Degrees of freedom of the MIMO rank-deficient interference channel with feedback

We investigate the total degrees of freedom (DoF) of the K-user rank-deficient interference channel with feedback. We focus on a symmetric case in which each node has the same number of antennas, the rank of each direct link is the same, and the rank of each cross link is the same. In this paper, we develop a new achievable scheme which employs interference alignment to efficiently utilize the dimension of the received signal space. In addition, we derive an upper bound for the general K-user case and show the tightness of the bound when the number of antennas at each node is sufficiently large. As a consequence of this result, we also show that if there are enough number of antennas at each node, the DoF gain increases proportionally with the number of users.