Secure Transmission for Hierarchical Information Accessibility in Downlink MU-MIMO

TL;DR

This paper introduces a hierarchical information accessibility model for physical layer security in downlink MU-MIMO systems, formulating a sum secrecy rate maximization problem and proposing a novel eigenvalue-based solution method.

Contribution

It formulates a new HIA model for physical layer security, approximates the non-smooth problem, and develops the GPI-HIA algorithm for improved secrecy rate performance.

Findings

GPI-HIA outperforms baseline methods in simulations

The eigenvalue problem approach effectively finds local optima

The model enhances security in hierarchical user access scenarios

Abstract

Physical layer security is a useful tool to prevent confidential information from wiretapping. In this paper, we consider a generalized model of conventional physical layer security, referred to as hierarchical information accessibility (HIA). A main feature of the HIA model is that a network has a hierarchy in information accessibility, wherein decoding feasibility is determined by a priority of users. Under this HIA model, we formulate a sum secrecy rate maximization problem with regard to precoding vectors. This problem is challenging since multiple non-smooth functions are involved into the secrecy rate to fulfill the HIA conditions and also the problem is non-convex. To address the challenges, we approximate the minimum function by using the LogSumExp technique, thereafter obtain the first-order optimality condition. One key observation is that the derived condition is cast as a functional eigenvalue problem, where the eigenvalue is equivalent to the approximated objective function of the formulated problem. Accordingly, we show that finding a principal eigenvector is equivalent to finding a local optimal solution. To this end, we develop a novel method called generalized power iteration for HIA (GPI-HIA). Simulations demonstrate that the GPI-HIA significantly outperforms other baseline methods in terms of the secrecy rate.