  Unmanned Aerial Vehicles (UAV)-enabled communication is a promising solution
for secure air-to-ground (A2G) networks due to the additional secure degrees of
freedom afforded by mobility. However, the jittering characteristics caused by
the random airflow and the body vibration of the UAV itself have a
non-negligible impact on the performance of UAV communication. Considering the
impact of UAV jittering, this paper propose a robust and secure transmission
design assisted by an novel active intelligent reflecting surface (IRS),where
the reflecting elements in IRS not only adjust the phase shift but also amplify
the amplitude of signals. Specifically, under the worst-case secrecy rate
constraints, we aim to minimize the transmission power by the robust joint
design of active IRS's reflecting coefficient and beamforming at the UAV-borne
base station (UBS). However,it is challenging to solve the joint optimization
problem due to its non-convexity. To tackle this problem, the non-convex
problem is reformulated with linear approximation for the channel variations
and linear matrix inequality transformed by S-procedure and Schur's complement.
Then, we decouple this problem into two sub-problems, namely, passive
beamforming and active IRS's reflecting coefficient optimization, and solve
them through alternate optimization (AO). Finally, the numerical results
demonstrate the potential of active IRS on power saving under secure
transmission constraints and the impact of UAV jittering.
