We design a new secure transmission scheme in the relay wiretap channel wherea source communicates with a destination through a decode-and-forward relay inthe presence of spatially random-distributed eavesdroppers. For the sake ofpracticality, we consider a general antenna configuration in which the source,relay, destination, and eavesdroppers are equipped with multiple antennas. Inorder to confuse the eavesdroppers, we assume that both the source and therelay transmit artificial noise signals in addition to information signals. Wefirst derive a closed-form expression for the transmission outage probabilityand an easy-to-compute expression for the secrecy outage probability. Notably,these expressions are valid for an arbitrary number of antennas at the source,relay, and destination. We then derive simple yet valuable expressions for theasymptotic transmission outage probability and the asymptotic secrecy outageprobability, which reveal the secrecy performance when the number of antennasat the source grows sufficiently large. Using our expressions, we quantify apractical performance metric, namely the secrecy throughput, under a secrecyoutage probability constraint. We further determine the system and channelparameters that maximize the secrecy throughput, leading to analytical securitysolutions suitable for real-world deployment.
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