  Drones in many applications need the ability to fly fully or partially
autonomously to accomplish their mission. To allow these fully/partially
autonomous flights, first, the drone needs to be able to locate itself
constantly. Then the navigation command signal would be generated and passed on
to the controller unit of the drone. In this paper, we propose a localization
scheme for drones called iDROP (Robust Localization for Indoor Navigation of
Drones with Optimized Beacon Placement) that is specifically devised for
GPS-denied environments (e.g., indoor spaces). Instead of GPS signals, iDROP
relies on speaker-generated ultrasonic acoustic signals to enable a drone to
estimate its location. In general, localization error is due to two factors:
the ranging error and the error induced by relative geometry between the
transmitters and the receiver. iDROP mitigates these two types of errors and
provides a high-precision three-dimensional localization scheme for drones.
iDROP employs a waveform that is robust against multi-path fading. Moreover, by
placing beacons in optimal locations, it reduces the localization error induced
by the relative geometry between the transmitters and the receiver.
