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

Sibo Zhang, Bruno Clerckx, David Vargas, Oliver Haffenden, Andrew Murphy

TL;DR

This work tackles RSMA in practical downlink systems with finite constellations and receiver non‑idealities. By deriving constellation‑constrained rate expressions and proposing low‑complexity, direction‑fixed precoders, it demonstrates that CC sum‑rate oriented designs unlock RSMA’s practical gains. A family of transceiver designs is introduced, spanning SIC and non‑SIC paradigms, with detailed complexity assessments. Link‑level simulations show RSMA retains superiority over SDMA under realistic constraints, and that SIC‑free variants—especially soft CWIC and soft SLIC—offer favorable trade‑offs for 6G‑scale deployments.

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 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 precoder design according to the receiver category. Through link-level simulations, the effectiveness of the proposed precoder 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.

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

TL;DR

This work tackles RSMA in practical downlink systems with finite constellations and receiver non‑idealities. By deriving constellation‑constrained rate expressions and proposing low‑complexity, direction‑fixed precoders, it demonstrates that CC sum‑rate oriented designs unlock RSMA’s practical gains. A family of transceiver designs is introduced, spanning SIC and non‑SIC paradigms, with detailed complexity assessments. Link‑level simulations show RSMA retains superiority over SDMA under realistic constraints, and that SIC‑free variants—especially soft CWIC and soft SLIC—offer favorable trade‑offs for 6G‑scale deployments.

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 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 precoder design according to the receiver category. Through link-level simulations, the effectiveness of the proposed precoder 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.
Paper Structure (26 sections, 2 theorems, 31 equations, 16 figures, 2 tables)

This paper contains 26 sections, 2 theorems, 31 equations, 16 figures, 2 tables.

Table of Contents

  1. Introduction
  2. RSMA System Model
  3. Low-complexity precoder designs for RSMA
  4. Sum-Rate Optimization
  5. Constellation-Constrained Sum-Rate Optimization
  6. Transceiver designs for RSMA
  7. Transmitter Design
  8. Receiver Designs
  9. Hard CWIC
  10. Soft CWIC 1
  11. Soft CWIC 2
  12. Joint De-mapper
  13. Soft SLIC
  14. Comments on different receivers
  15. Complexity
  16. ...and 11 more sections

Key Result

Proposition 1

The CC sum-rate of RSMA with SIC receivers is expressed as (CC_sum_rate_SIC) and can be well approximated by (CC_sum_rate_approx_SIC), where $\mathbf{p}_\text{c} = \sqrt{P_\text{T}t}\Bar{\mathbf{p}}_\text{c}$, $\mathbf{p}_k = \sqrt{\frac{P_\text{T}(1-t)}{K}}\Bar{\mathbf{p}}_k$, $\mathcal{X}_\text{c}

Figures (16)

  • Figure 1: RSMA for multi-user MISO.
  • Figure 2: Comparison of CC sum-rate for RSMA with SIC achieved by different methods of searching for $t^\star$ with $N_t=4$, $K=2$.
  • Figure 4: Transmitter architecture.
  • Figure 5: Hard CWIC.
  • Figure 6: Soft CWIC 1.
  • ...and 11 more figures

Theorems & Definitions (3)

  • Proposition 1
  • Proposition 2
  • Remark 1: Phase shift and search space