Generalized Degrees of Freedom of the Symmetric Cache-Aided MISO Broadcast Channel with Partial CSIT

TL;DR

This paper characterizes the generalized degrees of freedom (GDoF) for a cache-aided MISO broadcast channel with partial channel state information, revealing the interplay between spatial multiplexing and coded-multicasting gains.

Contribution

It provides the first order-optimal GDoF characterization for symmetric cache-aided MISO BC with partial CSIT, including decentralized placement strategies.

Findings

Achieves GDoF characterization up to a constant factor.

Demonstrates order-optimal GDoF in decentralized cache placement.

Uses a combination of achievability schemes and cut-set bounds.

Abstract

We consider the cache-aided MISO broadcast channel (BC) in which a multi-antenna transmitter serves $K$ single-antenna receivers, each equipped with a cache memory. The transmitter has access to partial knowledge of the channel state information. For a symmetric setting, in terms of channel strength levels, partial channel knowledge levels and cache sizes, we characterize the generalized degrees of freedom (GDoF) up to a constant multiplicative factor. The achievability scheme exploits the interplay between spatial multiplexing gains and coded-multicasting gain. On the other hand, a cut-set-based argument in conjunction with a GDoF outer bound for a parallel MISO BC under channel uncertainty are used for the converse. We further show that the characterized order-optimal GDoF is also attained in a decentralized setting, where no coordination is required for content placement in the caches.