Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> The demand for rich multimedia services over mobile networks has been soaring at a tremendous pace over recent years. However, due to the centralized architecture of current cellular networks, the wireless link capacity as well as the bandwidth of the radio access networks and the backhaul network cannot practically cope with the explosive growth in mobile traffic. Recently, we have observed the emergence of promising mobile content caching and delivery techniques, by which popular contents are cached in the intermediate servers (or middleboxes, gateways, or routers) so that demands from users for the same content can be accommodated easily without duplicate transmissions from remote servers; hence, redundant traffic can be significantly eliminated. In this article, we first study techniques related to caching in current mobile networks, and discuss potential techniques for caching in 5G mobile networks, including evolved packet core network caching and radio access network caching. A novel edge caching scheme based on the concept of content-centric networking or information-centric networking is proposed. Using trace-driven simulations, we evaluate the performance of the proposed scheme and validate the various advantages of the utilization of caching content in 5G mobile networks. Furthermore, we conclude the article by exploring new relevant opportunities and challenges. <s> BIB001 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> In this paper, the problem of content-aware user clustering and content caching in wireless small cell networks is studied. In particular, a service delay minimization problem is formulated, aiming at optimally caching contents at the small cell base stations (SCBSs). To solve the optimization problem, we decouple it into two interrelated subproblems. First, a clustering algorithm is proposed grouping users with similar content popularity to associate similar users to the same SCBS, when possible. Second, a reinforcement learning algorithm is proposed to enable each SCBS to learn the popularity distribution of contents requested by its group of users and optimize its caching strategy accordingly. Simulation results show that by correlating the different popularity patterns of different users, the proposed scheme is able to minimize the service delay by %42 and 27%, while achieving a higher offloading gain of up to 280% and 90%, respectively, compared to random caching and unclustered learning schemes. <s> BIB002 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> Small cells constitute a promising solution for managing the mobile data growth that has overwhelmed network operators. Local caching of popular content items at the small cell base stations (SBSs) has been proposed to decrease the costly transmissions from the macrocell base stations without requiring high capacity backhaul links for connecting the SBSs with the core network. However, the caching policy design is a challenging problem especially if one considers realistic parameters such as the bandwidth capacity constraints of the SBSs that can be reached in congested urban areas. We consider such a scenario and formulate the joint routing and caching problem aiming to maximize the fraction of content requests served locally by the deployed SBSs. This is an NP-hard problem and, hence, we cannot obtain an optimal solution. Thus, we present a novel reduction to a variant of the facility location problem, which allows us to exploit the rich literature of it, to establish algorithms with approximation guarantees for our problem. Although the reduction does not ensure tight enough bounds in general, extensive numerical results reveal a near-optimal performance that is even up to 38% better compared to conventional caching schemes using realistic system settings. <s> BIB003 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> Due to the exponentially increasing demands for multimedia services over recent years, the growing network traffic load becomes a severe concern for the mobile network operators (MNOs). However, the wireless link capacity, the radio access networks, and MNOs' backhaul networks cannot deal with the traffic load effectively. To solve this problem, content caching is regarded as an effective emerging technique to reduce the duplicated transmissions of the content downloads demanded by mobile users and improve users' quality of service (QoS). Therefore, in this paper, we mainly focus on the cooperative cell caching for future mobile networks, where each cell (e.g., base station) can cache popular contents for improving QoS especially on the overall delay performance of users. The task is formulated as a problem of minimizing the expected overall user delay of accessing the demanded contents. Instead of rewriting it as a non-linear and non-convex problem based on an approximate transformation, we convert it to a linear programming problem by using a novel equivalent transformation. To solve the problem, rather than using the existing branchand-bound (BNB) method, which suffers from exponential-time and exponential-space complexity, we propose a new distributed suboptimal algorithm, which has polynomial-time