  Aerial vehicles have recently attracted significant attention in a variety of
commercial and civilian applications due to their high mobility, flexible
deployment and cost-effectiveness. To leverage these promising features, the
aerial users have to satisfy two critical requirements: First, they have to
maintain a reliable communication link to the ground base stations (GBSs)
throughout their flights, to support command and control data flows. Second,
the aerial vehicles have to minimize their propulsion power consumption to
remain functional until the end of their mission. In this paper, we study the
trajectory optimization problem for an aerial user flying over an area
including a set of GBSs. The objective of this problem is to find the
trajectory of the aerial user so that the total propulsion-related power
consumption of the aerial user is minimized while a cellular-connectivity
constraint is satisfied. This problem is a non-convex mixed integer non-linear
problem and hence, it is challenging to find the solution. To deal with, first,
the problem is relaxed and reformulated to a more mathematically tractable
form. Then, using successive convex approximation (SCA) technique, an iterative
algorithm is proposed to convert the problem into a sequence of convex problems
which can be solved efficiently.
