Degrees of Freedom on the K-User MIMO Interference Channel with Constant Channel Coefficients for Downlink Communications

In this paper, we study degrees of freedom for the K-User multiple-input multiple-output (MIMO)-interference channel (IFC) with constant channel coefficients. In this channel, we investigate how many total number of transmit antennas, M₁ + M₂ + ¿ + M_K, are required in minimum to achieve d_i = 1,¿i degrees of freedom when all receivers have N = 2 antennas, which is a downlink communication scenario. To answer this question, we propose a new interference alignment scheme based on intersection subspace property of the vector space. The proposed interference alignment scheme can be easily generalized regardless of the number of users. In addition, we investigate degrees of freedom for the partially connected MIMOIFC where some arbitrary interfering links are disconnected due to the large path loss or deep fades. In this channel model, we examine how these disconnected links are considered on designing the beamforming vectors for interference alignment.