Flexible intelligent metasurface (FIM) is a recently developed, groundbreaking hardware technology with promising potential for 6G wireless systems. Unlike conventional rigid antenna array (RAA)-based transmitters, FIM-assisted transmitters can dynamically alter their physical surface through morphing, offering new degrees of freedom to enhance system performance. In this letter, we depart from prior works that rely on instantaneous channel state information (CSI) and instead address the problem of average sum spectral efficiency maximization under statistical CSI in a FIM-assisted downlink multiuser multiple-input single-output setting. To this end, we first derive the spatial correlation matrix for the FIM-aided transmitter and then propose an iterative FIM optimization algorithm based on the gradient projection method. Simulation results show that with statistical CSI, the FIM-aided system provides a significant performance gain over its RAA-based counterpart in scenarios with strong spatial channel correlation, whereas the gain diminishes when the channels are weakly correlated.

翻译：柔性智能超表面（FIM）是近期发展的一项突破性硬件技术，在6G无线系统中展现出广阔的应用前景。与传统的基于刚性天线阵列（RAA）的发射机不同，FIM辅助的发射机可通过形变动态改变其物理表面，为提升系统性能提供了新的自由度。本文区别于以往依赖瞬时信道状态信息（CSI）的研究，针对FIM辅助的下行多用户多输入单输出场景，探讨了在统计CSI条件下的平均和频谱效率最大化问题。为此，我们首先推导了FIM辅助发射机的空间相关矩阵，随后提出了一种基于梯度投影法的迭代FIM优化算法。仿真结果表明，在统计CSI条件下，当空间信道相关性较强时，FIM辅助系统相比基于RAA的系统具有显著的性能增益；而在信道弱相关时，该增益则逐渐减弱。