and linearspace complexity. Numerical evaluation results demonstrate that our proposed cooperative cell caching framework can reduce the expected overall delay significantly. <s> BIB004 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> Pushing and caching the popular multimedia data can effectively reduce the redundant content transmission and cope with the explosive traffic growth. In this paper, we contribute to analyzing the push-based and cache-based content delivery in the heterogeneous network (HetNet). When the network load is off-peak, the most popular contents can be pushed to the relays and the cache-enabled users via broadcasting, and then be cached down to be reused for frequent access. The locations of the base stations, relays and device-to-device pairs are first modeled as mutually independent Poisson Point Processes (PPPs). Then the energy consumption is derived based on the access protocol and the tier association priority. The impacts of network characteristics such as the heterogeneity of multimedia contents, node densities and the limited caching capacity are further elaborated. Besides, the node densities allocation strategy is discussed for full use of the caching resources, which provides valuable insights on the wireless intelligent network planning. <s> BIB005 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> Heterogeneous cellular networks (HCN) with embedded small cells are considered, where multiple mobile users wish to download network content of different popularity. By caching data into the small-cell base stations (SBS), we will design distributed caching optimization algorithms via belief propagation (BP) for minimizing the downloading latency. First, we derive the delay-minimization objective function (OF) and formulate an optimization problem. Then we develop a framework for modeling the underlying HCN topology with the aid of a factor graph. Furthermore, distributed BP algorithm is proposed based on the network's factor graph. Next, we prove that a fixed point of convergence exists for our distributed BP algorithm. In order to reduce the complexity of the BP, we propose a heuristic BP algorithm. Furthermore, we evaluate the average downloading performance of our HCN for different numbers and locations of the base stations (BS) and mobile users (MU), with the aid of stochastic geometry theory. By modeling the nodes distributions using a Poisson point process, we develop the expressions of the average factor graph degree distribution, as well as an upper bound of the outage probability for random caching schemes. We also improve the performance of random caching. Our simulations show that (1) the proposed distributed BP algorithm has a near-optimal delay performance, approaching that of the high-complexity exhaustive search method, (2) the modified BP offers a good delay performance at a low communication complexity, (3) both the average degree distribution and the outage upper bound analysis relying on stochastic geometry match well with our Monte-Carlo simulations, and (4) the optimization based on the upper bound provides both a better outage and a better delay performance than the benchmarks. <s> BIB006 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> Future mobile communications face enormous challenges as traditional voice services are replaced with increasing mobile multimedia services. To address the vast data traffic volume and the requirement of user Quality of Experience (QoE) in the next generation mobile networks, it is imperative to develop efficient content distribution technique, aiming at significantly reducing redundant data transmissions and improving content delivery performance. On the other hand, cloud computing as a new content-centric paradigm is exploited to fulfil the multimedia requirements by provisioning data and computing resources on demand. In this paper, we propose a cooperative caching framework which implements State based Content Distribution (SCD) algorithm for future mobile networks. In our proposed framework, cloud service providers deploy a plurality of cloudlets in the network forming a Distributed Cloud Service Networks (DCSN). We formulate a content distribution optimization model, and data contents are distributed in local cloudlets according to the optimal solution to minimize redundant content transmissions. We use simulation experiments to validate the effectiveness of our proposed framework. Numerical results show that the proposed framework can significantly improve content cache hit rate, reduce content delivery latency and outbound traffic volume in comparison with known existing caching strategies. <s> BIB007 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> Caching is an energy-efficient method to improve service availability with low cost, and the combination of centralized processing and distributed caching in cloud radio access networks (C-RANs) can reduce redundant traffic. In this paper, a cluster content caching scheme in C-RANs is proposed, which can maintain a balance between the storage volume and the hit ratio of caching, and mitigates the backhaul loadings in C-RANs. By establishing a Poisson point process-based model, the notion of effective capacity is