Aerial IRS-Assisted Secure SWIPT System With UAV Jitter

Intelligent reflecting surface (IRS)-assisted wireless communication has been recognized as an important way to enhance the security of unmanned aerial vehicle (UAV) networks. However, a single IRS may be unable to meet the transmission requirements in complex communication scenarios. In particular, due to the inherent instability of UAV platforms, the inevitable jitter caused by airflow and body vibration can have a great impact on transmission quality. In this paper, we study the multi-aerial IRS (AIRS) assisted secure simultaneous wireless information and power transfer (SWIPT) system with UAV jitter taken into account. For the purpose of exposition, two IRSs are deployed on two UAVs to reflect signals transmitted from the base station to an information user and an energy user; meanwhile an eavesdropper intends to eavesdrop on their messages. Angle estimation errors due to UAV jitter is transformed into the bounded channel state information (CSI) errors by applying linear approximations, and a joint optimization problem of the beamforming vector, AIRS phase shift matrices, and UAV trajectories is formulated to maximize the average secrecy rate (ASR). Since the problem is non-convex and the variables are strongly coupled, we propose an alternating optimization (AO) algorithm to deal with it. We decompose it into three sub-problems and adopt the Schur Complement, General S-Procedure, penalty dual decomposition (PDD), and successive convex approximation (SCA) methods to solve these non-convex sub-problems successfully. Numerical results show that UAV jitter could lead to system performance loss and demonstrate the performance gains of our proposed robust algorithm over other benchmark schemes.