  Up until now, path planning for unmanned aerial vehicles (UAVs) has mainly
been focused on the optimisation towards energy efficiency. However, to operate
UAVs safely, wireless coverage is of utmost importance. Currently, deployed
cellular networks often exhibit an inadequate performance for aerial users due
to high amounts of intercell interference. Furthermore, taking the never-ending
trend of densification into account, the level of interference experienced by
UAVs will only increase in the future. For the purpose of UAV trajectory
planning, wireless coverage should be taken into account to mitigate
interference and to lower the risk of dangerous connectivity outages. In this
paper, several path planning strategies are proposed and evaluated to optimise
wireless coverage for UAVs. A simulator using a real-life 3D map is used to
evaluate the proposed algorithms for both 4G and 5G scenarios. We show that the
proposed Coverage-Aware A* algorithm, which alters the UAV's flying altitude,
is able to improve the mean SINR by 3-4dB and lower the cellular outage
probability by a factor of 10. Furthermore, the outages that still occur have a
60% shorter length, hence posing a lower risk to induce harmful accidents.
