卫星互联网星间激光通信链路传输与路由交换技术研究（特邀）

随着低轨卫星互联网的迅猛发展,星间激光通信链路成为低轨大型星座互联互通的关键,也是用户接入卫星互联网实现全球范围内端到端交互的基础。与地球同步轨道的星间环网不同,由于低轨卫星的高动态性,造成星间链路需要不断动态重构,由此带来空间节点的编址方式、交换路由方法等诸多技术难题,是目前该领域关注的热点。此外,用户终端通过微波链路接入卫星互联网,需要微波链路与激光链路之间的汇集和分发,也是迫切需要研究解决的重点难点问题。     

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。     

面向6G通信的多层低轨卫星网络路由算法

在面向6G的移动通信网络中,低轨卫星网络（LEO, Low Earth Orbit）运行高度低、时延小,可大范围部署实现全球广域低时延通信。当前低轨卫星星座正朝着多层轨道面发展,多层轨道的跨层链路增加了数据传输路径,但跨层轨间链路的频繁通断,增大了多层LEO网络层间路由选择的难度。为此提出了一种面向6G移动通信的多层LEO卫星网络路由算法。首先建立跨层链路,面向端到端传输时延和可靠性需求,分析影响跨层轨间链路频繁通断的因素,基于LEO卫星网络虚拟位置思想,选择卫星节点对建立可靠跨层链路;然后实现路由选择,基于所建立的跨层星间链路,采用时空演化图模型刻画动态网络拓扑,设计最短路径算法计算最佳传输路径。最后,构建三层卫星网络场景对所提算法进行仿真验证。结果表明,相对于现有方法,所提算法在端到端时延和可靠性均有明显提升。     

LEO/MEO通信系统ISL性能分析与设计

由低轨(LEO)和中轨(MEO)卫星构成的卫星通信系统可以充分利用LEO和MEO的各自轨道优势,具有较好的组网通信性能。在LEO与MEO卫星之间建立星间链路,使卫星之间存在直接的通信路径,可以提高网络的自治性,减少传输时延,降低对地面站的依赖。本文首先分析建立MEO星座与低轨LEO星座星间链路的可行性,然后通过STK软件仿真影响LEO/MEO星间链路特征参数的变化情况,进一步分析LEO/MEo星间链路预算。     

低轨通信星座星间链路特点研究

随着全球宽带通信需求的增长,世界各国提出并建设了多种低轨通信星座,我国的卫星互联网系统也在紧张建设中,星间链路将是通信星座系统的重要组成部分。为研究星间链路特点和建链需求,以极轨通信星座为例,从几何角度给出了星间链路指向角和距离的数值计算公式,分析了顺行轨道星间链路的变化规律,并进一步研究了异轨星间反向缝建链的特点。研究结果表明,选取合适的星座参数,可以实现卫星跨反向缝的接续建链,从而保证反向缝两侧卫星之间始终存在可用的通信链路。     

低轨航空安全监视星座路由规划算法设计与仿真

针对基于低轨星间链路网络的航空安全信息传输的路由规划需求开展了路由规划算法设计,分别设计了多站就近落地、高可靠备份传输以及分区负载均衡等3种算法,并基于星间链路网络仿真平台进行了试验验证,试验结果表明所提出的算法能够满足低轨航空安全监视网络的高效、高可靠传输需求,可以为我国低轨航空安全监视系统建设提供一定的参考。     

卫星星间链路多普勒频移仿真

在卫星通信过程中,对具有相对运动的卫星,星间链路的多普勒频移是不能忽视的。分析了空间圆轨道卫星星间链路的距离以及距离变化率,并进行了公式推导。在此基础上提出了一种以链路距离变化率作为卫星相对运动速度来计算星间链路多普勒频移的新方法,并以铱星系统和某中轨卫星系统为例,分别对同层高度星间链路和异层高度星间链路的多普勒频移进行仿真,给出了仿真结果。分析与结果表明,该方法合理、有效。     

星空地一体化航空安全监控体制设计

针对运输航空全域实时连续监视领域存在的问题,在"泛在网络感知"理念的基础上,提出了"星地一体化网络监视"概念,通过构建全球覆盖的低轨星座PNTRC网络,使得该网络能够连续感知全球任一航班飞机,使其成为天地一体网络中的用户节点。通过对星载广播式自动相关监视(ADS-B)分集接收、星载GNSS接收定轨、星间链路数传及星地链路数传等关键技术的研究,实现了对星空地一体化广域航空安全监控体制的可行性验证。     

