas, number of users, user speeds and transmit power. Then, we study the power allocation between common and private streams and obtain a closed-form solution for the optimal power allocation that maximizes the obtained lower bound. The proposed power allocation greatly reduces precoder design complexity for RSMA. By Link-Level Simulations (LLS), we demonstrate that RSMA with the proposed power allocation is robust to degrading effects of user mobility and has significantly higher performance compared to conventional multi-user (massive) Multiple-Input Multiple-Output (MIMO) strategies. The work has important practical significance as results demonstrate that, in contrast to conventional multi-user (massive) MIMO whose performance collapse under mobility, RSMA can maintain reliable multi-user connectivity in mobile deployments.