  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.
