【作者】 吴廷勇；

【导师】 吴诗其；

【作者基本信息】 电子科技大学 ， 通信与信息系统， 2008， 博士

【摘要】 近年来,地面无线通信和Internet技术飞速发展,网络规模和用户数都呈爆炸式的增长。卫星通信作为重要的现代通信手段之一,也取得了极大的进步。由于不断增长的对宽带多媒体业务的移动性和服务质量(QoS)的需求,结合了TCP/IP技术和ATM技术的卫星通信系统,逐渐成为构建下一代全球移动网络的基础结构之一。在这种情况下,和地面有线网和3G移动网的相互融合一样,卫星通信网络和地面网络的差别也将逐渐消失而共存于一个全球覆盖的通用移动通信系统(UMTS)。该系统的根本目标是实现无所不在的、自由的信息交换,对移动性、QoS和全球无缝覆盖的良好支持是其最重要的特征。卫星通信以其固有的优势,必将在UMTS中扮演一个重要角色。然而,传统的静止轨道(GEO)卫星通信系统由于固有的缺点,已经很难满足现代多媒体实时应用需求。于是,研究焦点转向了非静止轨道卫星通信系统。根据非静止轨道卫星通信系统的特性和发展趋势,本文对非静止轨道卫星星座设计方法和星际链路特性进行了深入研究,内容涉及全球性星座设计、区域性星座设计、非静止轨道跟踪与数据中继卫星系统(TDRSS)的星座方案研究以及LEO/MEO双层卫星网络中层间星际链路建立策略研究。第一章为绪论。简单阐述了卫星通信的发展概况、现状和前景,卫星通信系统的一些关键技术,以及本文的创新点和内容安排。第二章是卫星星座设计概述。给出了卫星星座设计相关的基本知识和星座设计时的基本考虑,简介了极轨道星座和倾斜圆轨道星座这两类经典的非静止轨道全球性星座设计方法。第三章讨论了全球性正交圆轨道星座设计方法。推导了极轨道星座实现球冠覆盖时星座参数的精确计算公式,分析了精确计算公式与Beste的近似计算公式之间的关系,明确了近似计算公式的应用条件。提出了采用极轨道星座结合赤道轨道星座构建全球性正交圆轨道星座的思想,推导了正交圆轨道星座的参数计算公式,给出了一些星座方案,并与全球覆盖极轨道星座进行了覆盖性能的分析和比较,说明了正交圆轨道星座设计方法的有效性。第四章研究共地面轨迹区域性星座设计。深入分析了共地面轨迹星座的特性,提出了一种简约的描述共地面轨迹星座的编码标识方法,讨论了共地面轨迹星座与δ星座的等价条件。给出了该类型星座实现区域覆盖卫星通信系统时的通用优化设计方法和具体实现步骤,得到了一些适用于我国的优化星座方案。基于业务分布密度的时变特性对星座方案的参数进行了进一步的优化调整,使得星座的覆盖特性与业务分布密度特性更加一致,从而提升了星座系统的覆盖性能。采用遗传算法进行了共地面轨迹星座的优化设计,在计算时间大幅度减少的情况下,获得了精确度更高的优化星座参数,说明在区域性星座设计这样的课题中,引入遗传算法进行优化设计可以获得非常高的效率和非常好的效果。第五章研究适合于中轨跟踪与数据中继卫星系统采用的星座形式。系统地分析了静止轨道中继卫星系统存在的局限性,提出了采用中轨卫星星座构建跟踪与数据中继卫星系统的思想,给出了系统的网络结构并分析说明中轨中继卫星网络的业务流量特性,指出需要从对空覆盖性能、对地覆盖性能以及星际链路的实现难度3个方面来分析比较MEO-TDRSS的性能,并给出了多个实用的性能指标。以我国为例,仿真比较了采用不同类型星座实现的中轨中继卫星系统的性能差异,确定了适合中轨跟踪与数据中继卫星系统采用的星座类型。第六章主要研究了LEO/MEO双层卫星网络中层间星际链路(ILISL)建立策略。通过对已有的层间星际链路建立策略的研究,指出了已有建立策略导致网络拓扑结构稳定性降低的原因。从尽量降低层间星际链路重建所导致的网络拓扑重构次数,改善网络拓扑稳定性的角度出发,提出了3种基于集中重建思想的层间星际链路建立策略。数值仿真结果说明,新策略能够以可以接受的代价,大幅度降低LEO/MEO双层卫星网络的拓扑重构频率,增强网络拓扑结构的稳定性。第七章是全文总结。归纳了本文工作的主要贡献和创新性。更多还原

