Reconfigurable Intelligent Surface and UAV–Assisted THz Mobile Communications

Terahertz (THz) Communications are promising candidate for achieving ultra high data rate suitable for 5G and beyond. Unmanned Aerial Vehicle (UAV) is an emerging facility that can be utilized to assist wireless communications. A reconfigurable intelligent surface (RIS) is deployed such that the phase shifts of its elements are reconfigured to create favorable beam steering, which in turn mitigates undesired interference from other existing links in the network. In this paper, we consider a UAV equipped with an RIS operating in THz, where a cellular user link, in addition to a number of Device-to-Device (D2D) pairs links are considered. The direct paths between each two communicating nodes are considered as well as the RIS-reflected paths. Then, the sum rate is derived under this scenario. Accordingly, a joint power allocation and phase shifts optimization scheme is proposed for the sake of maximizing the sum rate. The proposed joint power allocation and phase shifts optimization scheme is evaluated in terms of the achieved sum rate. Numerical results show that the proposed scheme surpasses three other schemes, achieving the highest sum rate among them all, under varying different parameters in the network.