多层卫星网络激光星间链路空间特性仿真

多层卫星网络结构由于其鲁棒性强,可实现无缝覆盖等特点而成为研究热点。针对 高轨/中轨/低轨(GEO/MEO/LEO)多层卫星网络结构,研究了各个节点间的激光链路,推导出 了 不同轨道间两个卫星位置关系的坐标转换公式。对同层间激光链路(OISL)、异层间激光链路 ( OIOL) 俯仰角、方位角以及距离参数和GEO对LEO覆盖特性进行了仿真。结果表明,卫 星光学终端俯仰指瞄范围完全可以满足目标星的移动要求,但水平指瞄范围和扫描速度是影 响星间激光链路性能的主要因素。     

低轨卫星星座快速响应链路损毁路由算法

设计高效弹性的卫星路由算法是未来低轨(Low Earth Orbit, LEO)卫星通信技术的一个重要发展方向。为解决低轨卫星星座网络中星间链路发生故障后存在的传输中断和数据安全问题,提出了一种低轨卫星星座快速响应链路损毁路由算法(Quick-response Link Destruction Routing Algorithm for LEO Satellite Constellation, QRLDRA)。QRLDRA以星座可预测拓扑作为星间路由计算基础,增加星地回传路由设计,快速将星间链路异常回传至地面计算中心处理;引入多优先级动态队列,根据节点链路状态调整星间链路不同数据传输的优先级;综合路由计算、路由上注、链路检测等功能,完成对拓扑变化的及时响应。通过仿真实验与传统算法的比较发现,所提算法有效提高了数据端到端传输的成功率,为用户业务服务质量(Quality of Service, QoS)提供了可靠保障。     

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。     

ATM‐based multimedia communication via NGSO‐satellites

Future broadband satellite networks for multimedia will be seamlessly integrated into terrestrial broadband networks which often use asynchronous transfer mode (ATM) and recently also the less complex multi protocol label switching (MPLS) technique as transmission and switching protocol. In light of this, future broadband satellite networks may adopt the ATM transmission scheme and implement ATM or ATM‐like switches on board the satellites. However, as compared to communication in fixed networks, satellite communication is characterized by special constraints (e.g. signal delay, channel quality, dynamic network topology) that require novel ATM‐based communication technology for satellite systems. This paper presents results from the ATM‐Sat project that aims to complete this technically challenging and important R&D task in the cooperation between DLR, Fraunhofer Gesellschaft and Tesat‐Spacecom. In brief the following aspects have been addressed in the ATM‐Sat project:

• development of the concept and communication technology for a multimedia satellite system with,
  • non‐geostationary orbit (NGSO) satellites;
  • inter satellite links (ISLs);
  • on‐board ATM switching;
  • fixed and mobile terminals;
• verification of the developed communication technology with a demonstrator.

In particular the ATM‐Sat R&D tasks cover the system and protocol architecture, on‐board processing, ISL routing, up/downlink and on board ATM resource management (including medium access control), error control, IP over satellite‐ATM, and active intelligent antennas. Copyright © 2005 John Wiley & Sons, Ltd.     

Satellite constellation design for 5G wireless networks of mobile communications

Satellite constellation design plays an important role in satellite networks. Network constellation system design can affect the effectiveness of current improvements of the communications link and the management of the entire network. The power requirement of the mobile stations and ground stations is very high in a geostationary Earth orbit communication system, which means the terrestrial terminal is hard to be made handheld for fifth generation mobile communications. The emergence of nongeostationary orbit satellites such as low Earth orbit satellites greatly compensates for the disadvantage of geostationary Earth orbit satellites. Based on the classical constellation design method, the orthogonal circular orbit constellation is proposed. The design objectives considered here are the following: global Earth coverage by low Earth orbit satellites, the duration of continuously covering one mobile station by one satellite is more than 9.57 min, the access satellite link duration time of the mobile station is more than 4.79 min, and the number of satellites and orbits is to be minimum.     

