利用对地静止轨道卫星扩展因特网

介绍了利用卫星链路接入因特网的优缺点,说明了因特网的ＴＣＰ／ＩＰ协议在卫星条件下条件并不是最合适,并简要介绍了解决办法。     

WRC-19为非对地静止轨道卫星星座建立新“里程碑”

"WRC-19为非对地静止卫星(non-GSO)星座确定了一个稳定的监管框架,这将使得巨型卫星星座很快取得成果,并为世界各国公民提供更实惠的网络连接手段。"国际电联无线电通信局(BR)主任马里奥·曼尼维奇在2019年世界无线电通信大会(WRC-19)上表示。经过四周的激烈讨论,WRC-19形成了non-GSO卫星网络的投入使用定义,建立了基于一定时间阶段必须满足一定比例在轨卫星数量的要求("里程碑"),以及50/40G H Z频段非静止轨道卫星频率共用磋商机制的国际规则框架,对确定需要协调的卫星网络的列表、卫星网络数据项申报以及短期卫星任务相关规则进行了修订。     

WRC-19建立50/40GHz频段非静止轨道卫星频率使用规则和磋商机制

2019年世界无线电通信大会(WRC-19)1.6议题主要审议:为可能在37.5GHz～ 39.5GHz(空对地)、39.5GHz～42.5GHz(空对地)以及47.2GHz～50.2GHz(地对空)、50.4GHz～ 52.4GHz(地对空)频段内操作的非对地静止卫星固定业务(non-GSO FSS)卫星系统制定规则...     

中低轨道卫星移动通信系统的发展背景、组成及概况

本文在论述中低轨道卫星移动通信系统发展背景的基础上。研究了中低轨道卫星移动通信系统的组成，工作过程、传播特点．技术难点及需要解决的关键技术．并简要介绍了国外典型中低轨道卫星移动通信系统的发展概况。     

静止轨道卫星自动化干扰定位方案

在对静止轨道卫星上行干扰的定位过程中,复杂的分析工作往往需要花费数小时,当干扰信号为突发、短时类信号时,往往会错失定位时机,导致对这类信号的定位失败率非常高。为了解决静止轨道卫星干扰定位的滞后性问题,设计了一种针对静止轨道卫星干扰的自动化定位解决方案。对干扰定位工作中的邻星选择及定位方案设计、参考源信号的选择与发射等各关键环节进行了定量和定性分析,并通过仿真实验证明了该方案的可行性。该方案使得用机器代替人工分析成为可能,对卫星干扰源的快速和准确定位具有现实意义。     

静止轨道卫星系统中地面干扰源位置测定技术研究

本文描述了目前卫星通信系统中为了测定地面干扰源位置所采用的技术。通过研究提出了在RDSS导航系统中。如何通过被干扰的一颗卫星来测定地面干扰源位置的一种有效方法。     

静止轨道卫星移动通信系统的设计考虑

本文阐述了支持手持终端的卫星移动通信系统的服务功能,系统配置,通信体制和各组成部分的技术性能,最后给出了工程经济性能和财务评价初步结果。     

简析影响静止轨道卫星三星定位方法结果精度的主要因素

本文对静止轨道卫星三星定位方法的基本原理进行了简单介绍,结合实测数据,对影响定位结果精度的主要因素进行了分析,并针对各因素提出了优化定位结果的建议.     

卫星通信系列讲座之六 中低轨道卫星移动通信系统的发展背景、组成及概况

本文在论述中低轨道卫星移动通信系统发展背景的基础上,研究了中低轨道卫星移动通信系统的组成,工作过程、传播特点、技术难点及需要解决的关键技术,并简要介绍了国外典型中低轨道卫星移动通信系统的发展概况。     

车载非静止轨道卫星监测系统链路计算

非静止轨道(NGSO)卫星通信发展迅猛,但由于相关设备的缺乏,对其下行信号频率轨道资源占用情况监测较少,因此,设计NGSO监测系统为当前急需解决的问题。设计车载监测系统要求具有低的余量,而当前卫星监测系统通信链路计算过程考虑不够精确,文章通过研究ITU相关建议书,考虑NGSO通信链路中存在的大气、雨水、云层和电离层闪烁等相关因素,计算在特定接收余量下的车载监测系统地空链路损耗,为该系统设计提供更精确的依据,同时对GSO链路设计也具有参考意义。     

