On Interplay Between Network Topology and Alternating CSIT for Multi-Receiver Wiretap Channel

We study the problem of secure transmission over a Gaussian multi-input single-output (MISO) two receiver channel with an external eavesdropper under the assumption that links connecting the transmitter to three receivers may have unequal strength statistically. In addition to this, the state of the channel to each receiver is conveyed either perfectly "I') or with delay (D) to the transmitter. Let S-1, S-2, and S-3 he the channel state information at the transmitter (csro of user 1, user 2, and eavesdropper, respectively. The overall CSIT can then alternate between eight possible states, i.e., (S-1, S-2, and S-3) is an element of [P, D}(3). We denote by lambda(S1S2S3) the fraction of time during which the state S1S2S3 and S occurs; and, focus on a two state topological setting of strong v.s. weak links with symmetric alternating CSIT, lambda(PDD) = lambda(DPD). For this setting, we establish au inner hound on the Generalized Secure Degrees of Freedom (GSDoF) region with different topology states. The encoding scheme sheds light on the usage of both resources, i.e., alternating topology and CSIT; and, shows that as opposed to coding independently over different states, joint encoding across the CSIT and topological states, enables strictly better secure rates.