extended into C- RANs, which can capture the maximum content delivery capability of wireless channels with a specific QoS guarantee. Tractable expressions can be obtained in interference limited C-RANs, which show that the content caching scheme outperforms the centralized caching scheme, and provide insights on how to enlarge the the performance gains. <s> BIB008 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> Presented as an innovative paradigm incorporating the cloud computing into radio access network, cloud radio access networks (C-RANs) have been shown advantageous in curtailing the capital and operating expenditures as well as providing better services to the customers. However, heavy burden on the non-ideal fronthaul limits performances of C-RANs. Here we focus on the alleviation of burden on the fronthaul via the edge devices' caches and propose a fog computing based RAN (F-RAN) architecture with three candidate transmission modes: device to device, local distributed coordination, and global C-RAN. Followed by the proposed simple mode selection scheme, the average energy efficiency (EE) of systems optimization problem considering congestion control is presented. Under the Lyapunov framework, the problem is reformulated as a joint mode selection and resource allocation problem, which can be solved by block coordinate descent method. The mathematical analysis and simulation results validate the benefits of F-RAN and an EE-delay tradeoff can be achieved by the proposed algorithm. <s> BIB009 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> To guarantee the ubiquitous and fully autonomous Internet connections in our daily life, the new technical challenges of mobile communications lie on the efficient utilization of resource and social information. To facilitate the innovation of the fifth generation (5G) networks, the cloud radio access network (RAN) and fog network have been proposed to respond newly emerging traffic demands. The cloud RAN functions more toward centralized resource management to achieve optimal transmissions. The fog network takes advantage of social information and edge computing to efficiently alleviate the end-to-end latency. In this paper, we conduct a comprehensive survey of these two network structures, and then investigate possible harmonization to integrate both for the diverse needs of 5G mobile communications. We analytically study the harmonization of cloud RAN and fog network from various points of view, including the cache of Internet contents, mobility management, and radio access control. The performance of transition between the cloud RAN and the fog network has been presented and the subsequent switching strategy has been proposed to ensure engineering flexibility and success. <s> BIB010 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> Over recent years, the demand for rich multimedia services over mobile networks has been soaring at a tremendous pace. However, it is envisioned that traditional dedicated networking equipment in mobile network operators (MNOs) cannot support the phenomenal growth of the traffic load and user demand dynamics, but consume unnecessary energy resource inefficiently. The emerging techniques for mobile content caching and delivery become more and more attractive, by which popular content can be cached inside mobile front-haul and back-haul networks, so that demands to the same content from users in proximity can be easily accommodated without redundant transmissions from the remote resource, thereby eliminating duplicated traffic significantly. While the incorporation between advanced cloud computing technologies and network function virtualization (NFV) techniques has become an essential issue in the evolution process of mobile systems, in this article, we propose the concept of “Caching-as-a-Service” (CaaS), a caching virtualization framework along with the development of Cloud-based Radio Access Networks (C-RAN), and the virtualization of Evolved Packet Core (EPC). Then we study the potential techniques related to the cache virtualization, and discuss technical details of caching virtualization and system optimization for CaaS. We carry out numerical evaluation on proposed framework and show significant improvement on the performance of reducing inter-MNO traffic load and intra-MNO traffic load. <s> BIB011 </s> Information-centric mobile caching network frameworks and caching optimization: a survey <s> Caching Framework based on Mobile Cellular Networks <s> In cloud radio access networks (C-RANs), a substantial amount of data must be exchanged in both backhaul and fronthaul links, which causes high power consumption and poor quality of service (QoS) experience for real-time services. To solve this problem, a cluster content caching structure is proposed in this paper, which takes full advantages of distributed caching and centralized signal processing. In particular, redundant traffic on the backhaul can be reduced because the cluster content cache provides a part of required content objects for remote radio heads (RRHs) connected to a common edge cloud. Tractable expressions for both effective capacity and energy efficiency performance are derived, which show that the proposed structure can improve QoS guarantees with a lower cost of local storage. Furthermore, to fully explore the potential of the proposed cluster content caching structure, the joint design of resource allocation and RRH association is optimized, and two distributed algorithms are accordingly proposed. Simulation results verify the accuracy of the analytical results and show the performance gains achieved by cluster content caching in C-RANs. <s> BIB012
