Improved Memory-Rate Trade-off for Caching with Demand Privacy

We consider the demand-private coded caching problem in a noiseless broadcast network. It is known from past works that a demand-private scheme for N files and K users can be obtained from a non-private scheme for N files and NK users. We first propose a scheme that improves on this idea by removing some redundant transmissions. The memory- rate trade-off achieved using this scheme is shown to be within a multiplicative factor of 3 from the optimal for all the memory regimes when K < N. We further show that a demand-private scheme for N files and K users can be obtained from a particular known non-private scheme for N files and NK − K + 1 users. Finally, we give the exact memory-rate trade-off for demand- private coded caching problems with N > K = 2.