The Gaussian K-user interference and MΓK X channels are
investigated with no instantaneous channel state information (CSI) at
transmitters. 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 are obtained on the degrees of freedom (DoF) of these
channels under the above assumption. It is observed that, in contrast with no
CSIT and full CSIT models, when CSIT is delayed, the achievable DoFs for both
channels with full-duplex transmitter cooperation are greater than the best
available achievable results on their DoF without transmitter cooperation. Our
results are the first to show that the full-duplex transmitter cooperation can
potentially improve the channel DoF with delayed CSIT. Then, K-user
interference and KΓK 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 KΓK X channel. Next, the combination of delayed CSIT and output feedback, known
as Shannon feedback, is studied and strictly higher DoFs compared to the output
feedback model are achieved in the K-user interference channel when K=5 or
K>6, and in the KΓK X channel when K>2. Although being strictly
greater than 1 and increasing with size of the networks, the achievable DoFs in
all the models studied in this paper approach limiting values not greater than
2.Comment: 53 pages, 15 figures; Submitted to IEEE Transactions on Information
Theory, May 2012. To be presented in part in ISIT 2012, Cambridge, MA, US