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强大且可靠的多址接入与干扰管理技术。虽然下行链路多输入多输出（MIMO）RSMA已得到广泛研究，但上行链路MIMO RSMA尚未被充分探索。本文研究了在发送端具有完美信道状态信息（CSIT）与接收端具有完美信道状态信息（CSIR）条件下，上行链路RSMA在短包通信中的性能。我们提出了一个上行链路MIMO RSMA框架，并以最大最小公平性（MMF）为度量，在有限块长（FBL）约束下联合优化预编码器与合并器。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）方法将优化问题分解为两个子问题。针对这些子问题，我们提出了一种基于逐次凸逼近（SCA）的求解方法。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，我们设计并评估了上行链路MIMO RSMA架构的物理（PHY）层，该评估基于多用户链路级仿真（LLS），并考虑了有限星座调制、有限长极化码、消息分割、自适应调制编码以及接收端的连续干扰消除（SIC）。数值结果表明，在有限块长约束下，将RSMA应用于上行链路MIMO不仅能在最大最小公平性上超越传统传输方案（如空分多址（SDMA）与非正交多址接入（NOMA）），而且对网络负载表现出鲁棒性。同时，对来自多个用户的消息进行分割的优势也得到了阐明。链路级仿真结果证实了RSMA相较于SDMA和NOMA在最大最小吞吐量方面的提升。