  Localizing ground devices (GDs) is an important requirement for a wide
variety of applications, such as infrastructure monitoring, precision
agriculture, search and rescue operations, to name a few. To this end, unmanned
aerial vehicles (UAVs) or drones offer a promising technology due to their
flexibility. However, the distance measurements performed using a drone, an
integral part of a localization procedure, incur several errors that affect the
localization accuracy. In this paper, we provide analytical expressions for the
impact of different kinds of measurement errors on the ground distance between
the UAV and GDs. We review three range-based and three range-free localization
algorithms, identify their source of errors, and analytically derive the error
bounds resulting from aggregating multiple inaccurate measurements. We then
extend the range-free algorithms for improved accuracy. We validate our
theoretical analysis and compare the observed localization error of the
algorithms after collecting data from a testbed using ten GDs and one drone,
equipped with ultra wide band (UWB) antennas and operating in an open field.
Results show that our analysis closely matches with experimental localization
errors. Moreover, compared to their original counterparts, the extended
range-free algorithms significantly improve the accuracy.
