Maximum-rate Transmission with Improved Diversity Gain for Interference Networks

TL;DR

This paper combines interference alignment and space-time coding, specifically Alamouti codes, to enhance transmission rates and diversity gains in multi-user interference networks with two antennas per node.

Contribution

It introduces a novel design of alignment precoders that preserve maximum degrees of freedom while boosting diversity gain to 2 using Alamouti codes.

Findings

Maintains maximum DoF gain in interference networks.

Increases diversity gain to 2 in short-term regimes.

Improves ergodic mutual information in long-term regimes.

Abstract

Interference alignment (IA) was shown effective for interference management to improve transmission rate in terms of the degree of freedom (DoF) gain. On the other hand, orthogonal space-time block codes (STBCs) were widely used in point-to-point multi-antenna channels to enhance transmission reliability in terms of the diversity gain. In this paper, we connect these two ideas, i.e., IA and space-time block coding, to improve the designs of alignment precoders for multi-user networks. Specifically, we consider the use of Alamouti codes for IA because of its rate-one transmission and achievability of full diversity in point-to-point systems. The Alamouti codes protect the desired link by introducing orthogonality between the two symbols in one Alamouti codeword, and create alignment at the interfering receiver. We show that the proposed alignment methods can maintain the maximum DoF gain and improve the ergodic mutual information in the long-term regime, while increasing the diversity gain to 2 in the short-term regime. The presented examples of interference networks have two antennas at each node and include the two-user X channel, the interferring multi-access channel (IMAC), and the interferring broadcast channel (IBC).