Proactive Eavesdropping via Jamming over HARQ-Based Communications

TL;DR

This paper introduces a proactive jamming strategy to enhance wireless surveillance of HARQ-based links, optimizing eavesdropping success by adaptively jamming retransmissions under channel conditions.

Contribution

It proposes a threshold-based jamming power allocation scheme for proactive eavesdropping on HARQ links, improving success probability over passive methods.

Findings

Proactive jamming outperforms passive eavesdropping in success probability.

HARQ combining at the monitor further enhances eavesdropping performance.

Optimal jamming follows a threshold-based power policy depending on channel gain.

Abstract

This paper studies the wireless surveillance of a hybrid automatic repeat request (HARQ) based suspicious communication link over Rayleigh fading channels. We propose a proactive eavesdropping approach, where a half-duplex monitor can opportunistically jam the suspicious link to exploit its potential retransmissions for overhearing more efficiently. In particular, we consider that the suspicious link uses at most two HARQ rounds for transmitting the same data packet, and we focus on two cases without and with HARQ combining at the monitor receiver. In both cases, we aim to maximize the successful eavesdropping probability at the monitor, by adaptively allocating the jamming power in the first HARQ round according to fading channel conditions, subject to an average jamming power constraint. For both cases, we show that the optimal jamming power allocation follows a threshold-based policy, and the monitor jams with constant power when the eavesdropping channel gain is less than the threshold. Numerical results show that the proposed proactive eavesdropping scheme achieves higher successful eavesdropping probability than the conventional passive eavesdropping, and HARQ combining can help further improve the eavesdropping performance.