Multicast with Multiple Wardens in IRS-Aided Covert DFRC System

Physical layer security is a common concern in dual-function radar communications (DFRC) because of sharing of information between different emitters. We study covert communications between a DFRC unit and multiple legitimate users, with assistance from an intelligent reflecting surface (IRS). The system has multiple targets that need to be detected, and each target is collocated with a warden trying to detect the ongoing communication. We seek to maximize the worst-case data rate across users under radar detection constraint and covertness constraint. To this end, we superpose artificial noise with our message signal so that the wardens’ received signal statistics do not change significantly if communications suddenly starts. We formulate a highly non-convex optimization problem to determine the passive beamforming scheme for the IRS and active precoding scheme at the transmitter, and solve it using a combination of auxiliary matrices, alternating optimization, and a variant of stochastic gradient descent. Finally, we validate the proposed algorithm numerically.