Degrees of Freedom of the MIMO Z-Interference Channel With Delayed CSIT

The degrees of freedom region is established for the 2-user multiple-input multiple-output Z-interference channel with an arbitrary number of antennas at each node, under the assumption of delayed channel state information at the transmitters. A new interference alignment scheme is obtained and is shown to be optimal in the degrees of freedom (DoF) metric. When used over an interference channel with one cross-link being statistically weaker than the other three links, this scheme, by explicitly recognizing the relative weakness of that link, can lead to a DoF improvement over the DoF-optimal scheme designed for the fully connected interference channel, while also requiring no feedback of the weak link's channel state information.