On the Secure Degrees of Freedom of the K-user Interference Channel with Delayed CSIT

In this paper, the $K$-user interference channel with confidential messages is considered with delayed channel state information at transmitters (CSIT). We propose a novel secure transmission scheme in which the transmitters carefully mix information symbols with artificial noises to ensure confidentiality. Achieving confidentiality is challenging due to the delayed nature of CSIT, and the distributed nature of the transmitters. Our scheme works over two phases: phase one in which each transmitter sends information symbols mixed with artificial noises, and repeats such transmission over multiple rounds. In the next phase, each transmitter uses delayed CSIT of the previous phase and sends a function of the net interference and artificial noises (generated in previous phase), which is simultaneously useful for all receivers. These phases are designed to ensure the decodability of the desired messages while satisfying the confidentiality constraints. The proposed scheme achieves a sum SDoF of at least $\frac{1}{2} (\sqrt{K} -6)$. To the best of our knowledge, this is the first result on the $K$-user interference channel with confidential messages and delayed CSIT that achieves a SDoF which scales with $K$.