Content Delivery In Wireless Networks Research Articles

Clustering-based device-to-device discovery and content delivery in wireless networks

Device-to-device (D2D) cache placement and content delivery is a recent technology that exploits idle memory capacity of mobile devices and promises to fulfill users' content needs with very low delay and without using the scarce cellular network capacity. Recent literature on D2D caching mostly concentrated on optimal cache placement and mostly disregarded the required discovery mechanisms and the accompanying overhead. In this work we propose a clustering-based procedure that is used to cache content at the helper nodes along with advertisement and discovery procedures for content delivery. We implement a Long Term Evolution (LTE)-based simulation setup to evaluate the proposed schemes. Numerical results reveal that the clustering-based user and content discovery significantly improves cellular offloading and reduces the discovery overhead with a minimal sacrifice from delay.

Counterintuitive Characteristics of Optimal Distributed LRU Caching Over Unreliable Channels

Least-recently-used (LRU) caching and its variants have conventionally been used as a fundamental and critical method to ensure fast and efficient data access in computer and communication systems. Emerging data-intensive applications over unreliable channels, e.g., mobile edge computing and wireless content delivery networks, have imposed new challenges in optimizing LRU caching in environments prone to failures. Most existing studies focus on reliable channels, e.g., on wired Web servers and within data centers, which have already yielded good insights and successful algorithms. Surprisingly, we show that these insights do not necessarily hold true for unreliable channels. We consider a single-hop multi-cache distributed system with data items being dispatched by random hashing. The objective is to design efficient cache organization and data placement that minimize the miss probability. The former allocates the total memory space to each of the involved caches. The latter decides data routing and replication strategies. Analytically, we characterize the asymptotic miss probabilities for unreliable LRU caches, and optimize the system design. Remarkably, these results sometimes are counterintuitive, differing from the ones obtained for reliable caches. We discover an interesting phenomenon: allocating the cache space unequally can achieve a better performance, even when channel reliability levels are equal. In addition, we prove that splitting the total cache space into separate LRU caches can achieve a lower asymptotic miss probability than organizing the total space in a single LRU cache. These results provide new and even counterintuitive insights that motivate novel designs for caching systems over unreliable channels.

Cache-Assisted Content Delivery in Wireless Networks: A New Game Theoretic Model

With the rapid increase of mobile data traffic, efficient content delivery in wireless networks is increasingly important to provide broadcast and multicast services. To reduce network cost and enrich end-user quality of experience, Internet service providers (ISPs) and content providers (CPs) are expected to collaborate to improve content delivery services. However, the influence of content popularity has been generally overlooked, and profit split problem between ISPs and CPs has not been studied. We investigate the novel economic behaviors between ISPs and CPs in the presence of edge caches, and formulate the profit split problem as a centralized model, which can achieve optimal content caching and maximal network benefits. A Stackelberg game is designed to obtain its distributed win–win solution, where a feasible backward induction is proposed and the influence of edge caches and content popularity is analyzed. Simulation results show that the performance of our proposed Stackelberg game model is comparable to the centralized alternative and much better than existing ISP-CP cooperative schemes not considering cache deployment in the network.

Combining Contract Theory and Lyapunov Optimization for Content Sharing With Edge Caching and Device-to-Device Communications

The paper proposes a novel framework based on the contract theory and Lyapunov optimization for content sharing in a wireless content delivery network (CDN) with edge caching and device-to-device (D2D) communications. The network is partitioned into a set of clusters. In a cluster, users can share contents via D2D links in coordination with the cluster head. Upon receiving the content request from any user in its cluster, the cluster head either delivers the content itself or forwards the request to another node, i.e., a base station (BS) or another user in the cluster. The content access at the BS and in each cluster is modeled as a queuing system, where arrivals represent the content requests directed to respective nodes. The objective is to assign content delivery nodes to stabilize all queues while minimizing the time-averaged network cost given incomplete information about content sharing costs of the users and unknown distribution of the network state defined by users’ locations and their cached/requested content. The proposed framework allows the users to truthfully reveal their content sharing expenditures, minimize the time-averaged network cost and stabilize the queuing system representing the CDN. Based on this framework, a distributed content access and delivery algorithm where the node assignments are made by every cluster head independently is developed. It is shown that the algorithm converges to the optimal policy with the trade-off in total queue backlog and achieves a superior performance compared with some other D2D content sharing policies.

