Subspace Coding for Coded Caching: Decentralized and Centralized Placements Meet for Three Users

Coded caching is a new approach to decrease the communication load during the peak hours of the network. It provides a significant gain, that is maximized in the centralized setting, where the server controls the placement. In many situations, each user fills its cache without any information about the placement of other users. We show that subspace precoding for placement improves the delivery load of a decentralized caching system compared to uncoded placement. Surprisingly, the proposed scheme achieves the delivery load of the centralized placement for K = 3 users for the entire range of cache size.