MIMO DF Relay Beamforming for Secrecy with Artificial Noise, Imperfect CSI, and Finite-Alphabet

TL;DR

This paper proposes a MIMO decode-and-forward relay beamforming scheme with artificial noise and imperfect CSI to enhance secrecy rates against multiple eavesdroppers, considering finite-alphabet inputs and fixed common message rate.

Contribution

It introduces a robust optimization framework for secrecy rate maximization under imperfect CSI, power constraints, and artificial noise injection in MIMO relay systems.

Findings

Artificial noise improves secrecy rate under imperfect CSI.

Finite-alphabet inputs impact secrecy performance.

Imperfect CSI reduces achievable secrecy rates.

Abstract

In this paper, we consider decode-and-forward (DF) relay beamforming with imperfect channel state information (CSI), cooperative artificial noise (AN) injection, and finite-alphabet input in the presence of an user and $J$ non-colluding eavesdroppers. The communication between the source and the user is aided by a multiple-input-multiple-output (MIMO) DF relay. We use the fact that a wiretap code consists of two parts: i) common message (non-secret), and ii) secret message. The source transmits two independent messages: i) common message (non-secret), and ii) secret message. The common message is transmitted at a fixed rate $R_{0}$, and it is intended for the user. The secret message is also intended for the user but it should be kept secret from the $J$ eavesdroppers. The source and the MIMO DF relay operate under individual power constraints. In order to improve the secrecy rate, the MIMO relay also injects artificial noise. The CSI on all the links are assumed to be imperfect and CSI errors are assumed to be norm bounded. In order to maximize the worst case secrecy rate, we maximize the worst case link information rate to the user subject to: i) the individual power constraints on the source and the MIMO relay, and ii) the best case link information rates to $J$ eavesdroppers be less than or equal to $R_{0}$ in order to support a fixed common message rate $R_{0}$. Numerical results showing the effect of perfect/imperfect CSI, presence/absence of AN with finite-alphabet input on the secrecy rate are presented.