FemtoCaching: Wireless video content delivery through distributed caching helpers

Abstract

Abstract-Video on-demand streaming from Internetbased servers is becoming one of the most important services offered by wireless networks today. In order to improve the area spectral efficiency of video transmission in cellular systems, small cells heterogeneous architectures (e.g., femtocells, WiFi off-loading) are being proposed, such that video traffic to nomadic users can be handled by short-range links to the nearest small cell access points (referred to as "helpers"). As the helper deployment density increases, the backhaul capacity becomes the system bottleneck. In order to alleviate such bottleneck we propose a system where helpers with low-rate backhaul but high storage capacity cache popular video files. Files not available from helpers are transmitted by the cellular base station. We analyze the optimum way of assigning files to the helpers, in order to minimize the expected downloading time for files. We distinguish between the uncoded case (where only complete files are stored) and the coded case, where segments of Fountain-encoded versions of the video files are stored at helpers. We show that the uncoded optimum file assignment is NP-hard, and develop a greedy strategy that is provably within a factor 2 of the optimum. Further, for a special case we provide an efficient algorithm achieving a provably better approximation ratio of 1where d is the maximum number of helpers a user can be connected to. We also show that the coded optimum cache assignment problem is convex that can be further reduced to a linear program. We present numerical results comparing the proposed schemes.

Submodularity in Dynamics and Control of Networked Systems

“…Second, the analysis of [4,138] assumes that each node can compute the impact of each of its actions on the objective function at each time instant. Since the computation of many common objective functions requires global knowledge of the network topology and current value of the set [35,57,73], we do not make this assumption.…”

“…In addition to the problem of selecting leader nodes, our techniques have applications in wireless network design problems such as multi-carrier wireless scheduling [5], wireless content delivery through distributed caching [57], sleep-wake scheduling of sensors [73], and data forwarding [142].…”

“…Under our approach, a subset of nodes (e.g., a set of nodes to act as caches [57], leaders [35], or active sensors [73]) is selected by each node deciding, in a distributed fashion, whether to join the set based on the current and previous values of the objective function. In the case of unconstrained optimization, we introduce a probabilistic algorithm in which each node decides, at each tick of its internal clock, whether to join or exit the set based on the previously observed utility.…”

Caching with Unknown Popularity Profiles in Small Cell Networks

“…In [18], coded caching was shown to achieve multicast gain in a D2D network, where users had access to linear combinations of packets from cached files. The NP-hard nature of distributed caching was reported in [19], where approximation algorithms were proposed for video content delivery. In [20], the throughput scaling laws of random caching, where users with pre-cached information made arbitrary requests for cached files, was studied.…”

Small-cell caching mechanism for multi-service providers

“…To deal with the caching problem, several schemes have been proposed in previous works such as [1] and [2]. However, most of the current studies neglect the fact that contents are usually from different providers, who have the incentives to compete for the caching storage to better serve its own users.…”