An IR-HARQ Based RSMA for Reliable and Low-Latency Communication

In rate-splitting multiple access (RSMA) networks, high reliability is critical, and one efficient way to improve reliability is to use a hybrid automated repeat request (HARQ) protocol. However, the challenge lies in designing the HARQ in RSMA networks due to the combining and splitting procedures at the transmitter side. In this paper, we propose a novel transmission approach based on incremental redundancy (IR) that is also equivalent to the HARQ protocol for RSMA networks. The proposed strategy opens up a new path for RSMA networks where HARQ is challenging or cannot be applied. In particular, a redundancy version (RV) of each user's private data is constructed and placed in the common stream by making use of common stream properties such as transmitting it non-orthogonally with higher power, alongside the private stream. The efficacy of the proposed design is examined through various metrics, encompassing average transmission rate, outage analysis, energy efficiency (EE), and diversity order. Simulation results validate the superior performance of the proposed protocol, showcasing a significant improvement of up to 60%, 23%, and 79% in terms of packet error rate, average waiting time, and EE respectively, compared to the conventional HARQ RSMA.