Center for Pervasive Communications and Computing

In this paper we investigate the sum degrees of freedom (DoF) of multiple unicasts in a wireless network. With 2 source nodes, 2 destination nodes, there are a total of 4 independent unicast sessions (messages), one from each source to each sink node (this setting is also known as an X network), and also there is a delay-free relay working in full-duplex mode helping the transmissions from the source to destination nodes. For such a channel setting, we prove that 5/3 DoF is achievable almost surely for time-varying/frequency-selective channels, based on the ideas of aligned interference neutralization, linear forwarding and interference alignment. Also, the achievable scheme can be easily translated to the rational alignment scheme for the network with constant-values channel coefficients. In addition, we provide an intuition for the 5/3 DoF result from the perspective of counting the number of linear equations and variables.

We provide inner and outer bounds on the generalized degrees of freedom of the two user symmetric interference channel. The bounds are tight in the moderately weak and strong interference regimes. Feedback is shown to provide unbounded improvements to the generalized degrees of freedom of the two user interference channel in the very strong interference regime. It is also shown that feedback does not improve the GDOF of the channel if the interference is moderately weak or moderately strong. We also finally present bounds for the generalized degrees of freedom of the symmetric MIMO interference channel with feedback.

(This report is the exact paper submitted to IEEE GLOBECOM for review, April 1, 2008 on EDAS. Uploaded, for the record, as CPCC report in Oct. 2011.)