  The use of drone small cells (DSCs) which are aerial wireless base stations
that can be mounted on flying devices such as unmanned aerial vehicles (UAVs),
is emerging as an effective technique for providing wireless services to ground
users in a variety of scenarios. The efficient deployment of such DSCs while
optimizing the covered area is one of the key design challenges. In this paper,
considering the low altitude platform (LAP), the downlink coverage performance
of DSCs is investigated. The optimal DSC altitude which leads to a maximum
ground coverage and minimum required transmit power for a single DSC is
derived. Furthermore, the problem of providing a maximum coverage for a certain
geographical area using two DSCs is investigated in two scenarios; interference
free and full interference between DSCs. The impact of the distance between
DSCs on the coverage area is studied and the optimal distance between DSCs
resulting in maximum coverage is derived. Numerical results verify our
analytical results on the existence of optimal DSCs altitude/separation
distance and provide insights on the optimal deployment of DSCs to supplement
wireless network coverage.
