Stacked intelligent metasurface (SIM) is an emerging design that consists of multiple layers of metasurfaces. A SIM enables holographic multiple-input multiple-output (HMIMO) precoding in the wave domain, which results in the reduction of energy consumption and hardware cost. On the ground of multiuser beamforming, this letter focuses on the downlink achievable rate and its maximization. Contrary to previous works on multiuser SIM, we consider statistical channel state information (CSI) as opposed to instantaneous CSI to overcome challenges such as large overhead. Also, we examine the performance of large surfaces. We apply an alternating optimization (AO) algorithm regarding the phases of the SIM and the allocated transmit power. Simulations illustrate the performance of the considered large SIM-assisted design as well as the comparison between different CSI considerations.

翻译：堆叠智能超表面（SIM）是一种由多层超表面构成的新兴设计。SIM能够在波域实现全息多输入多输出（HMIMO）预编码，从而降低能耗与硬件成本。基于多用户波束赋形，本文聚焦于下行链路可达速率及其最大化问题。与以往多用户SIM研究不同，为克服大规模开销等挑战，我们采用统计信道状态信息（CSI）而非瞬时CSI。同时，我们考察了大规模表面的性能表现。针对SIM相位与发射功率分配，我们采用了交替优化（AO）算法。仿真结果展示了所考虑的大规模SIM辅助设计的性能，并比较了不同CSI考量方案的效果。