Centralized Caching with Unequal Cache Sizes

We address a centralized caching problem with unequal cache sizes. We consider a system with a server of files connected via a shared error-free link to a group of cache-enabled users, where one subgroup has a larger cache size than the other, and the number of files in the server is at least as large as the number of users. We propose a caching scheme for the considered system aimed at minimizing the load of worst-case demands over the shared link. Numerical evaluations show that our scheme improves upon the best existing explicit scheme by having a lower worst-case load, and performs within a multiplicative factor of 1.11 from the optimal scheme with uncoded placement and linear coded delivery. Unlike the optimal scheme-for which the placement, the delivery, and the load can be obtained by solving an optimisation problem, and become intractable as the number of users grows-our proposed scheme is an explicit scheme.