  The use of amateur drones (ADrs) is expected to significantly increase over
the upcoming years. However, regulations do not allow such drones to fly over
all areas, in addition to typical altitude limitations. As a result, there is
an urgent need for ADrs surveillance solutions. These solutions should include
means of accurate detection, classification, and localization of the unwanted
drones in a no-fly zone. In this paper, we give an overview of promising
techniques for modulation classification and signal strength based localization
of ADrs by using surveillance drones (SDrs). By introducing a generic altitude
dependent propagation model, we show how detection and localization performance
depend on the altitude of SDrs. Particularly, our simulation results show a 25
dB reduction in the minimum detectable power or 10 times coverage enhancement
of an SDr by flying at the optimum altitude. Moreover, for a target no-fly
zone, the location estimation error of an ADr can be remarkably reduced by
optimizing the positions of the SDrs. Finally, we conclude the paper with a
general discussion about the future work and possible challenges of the aerial
surveillance systems.
