  In this paper, we investigate resource allocation algorithm design for
multiuser unmanned aerial vehicle (UAV) communication systems in the presence
of UAV jittering and user location uncertainty. In particular, we jointly
optimize the two-dimensional position and the downlink beamformer of a
fixed-altitude UAV for minimization of the total UAV transmit power. The
problem formulation takes into account the quality-of-service requirements of
the users, the imperfect knowledge of the antenna array response (AAR) caused
by UAV jittering, and the user location uncertainty. Despite the non-convexity
of the resulting problem, we solve the problem optimally employing a series of
transformations and semidefinite programming relaxation. Our simulation results
reveal the dramatic power savings enabled by the proposed robust scheme
compared to two baseline schemes. Besides, the robustness of the proposed
scheme with respect to imperfect AAR knowledge and user location uncertainty at
the UAV is also confirmed.
