Proactive Eavesdropping of Jamming-Assisted Suspicious Communications in Fading Channels: A Stackelberg Game Approach

Proactive eavesdropping improves the wireless information surveillance performance by cognitively sending jamming signals to degrade the suspicious link condition. Current studies all considered that the suspicious users do not apply jamming to defend against the proactive eavesdropping. Contrary to that, this paper considers that a jammer sends jamming signals to degrade the eavesdropping link condition to protect the suspicious communications. A Stackelberg game framework is formulated to track the interactions between the jammer and the monitor and make strategy designs, where the monitor is the leader aiming at maximizing the successful eavesdropping probability and the jammer is the follower aiming at minimizing the successful eavesdropping probability. For the follower's problem, the optimal jammer's jamming power allocation policy with respect to the fixed monitor's jamming power is derived based on the sum-of-ratios optimization. Then for the leader's problem, the optimal monitor's jamming power allocation policy is obtained via the bisection search method and the sum-of-ratios optimization. Some design insights are discussed from the obtained policies. The effectiveness of the proposed scheme is verified by simulation results. It is shown that the jamming from the jammer deteriorates the eavesdropping performance and the proposed scheme outperforms various benchmark schemes in existing literature.