Retrospective Interference Alignment for the MIMO Interference Broadcast Channel

TL;DR

This paper proposes a new four-phase precoding strategy for the MIMO Interference Broadcast Channel with delayed CSIT, exploiting the common transmitter structure to improve degrees of freedom bounds.

Contribution

It introduces a novel four-phase precoding method that leverages the common transmitter in the IBC with delayed CSIT, surpassing previous bounds for certain antenna configurations.

Findings

New DoF inner bounds for $ ho > 2.6413$

Outperforms existing bounds in specific antenna configurations

Demonstrates benefits of exploiting common transmitter structure

Abstract

The degrees of freedom (DoF) of the multiple-input multiple-output (MIMO) Interference Broadcast Channel (IBC) with 2 cells and 2 users per cell are investigated when only delayed channel state information is available at the transmitter side (delayed CSIT). Retrospective Interference Alignment has shown the benefits in terms of DoF of exploiting delayed CSIT for interference, broadcast and also for the IBC. However, previous works studying the IBC with delayed CSIT do not exploit the fact that the users of each cell are served by a common transmitter. This work presents a four-phase precoding strategy taking this into consideration. Assuming that transmitters and receivers are equipped with $M,N$ antennas, respectively, new DoF inner bounds are proposed, outperforming the existing ones for $\rho = \frac{M}{N} > 2.6413$.