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With the development of virtual reality (VR) technology, the future of VR systems is evolving from single-user wired connections to multi-user wireless connections. However, wireless online rendering and transmission incur extra processing and transmission latency, as well as higher bandwidth requirements. To meet the requirements of wireless VR applications and enhance the quality of the VR user experience, this paper designs a view synthesis-based 360° VR caching system over Cloud Radio Access Network (C-RAN), where both mobile edge computing (MEC) and hierarchical caching are supported. In the system, an MEC-Cache Server is deployed in the pooled Base band Units (BBU pool) and used for view synthesis and caching. In addition, the remote radio heads (RRHs) can also cache some video contents. If the requested content of a specific view is cached in the BBU pool or RRHs, or can be synthesized with the aid of the cached adjacent views, it is unnecessary to request the content from the remote VR video source server. Therefore, the transmission latency and backhaul traffic load for VR services can be decreased. We formulate a hierarchical collaborative caching problem aiming to minimize the transmission latency, which is proved NP-hard. To address the impractical expenses of the offline optimal method, an online MaxMinDistance caching algorithm with low complexity is proposed. Numerical simulation results demonstrate that the proposed caching strategy provides significantly improved cache hit rate, backhaul traffic load, transmission latency, and Quality of Experience (QoE) performances relative to conventional caching strategies.

Recently, information centric wireless network (ICWN) has been concerned due to its flexible network structure and high efficiency of content delivery. Meanwhile, scalable video coding (SVC) is a promising solution to provide high quality of video services. Combining ICWN and SVC is expected to improve the performance of wireless video delivery services. Since caching strategy plays a significant role in ICWN, in this paper, we address the caching problem for scalable videos over ICWN in mobile scenarios. By jointly considering the layered structure of SVC and the hierarchical architecture of ICWN, we formulate an optimization problem to minimize the average download delay. A novel layered hierarchical caching method is proposed for solving the problem. Furthermore, we focus on a special but common case in which the above delay minimization problem is equivalently transformed into a cache hit ratio maximization problem. A simplified algorithm with 1/2 approximation ratio is provided. Finally, simulation results show that our proposed caching schemes outperform baseline methods in cache hit rate and delay performance.

Caching at the edge of wireless networks is a promising means of alleviating the heavy burden of backhaul links and reducing the latency of transmission and handover in a cloud radio access network (C-RAN). Although some effective caching schemes have been introduced to C-RAN, most of them are not designed with consideration of both user mobility and video segment popularity, which have influence on the performance of wireless caching. Therefore, this paper investigates the above-mentioned two factors for a cache-enabled C-RAN, and proposes two proactive caching strategies that are based on user mobility only, and both user mobility and video segment popularity, respectively. We design a novel controller, which is able to fully utilize the computational and storage resources, and acts the role of cache decision making for the baseband unit pool and remote radio heads. Numerical simulation results demonstrate that the proposed schemes significantly outperform traditional strategies by 20% and 16% in terms of average data transmission delay and cache hit rate, respectively.

To meet the requirements of lower latency and massive data transmission in wireless Virtual Reality (VR) applications, a mobile edge computing (MEC) enabled VR transmission system is proposed over Cloud Radio Access Network (C-RAN). In the proposed system, an MEC-Cache server is deployed in the pooled base band units (BBU pool) for VR video synthesizing and the video contents can be cached both in the BBU pool and the remote radio heads (RRHs). In addition, a hierarchical and collaborative caching problem is formulated as an integer linear program (ILP) that minimizes the transmission latency, and an online caching strategy is proposed to address the NP completeness of the problem. Rigorous numerical simulations show that, by considering the view synthesis feature of VR videos, the proposed caching scheme always yields better performance in terms of cache hit rate and average transmission latency than other employed caching algorithms.

Caching at the wireless edge is a promising way to alleviate the heavy burden of the backhaul links and reduce the latency of transmission and handover. Although some effective caching schemes have been introduced to Cloud based Radio Access Network (C-RAN), most of them were designed without consideration of users' mobility. In this paper, we investigate the mobility property in cache-enabled C-RAN, and propose a mobility aware proactive caching strategy. We aim to design a novel controller, which is able to utilize the computation and storage resources in C-RAN, and responsible for making cache decision for both the baseband unit (BBU) pool and Remote Radio Head (RRH). A transmission delay model is introduced to formulate the cache placement optimization problem. To solve the problem, we propose an algorithm named MAPCaching. Numerical simulation results show that MAPCaching significantly outperforms the Greedy and EPC caching strategies in terms of average content access delay and cache hit rate by 30% and 20%, respectively.