Degrees-of-Freedom Region of the MISO Broadcast Channel with General Mixed-CSIT

TL;DR

This paper derives the optimal degrees-of-freedom region for a two-user MISO broadcast channel with varying quality of current CSIT, extending previous models to more realistic asymmetric feedback scenarios.

Contribution

It generalizes existing results by deriving the DoF region for channels with asymmetric and partial CSIT, and proposes new multi-phase broadcast schemes to achieve this optimal region.

Findings

Derived the optimal DoF region for asymmetric CSIT quality.

Proposed novel multi-phase broadcast schemes.

Extended previous models to more realistic feedback scenarios.

Abstract

In the setting of the two-user broadcast channel, recent work by Maddah-Ali and Tse has shown that knowledge of prior channel state information at the transmitter (CSIT) can be useful, even in the absence of any knowledge of current CSIT. Very recent work by Kobayashi et al., Yang et al., and Gou and Jafar, extended this to the case where, instead of no current CSIT knowledge, the transmitter has partial knowledge, and where under a symmetry assumption, the quality of this knowledge is identical for the different users' channels. Motivated by the fact that in multiuser settings, the quality of CSIT feedback may vary across different links, we here generalize the above results to the natural setting where the current CSIT quality varies for different users' channels. For this setting we derive the optimal degrees-of-freedom (DoF) region, and provide novel multi-phase broadcast schemes that achieve this optimal region. Finally this generalization incorporates and generalizes the corresponding result in Maleki et al. which considered the broadcast channel with one user having perfect CSIT and the other only having prior CSIT.