Outage Constrained Robust Transmission Design for IRS-aided Secure Communications with Direct Communication Links

TL;DR

This paper develops a robust transmission design for IRS-assisted secure communications, optimizing beamforming and IRS phase shifts to minimize power while maintaining security under channel uncertainties.

Contribution

It introduces a joint optimization framework for beamforming, artificial noise, and IRS phase shifts considering imperfect CSI in secure IRS-aided systems.

Findings

Proposed algorithm outperforms benchmarks in power efficiency.

Effective handling of channel estimation errors improves security.

Optimization under partial and full CSI error scenarios is validated.

Abstract

In this paper, we investigate the robust outage constrained transmission design for an intelligent reflecting surface (IRS) aided secure communication system. We assume that a single-antenna legitimate receiver (Bob) served by a multi-antenna base station (BS) is overheard by multiple single-antenna eavesdroppers (Eves), and the artificial noise (AN) is incorporated to confuse the Eves. In particular, we aim to jointly optimize the transmit beamforming, the AN spatial distribution at the BS, and the passive beamforming at the IRS, where the Eve-related channels are assumed to be imperfect due to the channel estimation errors and their concealment. Two scenarios with partial channel state information (CSI) error of only cascaded BS-IRS-Eve channel and full CSI errors of both cascaded BS-IRS-Eve channel and direct BS-Eve channel are investigated under the statistical CSI error model. An outage-constrained power minimization problem is formulated by limiting the maximum allowable data rate of Eves and ensuring the minimum data rate requirement of Bob. To solve it, the Bernstein-type inequality and alternating optimization strategy are exploited, and artful mathematical manipulations are performed to facilitate the optimization on the phase shifts of the IRS. Simulation results confirm the performance advantages of the proposed algorithm.