In general, mobile clients access the network by connecting to one or multiple APs to obtain mobile multimedia services (e.g. audio and video), when their position changes, they change the AP which they connect to. In mobile cellular networks, the APs contain NodeBs in 3G networks and eNBs in 4G LTE networks BIB004 BIB001 , macro base stations(MBSs)and small cell base stations(SBSs) which are proposed in heterogeneous cellular network(HCN)  BIB001 BIB005 BIB002  BIB003 BIB006 , as well as Wi-Fi access points and worldwide interoperability for microwave access (WiMAX) base stations BIB001 . Figure 2 gives the typical architectures and scenarios of caching framework in mobile cellular networks. In mobile cellular network, caches can be deployed either in the core network or in the access networks, and also can be deployed both in the core network and access networks. The MBS and the SBSs are cooperative to cache contents in order to relieve the backhaul traffic load and improve hit rate of contents of mobile users. In cache-based Cloud Radio Access Networks(C-RAN), caches are deployed not only in base-band units (BBU) pool but also in some edge elements such as content access points(C-APs) and user equipments (UEs). In this section, the research issues focusing on the caching frameworks based on mobile cellular network are addressed. In  , a two-layer cellular caching framework is constructed to investigate cache aware user association policies. The architecture consisting of a single MBS and a set of SBSs is provided as the cache-enabled architecture based on SBSs, such as picocells, microcells or femtocells overlaid on existing macro-cellular wireless systems. The request is sent to the SBS at first, and if the SBS owns a copy of the requested item, the request can be satisfied locally; otherwise, the request that cannot be satisfied by the SBS is routed to the MBS BIB002 BIB003 . In BIB005 , a three-tier heterogeneous wireless network is put forwarded consisting of a number of macro base stations, relays and mobile users. BSs, relays and users are cooperative in transmitting content data. In BIB004 , a cooperative cell caching system consisting of some content providers(CPs) and a great number of cells is presented, CPs are outside the mobile network operator(MNO), while cells are inside the MNO network and covers the whole service area. Caching cooperation among cells are used to reduce the transmission latency due to short distance between the cells and mobile users, and redundant data streams are offloaded from the CPs at the same time, therefore heavy burdens on the backhaul channels are alleviated. The authors in BIB006 propose a mobile caching framework based on the underlying HCN topology. A factor graph is used to represent the framework, where vertex set consists of factor nodes and variable nodes. Each factor node is related to a mobile user and each variable node is related to a SBS. With the development of cloud computing and virtualization, C-RAN has become a new solution in cellular access network. In C-RAN, distributed remote radio heads (RRHs) connect to the BBU pool via fronthauls, while the BBU pool connects to the content cloud through backhaul. According to the C-RAN architecture, a cooperative caching framework is proposed in BIB007 based on Distributed Cloud Service Network architecture, in which several distributed cloudlets with local caches cooperate and share contents with each other. BIB012 BIB008 proposes a cluster content caching structure in Edge Cloud-Radio Access Networks (EC-RANs), in which baseband signal processing and control functions are partially decentralized in the edge equipments, such as base stations and UEs with cache, and a common local content cache is deployed in BBU so that cache can be shared by the RRHs within the cluster. A fog computing based RAN (F-RAN) architecture is proposed in BIB009 which user plane and control plane are decoupled. In F-RAN, MBSs are provided for control signal interaction on the control plane, while RRHs are deployed to enhance high speed data transmission on the user plane. Besides, F-RAN explores the potential of caching in the edge caching APs as well as the edge equipments, and UEs supports cooperative caching through device to device (D2D), therefore, the burden of the fronthaul and BBU pool can be alleviated. In BIB010 , a survey of C-RAN and fog network is presented to investigate architecture harmonization of C-RAN with fog computing network. Caching-as-a-Service (CaaS) is proposed in BIB011 as a caching virtualization framework which makes caching more flexible. CaaS instances can be created, migrated, scaled (up or down), shared and released adaptively in the mobile clouds depending on the user demands and requirements from 3rd-party service providers.