  In this paper, we study an unmanned aerial vehicle (UAV) communication
system, where a ground node (GN) communicate with a UAV assisted by intelligent
reflecting surface (IRS) in the presence of a jammer with imperfect location
information. We aim to improve the achievable average rate via the joint robust
design of UAV trajectory, IRS passive beamforming and GN's power allocation.
However, the formulated optimization problem is challenging to solve due to its
non-convexity and coupled variables. To overcome the difficulty, we propose an
alternating optimization (AO) based algorithm to solve it sub-optimally by
leveraging semidefinite relaxation (SDR), successive convex approximation
(SCA), and S-procedure methods. Simulation results show that by deploying the
IRS near the GN, our proposed algorithm always improves the uplink achievable
average rate significantly compared with the benchmark algorithms, while
deploying the IRS nearby the jammer is effective only when the jammer's
location is perfectly known.
