Intelligent surfaces represent a breakthrough technology capable of customizing the wireless channel cost-effectively. However, the existing works generally focus on planar wavefront, neglecting near-field spherical wavefront characteristics caused by large array aperture and high operation frequencies in the terahertz (THz). Additionally, the single-layer reconfigurable intelligent surface (RIS) lacks the signal processing ability to mitigate the computational complexity at the base station (BS). To address this issue, we introduce a novel stacked intelligent metasurfaces (SIM) comprised of an array of programmable metasurface layers. The SIM aims to substitute conventional digital baseband architecture to execute computing tasks with ultra-low processing delay, albeit with a reduced number of radio-frequency (RF) chains and low-resolution digital-to-analog converters. In this paper, we present a SIM-aided multiuser multiple-input single-output (MU-MISO) near-field system, where the SIM is integrated into the BS to perform beamfocusing in the wave domain and customize an end-to-end channel with minimized inter-user interference. Finally, the numerical results demonstrate that near-field communication achieves superior spatial gain over the far-field, and the SIM effectively suppresses inter-user interference as the wireless signals propagate through it.

翻译：智能表面代表了一种能够经济高效地定制无线信道的突破性技术。然而，现有研究通常聚焦于平面波前，忽略了由太赫兹频段大阵列孔径和高工作频率引起的近场球面波前特性。此外，单层可重构智能表面缺乏信号处理能力，无法减轻基站的计算复杂度。为解决这一问题，我们引入了一种由多层可编程超表面构成的新型堆叠智能超表面。SIM旨在替代传统的数字基带架构，以执行计算任务并实现超低处理延迟，尽管其射频链数量减少且数模转换器分辨率较低。本文提出了一种SIM辅助的多用户多输入单输出近场系统，其中SIM被集成到基站中，在波域执行波束聚焦，并定制一个端到端信道以最小化用户间干扰。最后，数值结果表明，近场通信在空间增益上优于远场，并且当无线信号通过SIM传播时，SIM能有效抑制用户间干扰。