LEO卫星网络动态混合卫星切换策略

LEO卫星网络切换协议中的路由选择策略应当综合考虑路由本身优化性,路由计算复杂性,路由更新的信令代价。提出适合LEO网络卫星切换要求的动态混合路由选择策略(DHRS:DynamicHybridRouteSelection),即发生卫星切换时,由卫星节点根据移动终端用户切换前所处位置和切换前路由表等信息,为移动终端选择合适的路由。     

LEO/MEO卫星网络中运用自组网思想的动态路由算法

分析了基于星际链路的LEO/MEO路由算法的特点及卫星网与自组网的相同之处，借鉴了自组网路由协议中适用于卫星网的部分，提出了LEO/MEO卫星网络中运用自组网思想的动态路由算法，并对算法进行了模型仿真和性能分析，这种算法增强了卫星网络的自适应性，使网络具有自治性强，功能更全面、系统开销小、适用范围广等特点。     

LEO＆MEO双层卫星网络路由技术研究

首先分别分析了GEO层、MEO层、LEO层卫星的优缺点，接着简述了LEO＆MEO双层卫星网络的特点及对路由算法的要求，然后对已有的卫星网络路由算法进行简要分析，最后提出了一套适合LEO＆MEO双层卫星网络的动态路由技术。在拓扑快照DT-DVTR路由算法和MLSR的基础上，设计了动态路由算法，该路由算法采用了主动路由和按需路由相结合的方式，使得路由查找时间短、效率高。     

基于STK的双层卫星星座设计及仿真

轨道与星座的设计是整个卫星通信系统设计的基础,合理的轨道设计与星座配置方案可以显著提高系统的整体性能。结合GEO卫星处理能力强,LEO卫星星地时延小的特点,以提供全球实时接入为目标,提出了一种由LEO卫星提供全球覆盖的GEO/LEO双层卫星网络星座设计方案。运用卫星覆盖带分析方法,确定由48颗LEO卫星完成全球覆盖。通过在STK仿真环境下进行计算机仿真验证,得到所设计的卫星星座可完成全天时全球覆盖。     

多层卫星网络链路中断容忍路由策略设计

链路中断和接续对卫星网络路由有重要影响,该文针对多层卫星网络,设计了链路中断容忍路由策略,利用非均匀时间段内卫星网络拓扑结构的可预测性进行路由表计算,采取动态的拥塞控制机制和洪泛策略,解决由于卫星运动、通信设备故障引发链路中断情况下的路由问题。仿真结果表明,该路由策略具有较高的链路利用率,能够减少动态路由计算中时延信息收集和星上路由表生成给卫星节点带来的时空开销。     

一种基于分时的LEO卫星网络无环路由算法

在分析传统卫星网络路由算法的基础上，提出一种基于分时的LEO卫星网络无环路由算法(DTRA)。针对卫星在各时间片之间进行路由表切换时可能出现的路由环问题，算法采用平滑路由表切换策略消除由于切换前后网络状态信息不一致而产生环路的可能性，保证分组在任何时刻都能够沿无环最短时延路径被转发。同时，DTRA也能够通过使用无环备份路径处理可能出现的链路拥塞、节点失败等突发情况。通过复杂性分析可知，算法只需较小的星上存储开销和星上处理开销，而无需星问通信开销。仿真实验结果也表明算法能够提供数据最优传送，具有较好的端到端时延性能。     

LEO网络中卫星切换的动态概率路由优化策略

在LEO卫星网络中，卫星切换方案需要在保证最小切换延时的同时，合理地使用网络资源，因此应该合理选择卫星切换中路由优化的触发条件。本文在综合考虑卫星切换中消耗的网络资源，包括带宽资源和信令资源的前提下，提出动态概率路由优化方案。指出在卫星切换中，为了达到对网络资源的有效使用，路由优化概率应该随LEO星座结构，呼叫带宽，业务分布等网络参数不同而动态变化。     

非静止轨道卫星系统考虑通信中断的服务质量分析

基于Globalstar和Odyssey两个Walker delta星座,建立星间链路网络,重点分析网络中的不同轨道间星间链的动态特性,特别是与星上跟瞄系统密切相关的俯仰角、方位角和链路长度变化,为卫星网络路由提供依据.对传统的卫星路由策略作了改进,利用卫星系统的冗余覆盖的特性,选择不同策略下的最优路径.针对用户不能忍受通信中断的情况,提出考虑消除中断的路由策略,进行服务质量的分析比较.同时也比较在消除中断的路由策略下,LEO同MEO网络差异之处.消除通信中断是以其它QoS性能下降为代价.     