Coded multicasting in cache-enabled vehicular ad hoc network

Caching popular content at a wireless network edge has attracted significant attention since it can deal with massive content delivery in wireless networks. Furthermore, coded multicasting can impressively reduce network traffic by eliminating duplicate data transmission. In this paper, we study to minimize data traffic and redundant problem by jointly considering coded multicasting and edge caching in vehicular ad hoc networks (VANETs). For a single RSU scenario, a maximum degree priority algorithm is proposed to partition users into multiple multicast groups. And then, we formulate the problem of minimum data traffic and minimum redundant rate data for each multicast group as a multi-objective optimization problem, which is a multi-objective set coverage problem. Subsequently, we propose an efficient heuristic algorithm with a subfile code technique and coded multicasting in each multicast group to solve the problem. For a dense network with coverage of multiple RSUs overlapped with each other, the network flow method is used to reassign users to a specific RSU, and then an effective algorithm is proposed to address the general problem. The simulation results show that our proposed algorithm can improve the bandwidth usage and reduce the redundant rate effectively.

Fundamental Storage-Latency Tradeoff in Cache-Aided MIMO Interference Networks

Caching is an effective technique to improve user perceived experience for content delivery in wireless networks. Wireless caching differs from traditional web caching in that it can exploit the broadcast nature of wireless medium and hence opportunistically change the network topologies. This paper studies a cache-aided MIMO interference network with 3 transmitters each equipped with M antennas and 3 receivers each with N antennas. With caching at both the transmitter and receiver sides, the network is changed to hybrid forms of MIMO broadcast channel, MIMO X channel, and MIMO multicast channels. We analyze the degrees of freedom (DoF) of these new channel models using practical interference management schemes. Based on the collective use of these DoF results, we then obtain an achievable normalized delivery time (NDT) of the network, an information-theoretic metric that evaluates the worst-case delivery time at given cache sizes. The obtained NDT is for arbitrary M, N and any feasible cache sizes. It is shown to be optimal in certain cases and within a multiplicative gap of 3 from the optimum in other cases. The extension to the network with arbitrary number of transmitters and receivers is also discussed.

Distributed Storage in Mobile Wireless Networks With Device-to-Device Communication

We consider the use of distributed storage (DS) to reduce the communication cost of content delivery in wireless networks. Content is stored (cached) in a number of mobile devices using an erasure correcting code. Users retrieve content from other devices using device-to-device communication or from the base station (BS), at the expense of higher communication cost. We address the repair problem when a device storing data leaves the cell. We introduce a repair scheduling where repair is performed periodically and derive analytical expressions for the overall communication cost of content download and data repair as a function of the repair interval. The derived expressions are then used to evaluate the communication cost entailed by DS using several erasure correcting codes. Our results show that DS can reduce the communication cost with respect to the case where content is downloaded only from the BS, provided that repairs are performed frequently enough. If devices storing content arrive to the cell, the communication cost using DS is further reduced and, for large enough arrival rate, it is always beneficial. Interestingly, we show that MDS codes, which do not perform well for classical DS, can yield a low overall communication cost in wireless DS.

Caching based socially-aware D2D communications in wireless content delivery networks: a hypergraph framework

The emergence of the D2D communications paradigm has transformed the way in which cellular networks are operated. Previous work in D2D communications, however, mainly focused on interference management and capacity maximization of both D2D links and cellular links. Recent literature has observed that the QoE can be greatly enhanced by caching contents in mobile devices, with a carefully designed caching strategy. In this article, we propose a novel hypergraph framework that designs the caching based D2D communication scheme by taking social ties among users and common interests into consideration. We first present the considered features of the D2D transmission scheme, social characteristics consideration, and interest similarity impact. The key concepts of hypergraph and related techniques, such as hypergraph coloring and multidimensional matching, are explained. Then some design issues with simulation results in the proposed framework are discussed in detail, which show the potential of the proposed approach. By jointly considering social ties, common interests, and the D2D transmission scheme, we believe the proposed framework explores new opportunities and future directions in caching based socially-aware D2D communications.

