On achievable degrees of freedom of 3-user MIMO interference channels

This paper studies the achievable degrees of freedom (DoF) of 3-user MIMO interference channels based on linear spatial beamforming scheme. Previous work mainly focus on the scenario where each user must have the same DoF and the achievable sum DoF is 3⌊D_out over/3⌋, where D_outer denotes the outer bound of sum DoF. In this paper, we investigate the scenarios where three users are allowed to have different DoF. Three interference alignment based signal transmission strategies are proposed and the achievable DoF is derived. We show that the achievable DoF of the proposed interference alignment scheme achieves the DoF of ⌊D_out⌋ in some cases, which is equal to or higher than 3⌊D_out over 3⌋.