Hierarchical Information Accessibility in Downlink MIMO Systems

In this paper, we consider a hierarchical information accessibility (HIA) model, which generalizes conventional physical layer security. In the considered model, multiple layers with different security priorities are assumed, where only the users in a higher priority layer are permitted to decode the message intended to lower priority layers. To maximize the sum secrecy rate of the considered system, we formulate an optimization problem with regard to precoders. To solve the formulated problem, we first approximate the objective function by using the LogSumExp technique and show that finding a local optimum is equivalent to finding a leading eigenvector of the first-order optimality condition of the reformulated problem. Accordingly, we propose a novel algorithm called generalized power iteration for hierarchical information accessibility (GPI-HIA) to obtain a solution. Via simulations, we demonstrate that the proposed method significantly outperforms other baseline schemes under the considered HIA scenario.