Efficient Cache Placement Strategy in Two-Tier Wireless Content Delivery Network

Internet content caching for multimedia services has received much attention mainly in the field of large-scale wired networking as a primary solution to save network resources and improve quality of service (QoS). Rapidly increasing consumption of multimedia content in mobile networks brings a challenge of how to efficiently deliver content in local wireless access networks. Cache embedment in wireless mesh environment is an intriguing attempt to enhance the QoS and service capacity, leading to the question of how to design an efficient content delivery network considering the inherent characteristics of the wireless environment. We propose and investigate an efficient cache placement strategy in novel two-tier wireless content delivery networks, which utilize separate channels for content dissemination and content service. Such a two-tier network system model helps to achieve much better content delivery performance with a greatly reduced system design complexity compared to single-tier network system models. Further, we incorporate a delay cost due to contention, which is mainly responsible for performance in shared-medium wireless networks, as a key metric for cache placement under the system model. After formally formulating the cache placement problem, we propose a cross-layer heuristic algorithm and demonstrate its performance compared with an optimal solution by integer linear programming. Simulation results show significant performance improvements by our strategy compared to the performance of existing representative strategies in terms of service delay, packet delivery ratio, and the amount of delivered packets within a given delay deadline.

An Efficient Video Content Delivery Strategy for Radio Access Network Environments

When a radio access network (RAN) environment cannot handle the tremendous mobile data traffic, users may experience degraded or declined services. To help process the large number of user video requests in RANs, a content delivery network (CDN) architecture has been recently introduced, which establishes a number of cache servers outside the source server for users to get the needed data from the nearest cache server. To upgrade the performance of a wireless CDN, this paper presents a new caching strategy based on analytical results of real user video request traces and specific caching considerations for videos with different popularity degrees. The new strategy first caches videos with high popularity to all helpers and then caches those with low popularity to the remaining helper storage to enhance the overall request hits. Performance evaluation exhibits that, when compared with other caching strategies, our new strategy is able to yield better request hits with low complexity and average delay time.

Lightweight caching strategy for wireless content delivery networks

Lightweight caching strategy for wireless content delivery networks

Optimal Energy Scheduling for Rate-Guaranteed Download Over Faded Multichannel Networks

In this contribution, we consider emerging wireless content delivery networks (CDNs), where multiple (possibly nomadic) clients download large-size files from <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">battery-powered</i> proxy servers via faded links that are composed of multiple slotted orthogonal bearers (e.g., logical subchannels). Since the considered transmit proxy servers are battery-powered mobile routers, a still open basic question deals with searching for optimal energy-allocation (e.g., energy scheduling) policies that efficiently split the available energy over the (faded) bearers. The target is to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">minimize</i> the resulting (average) download time when constraints on the average available energy per information unit (IU), peak-energy per slot, and minimum energy per bearer (e.g., rate-induced constraints) are simultaneously active. The performance and the robustness of the resulting optimal energy scheduler are tested on the last hop of Rayleigh-faded mesh networks that adopt the so-called ldquodirty paper strategyrdquo for broadcasting multiple traffic flows that are generated by proxy servers equipped with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">multiple</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">antennas</i> .

Minimization of Download Times for Large Files over Wireless Channels

The emerging proxy-based wireless content delivery networks (CDNs) should to be designed to download huge-size files over fading-affected channels. However, from a radio resource management point of view, several basic problems still need to be solved for such wireless delivery systems to operate efficiently. Specifically, due to the fading nature of the downlink channel, a still open basic problem is how to design optimal energy-allocation (for example, scheduling) policies that minimize the requested download time when constraints on the total available energy and peak energy are simultaneously active. In this contribution, this problem is solved for application scenarios where the downlink channel is slotted and continuous-state, the carried out traffic is elastic, and the resulting conveyed throughput is measured by any desired increasing concave rate function. Specifically, the optimal energy-allocation policy minimizing the download time is computed in closed form, and its performance is compared against that of a basic on-off heuristic energy scheduler on some Rayleigh-faded multi-antenna delivery systems of practical interest. The carried out performance comparisons point out that the presented optimal policy typically may outperform the heuristic one up to two orders of magnitude, especially when the delivery system is strongly energy limited.