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.