Interference considerations in frequency sharing between low earth orbit satellites and the geostationary fixed satellite and terrestrial service

Recently many companies and consortia have considered launching LEO satellites for such projects as remote sensing, transportation and mining operations. When the multiple low Earth orbit (LEO) satellites are transmitting they can interfere with existing terrestrial microwave and satellite earth-stations in the fixed and mobile service. The interference problem is related to the number of proposed LEOs and the altitude and consequently the time to orbit the earth. These systems usually consist of many small satellites, and each satellite stays in the beam of a terrestrial station for up to 72 seconds in each 222 minute orbit. Earth coverage could be obtained by 48 (LEO) satellites 1500 km above the earth in polar orbit, and hence at least one LEO would always be interfering with terrestrial networks. A technical evaluation would then be required to determine the resultant BER (bit error rate) effecting existing terrestrial services. A determination can then be made to support such a LEO system or object via official channels such as the ITU.     

GEO卫星测距系统设计

随着卫星测定轨精度的提高,现有测距系统难以满足要求.文中着重介绍了GEO卫星采用三点测距为实现高测距精度的方案,给出了三点测距系统的结构和功能,并分析测距系统模型,以及提高测定轨精度的因素,最后对测距性能进行了分析.     

对静止轨道卫星成像的SAL载星轨道

星载合成孔径激光雷达对卫星成像面临相对运动复杂、目标搜索困难、成像时机难把握等问题。以对静止轨道卫星成像为例,初步设计了一种适于对同步轨道卫星成像的载星轨道。推导了载星与目标间相对运动关系式;绘制并分析了两星相对运动曲线;分析了两星距离最近期间距离、径向速度、加速度变化规律。提出了基于径向速度门限的成像时机判定方法,研究了成像期间光束指向偏移和成像时机判决速度门限。研究结果表明:轨道高度低于目标星轨道,并与之有一定偏角的载星轨道适于对目标进行成像;两星相距最近的时间附近是较佳成像时机,可降低相位误差补偿难度,提高系统工作效率;在对目标进行搜索跟踪和判决成像时机时,系统需根据两星轨道特性进行动态调整。     

Effective utilization of the geostationary orbit for satellite communication

The geostationary satellite orbit has a finite capacity for communication satellites operating in the frequency spectrum available, but saturation could be delayed for a long time if various practices and principles of system design and use were agreed internationally and applied. Three broad areas are identified where action is needed, namely system engineering for an interference-limited environment, intersystem coordination of the use of orbit and the spectrum, and the ordering of the use of orbit and spectrum so that systems with radically different characteristics do not interfere. In each of the three areas, the main factors of concern ate identified, the benefits that would be achieved are deduced in broad terms, and the practical and economic feasibility of actually securing the benefit is reviewed for each factor.     

Fuzzy logic techniques for rendezvous and docking of two geostationary satellites

Assembling large structures in space requires the ability to manage rendezvous and docking operations. In future these techniques will be required for the gradual build up of big telecommunications platforms in geostationary orbit. This paper discusses the use of fuzzy logic to model and implement a control system for the docking/berthing of two satellites in geostationary orbit. The system mounted in a chaser vehicle determines the actual state of both satellites and generates torques to execute manoeuvres to establish the structural latching. The paper describes the proximity operations to collocate the two satellites in the same orbital window, the fuzzy guidance and navigation of the chaser approaching the target, and the final fuzzy berthing. The fuzzy logic system represents a knowledge-based controller that realizes the closed-loop operations autonomously, replacing the conventional control algorithms. The goal is to produce smooth control actions in the proximity of the target and during the docking to avoid disturbance torques in the final assembly orbit. The knowledge of the fuzzy controller consists of a data base of rules and the definitions of the fuzzy sets. The knowledge of an experienced spacecraft controller is captured into a set of rules forming the rules data base.     

Non‐geostationary satellite orbit communications satellite constellations history

This special issue of the journal on ‘constellations’ comes at a critical time in their development as a second wave of such non‐geostationary satellite orbit (NGSO) systems is being planned and deployed. These mega‐constellations as they have become known are, with a few exceptions, very much larger than those in the first wave and are focused on broadband and 5G applications rather than speech and narrow band data as those deployed in the first wave during the 1990s. However, as we explain in this editorial, there are many similarities in the design and business plans to the first wave and, perhaps, many similar lessons to be learned.     

