Title: Multiple Access Wiretap Channel with Noiseless Feedback,
Abstract: The physical layer security in the up-link of the wireless communication
systems is often modeled as the multiple access wiretap channel (MAC-WT), and
recently it has received a lot attention. In this paper, the MAC-WT has been
re-visited by considering the situation that the legitimate receiver feeds his
received channel output back to the transmitters via two noiseless channels,
respectively. This model is called the MAC-WT with noiseless feedback. Inner
and outer bounds on the secrecy capacity region of this feedback model are
provided. To be specific, we first present a decode-and-forward (DF) inner
bound on the secrecy capacity region of this feedback model, and this bound is
constructed by allowing each transmitter to decode the other one's transmitted
message from the feedback, and then each transmitter uses the decoded message
to re-encode his own messages, i.e., this DF inner bound allows the independent
transmitters to co-operate with each other. Then, we provide a hybrid inner
bound which is strictly larger than the DF inner bound, and it is constructed
by using the feedback as a tool not only to allow the independent transmitters
to co-operate with each other, but also to generate two secret keys
respectively shared between the legitimate receiver and the two transmitters.
Finally, we give a sato-type outer bound on the secrecy capacity region of this
feedback model. The results of this paper are further explained via a Gaussian
example.