Because of the relative movement between the leo satellites and the terrestrial user terminals , the very high handover rate during a call ’ s lifetime , including inter - spotbeam handover , inter - satellite handover and handover between satellite communication systems and terrestrial ones , will occur 由于低轨道卫星与地面用户终端之间存在相对运动,会引起切换问题,主要包括波束间切换,卫星间切换,以及卫星通信系统与地面通信系统之间的切换。
With the booming of internet , brower / server model is replacing client / server model step by step , internet explorer is a representative of thin client and will be widely used as user terminal in the future . so there is demand of merging oltp system into internet technology 随着internet的迅速发展，浏览器服务器模式逐步取代了客户端服务器模型，浏览器作为度客户端的代表，它成为互联网上通用客户端，因此需要构建基于internet的事务处理系统。
With high spectrum efficiency , large capacity and immunity for multipath fading , orthogonal frequency division multiplexing access ( ofdma ) technique is one of key skills in the fourth generation of mobile communication . in this paper , we discuss the basic principle of ofdma system , and propose a whole design of transceivers both in bs and in user terminal end . in the system synchronization aspect , we point out the effects of the carrier frequency offset , sampling offset , and symbol timing offset to the system , and investigate the estimation algorithms of carrier frequency offset and timing offset based on polyphase filter banks 本文阐述了ofdma系统的基本原理，给出了基站与用户端站上的收发信机的总体设计，并针对该系统中的同步技术，指出了载波频偏、采样钟偏移和符号定时偏差对该系统的影响，深入研究了基于多相滤波器组的载波频偏和定时偏差的估计算法，针对该系统中的信道估计技术，深入研究了基于导频符号的信道估计方法，从而提出了一系列的同步与信道估计的改进措施和新算法，本文还简要讨论了ofdma系统中的子载波、比特与功率的最佳分配算法，最后结合matlab仿真对这些算法的有效性和可行性进行了全面地分析与比较。
We have designed and established data collection center exchange network of sale of the whole company , and realized transfers demand of which met six power supply bureau load management systems by using five frequency point , and succeeded in solving the problem of data collection and control management that main station of power supply bureau provided user terminals 设计、建设了全公司营销数据采集中心交换网，实现了利用五对频点满足六个供电局负荷管理系统的数传需求，成功解决了供电局主站对用户终端的数据收集和控制管理问题。
The satellite mobile communication can realize the radio communication between the mobile terminals by using the satellite repeaters which acts as relay . among the satellite mobile communication systems , the leo - mss ( low earth orbit mobile satellite systems ) possess the wide development space due to their global seamless coverage , much shorter transmission delays , less power requirement for the user terminals and strong ability in anti - ruin 卫星移动通信是指利用卫星转发器作中继而实现移动终端之间的无线通信,其中低轨卫星通信系统以其全球覆盖、低的传输时延、低功耗、抗毁性强等特点而具有广阔的发展前景,并且是未来个人通信系统的重要组成部分。
