On the DoF region of the two-user Interference Channel with an Instantaneous Relay

TL;DR

This paper investigates the maximum degrees of freedom in a two-user multi-antenna interference channel with an instantaneous relay, proposing a linear strategy that maximizes sum DoF and is optimal in specific antenna configurations.

Contribution

It derives the achievable DoF region for all antenna configurations using a memoryless linear relay strategy focused on interference neutralization.

Findings

Achieves the largest sum DoF among linear strategies.

Proves optimality of the scheme for certain antenna setups.

Provides a comprehensive DoF region characterization.

Abstract

This paper studies the Degrees of Freedom (DoF) of the two-user multi-antenna Gaussian interference channel with an {\em instantaneous relay}, or relay without delay, where the relay transmitted signal in channel use $t$ can depend on all received signals up to and including that at channel use $t$. It is assumed that the two transmitters and the two receivers have $M$ antennas, while the relay receives through $N$ antennas and transmits through $L$ antennas. An achievable DoF region is derived, for all possible values of $(M,N,L)$, based on a memoryless linear transmission strategy at the relay that aims to {\it neutralize} as much interference as possible at the receivers. The proposed scheme is shown to attain the largest sum DoF among all memoryless linear transmission strategies at the relay and to actually be optimal for certain values of $(M,N,L)$.