In this paper, we address two crucial challenges in the design of cell-free (CF) systems: degradation in the performance of CF systems by imperfect channel state information at the transmitter (CSIT) and high computational/signaling loads arising from the increasing number of distributed antennas and parameters to be exchanged. To mitigate the effects of imperfect CSIT, we employ rate-splitting (RS) multiple-access, which separates the messages into common and private streams. Unlike prior works, we present a clustered CF multi-user multiple-antenna framework with RS, which groups the transmit antennas in several clusters to reduce the computational and signaling loads. The proposed RS-CF system employs one common stream per cluster to exploit the network diversity. Furthermore, we propose new cluster-based linear precoders for this framework. We then devise a power allocation strategy for the common and private streams within clusters and derive closed-form expressions for the sum-rate performance of the proposed cluster-based RS-CF system. Numerical results show that the proposed clustered RS-CF system and algorithms outperform existing approaches. % in terms of the sum-rate.

翻译：本文针对无蜂窝（CF）系统设计中的两个关键挑战展开研究：发射端非理想信道状态信息（CSIT）导致的CF系统性能下降，以及分布式天线数量增加与参数交换带来的高计算/信令负载。为抑制非理想CSIT的影响，我们采用速率分割（RS）多址接入技术，将消息分离为公共流和私有流。与以往研究不同，本文提出了一种基于速率分割的聚类无蜂窝多用户多天线框架，通过将发射天线分组为多个聚类来降低计算与信令负载。所提出的RS-CF系统为每个聚类配置一个公共流以利用网络分集增益。在此基础上，我们进一步为该框架设计了新的基于聚类的线性预编码器，并制定了聚类内公共流与私有流的功率分配策略，推导了所提基于聚类的RS-CF系统和速率的闭式表达式。数值结果表明，所提出的聚类RS-CF系统及算法在系统和速率方面优于现有方法。