The Gaussian K-user interference and M × K X channels are investigated with no instantaneous channel state information at transmitters (CSIT). First, it is assumed that the CSI is fed back to all nodes after a finite delay (delayed CSIT), and furthermore, the transmitters operate in full-duplex mode, i.e, they can transmit and receive simultaneously. Achievable results on the degrees of freedom (DoFs) of these channels under the above assumption are obtained. It is observed that, in contrast with no CSIT and full CSIT models, when CSIT is delayed, the achievable DoFs for both channels with the full-duplex transmitter cooperation are greater than the available achievable results on their DoF without transmitter cooperation.
Then, K-user interference and K × K X channels are considered with output feedback, wherein the channel output of each receiver is causally fed back to its corresponding transmitter. Our achievable results with output feedback demonstrate strict DoF improvements over those with the full-duplex delayed CSIT when K 5 in the K-user interference channel and K > 2 in the K × K X channel. Next, the combination of delayed CSIT and output feedback, known as Shannon feedback, is studied and strictly higher DoFs compared with the output feedback model are achieved in the K-user interference channel when K = 5 or K 6, and in the K × K X channel when K > 2.