Wireless video content delivery through distributed caching and peer-to-peer gossiping

We present a novel approach to handle the ongoing explosive increase in the demand for video content in wireless mobile devices. We show how distributed caching and collaboration between users and femtocell-like base stations without high-speed backhaul, which we call helpers, can greatly improve throughput without suffering from the backhaul bottleneck problem common to femtocells. We also investigate the role of collaboration among users - a process that can be interpreted as the mobile devices playing the role of helpers also. This approach allows an improvement in the video throughput without deployment of any additional infrastructure. The efficiency of the caching approach depends on two key system properties: (i) the configuration of the "effective" distributed cache, i.e., which user can connect to which helpers and (ii) the popularity distribution of the video files. As a function of these properties, we consider the wireless distributed caching problem, i.e., which files should be cached by which helpers. For the uncoded helper problem, a strictly optimum solution of this problem is NP-hard, but good approximation algorithms can be found. Furthermore if distributed coding is used for the caching, exact optimization can be done with polynomial complexity. For the configuration with mobiles-as-helpers problem, we adopt a simplified model wherein users are grouped into clusters within which communications is possible. A key question is the choice of the cluster dimension (collaboration distance), trading off spectral reuse with the probability of finding the desired video within the collaboration distance. Numerical optimization as well as general scaling laws are described. Simulations show that our approach can improve the data throughput by as much as 400 - 500% through addition of helpers, and more than an order of magnitude through the device- to-device communications.