The degrees of freedom region of the 3-User MIMO cyclic Z-interference channel with perfect and delayed CSIT

The degrees of freedom (DoF) region is obtained for the 3-user symmetric multiple-input multiple-output cyclic Z-interference channel with M transmit antennas and N receive antennas at each user-pair under the separate assumptions of perfect and delayed channel state information at the transmitter (CSIT). New communication schemes based on interference alignment are developed and are shown to be DoF-optimal for all choices of the number of antennas. For both perfect and delayed CSIT, the new schemes are shown to outperform those for the 2-user Z-interference channel in terms of sum DoF.