To Harvest and Jam: A Paradigm of Self-Sustaining Friendly Jammers for Secure AF Relaying

TL;DR

This paper proposes a novel approach using multi-antenna harvest-and-jam helpers in AF relay channels to enhance secrecy rates, employing optimization techniques for perfect and imperfect CSI scenarios.

Contribution

It introduces a joint optimization framework for artificial noise and beamforming in secure AF relaying with harvest-and-jam helpers, including robust schemes for imperfect CSI.

Findings

Semi-definite relaxation yields tight solutions for perfect CSI.

Proposed robust scheme balances complexity and performance.

Numerical results demonstrate effectiveness of the schemes.

Abstract

This paper studies the use of multi-antenna harvest-and-jam (HJ) helpers in a multi-antenna amplify-and-forward (AF) relay wiretap channel assuming that the direct link between the source and destination is broken. Our objective is to maximize the secrecy rate at the destination subject to the transmit power constraints of the AF relay and the HJ helpers. In the case of perfect channel state information (CSI), the joint optimization of the artificial noise (AN) covariance matrix for cooperative jamming and the AF beamforming matrix is studied using semi-definite relaxation (SDR) which is tight, while suboptimal solutions are also devised with lower complexity. For the imperfect CSI case, we provide the equivalent reformulation of the worst-case robust optimization to maximize the minimum achievable secrecy rate. Inspired by the optimal solution to the case of perfect CSI, a suboptimal robust scheme is proposed striking a good tradeoff between complexity and performance. Finally, numerical results for various settings are provided to evaluate the proposed schemes.