分集接收、路由选择

Y2000-62480-500 0100507低地球轨道卫星网络的数据报路由选择算法=Data-gram routing algorithm for LEO satellite networks[会,英]/Ekici.E.& Akyildiz,I.F.//2000 IEEE INFO-COM.Vol.2.—500～508(HC)卫星网络提供全局覆盖并支持大范围服务,低地球轨道(LEO)卫星具有短环形距离延迟,因此提高了其重要性,在 LEO 卫星网络中难题之一是开发专门有效的路由选择算法,本文介绍了 LEO 卫星网络数据报路由选择算法,此算法产生最小传播延迟路径,通过模拟评价了算法的性能,并讨论了其健壮性。参8     

多业务双层卫星网络的接入与切换策略分析

近年来,利用不同轨道高度卫星的各自优势组成多层卫星网络逐渐成为热门研究,文章针对多业务条件下GEO/LEO双层卫星网络中的接入与切换策略进行了深入分析,提出了一种参数加权平均的接入策略,并将其应用在一种改进的基于业务量的双层卫星网络接入与切换策略中。实验仿真表明,该改进策略能够在一定程度上改善不同级别用户的通信质量,更加合理地利用双层卫星信道资源。     

基于分布式星群的双层星座设计

当前,陆地通信系统已无法满足日益复杂的信息需求,利用空间信息网络实现全球范围内的无缝覆盖和高效容量传输成为研究热点。现有卫星通信系统以单层星座为主,缺少高低轨卫星之间的协同。提出了一种基于分布式星群的双层星座设计,以基于分布式星群的低轨卫星作为网络架构的基础,采用星间链路实现低轨卫星之间的通信,通过高轨卫星实现中低纬度地区覆盖性能加强。仿真结果表明,所提方法在仅依靠在国内部署卫星地面站的前提下可实现全球多重覆盖。     

基于PETRI网模型的LEO/MEO/GEO三层卫星网络的性能分析

基于Petri网模型方法和仿真方法,对一种低轨/中轨/同步地球轨(LEO/MEO/GEO)三层卫星网络进行了性能分析.首先建立了卫星网络的广义随机Petri网(GSPN)模型,采用SPNP6.0软件进行了网络性能分析.然后,将分析结果与采用OPNET软件对该三层卫星网络模拟的结果进行了比较,验证了模型的正确性,并得出了诸如在高网络负载的情况下三层网络结构的性能优于单层等新的结论.     

MLSR: a novel routing algorithm for multilayered satellite IPnetworks

Several IP-based routing algorithms have been developed for low-Earth orbit (LEO) satellite networks in recent years. The performance of the satellite IP networks can be improved drastically if multiple satellite constellations are used in the architecture. A multilayered satellite IP network is introduced that consists of LEO, medium-Earth orbit (MEO) and geostationary Earth orbit (GEO) satellites. A new multilayered satellite routing (MLSR) algorithm is developed that calculates routing tables efficiently using the collected delay measurements. The performance of the multilayered satellite network and MLSR is evaluated through simulations and analysis     

Analysis of LEO, MEO, and GEO global mobile satellite systems inthe presence of interference and fading

Several multisatellite and multispot systems have been recently proposed for provision of mobile and personal services with global coverage, adopting GEO or non-GEO (i.e., MEO, LEO) satellite constellations. The paper addresses an in-depth analysis of these constellations, evaluating both geometrical performance measures and cochannel interference levels caused by extensive frequency reuse. The geometrical analysis yields the statistics for coverage, frequency of satellite hand-overs, and link absence periods. The interference analysis is based on a general model valid for all access techniques, which is here applied to the case of FDMA. The outage probability as a function of the specification on carrier-to-interference power ratio is evaluated for four selected constellations. Several techniques are introduced for interference reduction in non-GEO systems, in which the satellites coverage areas may intersect: spot turnoff, intraorbital plane frequency division, and interorbital plane frequency division. The effects of Rice fading have also been analyzed by means of an analytic approximated method. The overall analysis allows a fair comparison between LEO, MEO, and GEO constellations     

