# Proactive Eavesdropping in Relaying Systems

## TL;DR

This paper explores strategies for a legitimate monitor to enhance eavesdropping on relaying communication links by adaptively switching roles and optimizing jamming, with results showing improved performance depending on monitor placement.

## Contribution

It introduces adaptive eavesdropping, jamming, and helper strategies with optimal beamforming and power control for improved surveillance performance.

## Key findings

- Proposed strategies outperform benchmark schemes.
- Monitor position significantly affects eavesdropping success.
- Optimal jamming beamformer enhances eavesdropping rate.

## Abstract

This paper investigates the performance of a legitimate surveillance system, where a legitimate monitor aims to eavesdrop on a dubious decode-and-forward relaying communication link. In order to maximize the effective eavesdropping rate, two strategies are proposed, where the legitimate monitor adaptively acts as an eavesdropper, a jammer or a helper. In addition, the corresponding optimal jamming beamformer and jamming power are presented. Numerical results demonstrate that the proposed strategies attain better performance compared with intuitive benchmark schemes. Moreover, it is revealed that the position of the legitimate monitor plays an important role on the eavesdropping performance for the two strategies.