On the Optimality of D2D Coded Caching with Uncoded Cache Placement and\n One-shot Delivery

Abstract

We consider a cache-aided wireless device-to-device (D2D) network of the type\nintroduced by Ji, Caire, and Molisch [1], where the placement phase is\norchestrated by a central server. We assume that the devices' caches are filled\nwith uncoded data, and the whole content database is contained in the\ncollection of caches. After the cache placement phase, the files requested by\nthe users are serviced by inter-device multicast communication. For such a\nsystem setting, we provide the exact characterization of the optimal\nload-memory trade-off under the assumptions of uncoded placement and one-shot\ndelivery. In particular, we derive both the minimum average (under uniformly\ndistributed demands) and the minimum worst-case sum-load of the D2D\ntransmissions, for given individual cache memory size at disposal of each user.\nFurthermore, we show that the performance of the proposed scheme is within\nfactor $4$ of the information-theoretic optimum. Capitalizing on the one-shot\ndelivery property, we also propose an extension of the presented scheme that\nprovides robustness against random user inactivity.\n