On Interference Networks with Feedback and Delayed CSI

The degrees of freedom (DoF) region of the two-user MIMO interference channel (IC) is completely characterized in the presence of noiseless channel output feedback from each receiver to its respective transmitter and with the assumption of delayed channel state information (CSI) at the transmitters. It is shown that having output feedback and delayed CSI at the transmitters can strictly enlarge the DoF region when compared to the case in which only delayed CSI is available at the transmitters. The proposed coding schemes that achieve the corresponding DoF region with feedback and delayed CSI utilize both resources, i.e., feedback and delayed CSI in a non-trivial manner. Furthermore, cases are identified in which output feedback and delayed CSI alone are sufficient to achieve the DoF region achievable with perfect, instantaneous CSI. Also, the DoF region of the scalar 2× 2× 2 two-hop interference network is characterized. It is shown that the total DoF for this network collapses from 2 (with instantaneous CSI) to 4/3 (with one-hop output feedback and delayed CSI).