卫星激光通信Ⅱ地面检测和验证技术

星间激光通信终端的主要技术指标和运行性能必须事先在地面实验室条件下进行模拟检验,因此在研制卫星激光通信终端的同时必须发展相应的系统性检测和验证平台,主要包括激光通信性能检验、光跟瞄性能检验和光束质量检验。本文综述了卫星激光通信终端检验技术的国外进展,介绍了我们全物理模拟的地面检测验证思路和方法。     

卫星激光通信复合轴光跟瞄技术及发展

卫星激光通信具有巨大的潜在应用价值,国际上已实现高码率、小型化、轻量化和低功耗激光通信终端,其中光学跟瞄系统的设计和控制是关键技术之一。由粗跟踪系统和精跟踪系统组成的复合轴系统能实现光跟瞄系统的大范围、高精度跟踪任务。对卫星激光通信光学跟瞄系统的特点和关键技术进行了讨论,介绍了光跟瞄技术中的扫描、捕获、指向、跟踪过程,综述了复合轴光跟瞄控制系统的国外研究进展。最后对卫星激光通信复合轴光跟瞄系统的应用前景进行了展望。     

带有前置EDFA卫星相干激光通信终端的信噪比分析

卫星激光通信链路是一项实现卫星大规模星座组网的关键技术。相干激光链路灵敏度高、抗背景干扰、速率升级空间大,在星间激光链路中应用广泛。文章建立了带有前置掺铒光纤放大器(EDFA)的卫星相干激光通信终端的信噪比分析模型,仿真分析了EDFA功率增益、EDFA噪声系数、本振光功率、信号光功率、光放后端光带宽、基带前端电带宽对终端输出信噪比的影响以及各种输出噪声功率占比的情况,得到了带有前置EDFA卫星相干激光通信终端的信噪比参数特性。     

衍射光学元件在卫星激光通信终端中的潜在应用

卫星激光通信技术是目前通信技术领域的研究热点,而光学子系统的优化设计是其重要研究方向。主要介绍了利用衍射光学元件实现卫星激光通信终端的小型化、集成化和高效化。文中首先简要介绍卫星激光通信系统的基本原理,随后介绍了衍射光学元件在卫星激光通信终端中的各种可能应用,包括光束整形和分光,光学滤波,防反射镀膜,像差和热差补偿等。给出了一个包含衍射光学元件的激光通信终端光学系统优化设计实例,相应的数值仿真结果表明:衍射光学元件与传统光学元件相比,具有明显优势。     

卫星间光通信技术

介绍了卫星间激光通信系统的构成,分析与比较了星间非相干的IM/DD系统和相干光通信系统的性能.指出对于同步卫星间这种超长距离的光通信系统,高的接收灵敏度是至关重要的,因而相干光通信技术更有优势;但对于中低轨道卫星光通信系统,由于多普勒效应的影响,采用IM/DD技术更为恰当.     

激光星间链路发展综述：现状、趋势、展望

由于激光通信在空间传输中波长短且方向性强,已成为下一代卫星通信与导航的重要手段。激光星间链路的高速率、高带宽、高安全性等特点,可以提供高质量卫星空间通信,同时其还可以提高星间测距的精度,因此,构建激光星间链路成为下一代卫星网络的研究重点之一。文中首先从技术层面介绍激光星间链路的基本组成,主要介绍了卫星激光建链模式、卫星激光信号调制模式及卫星激光载波波长三个重要技术点。从技术到现象,根据不同轨道高度和不同的任务需求,按照发射时间顺序综合调研并总结了近年来国内外典型中高轨和低轨卫星激光通信成果的发展现状与未来计划。通过调研,进一步从宏观角度分析出卫星激光通信发展标准化、兼容化、网络化和商业化四个趋势,并从微观角度总结了卫星激光终端弹性化和模块化的发展方向。最后,除了作为通讯手段,展望了星间激光链路用于卫星激光测距的良好前景。通过对激光星间链路的现状、趋势和展望的综合分析,旨在为未来激光星间链路的设计与优化提供一定的借鉴和参考,并为我国未来星间激光通信和测距技术的发展及研究提供方向参考。     

