Wireless Surveillance via Proactive Eavesdropping and Rotated Jamming

In this paper, we consider a wireless surveillance system, where two single-antenna legitimate devices work cooperatively to monitor a suspicious link between a source (S) and a destination (D). A rotated-jamming based proactive eavesdropping scheme is proposed. In our scheme, one device acts as a legitimate eavesdropper (E) to perform information interception while the other works as a helping jammer (J) to interfere with the suspicious link. The proposed scheme is based on the fact that the received information-bearing signal at E can be totally represented by its projection onto a specific direction $\mathbf {u}$ . If node J's jamming signal is adaptively rotated to be restricted in the direction orthogonal to $\mathbf {u}$ , the detection of S's information at E can be free-of-interference, and the legitimate eavesdropping is successfully realized. Meanwhile, since the jamming signal arrives at E and D through different channels, the orthogonality does not hold at D and the jamming signal cannot be eliminated, thereby causing an irreducible error floor at the suspicious destination. We develop a criterion of choosing the optimal direction $\mathbf {u^{\star }}$ such that the symbol error probability (SEP) at E can be minimized. Moreover, the performance of our scheme is analyzed in terms of SEP, relative eavesdropping rate, as well as surveillance success probability. Finally, simulation results verify the effectiveness of the proposed scheme.