On the Design of Artificial Interference Signals for Covert Communication Assisted by Multiple Friendly Nodes

In this paper, we consider a scenario of covert communication assisted by multiple friendly interference nodes, aimed at concealing the legitimate communication link under the surveillance of a warden. Its main content is summarized in the following: firstly, we propose a novel strategy for generating artificial noise signals. Specifically, in the absence of accurate channel information between the friendly interference nodes and the legitimate receiver, the statistical information of channel coefficients is leveraged to formulate an optimization problem to design the basis matrix of the artificial noise signal space. Secondly, we employ the Riemannian optimization framework to analyze the geometric structure of the basis matrix constraint and transform the original non-convex optimization problem to an unconstrained problem on complex Stiefel manifold. Additionally, we utilize the Riemannian Stochastic Variance Reduced Gradient (RSVRG) algorithm on complex Stiefel manifold to solve the problem, which has the advantage of low computational burden. Thirdly, we prove that the customized R-SVRG algorithm is theoretically guaranteed convergent. In the end, simulation results show that under some mild conditions on covertness and jamming power, the designed artificial noise signals can let the system enjoy better covertness and less impact on the legitimate communication link than the traditional artificial noise signals.