|Novel Converse for Device-to-Device Demand-Private Caching with a Trusted Server
|Kai Wan, Technische Universität Berlin, Germany; Hua Sun, University of North Texas, United States; Mingyue Ji, University of Utah, United States; Daniela Tuninetti, University of Illinois at Chicago, United States; Giuseppe Caire, Technische Universität Berlin, Germany
|N.4: Coded Caching II
|Networking and Network Coding
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|This paper considers cache-aided device-to-device (D2D) networks where a trusted server helps to preserve the privacy of the users’ demands. Specifically, the trusted server collects the users’ demands before the delivery phase and sends a query to each user, who then broadcasts multicast packets according to this query. Recently the Authors proposed a D2D private caching scheme that was shown to be order optimal except for the very low memory size regime, where optimality was proved by comparing to an outer bound without privacy constraint. The main contribution of this paper is a novel converse bound for the studied model where users may collude (i.e., some users share cache contents and demanded files, and yet cannot infer what files the remaining users have demanded) and under the placement phase is uncoded. To the best of the Author’s knowledge, such a general bound is the first that genuinely accounts for the demand privacy constraint, and was inspired by private information retrieval. The novel converse bound not only allows to show that the known achievable scheme is order optimal in all cache size regimes, but has the potential to be used in other variants of demand private caching.