Can Bob enhance the security of the multiple antenna wiretap channel?

We address the physical layer security question of whether a multiple antenna receiver can enhance the secrecy rate of the multiple-input multiple-output wiretap channel by transmitting artificial noise from some of its antennas to jam a multiple antenna eavesdropper. To answer this question we use a QoS-MMSE approach to formulate a global constrained optimisation problem that is efficiently solved after approximating it by a semidefinite program. Results suggest that an improvement in secrecy rate is possible by transmitting artificial noise from an appropriately chosen number of the receiver's antennas. We introduce two antenna configuration selection strategies to reduce system complexity and obtain the best secrecy performance.