Understanding the performance of multi-user multiple-input multiple-output (MU-MIMO) systems under imperfect channel state information at the transmitter (CSIT) remains a critical challenge in next-generation wireless networks. In this context, accurate statistical modeling of the signal-to-interference-plus-noise ratio (SINR) is essential for enabling tractable performance analysis of multi-user systems. This paper presents an improved statistical approximation of the SINR for downlink (DL) MU-MIMO systems with imperfect CSIT. The proposed model retains the analytical simplicity of existing approaches (e.g., Gamma-based approximations) while overcoming their limitations, particularly the underestimation of SINR variance. We evaluate the proposed approximation in the context of Rate-Splitting Multiple Access (RSMA)-enabled MIMO DL systems with outdated CSIT. The results demonstrate excellent accuracy across a wide range of system configurations, including varying numbers of users, antennas, and degrees of CSIT staleness.

翻译：理解发射机侧信道状态信息不完善条件下多用户多输入多输出系统的性能，仍是下一代无线网络面临的关键挑战。在此背景下，对信号与干扰加噪声比进行精确的统计建模，对于实现多用户系统可处理的性能分析至关重要。本文针对信道状态信息不完善的下行多用户多输入多输出系统，提出了一种改进的SINR统计近似模型。该模型在保持现有方法解析简洁性的同时，克服了其局限性——特别是对SINR方差的低估问题。我们在采用速率分割多址接入且具有过时信道状态信息的MIMO下行系统中评估了所提出的近似方法。结果表明，该模型在用户数、天线数和信道状态信息过时程度各异的广泛系统配置下，均表现出优异的准确性。