Degrees of Freedom and Sum Rate Maximization for Two Mutually Interfering Broadcast Channels

In this paper, we derive a precise expression of spatial degrees of freedom (DOF) for two mutually interfering broadcast channels (IFBC) as a function of arbitrary numbers of transmit antennas and users. The lower bound on the DOF is obtained by showing that the zero-forcing solution suffices to achieve all the DOF. Also, the upper bound which coincides with the lower bound is shown using Jafar's earlier work. From the derived result, we observe that disabling receive cooperation of the MIMO interference channel causes the DOF loss. Additionally, we propose a linear precoding scheme for the IFBC by extending one designed for broadcast channels with an aim of maximizing the sum rate performance. We utilize the fact that the precoding matrices in stationary point always satisfy the zero-gradient condition. Our result is confirmed through numerical simulations on the sum rate performance of the proposed precoding technique.