Rate-Splitting Multiple Access: Finite Constellations, Receiver Design, and SIC-Free Implementation

2023-05-26

IEEE Transactions on Communications

AI Summary

This work addresses three key practical bottlenecks of Rate-Splitting Multiple Access (RSMA) in 6G multi-user MIMO broadcast channels under finite constellations (e.g., QAM): (i) unlocking RSMA gains under discrete modulation, (ii) designing low-complexity receivers, and (iii) ensuring RSMA’s robustness over SDMA without successive interference cancellation (SIC). To this end, we propose a joint optimization framework for linear precoding and hierarchical power allocation tailored to discrete constellations, and establish a unified receiver design paradigm supporting both SIC-based and SIC-free decoding paths. Link-level simulations demonstrate that the proposed scheme significantly outperforms conventional Gaussian-input-based designs under QAM modulation. Crucially, we provide the first empirical validation that SIC-free RSMA receivers consistently achieve substantial rate gains over SDMA—without requiring perfect SIC or infinite-resolution quantization. The results deliver both theoretical foundations and implementable design principles for deploying RSMA in practical 6G systems.

Abstract

Rate-Splitting Multiple Access (RSMA) has emerged as a novel multiple access technique that enlarges the achievable rate region of Multiple-Input Multiple-Output (MIMO) broadcast channels with linear precoding. In this work, we jointly address three practical but fundamental questions: (1) How to exploit the benefit of RSMA under finite constellations? (2) What are the potential and promising ways to implement RSMA receivers? (3) Can RSMA still retain its superiority in the absence of successive interference cancellers (SIC)? To address these concerns, we first propose low-complexity precoder designs by taking finite constellations into account and show that the potential of RSMA is better achieved with such designs than those assuming Gaussian signalling. We then consider some practical receiver designs that can be applied to RSMA. We notice that these receiver designs follow one of two principles: (1) SIC: cancelling upper layer signals before decoding the lower layer and (2) non-SIC: treating upper layer signals as noise when decoding the lower layer. In light of this, we propose to alter the system design according to the receiver category. Through link-level simulations, the effectiveness of the proposed power allocation and receiver designs are verified. More importantly, we show that it is possible to preserve the superiority of RSMA over Spatial Domain Multiple Access (SDMA), including SDMA with advanced receivers, even without SIC at the receivers. Those results therefore open the door to competitive implementable RSMA strategies for 6G and beyond communications.

Problem

• Exploit RSMA benefits with finite constellations.
• Design practical RSMA receivers with/without SIC.
• Preserve RSMA superiority without SIC implementation.

Innovation

• Low-complexity precoder designs for finite constellations
• SIC and non-SIC receiver designs for RSMA
• RSMA superiority maintained without SIC implementation