  The usage of Reconfigurable Intelligent Surfaces (RIS) in conjunction with
Unmanned Ariel Vehicles (UAVs) is being investigated as a way to provide
energy-efficient communication to ground users in dense urban areas. In this
paper, we devise an optimization scenario to reduce overall energy consumption
in the network while guaranteeing certain Quality of Service (QoS) to the
ground users in the area. Due to the complex nature of the optimization
problem, we provide a joint UAV trajectory and RIS phase decision to minimize
transmission power of the UAV and Base Station (BS) that yields good
performance with lower complexity. So, the proposed method uses a Successive
Convex Approximation (SCA) to iteratively determine a joint optimal solution
for UAV Trajectory, RIS phase and BS and UAV Transmission Power. The approach
has, therefore, been analytically evaluated under different sets of criterion.
