Performance Analysis of UAV Assisted Mobile Communications in THz Channel

The huge available bandwidth in Terahertz (THz) frequency band is recently contemplated to achieve high data rate wireless communications. Consequently, THz communications are attractive candidates to fulfill the continuous ever–increasing requirements of future wireless networks. Numerous beyond 5G applications are highly considered for those systems such as high capacity backhaul, enhanced hotspot booths as well as short–range device–to–device (D2D) communications. Wireless communications systems that deploy unmanned aerial vehicles (UAVs) promise to achieve cost–effective wireless connectivity for devices without any need to pay for infrastructure coverage. When compared to terrestrial communications, wireless systems with UAVs are generally faster and more flexible to deploy or reconfigure. In addition, systems deploying UAVs are likely to have much better communication channels due to their high mobility capabilities. Accordingly, the presence of short–range line–of–sight (LOS) links prevail. In this paper, we consider a single–cell cellular network with a UAV deployed as a decode-and-forward (DF) relay in the full-duplex (FD) mode in order to assist a base station (BS) and extend its coverage over THz channel. A joint power allocation and trajectory optimization scheme that minimizes the outage probability of the link between the BS and a mobile device (MD) is derived in the presence of the interference of the D2D devices that share the same THz frequency band. Furthermore, the optimum powers of the MD and the UAV that maximize the achievable rate at the BS are obtained. The performance of the proposed schemes is compared with the fixed power allocation schemes which distribute the power equally among users. Numerical results show that the outage probability and the achievable rate at the BS using the proposed schemes are remarkably superior compared to the fixed power allocation schemes.