卫星激光通信技术现状及应用展望

简单介绍了卫星激光通信技术的特点，以及空间激光通信技术的迫切需求。总体上构建了一个卫星激光通信的系统．并详细分析了卫星激光通信的关键技术和影响卫星激光通信性能的因素。最后结合国内外卫星激光通信技术的发展现状和水平，提出了我国大力发展卫星激光通信技术和应用系统的建议。     

美国月球激光通信演示验证——实验设计和后续发展

针对2013年9月6日美国宇航局(NASA)发射的月球大气与尘埃环境探测器飞船上进行的月球激光通信演示验证(LLCD),从实验设计和后续发展方面进行综述。实验中,飞船上的LLCD太空终端与主要的月球激光通信地面终端或与欧洲空间局的月球激光通信地面系统完成双向通信,而与美国喷气推进实验室的月球激光通信"光通信望远镜实验室"(OCTL)终端仅进行下行链路通信。LLCD系统还进行了优于厘米精度测距的双向飞行时间测量。未来NASA的激光通信中继演示验证任务将基于LLCD系统的相关设计。最后对LLCD的启示进行了讨论。     

无线激光通信技术的实际应用

无线激光通信技术根据应用场合分为近地无线激光通信和星际激光通信.近地无线激光通信在地面架设,具有适合在特殊地形、地貌工作,带宽大,无电磁辐射,抗电磁干扰,机动灵活等特点,成为无法敷设光缆场合的有效补充手段.星际激光通信用于卫星之间,卫星与地面之间的信号传输,通信容量大,弥补了微波传输容量的不足,是未来星际通信的发展趋势.     

卫星激光通信技术

文章详细介绍了卫星激光通信技术在国外的最新发展状况；阐述了实现卫星激光通信的关键技术及其解决方案，特别对捕获、跟踪、瞄准系统进行了详细的分析；最后对卫星激光通信技术的发展作了展望。     

星间激光通信终端性能对比分析

提出了两种星间激光通信终端性能的比较方法，可为空间激光通信系统设计提供参考。以SILEX研究计划为例，简要分析了各种轨道之间光通信系统的特性及未来光学终端的升级方案。     

Experimental detection of mobile satellite transmissions with cyclostationary features

One of the important functions of cognitive radio (CR) technology is spectrum sensing. The implementation of an efficient spectrum sensing function can be quite challenging because of various factors such as multi‐path fading, low signal‐to‐noise ratio of the radio communication services to be detected and the requirement to detect and analyze the signal in a short time. As a consequence, it is important to quantitatively assess the performance of spectrum sensing techniques in various scenarios. This paper investigates different digital signal processing techniques for spectrum sensing in the context of mobile satellite transmissions: power sensing, cyclostationary sensing, efficient cyclostationary sensing based on FFT accumulation method and strip spectral correlation algorithm. This paper presents experimental results on the cyclostationary properties of GSM Thuraya mobile satellite communications in various conditions both for the uplink and downlink channels. The receiver operating characteristics are computed, and the results are presented for different algorithms and different positions of the satellite terminals. The experimental results show that the cyclostationary‐feature‐based detection can be robust compared to energy‐based technique for low signal‐to‐noise ratio levels. Copyright © 2014 John Wiley & Sons, Ltd.     

Improving satellite services with cooperative communications

This paper proposes new transmission schemes for the delivery of satellite services. In the proposed scenarios, mobile terminals are allowed to forward the signal received from the satellite. This scheme provides spatial diversity just like MIMO transmission schemes. Moreover, the coverage area is extended because masked terminals have an additional opportunity to get the service from neighboring terminals. We use the paradigm of cooperative communications to compare the advantages and limitations of several scenarios in hybrid terrestrial/satellite systems. In particular, we study the following basic transmission scheme: in a first time slot, the satellite sends its signal and, in a second time slot, mobile terrestrial terminals are relaying the satellite signal. An analysis framework is proposed and applied to this cooperation scenario at the destination terminal. The framework is modeling the cooperation process and clearly separates the control part from the data user part. The paper outlines the importance of the control part by evaluating the relay selection policy on a basic hybrid satellite/ad hoc system. Copyright © 2011 John Wiley & Sons, Ltd.     

