  This paper presents a new method for recharging flying base stations, carried
by Unmanned Aerial Vehicles (UAVs), using wireless power transfer from
dedicated, airborne, Radio Frequency (RF) energy sources. In particular, we
study a system in which UAVs receive wireless power without being disrupted
from their regular trajectory. The optimal placement of the energy sources are
studied so as to maximize received power from the energy sources by the
receiver UAVs flying with a linear trajectory over a square area. We find that
for our studied scenario of two UAVs, if an even number of energy sources are
used, placing them in the optimal locations maximizes the total received power,
while achieving fairness among the UAVs. However, in the case of using an odd
number of energy sources, we can either maximize the total received power, or
achieve fairness, but not both at the same time. Numerical results show that
placing the energy sources at the suggested optimal locations results in
significant power gain compared to nonoptimal placements.
