Over the last few years, C-RAN is proposed as a transformative architecture for 5G cellular networks that brings the flexibility and agility of cloud computing to wireless communications. At the same time, content caching in wireless networks has become an essential solution to lower the content- access latency and backhaul traffic loading, leading to user QoE improvement and network cost reduction. In this article, a novel cooperative hierarchical caching (CHC) framework in C-RAN is introduced where contents are jointly cached at the BBU and at the RRHs. Unlike in traditional approaches, the cache at the BBU, cloud cache, presents a new layer in the cache hierarchy, bridging the latency/capacity gap between the traditional edge-based and core-based caching schemes. Trace-driven simulations reveal that CHC yields up to 51 percent improvement in cache hit ratio, 11 percent decrease in average content access latency, and 18 percent reduction in backhaul traffic load compared to the edge-only caching scheme with the same total cache capacity. Before closing the article, we discuss the key challenges and promising opportunities for deploying content caching in C-RAN in order to make it an enabler technology in 5G ultra-dense systems.

中文翻译：

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5G 云无线接入网络中的协作分层缓存

在过去几年中，C-RAN 被提议作为 5G 蜂窝网络的变革性架构，为无线通信带来云计算的灵活性和敏捷性。同时，无线网络中的内容缓存已成为降低内容访问延迟和回程流量负载的重要解决方案，从而提高用户 QoE 和降低网络成本。在本文中，介绍了 C-RAN 中一种新颖的协作分层缓存 (CHC) 框架，其中内容在 BBU 和 RRH 处联合缓存。与传统方法不同，BBU 的缓存（云缓存）在缓存层次结构中提供了一个新层，弥合了传统的基于边缘和基于核心的缓存方案之间的延迟/容量差距。跟踪驱动的模拟表明，与具有相同总缓存容量的仅边缘缓存方案相比，CHC 可将缓存命中率提高 51%，将平均内容访问延迟降低 11%，并将回程流量负载降低 18%。在结束本文之前，我们将讨论在 C-RAN 中部署内容缓存以使其成为 5G 超密集系统中的使能技术的主要挑战和有希望的机会。