  In this paper, we study an unmanned aerial vehicle (UAV) enabled data
collection system, where an intelligent reflecting surface (IRS) is deployed to
assist in the communication from a cluster of Internet-of-Things (IoT) devices
to a UAV in the presence of a jammer. We aim to improve the energy efficiency
(EE) via the joint design of UAV trajectory, IRS passive beamforming, device
power allocation, and communication scheduling. However, the formulated
non-linear fractional programming problem is challenging to solve due to its
non-convexity and coupled variables. To overcome the difficulty, we propose an
alternating optimization based algorithm to solve it sub-optimally by
leveraging Dinkelbach's algorithm, successive convex approximation (SCA)
technique, and block coordinate descent (BCD) method. Extensive simulation
results show that the proposed design can significantly improve the
anti-jamming performance. In particular, for the remote jammer case, the
proposed design can largely shorten the flight path and thus decrease the
energy consumption via the signal enhancement; while for the local jammer case,
which is deemed highly challenging in conventional systems without IRS since
the retreating away strategy becomes ineffective, our proposed design even
achieves a higher performance gain owing to the efficient jamming signal
mitigation.
