Proactive Eavesdropping in Two-Way Amplify-and-Forward Relay Networks

Abstract

This article considers a proactive eavesdropping scenario, where two suspicious nodes exchange their information via one suspicious relay in two phases, the process of which is under the supervision of one legitimate monitor. Specifically, these two suspicious nodes broadcast their suspicious data in phase 1 and the relay forwards the amplified version of its received signal in phase 2, according to which two proactive eavesdropping strategies, i.e., "passive eavesdropping first" and "jamming first," are designed. Using the former strategy, the monitor proceeds eavesdropping with a minimum-mean-squar-error (MMSE) receiver in phase 1 and implements eavesdropping or simultaneous assisting and jamming in phase 2. Using the latter strategy, the monitor implements jamming in phase 1 and performs eavesdropping in phase 2. For these strategies, we provide the detailed analysis and formulate the corresponding optimization problems of sum eavesdropping rate maximization subject to finite transmit power of the monitor, each of which is then solved by carefully designing the power allocation scheme or the assisting/jamming beamformer at the legitimate monitor. In addition, for the "passive eavesdropping first" strategy, we also consider a more advanced MMSE with a successive interference cancellation (SIC) receiver and concurrently exploit the time-sharing (TS) technique to further improve the eavesdropping rate. Finally, simulation results indicate that the "passive eavesdropping first" strategy is more preferable compared to the "jamming first" strategy, and the SIC and TS are preferable for promoting the more effective eavesdropping.