Intelligent Reflecting Surface Empowered Physical-Layer Security: Signal Cancellation or Jamming?

This article pioneers an unprecedented strategy of secure transmission, in which intelligent reflecting surface (IRS) is used as a backscatter device to form and scatter jamming signal while the transmitter (Alice) is regarded as a radio-frequency (RF) source. Specifically, Alice transmits confidential signal to a single-antenna legitimate user (Bob) while the transmission is overheard by multiple single-antenna illegitimate users (Eves). The beamformer at Alice is designed to align with the estimated channel vector from Alice to Bob, in order that the proposed strategy is completely compatible with the common communication system without respect to wiretap. To achieve secure transmission, IRS is deployed to modulate the received confidential signal to jamming signal and reflect it so as to deteriorate the reception at Eves. Based on this model, the reflection coefficient vector of IRS is optimized to minimize the eavesdropped information amount while guaranteeing the reliable communication at Bob. By comparing with the familiar IRS-based beamforming scheme and the cooperative jamming scheme in extensive simulations, the feasibility and secrecy performance gain are confirmed for the proposed strategy of IRS-based backscatter jamming.