On the Secrecy Capacity Region of the 2-user Z Interference Channel with Unidirectional Transmitter Cooperation

TL;DR

This paper investigates how unidirectional transmitter cooperation can enhance secrecy capacity in a 2-user Z interference channel, using deterministic and Gaussian models, and finds near-optimal secure communication strategies with minimal capacity loss.

Contribution

It introduces new achievable schemes combining cooperative precoding and jamming for the Z-IC with secrecy constraints, establishing their optimality in deterministic models and near-optimality in Gaussian models.

Findings

Optimality of schemes in deterministic model across parameters

Secure sum GDOF is optimal in weak/moderate interference

Secure sum capacity is within 2 bits/s/Hz of outer bound in Gaussian case

Abstract

In this work, the role of unidirectional limited rate transmitter cooperation is studied in the case of the 2-user Z interference channel (Z-IC) with secrecy constraints at the receivers, on achieving two conflicting goals simultaneously: mitigating interference and ensuring secrecy. First, the problem is studied under the linear deterministic model. The achievable schemes for the deterministic model use a fusion of cooperative precoding and transmission of a jamming signal. The optimality of the proposed scheme is established for the deterministic model for all possible parameter settings using the outer bounds derived by the authors in a previous work. Using the insights obtained from the deterministic model, a lower bound on the secrecy capacity region of the 2-user Gaussian Z-IC are obtained. The achievable scheme in this case uses stochastic encoding in addition to cooperative precoding and transmission of a jamming signal. The secure sum generalized degrees 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 weak/moderate interference regime for all values of the capacity of the cooperative link. Interestingly, in case of the deterministic model, it is found that there is no penalty on the capacity region of the Z-IC due to the secrecy constraints at the receivers in the weak/moderate interference regimes. Similarly, it is found that there is no loss in the secure sum GDOF for the Gaussian case due to the secrecy constraint at the receiver, in the weak/moderate interference regimes. The results highlight the importance of cooperation in facilitating secure communication over the Z-IC.