Outage Probability Analysis of Uplink RIS and UAV—Assisted THz Mobile Communications

Reconfigurable intelligent surface (RIS) is considered as a promising low-cost technology that can adaptively control the phase of signals to boost the system performance. For a higher probability of line-of-sight (LOS) between communicating nodes and to substitute for loss due to long distance travelled, an unmanned aerial vehicle (UAV) is deployed. In this paper, we investigate the uplink RIS-assisted communication system in the terahertz (THz) band in the existence of a couple of underlaying device-to-device (D2D) pairs. The RIS is attached to the UAV for a higher mobility and channel gains quality. A closed form expression is derived for the outage probability at the base station (BS) for the considered scenario. The optimum UAV's position that minimizes this outage probability is obtained using Golden Search method. Moreover, the optimum phase shifts of the RIS elements that maximize the signal-to-interference-noise-ratio (SINR) at the BS are obtained. Numerical results are obtained to evaluate the performance of the outage probability of the system. The results show that using the optimum algorithm, the outage probability achieves the minimum value compared to other schemes.