Retrospective Interference Alignment for the 3-user MIMO interference channel with delayed CSIT

The degrees of freedom (DoF) of the 3-user multiple input multiple output interference channel (3-user MIMO IC) are investigated where there is delayed channel state information at the transmitters (dCSIT). We generalize the ideas of Maleki et al. about Retrospective Interference Alignment (RIA) to be applied to the MIMO IC, where transmitters and receivers are equipped with (M, N) antennas, respectively. We propose a two-phase transmission scheme where the number of slots per phase and number of transmitted symbols are optimized by solving a maximization problem. Finally, we review the existing achievable DoF results in the literature as a function of the ratio between transmitting and receiving antennas ρ = M/N. The proposed scheme improves all other strategies when ρ ∈ (1/2, 31/32].