Proactive Eavesdropping Strategies Using Hybrid Reflecting-Backscatter Intelligent Surface

This correspondence proposes to employ a hybrid reflecting-backscatter intelligent surface for proactive eavesdropping in a wireless information surveillance system. To be specific, some elements of intelligent reflecting surface (IRS) are used to reflect the incoming signal from the source, while the remaining recast the signal to artificial noise through backscatter techniques. To maximize the effective proactive eavesdropping rate, which is defined as the suspicious communication rate that satisfies the condition of successful eavesdropping, three strategies are presented, including Enhancing-Strategy, Jamming-Strategy and Hybrid-Strategy. For the first two, a semidefinite relaxation based algorithm is adopted to design the passive beamforming at IRS. For the last strategy, closed-form expressions of optimal solutions are derived. In addition to the passive beamforming design, the deployment of IRS is optimized by a simulated annealing algorithm. Finally, simulations verify the effectiveness of the proposed schemes.