中文摘要：

云无线接入网（cloud radio access network,C-RAN）被认为是有望解决第五代移动通信（5G）技术服务需求问题的核心技术方案之一,已有研究表明C-RAN具有显著的技术优势,能有效提升网络的谱效率和能效率.总结了C-RAN的研究现状,给出了其系统架构和核心关键技术挑战,并讨论了C-RAN架构相比传统方案具有的优势和性能提升.

英文摘要：

Cloud radio access network （C-RAN） has been proposed as one of the most promising solutions to meet the service requirements of the fifth generation （SG） wireless communication systems. The published achievements indicate that C-RAN has many advantages, which can improve the spectrum efficiency and energy efficiency simultaneously. The state-of-the-art research achievements, system architecture and key technology challenges in C-RAN were studied. Furthermore, the performance gains over the traditional systems were introduced as well.