The use of unmanned aerial vehicles (UAVs) as aerial communication platforms
is of high practical value for future wireless systems such as 5G, especially
for swift and on-demand deployment in temporary events and emergency
situations. Compared to traditional terrestrial base stations (BSs) in cellular
network, UAV-mounted aerial BSs possess stronger line-of-sight (LoS) links with
the ground users due to their high altitude as well as high and flexible
mobility in three-dimensional (3D) space, which can be exploited to enhance the
communication performance. On the other hand, unlike terrestrial BSs that have
reliable power supply, aerial BSs in practice have limited on-board energy, but
require significant propulsion energy to stay airborne and support high
mobility. Motivated by the above new considerations, this article aims to
revisit some fundamental tradeoffs in UAV-enabled communication and trajectory
design. Specifically, it is shown that communication throughput, delay, and
(propulsion) energy consumption can be traded off among each other by adopting
different UAV trajectory designs, which sheds new light on their traditional
tradeoffs in terrestrial communication. Promising directions for future
research are also discussed.

利用无人机作为航空通信平台对 5G 等未来无线系统具有高实用价值，本文旨在重新探讨无人机通信和轨迹设计中的基本权衡，通过采用不同的无人机轨迹设计来交换通信吞吐量、延迟和（推力）能量消耗等因素，并讨论未来研究的方向。