Approximate capacity of a class of gaussian broadcast interference channels

Abstract

We characterize approximate capacity region of a class of Gaussian broadcast interference channel (BIC), where one receiver of a two-user broadcast channel experiences interference coming from a point-to-point transmitter. As an intermediate model, we first consider a linear deterministic BIC. We show that in certain regimes the interference alignment scheme is necessary for ensuring the optimal performance. Moreover, we provide a simple method for determining the feasibility condition of interference alignment. With the understanding gained from the linear deterministic model, we propose inner bounds and outer bound for the Gaussian BIC whose gap lies within a constant number of bits in all values of the channel parameters. In order to realize interference alignment in the Gaussian model, we utilize lattice codes. However, instead of using lattice codes globally, we employ Gaussian codes for other unaligned signals. It helps to reduce unwanted gap that can be incurred by using lattice codes only. Deriving the outer bound involves genie-aided techniques, which have been popularly used in recent literatures.