Gaussian Z-interference channel with a relay link: Achievable rate region and asymptotic sum capacity

This paper studies a Gaussian Z-interference channel with a rate-limited digital relay link from the interference-free receiver to the interfered receiver. An achievable rate region is derived based on a combination of the Han-Kobayashi common-private information splitting technique and a partial interference-forwarding relaying strategy in which a part of the interference is decoded then forwarded through the digital link using a binning strategy for interference cancellation. The proposed strategy is shown to be capacity achieving in the strong interference regime, and asymptotically sum capacity approaching in the weak interference regime in the high signal-to-noise ratio and high interference-to-noise ratio limit.