A Study on Pathloss Model for UAV Based Urban Disaster and Emergency Communication Systems

In recent times, airborne Base Station (BS) or Unmanned Aerial Vehicle (UAV) mounted Evolved Node B (UeNBs) are used to provide broadband services, and rescue responses in emergency and natural disaster scenarios. Most of the prior studies on airborne BS assume outdoor users only and consider their position coordinates in a two-dimensional (2-D) plane considering only Euclidean distance based pathloss. However in urban natural disaster scenarios such as flooding or cyclone, users are trapped inside single or multi-storey buildings; user positions are in three-dimensional (3-D) plane. Reliable communication and rescue operations in such situation is possible if pathloss characteristics for both, user to UeNB (uplink) and vice versa (downlink), are known a-priori. Since pathloss in above scenarios is a combination of indoor and outdoor component, it becomes a challenge to adopt appropriate model which can be used during communications. In this paper, we have studied several state-of-the-art pathloss models applicable in the above scenarios and compared their performances. We have also studied the impact of indoor and outdoor environments on the uplink and downlink pathloss models. Our extensive simulation results give a full fledged insight to uplink and downlink channel characteristics of UAV based wireless emergency communication system. From our extensive studies and simulations, we have learnt that Winner II model [1] with additional indoor blockage component provides the best pathloss model for an urban emergency scenario. Furthermore, we have also analyzed the impact of different topological parameters such as UeNB hovering altitude, building heights, indoor and outdoor distance of users, etc., on the pathloss characteristics.