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.Comment: Submitted to IEEE for publicatio