Interference alignment in space, time and frequency: achievable DoF analysis

It is well established that the employment of interference alignment (IA) in the interference channel can enhance the achievable degrees of freedom (DOF) significantly. The feasibility of IA in a multi-carrier time-extended interference channel is considered. A new IA scheme is introduced that jointly performs the alignment over space, time and frequency. An asymmetric case is considered where the users are equipped with a different number of transmit/receive antennas. In the wake of this asymmetry, the feasible DoF of each user can be different. A closed-form necessary condition on the feasibility of asymmetric achievable DoF in the proposed scheme is derived.