Fundamental Limits of Device-to-Device Private Caching with Trusted Server
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In the coded caching problem as originally formulated by Maddah-Ali and Niesen, a server with access to a library including N files communicates via a noiseless broadcast link to K users that have local storage capability; in order for a user to decode the desired file from the coded multicast transmission, the demands of all the users must be globally known, which may violate the privacy of the users. To overcome this privacy problem, Wan and Caire recently proposed several schemes that attain coded multicasting gain while simultaneously guarantee information theoretic privacy of the users' demands. In device to device (D2D) networks, the demand privacy problem is further exacerbated by the fact that each user is also a transmitter, which should know the demanded messages of the other users in order to form coded multicast transmissions. This paper solves this seemingly unfeasible problem with the aid of a trusted server. Specifically, during the delivery phase, the trusted server collects the users' demands and sends a query to each user, who then broadcasts multicast packets according to this query. The main contribution of this paper is the development of novel achievable schemes and converse bounds for D2D private caching with a trusted server, where users may be colluding, that are to within a constant factor.
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