Intelligent reflecting surfaces (IRSs) 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 IRS-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 IRS, orientation and position of the IRS 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 IRS position optimization problem in arbitrary three-dimensional space, a dimensional-reducing theory is proved, which is useful to reduce the complexity of search method. The simulation results show that the proposed closed-form beamforming and phase shifts are near-optimal solutions. Besides, the IRS significantly enhances the performance of the communication system when it is deployed at the optimal position.

翻译：智能反射表面(IRS)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,我们研究了在自由空间运行的远方IRS辅助多投入单输出通信系统。为了最大限度地发挥从物理和电磁性质角度接收接收器的能量,优化,包括发射机的波束成形、IRS的相向转移、IRS的方向和位置被制定和解决。在利用视线特性后,我们产生了光学成形和相向转移的封闭式解决方案。对于在任意的三维空间的非三维IRS定位优化问题,已经证明了一个维度降低理论,这有助于降低搜索方法的复杂性。模拟结果表明,拟议的闭式成形和相向变化是近乎最佳的解决办法。此外,IRS在最优化位置部署通信系统时,其性能显著提高。