低轨大规模卫星星座系统建模与干扰分析

针对低轨(LEO)大规模卫星星座系统存在电磁空间复杂且难于观测的问题,对低轨卫星星座链路特征进行研究。以Starlink和OneWeb星座为研究对象,根据低轨卫星的星座参数,获取等效全向辐射功(EIRP)值并进行可视化处理;对获取到的低轨电磁卫星数据进行分析,获取数据的衰减特性和时间、频率等的数据关系,计算星间的链路干扰以及时间上的分布特征;获取相对干扰时间的特征值以及星间数据的衰减与时频的多维特性,并分析不同场景下的干扰时间特征,从多个维度分析低轨大规模卫星星座系统间星间链路的干扰情况并进行仿真验证。实验证明了低轨大规模卫星星座系统之间的星间链路存在干扰情况,且频率越高,干扰现象越明显。     

Signal design and system operation of GlobalstarTM versus IS‐95 CDMA – similarities and differences

The Globalstar^TM system provides telephone and data services to and from mobile and fixed users in the area between ±70 degrees latitude. Connection between user terminals and the PSTN is established through fixed terrestrial gateways via a constellation of low earth orbiting (LEO) satellites. Globalstar uses an extension of the IS‐95 CDMA standard that is used in terrestrial digital cellular systems. The LEO satellite link is sufficiently different from the terrestrial cellular link that certain departures from IS‐95 were needed both in signal design as well as in system operation. This paper describes some of the similarities and differences of Globalstar air interface versus IS‐95. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

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。     

面向低轨通信星座的导航定位方法比对研究

当前基于低轨卫星的导航定位方法研究成为国内外热点,其中基于低轨通信卫星的导航定位技术更是当前研究的重点方向。然而低轨通信星座较低的时空基准精度给导航定位带来了较大的挑战,针对弱时空基准约束的低轨卫星导航定位体制设计还处在研究的初级阶段。本文针对低轨通信星座的导航定位服务需求,基于LEO通信卫星的伪码测距信号与多普勒测频信号,开展精度因子（Dilution of Precision,DOP）及定位精度均方根误差（Root Mean Square Error,RMSE）分析,并对两类测量体制下的低轨通信星座导航定位服务性能进行分析论证。理论分析与仿真结果表明,在设定低轨通信卫星10 m～30 m弱时空基准误差的约束下,多普勒测频体制具有更优的导航定位精度,其周期平滑后的三维RMSE值为1.28 m,相比伪码测距体制下的三维RMSE值优化了86.8%;二维RMSE值为0.99 m,相比于伪码测距体制提升了52.9%。本文提出了一种较为可靠的低轨通信星座多普勒定位方案,为未来低轨通信卫星用于导航定位服务提供了有益参考。     

A dispersion flattened fiber front-haul transmission system with high bitrate signal at low input optical power

We propose a dispersion flattened fiber (DFF) front-haul transmission system with high bitrate, polarization multiplexing (PM) and quadrature amplitude modulation (QAM) signal at low input optical power. The modulation format of the system is PM-16QAM, and the bitrate is 256 Gbit/s. The transmission characteristics over DFF link system are experimentally studied, which are compared with those over non-zero dispersion shifted fiber (NZDSF) link and standard single mode fiber (SSMF) link. The experimental results show that the error vector magnitude (EVM) of 256 Gbit/s and PM-16QAM signal over 25 km DFF link is 0.75% better than that over 25 km NZDSF link at least, and the bit error rate (BER) and Q-factor are much better than those of NZDSF. Their EVM and BER are both decreased with the increase of input optical power, and the Q-factor is increased. Those characteristics over 25 km SSMF are the worst at the same case. The larger the dispersion is, the more the constellation points are deviated from their respective centers and the worse the constellation characteristics are. The greater the attenuation of the DFF is, the smaller the input power of the DFF is, the more the constellation points are deviated from their centers and the worse the constellation characteristics are. This study provides a new idea and experimental support for long span front-haul propagation in mobile communication.     

A methodology for rapidly evaluating the performance of some lowEarth orbit satellite systems

A top-down design methodology for LEO systems is illustrated by an example. The considered service is data messaging over local areas. The design method is based on a three-level approach: mission objectives, constellation selection and network design, and technical studies. It is shown that many alternatives are to be explored, and this requires a set of consistent and efficient simulation tools. The tools considered in the paper are a rapid computation algorithm for in-view period determination, and a discrete event simulation module. These tools are shown to provide the designer with means to rapidly select the appropriate constellation and evaluate the network performance     

