Sum Secrecy Spectral Efficiency Maximization in Downlink MU-MIMO: Colluding Eavesdroppers

Abstract

In this paper, we consider a single-cell downlink multi-user multi-input multi-output (MU-MIMO) system in which multiple eavesdroppers coexist. The eavesdroppers overhear confidential information sent from a base station (BS). In particular, we assume a scenario of colluding eavesdroppers in which they cooperate with each other to decode the information. We develop a secure linear precoding method that maximizes the sum secrecy spectral efficiency. To this end, we formulate an optimization problem and propose a computationally-efficient algorithm that achieves a sub-optimal stationary point of the problem. Simulation results validate the proposed algorithm. The proposed method possesses several benefits: i) it is applicable in general systems, for example, an arbitrary number of eavesdroppers and confidential information set, ii) the associated complexity is relatively low, and iii) it is also applicable when only channel covariance of the eavesdroppers is available.