Code Rate Maximization of Cooperative Caching in Ultra-Dense Networks

Cooperative caching using maximum distance separable (MDS) codes and repetition codes in ultra-dense networks is studied, with the objective of maximizing the code rate while ensuring that end users can restore the file from the associating small base stations (SBSs) without the use of the backhaul link. It is proved that MDS-coded caching is optimal in general. In contrast, repetition caching is optimal only for some special cases. Repetition caching is, in general, suboptimal, and the associated code rate maximization problem is shown to be NP-hard and a heuristic algorithm is designed to evaluate the potential coding gain in arbitrary 2-dimensional (2D) network. Simulation results show that MDS-coded caching can save about 40% storage space when compared with repetition caching, and this coding gain increases when the amount of overlapping between clusters increases.