  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.
