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 far-field RIS-assisted multiple-input single-output (MISO) communication system operating in free space. To maximize the received power of the receiver from the physics and electromagnetic nature point of view, an optimization, including beamforming of the transmitter, phase shifts of the RIS, orientation and position of the RIS is formulated and solved. After exploiting the property of line-of-sight (LoS), 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 are near-optimal solutions. Besides, the RIS significantly enhances the performance of the communication system when it is deployed at the optimal position.
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,能够重新配置无线传播环境。在本文中,我们研究了在自由空间运行的远场RIS辅助多投入单输出(MISO)通信系统。为了最大限度地发挥从物理和电磁性质角度接收的接收器的接收力,一个优化,包括发射机的波束成形、RIS的相位转移、RIS的方向和位置的形成和解决。在利用视线特性之后,我们得出了波束成形和相位转移的封闭式解决方案。对于在任意的三维空间的非三维空间的RIS位置优化问题,一个维度降低理论得到了证明。模拟结果表明,拟议的闭式成形和阶段转移是近于最佳的解决方案。此外,在将通信系统安装在最佳位置时,RIS极大地提高了通信系统的性能。