August 14, 2017

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

  • Erkip E.
  • Hassanzadeh P.
  • Llorca J.
  • Tulino A.

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 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 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 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.

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