  The Internet of Drones (IoD) recently gained momentum due to its high
adaptability to a wide variety of complex scenarios. Indeed, Unmanned Aerial
Vehicles (UAVs) can successfully be employed in different applications, thanks
to some technological and practical advantages: high mobility, capability to
extend wireless coverage areas, or ability to reach places inaccessible to
humans. Moreover, the employment of drones promisingly improves the performance
parameters of different network architectures. Nevertheless, the adoption of
networks of drones gives rise to several issues related to the unreliability of
the wireless medium, the duration of batteries, and the high mobility degree,
which may cause frequent topology changes. Also security and privacy issues
need to be properly investigated. With respect to other surveys on IoD-related
topics, the goal of the present work is to categorize the multifaceted aspects
of IoD, proposing a classification approach of the IoD environment that
develops along two main directions. At a macroscopic level, it follows the
structure of the Internet protocol stack, starting from the physical layer and
extending to the upper layers, without neglecting cross-layer and optimization
approaches. At a finer level, all the most relevant works belonging to each
layer of the stack are further classified, according to the different issues
peculiar of the layer, and highlighting the most relevant differences with the
other surveys present in literature. To provide a deeper insight in the theme,
the present work embraces many facets of the IoD, including privacy and
security considerations as well as the potential economic impact of the IoD.
Finally, a discussion on the main research challenges and possible future
directions is carried out, focusing on the open issues and the most promising
technologies that deserve to be further developed in the IoD field.
