On Secure Communications Over a Wiretap Channel With Fixed-Rate Transmission: Protocol Design and Queueing Analysis

In this letter, we consider a wiretap channel when a source node maintains two buffers (queues) to store its data and secret key packets. We propose two medium-access protocols. In the first proposed protocol, we assume that the legitimate source and its destination share random secret key packets when the main channel is better than either the channel between the eavesdropper and the source or the channel between the eavesdropper and the destination. These key packets are stored in a separate key queue at the source and its destination, and they are utilized to secure data packets whenever channel conditions favor eavesdropper channels over the main communication channel. In the second proposed protocol, the source employs a random-access scheme based on the link and queue states. Our numerical results demonstrate the gains of our proposed protocols in terms of the mean service rate of the data queue and the average queueing delay of the data packets.