On the degrees of freedom of three-user MIMO broadcast channel with delayed CSIT

We investigate the three-user MIMO Gaussian broadcast channel with i.i.d. fading and the same number of antennas at each receiver, and with the delayed channel state information at the transmitter (CSIT). We obtain achievability results on the degrees of freedom (DoF) of this channel and also show that our achievable DoF is tight for some ranges of transmit-receive antenna ratio. It is observed that when the number of antennas at the transmitter is strictly greater than that at each receiver, the DoF with delayed CSIT lies strictly between the DoF with perfect CSIT and DoF with no CSIT.