Fundamental Limits of Demand-Private Coded Caching

Abstract

We consider the coded caching problem with an additional privacy constraint that a user should not get any information about the demands of the other users. We first show that a demand-private scheme for N files and K users can be obtained from a non-private scheme that serves only a subset of the demands for the N files and N K users problem. We further use this fact to construct a demand-private scheme for N files and K users from a particular known non-private scheme for N files and N K − K + 1 users. It is then demonstrated that, the memoryrate pair (M, min{N, K}(1 − M/N )), which is achievable for non-private schemes with uncoded transmissions, is also achievable under demand privacy. We further propose a scheme that improves on these ideas by removing some redundant transmissions. The memory-rate trade-off achieved using our schemes is shown to be within a multiplicative factor of 3 from the optimal when K < N and of 8 when N ≤ K. Finally, we give the exact memory-rate trade-off for demand-private coded caching problems with N ≥ K = 2.

Coded Caching with Private Demands and Caches

“…One can see that in this example, the achieved load is 1 2 and the needed subpacketization level is 2. Whereas the achieved load by the virtual user scheme in [9] is 11 24 and the needed subpacketization level is 10.…”

“…The main advantage of the scheme in [10] is its subpacketization which is the same as the original MAN caching scheme (which is exponential to K). Other papers on demand privacy include [11]- [14], which we leave them to the readers.…”