On the Feedback Capacity of the Fully Connected $K$-User Interference Channel

TL;DR

This paper characterizes the feedback capacity and generalized degrees of freedom of a symmetric fully connected K-user interference channel, revealing that feedback benefits are limited except at a specific interference level.

Contribution

It introduces a new coding scheme called cooperative interference alignment and provides an approximate capacity characterization for certain SNR and INR regimes.

Findings

Per-user GDoF matches 2-user case except at =1

Feedback does not improve GDoF at =1

Proposes cooperative interference alignment coding scheme

Abstract

The symmetric K user interference channel with fully connected topology is considered, in which (a) each receiver suffers interference from all other (K-1) transmitters, and (b) each transmitter has causal and noiseless feedback from its respective receiver. The number of generalized degrees of freedom (GDoF) is characterized in terms of \alpha, where the interference-to-noise ratio (INR) is given by INR=SNR^\alpha. It is shown that the per-user GDoF of this network is the same as that of the 2-user interference channel with feedback, except for \alpha=1, for which existence of feedback does not help in terms of GDoF. The coding scheme proposed for this network, termed cooperative interference alignment, is based on two key ingredients, namely, interference alignment and interference decoding. Moreover, an approximate characterization is provided for the symmetric feedback capacity of the network, when the SNR and INR are far apart from each other.