Uav-assisted wireless communication system for on-demand coverage

Abstract

Unmanned aerial vehicles (UAVs) are thought to be the next-generation systems to enhance cellular coverage. The aerial nature of UAVs and their inherent characteristics, such as mobility, flexibility, and adaptive altitude, allow them to be deployed on an on-demand basis to assist the current cellular infrastructure by delivering additional coverage capabilities in either the hotspot or remote areas. Moreover, they can maintain line-of-sight (LoS) connection with the ground users leading to enhanced coverage and eciency. Therefore, it is desirable to use the UAV as an aerial base station (ABS) to improve the wireless services and coverage in hotspot areas, such as football stadiums, fairs, public safety services (for example, firefighters and military operations), etc. However, the use of UAVs as ABS requires some key design considerations, such as three-dimensional (3D) placement, communication-oriented trajectory design, energy eciency, maximizing the performance metric, etc., to meet the application-specific requirements. Therefore, this dissertation intends to study a UAV-assisted communication system wherein a UAV is to be deployed in a timely and energy-ecient manner to provide optimum coverage to ground users. In particular, we first study the optimal deployment location of the UAV to provide maximal performance to the ground users. After that, we obtain the UAV’s path from the initial to the deployment location while meeting the UAV’s energy and flight duration constraints. This scenario is very relevant to many practical applications where the deployment location is unknown and is based on ground users’ location, such as providing high-speed connectivity to the first responders in emergencies, o✏oading trac in a high-density area, such as football stadiums, or recovering the service in a disaster-a↵ected areas. We then study the velocity-acceleration and time profile to maximize the sum user throughput while considering the UAV kinematics (velocity and acceleration), mission completion time and UAV energy consumption as a function of velocity and acceleration as constraints. This is because the onboard energy available with the UAV, which is utilized in manoeuvring and hovering-related tasks, is determined by its flying velocity-acceleration profile and flight time. Notably, in missions requiring long battery endurance, the battery limitation problem inhibits the UAV from delivering long-term service. As a result, to maintain coverage continuity, we propose a UAV replacement mechanism (a way to provide an uninterrupted long-term service). UAV replacement indicates that the existing serving UAV must be replaced by another fully charged UAV when its available energy is exhausted. Finally, when multiple UAVs are deployed to provide service to multiple ground users spread over a given area, we study an association probability model based on a stochastic geometry framework for a UAV-assisted wireless communication network. The above works/setups can be applied to many practical applications, such as establishing two-way communication between first responders and firefighters in areas with inadequate coverage or trac o✏oading in a hotspot area, such as sports events.