Deployment Strategies for a Fleet of Unmanned Aerial Vehicles Providing Cellular and Data Services
Creators: name: Mohseni, Nima 
Publisher: name: University of Nevada, Las Vegas
Year: 2017

description: Wireless voice and data communications have become an essential part of our day to day lives. In order to provide these services to as many people as possible, a great infrastructure has been put in place over the last two decades throughout the world. The current infrastructure is mainly consists of cellular towers with gateways to the telecommunication backbone. The wireless infrastructure is doing an adequate job of providing voice and data services, getting more powerful and efficient every day. However, because wireless infrastructure is mainly based on fixed cell towers, it lacks the flexibility and dynamism that may be needed in several important scenarios. For example, a natural or man-made disaster, like an earthquake or war, often results in partial or full destruction of power grids and cellular infrastructure. Our current cellular system lacks the ability to restore the service in a timely manner in these situations, when it is needed the most. Another scenario where a fixed cellular system can be problematic is a metropolitan area where there is a great shift on the demand for services in specific areas at specific times. A more dynamic and mobile system is desirable in such situations. Another example can be a sports stadium or a big convention center that need to provide a large sum of users, service during an event. There are many such examples. However, if we put several fixed towers accommodating the need, they will be wasted the rest of the times. 
The emergence of unmanned aerial system (UAS) to be used in commercial and civilian applications provides a solution to add dynamism and flexibility to the current wireless infrastructure. In particular, we are looking at a UAS mainly consisting of several low end unmanned aerial vehicles (UAVs). Each of these UAVs will act as a wireless service provider making up a network which covers a specific area and route the communication through a ground station connected to the backbone or a satellite link. Such a system is very flexible and dynamic. This system can be deployed in an efficient and rapid manner when the need arises, such as a natural or man-made disaster. It can also be used as an auxiliary part of a normal working fixed infrastructure to add dynamism and provide additional temporary services in places and at times they are needed. These can be reused in other areas at other times. UAV networks may vary in different aspects such the dynamism of the network and topology of the network. If designed carefully, such a system not only can be lifesaving in a disaster relief, it can also be cost-effective to be used to complement to the cellular infrastructure in normal situations. 
Designing a UAS to provide wireless services requires a lot of interdisciplinary research from designing the UAVs themselves to designing the payload that provides the wireless services and accommodates wireless network interconnection to itself or to the ground station. In this thesis, we consider the limitations of the elements making such a system and how they impact the coverage they can provide in practical scenarios. We discuss systematic and physical attributes of UAVs and mathematically model the limitation they put on the system performance. After establishing reasonable restricting parameters, we define an optimization problem where for a given set of UAVs and a given area to provide service for, we answer the question of how to deploy each UAV such that we have maximum possible coverage. The idea of having a population map as an input to our optimization problem and how to obtain an approximate map has been discuss. Then, several sub-optimal solutions for the optimization problem are discussed, simulated and compared for some typical population maps. We also consider what changes when we apply the same approaches to larger areas and introduce the concept of reconfiguration as important part of the system in these cases. We then introduce different approaches for reconfiguration discussing their benefits and shortcomings. Our simulation results show that in order to have practical systems in large areas, either the number of UAVs should significantly increase, or one need to design very powerful payload providing higher capacity for individual UAV.