Borrowing Arrows With Thatched Boats: Exploiting The Reactive Primary Communications for Boosting Jamming-Assisted Proactive Eavesdropping

Abstract

This paper investigates a cognitive information surveillance scenario, where a half-duplex legitimate monitor (E) aims to eavesdrop the frequency division multiple access based suspicious downlink broadcasting communication, which shares the same spectrum with a primary downlink broadcasting system. Specifically, the suspicious transmitter (ST) employs water-filling power allocation over all orthogonal frequency bands (FBs) to maximize the sum suspicious communication rate of all suspicious receivers (SRs), while the primary transmitter (PT) purposely maximizes the minimum communication rate among the primary receivers (PRs). Under this setup, E picks up certain FBs to jam and eavesdrops over the remaining FBs, and intends to control its transmit jamming beamforming over the jammed FBs to deliberately interfere with the corresponding PRs and SRs, such that the PT and the ST will reactively reallocate their power to facilitate E's eavesdropping. Our objective is to maximize the sum instantaneous (ergodic) eavesdropping rate at E, by jointly optimizing its jamming set and the corresponding jamming beamformers. The optimization problem is non-convex and its approximate and sub-optimal solutions are provided by some convex optimization procedures, along with the optimal and greedy jamming set selections. Results show the effectiveness of our proposed jamming-assisted eavesdropping compared to competitive benchmarks.