Linear Degrees of Freedom of the MIMO XChannel with Delayed CSIT
Abstract
We study the degrees of freedom (DoF) of the multipleinput multipleoutput Xchannel (MIMO XC) with delayed channel state information at the transmitters (delayed CSIT), assuming linear coding strategies at the transmitters. We present two results: 1) the linear sum DoF for MIMO XC with general antenna configurations, and 2) the linear DoF region for MIMO XC with symmetric antennas. The converse for each result is based on developing a novel rankratio inequality that characterizes the maximum ratio between the dimensions of received linear subspaces at the two multipleantenna receivers. The achievability of the linear sum DoF is based on a threephase strategy, in which during the first two phases only the transmitter with fewer antennas exploits delayed CSIT in order to minimize the dimension of its signal at the unintended receiver. During Phase 3, both transmitters use delayed CSIT to send linear combinations of past transmissions such that each receiver receives a superposition of desired message data and known interference, thus simultaneously serving both receivers. We also derive other linear DoF outer bounds for the MIMO XC that, in addition to the outer bounds from the sum DoF converse and the proposed transmission strategy, allow us to characterize the linear DoF region for symmetric antenna configurations.
 Publication:

arXiv eprints
 Pub Date:
 May 2014
 DOI:
 10.48550/arXiv.1405.1091
 arXiv:
 arXiv:1405.1091
 Bibcode:
 2014arXiv1405.1091K
 Keywords:

 Computer Science  Information Theory
 EPrint:
 to be presented in part at ISIT 2014