Implement Blind Interference Alignment over Homogeneous 3-user 2x1 Broadcast Channel

TL;DR

This paper demonstrates how Blind Interference Alignment can achieve optimal degrees of freedom in homogeneous 3-user 2x1 broadcast channels without CSIT, and extends the approach to larger networks with high probability of feasibility.

Contribution

It provides a sufficient condition for achieving 3/2 DoF using BIA in 3-user channels and shows that for K>=11 users, BIA is feasible with high probability.

Findings

BIA achieves 3/2 DoF in 3-user 2x1 BC without CSIT.

For K>=11 users, BIA can be applied with over 95% certainty.

The method extends to larger homogeneous networks with independent coherence times.

Abstract

This paper first studies the homogeneous 3-user 2x1 broadcast channel (BC) with no CSIT. We show a sufficient condition for it to achieve the optimal 3/2 degrees of freedom (DoF) by using Blind Interference Alignment (BIA). BIA refers to the interference alignment method without the need of CSIT. It further studies the 2x1 broadcast network in which there are K>=3 homogeneous single-antenna users, and their coherence time offsets are independently and uniformly distributed. We show that, if K>=11, the two-antenna transmitter can find, with more than 95% certainty, three users to form a BIA-feasible 3-user BC and achieve the optimal 3/2 DoF.