Achieving the degrees of freedom of relay-aided interference broadcast channels

This paper studies the degrees of freedom (DoF) of relay-aided interference broadcast channels and the relay resource to achieve them. We show that, with the aid of half-duplex relays, a G-cell system can achieve GM_BS/2 DoF, where M_BS is the number of transmit antennas in each cell. By studying the interference-free constraints, we obtain a lower bound of the relay resource that ensures interference-free transmission. Instead of directly solving the complicated multivariate problem with cubic interference-free constraints, we propose to relax the problem to linear equations by randomly initiating certain variables, and derive an achievable bound on relay resource. Numerical results show that the relay-aided interference broadcast channels require less relay resource than relay-aided interference channels and transmission protocol has large impact on the required resources.