Wireless communication with unmanned aerial vehicles (UAVs) is a promising
technology for future communication systems. In this paper, we study
energy-efficient UAV communication with a ground terminal via optimizing the
UAV's trajectory, a new design paradigm that jointly considers both the
communication throughput and the UAV's energy consumption. To this end, we
first derive a theoretical model on the propulsion energy consumption of
fixed-wing UAVs as a function of the UAV's flying speed, direction and
acceleration, based on which the energy efficiency of UAV communication is
defined. Then, for the case of unconstrained trajectory optimization, we show
that both the rate-maximization and energy-minimization designs lead to
vanishing energy efficiency and thus are energy-inefficient in general. Next,
we introduce a practical circular UAV trajectory, under which the UAV's flight
radius and speed are optimized to maximize the energy efficiency for
communication. Furthermore, an efficient design is proposed for maximizing the
UAV's energy efficiency with general constraints on its trajectory, including
its initial/final locations and velocities, as well as maximum speed and
acceleration. Numerical results show that the proposed designs achieve
significantly higher energy efficiency for UAV communication as compared with
other benchmark schemes.

本文研究了通过优化无人机的轨迹与地面终端通信以实现能量效率，首先从理论上对固定翼无人机的推进能耗进行了建模，并定义了能量效率，然后提出了一种实际的圆形无人机轨迹以最大化通信能效，同时还提出了一种高效设计用于在无人机轨迹有约束的情况下最大化其能量效率。