FemtoCaching: Wireless video content delivery through distributed caching helpers

TLDR

When devices can access multiple caches, assigning files to helpers becomes nontrivial. The paper proposes femto caching to address the surge in mobile video demand, formalizes the distributed caching problem, proves its NP‑hardness, and develops approximation algorithms. It introduces helper nodes with limited backhaul but large storage that form a wireless distributed caching network, and evaluates them via simulations of a 3GPP LTE R8 campus scenario using a simplified 802.11n protocol. The short helper–device distances enable efficient cached file delivery, and simulations show that distributed caching can boost the number of served users by 400–500 %.

Abstract

We suggest a novel approach to handle the ongoing explosive increase in the demand for video content in wireless/mobile devices. We envision femtocell-like base stations, which we call helpers, with weak backhaul links but large storage capacity. These helpers form a wireless distributed caching network that assists the macro base station by handling requests of popular files that have been cached. Due to the short distances between helpers and requesting devices, the transmission of cached files can be done very efficiently. A key question for such a system is the wireless distributed caching problem, i.e., which files should be cached by which helpers. If every mobile device has only access to a exactly one helper, then clearly each helper should cache the same files, namely the most popular ones. However, for the case that each mobile device can access multiple caches, the assignment of files to helpers becomes nontrivial. The theoretical contribution of our paper lies in (i) formalizing the distributed caching problem, (ii) showing that this problem is NP-hard, and (iii) presenting approximation algorithms that lie within a constant factor of the theoretical optimum. On the practical side, we present a detailed simulation of a university campus scenario covered by a single 3GPP LTE R8 cell and several helpers using a simplified 802.11n protocol. We use a real campus trace of video requests and show how distributed caching can increase the number served users by as much as 400 - 500%.