Aligned Interference Neutralization and the Degrees of Freedom of the 2x2x2 Interference Channel

TL;DR

This paper introduces aligned interference neutralization, a novel technique that enables the 2x2x2 interference channel to achieve its maximum degrees of freedom of 2 in almost all cases, regardless of channel variation.

Contribution

It proposes a new interference alignment method called aligned interference neutralization, achieving the min-cut outer bound of 2 DoF for the 2x2x2 interference channel.

Findings

Achieves the min-cut outer bound of 2 DoF for almost all channel coefficients.

Applicable to both time-varying and fixed channels.

Introduces a new interference alignment technique, aligned interference neutralization.

Abstract

We show that the 2x2x2 interference channel, i.e., the multihop interference channel formed by concatenation of two 2-user interference channels achieves the min-cut outer bound value of 2 DoF, for almost all values of channel coefficients, for both time-varying or fixed channel coefficients. The key to this result is a new idea, called aligned interference neutralization, that provides a way to align interference terms over each hop in a manner that allows them to be cancelled over the air at the last hop.