In this paper, we propose an energy-efficient optimal<br>altitude for an aerial access point (AAP), which acts as a flying<br>base station to serve a set of ground user equipment (UE).<br>Since the ratio of total energy consumed by the aerial vehicle<br>to the communication energy is very large, we include the<br>aerial vehicle’s energy consumption in the problem formulation.<br>After considering the energy consumption model of the aerial<br>vehicle, our objective is translated into a non-convex optimization<br>problem of maximizing the global energy efficiency (GEE)<br>of the aerial communication system, subject to altitude and<br>minimum individual data rate constraints. At first, the nonconvex fractional objective function is solved by using sequential<br>convex programming (SCP) optimization technique. To compare<br>the result of SCP with the global optimum of the problem,<br>we reformulate the initial problem as a monotonic fractional<br>optimization problem (MFP) and solve it using the polyblock<br>outer approximation (PA) algorithm. Numerical results show that<br>the candidate solution obtained from SCP is the same as the<br>global optimum found using the monotonic fractional programming technique. Furthermore, the impact of the aerial vehicle’s<br>energy consumption on the optimal altitude determination is also<br>studied <br>