Power allocation for secrecy diversity in MISOME wiretap channels

We consider secure beamforming with artificial noise in a multiple-input single-output multiple-eavesdropper (MISOME) wiretap channel, where a transmitter has access to full channel state information (CSI) of a legitimate channel but only partial CSI of eavesdropper channels. In this paper, we first put forth a notion of symbol error probability (SEP) for confidential information-called the δ-secrecy SEP-to connect the reliability and confidentiality of the legitimate communication in MISOME wiretap channels. For single-antenna colluding and non-colluding eavesdroppers, we determine the optimal power allocation between the information-bearing signal and artificial noise to minimize the δ-secrecy SEP in the presence of weak or strong eavesdroppers, and further develop the switched power allocation for general eavesdropping attacks.