Performance Analysis of Uplink Rate-Splitting Multiple Access with Hybrid ARQ

TL;DR

The paper investigates uplink RSMA with a tailored HARQ strategy for two single-antenna users, enabling selective retransmissions of the strong-user split stream $s_{1,1}$ and the weak-user stream $s_2$ via a fixed decoding order. By optimizing the power split $\alpha$ to minimize the sum of post-retransmission error probabilities under Chase Combining and Incremental Redundancy, RSMA consistently reduces error probability, particularly for the weaker user, and lowers energy per packet compared to FDMA and NOMA baselines. The approach leverages RSMA’s interference-cancellation capability to decouple retransmissions and enhance diversity, with results showing promising gains for ultra-reliable low-latency and energy-constrained scenarios. The study provides a foundation for extending HARQ-RSMA to multi-user settings and invites further exploration of imperfect SIC effects.

Abstract

Rate-splitting multiple access (RSMA) has attracted a lot of attention as a general and powerful multiple access scheme. In the uplink, instead of encoding the whole message into one stream, a user can split its message into two parts and encode them into two streams before transmitting a superposition of these two streams. The base station (BS) uses successive interference cancellation (SIC) to decode the streams and reconstruct the original messages. Focusing on the packet transmission reliability, we investigate the features of RSMA in the context of hybrid automatic repeat request (HARQ), a well-established mechanism for enhancing reliability. This work proposes a HARQ scheme for uplink RSMA with different retransmission times for a two-user scenario and introduces a power allocation strategy for the two split streams. The results show that compared with non-orthogonal multiple access (NOMA) and frequency division multiple access (FDMA), RSMA outperforms them in terms of error probability and power consumption. The results show that RSMA with HARQ has the potential to improve the reliability and efficiency of wireless communication systems.

Figures (14)

• Figure 1: The retransmission schemes of FDMA, NOMA and RSMA
• Figure 2: An illustration of capacity region for two users.
• Figure 3: A 3-user case
• Figure 4: The number of users splitting messages.
• Figure 5: The situation that only $s_2$ needs retransmission. BS fails to decode $s_2$ and $s_{1,2}$, but only asks user 2 to retransmit $s_2$. Then, BS uses two interfered copies of $s_2$ to decode it, and then continues decoding $s_{1,2}$.

Theorems & Definitions (1)

• Remark 1