IRS Backscatter Based Hybrid Confidential Information and AN for Secrecy Transmission

Due to broadcast nature of electromagnetic waves, wireless communications are inherently vulnerable to the eavesdropping threat. To secure the air interface, this letter proposes a secrecy transmission strategy based on intelligent reflecting surface (IRS) backscatter. To be specific, the source (Alice) sends its confidential information to the legitimate user (Bob) with multiple passive eavesdroppers (Eves). To enhance the reception at Bob while deteriorating those at Eves, an IRS is deployed to convert the signal from Alice to a hybrid one consisting of confidential information and artificial noise through backscatter techniques. Based on this strategy, this letter minimises the transmit power at Alice, by optimising active and passive beamforming vectors under the constraints of the signal-to-interference-plus-noise ratios at Bob and Eve. To solve this problem, an alternative optimisation method is developed. The simulation results verify that the proposed strategy can achieve a secrecy performance gain.