Retrospective Interference Alignment for the MIMO Interference Broadcast Channel

Retrospective Interference Alignment is a linear precoding strategy that seizes delayed channel state information at the transmitters (CSIT), improving the degrees of freedom (DoF) that can be achieved without CSIT for both the broadcast and interference channels. However, little is known for other channel configurations. This work studies the multiple-input multiple-output interference broadcast channel (IBC) with delayed CSIT, 2 cells and 2 users per cell. Although some of the schemes designed for other channels may be applied, they do not exploit the specific topology of the IBC. In this regard, we proposes a precoding strategy that includes the concept of redundancy transmission, and takes into account that users of each cell are served by a common transmitter. Assuming that transmitters and receivers are equipped with M, N antennas, respectively, state-of-the-art achievable DoF are improved for rho = M/N > rho(A), with rho(A) approximate to 3.5414.