Interference Channels with Confidential Messages: Scaling up the Secure Degrees of Freedom with No CSIT

We consider the 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 with no channel state information at the transmitters (CSIT). We demonstrate that this is true whenever the channel impulse response (CIR) lengths from the legitimate transmitters towards their respectively intended receivers are larger than those from the interfering transmitters towards the unintended receivers. To design this scheme, we use: a) the simple channel matrix structures of the received signal space to eliminate interference and allow decodability at the intended receivers. b) an injection of artificial noise into the transmitted signal from a strategically chosen small number of transmitters that act as cooperative jammers in order to preserve confidentiality of messages at unintended receivers. This is the first work showing that the SDoF of the K-user IC-CM with ISI can linearly increase with K, the number of users.