  Cellular networks are promising to support effective wireless communications
for unmanned aerial vehicles (UAVs), which will help to enable various
long-range UAV applications. However, these networks are optimized for
terrestrial users, and thus do not guarantee seamless aerial coverage. In this
paper, we propose to overcome this difficulty by exploiting controllable
mobility of UAVs, and investigate connectivity-aware UAV path planning. To
explicitly impose communication requirements on UAV path planning, we introduce
two new metrics to quantify the cellular connectivity quality of a UAV path.
Moreover, aerial coverage maps are used to provide accurate locations of
scattered coverage holes in the complicated propagation environment. We
formulate the UAV path planning problem as finding the shortest path subject to
connectivity constraints. Based on graph search methods, a novel
connectivity-aware path planning algorithm with low complexity is proposed. The
effectiveness and superiority of our proposed algorithm are demonstrated using
the aerial coverage map of an urban section in Virginia, which is built by ray
tracing. Simulation results also illustrate a tradeoff between the path length
and connectivity quality of UAVs.
