Secure Transmission in the Presence of Full-Duplex Active Eavesdropper

We propose a secure transmission scheme for a wiretap channel, where a source transmits to a legitimate destination in the presence of a full- duplex eavesdropper. We assume that the full- duplex eavesdropper performs both eavesdropping and malicious jamming simultaneously. In order to combat the full-duplex active eavesdropper, the source transmits artificial noise (AN) signals, apart from information signals, to confuse the eavesdropper. We adopt the hybrid outage probability as the performance metric, which takes both the transmission outage probability and the secrecy outage probability into consideration. We derive a compact expression for the hybrid outage probability. Utilizing the derived expression, we determine the optimal power allocation factor between information signals and AN signals that minimizes the hybrid outage probability. We also examine the asymptotic hybrid outage probability in the high signal-to-noise ratio regime. Furthermore, we compare the secrecy performance achieved by a full-duplex active eavesdropper with that achieved by a passive eavesdropper, showing that active eavesdropping can be more harmful to the legitimate system.