Capacity Results on the Finite State Multiple-Access Wiretap Channel with Delayed State Feedback

In recent years, the finite state Markov channel (FSMC) in the presence of an eavesdropper has been shown to be a useful model for the physical layer security of the practical mobile wireless communication systems. In this paper, we extend this model to a multiple-access situation (up-link of the wireless communication systems), which we call the finite state multiple-access wiretap channel (FS-MAC-WT) with delayed state feedback. To be specific, the FS-MAC-WT consists of two transmitters, a legitimate receiver and an eavesdropper. The channel transition probability depends on a state which undergoes a Markov process, and the state is perfectly known by the legitimate receiver and the eavesdropper. The legitimate receiver intends to send the state back to the transmitters through noiseless feedback channels after some time delay. The main contribution of this paper is to provide inner and outer bounds on the secrecy capacity region of this new model, and these results are further explained via a degraded Gaussian fading example.