  To improve national security, government agencies have long been committed to
enforcing powerful surveillance measures on suspicious individuals or
communications. In this paper, we consider a wireless legitimate surveillance
system, where a full-duplex multi-antenna legitimate monitor aims to eavesdrop
on a dubious communication link between a suspicious pair via proactive
jamming. Assuming that the legitimate monitor can successfully overhear the
suspicious information only when its achievable data rate is no smaller than
that of the suspicious receiver, the key objective is to maximize the
eavesdropping non-outage probability by joint design of the jamming power,
receive and transmit beamformers at the legitimate monitor. Depending on the
number of receive/transmit antennas implemented, i.e., single-input
single-output, single-input multiple-output, multiple-input single-output and
multiple-input multiple-output (MIMO), four different scenarios are
investigated. For each scenario, the optimal jamming power is derived in
closed-form and efficient algorithms are obtained for the optimal
transmit/receive beamforming vectors. Moreover, low-complexity suboptimal
beamforming schemes are proposed for the MIMO case. Our analytical findings
demonstrate that by exploiting multiple antennas at the legitimate monitor, the
eavesdropping non-outage probability can be significantly improved compared to
the single antenna case. In addition, the proposed suboptimal transmit
zero-forcing scheme yields similar performance as the optimal scheme.
