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On Cache-Aided Multi-User Private Information Retrieval with Small Caches

Charul RajputB. Sundar Rajan
Dec 2022
In this paper, we propose a scheme for the problem of cache-aided multi-userprivate information retrieval with small caches, in which $K$ users areconnected to $S$ non-colluding databases via shared links. Each databasecontains a set of $N$ files, and each user has a dedicated cache of sizeequivalent to the size of $M$ files. All the users want to retrieve a filewithout revealing their demands to the databases. During off-peak hours, allthe users will fill their caches, and when required, users will demand theirdesired files by cooperatively generating query sets for each database. Afterreceiving the transmissions from databases, all the users should get theirdesired files using transmitted data and their cache contents. This problem hasbeen studied in [X. Zhang, K. Wan, H. Sun, M. Ji and G. Caire, \tqt{Fundamentallimits of cache-aided multiuser private information retrieval}, IEEE Trans.Commun., 2021], in which authors proposed a product design scheme. In thispaper, we propose a scheme that gives a better rate for a particular value of$M$ than the product design scheme. We consider a slightly different approachfor the placement phase. Instead of a database filling the caches of all usersdirectly, a database will broadcast cache content for all users on a sharedlink, and then the users will decide unitedly which part of the broadcastedcontent will be stored in the cache of each user. This variation facilitatesmaintaining the privacy constraint at a reduced rate.