On the Degrees of Freedom of MIMO X Networks With Non Non-Cooperation Transmitters
Abstract: This paper proposes novel transmission schemes for a class of interference networks that can achieve new tradeoff regions between the sum of degrees of freedom (sum-DoF) DoF) and channel state information (CSI) feedback delay with distributed and temperately-delayed temperately delayed CSI at the transmitter (CSIT). A significant impact of the results is they reveal that distributed and temperately temperately-delayed CSIT contributes to achieve better bet sum-DoF DoF than that without CSIT in a certain class of interference networks. Specifically, a distributed spacespace-time interference alignment (STIA) scheme is proposed for the two two-user user multiple-input multiple multipleoutput (MIMO) X channel via a novel precoding m method ethod called Cyclic ZeroZero padding. The achieved sum-DoFs sum DoFs herein for certain antenna configurations are greater than the best known sum-DoFs sum DoFs in literature with delayed CSIT. Furthermore, we propose a distributed retrospective interference alignment (RIA) scheme eme that achieves more than 1 sum-DoF sum for the K-user user single single-input singleoutput (SISO) X network. Finally, we extend the distributed STIA to the MĂ—N user multiple-input single-output output (MISO) X network, where each transmitter has N - 1 antennas and each receiver iver has a single antenna, yielding the same sum-DoF sum as that in the global and instantaneous CSIT case. The discussion and result of the MISO X network can be extended to the MIMO case due to the spatial scale invariance property.