Low earth orbit (LEO) satellite communication systems have gained increasing attention as a crucial supplement to terrestrial wireless networks due to their extensive coverage area. This letter presents a novel system design for LEO satellite systems by leveraging stacked intelligent metasurface (SIM) technology. Specifically, the lightweight and energy-efficient SIM is mounted on a satellite to achieve multiuser beamforming directly in the electromagnetic wave domain, which substantially reduces the processing delay and computational load of the satellite compared to the traditional digital beamforming scheme. To overcome the challenges of obtaining instantaneous channel state information (CSI) at the transmitter and maximize the system's performance, a joint power allocation and SIM phase shift optimization problem for maximizing the ergodic sum rate is formulated based on statistical CSI, and an alternating optimization (AO) algorithm is customized to solve it efficiently. Additionally, a user grouping method based on channel correlation and an antenna selection algorithm are proposed to further improve the system performance. Simulation results demonstrate the effectiveness of the proposed SIM-based LEO satellite system design and statistical CSI-based AO algorithm.

翻译：低地球轨道卫星通信系统因其广覆盖特性，作为地面无线网络的重要补充日益受到关注。本文提出一种基于堆叠智能超表面技术的低轨卫星系统创新设计方案。具体而言，将轻量化、低能耗的堆叠智能超表面安装在卫星上，直接在电磁波域实现多用户波束赋形，相较于传统数字波束赋形方案，大幅降低卫星处理时延与计算负荷。为克服发射端获取瞬时信道状态信息的挑战并最大化系统性能，基于统计信道状态信息建立了以遍历和速率最大化为目标的联合功率分配与堆叠智能超表面相移优化问题，并定制了一种高效的交替优化算法进行求解。此外，本文还提出了基于信道相关的用户分组方法与天线选择算法以进一步提升系统性能。仿真结果验证了所提基于堆叠智能超表面的低轨卫星系统设计方案及基于统计信道状态信息的交替优化算法的有效性。