DoF-Delay Trade-Off for the $K$-user MIMO Interference Channel With Delayed CSIT

TL;DR

This paper explores the trade-off between degrees of freedom and transmission delay in a K-user MIMO interference channel with delayed CSIT, proposing three linear precoding strategies based on interference alignment.

Contribution

It introduces three novel linear precoding strategies that explicitly relate achievable DoF to transmission delay, enhancing understanding of the DoF-delay trade-off in delayed CSIT scenarios.

Findings

Proposed strategies achieve DoF-delay trade-off analysis.

Strategies are effective for constant channels, not just time-varying.

Interference alignment is realized using delayed CSIT, user scheduling, and redundancy.

Abstract

The degrees of freedom (DoF) of the $K$-user multiple-input multiple-output (MIMO) interference channel are studied when perfect, but delayed channel state information is available at the transmitter side (delayed CSIT). Recent works have proposed schemes that achieve increasing DoF values, but at the cost of long communication delays. This work proposes three linear precoding strategies, formulated in such a way that the achievable DoF can be derived as a function of the transmission delay, thus elucidating its achievable DoF-delay trade-off. All strategies are based on the concept of interference alignment, and built upon three main ingredients: delayed CSIT precoding, user scheduling, and redundancy transmission. In this respect, the interference alignment is realized by exploiting delayed CSIT in order to align the interference at the non-intended receivers along the space-time domain. Finally, the latter part of this work settles that all the proposed strategies work also for constant channels, except for SISO. In such a case, the schemes can be made feasible by resorting to asymmetric complex signaling concepts. This conclusion removes the time-varying channels assumption unnecessarily common along all the literature on delayed CSIT.