3D UAV Placement and Trajectory Optimization in UAV Assisted Wireless Networks

In view of their mobility, maneuverability, flexibility, ease of deployment, and relatively low cost, UAVs have recently found applications in areas besides the military missions. UAVs can function either as special flying users in coexistence with terrestrial users, commonly called as cellular-connected UAVs, or can be employed as flying base stations, commonly called UAV- assisted communication that can provide on-demand and reliable wireless access to intended areas. Despite these advantages, the road to integrating UAVs in wireless communication is not without challenges. Efficient 3D deployment and trajectory optimization of UAVs are among the key challenges in UAV- assisted wireless networks due to a number of factors that need to be considered. In this paper, focusing on UAV-assisted wireless networks, we provide a survey on 3D UAV placement and trajectory optimization. In addition, we highlight the existing challenges and open research issues in order to spur further investigation in this area.