  Unmanned aerial vehicles (UAVs) have been actively studied as moving
cloudlets to provide application offloading opportunities and to enhance the
security level of user equipments (UEs). In this correspondence, we propose a
hybrid UAV-aided secure offloading system in which a UAV serves as a helper by
switching the mode between jamming and relaying to maximize the secrecy
sum-rate of UEs. This work aims to optimize (i) the trajectory of the helper
UAV, (ii) the mode selection strategy and (iii) the UEs' offloading decisions
under the constraints of offloading accomplishment and the UAV's operational
limitations. The solution is provided via a deep deterministic policy gradient
(DDPG)-based method, whose superior performance is verified via a numerical
simulation and compared to those of traditional approaches.
