  As an autonomous vehicles, Unmanned Aerial Vehicles (UAVs) are subjected to
several challenges. One of the challenges is for UAV to be able to avoid
collision. Many collision avoidance methods have been proposed to address this
issue. Furthermore, in a multi-UAV system, it is also important to address
communication issue among UAVs for cooperation and collaboration. This issue
can be addressed by setting up an ad-hoc network among UAVs. There is also a
need to consider the challenges in the deployment of UAVs, as well as, in the
development of collision avoidance methods and the establishment of
communication for cooperation and collaboration in a multi-UAV system. In this
paper, we present general challenges in the deployment of UAV and comparison of
UAV communication services based on its operating frequency. We also present
major collision avoidance approaches, and specifically discuss collision
avoidance approaches that are suitable for indoor applications. We also present
the Flying Ad-hoc Networks (FANET) network architecture, communication and
routing protocols for each Open System Interconnection (OSI) communication
layers.
