Ergodic Sum-Rate Analysis and Optimization of RSMA-Based CF-mMIMO Systems Under the FBL Regime With Imperfect SIC

This paper investigates the application of rate-splitting multiple-access (RSMA) in cell-free massive multiple-input multiple-output (CF-mMIMO) systems. Considering a practical system under the finite blocklength (FBL) regime, we address performance degradation caused by imperfect successive interference cancellation (SIC) and provide theoretical analyses of the ergodic sum rate (ESR) under different types of channel state information (CSI). For statistical CSI, the use-and-then-forget principle is employed to mitigate outdated CSI, while for instantaneous CSI, the moment matching method is utilized to perform a more accurate ESR analysis. To enhance spectral efficiency while ensuring reliability, we approximate the multivariate expression under the FBL regime and propose a joint power allocation and rate-splitting scheme which mitigates interference resulting from imperfect SIC and CSI. Simulation results validate the accuracy of the performed analyses and demonstrate that the proposed joint scheme outperforms conventional schemes.