On the Secrecy Capacity Region of the Two Two-User User Symmetric Z Interference Channel With Unidirectional Transmitter Cooperation
Abstract: In this paper, the role of unidirectional limited rate transmitter cooperation is studied for the two-user user symmetric Z interference channel (Z (Z-IC) IC) with secrecy constraints at the receivers, in achieving two conflicting goals simultaneously: mitigating interference rference and ensuring secrecy. First, the problem is studied under the linear deterministic model. A novel scheme for partitioning the encoded messages and outputs based on the relative strengths of the signal and interference is proposed. The partitioning reveals the side information that needs to be provided to the receiver and facilitates the development of tight outer bounds on the secrecy capacity region. The achievable schemes for the deterministic model use a fusion of cooperative precoding and transmission trans of a jamming signal. The optimality of the proposed scheme is established for the deterministic model for all possible parameter settings. The insights obtained from the deterministic model are used to derive inner and outer bounds on the secrecy capacity apacity region of the two two-user Gaussian symmetric Z-IC. IC. The achievable scheme for the Gaussian model uses stochastic encoding in addition to cooperative precoding and transmission of a jamming signal. For the Gaussian case, the secure sum generalized degre degrees es of freedom (GDOF) is characterized and shown to be optimal for the weak/moderate interference regime. It is also shown that the secure sum capacity lies within 2 bits/s/Hz of the outer bound for the