Improved approximation of storage-rate tradeoff for caching via new outer bounds

Caching is a viable solution for alleviating the severe capacity crunch in modern content centric wireless networks. Parts of popular files are pre-stored in users´ cache memories such that at times of heavy demand, users can be served locally from their cache content thereby reducing the peak network load. In this work, we consider a central server assisted caching network where files are jointly delivered to users through multicast transmissions. For such a network, we develop a new information theoretic lower bound on the fundamental cache storage vs. transmission rate tradeoff, which strictly improves upon the best known existing bounds. The new bounds are used to establish the approximate storage vs. rate tradeoff of centralized caching to within a constant multiplicative factor of 8.