Optical Communications in Space – a Challenge for Europe

The successful test of a laser communication link between an ESA data-relay satellite and an Earth observation satellite marks a milestone in the development of optical space communications. It is the right moment to look back on more than 20 years of R & D effort in Europe. The paper gives an overview of the optical space communication activities at the European Space Agency (ESA), which have started in summer 1977, when ESA placed the first technology study contract in the domain of intersatellite optical links, and reports on the most recent European systems andhardware technology efforts aimed at the development of small and compact laser terminals for global mobile communication systems and satellite-based data networks.     

光通信中一种非线性系统的仿真研究

任何含有有源器件的微波放大电路在一定情况下都会表现出非线性特性.针对光反馈半导体激光器收发系统微分方程组的特点,根据龙格-库塔算法的思想和模型中的特点,提出了对当前迭代式中所需要的之前斜率值的估计算法,并对发射与接收信号进行了仿真,结果表明该算法可以使得接收端与发射端快速收敛一致,并能有效对该类系统进行仿真分析.

Abstract：

Microwave amplifying circuits composed of active devices have nonlinear characteristics in certain conditions.According to Runge-Kutta algorithm and the features of differential equations for semiconductor laser transimitting and receiving system,an approach for computing gradients in iterative formula is presented,and the transmitting and receiving signals are simulated.The simulation results show that the quick convergence uniformity at both input and output terminals can be acquired by this algorithm.And this algorithm can also be used to simulate all this kind of systems effectively.     

Transmission of group 3 facsimile over inmarsat maritime digital satellite mobile channels

The importance of facsimile communication over public telephone networks is evidenced by the rapid growth in the number of Group 3 facsimile end-user terminals. In this paper the main characteristics of a real-time bit-rate reducing approach are described whereby facsimile signals are demodulated and their associated protocols converted by a facsimile interface unit (FIU) to a format suitable for transmission over Inmarsat-B maritime digital satellite channels. The FIU concept was developed to allow ‘off-the-shelf’ facsimile terminals to be interconnected via the PSTN through Inmarsat's satellite networks and to permit the provision of enhanced user services by converting Group 3 facsimile protocols to broadcast operation. In addition, the FIU concept is designed to compensate for the longer access and transport link delays encountered in mobile satellite systems, and to permit facsimile call recovery procedures to be successfully concatenated with satellite channel error detection mechanisms.     

Preliminary plans for a propagation experiment in Mali

Measurements of propagation effects on satellite down-links to tropical locations are rare. This paper describes two experiments that will provide new and useful data for radiowave propagation in tropical Africa. A discussion of the African tropical climate is included that shows the wide range of rainfall patterns throughout the continent. Also, the broad distribution of climate in Mali, the West African country where the experiments will be located, is described. A rain-rate measurement programme involving autonomous terminals based on tipping bucket rain-gauges is presented. An experiment measuring the slant-path attenuation of the 12·5 GHz beacon of the ESA satellite OLYMPUS is described. The paper also discusses how the measured data in both experiments will be relayed daily from Mali to Virginia Tech by the low earth orbit satellite VaSTAR.     

Standardized testing conditions for satellite communications on‐the‐move (SOTM) terminals

Performance validation of Satcom on‐the‐move (SOTM) terminals is becoming more important as the satellite operators continue to recognize the negative influence of suboptimal terminals on their satellite networks. Traditionally, SOTM testing is performed with actual operational satellites in field tests, which lack repeatability. The capability to repeat the conditions in which SOTM terminals are tested is important, especially when the performance of multiple terminals is compared. This contribution describes how the qualification test of SOTM terminals can be conducted in a laboratory environment so that repeatability can be ensured. A major advantage of a laboratory environment is the ability to test the complete terminal as if it was in the field of operation, yet without the involvement of real satellites effectively reducing the costs of testing. The main contributions of this paper are motion and shadowing profiles suitable for standardization of SOTM testing. Standardization of such profiles is necessary to guarantee a fair comparison of the performance of different terminals. Moreover, the paper presents the methodology for testing SOTM terminals at the Fraunhofer Facility for Over‐the‐air Research and Testing, * * * https://www.iis.fraunhofer.de/en/profil/standorte/forte.html the procedure used to obtain the proposed profiles and results of testing a Ka‐band SOTM terminal, taken as an example.