Achieving the optimal DoF with feedback and mixed CSIT for the 3×2 X-channel

There is an increasing demand of robust interference management methods which provide strong performance even when channel state information is imperfect. To investigate this aspect, we study the 3 × 2 single-input single-output (SISO) X-channel where each transmitter wants to send an independent message to each receiver. We assume that each receiver is allowed to convey perfect outdated and imperfect instantaneous channel state information to the transmitter (CSIT). Furthermore a single transmitter-receiver pair exists that allows for output feedback. For this model, we establish a lower bound on the sum degrees-of-freedom (DoF) by introducing a new achievability scheme. We show that, finite quality CSIT and partial output feedback together compensate for the absence of perfect CSIT.