On the achievability of the degrees of freedom for the three-cell MIMO interfering broadcast channel with minimum spatial dimensions

We consider the three-cell MIMO interfering broadcast channel (IBC) with K users assigned to each base station. Each base station has M = 2K + 1 antennas and each user has N antennas. We propose two different linear precoding schemes to achieve the optimal degrees of freedom (DoF) for the case in which each user receives only one data stream. The first scheme finds the transmit precoders and receive beamformers using a sequence of closed-form steps that is initiated by the solution of an optimization problem on the Grassmannian manifold. One advantage of this scheme is the ability to achieve the optimal DoF with the minimum possible number of transmit and receive antennas. In the second scheme, the users in one cell will have additional K - 1 antennas, but we have been able a closed-form solution for each step of the generation of the transmit precoders and receive beamformers.