On the Achievable DoF and User Scaling Law of Opportunistic Interference Alignment in 3-Transmitter MIMO Interference Channels

TL;DR

This paper introduces opportunistic interference alignment schemes for 3-transmitter MIMO interference channels, enabling near interference-free DoF without full channel knowledge by exploiting user diversity and alignment feedback.

Contribution

It proposes new OIA schemes that do not require full CSI and demonstrates how user scaling achieves desired DoF in 3-transmitter MIMO systems.

Findings

Achieves interference-free DoF via user selection

Requires specific user scaling laws for non-zero DoF

Proposes and compares two OIA schemes with existing methods

Abstract

In this paper, we propose opportunistic interference alignment (OIA) schemes for three-transmitter multiple-input multiple-output (MIMO) interference channels (ICs). In the proposed OIA, each transmitter has its own user group and selects a single user who has the most aligned interference signals. The user dimensions provided by multiple users are exploited to align interfering signals. Contrary to conventional IA, perfect channel state information of all channel links is not required at the transmitter, and each user just feeds back one scalar value to indicate how well the interfering channels are aligned. We prove that each transmitter can achieve the same degrees of freedom (DoF) as the interference free case via user selection in our system model that the number of receive antennas is twice of the number of transmit antennas. Using the geometric interpretation, we find the required user scaling to obtain an arbitrary non-zero DoF. Two OIA schemes are proposed and compared with various user selection schemes in terms of achievable rate/DoF and complexity.