Delay Analysis of Layered Video Caching in Crowdsourced Heterogeneous Wireless Networks

Caching popular content at small-cell base stations (SCBSs) and user equipments (UEs) can significantly reduce the network backhaul traffic while improving user satisfaction. This is also enabled by novel video encoding techniques, such as scalable video coding (SVC), which combine layers to offer content with different qualities without re-encoding. Despite some recent works, the performance of layered video delivery in crowd-sourced heterogeneous networks (HetNets) is still unexplored. This article provides an analytical characterization the delay of video delivery in a network with multiple cache-enabled SCBSs and UEs, each storing part of the available video layers based on their popularity. Accordingly, video requests from an UE can be served by either SCBSs or UEs nearby. Our main objective is to maximize the cache hit probability by caching appropriate video layers, thereby minimizing the average video delivery delay. We formulate the problem of minimizing the delivery delay of layered video caching as an integer linear program. We then apply the difference of convex functions technique to identify the set of optimal video layers to be cached at each SCBS and UE in an iterative manner. Our results obtained by using a real video dataset demonstrate that our proposed solution significantly reduces the video download time of all UEs in the network.