On Degrees of Freedom Region of MIMO Networks without CSIT

TL;DR

This paper characterizes the degrees of freedom region for 2-user MIMO networks without channel state information at the transmitter, highlighting the potential of interference alignment under these conditions.

Contribution

It provides the first complete DoF region characterization for 2-user MIMO broadcast channels and tight outer bounds for interference channels without CSIT.

Findings

DoF region for 2-user MIMO broadcast channel characterized.

Tight outer bounds for 2-user MIMO interference channel established.

Interference alignment shows potential even without CSIT.

Abstract

In this paper, we study the effect of the absence of channel knowledge for multiple-input-multiple-output (MIMO) networks. Specifically, we assume perfect channel state information at the receivers, no channel state information at the transmitter(s), and independent identically distributed (i.i.d.) Rayleigh fading across antennas, users and time slots. We provide the characterization of the degrees of freedom (DoF) region for a 2-user MIMO broadcast channel. We then provide a DoF region outer bound for a 2-user MIMO interference channel. This bound is shown to be tight for all possible combinations of the number of antennas at each node except for one case. As a byproduct of this analysis we point out the potential of interference alignment in the 2-user MIMO interference channel with no CSIT.