Reconfigurable intelligent surfaces (RISs) are envisioned to be a disruptive wireless communication technique that is capable of reconfiguring the wireless propagation environment. In this paper, we study a free-space RIS-assisted multiple-input single-output (MISO) communication system in far-field operation. To maximize the received power from the physical and electromagnetic nature point of view, a comprehensive optimization, including beamforming of the transmitter, phase shifts of the RIS, orientation and position of the RIS is formulated and addressed. After exploiting the property of line-of-sight (LoS) links, we derive closed-form solutions of beamforming and phase shifts. For the non-trivial RIS position optimization problem in arbitrary three-dimensional space, a dimensional-reducing theory is proved. The simulation results show that the proposed closed-form beamforming and phase shifts approach the upper bound of the received power. The robustness of our proposed solutions in terms of the perturbation is also verified. Moreover, the RIS significantly enhances the performance of the mmWave/THz communication system.

翻译：重新配置智能表面(RIS)被认为是一种破坏性无线通信技术,能够对无线传播环境进行重新配置。在本文中,我们研究了远方行动中自由空间的RIS辅助多投入单输出(MISO)通信系统。为了最大限度地扩大从物理和电磁性质角度获得的能量,全面优化,包括发射机的波束成形、RIS的相位转移、RIS的方向和位置得到拟订和处理。在利用视线链接的特性之后,我们得出了波形和相位变化的封闭式解决方案。对于在任意的三维空间的非三维空间的RIS定位优化问题,一个维度减低理论得到了证明。模拟结果表明,拟议的闭式调整和阶段转移方法接近了接收能量的上层。我们还核实了在扰动方面拟议解决办法的稳健性。此外,RIS大大增强了毫米Wave/Thz通信系统的性能。