Private Information Retrieval in Wireless Coded Caching

We consider private information retrieval (PIR) in a content delivery scenario where, to reduce the backhaul usage, data is cached using maximum distance separable codes in a number of small-cell base stations (SBSs). We present a PIR protocol that allows the user to retrieve files of different popularities from the network without revealing the identity of the desired file to curious SBSs that potentially collaborate. We formulate an optimization problem to optimize the content placement and the number of queries of the protocol such that the backhaul rate is minimized. We further prove that, contrary to the case of no PIR, uniform content placement is optimal. Compared to a recently proposed protocol by Kumar et al. the presented protocol gives a reduced backhaul rate.