Retrospective Interference Neutralization for the Two-Cell MIMO Interfering Multiple Access Channel

In this paper, we study the degrees of freedom (DoF) of the two-cell multiple-input multiple-output (MIMO) interfering multiple access channel (IMAC) with hybrid channel state information at the transmitters (CSIT). We propose a retrospective interference alignment neutralization (RIAN) method by using hybrid CSIT. The approach consists of two steps: 1) interference alignment and 2) retrospective interference neutralization. In the first step, all users are scheduled to transmit fresh symbols and each base station (BS) design interference alignment matrix to align interference. In the second step, each user sends the previously transmitted symbols by using the beamforming so that each BS can exploit the aligned interference information to neutralize all interference symbols. We show that the proposed RIAN scheme can obtain a higher DoF than the existing retrospective interference alignment schemes based on completely delayed CSIT.