Secure degrees of freedom of the multiple access wiretap channel with no eavesdropper CSI

Abstract

We consider the K-user Gaussian multiple access wiretap channel (MAC-WT), where no eavesdropper channel state information (CSI) is available at the transmitters. We show that the exact sum secure degrees of freedom (s.d.o.f.) of this channel model is equation. This result shows that, under the condition of no eavesdropper CSI, the MAC-WT acts like a single-transmitter K-1 helper wiretap channel. We further show that, when a subset of the transmitters have eavesdropper CSI, then higher sum s.d.o.f. can be achieved, and the system can be operated as a MAC-WT for the users with eavesdropper CSI, with the remaining users acting as helpers. In particular, if m of the K transmitters have eavesdropper CSI, we show that equation sum s.d.o.f. can be achieved, showing the benefits of having the eavesdropper CSI at the transmitters.