Proactive Monitoring via Passive Reflection Using Intelligent Reflecting Surface

To monitor wireless suspicious transmissions, we propose an intelligent reflecting surface enabled legitimate monitoring system. In the system, the monitor employs the passive reflection for constructive or destructive signal forwarding. For constructive passive reflection, we maximize the average monitoring rate by approximating the cumulative distribution function of outage probability at the suspicious destination, i.e., the Marcum Q-function, by a closed-form expression. For destructive passive reflection, we derive the optimal transmission rate of the suspicious source. Furthermore, we propose to obtain the locally optimal reflection coefficients by the alternating direction method of multipliers (ADMM). Numerical results demonstrate that our proposed ADMM-based passive reflection scheme achieves almost the same average monitoring rate as the upper bound.