In this paper, we consider secure communications between a single antenna transmitter and a single antenna receiver in the presence of a multiple antenna eavesdropper employing MRC or SDC reception. We show that an M-antenna eavesdropper performing SDC reception has precisely the same degrading effect on secrecy as M single antenna eavesdroppers under independent fading conditions. We also show that an M-antenna eavesdropper performing MRC reception causes greater secrecy degradation than an M-antenna eavesdropper performing SDC reception or M single antenna eavesdroppers. We also derive closed-form expressions for the asymptotic high SNR outage secrecy capacity for both the MRC and the SDC eavesdropper cases. Various numerical results are presented that corroborate the analysis.