基于遗传算法的低轨天基雷达星座设计

从目标监视性能的角度出发,分析了低轨天基雷达星座的卫星总数、能量需求以及星座发射费用等优化目标。综合考虑了Walker星座的碰撞等约束问题,建立了低轨天基雷达星座设计的优化目标。提出了一种基于遗传算法的低轨天基雷达星座设计方法。根据天基雷达星座的特点,该算法在进化过程中使用了非可行解修正和约束分级等约束处理方法,有效提高了算法的运算效率。通过仿真实验验证了该方法能够有效的同时优化低轨天基雷达星座的构形和卫星参数。     

PSK to CSK mapping for hybrid systems involving the radio frequency and the visible spectrum

This paper presents an efficient technique to map phase shift keying (PSK) signalling to colour shift keying (CSK) constellation, to establish a full link in hybrid systems involving the radio frequency (RF) and the visible spectrum. It fits in systems combining (first link) wireless communication technologies such as the wireless fidelity (WiFi) or wired communication technologies such as power line communications (PLC) to visible light communications (VLC) technology (second link). On the first link, PSK technique is used to convey the information, while, on the second link, a technique based on colour variation is deployed. WiFi standards targeted are those that employ PSK as sub-carrier modulation techniques (IEEE 802.11a/11g/11n). The PSK complex constellation observed at the output of the first link is converted into colours using the hue-saturation-value/intensity (HSV/I) colour models. The constant lighting required in VLC corresponds with the coordinate I of the HSI and the colour constraint is met by assigning adequate current intensities to the red-green-blue LEDs (RGB-LEDs) used. The design meets the requirements of CSK constellation design outlined in IEEE 802.15.7. The performance of the system is analysed through bit error rate curves obtained by simulations, for binary PSK (BPSK) and quadrature PSK (QPSK), 8PSK and 16PSK constellations. The results show that as the constellation size increases, the performance of the system decreases.     

中国低轨移动卫星通信系统星座设计

本文研究低轨移动卫星通信系统设计中的一个基本问题－－星座设计问题，并给邮了我国低圆轨道移动卫星通信系统的星座设计方案，该星座是以三个轨道平面组成的２４颗星系统，它的高度为１３２６ｋｍ，轨道参数由本文提出的优化算法进行设计，本文用统计的方法对我国低轨系统方案和Ｇｌｏｂａｌｓｔａｒ系统（２４颗星方案）的覆盖性能进行分析比较，结果表明本文提出的系统对我国的覆盖特性优于Ｇｌｏｂａｌｓｔａｒ系统，本文还对圆     

APPLICATION OF FREQUENCY DIVERSITY FOR DIMENSIONING A Ka-BAND SATELLITE SYSTEM

The growth of the demand for telecommunication services is going to saturate the frequency bands usually used (C or K_u). For this reason the K_a-band is much considered and is going to be highly used. To meet the requirements of a more developed market a satellite system in K_a-band with European coverage and better performance than those of common VSATs, especially in terms of capacity and of link availability, is proposed and characterized. The negative effect due to the high rain attenuation, that represents the main impairment using K_a-band, can be mitigated using one or more fade countermeasures. Frequency diversity, which well suites the characteristics of the proposed systems, has been analysed and characterized in detail using a model developed at Politecnico di Milano. Its performances are shown as a function of different system parameters such as total number of stations, number of assisted stations, link availability and statistical dependence among stations. The aim of the paper is to introduce a design methodology and to show the advantages obtainable using frequency diversity for a K_a-band system with higher performances than common VSATs. The advantages achieved for rain margins are shown and system design parameters are then compared with those of an uncompensated system. Using this type of countermeasure, the dimensioning of the whole system (both payload and earth-station) is proved to be much less severe.     

Walker星座卫星网络拓扑结构动态性分析

对低轨道(LEO)、Walker星座类型的卫星网络拓扑结构动态变化特征进行量化,给出了精确计算系统周期内网络时间片数量和时间片长度的公式。通过研究,一方面弥补了卫星网络研究中对拓扑结构时间片特征的简单假设,另一方面也为未来卫星网络星座的设计提供一定的指导。     

Data collection from the Antarctic region through a W‐band low Earth orbit satellite

The DAVID (DAta and Video Interactive Distribution) mission is being carried out in the framework of the Science Small Missions Program of the Italian Space Agency. The mission is aimed at the deployment of two scientific telecommunication experiments through a low Earth orbit (LEO) satellite. The paper will focus on one of these experiments, that will test a satellite system architecture for the exchange of a large amount of data and high definition images through a W‐band link and a Ka‐band inter‐satellite link between the LEO and the ARTEMIS satellite. The proposed architecture, that will explore various innovative aspects, will also allow for the first time the distribution of large volumes of scientific data collected from the Antarctic region and other extremely remote areas of the Earth. The availability of a return link in the envisaged system will also allow interactive control of the various laboratories located in the remote sites. Copyright © 2001 John Wiley & Sons, Ltd.     

