Rate-Splitting Multiple Access (RSMA) has emerged as a potent and reliable multiple access and interference management technique in wireless communications. While downlink Multiple-Input Multiple-Ouput (MIMO) RSMA has been widely investigated, uplink MIMO RSMA has not been fully explored. In this paper, we investigate the performance of uplink RSMA in short-packet communications with perfect Channel State Information at Transmitter (CSIT) and Channel State Information at Receiver (CSIR). We propose an uplink MIMO RSMA framework and optimize both precoders and combiners with Max-Min Fairness (MMF) metric and Finite Blocklength (FBL) constraints. Due to the high coupling between precoders and combiners, we apply the Alternating Optimization (AO) to decompose the optimization problem into two subproblems. To tackle these subproblems, we propose a Successive Convex Approximation (SCA)-based approach. Additionally, we introduce a low-complexity scheme to design the decoding order at the receiver. Subsequently, the Physical (PHY)-layer of the uplink MIMO RSMA architecture is designed and evaluated using multi-user Link-Level Simulations (LLS), accounting for finite constellation modulation, finite length polar codes, message splitting, adaptive modulation and coding, and Successive Interference Cancellation (SIC) at the receiver. Numerical results demonstrate that applying RSMA in uplink MIMO with FBL constraints not only achieves MMF gains over conventional transmission schemes such as Space Division Multiple Access (SDMA) and Non-orthogonal Multiple Access (NOMA) but also exhibits robustness to network loads. The benefits of splitting messages from multiple users are also illustrated. LLS results confirm the improved max-min throughput benefits of RSMA over SDMA and NOMA.

翻译：速率分割多址接入（RSMA）已成为无线通信中一种高效且可靠的多址接入与干扰管理技术。尽管下行多输入多输出（MIMO）RSMA已被广泛研究，但上行MIMO RSMA的探索尚不充分。本文研究了在发送端完美信道状态信息（CSIT）和接收端完美信道状态信息（CSIR）条件下，短包通信中上行RSMA的性能。我们提出了一种上行MIMO RSMA框架，并基于最大最小公平性（MMF）准则和有限块长（FBL）约束对预编码器与合并器进行联合优化。由于预编码器与合并器之间存在高度耦合，我们采用交替优化（AO）将原优化问题分解为两个子问题。为求解这些子问题，我们提出了一种基于逐次凸逼近（SCA）的方法。此外，我们引入了一种低复杂度方案来设计接收端的解码顺序。随后，通过多用户链路级仿真（LLS），考虑有限星座调制、有限长度极化码、消息分割、自适应调制编码以及接收端连续干扰抵消（SIC），设计并评估了上行MIMO RSMA架构的物理层（PHY）。数值结果表明，在FBL约束下将RSMA应用于上行MIMO，不仅能比传统传输方案（如空分多址接入（SDMA）和非正交多址接入（NOMA））获得MMF增益，还能对网络负载表现出鲁棒性。同时，多用户消息分割的优势也得到了验证。LLS结果进一步证实了RSMA在最大化最小吞吐量方面优于SDMA和NOMA。