Interference Channels with Confidential Messages: Leveraging OFDM Transmission to Scale up Secure Degrees of Freedom with No CSIT

We consider the problem of K-user interference channel with confidential messages (IC-CM) with intersymbol interference (ISI). The main contribution of this paper is to show that sum-secure degrees of freedom (SDoF) can be made to linearly increase with the number of users K in the absence of channel state information at the transmitters (CSIT). The proposed scheme entails three main ingredients : a) leveraging the simple channel matrix structures resulting from the orthogonal frequency division multiplexing (OFDM) type transmission technique in order to eliminate interference and allow coherent decoding of each message at its respectively intended receiver. b) exploiting the inherent heterogeneity in channel impulse response (CIR) lengths between the transmitters and the receivers (which results from the wireless multipath propagation), and c) injection of artificial noise into the transmitted signal from a strategically chosen small number of transmitters J that act as cooperative jammers in order to preserve full confidentiality of the messages at the unintended receivers. This is the first work showing that the SDoF of the K-user IC-CM with ISI can linearly increase with the number of users without CSIT.