【作者】 张涛；

【导师】 李强； 杨奇；

【作者基本信息】 华中科技大学 ， 电子与通信工程， 2017， 硕士

【摘要】 随着通信与网络技术的发展,近年来以视频为主的多媒体业务的兴起导致移动数据量出现陡增趋势,给无线移动通信网络带来了巨大的挑战。一方面,通过各种技术提高无线电频谱效率虽然能在一定程度上提升通信系统容量,但扩容力度远不及多媒体业务增长的速度。另一方面,研究发现互联网内容的流行度服从Zipf分布,即由于用户偏好而导致少部分流行度高的内容贡献了大部分的业务负载。而在传统的集中式通信网络架构中用户的业务流量反复经由接入网-核心网交换-远端内容服务器传输,这将会导致回程链路拥塞、延时大,资源利用率低等诸多问题。针对这一内容复用特性,为了缓解蜂窝移动网络海量业务需求与回程链路容量间的矛盾,将内容缓存在离用户更近的网络边缘成为业界关注焦点。本文提出一种面向软件定义无线接入网(SD-RAN)的协作内容缓存网络架构,其中,由宏蜂窝基站(MBS)提供控制覆盖,小蜂窝基站(SBS)提供数据覆盖。通过在网络边缘的MBS与SBS中部署存储单元用于缓存热点流行内容,可以有效缓解蜂窝网络回程链路容量瓶颈,降低网络能耗与信号传输时延。具体的,为了优化存储资源的分配从而更加高效的缓存内容,在总体存储资源受限的条件下,本文以同层协作缓存为基础提出了一种通过建立MBS与SBS之间协作的跨层协作内容缓存策略与算法。本文以用户的平均内容获取开销作为优化目标,推导出在该策略下的最优存储分配参数闭合表达式。通过仿真分析能够证明该算法以最优存储分配参数的平均内容获取开销将会显著降低。同时,本文也对跨层的非协作内容缓存策略进行了研究,提出了能降低SD-RAN内容获取开销的缓存算法。通过仿真实验及结果对比,表明跨层协作缓存算法在不同参数下的系统性能要优于跨层非协作缓存算法的性能。此外,可通过折中同层协作算法与跨层协作算法进一步优化系统中内容存储以降低用户内容获取开销。更多还原

【Abstract】 With the development of communication and network technologies,video-based multimedia services have led to the growth spurt of moving data,which brings great challenges to wireless mobile communication network.On the one hand,a variety of technologies that improve the radio spectrum can enhance communication system capacity to a certain extent,but the expansion is far less than the growing speed of multimedia business.On the other hand,current studies have found that the popularity of Internet contents follow the Zipf distribution,i.e.,the user preference will lead to the small number of popular contents contribute to the most of traffic load.In the traditional centralized communication network architecture,the user’s traffic have to traverse repeatedly the access network-core network(switch)-remote content server,which thus lead to backhaul link congestion,delay,low resource utilization and other issues.Considering the content reuse characteristic,network edge caching strategy that brings the contents closer to user has been widely studied in order to alleviate the contradiction between the massive business demand and backhaul link capacity of cellular mobile network.This paper proposes a cooperative content caching system architecture for Software-Defined Radio Access Networks(SD-RAN),where Macro-cell Base Station(MBS)provides control coverage and Small-cell Base Stations(SBSs)provide data coverage.By deploying storage units in the MBS and SBS located at the network edge,which can alleviate effectively the bottleneck of the backhaul capacity,reduce the network energy consumption and signal transmission delay.Specially,in order to optimize the allocation of storage resource with a sum storage constraint for more efficient contents caching,this paper proposes a cooperative cross-layer caching strategy and algorithm by establishing collaboration between SBS and MBS.In the paper,the average content provisioning cost is taken as optimization target.The optimal storage allocation factor at which the average content provisioning cost of the SD-RAN is minimized is analytically obtained in a closed form.The simulation results show that the average content provisioning cost of the proposed cross-layer algorithm using the optimal storage allocation factor will be significantly reduced.This paper also studied the baseline cross-layer non-cooperative content caching strategies.Simulation and comparison analysis results demonstrate that the performance of the cross-layer cooperative caching algorithm always outperforms the non-cooperative content caching algorithm under different parameters.In addition,there existing trade-off between SBS-SBS cooperative caching and SBS-MBS cooperative caching strategy which can be further optimized for lower content provisioning cost.更多还原