MIMO场景下的低轨卫星选星算法

低轨(LEO)宽带星座卫星通信作为地面5G无线通信系统的重要补充,始终面临地面可视卫星数量大、传统选星算法计算复杂度高等难题。为实现高效的卫星分组选择算法,基于多输入多输出(MIMO)系统原理,以大尺度路径损耗模型为基础,结合递减卫星选择算法,从而以较低计算复杂度、更快收敛速度有效逼近最优容量性能。该算法在典型LEO星座系统构型下通过数值仿真得到了验证,为未来5G低轨卫星星座通信传输方案设计提供了一种参考思路。     

Capacity provisioning and failure recovery for Low Earth Orbit satellite constellation

This paper considers the link capacity requirement for an LEO satellite constellation. We model the constellation as an N×N mesh‐torus topology under a uniform all‐to‐all traffic model. Both primary capacity and spare capacity for recovering from a link or node failure are examined. In both cases, we use a method of ‘cuts on a graph’ to obtain lower bounds on capacity requirements and subsequently find algorithms for routing and failure recovery that meet these bounds. Finally, we quantify the benefits of path‐based restoration over that of link‐based restoration; specifically, we find that the spare capacity requirement for a link‐based restoration scheme is nearly N times that for a path‐based scheme. Copyright © 2003 John Wiley & Sons, Ltd.     

Efficient integration of isochronous and data bursty traffics in low earth orbit‐mobile satellite systems

This paper focuses on the radio resource management in low earth orbit‐mobile satellite systems (LEO‐MSSs) based on a time division multiple access (TDMA) air interface. A novel demand–assignment medium access control (MAC) protocol, named DRAMA+ (dynamic resource assignment multiple access—enhanced version), is proposed, where voice and Web traffic sources obtain transmission slots through requests sent by means of a random access phase. The round‐trip propagation delay (RTD) of LEO‐MSSs prevents an immediate feedback for each transmission attempt. Therefore, the main concern of the DRAMA+ scheme is to realize an efficient access phase. All the transmission requests successfully received at the satellite are managed by an on board scheduler. We have shown that DRAMA+ outperforms other techniques appeared in the literature in terms of voice quality, transmission delays for bursty data traffics and resource utilization. Moreover, a performance analysis of an ideal version of the DRAMA+ scheme has permitted us to prove the potentialities of the proposed DRAMA+ technique. Stability issues have been addressed as well as the impact on the DRAMA+ performance of the LEO satellite constellation RTD value. Copyright © 2002 John Wiley & Sons, Ltd.     

LEO卫星移动通信系统空间网络技术分析

在分析LEO卫星星座移动通信系统空间段网络功能和特点的基础上,进行了星座网络路由和交换技术体制的分析和论证,提出了以支持话音业务为主的LEO卫星移动通信系统星座网络路由和交换技术方案。星座网络采用定长信元格式交换体制,采用动态拓扑离散化的拓扑快照静态路由策略。这种静态路由离线计算方式和定长信元交换相结合,提高了网络交换的效率和转发速率。     

中低轨卫星跨层激光链路二次同步切换方法

中低轨卫星之间跨层激光链路的无缝切换直接决定了双层卫星光网络的稳定性.异步切换方法会导致网络拓扑频繁重构,而集中同步切换将造成两层间连接中断,网络运行状态失控.为此,本文提出了中低轨卫星星座激光链路的二次同步切换方法,在保证中低轨道卫星连通的基础上,可降低网络拓扑重构频率.研究了整数周期比的中轨道和低轨道卫星空间位置特性,建立了中低轨卫星星座构形二阶非球摄动模型,确定了中低轨道之间轨道周期比为3的双层卫星星座构形.按连接和切换顺序将该星座构形中跨层激光链路分为两组,以相对周期的1/4为基准,每次令其中一组同步切换,通过交替完成切换.研究结果表明,二次同步切换方法使得网络拓扑重构频率降低到链路切换频率的1/7,比集中切换方法在网络平均时延方面降低了30ms.     

LEO satellite communication networks—a routing approach

In the modern world of telecommunications, the concept of wireless global coverage is of the utmost importance. However, real global coverage can only be achieved by satellite systems. Until recently, the satellites were in geostationary orbit and their high altitude could not allow real‐time communication such as cellular networks. The development of LEO satellite networks seems to overcome this limit. However, LEO satellite systems have specific characteristics that need to be taken into account. In the same manner, the TCP/IP standard was developed for terrestrial network. The need is then to come up with a solution that would permit the use of TCP/IP on LEO satellite networks without losing too many packets. The idea is to develop a routing algorithm that maximizes the RTT delays compared to the TCP timer granularity. For that matter, we use an FSA‐based link assignment that simulates the satellite constellation as a fixed network for a predetermined time interval. In this configuration, the problem becomes a static routing problem where an algorithm can find the best solution. Copyright © 2003 John Wiley & Sons, Ltd.