异构网络中网络接入选择策略研究

发布时间：2018-12-15 08:25

【摘要】：通信技术和移动业务广泛而成功的发展运行,导致了包括3G、4G、WLAN、Wi MAX、LTE-A等各种无线通信技术被异构融合部署形成异构无线网络。并且异构网络因其可以显著提高单一网络的服务保障和接入能力,近年来,也被广泛关注和研究应用。再加上选择接入某个网络是用户终端与该网络建立连接前的首要步骤和关键准备工作,是确定用户发起业务呼叫后将使用何种网络完成通信需求的重要行为和决定环节。故用户依赖一个各方面性能突出而智能的网络选择策略,帮助他们完成接入网络的选择,成为异构网络环境中要解决的关键问题之一。本文首先针对现有异构网络选择策略很少将用户特性和网络特性全面联合起来去设计选网算法这一现状,研究了高移动速度用户和低移动速度用户在由宏基站和微基站构成的双层异构网络上的基于用户终端的网络选择策略。因为移动性是用户最本质的属性,所以对高移动速度用户网络选择策略的设计,会因为既要避免不合理的频繁切换,又要综合整个系统吞吐量性能的优劣而复杂难求。再加上已有研究总是将基站位置建模为传统正六边形,忽略了实际覆盖情景。面对这些问题,本文结合随机几何理论建模异构网络场景,研究了微蜂窝上驻留时间可能会很小的高移动速度用户,和要连接至宏蜂窝上却位于微蜂窝覆盖区内的一部分高移速用户,他们在接入选择时的带宽预留和带宽分配问题。该策略先用系统接入高移速和低移速终端的网络容量减去网络切换开销,得到关于全网络收益的效用函数,然后证明该效用函数的最优解是关于限制条件的一个凸优化问题,并用梯度下降法的迭代过程,得到高移速和低移速用户在宏、微蜂窝上接入选择时的预留带宽、分配带宽和接入概率的最优解。另一方面,考虑到传统马尔科夫决策模型在进行重叠区域中实时/非实业务的垂直切换决策时,通常会忽略业务QoS差异而导致整个网络的资源利用不充分这一问题,本文针对实时业务的垂直切换行为,给出其马尔科夫决策过程中行动集合的改进结果,并将改进后的马尔科夫决策过程与我们重新设计的带宽预留机制结合,提出一种基于全网络的联合呼叫接入选择策略。仿真结果表明:本文研究的针对用户终端的和全网络的呼叫选择策略优化方案,在新呼叫阻塞率、切换掉线率、全网络容量收益这几个方面均有良好的表现和改进。
[Abstract]:The extensive and successful development and operation of communication technology and mobile services lead to heterogeneous wireless networks such as 3GN 4G WLAN Wi MAX,LTE-A and other wireless communication technologies. Heterogeneous networks have been widely studied and applied in recent years because they can significantly improve the service security and access capability of a single network. In addition, choosing to access a network is the first step and the key preparation work before the user terminal establishes the connection with the network. It is also an important behavior and decision link to determine which network will be used to fulfill the communication requirements after the user initiates the service call. Therefore, users rely on an intelligent network selection strategy with outstanding performance in various aspects to help them complete the selection of access networks, which has become one of the key problems to be solved in heterogeneous network environments. In this paper, first of all, we focus on the fact that the existing heterogeneous network selection strategies seldom combine user characteristics with network characteristics to design network selection algorithms. The network selection strategies based on user terminals for high mobile speed users and low mobile speed users on a two-layer heterogeneous network composed of a macro base station and a microbase station are studied in this paper. Because mobility is the most essential attribute of users, the design of high mobile speed user network selection strategy will be complex and difficult because of avoiding unreasonable frequent switching and integrating the throughput performance of the whole system. In addition, previous studies always model the base station position as the traditional hexagonal, ignoring the actual coverage scenario. In view of these problems, this paper combines stochastic geometry theory to model heterogeneous network scenarios, and studies the high mobile speed users whose residence time on microcellular may be very small. And a portion of high speed users who are connected to a macro cell but are located in the microcellular coverage area, and their bandwidth reservation and bandwidth allocation problems in access selection. In this strategy, the network capacity of high and low speed terminals is used to subtract the network switching overhead, and the utility function of the whole network income is obtained. Then, it is proved that the optimal solution of the utility function is a convex optimization problem with restricted conditions. By using the gradient descent method, the optimal solutions of reserved bandwidth, allocated bandwidth and access probability for users with high and low moving speeds in macro and microcellular access are obtained. On the other hand, when traditional Markov decision models make vertical handoff decisions for real-time / non-real services in overlapped regions, the differences in service QoS are usually ignored, which leads to the insufficient utilization of resources in the whole network. In this paper, for the vertical handoff behavior of real-time services, the improved results of the action set in the Markov decision process are given, and the improved Markov decision process is combined with the bandwidth reservation mechanism redesigned by us. A joint call access selection strategy based on the whole network is proposed. The simulation results show that the optimization scheme of call selection strategy for user terminals and the whole network has good performance and improvement in the aspects of new call blocking rate, handoff drop rate and total network capacity income.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.5

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