行星表面有人探索高速无线网络体系架构及关键技术

针对行星表面有人探索任务对高速无线通信的需求，提出了一种基于异构组网思想的网络体系架构，并对关键技术进行了分析和设计。该架构采用“三网两体制”的设计思路，将整个网络分为高速传输网、多媒体接入网、覆盖扩展网三个组成部分，三层网络分别完成高速骨干传输、多节点多业务接入、覆盖范围灵活改变的功能。根据三个网络不同的节点处理能力和传输需要，设计了高速传输体制、灵活接入体制两种传输体制，及基于无线多跳的覆盖扩展技术、多子网通信切换技术、多体制融合技术等关键技术。该网络架构具有裁剪灵活、协议开销小、支持业务类型多等特点。     

Routing optimization based on topology control in satellite network

A new double-layer satellite network model for space networking was established and a routing algorithm based on topology control (TCRA) was proposed considering the advantages of low earth orbit and stationary earth orbit satellite networks.This model used virtual node strategy and satellite grouping idea,which regarded the coverage area of each low earth orbit satellite as a virtual node.The network took into account the influence of the polar area on the division of the satellite footprints,such that the upper management satellites can accurately acquire the topology of the lower satellites.Using the improved virtual node strategy,the time slices were superior to other network models in quantity,length and other aspects.Based on the network topology,stationary earth orbit satellites calculate routing for low earth orbit satellites,while low earth orbit satellites were responsible for forwarding data.The simulation results show that the routing algorithm is superior to other algorithms in average end-to-end delay and packet loss rate.     

一种星地一体化路由设计的卫星IP网络

现有大部分支持IP的卫星系统只是提供一个连接地面路由器的物理通道,难以满足宽带接入、多媒体服务以及星地网络一体化等新的需求.为此,提出了一个分组传输和交换均基于IP的GEO卫星系统,并从传输网络和路由结构两方面进行了描述.并针对星上资源紧张的现状,采用了一种地面路由星上交换的新设计思路.通过星上IP交换可实现大量终端间的单跳通信,一个可扩展的集中式IP路由结构可有效减少通过卫星的路由流量,使得通信效率提高的同时,能实现卫星网络与Internet的无缝兼容.     

QoS management in trunk-and-branch switched Ethernet networks

A likely architecture for the future broadband access network will consist of a trunk-and-branch topology, with very high bandwidth trunks (e.g., 1-10 Gb/s), connected to high-bandwidth drops (or branches) to homes and businesses. A multihop switched Ethernet data transport can be used over this access network. Wang (see Internet QoS: Architectures and Mechanisms for Quality of Service, Morgan Kaufmann, 2001) discussed the benefits of upgrading the hybrid fiber coax plant into a distributed switched Ethernet trunk-and-branch network capable of fiber-like transmission speeds. This article focuses on QoS management in the proposed next-generation broadband access network (NGBAN) based on a multihop switched Ethernet network architecture. This network architecture and QoS management framework are more generally applicable, and we anticipate they will form the basis for the "last mile" independent of the physical medium.     

Can satellites unblock the Internet?

Anyone who has surfed the Internet knows how slow it can be. Some have even suggested that it could become entirely gridlocked early in the next millennium. The author explains how satellites could help avert such a catastrophe. The primary advantage of a satellite system for Internet delivery is the same as it is for other types of communication: coverage area. A single satellite in geostationary orbit can serve approximately one third of the planet's surface, so three can cover most of the world's population. For regions where terrestrial infrastructure is limited or nonexistent, satellite coverage may be the only option. The author discusses the proposed Teledesic broadband low Earth satellite system operating in the Ku band, which is backed by Microsoft, and its only direct competitor SkyBridge which is backed by Alcatel and Loral. The author also discusses the geosynchronous Earth orbit broadband satellite systems. The commercial viability of these systems is discussed     

Theatre in the Sky: a ubiquitous broadband multimedia‐on‐demand service over a novel constellation composed of quasi‐geostationary satellites

To meet an ever‐growing demand for wideband multimedia services and electronic connectivity across the world, development of ubiquitous broadband multimedia systems is gaining a tremendous interest at both commercial and academic levels. Satellite networks will play an indispensable role in the deployment of such systems. A significant number of satellite communication constellations have been thus proposed using Geostationary (GEO), Medium Earth Orbit (MEO), or Low Earth Orbit (LEO) satellites. These constellations, however, either require a potential number of satellites or are unable to provide data transmission with high elevation angles. This paper proposes a new satellite constellation composed of Quasi‐GeoStationary Orbit (Quasi‐GSO) satellites. The main advantage of the constellation is in its ability to provide global coverage with a significantly small number of satellites while, at the same time, maintaining high elevation angles. Based on a combination of this Quasi‐GSO satellites constellation and terrestrial networks, the paper proposes also an architecture for building a global, large‐scale, and efficient Video‐on‐Demand (VoD) system. The entire architecture is referred to as a ‘Theatre in the Sky’. Copyright © 2006 John Wiley & Sons, Ltd.