On Secure Degrees of Freedom for Three-User MISO Broadcast Channel With Three Messages

We study a three-user multiple-input single-output (MISO) broadcast channel with confidential messages (BCCM). We have three messages where each of them is intended to the corresponding receiver. We impose confidentiality constraints for two of the messages at the receiving terminals. Half of the time, the channel state information (CSI) of all receivers are known perfectly at the transmitter. At the other half, the CSI of one of the receivers is available with some delay. The main contribution of this paper is to find the sum secure degrees of freedom (SDoF) of the proposed channel. We utilize the alternating CSIT scheme to design the precoding matrices. The proof of the converse is challenging for this model. The idea of the converse proof is to adapt the well known statistical equivalent property (SEP) lemma for our model.