This work investigates the design of Hybrid Automatic Repeat Request (HARQ) strategies for downlink Rate-Splitting Multiple Access (RSMA). The existence of private and common stream as well as their conditioning for Successive Interference Cancellation (SIC), gives rise to an expanded set of opportunities for retransmission of failed packets. Specifically, we devise a scheme in which the retransmissions are scheduled through the common stream, which offers a higher success probability. With this, the common stream needs to carry both new and retransmitted bits, which leads to a layered HARQ (L-HARQ) strategy which is capable of trading off throughput and reliability. Simulation results demonstrate that the devised HARQ scheme outperforms RSMA with conventional HARQ, where each retransmission is handled independently through its own stream. It also helps in closing the throughput gap between HARQ and Adaptive Modulation and Coding (AMC) in the high Signal-to-Noise Ratio (SNR) regime while also achieving a decreased Packet Error Rate (PER) and a lower latency.

翻译：本文研究了下行链路速率分割多址接入（RSMA）的混合自动重传请求（HARQ）策略设计。私有流与公共流的存在及其对连续干扰消除（SIC）的条件约束，为失败数据包的重传提供了更多机会。具体而言，我们设计了一种通过公共流调度重传的方案，该方案具有更高的成功概率。由此，公共流需同时承载新传与重传比特，从而形成一种能够在吞吐量与可靠性之间进行权衡的分层HARQ（L-HARQ）策略。仿真结果表明，所提出的HARQ方案优于采用传统HARQ的RSMA方案（传统方案中每个重传通过其自身流独立处理）。该方案还有助于在高信噪比（SNR）区间缩小HARQ与自适应调制编码（AMC）之间的吞吐量差距，同时实现更低的误包率（PER）与更低的时延。