Codeword-Segmentation Rate-Splitting Multiple Access and Evaluation under Suboptimal Decoding

TL;DR

This paper introduces Codeword-Segmentation RSMA, a new downlink multiple access scheme that encodes messages directly, segments codewords, and improves sum-rate performance with a novel analysis framework and practical implementation benefits.

Contribution

The paper proposes CS-RSMA, a novel encoding and segmentation scheme for RSMA, along with a new performance analysis framework and optimized precoding strategies.

Findings

CS-RSMA outperforms conventional RSMA in sum-rate.

CS-RSMA achieves similar fairness performance as conventional RSMA.

Physical-layer implementation of CS-RSMA shows practical benefits.

Abstract

Rate-Splitting Multiple Access (RSMA) has been recognized as a promising multiple access technique. We propose a novel architecture for downlink RSMA, namely Codeword-Segmentation RSMA (CS-RSMA). Different from conventional RSMA which splits users' messages into common and private parts before encoding, CS-RSMA encodes the users' messages directly, segments the codewords into common and private parts, and transmits the codeword segments using common and private streams. In addition to the principle of CS-RSMA, a novel performance analysis framework is proposed. This framework utilizes a recent discovery in mismatched decoding under finite-alphabet input and interference, and can better capture the receiver's complexity limits. Precoder optimization under finite alphabets and suboptimal decoders for conventional RSMA and CS-RSMA to maximize the Sum-Rate (SR) and the Max-Min Fairness (MMF) is also addressed. The numerical results reveal the theoretical performance of conventional RSMA and CS-RSMA. We observe that CS-RSMA leads to better performance than conventional RSMA in SR, and similar performance in MMF. Furthermore, a physical-layer implementation of CS-RSMA is proposed and evaluated through link-level simulations. Aside performance benefits, we also demonstrate that CS-RSMA brings significant benefits on the encoding/decoding, control signaling, and retransmission process compared to conventional RSMA.