Retrospective interference alignment

In this paper, we explore the possibility of achieving interference alignment with delayed CSIT when the transmitters are distributed. Our main contribution is an interference alignment scheme, called retrospective interference alignment, that is specialized to settings with distributed transmitters. With this scheme we show that the interference channel with 3 users with only delayed channel state information at the transmitters can achieve 9/8 DoF, while the the 2 user X channel is able to achieve 8/7 DoF. We also consider another setting where delayed channel output feedback is available to transmitters. In this setting the 3 user interference channel and the 2 user X channel are shown to achieve 6/5 and 4/3 DoF, respectively.