# Rate-Memory Trade-off for the Two-User Broadcast Caching Network with Correlated Sources

## TL;DR

This paper investigates the fundamental rate-memory limits in a two-user broadcast caching network with correlated sources, proposing a correlation-aware scheme that nearly achieves optimal performance across various cache sizes.

## Contribution

It introduces a novel two-step correlation-aware cache-aided coded multicast scheme that exploits source correlation to improve caching efficiency.

## Key findings

- The proposed scheme matches the lower bound in a significant memory regime.
- It is within half of the conditional entropy for all other memory sizes.
- Provides a new lower bound on the peak rate-memory trade-off.

## Abstract

This paper studies the fundamental limits of caching in a network with two receivers and two files generated by a two-component discrete memoryless source with arbitrary joint distribution. Each receiver is equipped with a cache of equal capacity, and the requested files are delivered over a shared error-free broadcast link. First, a lower bound on the optimal peak rate-memory trade-off is provided. Then, in order to leverage the correlation among the library files to alleviate the load over the shared link, a two-step correlation-aware cache-aided coded multicast (CACM) scheme is proposed. The first step uses Gray-Wyner source coding to represent the library via one common and two private descriptions, such that a second correlation-unaware multiple-request CACM step can exploit the additional coded multicast opportunities that arise. It is shown that the rate achieved by the proposed two-step scheme matches the lower bound for a significant memory regime and it is within half of the conditional entropy for all other memory values.