Autonomous navigation of service spacecrafts on geostationary orbit using GNSS signals

In this paper we consider the possibilities of navigation of spacecrafts designed to service artificial Earth satellites on the geostationary orbit and of space debris removal in the near-Earth space using the signals of Global Navigation Satellite Systems. We have formulated the methodology for estimation of the signals availability of navigation satellites on the geostationary orbit through the utilization of almanac of GPS and GLONASS. It has been demonstrated that in the case of reception of navigation signals, which are radiated by the antenna system within the limits of main lobe of the radiation pattern (RP), the availability of satellite navigation signals on the geostationary orbit is very low even if we utilize GPS and GLONASS simultaneously. We present the simulation results of the received on the geostationary orbit navigation satellites using the signals radiated in the main lobes in the range from ±13.8 to ±23.5° for the L1 frequency, from ±13.8 to ±26° for the L2/L5 frequencies and in the side lobes in the range from ±30 to ±60° of RP of the satellite antennas. The simulation of the navigation satellites available on the geostationary orbit is given on the 24-hour time interval. Presented results are illustrated by the calculations of number of visible satellites and by the geometric factor.     

Closer spacing of geostationary satellites through adaptive nulling at the ground terminal

The results of a preliminary study suggest that interference to the downlink of one geostationary satellite from that of another satellite in the adjacent orbital slot can be substantially reduced by the addition of a simple adaptive nulling system to the ground terminal antenna. Alternatively, the nulling system allows the satellites to be spaced significantly closer together with no increase in interference. Significant improvement is obtained with simple open-loop antenna pointing. The improvement is greater, however, if the adaptive antenna automatically tracks the direction of the desired source. For a dish antenna with a single receiving feed horn, the extra hardware required to provide the adaptive capability consists of two more receiving feed horns, a variable weighting device for each of the feed lines (now three in number) and the adaptive control electronics. An example shows that the minimum spacing between one satellite and an interfering satellite, consistent with certain assumed operating requirements, could be reduced from the2.25degneeded for a simple single beam antenna to1.35deg, for the adaptive antenna using open loop pointing, to as little as0.7deg, for the adaptive antenna using automatic pointing. The adaptive hulling also provides essentially the same protection against downlink interference from the two other satellites occupying the slots on both sides of the satellite serving the terminal. The three degrees of freedom of the postulated nulling system, however, cannot cope with three or more nearby interfering satellites.     

Semi-Markov multistate modeling of the land mobile propagation channel for geostationary satellites

This paper describes a new semi-Markov propagation channel model for land mobile satellite systems using geostationary satellites. The multistate model switches between propagation states representing line-of-sight, shadowing, or blockage of the signal. The duration of times spent in each state follow probability distributions recommended by the radiocommunication sector of the International Telecommunication Union (ITU-R). The actual parameters to be used with the ITU-R distributions were modified and fitted to observed data. The open-area state durations follow a power-law distribution, while the state durations for both the shadowed and the blocked states follow a lognormal distribution. Parameters for both two- and three-state models are extracted from an L-band measurement campaign performed by Inmarsat in the United Kingdom. Propagation channel models characterizing the fading within the open, shadowed, or blocked propagation states are described as well. The semi-Markov models represent an improvement over the more commonly used Markov models where the duration in each state follows an exponential distribution. The new model enables more accurate prediction and simulation of system performance and availability.     

地球同步轨道红外相机的热辐射杂散光集成法

地球同步轨道上的三轴稳定卫星所处的空间环境复杂,仪器背景辐射变化较大。传统杂散光分析法无法模拟非均匀温度场,且无法实时计算仪器背景,仿真误差较大。提出用热辐射杂散光集成法来分析在轨红外相机的仪器背景辐射,通过更趋于在轨真实温度的且具有温度梯度的实时温度场,结合辐射传递因子,计算探测器上的仪器背景辐射以及相机的信杂比。将热辐射杂散光集成法、传统杂光分析法计算信杂比与在轨实测信杂比进行对比,热辐射杂散光集成法误差小于17%,而传统杂光分析法误差达114%。表明热辐射杂散光集成法的仿真结果更趋近于在轨实际情况,仿真效率和仿真精度更高。