【Abstract】 With the rapid development of terrestrial wireless communication and Internet technologies in recent years, the network dimension and the number of users of these systems are increasing exponentially. As one of the most important modern communication technologies, satellite communication has achieved great progress during the past three decades. With the increasing demands for high mobility and quality of service (QoS) in broadband multimedia services, satellite communication networks adopting ATM and TCP/IP technologies are going to build a part of the future global mobile communication networks infrastructure. In this scenario, distinctions between satellite communication networks and terrestrial networks will cease to coexist in the universal mobile telecommunication system (UMTS), just like the convergence of the terrestrial fixed networks and the 3G mobile networks. Pervasive and ubiquitous information exchange is the primary purpose of creating an integrated UMTS. Mobility, QoS and global seamless coverage are the most important characteristics of UMTS. Satellite communications will play an important role in UMTS for their inherent advantages, such as wide area coverage, unique broadcast capability and no regional restrict. In practice, GEO satellite communication systems are incompetent to surppoting real-time multimedia services because of their intrinsic drawbacks. Hence, Non-geostationary orbit (NGEO) satellite communication system with lower transmission delay and attenuation becomes the one in focus. According to the peculiar techniques and development trends of the NGEO satellite communication systems, this dissertation mainly focuses on the NGEO satellite constellation design technologies and the characteristics of inter-satellite link (ISL), including global and regional coverage satellite constellation design, satellite constellation schemes study for NGEO tracking and data relay satellite system (TDRSS) and inter-layer inter-satellite link (ILISL) establishment strategies for two-tier LEO/MEO satellite networks.Chapter 1 is the preface. The development, status and perspective of the satellite communications and some key techniques of the mobile satellite communication networks are introduced concisely. The contents of this dissertation are also outlined. Chapter 2 outlines satellite constellation design. The theories behind the design of satellite constellation and some design considerations are presented. Two types of classical NGEO global coverage satellite constellation design methods, polar orbit constellation and inclined circular orbit constellation, are also briefly introduced.Chapter 3 studies the design of orthogonal circular orbit satellite constellation with global coverage. The precise constraint equation for polar constellation supporting coverage beyond specified latitude is derived. The relationship between the precise constraint equation and Beste’s approximate constraint equation is analyzed and the applicable condition of Beste’s approximate constraint equation is also indicated. The idea of orthogonal circular orbit satellite constellation, which is a combination of polar orbit constellation and equator orbit constellation, is proposed and the constellation parameter constraint equation is derived. Some orthogonal circular orbit constellation schemes are presented. By making a coverage performance comparison of orthogonal circular orbit constellation schemes with corresponding polar constellation schemes, the validity of orthogonal circular orbit satellite constellation is verified.Chapter 4 focuses on the design of regional coverage satellite system with common-track constellation. The characteristics of common-track constellation are studied thoroughly. A coded notation which can describe common-track constellation entirely is proposed and the restricted equivalent relationship to the Walker’sδconstellation is given. An optimization design method for implementing regional coverage satellite system with common-track constellation and and detail design steps are presented, and some optimal constellation schemes for China are obtained. Moreover, the parameters of these optimal constellations were adjusted again according to the time-varying traffic distribution density, which improved the consistency between the coverage performance of constellations and the traffic distribution density and hence improve the overall system coverage performance. Finally, the optimization design method for regional coverage common-track satellite constellation based on Genetic Algorithm Toolkit (GATOOL) of MATLAB is studied. Simulation results show that the parameter precision of these optimal constellations is improved while the computation time is reduced greatly. These results verify the efficiency of the GA in the task of satellite constellation design.The satellite constellation classes, which are suitable for MEO-TDRSS, are investigated in chapter 5. The limitations of GEO-TDRSS are analyzed systematically. The idea of MEO-TDRSS is proposed, the generic network architecture and traffic distribution characteristic of MEO relay satellite system are presented. These studies show that, to compare the performance of MEO-TDRSS entirely, the coverage performance for low-altitude celestial and for ground and inter-satellite link (ISL) implementation complexity are required to be analyzed. Take China as example, the coverage performance and intersatellite links properties of four constellation schemes with different constellation types are compared by simulations. Then, the appropriate satellite constellation types for the implementation of MEO-TDRSS are advised.Chapter 6 studies the ILISL establishment strategies for two-tier LEO/MEO satellite networks. Based on the in-depth investigation of these existing strategies, the inherent disadvantage of these existing strategies which decreases the topological stability of the two-tier satellite network is indicated. Then, three new ILISL establishment strategies based on the idea of convergent reconstruction are proposed to improve the topological stability of the two-tier satellite network by minimizing the number of topology reconfigurations. Numerical results show that these proposed strategies can substantially reduce the number of the network topology reconfigurations and hence improve the topological stability of the two-tier LEO/MEO satellite networks with acceptable cost of increased number of ILISL reconstructions and mean ILISL distance.Chapter 7 is the summarization of this dissertation, and indicates the contributions of our studies.更多还原