  The use of aerial anchors for localizing terrestrial nodes has recently been
recognized as a cost-effective, swift and flexible solution for better
localization accuracy, providing localization services when the GPS is jammed
or satellite reception is not possible. In this paper, the localization of
terrestrial nodes when using mobile unmanned aerial vehicles (UAVs) as aerial
anchors is presented. We propose a novel framework to derive localization error
in urban areas. In contrast to the existing works, our framework includes
height-dependent UAV to ground channel characteristics and a highly detailed
UAV energy consumption model. This enables us to explore different tradeoffs
and optimize UAV trajectory for minimum localization error. In particular, we
investigate the impact of UAV altitude, hovering time, number of waypoints and
path length through formulating an energy-constrained optimization problem. Our
results show that increasing the hovering time decreases the localization error
considerably at the cost of a higher energy consumption. To keep the
localization error below 100m, shorter hovering is only possible when the path
altitude and radius are optimized. For a constant hovering time of 5 seconds,
tuning both parameters to their optimal values brings the localization error
from 150m down to 65m with a power saving around 25%
