Content Delivery over Broadcast Erasure Channels with Distributed Random Cache

TL;DR

This paper investigates the capacity of content delivery over broadcast erasure channels with distributed random caching at receivers, analyzing how different levels of channel state and cache information at the transmitter affect performance.

Contribution

It derives new capacity bounds for various information availability scenarios, revealing cases where limited information yields optimal capacity.

Findings

Capacity bounds are established for different channel state and cache information levels.

Matching inner and outer bounds characterize the capacity region in several scenarios.

Capacity regions can be identical even with limited channel or cache information.

Abstract

We study the content delivery problem between a transmitter and two receivers through erasure links, when each receiver has access to some random side-information about the files requested by the other user. The random side-information is cached at the receiver via the decentralized content placement. The distributed nature of receiving terminals may also make the erasure state of two links and indexes of the cached bits not perfectly known at the transmitter. We thus investigate the capacity gain due to various levels of availability of channel state and cache index information at the transmitter. More precisely, we cover a wide range of settings from global delayed channel state knowledge and a non-blind transmitter (i.e. one that knows the exact cache index information at each receiver) all the way to no channel state information and a blind transmitter (i.e. one that only statistically knows cache index information at the receivers). We derive new inner and outer bounds for the problem under various settings and provide the conditions under which the two match and the capacity region is characterized. Surprisingly, for some interesting cases the capacity regions are the same even with single-user channel state or single-user cache index information at the transmitter.