Joint Trajectory and Beamforming Design in UAV-IRS Assisted Covert Communication Systems

In this paper, we present a unmanned aerial vehicles (UAV) relay covert communication scheme assisted by an intelligent reflecting surface (IRS), which is exploited to improve channel quality between transmitter and legitimate user. Specifically, we formulate a nonconvex optimization problem to maximize average covert rate, where trajectory of the UAV, transmit beamforming (TB) at Alice, and passive beamforming (PB) of the IRS under the covert constraint are considered. To tackle the difficult problem, we divide it into trajectory optimization (TO) subproblem, TB optimization subproblem, and PB optimization subproblem and then solve them alternately via successive convex approximation algorithm and semidefinite relaxation technique respectively. Numerical results demonstrate the effectiveness of the proposed approach and provide insights on how covert rate is influenced by the trajectory, TB, and PB.