Cooperative beamforming of full-duplex relays for improving physical layer security

Abstract

In this paper, we consider secure communications of one source-destination pair in the presence of one eavesdropper, when full-duplex decode-and-forward cooperative relays operate to enhance physical layer security. While the conventional half-duplex relay receives the signal from the source and forwards the re-encoded signal to the destination in two separated time slots, the full-duplex relay (FDR) performs the transmission and reception at the same time, which can ideally double the secrecy capacity. However, because of the simultaneous transmission and reception, each FDR suffers from both its own self-interference and the interference from the other cooperative FDRs. When the conventional cooperative relaying schemes are used in full-duplex relaying, it is obviously expected that the self-interference signals cause severe degradation of the secrecy capacity. Here, we propose an iterative transmit power allocation and relay beamforming weight design scheme for cooperative FDRs to enhance the secrecy rate as well as suppress the self-interference signals. Numerical results present that the FDRs with the proposed scheme significantly improve the secrecy rate compared with the conventional half-duplex relays. Copyright (C) 2015 John Wiley & Sons, Ltd.