Robust Secure Transmission in MISO Channels Based on Worst-Case Optimization

TL;DR

This paper develops robust transmission schemes for MISO wiretap channels with imperfect CSI, optimizing secrecy rates under various power constraints and demonstrating improved security performance through worst-case design and cooperative jamming.

Contribution

It introduces a worst-case secrecy rate maximization framework for robust MISO wiretap channels, including novel solutions for both individual and global power constraints.

Findings

Robust design enhances secrecy rate under channel uncertainties.

Joint optimization improves performance with global power constraints.

Cooperative jamming increases security when CSI is imperfect.

Abstract

This paper studies robust transmission schemes for multiple-input single-output (MISO) wiretap channels. Both the cases of direct transmission and cooperative jamming with a helper are investigated with imperfect channel state information (CSI) for the eavesdropper links. Robust transmit covariance matrices are obtained based on worst-case secrecy rate maximization, under both individual and global power constraints. For the case of an individual power constraint, we show that the non-convex maximin optimization problem can be transformed into a quasiconvex problem that can be efficiently solved with existing methods. For a global power constraint, the joint optimization of the transmit covariance matrices and power allocation between the source and the helper is studied via geometric programming. We also study the robust wiretap transmission problem for the case with a quality-of-service constraint at the legitimate receiver. Numerical results show the advantage of the proposed robust design. In particular, for the global power constraint scenario, although cooperative jamming is not necessary for optimal transmission with perfect eavesdropper's CSI, we show that robust jamming support can increase the worst-case secrecy rate and lower the signal to interference-plus-noise ratio at Eve in the presence of channel mismatches between the transmitters and the eavesdropper.