Energy-Efficient Legitimate Monitoring and Interfering in Wireless Networks via RIS-Assisted Approach

In this paper, we consider a reconfigurable intelligent surface (RIS)-assisted legitimate monitoring and interfering system, and propose a three-stage scheme to conduct pilot spoofing on suspicious transmitter (ST), monitor suspicious communications, and prevent suspicious receiver (SR) from successful decoding, respectively. In pilot transmission (PT) stage, the SR transmits pilot signal to the ST, and legitimate monitors (LMs) control RIS phase shift matrix by the proposed Majorization-Minimization (MM) based scheme, leading to deviation for ST’s channel estimation. In data transmission (DT) stage, the ST transmits suspicious information to the SR. An Alternating Direction Method of Multipliers (ADMM) based scheme is proposed to optimize RIS phase shift matrix, enhancing stability and effectiveness of LMs’ monitoring performance. In interference signal transmission (IT) stage, the legitimate jammer (LJ) aims to transmit interference signal with lower power to jam the SR. To achieve this objective, we propose a Semidefinite Relaxation-Alternating Optimization (SDR-AO) based scheme and a Block Coordinate Descent (BCD) based scheme to jointly optimize RIS phase shift matrix and minimize LJ’ transmission power. Numerical results demonstrate that our proposed schemes are superior to other comparative schemes. It also confirms that the pilot spoofing can reduce the transmission power consumed by LJ. Moreover, we effectively optimize deployment location of RIS, LMs and LJ. We also verify that the performance of distributed RISs deployment is superior to that of single RIS system.