Performance evaluation of an optimized intersegment handover procedure for hybrid constellation satellite systems

Satellite system architectures based on geostationary or Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) constellation suffer from their intrinsic limitations in terms of coverage or flexibility. Traffic requirements concerning broadband services are expected to be very uneven both in time and space. To match this requirement and to improve coverage an innovative satellite system architecture, composed of a LEO/MEO segment to complement a Geostationary Earth Orbit (GEO) segment, has been proposed. In this scenario, to achieve interworking and to make it possible to hold the call while switching between the two segments, efficient intersegment handover (ISHO) procedures must be identified. The paper, after introducing the classical ISHO schemes, aims at defining and analysing an ISHO procedure developed to perform handover in case of hybrid constellations based on the use of both GEO and LEO/MEO orbits. Performance evaluation will be carried out for different system configurations utilizing a dynamic satellite constellation simulator in the time domain. The execution delay and its complementary cumulative distribution have been evaluated for different constellation geometry at different distances from the gateway. Copyright © 2002 John Wiley & Sons, Ltd.     

Low earth orbit satellite systems for communications

It may be that we are now entering the era of LEO constellation satellite communications after thirty years of domination by the GEO systems. This paper heralds the coming of the new era with a tutorial approach to the system design and trade-offs of LEO constellation system design. It discusses orbital configurations, network topologies and routeing considerations, multiple access schemes and link performance design. In so doing it brings out the major design parameters and how they interact with each other. Also considered are the service applications for the LEO constellation systems, and the important difference between real-time and delayed communication systems is highlighted. Examples of single and multi-beam (cellular) coverage system link designs are presented for L-K_a frequency bands. Future papers will consider aspects of the LEO spacecraft and launchers.     

面向低轨卫星网络的组网关键技术综述

随着信息通信技术的不断发展，人类对于扩大网络覆盖范围和降低通信时延的要求越来越高。低轨卫星网络是一种利用轨道高度较低的卫星构建的网络体系，具有覆盖范围广、通信时延低等优势。基于此，首先概述了低轨卫星网络的国内外发展现状及其组网所面临的挑战，进一步阐述了低轨卫星网络组网关键技术难点及建议，最后结合分布式、博弈论和人工智能等方法，对潜在可行的低轨卫星组网方案进行了探讨。     

GEO与LEO间激光通信轨道特性仿真

为了优化GEO与LEO间激光通信系统的性能,建立了卫星通信轨道特性仿真模型。通过对一年内卫星数据的分析可知,卫星通信终端间的多普勒频移变化范围约为5109 Hz,可以使用多普勒频移补偿方法减少GEO与LEO之间的多普勒频移影响。对于相干通信,终端必须进行频移补偿;提前量角的范围大于激光束散角,因此终端需要进行提前量补偿,激光通信系统可根据提前量角对视轴进行提前修正,以减少相对速度对激光通信的影响;太阳干扰和地球遮挡的时间较长,应该进行卫星组网以改善可通率,在通信过程中应根据通信终端时间,优化两个通信终端的工作流程;GEO和LEO终端的视轴变化情况不同,因此应该为卫星设计不同结构。     

Personal communications by satellite

Personal communications (PC) refers to two-way voice (and possibly data) communications to a small hand-held unit, capable of being carried by a person and used in various locations. PC via satellite refers to the case where this hand-held unit communicates directly with a satellite to provide the duplex voice (or data) service. Both geosynchronous earth orbit (GEO) and low earth orbit (LEO) satellites have been considered to provide this service. GEO and LEO satellite systems must compete with existing mobile cellular radio systems both in meeting performance requirements and service costs, if they are to be a significant supplier of PC services. GEO and LEO systems each have unique advantages and disadvantages when used to provide a PC service. While these general characteristics are identified in Section 1 of the paper, a more quantitative comparison is needed. This quantitative comparison is made by comparing a GEO PC satellite system, operating at EHF (K_a-band) frequencies with a LEO system operating at UHF (L-band) frequencies, including service costs for both systems. The two systems used in the comparison are examples of realistic GEO and LEO system designs for PC service, and although it is not exhaustive, the comparison points out some of the key differences between GEO and LEO systems that affect service performance and cost.