Precoder design for AF cooperative systems with multiple wiretapping relays

This paper considers an amplify-and-forward (AF) cooperative system with multiple relays which may eavesdrop on the source signal without authorization. In conventional cooperative system where the relays are assumed trustworthy, the precoding design usually tends to optimize quality of the received signal at the relays. However, the considered system relies on the relays´ assistance and requires to prevent source information eavesdropped by the relays. With this regard, we proposed that the destination transmits artificial noise to interfere the signal reception of wiretapping relays. The artificial noise can be fully eliminated at the destination with perfect channel information. We propose a precoder design for the cooperative system that aims to maximize the received SNR at the destination subject to constraining quality of received signal at the relays. It shows through simulation results that the proposed scheme is able to improve the secrecy capacity of the cooperative system with wiretapping relays effectively.