Distributed Space-Time Interference Alignment with Moderately-Delayed CSIT

TL;DR

This paper introduces a distributed interference alignment technique utilizing moderately-delayed CSIT, improving the sum degrees of freedom in interference networks and matching the performance of instantaneous CSIT under certain conditions.

Contribution

It proposes a novel interference alignment method with distributed and delayed CSIT, characterizing the trade-offs and demonstrating its effectiveness in enhancing sum-DoF.

Findings

Distributed and moderately-delayed CSIT improves sum-DoF over no CSIT.

Method achieves sum-DoF equivalent to instantaneous CSIT in certain X-channels.

Sum-capacity is characterized within a constant gap for specific channel coefficients.

Abstract

This paper proposes an interference alignment method with distributed and delayed channel state information at the transmitter (CSIT) for a class of interference networks. The core idea of the proposed method is to align interference signals over time at the unintended receivers in a distributed manner. With the proposed method, achievable trade-offs between the sum of degrees of freedom (sum-DoF) and feedback delay of CSI are characterized in both the X-channel and three-user interference channel to reveal the impact on how the CSI feedback delay affects the sum-DoF of the interference networks. A major implication of derived results is that distributed and moderately- delayed CSIT is useful to strictly improve the sum-DoF over the case of no CSI at the transmitter in a certain class of interference networks. For a class of X-channels, the results show how to optimally use distributed and moderately-delayed CSIT to yield the same sum-DoF as instantaneous and global CSIT. Further, leveraging the proposed transmission method and the known outer bound results, the sum-capacity of the two-user X-channel with a particular set of channel coefficients is characterized within a constant number of bits.