  Recently, Unmanned Aerial Vehicle (UAV) based communications systems have
attracted increasing research and commercial interest due to their cost
effective deployment and ease of mobility.During natural disasters and
emergencies, such networks are extremely useful to provide communication
service. In such scenarios, UAVs position and trajectory must be optimal to
maintain Quality of Service at the user end. This paper focuses on the
deployment of an SDN-based UAV network providing communication service to the
users. We consider the deployment of the system in stadiums and events. In this
paper, we propose a scheme to allocate UAVs to the users and a traffic
congestion algorithm to reduce the number of packets dropped to avoid
re-transmissions from the user end. We also propose an energy efficient multi
hop routing mechanism to avoid the high power requirement to transmit longer
distances. We assume that all the back-haul links have sufficient capacities to
carry all the traffic from the front-haul links and the design of UAVs must
consider their power requirements for both flight and transmission.
