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

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.