低轨卫星移动通信系统中的切换策略研究

发布时间：2018-08-22 20:47

【摘要】：低轨卫星通信系统因其全球无缝覆盖、系统容量充足以及传播时延较低等特点,成为未来个人移动通信系统的重要组成部分。相比地面蜂窝移动网络,低轨卫星作为通信系统的骨干节点在太空环境中高速运动,致使终端用户在服务卫星问频繁切换。由于切换技术涉及卫星系统无线资源分配、网络拓扑重构、路由更新等多个方面,目前已成为空天网络研究的热点问题之一。现有的卫星切换策略多集中于优化切换性能和通信质量方面的指标,对切换所影响的系统TCP性能关注不足。因此,从卫星系统的传输性能切入对切换策略进行研究分析极具现实意义。本文结合低轨卫星通信系统的切换特点,在分析星地链路切换造成终端通信路径改变,导致传输时延变化的基础上,针对多种场景适当补偿因切换产生的传输延迟差,降低链路延迟的剧烈抖动,提升卫星TCP协议传输性能。为此,本文对卫星网络时延补偿切换机制进行深入讨论,通过建立基于贝叶斯理论的混合概率时延异常值检测模型,引入类别判决门限控制分类过程,结合滑窗技术及时修正类别集合及模型参数,排除因卫星网络状态改变而突变的补偿时延,提高了时延估计的准确率。仿真结果表明,本文提出的网络补偿时延优化方案相对于原有方法在准确率和错误率方面均有一定程度的改善,且在大样本检测数据下仍具有较好的表现。在前叙章节优化的网络补偿时延切换机制的基础上,本文将该策略横向扩展到双层卫星通信系统中,通过对该模型下切换场景的详细分析,针对存在的时延补偿多样性的问题,提出了基于预测控制的网络补偿时延调整策略。仿真验证了改进后策略的有效性和准确性：较采用单一固定的补偿时间来满足所有切换场景的做法,本文改进的策略使系统具有较好的TCP性能提升。
[Abstract]:LEO satellite communication system has become an important part of future personal mobile communication system because of its seamless global coverage, sufficient system capacity and low propagation delay. Compared with terrestrial cellular mobile network, LEO satellite, as the backbone node of communication system, moves at high speed in space environment, resulting in end users serving satellites. Because handoff technology involves wireless resource allocation of satellite system, network topology reconfiguration, routing updating and so on, it has become one of the hot issues in space-space network research. Therefore, it is of great practical significance to study and analyze the handoff strategy from the transmission performance of satellite system.
Combining with the handover characteristics of LEO satellite communication system, this paper analyzes the terminal communication path changes caused by satellite-to-ground link handover, and then compensates the transmission delay difference caused by handover in various scenarios, reduces the jitter of link delay and improves the transmission performance of satellite TCP protocol. The mechanism of delay compensation handover in satellite networks is discussed in depth. A mixed probability delay anomaly detection model based on Bayesian theory is established. Class decision threshold is introduced to control the classification process. The sliding window technique is combined with time correction of class set and model parameters to eliminate the compensation delay caused by the abrupt change of satellite network state and improve the time delay. Simulation results show that the proposed network compensation delay optimization scheme has a certain degree of improvement in accuracy and error rate compared with the original method, and still has a good performance in large sample detection data.
Based on the network compensation delay handover mechanism optimized in the previous chapter, this paper extends the strategy horizontally to the two-tier satellite communication system. By analyzing the handover scenarios under this model in detail, aiming at the problem of diversity of delay compensation, a network compensation delay adjustment strategy based on predictive control is proposed. Effectiveness and accuracy of the improved strategy: Compared with using a single fixed compensation time to satisfy all switching scenarios, the improved strategy makes the system have better TCP performance.
【学位授予单位】：北京邮电大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN927.23

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