On the Degrees of Freedom of MIMO X Networks with Non-Cooperation Transmitters

TL;DR

This paper introduces novel transmission schemes for interference networks with delayed or partial CSIT, achieving higher degrees of freedom than previous methods and extending to various MIMO and SISO X network configurations.

Contribution

It proposes a distributed space-time interference alignment scheme using Cyclic Zero-padding and extends retrospective interference alignment to multiple network configurations, improving sum-DoF performance.

Findings

Achieved higher sum-DoF than existing delayed CSIT schemes for certain MIMO configurations.

Proposed a distributed retrospective interference alignment scheme for K-user SISO X networks.

Extended the distributed STIA to MxN MISO X networks with optimal sum-DoF.

Abstract

Due to limited backhaul/feedback link capacity and channel state information (CSI) feedback delay, obtaining global and instantaneous channel state information at the transmitter (CSIT) is a main obstacle in practice. In this paper, novel transmission schemes are proposed for a class of interference networks that can achieve new trade-off regions between the sum of degrees of freedom (sum-DoF) and CSI feedback delay with distributed and temperately-delayed CSIT. More specifically, a distributed space-time interference alignment (STIA) scheme is proposed for the two-user multiple-input multiple-output (MIMO) X channel via a novel precoding method called Cyclic Zero-padding. The achieved sum-DoFs herein for certain antenna configurations are greater than the best known sum-DoFs in literature with delayed CSIT. Furthermore, we propose a distributed retrospective interference alignment (RIA) scheme that achieves more than 1 sum-DoF for the K-user single-input single-output (SISO) X network. Finally, we extend the distributed STIA to the MxN user multiple-input single-output (MISO) X network where each transmitter has N-1 antennas and each receiver has a single antenna, yielding the same sum-DoF as that in the global and instantaneous CSIT case. The discussion and the result of the MISO X network can be extended to the MIMO case due to spatial scale invariance property.