Hierarchical Coded Caching

The growing demand for bandwidth-hungry internet services such as YouTube and Netflix have led to a sharp increase in the internet data traffic. Caching of popular content during the off-peak hours, in storage memories distributed across the network, is a possible strategy to reduce the network load during peak hours. Recent work has shown the significant benefits of storing coded content across the caches and using coded-multicast transmissions during file delivery, as opposed to conventional caching schemes which simply replicate content across the caches and use orthogonal unicast transmissions for delivery. While previous work focused on minimizing the server transmission rate in a network with a single layer of caches, we consider a more practical hierarchical caching network with two layers of caches and propose a caching scheme with a simple, intuitive structure which efficiently stores coded content across the two cache layers. Furthermore, we prove that the required transmissions rates for our proposed scheme in each layer of the hierarchical network are in fact within a constant multiplicative and additive gap of the minimum feasible rates.