On achieving optimal degrees of freedom of MIMO cellular networks using decomposition

This paper investigates the significance of decomposition-based schemes in achieving the optimal degrees of freedom (DoF) of multiple-input multiple-output (MIMO) cellular networks. We consider MIMO cellular networks with G cells, K users/cell with M antennas at each user, and N antennas at each base-station (BS). We assume all channels to be generic and time varying. We show that KMN over KM + N DoF/cell can be achieved through one-sided decomposition of a MIMO cellular network (on the user side), followed by the use of an asymptotic interference alignment scheme. We then prove that such an approach achieves the optimal DoF whenever M over N = 1 over q, where equation. The optimality is proved using a new set of outer bounds on the DoF of a MIMO cellular network. Finally, we comment on the DoF achieved using two-sided decomposition, and the optimal DoF of cellular networks with single-antenna users and cellular networks with two cells.